How do the casting resins differ?

Most casting resins are thermosets, which means that they cannot be deformed once they have cured. Polyurethane rubber, which can be used for both moulding and casting, is an elastomer. 

Casting resins can be distinguished on the basis of numerous criteria such as shrinkage and temperature development during curing, transparency, UV, moisture or temperature resistance, odour development – and last but not least, price. 

While polyurethane resin is odourless and epoxy resin has a low odour, polyester resin has an intense odour due to its composition and should only be processed with a suitable protective mask and in well-ventilated rooms or outdoors.  Unlike the other resins, acrylic resin is solvent-free and nontoxic.

Epoxy resin and polyester resin are transparent resins. Compared to epoxy resin, polyester resin is easier to work with because you don't have to be quite as precise with the proportions of resin and hardener. Polyester resin is also much cheaper than epoxy resin, but has the disadvantage of shrinkage of up to 10 %, which is a major disadvantage for some applications, whereas this is minimal with epoxy resin. With epoxy resin and with polyester resin, care must be taken that a certain maximum thickness of the layers is not exceeded, as otherwise the reaction temperatures can become very high, which in turn can impair the material quality (e.g. clouding).

Polyurethane resin has low shrinkage and lower temperature development during curing than other resins, especially when processed with fillers. There are also polyurethane casting resins that are very thin and have a very short pot life and demoulding time. With these rapid casting resins, it is possible to produce casts in a very short time. By using fillers such as Fillite Micro-Hollow Balls, particularly light moulds can be built and the casting of thicker resin layers is possible. With PUR resins, care must be taken to ensure that all surfaces with which the casting resin comes into contact are completely dry, otherwise undesirable foaming may occur.

Acrylic resin has very different properties to the other resins due to its composition: it is an opaque material that looks like plaster but is harder. Acrylic resin has a good adhesiveness, so that it can be used to coat numerous materials better than plaster. In addition, there is low heat development during curing. Acrylic resin is non-toxic and very easy to work with and is therefore also good to use in the educational or therapeutic field, for example.

Casting, coating, laminating

Synthetic resins can be used for casting, coating and laminating: With the transparent epoxyand polyester casting resins, objects can be cast and objects can be moulded. The casting resins are cast in several layers for larger objects, the transparency of the material is maintained. Objects can also be coated with the casting resins. For this purpose, the resin is also poured or applied with a brush or, for example, thickened with a filler.

In addition to casting resins, there are so-called gel coats. These are special coating resins with yet other properties: The transparent polyester gelcoat, for example, is impact-resistant and makes the coated object waterproof and chemical-resistant.

By laminating you can build thin-walled stable moulds, for example: When laminating with resin, several thin fibre-reinforced (glass fibre, glass fabric, carbon fibre) resin layers are placed on an object to be moulded or in a mould made of e.g. silicone or polyurethane rubber. There are also special laminating resins.

Building support moulds from synthetic resin

Flexible moulds, e.g. made of Silicone often need a support mould. This can be made from plaster, for example, but acrylic resin is also excellent for this purpose. Very stable support moulds, which are considerably lighter than plaster moulds, especially for large moulds, can be made, for example, from epoxy resin with added fibres. Multi-part support moulds made of synthetic resin can also be screwed together, which is not possible with plaster moulds.

Fillers and pigments for synthetic resins

Synthetic resins can be very well coloured. It is essential to ensure that the pigments, colour powders and colour pastes are suitable for the chosen synthetic resin, not all materials are compatible. Basically, it is best to first make a test piece in the desired colour.

With metal powders you can not only colour synthetic resins, but also use the so-called cold casting process: A high proportion of metal powder makes objects cast in this way look like cast metal objects, which can even be patinated. Cold casting offers a good alternative when real metal casting is out of the question, e.g. due to the time-consuming process.

In addition to pigments or metal powders, one can also add fillers to synthetic resins, which change the flowability of the material: With Talkum or AEROSIL, for example, epoxy, polyester or polyurethane casting resins can be thickened to make them filler-ready. FILLITE micro hollow beads make resin compounds lighter - this can be an advantage, especially for large moulds. In addition, the filler makes up a large part of the volume, so that less casting resin is needed. This also affects the price, because the filler is cheaper than the resin. Again, apart from the quantity ratios, make sure that all materials are compatible.

Release agent to protect the master model & for perfect demoulding

When moulding objects or bodies, release agents first ensure that the original object, the master model, is not damaged by the moulding process. Release agents prevent „sticking“ or the (chemical) reaction of the surface of the model and the moulding compound or the mould (e.g. silicone mould) and the casting compound or different mould parts with each other. During casting, depending on the casting compound and the material of the mould, the mould must also be protected from damage by the casting material. The appropriate release agent is selected depending on the materials that meet in each case.