Centrifugal casting

Centrifugal casting process: molten metal is poured into a hollow cylindrical mold spinning about a horizontal or vertical axis at speeds generating more than 100 Gs of centrifugal force. The centrifugal force distributes the molten metal and shapes it into a tubular/cylindrical forms. The high  forces involved in this casting method means that the less dense materials including impurities are forced into the center where they can be subsequently removed and gas related defects and shrinkage porosity are reduced thus parts made from centrifugal casting exhibit denser, closer grained structure with improved physical qualities such as tensile strength, yield strength, elongation and uniformity.

Centrifugal casting tube

Ductile iron pipe,
Wear-resistant iron tube
Corrosion-resistant cast iron pipe
Alloy steel sleeve
Martensitic stainless steel tube

Centrifugal casting
Centrifugal casting

Austenitic stainless steel pipe
Duplex stainless steel pipe
Nickel-base alloy tube
Titanium-based alloys tube
Non-ferrous metal pipe

Technical specification

Advantage:

1.There is almost no metal consumption at inject system and gating system, so production rate improved much.

2.There is no core when produce hollow castings so greatly improve the metal filling capacity, lower the ratio of wall thickness to length or diameter and simplify the process of sleeve and pipe production.

3.High density, less of defects like pores and slag, high mechanical property.

Easy to manufacture cylinder or sleeve type composite metal castings such as steel back copper sleeve, bimetallic roller, thin wall castings.

Disadvantage:

1.There are certain limitations in the production of special shaped castings.

2.The inner diameter is not accurate. The surface of inner hole is relatively rough, the quality is poor and the machining allowance is big.

3.It is easy to produce specific gravity segregation. So it is not suitable for easy to segregate like lead bronze, especially not suitable for the casting of the impurity specific gravity greater than the alloy metal liquid.

Processes:

Metal filter, pouring temperature, casting speed, slag solidification and coating use, casting off mold, gating system and pouring quantitative are all required to identify and solved in centrifugal casting. They directly affect the casting quality and production efficiency.

Metal filter:

There are more dregs difficult to remove in some alloy liquid.  can placed filters at pouring system to remove scum, such as foam ceramic filter, glass fiber filter.

Pouring temperature:

Centrifugal castings are mostly tube, sleeve or ring type, the filling resistance is small, and the centrifugal force can strengthen the metal filling ability, therefore, centrifugal casting pouring temperature can be relatively lower 5 ~ 10 ° C than gravity pouring temperature.

Casting speed:

The casting speed is an important technological factor of the centrifugal casting. The casting speeds while cast forming is vary with different parts and different process.

Low casting speed cause inadequate filling for the vertical casting and like rain phenomenon of liquid metal for horizontal casting. Also it can cause defects like loose textures, slag and uneven inner surface.

Higher casting speed can cause crack, segregation on the parts and expansion box for the sand centrifugal casting. Also it can cause machine vibration, wear, power consumption is too large, etc. So speed selection principle should be on the premise of guarantee the quality of castings, the smallest value is best.

Slag utilization:

To overcome the defects of subcutaneous shrinkage cavity caused by bi-directional solidification of thick wall centrifugal casting the slagging agent can be poured with liquid metal into mold. The slag covers on the inner surface to prevent heat dissipation. It causes directional solidification from inner to outside to eliminate subcutaneous shrinkage cavity. At the same time, the slagging agent can also be refined metal effect.

Coating:

Centrifugal casting coating is vital for the quality of the product. It should be different coating according to different materials.

Casting off mold:

In order to improve production efficiency the casting off mold should be as soon as possible on the premise of guarantee quality. Sometimes the castings taken off mold  immediately kept into the furnace or a pile of sand in order to prevent the casting crack. As for some castings which is not easy to take off mold but need to slowly cooling to prevent crack it should take away from machine immediately after stop rotation and bury into sand to cooling down slowly until reach to room temperature.

Pouring system:

Centrifugal casting pouring system mainly refers to poured cup and pouring groove connected to it, and sometimes also comprises a pouring channel in the mold. we paid attention following principles  when designing pouring system.

1. As for castings are long and large diameter the pouring system should make sure the metal liquid can quickly and evenly spread on the inner surface of the mold.

2. As for easy oxidation of pouring liquid metal or using centrifugal sand mold, the pouring groove should balance the metal filling into the mold, as far as possible to reduce metal spatter, reduce the erosion to sand mold.

3. When cast shaped castings, it should be able to make the liquid metal flows into the cavity smoothly for the channel.

At the end of casting the pouring cup and the pouring groove should be no metal and slag. It should be easy to remove if there are any residual metal and slag.

 

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