Casting, coating, laminating, supporting with synthetic resin    

How do the casting resins differ?

Most casting resins are duroplastics, which means that they can no longer be moulded once they have hardened. Polyurethane rubber, which can be used for both moulding and casting, is an elastomer.

The casting resins can be differentiated on the basis of numerous criteria such as the shrinkage and temperature development during curing, the transparency, the UV, moisture or temperature resistance, odour development – and last but not least the 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 used with a suitable protective mask and in well-ventilated rooms or outdoors. Unlike the other resins, acrylic resin is solvent-free and non-toxic.

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

Polyurethane resin has a 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 fluid and have a very short pot life and demoulding time. These fast casting resins can be used to produce moulds in a very short time. By using fillers such as Fillite filler / hollow microspheres , particularly lightweight moulds can be built and thicker layers of resin can be poured. 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 completely different properties to other synthetic resins due to its composition: it is an opaque material that looks like plaster but is harder. Acrylic resin has good adhesion properties, meaning that it can be used to coat a wide range of materials better than plaster. It also generates low heat when curing. Acrylic resin is non-toxic and very easy to work with, making it ideal for use in educational or therapeutic settings, for example.

Casting, coating, laminating

Synthetic resins can be used for casting, coating and laminating: Transparent epoxy and polyester resins can be used to mould objects and mould objects. The casting resins are cast in several layers for larger objects, while the transparency of the material is retained. Objects can also be coated with the casting resins; for this purpose, the resin is also cast or applied with a brush or, for example, thickened with a filler using a spatula.

In addition to casting resins, there are also so-called gelcoats. These are special coating resins with even more different properties: The transparent polyester gelcoat, for example, is impact-resistant and makes the coated object waterproof and chemical-resistant.

Laminating can be used, for example, to build thin-walled, stable moulds: When laminating with synthetic 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 silicone or polyurethane rubber, for example. There are also special laminating resins.

Build support moulds from synthetic resin

Flexible casting moulds, e.g. made of silicone often require a support mould. This can be made from plaster, for example, but acrylic resin is also ideal for this purpose. Very stable support moulds, which are significantly lighter than plaster moulds, especially for large moulds, can be made from epoxy resin with added fibres, for example. 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 coloured very well. It is important to ensure that the pigments, colour powders and colouring pastes are suitable for the selected synthetic resin, not all materials are compatible. It is generally best to first produce 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 the objects moulded in this way appear like cast metal objects, which can even be patinated. Cold casting offers a good alternative if real metal casting is not an option, for example due to the complex process involved.

In addition to pigments or metal powders, fillers can also be added to synthetic resins to change the flowability of the material: With talcum powder or AEROSIL can be used to thicken epoxy, polyester or polyurethane casting resins, for example, to make them fillable. FILLITE filler / hollow microspheres make synthetic resin compounds lighter - this can be an advantage, especially for large moulds. In addition, the filler accounts for a large proportion of the volume, so less casting resin is required. This also has an effect on the price, as the filler is cheaper than the resin. In addition to the quantity ratios, it is also important to ensure 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 casting mould (e.g. silicone mould) and the casting compound or different casting mould parts with each other. During casting, the mould must also be protected from damage by the casting material, depending on the casting compound and the material of the mould. The appropriate release agent is selected depending on the materials that come into contact with each other.