Designing an Automatic Coolant Monitoring System for CNC Machines

[kunalvanjare]

Hey guys,

I am designing a system that would monitor the coolant tanks of about 10 CNC machines through a centralized system consisting of valves, a pump & a refractometer. The system would be connected to the tanks through fixed piping in the plant.

A pump would draw small amount of liquid from each tank sequentially and an online refractometer will check the concentration of the drawn liquid. If the concentration is above or below the desired level, we have to initiate a coolant make-up (refill) operation which would actuate another pump that will transfer appropriate quantity of coolant & water in the right make-up concentration into the Coolant Tank.

I have a few queries which I would highly appreciate if you guys could throw some light on :-

1. Can I use one single centralized pump to draw liquid from 10 tanks (the machines may be as far as 50 feet from the pump) , because having one pump per tank is difficult due to the increased plumbing & cost. If it is possible, what type of pump would suit this application?

2. Make-up of coolant requires a formula in which I need to know the quantity of liquid in the tank. Are there level sensors that provide continuous measurement of the liquid in a tank?

3. While adding liquid into the Coolant tank, how do I measure the exact quantity of liquid flowing through the pipe? Can I use Flowmeters? What type?

Any help on the above would be greatly appreciated.

Thanks,
KV

 

[berkeman]

I'd be more inclined to distribute the whole thing to the CNC machine locations. Are the CNC machines already connected to a network (how do they get their programs?)? Do you have a building Ethernet network? Are the CNC machines programmable (can you add in your own code to perform this extra task of monitoring)? If not, you could network control nodes (based on Arduinos or Raspberry Pis or whatever) via Ethernet...

EDIT/ADD -- BTW, the CNC machine manufacturer might be interested in adding this capability into their machines. Which manufacturer do you use?

 

[jrmichler]

If you are drawing only a small amount of liquid from each tank (less than 1 liter?) for analysis, then look at peristaltic pumps. They handle liquids of varying viscosity, and liquids with small particles. Since small peristaltic pumps can be purchased for less than $150 US, it would be better (and probably lower cost) to put one pump on each CNC machine. Valves will cost about as much, and are subject to problems from metal particles in the coolant. Here is one source: https://assets.omega.com/pdf/pumps-and-mixers/peristaltic-pumps/FPU400.pdf. I have had good experiences dealing with this company.

There are many different level transmitters (search the term) available. They differ in accuracy, cost, allowable ambient temperature, range, and many other factors. You will need to study the product data sheets.

Peristaltic pumps are positive displacement pumps. Size the feed pump for an appropriate flow rate, then just run it for a specified period of time to get the amount you want. Or you can just monitor the level transmitter, and pump until the level reaches a specified level. Here again, you will be better off with ten pumps than with one pump and ten valves.

Stay away from flowmeters if at all possible. They are far more challenging to apply than pumps and level transmitters.

 

[kunalvanjare]

I'd be more inclined to distribute the whole thing to the CNC machine locations. Are the CNC machines already connected to a network (how do they get their programs?)? Do you have a building Ethernet network? Are the CNC machines programmable (can you add in your own code to perform this extra task of monitoring)? If not, you could network control nodes (based on Arduinos or Raspberry Pis or whatever) via Ethernet...

EDIT/ADD -- BTW, the CNC machine manufacturer might be interested in adding this capability into their machines. Which manufacturer do you use?

Thanks for the response. What we're designing here is a system independent of each CNC program. It will be a closed-loop system that identifies changes in the Coolant level in each machine & automatically tops-up the required fill.

 

[kunalvanjare]

If you are drawing only a small amount of liquid from each tank (less than 1 liter?) for analysis, then look at peristaltic pumps. They handle liquids of varying viscosity, and liquids with small particles. Since small peristaltic pumps can be purchased for less than $150 US, it would be better (and probably lower cost) to put one pump on each CNC machine. Valves will cost about as much, and are subject to problems from metal particles in the coolant. Here is one source: https://assets.omega.com/pdf/pumps-and-mixers/peristaltic-pumps/FPU400.pdf. I have had good experiences dealing with this company.

There are many different level transmitters (search the term) available. They differ in accuracy, cost, allowable ambient temperature, range, and many other factors. You will need to study the product data sheets.

Peristaltic pumps are positive displacement pumps. Size the feed pump for an appropriate flow rate, then just run it for a specified period of time to get the amount you want. Or you can just monitor the level transmitter, and pump until the level reaches a specified level. Here again, you will be better off with ten pumps than with one pump and ten valves.

Stay away from flowmeters if at all possible. They are far more challenging to apply than pumps and level transmitters.

hey man, at this point, we're not sure how much liquid is to be drawn. Maybe 1 Liter would not be enough. Plus there is the problem of what to do with the drawn liquid after analysis? Should we send it back to the tank (increased plumbing headaches) or just drain it (wastage).

But considering we have to draw around 1-5 Litres, I will have a look at Peristaltic pumps. The system may have to be designed for more than 10 machines, thus having one pump per machine might be difficult because of the additional hassle of installing the pump on each machine. Not to mention the cost.

We use level transmitters of the magnetic reed type. Which level sensors do CNC coolant tanks have fitted in them? Can't I just make use of the inputs I receive from those, instead of installing a new level sensor on each tank for my system?

If not flowmeters, then how do I monitor how much liquid is flowing through the pipe?

 

[Asymptotic]

A pump would draw small amount of liquid from each tank sequentially and an online refractometer will check the concentration of the drawn liquid.

(the machines may be as far as 50 feet from the pump)

Have you accounted for how much coolant resides in the line?
For example, a 50 foot run of 1/2" x 0.028" wall stainless steel tubing holds about 1.5 liters.
Will it be filtered? If not, metal particles will settle out in the line.

A potential problem to be aware of with a common system is bacteriological cross-contamination. Another is what will occur when this single refractometer drifts out of calibration.

I'm imagining evaporation loss increases coolant concentration over time. Is there anything that ever thins it out? If no, wouldn't it be easier to add make-up water alone to restore concentration to the desired value?

It would be costly up front (and you'd have to factor in maintenance costs) but if make-up water is all that is required to maintain concentration, it may be cheaper in the long run to fit each machine with a refractometer, monitor continuously, and add water as needed.

Unresolved is what to do when it drifts out of calibration, and how to sense when that happens, but at least it will affect only a single machine.

Another thought: Although it exacerbates the effects of a single point failure inherent in a common system, what about radically lowering the level sensor in each CNC machine tank, and run a continuous loop of properly tempered coolant to use as make-up?

 

[kunalvanjare]

Have you accounted for how much coolant resides in the line?
For example, a 50 foot run of 1/2" x 0.028" wall stainless steel tubing holds about 1.5 liters.
Will it be filtered? If not, metal particles will settle out in the line.

A potential problem to be aware of with a common system is bacteriological cross-contamination. Another is what will occur when this single refractometer drifts out of calibration.

I'm imagining evaporation loss increases coolant concentration over time. Is there anything that ever thins it out? If no, wouldn't it be easier to add make-up water alone to restore concentration to the desired value?

It would be costly up front (and you'd have to factor in maintenance costs) but if make-up water is all that is required to maintain concentration, it may be cheaper in the long run to fit each machine with a refractometer, monitor continuously, and add water as needed.

Unresolved is what to do when it drifts out of calibration, and how to sense when that happens, but at least it will affect only a single machine.

Another thought: Although it exacerbates the effects of a single point failure inherent in a common system, what about radically lowering the level sensor in each CNC machine tank, and run a continuous loop of properly tempered coolant to use as make-up?

1. A inline filter can be added before the make-up coolant+water enters the tank.

2. Regarding calibration of the refractometer, I will get in touch with the manufacturer and if required, periodic re-calibration services can be arranged.

