HSS Roll Manufacturing Technology
HSS Roll Manufacturing Technology
The main technologies for manufacturing HSS rolls are forging, casting, spray forming, hot isostatic pressing, etc. The more common methods in industrial production are centrifugal casting, CPC, ESR and ESSLM
1. Casting HSS Rolls
The improvement of casting HSS roll manufacturing technology mainly focuses on improving the purity and uniformity of steel, improving roll strength and metallurgical bonding between the roll outer layer and the roll core. The appropriate manufacturing method can be selected according to the required roll performance, specifications and production costs.
(1) Centrifugal Casting Method
The main feature of centrifugal casting rolls is that the liquid outer layer material and the core material are poured into the mold at a certain time interval. The centrifugal rotation time, the interval time for pouring the roll core metal liquid, the pouring temperature and preventing the segregation of outer layer elements and the interface oxidation of the inner and outer layer materials are the key to the success of this method of manufacturing rolls. High-speed steel contains more W, Cr, Mo and V elements, and these elements and their carbides have a large density difference. Under ordinary centrifugal casting conditions, the high-speed steel roll element segregation is serious.
(2)Continuous Pouring Process for Cladding (CPC)
CPC is a new method that is different from the traditional composite process. In the past, the order of composite pouring was first outside and then inside, while this method is first inside and then outside. The key points of the CPC are to first load the roll core into the ingot pulling mechanism, and then pour the smelted outer layer of high-speed steel molten steel between the roll core and the water-cooled crystallizer. By controlling the ingot pulling speed, the core rod and the outer layer of molten steel are metallurgically combined in the crystallizer, and the structure after cooling is controlled to finally obtain a composite roll, which is machined and heat treated to become a finished roll.
The HSS roll produced by the CPC method has a fine, uniform structure with few inclusions, and almost no defects such as shrinkage cavities and looseness. The comprehensive performance is significantly better than that of ordinary centrifugally cast HSS rolls. It not only overcomes the segregation defects of centrifugally cast rolls, but also the core of the roll can use high-strength forged steel, and the roll core has higher strength.
(3) Electro-slag Remelting (ESR)
Electroslag remelting is a remelting process widely used in the production of high-quality steel. Initially, the process was mainly used for deoxidation and desulfurization. Combined with the effect of controlling solidification, the distribution characteristics of non-metallic inclusions are greatly improved. Its main advantages are as follows:
a) Refinement of grains;
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b) Reduction of non-metallic impurities and inclusions in steel;
c) Improvement of hot working properties of steel;
d) Reduction of macro-segregation and micro-segregation of organization, and improvement of carbide distribution in tool steel and die steel.
The biggest problem with the ESR method is that it is costly and difficult to manufacture larger rolls. In addition, the electroslag slag contains more CaF, which will emit harmful gases such as HF, SiF4, and SF6, endangering the health of workers and causing environmental pollution.
(4) ESSLM
In 1996, the ELMET Roller Company of Ukraine developed a new process for manufacturing HSS composite rolls by liquid metal electroslag melting. It is a new roll manufacturing method based on the CPC method with electroslag purification.
When the roll is manufactured by the ESSLM method, its outer layer is solidified in a specially designed conductive water-cooled copper crystallizer. The crystallizer not only solidifies the poured outer layer of molten steel, but also serves as a non-consumable electrode in the electroslag process. At the beginning of the composite process, the mandrel, which is the core of the HSS roll, is first inserted into the crystallizer and coaxial with it. The gap between the outer surface of the shaft and the inner surface of the crystallizer determines the thickness of the outer layer of the roll. Then the molten slag in another melting device is poured into the gap between the crystallizer and the mandrel. The slag forms a slag pool, and its heat preheats the surface of the mandrel. Then the outer layer of high-speed molten steel is poured in, which can be poured continuously or according to a pre-set program. The molten steel floats the slag and is refined by the slag when passing through the slag pool. The molten steel fuses with the preheated mandrel surface and solidifies due to the cooling of the crystallizer to form a composite layer. The solidified part is continuously pulled out of the crystallizer by means of a moving device (or the crystallizer is moved up), and the upper molten steel is continuously injected until the predetermined roll length is reached.
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Cited: Manufacturing Technology of High Speed Steel Roll