Since the roll is the main consumable part of the rolling mill, in order to obtain good cutting performance and service life, surfacing welding technology is used in the manufacturing process to increase the hardness of the roll body, thereby increasing the service life of the roll. There are also failure forms such as cracks, peeling, and breakage of some rolls after a long working time, such as direct scrapping, the cutting cost is too high, and the cutting efficiency is affected. The surfacing method is often used to repair the roll, which not only does not affect the cutting efficiency of the rolling mill, but also reduces the cutting cost.

The following is a brief introduction to the failure mode of the roll and how to choose the blade for cutting and processing the surfacing roll.

The failure mode of the roll

The quality of the roll directly affects the working efficiency of the rolling mill, the quality and output of the rolled product, and the consumption of the roll. And as an important consumable part in the rolling process, the roll will be damaged due to many reasons in the normal rolling process. Especially the working environment of hot rolling rolls is even worse. Among them, the main failure forms of rolls are cracks, spalling and fracture, etc., any of which will affect the service life of rolls.When encountering the above failure forms, surfacing welding is generally used to restore the performance of the roll and restore the normal work of the roll, which not only does not affect the cutting efficiency, but also reduces the cutting cost.

According to the different requirements for the use of rolls, the requirements for surfacing materials

According to the different requirements for the use of the roll, the selection of the surfacing material is also different. According to its alloy type, it can be classified into eight categories. Two of them are briefly introduced below:

1. Low-alloy steel: This type of alloy is cheap. The surfacing metal structure is mainly sorbite or troostite. It has good impact toughness, good crack resistance, hardness HRC30-35, and is easy to cut. It has a certain wear resistance, but it cannot further improve the service life of the roll.

2. Hot work die steel: This kind of material has good red hardness, high temperature wear resistance and high impact toughness. After welding and stress relief annealing, the hardness is generally HRC45-50, and the service life is 1-5 times longer than the original roll. times.

3. Dispersion hardened steel: 15Cr3Mo2MnV, etc., as-welded hardness HRC35-38, easy to cut. The hardness can be increased to HRC46-47 after dispersion hardening treatment at 560°C for 15 hours.

The surface hardness of the roll can be improved by surfacing welding, thereby prolonging the service life of the roll.

Matters needing attention in roll surfacing welding

(1) Before surfacing welding, the fatigue layer or defects on the surface of the roll body, especially the cracks must be completely removed;

(2) During surfacing, in order to prevent cracks, the roll body must be preheated by cutting and processing, and the preheating temperature depends on the roll and surfacing materials;

(3) The key link of success or failure of surfacing welding during welding. In order to obtain an ideal surfacing layer, certain variable factors must be considered comprehensively, such as: welding voltage, welding speed, roll speed, heat preservation of rolls, welding current, welding materials, etc. For some roll cores containing carbon and high alloy elements, in order to prevent cracks in the brittle zone, in addition to certain preheating measures, a low-carbon and low-alloy transition layer is often used for pre-surfacing transition layer.

(4) Slow cooling and turning of the roll after surfacing. In order to reduce cracks caused by bulk stress caused by different cooling rates on the surface and inside, the cooling rate should be controlled. Finally, turn and cut the roll after surfacing to restore to its original size and smoothness. And the performance of the roll after surfacing: 1) The service life of the roll after surfacing is generally more than doubled; 2) The cost per ton of steel is greatly reduced and the production effect is improved; 3) The roll after surfacing has good Crack resistance, wear resistance, cold and heat fatigue resistance.

How to choose cutting tool material for machining surfacing roll

The hardness of the roll body of the surfacing parts is increased, and the roll body is not regular, so it is difficult to turn. The rolls after surfacing can be selected from Halnn CBN tools BN-K1 and BN-S20. CBN tool BN-K1 is mainly used in high-hardness cast iron rolls, while BN-S20 grade CBN tools is mainly used in high-hardness cast steel/forged steel rolls. For specific cutting parameters, see Halnn Superhard Non-metallic Adhesive CBN cutting data table of tools BN-K1 grade and BN-S20 grade.

Table of cutting materials and cutting parameters of Halnn superhard CBN tools BN-K1 and BN-S20

Summary

For the surfacing parts, the hardness of the roll itself is high, and the surface is uneven, which once affected the cutting efficiency during the cutting process. For the cutting tool industry, as long as it follows the development of the times to develop high-quality and high-efficiency cutting tool materials or cutting tool grades , can occupy the cutting tool market, obtain higher benefits for the company, and thus promote the development of machinery manufacturers.