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The advantages and disadvantages of main shell making precision casting process

by:XEX     2021-01-24
Current domestic production of precision casting and the advantages and disadvantages of the main shell making technology are as follows: 1, the current domestic casting shell making technology are widely used in the production of three types: type A and sodium silicate shell; B, the composite shell; C, silica sol shell; D type sodium silicate shell the process in the country for nearly 50 years of production history, the factory points still occupies the quite a proportion of precision casting factory in our country. Back through the years layer shell of refractory improvement and popularization and application of new curing agent, sodium silicate shell strength have multiplied, the casting surface quality, dimensional accuracy and yield had greatly improved. Low cost, the shortest production cycle, high hulling performance and high permeability is still less than any other type of shell process. 1. The main problems of 1 ( 1) A high content of sodium silicate binder is the inherent drawback of Na2O, shell high temperature strength and creep resistance than silicon solvent as shell. Combined with the refractory material on the surface using price inferiority, grain size distribution of quartz sand, Powder) And therefore must not obtain high quality casting. ( 2) Shell production condition is poor, the lack of strict production process and the control of parameters. Due to the highly corrosive hardener, dust removal equipment simple, rarely workshop, constant temperature and humidity, dust production environment. Affecting the quality of shell and casting coating preparation, hardening, dry and dewaxing process, few operating specifications as stipulated in the industry under strict control. Shell dry place, such as temperature, humidity, wind speed is uncontrolled, reason often occur at high and low temperature or plum rains season batch scrap quality accident. All in all, most of the factories to stay in the workshop phase, skill rather than rely on the scientific quality management for production. This is sodium silicate shell casting quality is not stable for decades, one of the main reasons for high reject rate and repair rate. 2, the composite shell at present a lot of factory will be the first and second switching mullite powder and zircon powder and silica sol shell. Back layer still want to use the original type sodium silicate shell process. It is combined with silica sol shell fine surface quality and sodium silicate the advantages of low cost, short cycle of an improved scheme. Compared with sodium silicate shell, the casting surface quality are greatly improved, reduced the surface roughness and surface defects, repair rate decline. Similar to sodium silicate shell production cycle. 2. The main problems of 1 ( 1) Due to the back layer kept sodium silicate binder, so its shell overall high temperature strength, creep resistance, lower than the silica sol shell casting dimension accuracy of castings and shape tolerance than silica sol shell. ( 2) Permeability is less than sodium silicate shell silica sol shell, shell type high temperature strength less than silica sol shell, easy to cause waste. ( 3) Composite shell casting quality stability is better than sodium silicate, but is much less than the silica sol shell. ( 4) Composite shell with high price zircon powder surface, its shell cost is one type of sodium silicate shell type 4. 5 times, if the back layer USES the mullite sand powder, its shell is almost the same cost and silica sol shell, its low cost advantage is not obvious. ( 5) The composite shell medium temperature wax material cannot be used. Medium temperature wax cannot use hot water dewaxing. Dewaxing in autoclave, due to high temperature and high pressure, the temperature wax liquid and sodium silicate in the back layer and residual hardener of saponification reaction, violently without recycling can't reuse. 3, silica sol shell in the 1960 s, silica sol as the ceramic shell mold of binder used in foundry industry, with its incomparable advantages gradually replaced immediately once widely used preparation technology, pollution, high cost of sodium silicate and hydrolyzed ethyl silicate ester. Practice proves that using liquid silica sol as the ceramic shell mold adhesive has the following advantages: simple preparation process, the coating is easy to store, dip coating used slurry can continue to use after adjusting composition, reduce material consumption, dip coating process performance is stable, easy to operate, cancelled with the ammonia dry when hydrolyzed ethyl silicate ester, working environment improved, humidity of hot air drying, the shell mold strength is high, use water-based silica sol, good safety. Allegedly, from ethyl silicate after using silica sol, 20 ~ 30% reduction in energy consumption, shell mold qualified rate increased by 15 to 20%, greatly improve work environment. 3. Silica sol (1 Low temperature wax) Shell of low temperature wax molding easy, simple equipment, wax mold surface roughness were similar, process than composite shell stable quality, especially the casting dimension accuracy is high, because it has no sodium silicate, shell type high temperature performance is good, after roasting shell permeability is high, creep resistant capability is strong, can be suitable for thin-walled parts, complex structure of medium and small parts, and can produce weighing up to 50-100 kg of large pieces. 3. 1. 1 there is a problem, 1) Most shell in the water because of the low-temperature wax dewaxing, saponification residues are difficult to be mixed, the surface of the shell type variation in casting repair rate is a bit high.
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