You will use about half as much (by weight) of resin as you will fibreglass chopped-strand matting.
As a guide, for every square metre you will need about 280 grams for each millimetre thickness.
As an example, if you are producing a tool of area 0.75 sq m area, to a thickness of 3mm you will need 280 x 0.75 x 3 = 630 grams.
The time taken for epoxy resins to cure is dependent on the temperature.
If the workshop is too cold the pot life and curing times will be much longer. Below about 18°C curing is very slow indeed.
If the workshop is too warm the pot life and cure time will be shorter, and this may cause other problems.
We recommend you try to keep your workshop between 20°C and 25°C for best results. The workshop may be cooler at night than during the day and parts left overnight to cure may take longer.
Also ensure you are using the correct mixing ratio.
A cloudy or ‘blushed‘ surface is indicative of too much moisture present during curing.
Remove these surface coats and apply them again in a drier atmosphere.
When building tools or parts that require several pours or layers it is important to ensure the layers bond together well.
The second and subsequent layers should be made when the previous layer is only slightly warm to the touch and tack-free.
Do not allow any moisture, for example damp air, to come into contact with the resin as it cures; this can cause it to ‘blush‘ or look cloudy and inhibits adhesion of subsequent layers.
A thin dusting of the surface with dry silica sand will also improve adhesion.
When casting resins, joints between tool sections should be ground and chemically etched to ensure a good bond.
Epoxy tools are sensitive to sudden changes in temperature; they must be slowly warmed to moulding temperature and slowly cooled back down to room temperature.
Never take an epoxy tool out of an oven ‘to cool‘ as this will cause thermal shock.
If possible, apply thermocouples to the inside and surface of the tool and ensure the difference is never more than 30°C.
Materials should be stored on pallets, between 18°C to 21°C, away from sources of heat and sunlight.
It is not recommended to store materials on concrete or cold floors
There are four main causes of bubbles forming on the surface of a part
1. Inaccurate weighing of the components
Take care to measure the components out accurately
Ensure the scales used are calibrated regularly.
2. Incomplete mixing of the components
If the components have not been thoroughly mixed, soft spots or bubbles can appear on the surface or within the part.
3. Air may have been entrapped during the mixing process, and not had time to disperse fully before the resin cured.
Given enough time, air entrapped through overly enthusiastic mixing would slowly come out of the mix; in practice the resin may start to thicken and trap the bubbles in first.
The isocyanate component (Part B) of a polyurethane system has a freezing point around 20°C. As a result, if it is stored for long periods below this temperature it will crystallise.
It can be re-melted again by warming to around 60°C for 3/4 hour and then stirring.
You must not use it while still warm as this will inevitably lead to extremely short pot life and poor properties. It is essential that once re-melted, the isocyanate is allowed to cool back down to room temperature.
Freezing and re-melting has no adverse affects on the product.
Polyurethanes can be coloured with special polyurethane pigments, which can be either liquid or powder.
When colouring flexible resins, we recommend you use powdered pigments as they affect the mechanical properties less.
Due to variations in the base colour of the polyurethane exact colour matches may be difficult to achieve.
Typical concentrations of pigment are 1% - 3% by weight
We do not recommend concentration of the pigment to be more than 3% as this can compromise the mechanical properties of the material.
Always perform a test specimen.
Polyurethane parts can be successfully painted, but it is important that the surface is correctly prepared.
Check that the surface of the part does not have an oily feel to it; this is indicative of an incorrect resin/hardener mix, and will prohibit good adhesion; remake the part with the correct ratio.
Do not use a silicone release agent; this may mix with the resin and prohibit binding of the primer.
Allow the part to fully cure for at least 24 hours after moulding.
Thoroughly clean the part with an automotive grease and silicone wax remover, such as acetone.
Sand, using 240 grit paper, or sand-blast the surface of the part to etch the surface and give a ‘key‘.
Apply a thin polyurethane primer coat.
The most common cause of brittle parts is due to incomplete cure or incorrect storage of the material.
