Casting defects and countermeasures

A, casting the reason of shrinkage cavity and countermeasures
Main reasons of alloy solidification shrinkage casting shrinkage and alloy melts to absorb a large amount of oxygen in the air. Nitrogen, etc., the solidification alloy casting shrinkage cavity gas
The solution: (1) set savings goals. 2) the diameter of the bold casting way or shorten the length of the casting way. 3) increase the amount of metal. 4) use the following methods, to prevent the occurrence of depression organization oriented to casting direction. A. the root cool in casting way. B. to prevent vertical impact cavity has molten metal, casting should be into arc. C. oblique placed cast
Second, the reason of casting surface roughness is not smooth
Cavity surface roughness and occurs on the surface of molten metal and cavity chemical reactions, mainly reflects the following situations.
1) the embedding coarse particles, not fine after mixing. 2) after solidification of the embedding material directly into the muffle furnace roasting, too much water. 3) with burning heat up too fast, the expansion of cavity in the different positions, make cavity interior surface spalling. 4) the highest temperature roasting or baking time is too long, make the cavity inside is too dry, etc. 5) metal melting temperature or cast of roasting temperature, react with metal cavity, burning stick on the surface of casting the embedding materials. 6) mould roasting is not sufficient, molten metal casting is fashionable, cause the decomposition of the embedding material, occurred more gas, on the casting surface pitting. 7) after casting molten metal into the cavity caused by high temperature in certain local area, local rough casting surface.
The solution: a. Do not excessive molten metal. B. mould roasting temperature not too high. C. don't too low calcination temperature of the mold (phosphate embedding materials roasting temperature is 800 degrees - 800 degrees) d. avoid organization oriented to casting direction, the phenomenon of the sag. E. on type wax coating to prevent burn sticky liquid.
Third, cracks in the casting
There are two major reasons. One is usually due to its metal solidification too fast, produce the casting defects (joint); 2 it is because of the high temperature cracking.
1) in metal solidification too fast, the casting joint, can control the cast into time and solidification time to solve it. Cast into the time related factors: the shape of the wax type. Cast to the number of thickness. Pressure casting (casting machine). The embedding material permeability. Coagulation time related factors: the shape of the wax type. The highest roasting temperature casting ring. The type of the embedding materials. The type of metal. The temperature of the casting. 2) because of the high temperature cracks, and the mechanical properties of metals and materials are concerned. Easy to produce cracks in the following circumstances: cast into high temperature cracks easily; High strength of the embedding material cracks easily; Extensibility small flipping alloy of nickel and cobalt flipping alloys are prone to cracking.
Solution: use the low strength of the embedding material; As far as possible to reduce metal cast into temperature; Do not use the small ductility. An alloy of brittle.
Fourth, the causes and countermeasures of spherical protrusions
Mainly the embedding material mixed residual air (bubble) stay on the surface of wax type and cause.
1) vacuum reconcile the embedding material, the use of vacuum after the embedding effect is better. 2) on the surface of wax type injection before embedding surfactants (such as rijin company castmate) 3) put the embedding material coated on the wax type. 4) adopt the method of pressurized embedding, extrusion of bubbles. 5) pay attention to the direction of the wax type, when the embedding wax mould and casting have sunken the link below. 6) to prevent the embedding into the bubble. Casts ring and seat. Buffer paper must be closed; Need along the circle of casting wall perfusion embedding material (using shock machine). 7) the filling of casting after not shock.
Five, the casting flash is how
Mainly for casting crack, crack of molten metal into the cavity.
Solution: 1) change the embedding condition: the use of high strength of the embedding materials. The strength of gypsum class materials are lower than that of phosphate embedding material, so it should be careful when using. Try to use a circle casting. No circle casting, casting ring cracks easily, so need to note. 2) roasting conditions: don't directly in the embedding material after solidification roasting (should be in a few hours before roasting. Should be slowly rising. Immediately after roasting casting, don't repeat roasting cast circle.
Six, the different kinds of alloy casting shrinkage rate is different
Understand alloy shrinkage rate, can choose the right special liquid concentration, improve the casting precision. (medical education network to collect)
Seven and condition of casting, precision casting defects and may also be affected