How to clean injection moulds

The injection moulding of thermoplastic materials is one of the most widely utilised processes in the transformation of polymeric materials and is responsible for the production of many objects for daily use, from components for the automotive sector and caps for food or pharmaceutical products, to numerous forms of packaging.

The injection moulding process consists of melting plastic pads or granules and once they become sufficiently malleable, are injected under pressure into the mould, where they solidify until the final product is obtained and allows the mould to open.

To carry out the injection moulding, a press consisting of the injector unit and the closing unit is used.

The injector is basically a cylinder with a heated inner chamber (to bring the plastic to the melting point) where a worm screw is inserted which, with its rotary movement, advances the molten polymer mass until the mould is filled.

The closure, on the other hand, is the part where the steel mould is mounted and has the task of keeping the injector closed during the injection phase: the moulds are, in fact, made up of two parts – one fixed and one mobile – which would tend to separate due to the high pressure generated by the injector. The fixed part contains the inlet channel of the plasticized fluid pushed by the injector, while the mobile part contains the mechanisms necessary for opening the mould (plates, columns and extractors) and therefore for the extraction of the product.

Injection moulding is a widely used process in mass production, therefore it is essential that the process is flawless in order to avoid unnecessary costs incurred from having to redo results or repair and or replace equipment and to ensure the quality of a large number of pieces.

Proper lubrication of the mould extraction mechanisms or mould cooling channels free from limescale and rust accumulations, are elements to pay attention to in the maintenance of injection moulding machines. But the perfect cleanliness of the mould figures is perhaps the most important factor to ensure the highest quality of production.

It’s easy for a small imperfection in the surface of the mould, in contact with the molten polymer material, to create a defect in the final part once it has cooled. For this reason it is essential to rely on cleaning systems that not only carefully remove the residues that can be deposited on the mould figures (especially the smallest and richest ones), but also in order to prevent any damage to the mould.

The residues to be removed are usually deposits of release agents and lubricating oils – used to allow the detachment of the artifacts from the walls of the moulds and the correct sliding of the mobile part of the mould. In addition, it is also possible that the moulds must be cleaned of residues left by the gases that are created in the presence of pressure and high temperatures (the so-called “flare-ups”).

In order to avoid any damage to the surface of the mould, operations such as sandblasting, the small “clothespins” used to clean the surface of the mould or the use of aggressive and potentially corrosive substances are absolutely to be avoided as they could be counterproductive.

Even resorting to manual washing processes with rags and solvents may not be the best solution, as it could lead to unsatisfactory cleaning standards, especially in the case of moulds with complex geometries and small figures.

Finally, given the considerable impact of a mould on the quality of mass production, it would be advisable to proceed with a standardized washing process that always uses the same products: in this way it will be possible to minimize the possible variability of the production parts due to the level of cleanliness of the mould, eliminating the human factor from the equation.

Automatic parts washers that use gentle water-based detergents are almost always the best choice for washing injection moulds.

In the case of complex moulds and with very small parts it may be necessary to resort to ultrasonic cleaning technology that allows you to reach every millimetre of the mould surface effectively. Ultrasonic cleaners have special features that generate micro-explosions in the washing fluid that the mould is immersed in. These in turn create friction that enhances the cleaning effect of the fluid, even when dealing with fine surface details.

For simpler moulds, however, a rotating basket parts washing machine can be sufficient to ensure standardization, effectiveness and delicacy of washing.

The only exceptions are hot chamber moulds and mirror-polished moulds.

Contact us to discover the best solution for your mould washing needs