3. A sump may become lean due to human error during re-filling. Or due to drag-out of coolant with chips & splashing onto the walls of the machine. Also, some amount of oil & other contamination gets added to the sump which can alter the concentration of coolant making it lean. But the main cause is always due to evaporation.

4. It is always advisable to have a refractometer on every tank. But trust me, the cost for a plant with more than 100 machines would become way too high for this to ever get considered. Specially in a country like India :P

5. Simply adding water can actually be detrimental to the sump because the 'cooling' characteristics of the coolant reduces over time. So even if you balance out the concentration by simply adding water, the effect of the coolant will not be the same. Hence make-up liquids always contain a small amount of coolant concentrate. Plus, if there is no control on the quality of water, then that can create a major problem due to addition of minerals.

6. I'm not sure I understood your last point. Please elaborate.

 

[Asymptotic]

Thanks for the additional details and clarifications above.

6. I'm not sure I understood your last point. Please elaborate.

I'm envisioning each CNC machine has a sizable coolant reservoir. You propose to analyze and modify coolant quality for each machine from a central location, but to do so involves several difficult challenges. I'm wondering if it might be possible to operate with a bare minimum fluid level in the reservoir so there isn't a large volume of fluid to degrade, and use the central system to feed it with the desired mix of water and coolant.

The central system would consist of a mixing tank, water make-up valve, perhaps a peristaltic pump to meter coolant addition, and the refractometer. Coolant mixture would be pumped into a feed line that returns to the mixing tank fitted with drops at each CNC machine.

Each CNC machine would control a make-up solenoid valve to feed mixture from it's respective drop. Solenoid control could be done with two level switches slightly offset in height from one another ('make-up required' and 'make-up satisfied'), or by a single level sensor with timed hysteresis (start make-up at the high-to-low 'makeup required' transition, and use a time-off relay set to a suitably brief timeout) to prevent the solenoid valve from short-cycling.

With reservoir level kept intentionally low it is desirable to add another level sensor located somewhat below the make-up height to indicate when insufficient fluid is available to operate the CNC safely, and to provide a 'low coolant level shutdown' signal (rather than run without coolant until the tooling eats itself and the workpiece is damaged) for when the central makeup system goes off-line, CNC machine make-up valve doesn't operate, a massive coolant leak occurs at the CNC machine, etc.

 

[kunalvanjare]

Hey guys, there are Venturi or water driven Coolant Proportioning Pumps available in the market. These pumps have a manual setting for maintaining the concentration.

Is there a way I can do this automatically? I mean, are there any such pumps that can be controlled by PLC i.e the opening size may be opened automatically be a solenoid valve and not by manually rotating a knob by hand?


Kindly refer above URL for a video on the Coolant mixers.

 

[kunalvanjare]

Thanks for the additional details and clarifications above.I'm envisioning each CNC machine has a sizable coolant reservoir. You propose to analyze and modify coolant quality for each machine from a central location, but to do so involves several difficult challenges. I'm wondering if it might be possible to operate with a bare minimum fluid level in the reservoir so there isn't a large volume of fluid to degrade, and use the central system to feed it with the desired mix of water and coolant.

The central system would consist of a mixing tank, water make-up valve, perhaps a peristaltic pump to meter coolant addition, and the refractometer. Coolant mixture would be pumped into a feed line that returns to the mixing tank fitted with drops at each CNC machine.

Each CNC machine would control a make-up solenoid valve to feed mixture from it's respective drop. Solenoid control could be done with two level switches slightly offset in height from one another ('make-up required' and 'make-up satisfied'), or by a single level sensor with timed hysteresis (start make-up at the high-to-low 'makeup required' transition, and use a time-off relay set to a suitably brief timeout) to prevent the solenoid valve from short-cycling.

With reservoir level kept intentionally low it is desirable to add another level sensor located somewhat below the make-up height to indicate when insufficient fluid is available to operate the CNC safely, and to provide a 'low coolant level shutdown' signal (rather than run without coolant until the tooling eats itself and the workpiece is damaged) for when the central makeup system goes off-line, CNC machine make-up valve doesn't operate, a massive coolant leak occurs at the CNC machine, etc.

Thanks for the suggestion. Firstly, if we have a centralized system that would actually feed the desired mix of water and coolant for about 10 machines, wouldn't I require a large volume of water & coolant in that centralized unit? Because I have to properly mix the coolant concentrate with water before feeding into the machine tank.

Mixing of coolant with water can be done using Coolant Proportioning Pumps. These are small, wall mounted or drum mounted pumps that operate on venturi principle and the accuracy obtained is pretty good.

The only problem with this is that the control of concentration is purely manual (knob rotation by hand) and I haven't been able to find any such pump that would operate completely automatically. Video of such a pump can be found in my previous post.

 

[Asymptotic]

Hey guys, there are Venturi or water driven Coolant Proportioning Pumps available in the market. These pumps have a manual setting for maintaining the concentration.

Is there a way I can do this automatically? I mean, are there any such pumps that can be controlled by PLC i.e the opening size may be opened automatically be a solenoid valve and not by manually rotating a knob by hand?


Kindly refer above URL for a video on the Coolant mixers.

It would take some doing, but a geared stepper motor or small DC servo could be coupled to the shaft in place of the knob. Limit switches would typically be placed at each end of travel (CW and CCW) to prevent overtravel, and/or an encoder used for rotary feedback of valve stem position, and a control system built to drive it. Fairly costly.

Groz doesn't provide enough information about this venturi mixer to determine whether it is worth the effort.
The two models indicated for metalworking fluids are CMX/1 (0 to 11%) and CMX/3 (0-9%) with both rated for 1100 liter/hour (290 gallon/hour) throughput at 57 PSI inlet pressure.

Thoughts that come to mind:
1. How much coolant/water mixture is used per hour per CNC machine?
2. What is the acceptable range of brix readings from the refractometer?
2. A pressure regulator in the water supply at each venturi pump would be required for any chance at mixture concentration repeatability. The regulator will have a sensitivity (how much pressure change is required to actuate a control response) specification. Will water supply pressure variation affect the resulting mix enough to matter?

 

[kunalvanjare]

It would take some doing, but a geared stepper motor or small DC servo could be coupled to the shaft in place of the knob. Limit switches would typically be placed at each end of travel (CW and CCW) to prevent overtravel, and/or an encoder used for rotary feedback of valve stem position, and a control system built to drive it. Fairly costly.

Groz doesn't provide enough information about this venturi mixer to determine whether it is worth the effort.
The two models indicated for metalworking fluids are CMX/1 (0 to 11%) and CMX/3 (0-9%) with both rated for 1100 liter/hour (290 gallon/hour) throughput at 57 PSI inlet pressure.

Thoughts that come to mind:
1. How much coolant/water mixture is used per hour per CNC machine?
2. What is the acceptable range of brix readings from the refractometer?
2. A pressure regulator in the water supply at each venturi pump would be required for any chance at mixture concentration repeatability. The regulator will have a sensitivity (how much pressure change is required to actuate a control response) specification. Will water supply pressure variation affect the resulting mix enough to matter?

Hey man, thanks for responding so quickly. Your posts are insightful as ever.

So I will try to respond to your queries as below :-

1. How much coolant/water mixture is used per hour per CNC machine?
Reply - From our experience, a CNC machine tank capacity ranges from 200-300 Litres on average. There are machining centres with larger capacity tanks, but mostly the ones found in the plant would have tank capacities approx 200-300 Ltrs. Now it is difficult to calculate a per hour consumption, but the losses due to evaporation & dragout at the end of the day can be estimated around 10-15%. This again, is purely an estimation and wil vary from customer to customer.

