Common Wear Phenomena of Rolls for Cold Forming Profile and Their Causes

Rolls for cold forming profile are core components of cold roll forming machines, which directly contact with metal strips or coils to realize the continuous transverse bending of materials and form profiles with specific cross-sections. In the long-term production process, affected by factors such as material properties, forming process, and equipment operation, cold forming rolls are prone to various wear phenomena. These wear problems not only reduce the service life of the rolls, but also affect the forming precision and surface quality of the profiles, leading to increased production costs and potential production accidents. This article will systematically sort out the common wear phenomena of cold forming profile rolls, deeply  their causes, and provide professional reference for roll use, maintenance and fault diagnosis in related enterprises, helping to reduce wear losses and ensure stable production.

I. Common Wear Phenomena of Rolls for Cold Forming Profile

According to the actual production experience and maintenance data, the common wear phenomena of cold forming profile rolls are mainly concentrated in 5 types, which are significantly different in performance and appearance, and can be directly identified through visual inspection and simple measurement, specifically as follows:

1. Uneven Wear of Roll Grooves

This is the most common wear phenomenon of cold forming rolls, especially for rolls with special-shaped grooves (such as angle steel, channel steel forming rolls). The wear degree of each part of the roll groove is quite different: the wear of the corner, side wall and arc area of the groove is more serious, while the wear of the straight section is relatively slight. In severe cases, the corner of the groove becomes rounded, the side wall is uneven, and the arc radius changes, which leads to the inconsistency of the cross-section size of the formed profile and the unqualified product shape.

2. Surface Abrasion and Scratching

The surface of the roll appears uniform or local wear marks, scratches or grooves, which are usually parallel to the rotation direction of the roll. When the wear is slight, the roll surface is rough; when the wear is serious, obvious deep scratches will appear, which will directly scratch the surface of the metal strip during the forming process, resulting in surface defects such as scratches and burrs on the profile, affecting the appearance quality of the product. This phenomenon is more common in the rolls used for forming high-strength or high-hardness metal materials.

3. Roll Surface Spalling

Local peeling occurs on the surface of the roll, forming irregular concave and convex defects, and the peeled area is usually accompanied by obvious cracks. This kind of wear is destructive. Once spalling occurs, the roll can no longer be used normally. The spalling area will not only damage the profile surface, but also may cause the roll to be stuck during operation, leading to production interruption. This phenomenon is mostly found in the working rolls of cold tandem mills and high-load cold forming rolls.

4. Thermal Fatigue Cracking and Wear

The surface of the roll appears fine and dense cracks, which are mostly distributed in a network or linear shape, and are often accompanied by local oxidation. This kind of wear is caused by the alternating action of thermal stress. During the cold forming process, the roll surface is in contact with the metal strip, and the temperature rises and falls alternately, resulting in repeated expansion and contraction of the roll surface, and finally forming thermal fatigue cracks. If the cracks are not handled in time, they will continue to expand, leading to spalling of the roll surface and further damage.

5. Adhesive Wear

During the forming process, the metal particles on the surface of the strip adhere to the surface of the roll, forming small protrusions. With the rotation of the roll, these protrusions will cause continuous friction and wear on the strip and the roll itself, and even lead to the adhesion between the roll and the strip, resulting in surface adhesion defects of the profile. This kind of wear is more likely to occur when the forming speed is too fast, the lubrication is insufficient, or the surface of the strip is not clean.

II. Causes of Common Wear Phenomena of Cold Forming Profile Rolls

The wear of cold forming profile rolls is not caused by a single factor, but the result of the combined action of material, process, operation and other multiple factors. The causes corresponding to different wear phenomena are different, and the specific is as follows:

1. Causes of Uneven Wear of Roll Grooves

The core cause of uneven wear of roll grooves is the uneven stress during the forming process. Firstly, the special-shaped groove of the cold forming roll has different working roll diameters at each point, resulting in different pressures on the strip at each position of the groove during the rolling process, and the wear amount of the roll is quite different. For example, the corner and side wall of the groove bear greater pressure, so the wear is more serious. Secondly, the unreasonable design of the roll groove, such as the inappropriate slope of the side wall and the insufficient radius of the arc, will lead to uneven clamping force on the strip, accelerate the local wear of the groove. In addition, the uneven hardness of the roll itself is also an important factor. After the roll is turned many times, part of the groove is out of the working layer, resulting in a large hardness difference between each part of the groove, and the part with low hardness wears faster.

