In the production of used ERW tube mills, the roll is the key and important special tool. Roll consumption is also a key tool for manipulating product costs. In addition, the normal operation of the roll will directly affect the output and quality of welded pipe manufacturing. Therefore, welded pipe manufacturers attach great importance to and strive to improve the service life of the roll.

Selection of raw materials for butt welded tube rolls of used ERW tube mill

The material of the roll directly affects the service life of the roll. The selection of the raw material of the roll needs to be comprehensively considered from the following aspects:

• It must have high and well-proportioned hardness and wear resistance, and the extrusion forming roller must also have excellent heat resistance.
• It must have sufficient strength (including fatigue strength) and appropriate toughness.
• It must have good cutting performance, heat treatment process characteristics, and cold working performance.
• The price of materials should be cost-effective and easy to obtain
• Different raw materials should be selected for rolls in different working environments.

The damage method of the roll

The rolls of welded pipes in used ERW tube mills can be destroyed in various ways.

Some damage will happen suddenly, and some damage is likely to happen gradually. There are the following types of damage to the roll.

Disadvantages related to roll manufacturing

Disadvantages of raw materials: sometimes there are interlayers, or vertical and horizontal cracks inside the raw materials. The unevenness of the structure or composition of its raw materials can also lead to poor roll characteristics and cause premature destruction in certain places.

Disadvantages of the heat treatment process: the hard bottom layer of the roll is too thin, too thick, and uneven, which will cause the uneven wear surface afterwards. In addition, the poor structure of the microscope and insignificant cracks and stress concentration during the entire heat treatment process can also cause damage to the roll.

Others: stress concentration caused by design or machining (remaining knife marks, insufficient fillet at the step, poor keyway corners or other chamfers), and inappropriate welding or surfacing, or improper welding process , Resulting in cracks in the heat-affected zone.

Breaks related to the actual operation of the unit

Hot cracking and spalling are the key elements that limit the service life of the roll. These shortcomings are related to the production process of the unit. After this element causes damage to the roll surface, the roll pass must be trimmed according to the grinding. If the grinding is too large, it will directly affect the service life of the roll.

Hot cracking of the roll: Hot cracking is generally regarded as the early form of hot cracking and a thermal fatigue phenomenon. Due to the influence of thermal stress, the net-like structure cracks or cracks are generated on the surface of the roll. These cracks deepen with the extension of rolling time. This kind of situation occurs more frequently in the squeeze forming rolls welded by the electric welding of the used ERW tube mill.

Roll spalling: It is a fatigue fracture, in the form of large spalling of the roll body or partial spalling of a small shallow part. The spalling is caused by thermal and mechanical forces. The severe cyclic stress and work hardening also affect the spalling.

The key reasons for roll spalling include:

• The load is too heavy;
• The rolling mill vibrates, and the convex shape of the roll is inappropriate;
• Incorrect cooling, severe scratches on the roll;
• Poor use and operation;
• The fatigue strength of the roll material is low.

The overload is one of the important and common causes of peeling, and the overload is caused by many factors. Large spalling is generally the result of the comprehensive influence of large external stress, internal stress and thermal stress.