Frequently Asked Questions ebalta offers free technical support on all of our products and can help you with a wide range of technical issues from product recommendations and technical information to material demonstrations and specialist process development.
Please refer to our on line resource of technical FAQ's below or call: +44 1332 814700 if you need to arrange to speak to a technical specialist.
All polyurethanes shrink as they cure. They also give out heat as they cure, known as “exotherm”. The amount of shrinkage depends on several factors:
1. Keep to maximum thickness specification
Each material has a specified maximum thickness before excessive shrinkage occurs. Please refer to the product technical data sheet.
Check that your application falls within this specification.
2. Workshop temperature
Higher workshop temperatures increase shrinkage.
Keep the workshop between below 25°C.
3. Minimise section thickness
Thicker sections create more heat and so increase shrinkage.
Try to build up the part in layers, or fill the material with specified powders.
Use a core to minimise the volume of resin required.
4. Tool material
The thermal conductivity of the tool material also affects shrinkage;
Materials with high conductivity like metal take the heat out of the part fast and reduce shrinkage.
Insulating materials, such as wood, tend to increase shrinkage and will also invite moisture resulting in a poor surface finish.
5. Allow the material to gel
If heat-curing a tool in an oven, allow the material to gel before putting it in the oven. This will allow the chemical reaction to take place.
6. Use a filler
Fillers act in two ways
They absorb heat, reducing the temperature of the mix
They displace resin which would otherwise be adding more heat
Aluminium powder or beads make very successful fillers
