Technical key points of centrifugal casting of copper sleeves

Copper sleeve, also called brass bush, copper sleeve centrifugal casting refers to a casting method in which copper liquid is poured into a high-speed rotating casting centrifuge and solidified under the action of centrifugal force. Centrifugal casting has been widely used in the production of pipe and sleeve castings, such as centrifugal casting of copper sleeves, cylinder liners, seamless steel pipe blanks, etc.

In centrifugal casting production, mold rotation speed, pouring system, pouring ration, solidification under slag, metal filtration, coating use, pouring temperature, casting release, etc. are process issues that must be determined or solved, because they directly affect the quality and quality of castings. Productivity.

(1) Mold speed is an important process factor in centrifugal casting. Different castings and different casting processes have different mold speeds when forming castings. Too low a casting speed will lead to poor mold filling with molten metal during vertical centrifugal casting, and rain of molten metal during horizontal centrifugal casting. It will also cause looseness, slag inclusions, and uneven inner surface defects in the casting;

If the casting speed is too high, defects such as cracks and segregation are prone to occur on the copper sleeve. Defects such as expansion boxes will be formed on the outer surface of the sand centrifugal casting. It will also cause the machine to experience large vibrations, increased wear, and excessive power consumption. Therefore, the principle of selecting the casting speed should be to select the smallest value while ensuring the quality of the casting.

(2) Gating system: The gating system during centrifugal casting mainly refers to the pouring cup that accepts metal and the pouring trough connected to it, and sometimes also includes the runner in the mold. When designing the gating system, the following principles should be noted:

(3) Pouring quantitative The inner diameter of centrifugal castings is often determined by the amount of molten metal poured. During centrifugal pouring, the amount of molten metal entering the mold must be controlled to ensure the inner diameter.

(4) Utilization of slag In order to overcome the subcutaneous shrinkage defects caused by the bidirectional solidification of centrifugal castings with thick-walled bushings, the slag-forming agent can be poured into the mold together with the molten metal during pouring, and the slag will cover the inner surface of the casting. , prevent heat dissipation on the inner surface, create sequential solidification conditions from outside to inside, and eliminate subcutaneous shrinkage cavities. At the same time, the slag-forming agent can also play the role of refining the molten metal.

The method of pouring the slag-forming agent is: sprinkle the powdered slag-forming agent in the pouring trough during pouring; pour the molten slag and molten metal into the mold together.

(5) Filtration of molten metal: Some alloy liquids contain a lot of slag that is difficult to remove. Various filters can be placed in the pouring system to remove the slag, such as foam ceramic filters, glass fiber filters, etc.

(6) Use of paint The composition of paint for centrifugal metal molds is similar to that of gravity metal mold casting. When pouring slender centrifugal castings, since it is difficult to remove the residual paint on the working surface of the casting mold, the residual strength of the binder in the paint composition after high-temperature work should be as low as possible to facilitate removal.

(7) Pouring temperature Most centrifugal castings are tubular, sleeve-shaped, and ring-shaped parts. The resistance encountered when the molten metal is filled is small, and centrifugal pressure or centrifugal force enhances the filling ability of the molten metal. Therefore, the pouring during centrifugal casting The temperature can be 5~10°C lower than during gravity pouring.

(8) Casting stripping In order to improve production efficiency, castings should be stripped as early as possible while ensuring quality. Sometimes in order to prevent the castings from cracking, the castings after demolding should be immediately placed in a holding furnace or buried in a sand pile to cool down. For some castings that are not easy to de-mold and require slow cooling to prevent cracking, the mold with the casting can be removed from the centrifugal casting machine immediately after the mold stops rotating, buried in a sand pile to cool slowly, and then de-moulded when it reaches room temperature.