When human beings created the rolling mill, there were rolls. The early rolls were integrally cast with sand molds, and metal mold casting was invented later. Roll manufacturing technology took a leap forward when rolls were poured with tangential gates from the bottom of the mold. With the development of the steel rolling industry, steel rolling workers have higher and higher requirements for the performance of the roll, which requires high hardness of the roll body, good wear resistance, good impact resistance and thermal crack resistance, and no slippage, while the requirements for the core of the roll It is high strength, continuous rolling and small deformation. These properties are often contradictory. In order to solve this problem, roll developers have thought of producing composite rolls by half flushing or full flushing.
Producing composite rolls by half flushing
The semi-flushing method is to pour alloy molten iron from the bottom of the mold, stop pouring when the molten iron reaches the junction of the upper roll neck and the roll body, let it stand for a period of time, and add the remaining molten iron in the ladle to a certain amount when the roll body forms a shell. A certain amount of ferrosilicon powder is stirred and then poured, so as to achieve the purpose of improving the strength of the roll core.
Producing composite rolls by full flushing
The full flushing method is to pour alloy molten iron from the bottom of the casting mold. When the molten iron reaches the junction of the upper roll neck and the roll body, stop pouring and let it stand for a while. When the roll body forms a shell, replace it with another bag of high-strength one. The core molten iron continues to be poured along the bottom gate, and the original core molten iron is replaced from the riser end. The birth of composite rolls has made another leap forward in the production technology of rolls.
Over the past 35 years, the manufacturing technology of centrifugal compound rolls has developed rapidly, and it can be said that eight generations of centrifugal compound rolls have been formed.
Birth and development of centrifugal composite rolling mill rolls
Chilled compound roll and infinite chilled compound roll
The first generation is chilled compound roll and infinite chilled compound roll. — That is, the outer material of the roll is chilled cast iron or infinitely chilled cast iron, and the core material of the roll is gray cast iron. The technical key of this generation of composite rolls is to solve the centrifugal composite process, the development of mold slag and the development of cold coating.
Spherical core composite roll
The second generation is the spherical core composite roll. — That is, the outer material of the roll is chilled cast iron or infinitely chilled cast iron, and the core material of the roll is ductile iron. The technical key of this generation of composite rolls is to solve the influence of the black line of the roll bonding layer on the anti-stripping performance of the rolls.
Nodular composite cast iron roll
The third generation is the nodular composite cast iron roll. ——That is, the outer layer material of the roll is alloy ductile iron, and the core material of the roll is also ductile iron. The technical key of this generation of composite rolls is how to prevent the nodular recession and remelting of the outer layer of ductile iron.
High chromium composite cast iron roll
The fourth generation is high chromium composite cast iron roll. ——That is, the outer material of the roll is high chromium cast iron, and the core material of the roll is nodular cast iron. The technical key of this generation of composite rolls is how to prevent or reduce the damage caused by the expansion of chromium in the outer layer to the core. Therefore, sometimes a three-layer composite has to be used.
High chromium composite cast steel roll
The fifth generation is high chromium composite cast steel roll. —— That is, the outer material of the roll is high chromium steel, and the core material of the roll is ductile iron or graphite steel. The technical key of this generation of clad rolls is still to reduce the diffusion of chromium from the outer layer to the core and to determine the parameters of the centrifugal clad process.
Composite cast steel or composite semi-steel roll
The sixth generation is composite cast steel or composite semi-steel roll. —— That is, the material of the outer layer of the roll is alloy steel or semi-steel, and the material of the core of the roll is ordinary cast steel or graphite steel. The technical key of this generation of composite rolls is the determination of centrifugal composite process parameters and the development of high melting point mold powder.
High-speed steel or semi-high-speed steel composite rolls
The seventh generation is high-speed steel or semi-high-speed steel composite rolls. — That is, the outer material of the roll is high-speed steel or semi-high-speed steel, and the core material of the roll is ductile iron or graphite steel or forged steel. The technical key of this generation of composite roll is the determination of centrifugal composite process parameters and the formulation of heat treatment process plan.
Tungsten carbide composite roll
The eighth generation is tungsten carbide composite roll. ——That is, the outer material of the roll is amorphous such as tungsten carbide or ceramic steel, and the core material of the roll is ductile iron or cast steel. The technical key of this generation of composite rolls is the determination of centrifugal process parameters and the as-cast cracks caused by shrinkage stress.
