Thermoforming 65kg/m3 PET foam blocks

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#1

Hello!,
my plan is to give a block of PET foam with the density of 65kg/m3 and with the dimensions of 165cm x 50cm x 6cm a banana shape (front and end approx 10cm up). I already built a mould with the shape of the finished product but the heating device is missing. Since the thermoforming temperature is about 210 degrees celsius my plan would be to use a extended kitchen oven for heating.

[ol]
[li]Can you technically thermoform a 6cm thick block this wide with homemade equipment?
[/li][li]For heating I heard IR would be the best because of the deep penetration of the material, wouldn´t be hot air possible too? (but slower?)
[/li][li]When the material is hot enough, do I need a positive mould to put on top of the foam too, or is it enough when I slowly press it down with my hands?
[/li][/ol]

I attached some pictures of the foam blocks and mould. Thanks for your answers!

Regards, Max

#2
  1. Never tried it with homemade equipment but why not. Homemade oven + vac bagging and allowing for springback could work for low volumes. Perhaps even a heated tool would be good.
  2. IR is great if you match the emission spectrum of the heaters to the absorption spectrum of the material and any other materials in the way such as diaphragms. If you want a good set up for this I can point you to people who can do it.
  3. I cant imagine you will be pressing down with your hands at 210 deg C will you?!? You will need something else likely.
#3

It is very difficult to heat foams with hand hot air guns or other as they will always just heat a small area rather than the whole piece.

Usually for PVC or acrylic foams I use an oven and vacuum bag process at 90-100 deg C. You needs to hold the vacuum until the foam is cooled.

Your bend is not that great, if you can shape your blank with the complete shape first, then laminate and vac bag onto you mould in one shot you will find that the cured laminate will lock in your rocker shape without the need to heat form the foam first.

If you really need to form the foam shape first then you could also consider laminating the foam together in thinner layers like plywood. So for your 60mm you vacumm laminate 3 x 20mm layers to your mould with some glue in-between. Onced cured the rocker will also be locked in (maybe a small amount of spring back).

Kite board?

#4

Thanks for your answers, I really appreciate it!

I built myself a hot air oven (See attachement!) and the first try to heat the block should be today. A heated tool would be great, but I cant afford it yet. I also bought a vacuum pump but im missing a vac bag that can withstand 200 Celsius. Im currently searching for something, anyone got other ideas what I could use?

Yes, it will be some sort of Kiteboard! Good guess! Im using this new type of blank because of its environmental friendliness. Thanks for the hint with laminating first and then heating, it would save alot of time! I will try it once i know wheter the blanks are working good or not!

#5

The idea with laminating the foam is that you don’t need to heat it at all.