The Process Research Of Producing Medium-and-large Scale Aluminium Casting Using Transfer Coating

According to the need of producing , this paper presents the view of producing medium-and-large-sized Aluminium alloy casting with transfer coating, the research and application of transfer coating at home and abroad is synthetically described since its appearance, meaning and purpose for producing medium-and-large-sized Aluminium alloy casting with transfer coating is studied. Theory analyses in depth the necessary condition of coating transferring ,and the mechanism of interface adhered and the influence factor of the intensity of the adhered interface, the conclusion is obtained that if suitable binder, hardener, special craft method is selected, not only they can improve intensity of the interface, but also they can solve some problem of the solvent relocation, coating flowing which lie on the direct transfer coating, summarizing the difficult to realize the coating directly transferred. Utilizing the existing foundation, under the condition of not needing to add any facility, through designing the concrete testing program, the ingredient of the sodium silicate transfer coating is made, a mold release agent with low cost, high efficiency and low pollution was developed as well as the organic ester hardener suitable to harden rapidly, some main performance such as the density, suspension, permeability, lasting temperament, coating intensity, transferring and the drawing intensity σ_T-M and shearing intensity τ_T-M of the model—coating interface was measured accurately, the method of he coating performance determination was introduced briefly;the casting process of the self-harden sodium silicate transfer coating is studied systematically and the high precision dimension and the bright and clean surface of Aluminium alloy casting is obtained. Discussing the exertion principle of the mold release agent in detail, pointing out the oil type, cream type and solution type of mold release agent are unsuitable to use on site, only the characteristic of mold release agent of compound cream is fit for the on-the-spot requirement. Self-developed compound mold release agent TM1, proved by on-the-spot experiment and pilot production, which enables the adhesion strength of the interface of mold of sodium silicate coating similar to other compound mold release agents, and the resistance of mole release is far lower than other mold release agent, which is suit to the process requirement entirely. The choice of synthesized binder, fire-resistance aggregation, hardener and the preparation of transfer coating is made. The relationship of the principle of hardening and dosage of hardener of transfer coating with the initial solidification, mold release time, temperature and so on are further studied. It concluded that if the traditional adding method of hardener is continue to be adopted, it is impossible to solve the unloading mold difficulty, coating gluing mold, solvent moving, the short using life and the long production lead time of coating of transfer coating at present. Furthermore, the coating flowing on the large area of mold and it is easy to impact the vertical corner of the model, projecting part of coating, the losing of coating for friction and so on. So a new approach mustbe opened up, applying spray technology. Practice has proved, utilizing self-developed interior spray gun to spray, which could achieve the coating mixture with low requirement, the consumption saving, long using life, and the high speed hardening of coating, mold releasing on time and make the speed of molding production close to the traditional sodium silicate molding production, which have widely practicability. The molding process of transfer coating is similar to sodium silicate, but the coating is prior to function the molding process. It must solve the problem the time of mold release, unloading mold, gas forming property and so on.The experimental research indicated that the hardening molding process of the self-harden transfer coating CO2 sodium silicate back sand of the self-developed Quart powder-Sodium silicate-Glycerine Acetic acid Aster series, by determining the precision of the dimension and the cleanliness of the surface and the cost analysis, which could overcome solvent moving result in the low strength area and shorten the time of mold release for waiting greatly, that make the speed of molding production close to the traditional sodium silicate molding production. For solving the difficulty of the front face transferring the coating, which apply the transfer coating technology only for the production of the sand mold and the art of relieve to the casting production of mechanical accessory. The obtained coating have high strength, combing with sand mold firmly, not blowing skin and peel off during the firing and gating. The dimension precision of Aluminium alloy casting achieve CT6-8, the surface roughness of Aluminium alloy casting achieve Ra6.3nm-12.5um, which is equivalent to the Sodium Silicate losing -wax exactitude casting, comparing to losing -wax exactitude casting process ,the procedure is simplified, the coat cut greatly, and the efficiency is greatly improved, furthermore it is not restricted by the dimension of casting. This new molding process is worthy of widening the application.