(1)V process technology A. will pre heat the plastic film under negative pressure and suck it on the whole surface of the pattern and the template, then spray the fast drying coating evenly on the film. B. put the sandbox with the suction chamber. C. filling without binder, dry sand and water additions, while sand edge slightly vibration, to ensure that the dry sand fill sand box. Scrape the flat, and cover the material film at the top of the sand box and vacuum through the wall of the box box. D. turn over the box and start the mold. Due to the effect of atmospheric pressure, the plastic film is evenly pasted on the sand mold, and the molding sand is in a tight state. The sample is taken out to achieve the sand mold with a hardness of about 90 degrees. E. type, the negative pressure of the mold has been maintained until the casting is completed. F. negative pressure is released, the mold breaks on its own, can be easily removed from the mold dry sand casting. (2) The feature of V method 1. advantages (1) the molding of dry sand simplifies the sand treatment, and the recovery rate of the old sand is over 95%. (2) the film is covered on the surface of the mold, and the pattern is not directly contacted with the sand mold, so that it is easy to drawing the mold. The pattern has little or no inclination, which improves the dimension accuracy of the casting and reduces the wear to the pattern. (3) pouring in the negative pressure, the fluidity of the metal liquid is good, and can be poured out of 2--3mm thin wall castings. (4) the environment of the workshop is improved without the need of vibration and sand dropping equipment. 2. shortcomings The molding operation is complex and the molding productivity of small castings is not high. It is difficult for mechanized water production to maintain negative pressure from molding, combination and casting until the casting is sanding. In addition, the elongation of the plastic film and the limitation of the formability affect the expansion of the application range of the method. It is used to produce medium sized, simple shape and precise castings, which can be used in cast iron, cast steel and non iron alloy, in all kinds of mass production.
