Application of centrifugal casting:
Castings with significant production benefits include:
① Bimetallic cast iron roll;
② Heating furnace bottom heat-resistant steel roller table;
③ Special steel seamless steel pipe;
④ Brake drum, piston ring blank, copper alloy worm gear;
⑤ Special shaped castings such as impellers, metal false teeth, gold and silver mesons, small valves and cast aluminum motor rotors.
Centrifugal casting was first used to produce cast pipes, and then this process developed rapidly. Centrifugal casting process is adopted in metallurgy, mining, transportation, irrigation and drainage machinery, aviation, national defense, automobile and other industries at home and abroad to produce steel, iron and non-ferrous carbon alloy castings. Among them, the production of centrifugal cast iron pipe, cylinder liner and shaft sleeve of internal combustion engine is the most common. For some forming tools and gear castings, centrifugal force can also be used to pour the melt mold shell, which can not only improve the precision of castings, but also improve the mechanical properties of castings.
Castings with large production output include:
① Iron pipe: nearly 1/2 of the total output of ductile iron castings in the world is produced by centrifugal casting
② Cylinder liners for diesel and gasoline engines
③ Various types of steel sleeves and pipes
④ Bimetal steel back copper sleeve, bearing shells of various alloys
⑤ Paper machine drum.
Advantages and disadvantages of centrifugal casting:
① There is almost no metal consumption in the gating system and riser system, which improves the process yield;
② The core can not be used to produce hollow castings, so the metal filling capacity can be greatly improved when producing long tubular castings, the ratio of casting wall thickness to length or diameter can be reduced, and the production process of sleeve and pipe castings can be simplified;
③ The casting has high density, less porosity, slag inclusion and other defects, and high mechanical properties;
④ It is convenient for manufacturing barrel and sleeve type composite metal castings, such as steel backed copper sleeve, bimetal roll, etc; When forming castings, the filling ability of metal can be improved by centrifugal force, so thin-wall castings can be produced.
Filtration of liquid metal
Some alloy melts contain many dregs that are difficult to remove. Various filter screens can be placed in the pouring system to remove the dregs, such as foam ceramic filter screen, glass fiber filter screen, etc.
pouring temperature
Most centrifugal castings are tubular, sleeved and annular pieces. The resistance encountered by liquid metal during mold filling is small, and centrifugal pressure or centrifugal force can strengthen the filling ability of liquid metal. Therefore, the pouring temperature during centrifugal casting can be 5~10 ° C lower than that during gravity casting.
Mold speed
It is an important process factor in centrifugal casting. Different castings, different casting processes, and different mold speeds during casting formation.
Low mold speed will lead to poor mold filling of liquid metal in vertical centrifugal casting, and rain of liquid metal in horizontal centrifugal casting, as well as loose, slag inclusion and uneven defects on the inner surface of the casting;
If the mold speed is too high, cracks, segregation and other defects are easy to appear on the castings. Defects such as expansion box will form on the outer surface of sand mold centrifugal casting, which will also cause large vibration, increased wear and excessive power consumption of the machine. Therefore, the selection principle of mold speed should be to select the minimum value on the premise of ensuring the casting quality
Utilization of slag
In order to overcome the subcutaneous shrinkage defects caused by the bidirectional solidification of thick wall centrifugal castings, the slagging agent and the liquid metal can be poured into the mold together during pouring, and the slag covers the internal surface of the casting to prevent the heat dissipation of the internal surface, create a sequential solidification condition from the outside to the inside, and eliminate the subcutaneous shrinkage. At the same time, the slag making agent can also play a role in refining the molten metal.
The method for casting slag forming agent is as follows: powder slag forming agent is sprinkled in the pouring tank during casting; Pour molten dregs and molten metal into the mold.
Application of paint
The composition of coating for centrifugal metal mold is similar to that for gravity metal mold casting. When casting slender centrifugal castings, it is difficult to remove the residual paint on the mold working face, so the residual strength of the binder in the paint composition after high-temperature work should be as low as possible to facilitate removal.
Casting demoulding
In order to improve production efficiency, casting stripping should be carried out as early as possible on the premise of ensuring quality. Sometimes, in order to prevent the casting from cracking, the casting after demoulding shall be immediately put into the holding furnace or buried in the sand pile for cooling. For some castings that are not easy to demould and need slow cooling and crack prevention, the casting mold with castings can be removed from the centrifugal casting machine immediately after the mold stops rotating, buried in the sand pile for slow cooling, and demoulding can be carried out at room temperature.
gating system
The gating system in centrifugal casting mainly refers to the pouring cup receiving metal and the pouring groove connected with it, sometimes including the runner in the mold. When designing the gating system, the following principles should be noted:
① When pouring the castings with long length and large diameter, the pouring system shall enable the liquid metal to be evenly spread on the inner surface of the mold quickly;
② When pouring oxidizable metal liquid or using centrifugal sand mold, the pouring groove shall enable the metal liquid to fill the mold in a balanced way, so as to minimize the splash of metal liquid and reduce the erosion of sand mold;
③ When casting shaped castings, the runner in the mold shall enable the metal liquid to flow smoothly into the mold cavity;
④ After pouring, there shall be no metal and slag left in the pouring cup and pouring groove. Residual metal and slag, if any, shall also be easily removed.
Pouring quantity
The inner diameter of centrifugal casting is often determined by the amount of molten metal poured. Therefore, during centrifugal casting, the amount of molten metal poured into the mold must be controlled to ensure the inner diameter. The installation of pressure sensor on the pouring ladle frame for automatic quantitative centrifugal pouring and quantitative electromagnetic pump pouring of insulation induction furnace has also been applied in production.