2. What is the acceptable range of brix readings from the refractometer?
Reply - 5-10%. As per requirement in each machine. A lot of companies use the same concentration in the entire line or cell. But there are certain cases where a single line may have different concentrations of the same coolant.

2. A pressure regulator in the water supply at each venturi pump would be required for any chance at mixture concentration repeatability. The regulator will have a sensitivity (how much pressure change is required to actuate a control response) specification. Will water supply pressure variation affect the resulting mix enough to matter?
Reply - A pressure regulator would be required, agreed. I am not sure how much a pressure variation would change the resultant concentration to be honest with you. We might just go ahead and build a prototype without a pressure regulator initially (once we're able to find a solution to all the other issues :/)

The pressing issue right now is how to mix the coolant & water in the desired concentration in an inline process. I have come across some documents mentioning use of Pulse Width Modulation. But I have 0 knowledge about this technology and even some research on it has left me clueless as to how the damn thing would work for this application (Link to the document - http://s000.tinyupload.com/index.php?file_id=07047886135675729106)

 

[Asymptotic]

if we have a centralized system that would actually feed the desired mix of water and coolant for about 10 machines, wouldn't I require a large volume of water & coolant in that centralized unit?

Yes. However, the simplicity of maintaining one large tank with the proper coolant mix, and sending it to the CNC machines where they use it almost on an 'as-needed' basis must be weighed against the complexities of doing it in other ways.

Two mixing/delivery tanks may be required at the central location depending on how long the CNC machine can operate without refilling the local reservoir, and how long it takes to prepare a new batch of coolant mixture for delivery.

Tank size is determined by how much solution is used per hour per CNC machine, the number of CNC machines, and desired number of tank mixing operations per day. For instance, At 1 LPH/machine and 10 CNC machines (10 LPH) the tank would need to hold 60 liters to sustain 6 hours of operation.

If each CNC machine requires coolant make-up at 1 liter/hour, and the local reservoir holds 1 liter of reserve capacity (volume between the make-up level switch and safety shutdown switch) then a single central mixing/delivery tank would need to be refilled and mixed to proper concentration within 1 hour.

Another approach is to emulate how water softener systems operate. Deliver from one tank while preparing another batch of mixture in the other, and switch between them when the delivery tank goes low.

 

[Asymptotic]

I'll have to ponder on the info in post #9.

You might find this attempt at a closed loop metalworking fluid system informative.
https://www.researchgate.net/publication/315977778_Real_Time_Monitoring_and_Automatic_Regulation_System_for_Metalworking_Fluids

 

[bobob]

Any help on the above would be greatly appreciated.
Thanks,
KV

As I understand your question, you cannot do this, at least if you need to maximize the utilisation of all of your machines. Different materials and different cutting tools require different coolants and different operations require coolant to be supplied in different ways. (As an example of the latter, if you have a machine facing a piece, then there will be the coolant for that specific material being sprayed onto the surface, while if you are drilling through a different, or even the same material, you will probably be using a different coolant which is supplied through passages in the drill bit itself.) You could probably do this if all of your cnc machines are cutting the same material using the same type of cutting tool (i.e., carbide, TiN, whatever), but I think it will be less than ideal if you have one machine cutting aluminum with HSS and another machining stainless with some coated cutting tool. It will probably work ok if you don't intend to max out the machines to process parts as quickly as possible, though (and you don't have really strict requirements on surface finish). As far as I know, most cnc machines are self contained in that each one has its own coolant reservoir, but I could be mistaken about that last statement.

All of the various devices you mention could certainly be applied to accomplish what you are wanting to accomplish. The real question is that if you do build such a system, how will being tied to a common coolant system affect your ability to process multiple parts from different materials using different cutting tools?

 

[Asymptotic]

@bobob makes several excellent points. A central mixing and distribution system isn't well suited to applications where end users (individual CNC machines) require different mixtures.

More generally, it is difficult to automate a process when the constituent elements aren't well characterized. An approach I've used in such situations is:

1. At first, to do everything by myself, manually, while keeping meticulous records of what I'm doing, and reading up on all of the individual elements. Where an element isn't extensively documented by the manufacturer (in this case, Groz doesn't say much about the venturi mixer/pump except that settings are derived by trial and error) it is useful to conduct one or more sets of tests to determine what the device's actual capabilities are. From their manual:

NOTE​

• The Mixture Ratios have been specified after testing at a water pressure of 4 kg / cm2 (57 PSI)​

• Actual Mixture Ratios may vary as per the water pressure​

• Higher water pressure leads to higher concentration & vice versa​

• The Regulating Scale effectively gives a value based on trial & error. It should not be taken as an absolute Percentage Ratio​

CAUTION​

• The Mixer must be mounted horizontally within +/- 10° (because of the ball check valve)​

• The outlet is supplied with a PVC Hose which must always be open​

• Hose must not be connected to any device that can restrict liquid flow​

Here, I'd start out by setting up the venturi pump with a pressure regulator and pressure gauge, measure flow rate (probably using the time-honored 'timed bucket' method), and measure the resulting concentration with a handheld refractometer for each 10% change in valve position at a particular pressure, punch the resulting numbers into a spreadsheet, and check the resulting curve for linearity. I'd do this for a range of water inlet pressures to learn what effect pressure has on throughput and concentration and in the process develop a set of curves describing pump operation.

2. Once I had a good grasp of the essentials I'd build a 'semi-automatic' system that would automate those processes that were well understood, but still require human intervention where question marks remained. In this instance, it may take the form of a roll-around cart equipped with a mixture reservoir, drum of coolant concentrate, venturi pump, pressure regulator, hose connections to the raw water source, refractometer, and a transfer pump to move mixed solution to the CNC machine.

Through additional experimentation and observations those question marks would be checked off, and additional layers of automation could be added to the 'semi-auto' system until it became fully automated.

It sounds like a lot of work, and it is. However, a practitioner learns a lot in the process of doing that work. Very often, things that don't exist in manufacturer's specification sheets and other documentation, better ways of attacking the problems, and so on. Generally, a piecewise, 'bottom up' approach greatly increases the chances the final automation system will perform adequately.

Generally, a piecewise 'bottom up' approach to building an automation system is more successful

 

[kunalvanjare]

I'll have to ponder on the info in post #9.

You might find this attempt at a closed loop metalworking fluid system informative.
https://www.researchgate.net/publication/315977778_Real_Time_Monitoring_and_Automatic_Regulation_System_for_Metalworking_Fluids

I've gone through this. It is quite in-line with what I have thought, but they have only designed that system for one CNC. It'll be a completely different proposition for say about 10 machines together.

Although it is pertinent to note that they do not use any venturi mixers and rely on the age-old method of a mechanical stirrer in a tank to mix coolant concentrate and water.

 

[kunalvanjare]

As I understand your question, you cannot do this, at least if you need to maximize the utilisation of all of your machines. Different materials and different cutting tools require different coolants and different operations require coolant to be supplied in different ways. (As an example of the latter, if you have a machine facing a piece, then there will be the coolant for that specific material being sprayed onto the surface, while if you are drilling through a different, or even the same material, you will probably be using a different coolant which is supplied through passages in the drill bit itself.) You could probably do this if all of your cnc machines are cutting the same material using the same type of cutting tool (i.e., carbide, TiN, whatever), but I think it will be less than ideal if you have one machine cutting aluminum with HSS and another machining stainless with some coated cutting tool. It will probably work ok if you don't intend to max out the machines to process parts as quickly as possible, though (and you don't have really strict requirements on surface finish). As far as I know, most cnc machines are self contained in that each one has its own coolant reservoir, but I could be mistaken about that last statement.