Make sure the mould temperature is at least 20°C
Check the technical data sheet for product storage information.
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 s
There are three main reasons why polyurethane parts may have soft spots:
1. The mixing ratio was incorrect
Either too much resin or too much hardener will result in incomplete cure and softer parts
Take care measuring out the components
Ensure the scales are regularly calibrated
2. The components have not been mixed properly
Stir the resin and hardener separately, before stirring in any fillers.
When fully mixed, continue stirring and scraping both the bottom and sides of the container frequently.
If you are not certain it is fully mixed — keep stirring! A couple of minutes longer here can make the difference between a good and a scrapped part.
Dimples, or sink-marks, usually appear where there is a change of section on the reverse side of the component, such as ribs, bushes or other changes in geometry.
They are caused in the material shrinking more where it is thickest.
Reducing the speed of the cure, by working at a slightly lower temperature will help.
Using fillers will also help reduce sink marks.
If there is no change of section by the sink mark, it is probably caused by the release agent.
If using a silicone tool, try using no release agent.
There are several reasons parts can be stuck into the tool and hard to remove.
1. Insufficient or the wrong type of release agent was used
Use the type of release agent recommended on the packaging.
2. The mould is old and rigid
Silicone moulds have a lifetime of 20 to 30 casts. Over that time the surface of the tool will be attacked by the hardener and will become brittle and hard.
You can see if a tool is old and brittle just by looking at it; if the otherwise transparent silicone turns opaque and brown in colour it is nearing the end of its life.
A new silicone tool may be required
3. Undercuts are too big
If overhangs and undercuts are too large, cut the tool to give loose pieces that enable the part to removed without having to stretch the mould too much.
There are three common reasons why parts are incomplete:
1. Not enough material was prepared
Recalculate the amount required and try again
2. The material had started to cure before the mould was filled
Pour the material as soon as it is fully mixed
Choose a material with a longer pot life
3. Air was trapped in the tool
When a silicone mould is made, thin wires are generally cast into it to vent the air from the tool to use as the material is poured in.
To add extra vents after the tool is made insert thin tubes, such as hypodermic needles.
There are two reasons why clear parts can have an imperfect surface
1. The wrong mould material was used
For casting clear polyurethanes, use only silicone HQA40 material, which is a translucent silicone.
Only addition cure silicone should be used for clear polyurethane casting
Condensation cure silicones will cause inhibition and leave a sticky surface.
2. Release agents were used
For perfect surfaces, no release agents can be used, as they give the surface a structure that looks opaque or spotty.
Any of our wax-based release agents will work well in this application.
Thick-walled parts, built up in several pours, can delaminate if one of the layers has cured too much before the next layer is poured.
The second and subsequent pours can usually be made between 3/4 hour and 1 hr after the previous pour.
Delamination may occur if the original surface is moist or greasy, not allowing it to bond with the subsequent layers.
ebaboard can be joined to make longer, wider and thicker blocks using our specifically designed bonding agents.
Ideally joints should be kept away from critical surfaces as a slight witness may be visible even after machining and painting.
Resins are reactive chemicals, and whilst they are safe when handled correctly, they can have unpleasant side effects if miss-used.
Always wear protective glasses when handling resins, especially when pouring mixing or brushing them, as splashes can otherwise easily get into your eyes.
Always wear suitable gloves when handling resins. It is easy to become complacent because the effects of skin contact are often not immediate. Too much skin contact can lead to conditions such as dermatitis, and once this has happened the user is often sensitised, and then much more prone to such problems.
When you have finished working for the shift, remove your coat, gloves and protective glasses and wash your hands thoroughly.
Never eat or drink in the workshop; keep food and chemicals apart.
Some silicones, known as ‘addition cure‘ silicones, can be stopped from curing properly by the material against which they are being cast.
This is known as ‘inhibition‘
The most common materials that cause inhibition are certain stereolithography materials and polyester.
Ensure the master pattern is very clean; if possible use IPA.
Paint the master pattern with a PVA sealant.