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 Products > Mechanical workings > Rolling Mills > Working rules for plate, wire and bar |
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General working rules for plate
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| 1) Ensure that the rollers are perfectly aligned. If the plate shifts sideways during the process and there is more squashing on one side (sweeping shape), the rollers must be realigned. Disengage the central pinion and rotate the side gears counterclockwise to decrease roller opening or clockwise to increase the opening. Usually, angular movement of a gear tooth corresponds to a vertical movement of the roller bushing by approximately 0.01 ÷ 0.02 mm (the exact value is listed in the rolling mill operation and maintenance manual). 2) Percentage of reduction with each passage Settings for each passage to reduce plate thickness should not exceed 10% of the initial thickness when entering the rollers. For example: initial thickness 5 mm > maximum reduction equal to 0.5 mm Higher percentages could make plate edges wrinkle. 3) Plate positioning Do not overturn or rotate (head-tail) the plate during subsequent passages so that progressive deformation of material molecules is not modified. When plate thickness is reduced, it is a good idea to hold it on roller entrance, pressing it against the plate guide, which helps the plate stay straight and prevents it from shifting sideways. 4) Material annealing When the plate thickness has been reduced by 50% of its initial thickness, it usually must undergo the annealing process. The annealing process for non-ferrous materials (baking at 550÷600° C for 30÷40 minutes, then cooled in water) readjusts the crystal lattice of the rolled material, which eliminates stress and hardening. Depending on the type of alloy processed, annealing may be necessary prior to rolling, and in some cases it is not needed (i.e., silver 900). Annealing prevents cracking due to hardening, especially edge checks and cracks. |
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General working rules for wire and bar
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1) Ensure that rollers are perfectly in contact Usually square edged wires are chamfered using closed rollers,so that a serie o square channels will gradually reduce wire size according to a regular pace. 2) Insertion of the wire in the first channel To facilitate insertion of the round wire into the first square channel when the wire dimension is too big, the wire tip must be sharpened using a hand-powered or electric tool (a hammer or tip roller). Rolling can even be started with open rollers in the first channels to help insert the wire. In this case, the wire must be rolled in the closed channel before it passes to the next channel, to avoid the formation of burrs. 3) Rotation of the wire at 90 degrees During the rolling process, the wire section must be rotated 90 degrees when exiting each channel and before entering the next channel. This is absolutely indispensable to prevent the formation of burrs. In fact, chamfered rolled edges find themselves, in the next channel, in correspondence with the roller line of contact and do not form burrs due to the chamfering. 4) Different work channels During the work process, several channels can be fed simultaneously to speed up the rolling process. This occurs when the wire is relatively thin, to permit easy bending under the stand, so it can be fed into the next channel without waiting until it has completely exited the work channel. Naturally, depending upon the type of material and amount of reduction, the number of channels working simultaneously may differ and should not be too many (no more than 4÷5) to prevent anomalous bending of the rollers, which could create burrs. 5) Material annealing When the wire thickness has been reduced by 50% of its initial thickness, it usually must undergo the annealing process. The annealing process for non-ferrous materials (baking at 550÷600° C for 30÷40 minutes, then cooled in water) readjusts the crystal lattice of the rolled material, which eliminates stress and hardening. Depending on the type of alloy processed, annealing may be necessary prior to rolling, and in some cases it is not needed (i.e., silver 900). Annealing prevents cracking due to hardening, especially edge checks and cracks. |
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