Abstract: Aiming at the problems in the repairing process of narrow-strip steel rollers, improvement opinions and solutions are proposed to increase its service life and reduce production costs.
As one of the most important processing parts and consumable parts of the rolling mill, the roll is subjected to fatigue stress and thermal cycling during use, which will cause serious fatigue wear and thermal fatigue cracks. In view of the high cost of rolls and high scrap rate, We currently choose the repair method of turning, grinding and reusing the rolls.
We have collected 50 rolls and made statistics on the processing volume. See the table below (unit:mm)
The calculation formula for the amount of loss (first roll diameter-last roll diameter) ÷ number of uses = loss
The calculated loss of each roller is shown in the following table:
Add up the 50 values to get 69.27mm and then calculate the average value: 69.27÷50=1.39mm. The 1.39mm obtained is to improve the average processing loss of the front roller.
1. Current problems and solutions
1.1 Imperfect turning process
(1) The turning efficiency is low, and the feed rate and speed have no clear limits on roughing and finishing. Solution: Clearly distinguish the values of feed and speed in roughing and finishing.
(2) The machining loss in the turning process is large, and there is no segmented turning, so that the cylindricity of the processed roll does not meet the tolerance requirements, so repeated dressing.
Solution: adopt segment turning process
(3) The choice of turning tool material is unreasonable, and the strength of the 767 bit is insufficient, and it wears quickly during processing.
Solution: Use machine-clamped ceramic tools for turning.
1.2 The grinding process is not perfect.
(1) The grinding efficiency is low, and the feed rate and speed are not well matched during the machining process.
Solution: re-match the feed and speed of roughing and finishing.
(2) The processing loss in the grinding process is large, and there is no distinction between manual feed and automatic feed.
Solution: Change automatic feed to manual feed.
(3) The choice of the material of the grinding wheel is unreasonable, the material is soft, wears quickly, and the surface accuracy of the roll after processing does not meet the requirements.
Solution: Use microcrystalline corundum grinding wheel for grinding.
2.Roll repair process
2.1 Turning process
(1) Before processing the roll, use a dial indicator to check the coaxiality of the roll. During the processing, it should be controlled between 0 and 0.15mm, and should not exceed the tolerance.
(2) The spindle speed of the lathe during rough machining is 80~108r/min, and the cutting amount is 0.9mm/r. The lateral feed depends on the degree of roll wear, but cannot exceed 1mm. The spindle speed of the lathe remains unchanged during finishing. , The cutting amount is 0.2~0.4mm, and the lateral feed amount is 0.1~0.2mm
(3) The rough machining tool setting is located at the minimum wear diameter of the roll, and then the turning is carried out in the direction of both ends in sections.
(4) After the rough turning is completed, start the tool setting from one end of the roll, the cutting amount is 0.2~0.4mm, the lateral feed is 0.1~0.2mm, and the finishing is performed.
(5) After processing, use an outside micrometer to measure the two ends and middle diameter of the roll to determine whether the processing meets the technical requirements.
2.2 Tool and grinding wheel requirements. The turning tool is made of ceramic blades, and the material of the grinding wheel is microcrystalline corundum. The strength is 60.
The soft and bonding agent is ceramic.
3.1 Cost calculation of roll loss: Before the improvement, each roll is processed on average once and its process loss is 1.39mm, which is converted into weight: G1=πxDx(d/2)xLxp.
G1: weight loss in the previous process; D: average roll diameter; d: process loss; L: roll length;
After the improvement, each roll is processed once and its process loss is 0.79mm, and the converted weight is: G2=πxDx(d/2)xLxp. Calculate G2=1.34(kg)
After the improvement, the average weight saved is G1-G2=1.02 (kg). According to the current average roll price of 15 yuan/kg, each processing roll can save 15.3 yuan.
3.2 Grinding wheel consumption cost calculation: Before the improvement, each grinding wheel can grind an average of 80 rolls. The price of the grinding wheel is 529.92 yuan/piece, and the average consumption cost of the grinding wheel per roll is 6.624 yuan/piece. After the improvement, each grinding wheel can grind 220 rolls on average. The price of the grinding wheel is 581.2 yuan/piece, and the average consumption cost of the grinding wheel for each roll is 2.64 yuan/piece. After the improvement, the average cost of grinding wheel consumption per roll can be reduced by 3.98 yuan/piece.
3.3 Turning cost calculation: Before the improvement, each 767 head can process 17 rolls on average, and the average price is 30 yuan/piece. In addition, the cost of tool body and sticking tool is 15 yuan, and the average price of each turning tool is 45 yuan/piece. Finally, the average cost of turning tool consumption per roll is 2.65 yuan/piece.
After the improvement, each ceramic cutter head can process 64 sticks on average, 6 with an average price of 89.75 yuan/piece; other no additional fees. Finally, the average cost of turning tools per roll is calculated to be 1.40 yuan/piece. After the improvement, the average cost of turning tool consumption per roll can be reduced by 1.25 yuan/piece.
Finally, by adding up the savings and reduced costs of the above three items, the average cost savings per roll processing procedure is: 15.3+3.98+1.25=20.53 yuan/piece, calculated according to the average monthly processing of 794 rolls in the previous period, each month Compared with the pre-improvement, the cost saving is 16,300.82 yuan, and the annual intensive cost is 195,609.84 yuan. The actual operation results have proved that through the improvement and improvement of the roll turning and grinding process, the shortcomings and defects of the original process have been compensated, the best efficiency of the equipment has been brought into play, the repair cost has been reduced, the production efficiency has been improved, and the energy saving and consumption reduction of the main line is indirectly done. Made a contribution.