All of the various devices you mention could certainly be applied to accomplish what you are wanting to accomplish. The real question is that if you do build such a system, how will being tied to a common coolant system affect your ability to process multiple parts from different materials using different cutting tools?

Hello @bobob, we set out on designing this system only considering the fact that it would work for a line of machines using the same coolant. Concentrations do vary, mind from one machine to the next.

How the coolant will be sprayed onto the workpiece is not really in our scope as we shall limit our scope till how or in what condition we deliver the coolant into the machine coolant tank.

All of the various devices you mention could certainly be applied to accomplish what you are wanting to accomplish.

Help, please :/

 

[Tom.G]

I mean, are there any such pumps that can be controlled by PLC i.e the opening size may be opened automatically be a solenoid valve and not by manually rotating a knob by hand?

If it is the valve opening you are trying to control, there is such a thing as a Proportional Valve (Google it) used in industrial control. They are often controlled by a PLC and typically use a 4-20mA current loop interface, although I think I've also seen them with a Voltage interface.

If you have a mixer per machine, some clever engineering may obviate the need for a PLC, with the mix percentage manually set by a calibrated knob. This is assuming that the need for a fill is based only on the fluid level and not on its make-up or contamination level.

Cheers,
Tom

 

[kunalvanjare]

Guys, going to bump this thread again.

Found this interesting product - https://will-fill.com/en/products

Went through this for a while and I think it has a venturi mixer that draws the coolant concentrate automatically with the help of water. But I've seen they mention using a PID for 'autonomous adjustment'. Wonder how that works?

 

[Asymptotic]

Guys, going to bump this thread again.

Found this interesting product - https://will-fill.com/en/products

Went through this for a while and I think it has a venturi mixer that draws the coolant concentrate automatically with the help of water. But I've seen they mention using a PID for 'autonomous adjustment'. Wonder how that works?

This device could be the greatest thing since sliced bread, or a triumph of contentless marketing speak. It is impossible to tell which with the meager details provided. Found slightly more information on a vendor site. The unit appears to have a built-in refractometer and pH probe.
https://www.cis-tools.co.uk/will-fill-landing-page/

It looks like one of these units are required for each CNC machine. If the cost of equipping each machine with an off-the-shelf inline refractometer was prohibitive this approach would be as well.

From the FAQS.

Is the introduction of the emulsion concentrate controlled by water pressure?

No, parameters such as water pressure, intake length, temperature and viscosity can significantly influence the required mixture. As a result, Will-Fill has no mechanical connection between the input of the concentrate and the water inlet.​

This strongly suggests a built-in venturi mixer is not involved.

PID is one way to perform closed loop feedback control. Without additional information it's impossible to say how PID applies in this case. Do they control brix, pH, or both? And how do they go about it?
https://en.wikipedia.org/wiki/PID_controller

 

[kunalvanjare]

This device could be the greatest thing since sliced bread, or a triumph of contentless marketing speak. It is impossible to tell which with the meager details provided. Found slightly more information on a vendor site. The unit appears to have a built-in refractometer and pH probe.
https://www.cis-tools.co.uk/will-fill-landing-page/

It looks like one of these units are required for each CNC machine. If the cost of equipping each machine with an off-the-shelf inline refractometer was prohibitive this approach would be as well.

Yeah I'm well aware of the fact that each machine would require one of these units. The thing is that I have been working or rather trying to come up with a design for using a single refractometer on multiple machines but I've only drawn blanks so far.

This system seemed rather attractive (although applicable only for one machine). Maybe a system that monitors the concentration & performs diagnostic actions (re-fill / make-up) at the best possible price would be the way to move ahead in this. Till I have my own Eureka moment, that is.

I will look further into the PID aspect. Prima facie, I am yet to understand how these guys decide how much liquid (water+concentrate) to fill in the tank depending on the input received from the level sensor.

God this project will drive me crazy very soon !

 

[Sam Phillips]

I have done a large amount of plumbing in my day, and I think I can offer some help here. Before I try though, I just want to make sure that I'm understanding the core problems as I have been reading down the posts:

1. You have several machines in a factory that require coolant solution (powder or concentrate?) and water to be supplied in various concentrations depending on the immediate tasks the CNC machine is doing at that time.

2. You want a system that is fairly automated so that human error does not damage a machine through inadequate coolant or coolant not meant for the current task.

3. You want to minimize waste from high concentrated coolant being used on tanks that don't need it

4. You want the system inexpensive and simple

5. You want to use a refractometer to verify that the various coolant concentrations

My questions are:

1. How much separation happens over time from the coolant and water?

2. Do the individual CNC machines recycle coolant back into their main coolant tank or do they drain used coolant?

3. How big of a room are we talking about?

4. Is their a subfloor that plumping can be run, or does all of the plumbing need to be overhead?

 

[kunalvanjare]

I have done a large amount of plumbing in my day, and I think I can offer some help here. Before I try though, I just want to make sure that I'm understanding the core problems as I have been reading down the posts:

1. You have several machines in a factory that require coolant solution (powder or concentrate?) and water to be supplied in various concentrations depending on the immediate tasks the CNC machine is doing at that time.

2. You want a system that is fairly automated so that human error does not damage a machine through inadequate coolant or coolant not meant for the current task.

3. You want to minimize waste from high concentrated coolant being used on tanks that don't need it

4. You want the system inexpensive and simple

5. You want to use a refractometer to verify that the various coolant concentrations

My questions are:

1. How much separation happens over time from the coolant and water?

2. Do the individual CNC machines recycle coolant back into their main coolant tank or do they drain used coolant?

3. How big of a room are we talking about?

4. Is their a subfloor that plumping can be run, or does all of the plumbing need to be overhead?

Hello Sam, please note point-wise reply.

1. Coolant solution needs to be introduced into the machine tank in an emulsion form (water + concentrate duly mixed). We want to control 10 machines from one central system. Each machine shall have the same coolant albeit at different concentrations. If that is one problem we're unable to solve, then maybe we can think of situations where all machines have the same coolant at the same concentration.

2. Yes. But not worried about wrong type of coolant as we shall limit the system to only one type of coolant as mentioned in the previous point.

3. Refer point #2

4. Absolutely. The easiest way of achieving this would have been to install a process refractometer and all necessary tools on each machine. But the cost is proving to be prohibitive.

5. Yes.

Reply to your other questions :-
1. Not sure I get what you mean by separation. Do you mean reduction in volume of the tank due to evaporation or drag-out? If yes, then that is variable. We will have to install a Level Transmitter in each tank to continuously monitor the coolant level.

2. Yes each machine has an inbuilt tank of approx 200-300 Litres capacity. Coolant after being sprayed on the workpiece drains through a filter into this tank. it is then re-used for spraying inside the machine. It is a closed-loop system and no coolant is drained.

3. Since we're considering 10 machines, the total area (again variable) since all machines would be in one 'line' will be approx 100 ft. from one end to the other.

4. No. All plumbing needs to be overhead.

 

[kunalvanjare]

I'll have to ponder on the info in post #9.

You might find this attempt at a closed loop metalworking fluid system informative.
https://www.researchgate.net/publication/315977778_Real_Time_Monitoring_and_Automatic_Regulation_System_for_Metalworking_Fluids

Did you manage to go through the system in the document that I linked to in Post #12.. the link - http://s000.tinyupload.com/index.php?file_id=07047886135675729106

This is for a system called 'Flexxcool' (can be found online. they even have a youtube video walkthrough). They use Pulse Width Modulation to control the concentration of the make-up fluid. Their system is capable of handling maximum 55 machines in the plant! (not necessarily at the same concentration).

I'm going to go through that same document again. Just wanted to know if you had the chance to go through it. Do let me know. thanks

 

[Asymptotic]

Yes, I've looked at the patent application. Water and concentrate are both fed to two mixing bodies, one set to the low end of the required % concentration range, the other to the high end, and concentration of the delivered mixture is achieved by pulse width modulating two valves connected to their outlets.

