Maintaining 120 Degrees on a Chrome Roller: Electric vs Water Heating Solutions

[TREK9.9]

Can anyone give me ideas on how to heat a metal chromed roller to maintain 120 degrees on the outer surface. I currently use a pressurised water heater and a hollow mild steel chromed roller with a 12.5mm thick wall. Can it be done with electric rather than water? The roller has a diameter of 6" and is 750mm long. It also turns at 40 rpm.

 

[sophiecentaur]

Hi and welcome.
I should have thought that an electric heater with a thermostat would be much easier and safer than using pressurised (yikes!) water. Or you could always use a different liquid - say a mineral oil - which wouldn't need to be pressurised. How is the hot water temperature regulated? Is it based on pressure / boiling point?
A few more details could be useful.

 

[TREK9.9]

The water is currently pressurised and heated by a 12kw temperature control unit made by Tool Temp. Water flows through the roller and is kept at a set temperature by the unit. I need to use an alternative to this unit as they are too expensive.

 

[sophiecentaur]

If you're talking in terms of 12kW of Power then I am not surprised that the unit is expensive. The pressure needed to have liquid water at 120C would be extreme - but I just had a thought: this would be 120F? But then, why would it need to be pressurised? I think we need some clarification.

Also, about the price that you think is "too expensive": I wonder what your expectations are about good value for specialist engineering.

 

[TREK9.9]

It's 140 degrees c and a heater unit is £3000 Uk Pounds.

 

[sophiecentaur]

I'm not surprised they want a lot of money (and it isn't a vast amount for professional gear, actually) for a system operating at 3.5 Atmospheres (excess pressure for operating at 140C)! I can only suggest that you use a more suitable fluid which wouldn't actually boil at 1 Bar. It wouldn't be difficult to use an immersion heater in a tank of oil. You would need a suitable thermostat and a (Central Heating?) pump to circulate the water round in the roller.
Perhaps there is a good reason for their using water in this particular case?
Does the roller have connections to let the fluid flow round? Are you starting from scratch? How big is the arrangement?

 

[TREK9.9]

The water does flow round via a rotary union. The roller has a diameter of 139.7mm x 12.5mm wall x 700mm long. We use this set up now but would like to see if there is anything available to heat a roller to the same temperature but not use a liquid if possible.

 

[krysith]

The real question should be, what heat flux do you need? The roller is rolling something, and I presume that it is transferring heat to what it is rolling. In addition, it is also losing heat to the ambient air. Depending upon how and why you are transferring heat, most of your heat energy might be being wasted.

So first, determine how much heat you actually need to use. You might be able to save yourself lots of money through insulating certain areas (like putting a cover over the rollerway). Then see what kind of heat flow you need. You might be able to use a much smaller heat source. I would think that an electric heater would be a better choice than pressurized water. The only advantage hot water has is extra thermal inertia if you need that for some reason.

 

[sophiecentaur]

It may depend on the amount of heat that the rolled material is taking from the roller. Water is great stuff for getting heat to where you need it and for keeping the temperature distribution nice and even all over a surface. What is your requirement for this? Is it tolerant or fussy?

There are many facets to this sort of problem and I am only kicking it around as I have no idea about the details. It may be that the present system is over-engineered for your requirement but there may be some crucial factor that requires the water system.
I still say that a pressurised system seems a bit over the top for most applications.

btw, if you wanted to use an electrical heating system, it would be relatively easy to get the power into the roller using slip rings in place of the rotating water ports.

 

[TREK9.9]

The roller needs heating evenly as it is used to heat thermal laminating film. The film is wrapped 3/4 of the way round the roller and the heat activates the adhesive in the film.

 

[Danger]

The roller needs heating evenly as it is used to heat thermal laminating film. The film is wrapped 3/4 of the way round the roller and the heat activates the adhesive in the film.

Okay... "HIGH-SCHOOL DROPOUT ALERT!"
Is there any particular reason that the whole roller has to be hot? From the description as I've read it, only the surface matters. Heating the rest of it would be a waste of energy. So, couldn't a high-resistance electrical coil in a mostly-shielded reflective trough just before the contact patch serve the purpose? I do realize that the patch would cool sooner that way, but maybe it could hold enough heat to finish the task. I don't know anything about thermodynamics, but my past experience in burning myself upon all manner of things suggests to me that 12.5mm of mild steel holds onto heat pretty damned well. I don't think that it would cool down a lot at 40rpm.

edit: I know that some of that sounds self-contradictory, but it's because I wrote it on the fly. An infrared source would in fact heat the whole roller as to its circumference, which seems to conflict with my mention of "heating the rest... ...would be a waste". My meaning in the original statement, though, was that the water has to heat the entire system of pipes, bearings, axles, lubricants, etc. which would not be necessary with surface heating.

 

[sophiecentaur]

Does your present system actually take 12kW on a continuous basis?

 

[TREK9.9]

No, it goes on and off as required.

 

[sophiecentaur]

Sorry, I didn't ask the right question, really. 12kW is a massive amount of power for an application (whole house heating might be no more than that).
Do you really need 12kW, if it "goes on and off"?

What about putting two 3kW heaters inside the drum and filling it with oil, to get an even temperature distribution as the roller rotates. Naturally, some insulation could make life easier. How much are you prepared to experiment and at what rate would you charge your time? £3k doesn't pay for many days of R&D.

You still don't seem to want to commit yourself about actual requirements. How even does the temperature need to be over the drum and over time? Are we talking +/- 1C or +/- 10C? It's all very relevant if you want the best solution. It way well be that your £3k kit is more than you need or it may be that it is only just adequate. I think you might find it very hard to get the existing performance cheaper than with the present system. This may be why they have used a system which, at first sight, seems a bit bizarre.
If you were to pay someone to advise you, they would charge quite a lot of money and they would be asking all these, and more, detailed questions.
If it happens that you only need to warm up your laminate in a non-fussy way, you may do it a lot cheaper but . . . . so far there can be no answer, I think.

 

[Walshy]

Trek9.9 - Did you ever get this working i need to engineer a test rig to that requirement

Can you help