Designing an Automatic Coolant Monitoring System for CNC Machines

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

Mentor
55,115
5,338
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

Science Advisor
758
637
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.
 
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.
 
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?
 
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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?
 
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.
 
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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.
 
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.
 
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 havent been able to find any such pump that would operate completely automatically. Video of such a pump can be found in my previous post.
 
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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?
 
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)
 
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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.
 
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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?
 
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@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
 
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.
 
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

Science Advisor
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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
 
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?
 
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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
 
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 !
 
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?
 
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.
 
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
 

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