Their website and video both have low information content to the point where it is impossible to determine how they are going about it in practice. http://www.flexxcool.com/

In particular, how does their control system know brix % at each machine so it can prepare makeup coolant at the proper mixture percentages? Neither the patent nor website makes mention of how this is done, but the easiest way would be with refractometers at each usage location.

 

[kunalvanjare]

Yes, I've looked at the patent application. Water and concentrate are both fed to two mixing bodies, one set to the low end of the required % concentration range, the other to the high end, and concentration of the delivered mixture is achieved by pulse width modulating two valves connected to their outlets.

Their website and video both have low information content to the point where it is impossible to determine how they are going about it in practice. http://www.flexxcool.com/

In particular, how does their control system know brix % at each machine so it can prepare makeup coolant at the proper mixture percentages? Neither the patent nor website makes mention of how this is done, but the easiest way would be with refractometers at each usage location.

I have had one email exchange with them in which their representative mentioned the fact that they use Ultrasonic non-contact sensors to determine the coolant level. Not sure if he means the liquid level or concentration as the words he used were quite vague. They specifically mentioned that they do not use Inline refractometers because they tend to get dirty over time and throw false readings.

But the refractometers I will use will have an ultrasonic cleaning attachment that periodically cleans the prism surface so that is not an issue for me.

But, having one refractometer on each tank again...

Also, could you tell me how the pulse width modulation works for the two valves? What type of valves can you use?

 

[Asymptotic]

they use Ultrasonic non-contact sensors to determine the coolant level. Not sure if he means the liquid level or concentration

Can't mean the concentration. That's not within the capability of an ultrasonic level sensor.

Also, could you tell me how the pulse width modulation works for the two valves? What type of valves can you use?

It is outlined in the patent application.

An embodiment of the proposed coolant distribution system 10 uses two​

premixed streams of coolant at either extreme of a range​

of concentration, and to mix these two streams in the​

correct percentage to obtain the desired concentration.​

[0025] The desired degree of mixing is achieved by​

calculating a duty cycle for a pwm (pulse width modulation)​

signal to the valve 20 and to the valve 22 and adjusting​

the pwm duty cycle as follows:​

C1= Concentration of mixing valve 20​

C2= Concentration of mixing valve 22​

CM= Desired concentration for a respective machine 30.​

​

​

PWMF = Total cycle time of pwm signal​

TV1= On time for Valve 20​

TV2= On time for Valve 22​

​

​

[0026] In Fig. 1, V1 is valve 20 and V2 is valve 22 in the above description.​

For any reasonable cycle time ("PWMF" in their notation), let's say 10 seconds to make the math easy, practically any solenoid valve chemically compatible with the coolant ought to operate well.

The shorter the cycle time is made, the less accurate metering will become. It takes x amount of time for the valve to shift from full closed to full open position and visa versa, and this "in between" regime becomes a greater percentage of overall cycle time.

 

[Sam Phillips]

My question about separation refers to the mixture at rest. Will the concentrate slowly separate from the water (think of dirty water with the particles slowly drifting to the bottom) or is it fully dissolvable like salt water where time will never cause the dissolved material to separate.

New question for you. Is a refractometer the only way to measure the concentration in the fluid, or is it the only way you have tried (industry standard?)? The reason this is important is that there are many other cheaper sensors that you could use, and if you can graph a direct correlation between their reading and the refractometer, then you could use the cheaper sensor. The first thought that comes to mind is a sensor that tests waters conductivity. If you had a sensor on your incoming water line to provide a baseline for what the city is providing, then anything you dissolve in that water should chance the conductivity of the resulting fluid.

Conductivity sensors are anywhere from $10-200 depending on the maker and the accuracy. And if you can test cheaply and constantly and each machine, then this problem gets much easier.

 

[kunalvanjare]

My question about separation refers to the mixture at rest. Will the concentrate slowly separate from the water (think of dirty water with the particles slowly drifting to the bottom) or is it fully dissolvable like salt water where time will never cause the dissolved material to separate.

The coolant is always present in an emulsified form i.e it is mixed with water and is fully dissolved. There usually is sedimentation found in the tank but that is mostly due to metal particles, chips that settle down along with oil particles and form kind of a sludge.

New question for you. Is a refractometer the only way to measure the concentration in the fluid, or is it the only way you have tried (industry standard?)? The reason this is important is that there are many other cheaper sensors that you could use, and if you can graph a direct correlation between their reading and the refractometer, then you could use the cheaper sensor. The first thought that comes to mind is a sensor that tests waters conductivity. If you had a sensor on your incoming water line to provide a baseline for what the city is providing, then anything you dissolve in that water should chance the conductivity of the resulting fluid.

Conductivity sensors are anywhere from $10-200 depending on the maker and the accuracy. And if you can test cheaply and constantly and each machine, then this problem gets much easier.

Refractometers are the industry standard of measuring concentration of coolant. Not sure if conductivity sensors are used for this application.

 

[kunalvanjare]

Sorry for the inactivity on this. Unable to come up with a solution for a centralized system, I have decided to pursue this for one Machine Sump initially and maybe add a machine or two to this just to avoid the insane amount of piping & valves that would be required to control 10 or more machines from one unit.

@Asymptotic , I am designing a system as described above and have encountered a problem. Please see this image :-

I'll describe how this works.

1. An online refractometer & continuous level transmitter (capacitive or ultrasonic) continuously monitor the concentration & level of liquid in the machine sump. Both these inputs are fed to the PLC through 4-20 mA.

2. I have another mixing tank with a mechanical motorized stirrer. Depending on the inputs of concentration & level, I will decide the amount of re-fill required (how much volume at what concentration) using a formula which will be fed to the PLC. Refer this tool - http://www.qtstools.com/document_library/tech-resources/Coolants/Refill%20Concentration%20Calculator.xls

3. Now that I know how much liquid & concentration is required to maintain the sump at the desired volume & concentration, I have to fill the mixing tank with the exact amount of DM water (from the DM water supply) & coolant concentrate.

4. After mixing, the mixed coolant shall be transferred to the machine sump.

Now, I have a couple of issues here.

1) Depending on the input of current concentration & current volume of liquid in the machine sump, how do I fill the Mixing Tank with just the right amount of DM water & Coolant concentrate? Consider DM water shall be supplied through piping and not from a tank.

2) If I fill the mixing tank without metering or measuring the volume of DM water & coolant concentrate, can I use a Proportioning or Automatic Flow Control Valve on the outlet of the Mixing Tank? This valve would be synchronized through PLC with the Concentration & Level parameters to supply just the right amount of mixed liquid to maintain correct concentration & liquid level in the machine sump. But in this case, how do I know how much coolant concentrate to draw into the Mixing Tank? Using Venturi Mixers is not possible as the purpose of an automated system is defeated when you have to adjust the orifice opening everytime there is a change in concentration.

Any clarity on the above would be hugely appreciated.

 

[Tom.G]

Try these for both water and coolant volumes.

https://www.google.com/search?&q=metering+pump+plc+controlled
https://www.google.com/search?&q=controlled+volume+metering+pump+plc+controlled
https://www.google.com/search?&q=flow+totalizer+plc+controlled
Cheers,
Tom

 

[Asymptotic]

In post #31, I'm uncertain why a proportional valve is placed between the mixing tank and machine sump.
Seems to me this would control only the flow rate between mix tank and sump.

What range of concentration is satisfactory? For example, if the target is 3.5%, can the final mix vary between, say, 3.2 to 3.8% and still allow satisfactory machine tool operation?

