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Frequently asked questions Q. Why is my laminate / gelcoat still soft even after the suggested cure times on the technical data sheet? A. The potlife and cure times of thermoset resins are dependent on temperature. The information stated on our technical data sheets is usually quoted at 20oC. If the ambient temperature drops below this, as often it does in the winter and in the evenings, the potlife and cure times of the epoxy resin is extended.
Q. Why is my epoxy tool de-laminating? A. The second layer of gelcoat and subsequent layers of laminate must be applied at the ‘drag free’ stage. This is the point at which you can drag your finger lightly across the gelcoat or laminate without any material coming off on to your finger, but leaves a slight trail behind your finger. If you leave layers to fully cure between coats adhesion between layers is lost and de-lamination will occur.
Q. What coverage area can I expect to get with a 1Kg kit of EP 401? A. 1mm layer = 3570 cm2
Q. How much laminating resin do I require if I am using 600g chopped strand mat? A. Roughly speaking you need 1Kg of resin for every 2Kg of chopped strand mat. Q. My polyurethane unit has air bubbles on the surface. A. When mixing the two components of a polyurethane together air may be introduced in to the mix, and may not have time to escape before curing. To solve this problem the polyurethane may be vacuumed before pouring in to the mould to pull all the mixed air out of the product. The material can also be vacuumed in the mould if the potlife permits. Also moisture has the effect of producing gas bubble within a polyurethane. This can be avoided by ensuring the mould is moisture free and the polyurethane is kept in sealed containers.
Q. The part B (isocyanate) component of my polyurethane system has got crystals and lumps in it. A. Isocyanates have a tendency to crystallise (freeze) at temperature below 20oC. If the isocyanate has been stored in temperature below 20oC for long periods of time it may start to crystallise. Heating the isocyanate to 60oC for 30-60 minutes can reverse the crystallisation. It is important to let the isocyanate cool down again before using it as the potlife of the system will be drastically reduced.
Q. Can I pigment my polyurethane? A. You can pigment polyurethanes with liquid polyurethane pigments. These are added and mixed in with the part A component of the system in concentrations of 1-3 % by weight. When using flexible polyurethanes it is advisable to use powder pigments, as liquid pigment can change the physical properties of the product. The natural colour of the cured polyurethane can vary from beige to water clear depending on the product, therefore it maybe difficult to get exact colour matches, contact Alchemie for colour matching details.
Q. Why is my polyurethane unit brittle? A. Brittle parts are often caused by mould temperature. If the mould being used is cold (below 20oC), then under-cure might take place and the unit may have poor mechanical properties.
Q. Can your polyurethanes be used for food applications? A. No, because the cured polyurethane contains a small amount of free isocyanate monomer. Q. My addition cure silicone has sticky uncured patches on the surface of the mould. A. Addition cure silicones are inhibited by certain materials which can cause the silicone not to cure in places that have been in contact with such materials. One such material is polyester, but for a comprehensive list of materials that inhibit addition cure silicone please contact Alchemie’s technical department.
Q. Can I heat cure my silicone rubber to speed up the cure? A. Addition cure silicone can be force cured by heating it in an oven. This drastically reduces the cure time of the rubber. At 20oC the rubber will usually take 18-24 hours to cure, at 60oC it will take approximately 2 hours to cure, and at 80oC it will take approximately 1 hour to cure. Condensation cure silicone cannot be force cured by heating, but can be accelerated by adding a special catalyst, contact Alchemie technical department for details.
Q. Do I require a vacuum chamber for using silicone rubber? A. When using addition cure silicones we recommend you vacuum the material for the best results due to the viscosity of the material. However it is not always necessary to vacuum the condensation cure silicones due to their lower viscosity, but if you have access to a vacuum chamber it is always better to vacuum the material.
Q. Can I cast low melt alloys (less than 300oC) into your silicone rubber? A. Yes you can, but do not expect to get more than 5 or 6 units out of the mould. Q. What is the best release agent to release silicone from silicone? A. The best release agent to use is a home-made one made by dissolving 3% Vaseline in white spirit. This is then painted on to the surface of the silicone rubber you wish to release in several layers, and allowed to dry.
Q. What is the best release agent to release polyurethane from polyurethane? A. For the best results you need to use a wax based release agent either suspended in a solvent or an aerosol, such as Alchemix R7 or R5. Q. Can your modelboard be adhered together to give a thicker sheet? A. Yes they can using our adhesive Alchemix EP5941.
If you have any technical questions regarding the application or use of our material please contact the Alchemie technical department.
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 email: sales@alchemie.com |
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