Over the past 10–15 years, cold-hardening mixtures (CHM) with synthetic resins have become the mainstay in the manufacture of cores and moulds for the production of various types of castings from iron-carbon and non-ferrous alloys, both in single-piece and serial production at enterprises in Ukraine as well as in other industrially developed countries around the world.
Every year, the use of CHM with synthetic resins increases. This is due to the fact that the use of such mixtures can provide high strength with a low consumption of the main binding component (resin), and at the same time makes it possible to regulate the hardening speed of the mixture depending on the concentration of the binding component. In addition, such mixtures can be easily knocked out of the internal cavities of complex configurations of castings and large-sized castings from moulds (caissons). The use of mixtures also reduces the energy intensity of the process, for example, by reducing or eliminating the drying operation, simplifies and reduces the time of technological processes for the manufacture of castings.
A distinctive feature of the use of CHM with synthetic resins is that during the preparation of mixtures, the manufacture of moulds, cores, the process of pouring liquid metal into moulds, knocking out and other stages of work, various substances are released into the atmosphere, as well as products of thermal decomposition of resins, for example, in the form of gases, condensate, etc. As a result, working conditions in foundries or areas may deteriorate. For example, during the manufacture of large-sized castings, the release of such substances and products of thermal decomposition into the atmosphere can reach about 30-40%.
However, today, especially in the manufacture of large castings, it is practically impossible to abandon CHM with synthetic resins.
Therefore, the above-mentioned features of the use of CHM with synthetic resins require the implementation of measures aimed at reducing emissions of substances and various products of resin thermal destruction into the atmosphere of the workshop by introducing appropriate equipment (devices, means) or creating environmentally friendly compounds and compositions of cold-hardening mixtures while preserving their main physical, mechanical and technological properties.
Today, most foundries using the CHM process for casting have adopted no-bake moulding techniques, which undoubtedly simplify the knockout process but also require increased consumption of mixtures and, accordingly, binding compounds.
The amount of compounds released into the atmosphere from synthetic resins can be reduced, as can the amount of moulding mixture used in the manufacture of casting moulds, through the use of special moulding and modelling equipment. The use of moulds can reduce the layer and thickness of the moulding mixture between the walls of the moulds and the cavity of the mould, as well as reduce its quantity. At the same time, the reduced layer of the sealing mixture in the mould ensures the specified set of mechanical properties.
Another promising area is the development of new CHM compositions with synthetic resins, replacing toxic substances such as phenol, formaldehyde and cresol with more environmentally friendly resins. One of the compounds based on oligofurfuryl oxysiloxanes, for example, can fully meet these requirements. Its main feature is the absence of toxic substances in its composition, thanks to which it is recognised as environmentally friendly.
An interesting development is a set of equipment designed and implemented at a number of enterprises for removing gases during mould filling, followed by their neutralisation and elimination of harmful emissions into the environment.
This complex uses special moulds equipped with special pins for vacuuming the moulds, as well as special filters and valves for gas removal. The moulds are vacuumed during the pouring of liquid metal and the cooling of the casting moulds. The gases released during pouring are fed to an absorption-biochemical unit for gas neutralisation. The principle of operation of such a unit is based on the processes of absorption and solubility of harmful organic substances in technical water, followed by their biochemical oxidation by microorganisms to harmless components of CO2 and H2O. Air purified of harmful gases is released into the atmosphere.
The developed equipment complex also allows obtaining high-quality castings, practically without gas cavities, the presence of which is often associated with the low speed of gas removal from the moulds when pouring liquid metal.
Another approach to improving working conditions in workshops using CHM with synthetic resins is the development of automation systems for the manufacture of moulds and cores. For this purpose, moulding units (equipment) with automatic loading of raw materials, as well as equipment for compacting the moulding mixture in moulds or core boxes, are available and used in foundries.
In the relevant moulding and core areas, closed-cycle supply and exhaust ventilation systems with air purification devices and accessories (filters) may be additionally provided.
All of the above measures will help to ensure favourable working conditions in workshops when using CHM with synthetic resins.
For detailed information, assistance and advice on recommendations for selecting appropriate measures and equipment, please contact the company’s specialists, whose contact details are listed on the UKRFAVORIT LLC website. The company’s professional engineers will answer your questions and help you modernise your existing equipment or offer new equipment that will improve working conditions at your enterprise.
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