Thermally conductive plastic or diecast aluminum
Thermally conductive plastic or diecast aluminum
(OP)
I have been asked to draw up a heat transfer pad for a medical device.This is a first draft, subject to external peer review later. Right now having drawn the thing up, the question "What are you going to make it out?" of comes up.
Most of the device will be injection molded plastic, and the suggestion has been made, that this be used for the heat transfer pad. I had suggested Diecast Aluminum, but the feeling was that for a 500 part run that the dies would be much more expensive than a conventional injection molding die. Thermally conductive plastic has been suggested, however I know very little about this other than an article I found on google. Can anybody out there point me in the right direction.
B.E.
http: //www.desi gnnews.com /article/1 65-Thermal ly_conduct ive_plasti cs_beat_th e_heat.php
Most of the device will be injection molded plastic, and the suggestion has been made, that this be used for the heat transfer pad. I had suggested Diecast Aluminum, but the feeling was that for a 500 part run that the dies would be much more expensive than a conventional injection molding die. Thermally conductive plastic has been suggested, however I know very little about this other than an article I found on google. Can anybody out there point me in the right direction.
B.E.
http:






RE: Thermally conductive plastic or diecast aluminum
Plastics injection moulds are also quite expensive. cast zinc or aluminium would be my choices or maybe even pressed metal.
Regards
Pat
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RE: Thermally conductive plastic or diecast aluminum
We are currently working with these on a project:
http://coolpolymers.com/
H
www.tynevalleyplastics.co.uk
RE: Thermally conductive plastic or diecast aluminum
Dan - Owner

http://www.Hi-TecDesigns.com
RE: Thermally conductive plastic or diecast aluminum
I would think the first issue to resolve is how much heat do you need to dump and let that determine the interface.
Harold
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RE: Thermally conductive plastic or diecast aluminum
I'm currently looking at getting a small electronics enclosure, with heat management requirements, made this way.
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Thermally conductive plastic or diecast aluminum
Based on this it would appear that my first thought of diecast or lostwax metal would be the way to go.
I get the idea that the thermally conductive resins have a high metal filler load and can be abrasive on the dies.
I am meeting with the customer and an injection molder next Monday. By then I should be able to ask intelligent questions ( I hope.)
B.E.
RE: Thermally conductive plastic or diecast aluminum
Given it's from an RPM company I'm not gonna claim it's truely objective but take a look at this for more general cost comparison.
http://www.aljcast.com/advant.html
It may not be an issue for your part, but I think the RPM process, or at least some variations of it, can give better tolerances than investment. Not sure if that's a concern for you though.
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Thermally conductive plastic or diecast aluminum
I know this is counterintuitive and I am not an expert but I read a very convincing article explaining this in detail. I've seen the same effect when I worked at Electrolux, we made a water condenser out of plastic and it was better than the same thing made in aluminium and we didn't understand why.
See Compounding World February 2010
http://cde.cerosmedia.com/1X4b792136ec3ad436.cde
Free download.
Chris DeArmitt PhD FRSC CChem
www.phantomplastics.com
Consultant to the plastics industry
RE: Thermally conductive plastic or diecast aluminum
RE: Thermally conductive plastic or diecast aluminum
Great info.
I have used aluminium flake filled nylons and acetals in the past for electric motor housings that needed electrical insulation of some sort but good thermal conductivity. It ended up several pieces with a metal housing and plastic insulators where required instead of he original one piece hoped for. It was a submersible pump for garden fountains. The nylon also allowed to much water to diffuse through it.
In testing they where too conductive of electricity and not conductive enough of heat and their performance was erratic and physical properties where absolute rubbish. That experience might have tainted my views, but my conclusion was plastics are not very useful at conducting heat. A wax model from which a silicon rubber tool is made which is used to injection mould wax plugs for lost wax casting is a relatively cheap method for very small numbers. It is commonly used in the jewelry industry.
Regards
Pat
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RE: Thermally conductive plastic or diecast aluminum
The RPM process looks similar to the method used for casting wax preforms for lost wax molding.
Pud.
That is an interesting material I will mention this when we meet with the molder. It looks like its thermal conductivity is approaching that of aluminum.
Demon 3
This is the thing that started this question. This heat transfer pad is a small dome that fits in the palm of the hand with a labyrinth on the under side with water circulating in it. Not unlike some heat sinks.
Patprimmer
When I see a molding expert like you shrug off thermally
conductive plastics, I pay attention. If the local molder has the same opinion, I guess I know which way we will go.
I am familiar with silicone rubber molds for wax preforms and agree that that lost wax or CNC machining may be the way to go.
MacGyverS2000
I ran up a tool path for a cnc router, it would take two operations, one for the inside and one for the outside about 15 mins per part. I have to see how that compares to molding.
All
Thank you for the inputs I will see how the meeting with the molder and customer turns out.
B.E.
RE: Thermally conductive plastic or diecast aluminum
Chris
Chris DeArmitt PhD FRSC CChem
www.phantomplastics.com
Consultant to the plastics industry
RE: Thermally conductive plastic or diecast aluminum
Keep in mind that all materials resist the flow of heat so having a heat path that is short and wide in area is best. Heat-pipes can often be an elegant solution. They have can achieve thermal conductivity equivalent to 50,000. But you still have to get heat in and out of the pipe.
RE: Thermally conductive plastic or diecast aluminum
As mentioned, to get very high conductivity requires percolation (a pathway of touching particles). That is facilitated by high aspect ratio fillers with fibrous or platy structure.
Chris DeArmitt PhD FRSC CChem
www.phantomplastics.com
Consultant to the plastics industry
RE: Thermally conductive plastic or diecast aluminum
RE: Thermally conductive plastic or diecast aluminum
For lower volume work they have some advantages over investment casting, so depending on your volumes might be worth looking at.
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Thermally conductive plastic or diecast aluminum
Ok so they just use the rubber to make the mold and skip the wax.
I got foiled a little today, My customer took my drawings to the molder without me, and has not reported back yet.
B.E.
RE: Thermally conductive plastic or diecast aluminum
http://www.aljcast.com/rpm.html
http://www.trilore.com/RPM%20Process.htm
I feel like I'm maybe pushing this a bit hard, sorry if that's the case, however given the 500 production run and the relatively low tooling cost it may be appropriate.
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Thermally conductive plastic or diecast aluminum
Looking at these two sites is blowing the cobwebs off.
Before I left the UK and came over here, the company I was employed at, as a drafter, had a 10 ton foundry. We mostly used to sand cast iron, but we also did some brass and bronze work, and for that we used to, use plaster, to get fine detail.The last time I drew casting details was in BS 308 (pre1968) and I think that standard has been dead and buried for many years.
Any way this is getting away from the point, I will pass this info on to my customer, and see if he wants to follow up. Thank you again for the information.
Brian.
RE: Thermally conductive plastic or diecast aluminum
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Thermally conductive plastic or diecast aluminum
My customer reported back to me today. After discussion with the molder, they are going to use metal for the heat transfer pad.
One thing that disturbed me, but did not surprise me, is that the proto typing and mold building is going to be done in Taiwan.
Anyway my part is done, I thank everybody for their suggestions and please consider this thread closed.
B.E.