Characteristic in Centrifugal Casting of Nickel material with WC

Mar 10,2016

At present, Nickel(Or Cobalt) base alloy mixed with WC granules, for example the alloy α301 made by Shanghai alpha, and the alloy Xaloy 800, in centrifugal casting process, to make a part such as bimetallic barrel in plastic machine industry, now almost no one company can accurately and factitiously control the hardness and thickness of alloy layer in China. Only a few companies all around the world can make effective control to these two factors mentioned above through special means. For the purpose of making it clear, we have to refer to the principle of centrifugal casting molding of bimetallic parts, which is to make use of the close melting point of base material and alloy material. That’s to say when the alloy material is up to its melting point and over, it would be transformed into liquid, and the base material now is not up to its melting point, it is still in solid state. At that moment, the alloy material is cooled under proper centrifugal effect and adhere to the inner hole surface of sleeve. However, if there is WC granules, which are with much higher melting point, with bad intermiscibility, with special specific gravity, and with high proportion-up to 25~30%, mixed inside the alloy layer material, the centrifugal casting becomes much complicated, the molding condition becomes much demanding. It is necessary for us to deeply research this complication and rigour of this centrifugal casting, this would help us to find a solution to make more effective and more accurate control.

There are at least two characteristics of basic, very hard for us to confronting, in the centrifugal casting molding of α301 alloy sleeve as show below, specially when this alloy is with high proportion WC granules.

First characteristic is to analyse the reciprocal movement of WC granules together with Nickel molecule inside α301 alloy under a condition of high temperature and centrifugation. As is well-known, the melting point of pure nickel is only 1450℃, its specific gravity is 8.902g/cm3. But for the metal “W”’, the melting point is up to 3380℃ and its specific gravity is up to 9.254g/cm3, to compare both melting point and specific gravity, it is more than two times and over. Therefore, at the moment when Ni is melted into“liquid phase”, the WC granules inside α301 alloy material are still in“solid phase”. And more the specific gravity of WC is much bigger than Ni, these WC granules proportion of which is even up to 25~30%, now stay in the liquid “Ni”, move forward to the stronger centrifugation force direction under a separate force by centrifugal effect, so that now the WC granules is more close to the joint plane near to base material, NOT close to the inner wall of sleeve. It means the high wear-resistant WC granules do not evenly disperse the lining metallogaphic structure. The sleeve working surface which is in need of more wear-resistant ability by increasing distribution of hard phase, now the proportion of WC granules is exactly not more.

Second characteristic is to analyse the reciprocal movement of WC granules, together with Nickel molecule inside α301 alloy, and more together with molecule of base material under a condition of high temperature and centrifugation. In conventional practice, steel 45 (Germanic name CK45, No.1.1191) is elected as to be this sleeve base material. As is well-known, It is one kind of middle carbon steel, except iron, total of other chemical composition percentage, including C, Si, Mn etc, is no more than 3%. Compare with nickel material of α301, the melting point of steel 45 is higher. In centrifugal casting, under a high temperature and a centrifugal force, Nickel molecule, together with WC granules move and oppress forward to the border surface of steel 45 where the molecules is now active, very close to the meltdown point. The material Nickel, and other various of alloy elements get carbon atoms from the meltdown border surface of steel 45, and generate new and more active collections of carbide molecules, such as nickel carbide, silicon carbide, chrome carbide. Conversely, these newly-generated carbide molecules make the melting point of border surface of steel 45 getting down, which further cause stronger flowability. Under this circumstance, nickel in base material, and those carbide molecules: Nickel carbide, Silicon carbide, Chrome carbide..., which are just formed, proportion is not less relatively, now bring together with WC granules, continuously,unfailing transit into the new melted border surface of steel 45 under the high temperature, extend the ally layer. And the high proportion of carbide molecules from steel 45 oppositely move into the alloy layer, combined by active alloy elements…, The result through these inter-permeating, inter-transfering, inter-interferering, inter-locking active scene in the metallogaphic structure on the meltdown border surface, causes an increase of alloy layer thickness, and a drop of alloy layer hardness, which shouldn"t be emerged.

These two characteristics above during the molding of α301 alloy sleeve which is with high percentage of WC are effected by a temperature, and a duration time under the high temperature. The higher the temperature, and the longer the time, these two characteristics of these three leading material of α301 bimetallic sleeve would reflect more obvious, the alloy hardness and alloy thickness would be more difficult to be controlled. The detectable result that It possibly causes is, alloy thickness is beyond a size which we set, hardness profile is out of limits, the proportion of mincroscopy hard phase in alloy layer is not enough seriously and disperses unevenly. This result would directly threaten a due working life of α301 alloy sleeve.

After researching the situation above, we could find the centrifugal casting for α301 alloy sleeve is totally different from iron-based α101 alloy sleeve. The centrifugal casting process for α301 alloy sleeve requires accurate control on a temperature and on a duration time, the molding condition is specially rigorous and it is extremely difficult.

Chief Engineer Office
Shanghai Omega Machinery Co., Ltd

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