 

[kunalvanjare]

In post #31, I'm uncertain why a proportional valve is placed between the mixing tank and machine sump.
Seems to me this would control only the flow rate between mix tank and sump.

The diagram was a work-in-progress. My doubts regarding placement of the proportional valve where mentioned later in that same post. Still unclear whether proportional valves fitted at the inlet of the mixing tank to control flows of water & coolant could help? Individual valves for both of course..

What range of concentration is satisfactory? For example, if the target is 3.5%, can the final mix vary between, say, 3.2 to 3.8% and still allow satisfactory machine tool operation?

Absolutely

 

[kunalvanjare]

Try these for both water and coolant volumes.

https://www.google.com/search?&q=metering+pump+plc+controlled
https://www.google.com/search?&q=controlled+volume+metering+pump+plc+controlled
https://www.google.com/search?&q=flow+totalizer+plc+controlled
Cheers,
Tom

I'm not sure how a metering pump would work for this application, since the Water would be supplied through the plant's piping. To draw coolant concentrate from the drum, I would require something like a Drum Pump.

A Totalizer would have to be installed on the Panel right? Doesn't it require a Flow Meter to be used along with it?

I'm looking for a valve that would probably adjust its opening size as per the Analog signal from the PLC corresponding to the Concentration & Volume readings.

 

[Asymptotic]

Machine sump 'knowns'
Sump coolant concentration (sensed by refractometer)
Sump liquid level (sensed by continuous level transmitter)

Desired goal
Refill sump to desired level with a mixture of water/coolant concentrate to achieve a desired % concentration.

What you must do is come up with a way to achieve this goal while keeping in mind the "engineer's trilemma" - "Quick, Cheap, Good: Pick two."

My question of "if the target is 3.5%, can the final mix vary between, say, 3.2% to 3.8%" was to learn how tightly constrained the control system must be (i.e. - does it have to be essentially dead-on with very tight control of coolant %, or is a fair amount of "slop" acceptable).

How can the desired goal be met?
Two general approaches are 'continuous' and 'batch'. A batch system is easier to design and build than a continuous system, and due to it's simplicity, if it can meet the goal is often a better choice.

Batch system outline
Size the mixing tank to hold about as much volume as the machine sump requires when it signals "make-up required".

Mix tank level can be monitored with a 'low level' float switch set very close to the bottom, and a 'full level' float corresponding to a desired mixed volume. The distance between low and high level floats defines the effective volume of the mix tank, and also how much fluid is delivered to the sump when it signals "make-up required".

Use a N.C. solenoid valve to switch mixing tank water supply, and a peristaltic metering pump to transfer concentrate to the mixing tank. You'll have to read through manufacturer's catalogs to find a peristaltic pump with the required volumetric output, and also think about how to control it. Traditionally, they come in fixed and variable output models. Adjustable pumps cost more. The ones I've used mechanically altered the effective pump tube length, but (even more costly) programmable, variable speed peristaltic pumps with PLC interfacing options are also available.

Look over both types, but a fixed pump may be fine in this application (see caveat below).

Choose one that accepts heads for several sizes of pump tube in case it becomes necessary to change basic flow rate after initial installation. The pumps I've used were rated in gallons per day (GPD), and could be set up with 1/16", 1/8", 3/16", and 1/4" diameter tubing to have corresponding flow rates of 8.75, 34.62, 82.17, and 143.79 GPD.

Let's say a fixed output pump head is rated 82.17 GPD, and the PLC has calculated (based on sump % concentration and current volume) that 2 liters of concentrate are required to fill the mix tank to the required concentration. 82.17 GPD works out to 216 ml/minute. How long must the pump run to transfer 2 liters of concentrate to the mixing tank? It works out to 9.26 minutes.

Batch prep, option 1:
Use the PLC to switch on the peristaltic metering motor for 9.26 minutes, then turn on the water fill valve until mixing tank level reaches the high level float. Turn on, and run the propeller mixer long enough for thorough mixing, then open a solenoid valve (if the mixing tank is higher than the sump, and gravity feed is possible) or turn on a transfer pump to move this fresh mix into machine sump. When the low level float switch is triggered. stop the transfer, turn off the mixer motor, and consider the mix tank available to start another batch.

Batch prep option 1 critique:
Doing concentrate and water fills in this stepwise fashion is very simple, but causes some amount of mixture % variation. How much it matters depends on mix tank dimensions (hence, volume), etc., and you'll have to run calculations to see if it matters enough.

Preferably, both water and concentrate are added in unison, but a problem with the above approach is the time to fill the mix tank with water is probably much less than the time to meter concentrate into it. If both water and concentrate fill commence at the same time, the high level float will trigger before metering pump delivery is done.

A slightly more complex approach is to fit the water line with a manual flow control valve, and adjust it to fill the tank to full level in less time than it takes for the concentrate metering pump to complete it's task. It too won't deliver a perfect concentration ratio, but will be a lot closer than the stone age, solenoid valve only approach above, and with your rather broad range of acceptable concentrations ought to be close enough.

In either case, acceptable results depend on the metering pump operating correctly. The control system doesn't know if the coolant concentrate container goes empty, a leak develops in the suction line (causing the pump to become air-bound on stop delivery), or a delivery line leak develops (concentrate spills to the floor instead of feeding into the mix tank), or the pump itself fails.

Several manufacturers make low flow rate switches and totalizers suited for peristaltic pump service, and could be added to the control system. Keep in mind that continuously variable peristaltic pumps designed for PLC control may have these built in for precisely this type of fault detection.

A Totalizer would have to be installed on the Panel right? Doesn't it require a Flow Meter to be used along with it?

It is useful to think of a totalizer as a flowmeter with memory. That memory may be mechanical (gear driven number wheels) or electronic. If you have a 4-20 ma flowmeter feeding into a PLC, program the PLC to keep track of totalized flow.

 

[kunalvanjare]

Machine sump 'knowns'
Sump coolant concentration (sensed by refractometer)
Sump liquid level (sensed by continuous level transmitter)

Desired goal
Refill sump to desired level with a mixture of water/coolant concentrate to achieve a desired % concentration.

What you must do is come up with a way to achieve this goal while keeping in mind the "engineer's trilemma" - "Quick, Cheap, Good: Pick two."

My question of "if the target is 3.5%, can the final mix vary between, say, 3.2% to 3.8%" was to learn how tightly constrained the control system must be (i.e. - does it have to be essentially dead-on with very tight control of coolant %, or is a fair amount of "slop" acceptable).

How can the desired goal be met?
Two general approaches are 'continuous' and 'batch'. A batch system is easier to design and build than a continuous system, and due to it's simplicity, if it can meet the goal is often a better choice.

Batch system outline
Size the mixing tank to hold about as much volume as the machine sump requires when it signals "make-up required".

Mix tank level can be monitored with a 'low level' float switch set very close to the bottom, and a 'full level' float corresponding to a desired mixed volume. The distance between low and high level floats defines the effective volume of the mix tank, and also how much fluid is delivered to the sump when it signals "make-up required".

Use a N.C. solenoid valve to switch mixing tank water supply, and a peristaltic metering pump to transfer concentrate to the mixing tank. You'll have to read through manufacturer's catalogs to find a peristaltic pump with the required volumetric output, and also think about how to control it. Traditionally, they come in fixed and variable output models. Adjustable pumps cost more. The ones I've used mechanically altered the effective pump tube length, but (even more costly) programmable, variable speed peristaltic pumps with PLC interfacing options are also available.

Look over both types, but a fixed pump may be fine in this application (see caveat below).

Choose one that accepts heads for several sizes of pump tube in case it becomes necessary to change basic flow rate after initial installation. The pumps I've used were rated in gallons per day (GPD), and could be set up with 1/16", 1/8", 3/16", and 1/4" diameter tubing to have corresponding flow rates of 8.75, 34.62, 82.17, and 143.79 GPD.

