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Large plane castings of the surface coating reinforcement treatment

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The name of the casting is to find the line terminal, casting material is ZCu99.7, casting mass: 19kg. casting processing situation: cylindrical, upper and lower end face; cylindrical inner hole: the thickness of the square plate on both sides of the face (actually there are 4 large plane); φ14 reaming hole, a total of 20 holes. Special treatment requirements for the casting: after finishing, the casting should be silver-plated as a whole, and the importance of no casting defects and electrical conductivity.

Description of the large plane: on both sides of the outer diameter of the cylinder down the vertical direction, 45 ° C tilt connected with 2 square plate, length 180mmX width 130mmX thickness 23mm (actually there are 4 large planes), in the plane of the square plate, there are 6 φ14 perforations. Defects of the castings: on the large plane, the surface layer is locally small-scale off, forming sand trap, after processing, exposing the defects , it is difficult to meet customer requirements.

Large cast steel

Strengthening treatment method: first on the rectangular large plane, with a slightly wider row of pen carefully brush 1 ~ 2 times the surface layer slurry, and then put into the paint bucket overall dip surface layer slurry (270 mesh quartz powder + relative density of 1.28 water glass ten active agents and n-octanol), viscosity value of 20s, sprinkle 70 mesh quartz sand, natural drying before hardening 60min, the die set immersed in the relative density of 1.15 water glass, immediately raised Immerse the die set into the water glass with a relative density of 1.15, immediately put out the die set, fast, then sprinkle the remaining drops of water glass on the die set, put it into the ammonium chloride solution with a relative density of 1.07~1.08 for 10min, remove the die set and rinse it with water, dry it naturally for 40min, the first layer of coating is finished, and the strengthening treatment is also completed. The reinforced treated surface layer is placed for a long time without “peeling”, that is, the surface layer does not delaminate with the wax mold, even if it is placed for 24h in the high temperature season of 37°C and 38°C. No sand sticking to the casting and easy to clean. The reason why such “strengthening” effect is achieved is analyzed as follows.

By the natural drying of the surface layer before hardening, and then add a layer of water glass (relative density of 1.15), so that the water glass infiltration into the surface layer, did not wait for the gel layer back to dissolve, immediately put into the ammonium chloride solution to harden, the need for chemical hardening of the surface layer of the coating, and the water glass infiltration together to get hardened. Together with the chemical hardening after drying, the surface layer can play a “strengthening” role.

In order to illustrate this reasoning, silica-sol surface crust as an example, the surface layer dipped in sand and fully dry, before coating the second layer, the module will be dipped in silica-sol first, immediately remove, dry silica-sol, and then coated with the second layer, not seen gelling back into the solution, which is typical of the protection of the surface layer, effective reinforcement process measures. In theory, called “pre-wetting agent”, with silicone sol containing 25% silica, coating “wet” although “wet”, but will not make silica gel back to the solution, the purpose is to increase the coating strength.

Silica sol – water glass composite crust, the first layer of zirconium powder wrong sand coating dry, before applying the second layer, the module will be dipped in water glass (water glass relative density of 1.15 or so), quickly removed to drain, and then dipped in water glass slurry, sprinkle quartz sand. Dip a layer of water glass, is to let the silica sol coating and water glass coating in the composite bond better, to avoid the first layer and the second layer of different materials produced between the delamination, such a process is widely used, the effect is very good, will not occur dioxygen silica gel re-soluble.

Surface Coating

In addition, why the casting does not stick to the sand? The reason is that the surface layer slurry with a relative density of 1.28 water glass preparation, by the natural drying of the surface layer before hardening, although the water glass infiltration, its relative density is lower than 1.28, so there is no impact.


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