The forming roll materials commonly used in cold roll forming machines are as follows:
1. Low carbon steel, turned and polished, but not hardened;
2. Grey cast steel turned and polished, not hardened;
3. Low alloy tool steel, surface hardness is 60 ~ 63HRC, sometimes chrome plated;
4. High-carbon and high-chromium tool steel, with a surface hardness of 60-63HRC, sometimes chrome-plated;
5. Green aluminum (commonly used aluminum alloy).
Product batch is the main factor affecting the selection of forming roll material. The most commonly used forming roll materials are GCr15 rolling bearing steel, 45 high-quality carbon steel, Cr12MoV, 3Cr2W8V die steel, etc.
For the production of special-shaped profiles in small batches of cold roll forming machines, when repeated orders are unpredictable, low-carbon steel and gray cast iron are often used to manufacture forming rolls. When the strip is soft and the bending radius is large, this forming roll can also be used to produce medium batches of profiles, thus reducing the cost of the forming roll material.
When production batches increase, case-hardened and polished tool steels such as GCr15 should be used. This steel is less expensive than high-alloy tool steel and is easy to machine and heat treat. A layer of chrome (25μm) on the forming rolls of this material reduces scratching and increases regrind cycles.
When the production batch is large (>1.5×106MM), it is more economical to use high-alloy die steel (such as Cr12MoV) to manufacture the forming roll.
In addition to the product batch, other influencing factors are the difficult deformation of the strip (eg stainless steel), the extremely small bending radius, and the surface condition of the strip (eg unpickled hot-rolled strip or surface-coated coil).
During the cold forming process, surface scratches and heat are caused by the surface friction between the roll and the strip, so the forming roll must be lubricated and cooled during the forming process.
Lubricants for cold roll forming machines are roughly classified into water-insoluble lubricants and water-soluble lubricants. The most widely used are water-soluble emulsions. Its adhesion oil film is thick, and its lubricity and rust prevention ability is good. However, care should be taken to prevent the lubricant remaining on the surface of the profile from decomposing of oil and water during storage and causing local rust. Although organic dissolving lubricants have slightly poorer lubricating properties, through the action of surfactants, they have a low degree of pollution to profiles and equipment, thus keeping the production environment clean.
The selection of the appropriate lubrication method should take into account various requirements such as the type of strip, the shape of the finished product, and the type of lubricant.
For the unpickled hot-rolled steel sheet, it is best to use a high-pressure-resistant metal powder that is easy to clean and has penetrating power during the forming process of the cold roll forming machine. For pickled hot-rolled strips and cold-rolled steel sheets, it is better to use clean lubricants with good water solubility. For organic-coated boards, lubricants are generally not used, but protective polyethylene plastic tape is used. Although process lubrication is beneficial and often required in the forming of the cold roll forming machine, the removal of lubricant on the surface of the finished product and the measures for rust prevention are an item that increases the cost. Therefore, the use of process lubrication requires each manufacturer according to its production conditions to be considered as appropriate.
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