Let's say a fixed output pump head is rated 82.17 GPD, and the PLC has calculated (based on sump % concentration and current volume) that 2 liters of concentrate are required to fill the mix tank to the required concentration. 82.17 GPD works out to 216 ml/minute. How long must the pump run to transfer 2 liters of concentrate to the mixing tank? It works out to 9.26 minutes.

Batch prep, option 1:
Use the PLC to switch on the peristaltic metering motor for 9.26 minutes, then turn on the water fill valve until mixing tank level reaches the high level float. Turn on, and run the propeller mixer long enough for thorough mixing, then open a solenoid valve (if the mixing tank is higher than the sump, and gravity feed is possible) or turn on a transfer pump to move this fresh mix into machine sump. When the low level float switch is triggered. stop the transfer, turn off the mixer motor, and consider the mix tank available to start another batch.

Batch prep option 1 critique:
Doing concentrate and water fills in this stepwise fashion is very simple, but causes some amount of mixture % variation. How much it matters depends on mix tank dimensions (hence, volume), etc., and you'll have to run calculations to see if it matters enough.

Preferably, both water and concentrate are added in unison, but a problem with the above approach is the time to fill the mix tank with water is probably much less than the time to meter concentrate into it. If both water and concentrate fill commence at the same time, the high level float will trigger before metering pump delivery is done.

A slightly more complex approach is to fit the water line with a manual flow control valve, and adjust it to fill the tank to full level in less time than it takes for the concentrate metering pump to complete it's task. It too won't deliver a perfect concentration ratio, but will be a lot closer than the stone age, solenoid valve only approach above, and with your rather broad range of acceptable concentrations ought to be close enough.

In either case, acceptable results depend on the metering pump operating correctly. The control system doesn't know if the coolant concentrate container goes empty, a leak develops in the suction line (causing the pump to become air-bound on stop delivery), or a delivery line leak develops (concentrate spills to the floor instead of feeding into the mix tank), or the pump itself fails.

Several manufacturers make low flow rate switches and totalizers suited for peristaltic pump service, and could be added to the control system. Keep in mind that continuously variable peristaltic pumps designed for PLC control may have these built in for precisely this type of fault detection.
It is useful to think of a totalizer as a flowmeter with memory. That memory may be mechanical (gear driven number wheels) or electronic. If you have a 4-20 ma flowmeter feeding into a PLC, program the PLC to keep track of totalized flow.

Hey, sorry for the late response.

I have gone through your post and believe that this would work when there is no fluctuation in the daily 'range' of make-up fluid. For example if approx 50 Ltrs of make-up is required, the mix tank has to be sized accordingly. How about cases where there would be more liquid required? Also filling concentrate using a peristaltic pump can be time-consuming.

I have something in mind :-

1. A refractometer & level transmitter record the current values of concentration & volume of liquid in the sump and feed the PLC.

2. Using this data the PLC actuates two valves to varying degrees (that will be calibrated with the output signal). One valve is for the plant's water supply. The other for the coolant concentrate inlet.

3. Both these inlets will be taken to a Venturi Injector (not a mixer.. but an injector, something that is used in irrigation to mix fertilizers apparently). Link - https://mazzei.net/venturi_injectors/

4. What this achieves is proportionate flow of water through the Venturi getting mixed with metered flow of coolant without the need for a pump or secondary mixing tank or mechanical blades etc.

Inspiration for this was taken from - http://s000.tinyupload.com/index.php?file_id=20469651419304289113

Doubts :-

1. This requires a Flow Control Valve with flow-meter/totalizer for both water & coolant lines into the Venturi Mixer.
2. Not sure whether a metered flow of water into the Venturi will be able to draw the required volume of coolant when the coolant line itself is controlled by the valve. Maybe the mixing time might increase, or maybe the mixing will not be adequate.This system can be made into a semi-automatic one if the operator can enter the current concentration of coolant in the machine sump by himself into the HMI of the system. This rules out the requirement of an Inline Refractometer thus drastically reducing the cost of the system.

Once the current concentration is set, the system can automatically determine the volume(through level transmitter) & concentration (through formula) of the make-up liquid.

Would love to hear your views on this.

 

[Asymptotic]

I have gone through your post and believe that this would work when there is no fluctuation in the daily 'range' of make-up fluid. For example if approx 50 Ltrs of make-up is required, the mix tank has to be sized accordingly. How about cases where there would be more liquid required?

What would those cases be?
Sump level is what triggers the make-up cycle during normal operation.

That leaves the case of a "dry" start-up where the machine has been intentionally drained.
If the sump holds 150 liters, for example,

Option 1
Manually mix concentrate with the required amount of water to fill the sump before CNC machine operation commences.

Option 2
Allow the 50 liter capacity automated system to cycle three times to fill the 150 liter sump.

Also filling concentrate using a peristaltic pump can be time-consuming.

In an automated system, so long as the time it takes to meter and mix the refill charge is less than the interval between "sump full" and "sump requires make-up", does it matter how time-consuming it is?

2. Using this data the PLC actuates two valves to varying degrees (that will be calibrated with the output signal). One valve is for the plant's water supply. The other for the coolant concentrate inlet.

3. Both these inlets will be taken to a Venturi Injector (not a mixer.. but an injector, something that is used in irrigation to mix fertilizers apparently). Link - https://mazzei.net/venturi_injectors/

4. What this achieves is proportionate flow of water through the Venturi getting mixed with metered flow of coolant without the need for a pump or secondary mixing tank or mechanical blades etc.

What type of valves? I'm doubtful a PWM-based approach using on/off valves as expressed in earlier posts would work well on this venturi injector. Actual proportioning valve(s) would probably be required, however ...

1. Outlet back-pressure controls how much suction (concentrate) flows through this venturi injector.

2. Built a set of total flow curves for model 283 injector from performance tables in the specification PDF.
Total flow is the fixed "motive" water flow at a particular inlet PSI plus the rated suction flow for given injector outlet pressures.

An injector doesn't necessarily provide a linear relationship over the entire flow range for a given inlet water pressure. It would be desirable to operate the venturi in the linear part of its range for proportionality. For example, with a 50 PSI inlet pressure, a big dead spot exists between 0 and 15 PSI of outlet pressure before changing it has an effect on either total flow or mixture concentration.

3. Points 1 and 2 may be beside the point. If I recall correctly, you are looking for mixture concentrations of under 10%. Can this device deliver them? Suction flow is higher than motive flow for all devices throughout their performance range. For example, motive flow is 0.39 GPM for the model 283 at 30 PSI inlet pressure, and suction flow is 0.80 GPM. This is a total flow of 1.19 GPM.

0.80/1.19 = 67.2% inlet water/suction fluid concentration. This may or may not give acceptable results.

What is the the % Brix reading of fresh concentrate? If it starts out suitably low, then acheiving the desired mixture concentration may be possible.

I'm not saying something like this couldn't be done, simply that there is more to it than it appears at first glance. It is necessary to perform sample calculations to determine whether any particular approach is within the realm of possibility.

 

[ktswastetech]

Hello. Jumping in on this discussion, hopefully not being intrusive.

I am designing the exact system that you have described. However, in my case, the coolant concentration at 15 different machine sumps is all the same. I am proposing the installation of an overhead clean supply and dirty return piping system (3/4" pipe). At each machine sump I will have an AOD dirty transfer pump, and an automatically controlled clean fill valve (controlled by level in the sump).

The clean and dirty piping system will be tied into a centrally located "filter system) where the coolant will be filtered, tramp oil will be removed, and the concentration of coolant can be maintained (in one location).

