Mill rolls are the main consuming part of the rolling mill. According to material, it can be divided into cast alloy steel rolls, high-speed steel (HSS) rolls, high carbon high-speed steel rolls and tungsten carbide rolls, etc. especially for large roll, it is difficult to machine because of its high hardness, uneven allowance and irregular surface, The bn-k1 grade of non-metallic binder cubic boron nitride tool effectively solves the problem of difficult machining of casting roller.
Characteristics and heat treatment process of roller
In the rolling mill of iron and steel plant, the pressure produced by rolling a pair or group of rollers is used to roll the steel. As the roll needs to bear the dynamic and static load, wear and temperature change during rolling, the following characteristics should be ensured for the roll:
Good wear resistance
Good impact resistance and hot cracking resistance
The heat treatment process of roll:
The roll needs to be annealed before rough machining to eliminate the internal stress;
After rough machining, quenching and tempering are carried out to improve the surface hardness of the roll and obtain good performance.
After heat treatment, the hardness of the roller is generally higher than hrc45, some even as high as HRC60, which is difficult to process.
How to select tool material for turning casting roll?
As the roll belongs to the casting molding, the tool material selected in the processing is very important, which requires not only high hardness, strength, good wear resistance, but also good impact resistance. Cemented carbide tools (such as YG6 and YG6X) are recommended for casting rolls below hrc45;
For casting rolls above hrc45, it is recommended to use ceramic tools and cubic boron nitride tools. Ceramic tools are only suitable for the finishing process due to their brittleness. Traditional cubic boron nitride tools are also suitable for the finishing process. However, the bn-k1 brand of Valin superhard cubic boron nitride tools is different. They can not only rough the surface of casting rolls but also process with large allowance, Intermittent processing does not break the knife.
Bn-k1 belongs to the non-metallic adhesive cubic boron nitride tool. On the basis of ensuring the hardness and wear resistance of the traditional cubic boron nitride tool, it improves the impact resistance of bn-k1. It can be rough and finish machining, saving the processing cost and improving the processing efficiency.
Models of common turning tools and blades
Model selection of common clamping tools for roll turning: Heavy roll lathe is often used for large roll processing, and 40 * 40 tool square of tool holder is commonly used for the heavy roll; The commonly used tool holder angle is 45 degrees, and the tool holder angle is 45 degrees. Some small rolls also use 25 * 25 and 32 * 32 clamping tool handles. The main deflection angle of the tool holder is selected according to the “length diameter ratio” of the roll. The slender roll is usually processed with a 90-degrees or 75-degree tool, while the thick roll is usually processed with 45 degrees or arc tool.
The model of cubic boron nitride blade is selected according to the cutting allowance and processing condition of turning roll: when bn-k1 cubic boron nitride blade is used to process cast iron roll, rnmn200800, rnun200800, rnmn150700, rnun160800, rnun150716 and rnmn150716 are generally used. Among them, bn-k1 grade is selected for alloy cast iron and chilled cast iron, and bn-s20 grade is selected for casting high speed steel. Bn-s20 grade is also a non-metallic adhesive cubic boron nitride tool, which has better impact resistance and is suitable for processing cast steel / forged steel parts. Bn-k1 grade is mainly used for processing cast iron parts, and rough and finish processing of the above two kinds of tool grades are OK.
Case study of bn-k1 grade CBN tool for machining cast iron roll
High nickel chromium alloy cast iron roll
AP = 4mm, FR = 1mm, VC = 55m / min
Compared with the European and American brand ceramic blade: on the basis of feed rate 2 times higher than the ceramic tool, the single blade life is 6 times of the ceramic blade.