2. Causes of Surface Abrasion and Scratching

This kind of wear is mainly caused by friction and scratch between the roll and hard impurities or the strip itself. On the one hand, if the metal strip contains solid impurities such as sand and iron filings, or the surface of the strip has burrs and hard protrusions, these hard substances will scratch the roll surface during the forming process, resulting in scratches and wear marks. On the other hand, the material selection of the roll is improper. If the hardness and wear resistance of the roll material (such as C12MoV) do not meet the requirements, or the heat treatment process is not up to standard, the wear resistance of the roll surface will be reduced, and it is easy to be worn and scratched during long-term operation. In addition, the excessive forming pressure and too fast forming speed will also increase the friction between the roll and the strip, accelerating surface wear.

3. Causes of Roll Surface Spalling

The main causes of roll surface spalling are internal defects of the roll and excessive stress. Firstly, there are metallurgical inclusion defects in the roll body. The inclusions will cut off the continuity of the roll material, reduce its mechanical properties, and cause local stress concentration, which provides favorable conditions for the initiation and expansion of cracks. With the continuous action of rolling force, the cracks expand to a certain extent and then peel off, forming spalling defects. Secondly, the excessive mechanical stress during the forming process, such as the uneven distribution of rolling force, the excessive bending stress and contact stress of the roll, will lead to the accumulation of internal stress of the roll, and finally cause the surface to peel off. In addition, the improper heat treatment of the roll, such as insufficient quenching and tempering times, will lead to uneven hardness and poor toughness of the roll, which is easy to cause spalling under the action of alternating load.

4. Causes of Thermal Fatigue Cracking and Wear

This kind of wear is mainly caused by the alternating action of thermal stress. During the cold forming process, the roll surface is in contact with the metal strip, and the temperature rises instantaneously; after the strip leaves the roll gap, the roll surface is cooled by the cooling water and the roll body itself, resulting in alternating heating and cooling of the roll surface. This alternating temperature change will cause repeated expansion and contraction of the roll surface, and the internal stress of the roll will continue to accumulate, eventually forming thermal fatigue cracks. In addition, the improper cooling system, such as insufficient cooling water, uneven cooling, or the temporary shutdown of the equipment during production, will lead to excessive temperature gradient of the roll, aggravating the generation and expansion of thermal fatigue cracks.

5. Causes of Adhesive Wear

The main causes of adhesive wear are insufficient lubrication and excessive contact between the roll and the strip. Firstly, the lack of effective lubrication during the forming process will increase the friction between the roll and the strip, and the metal particles on the surface of the strip will adhere to the roll surface under the action of pressure and friction, forming adhesive points. With the rotation of the roll, these adhesive points will be torn, leading to wear of the roll surface and the strip. Secondly, the forming speed is too fast, the contact time between the roll and the strip is too long, or the surface of the strip is not cleaned, which will increase the adhesion probability between the roll and the strip. In addition, the surface roughness of the roll is not up to standard, and the friction coefficient is too large, which will also accelerate the occurrence of adhesive wear.

III. Key Reminder

The wear of cold forming profile rolls is an inevitable normal phenomenon in the production process, but through scientific material selection, reasonable process optimization and standardized operation and maintenance, the wear speed can be effectively slowed down, and the service life of the rolls can be prolonged. For example, selecting roll materials with high wear resistance and carrying out laser surface strengthening treatment can improve the wear resistance of the roll surface; optimizing the design parameters of the roll groove can make the stress distribution uniform; strengthening the filtration of the strip and the lubrication of the roll can reduce the friction and scratch between the roll and the strip.

Conclusion

The common wear phenomena of cold forming profile rolls mainly include uneven wear of roll grooves, surface abrasion and scratching, surface spalling, thermal fatigue cracking and wear, and adhesive wear. These wear phenomena are caused by the combined action of uneven stress, improper material selection, unreasonable process design, insufficient lubrication, internal defects of the roll and other factors. Mastering the common wear phenomena and their causes of the rolls is of great significance for enterprises to carry out daily maintenance, timely fault diagnosis and reasonable replacement of rolls.

In actual production, enterprises should formulate targeted maintenance and protection measures according to the wear status of the rolls, timely deal with the wear defects of the rolls, avoid the expansion of faults, ensure the stability of the cold forming production process, improve the product quality, and reduce the production cost.