Each AOD pump will be set up to run (pump dirty coolant from the sump) for a period of time (say 30 minutes at a rate of 10 to 15 GPM), back to the central filter system. When the level in the sump drops to the appropriate level, clean coolant will fill the sump back up. The clean coolant will come from the central filter system clean tank, also fed by an AOD pump.

With this set-up, the level in the sump tanks will always be maintained at the proper level and the proper concentration. The customer will no longer have to check concentration at each sump or top off each sump. Because of the constant "turnover" of the coolant in each sump, the concentration will always be the same as the concentration in central system clean holding tank.

 

[kunalvanjare]

Hello. Jumping in on this discussion, hopefully not being intrusive.
I am designing the exact system that you have described. However, in my case, the coolant concentration at 15 different machine sumps is all the same. I am proposing the installation of an overhead clean supply and dirty return piping system (3/4" pipe). At each machine sump I will have an AOD dirty transfer pump, and an automatically controlled clean fill valve (controlled by level in the sump). The clean and dirty piping system will be tied into a centrally located "filter system) where the coolant will be filtered, tramp oil will be removed, and the concentration of coolant can be maintained (in one location). Each AOD pump will be set up to run (pump dirty coolant from the sump) for a period of time (say 30 minutes at a rate of 10 to 15 GPM), back to the central filter system. When the level in the sump drops to the appropriate level, clean coolant will fill the sump back up. The clean coolant will come from the central filter system clean tank, also fed by an AOD pump. With this set-up, the level in the sump tanks will always be maintained at the proper level and the proper concentration. The customer will no longer have to check concentration at each sump or top off each sump. Because of the constant "turnover" of the coolant in each sump, the concentration will always be the same as the concentration in central system clean holding tank.

Hello @ktswastetech , welcome and thanks for contributing to this.

What you have proposed is workable provided all machines are at the same %concentration, which is not the case with our application.

Although, how do you supply to 15 sumps using one pump from the central reservoir? And, do you cut-off supply to the sump after receiving the 'high level' input from the machine?

 

[ktswastetech]

Hello @ktswastetech , welcome and thanks for contributing to this.

What you have proposed is workable provided all machines are at the same %concentration, which is not the case with our application.

Although, how do you supply to 15 sumps using one pump from the central reservoir? And, do you cut-off supply to the sump after receiving the 'high level' input from the machine?

The one pump at the central reservoir is an AOD pump that is "always on" so it will keep the clean supply header pressurized. At each sump, I am using a Normally Open air controlled level switch that is connected to an automatic ball valve that will be connected to the clean supply drop. The automatic ball valve has an air actuator that is air to open/spring to close.

Also, at each sump, I am installing a 120 VAC single phase "smart outlet". The outlet will be used to power a solenoid valve that will control the air feed to the dirty sump pump. The customer will be able to program each outlet (via an app on his phone) so that only one sump pump runs at a time. He will also set how long the pump will run. Once the level in the sump drops a certain amount, the air controlled level switch will open the automatic ball valve, allowing the sump to "refill" to the desired level.

 

[kunalvanjare]

The one pump at the central reservoir is an AOD pump that is "always on" so it will keep the clean supply header pressurized. At each sump, I am using a Normally Open air controlled level switch that is connected to an automatic ball valve that will be connected to the clean supply drop. The automatic ball valve has an air actuator that is air to open/spring to close. Also, at each sump, I am installing a 120 VAC single phase "smart outlet". The outlet will be used to power a solenoid valve that will control the air feed to the dirty sump pump. The customer will be able to program each outlet (via an app on his phone) so that only one sump pump runs at a time. He will also set how long the pump will run. Once the level in the sump drops a certain amount, the air controlled level switch will open the automatic ball valve, allowing the sump to "refill" to the desired level.

This may sound stupid, but wouldn't an 'always on' pump with a pressurized pipe lead to backpressure or overload on the pump in cases where none of the automatic re-fill valves are open?

I didn't quite understand the significance of the smart outlet. Could you please elaborate.

Also, is maintenance of coolant in the central reservoir in your scope? I mean the refractometer, the filtration system etc..

And why a pneumatic float switch and not a simple magnetic float switch?

 

[ktswastetech]

An AOD pump = Air Operated Double Diaphragm Pump - This pump can be deadheaded to provide a constant pressurized clean return header.

A smart outlet is an outlet that can be controlled by an App on your phone or smart device via WiFi. An example is GE Enbrighten Z-Wave Plus Smart Receptacle Outlet. One outlet on the receptacle can be set up to turn on/off based on a schedule. I am simply plugging in an electrically actuated 120 VAC solenoid that will control the air feed to the sump pump. By using the smart outlet, the customer can set up a plant schedule for when each pump at a machine sump is to come on, and for how long. This way he can control when the turnover occurs at each sump and for how long (based on sump size).

Yes, maintenance of the coolant is in my scope. I am providing the equipment/tankage that will:
- receive the dirty coolant - into a dirty tank
- constantly remove tramp oil and large solids via a tramp oil coalescor and floating skim head
- coalescor loop also circulates the coolant from the dirty tank to the clean tank
- constantly filter the coolant via a separate filtration loop consisting of an AOD pump, inline magnetic filter and two bag filters in series - filters coolant in the clean tank
- coolant concentration will be monitored manually via a refractometer
- coolant make-up will be done manually with a crown proportioning pump, plant water feed, and coolant concentrate
- control of bacteria via ozone generators - one in each tank clean/dirty

 

[kunalvanjare]

An AOD pump = Air Operated Double Diaphragm Pump - This pump can be deadheaded to provide a constant pressurized clean return header.

A smart outlet is an outlet that can be controlled by an App on your phone or smart device via WiFi. An example is GE Enbrighten Z-Wave Plus Smart Receptacle Outlet. One outlet on the receptacle can be set up to turn on/off based on a schedule. I am simply plugging in an electrically actuated 120 VAC solenoid that will control the air feed to the sump pump. By using the smart outlet, the customer can set up a plant schedule for when each pump at a machine sump is to come on, and for how long. This way he can control when the turnover occurs at each sump and for how long (based on sump size).

Yes, maintenance of the coolant is in my scope. I am providing the equipment/tankage that will:
- receive the dirty coolant - into a dirty tank
- constantly remove tramp oil and large solids via a tramp oil coalescor and floating skim head
- coalescor loop also circulates the coolant from the dirty tank to the clean tank
- constantly filter the coolant via a separate filtration loop consisting of an AOD pump, inline magnetic filter and two bag filters in series - filters coolant in the clean tank
- coolant concentration will be monitored manually via a refractometer
- coolant make-up will be done manually with a crown proportioning pump, plant water feed, and coolant concentrate
- control of bacteria via ozone generators - one in each tank clean/dirty

Got it!

I'm assuming the piping won't be under your scope would it?

 

[ktswastetech]

Actually it is, I am doing the complete design. I also sell equipment that will be part of the entire bid package. I just finished the drawings that will be submitted to various contractors for bidding. I am a mechanical engineer and have been doing this type of work for the past 20 years. In this case, my customer has asked for a "turn key" quote.

 

[berkeman]

@kunalvanjare and @ktswastetech -- could you please take that part of this discussion to private messages (PMs)? Otherwise it looks like we are helping with a transaction in the open forums. Thanks.

 

[kunalvanjare]

@kunalvanjare and @ktswastetech -- could you please take that part of this discussion to private messages (PMs)? Otherwise it looks like we are helping with a transaction in the open forums. Thanks.

Noted.

 

[ktswastetech]

Yes, sorry, new here.

 

[berkeman]

Yes, sorry, new here.

No worries. You haven't posted any spam so far, and your responses are very helpful for the OP.