3.4 粗轧机工作辊的使用

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提高轧制周期是粗轧机架工作辊 提高轧制周期 的主要目标。在过去几年,轧制周 期不断提高。近年来，在可逆粗 轧机5-7道次的碳钢轧制中，轧制 周期已经达到和超过50000吨。 当然，对于增加轧制周期的追求 对于增加轧制周期的追求 需建立在注意避免轧制事故的基 础上（特别是注意避免辊身边部 础上 剥落的风险）。 事实上，工作辊和支撑辊的过度 磨损会造成辊身边部区域应力过 大，如右图所示。
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WEAR PROFILE In the wear profiles it is notable bigger wear ( + 20 ÷ 50 %) of bottom roll compared with top roll; therefore the wear control should be made on the bottom roll : usually for this roll wear of 1,5 mm on diameter is not exceeded. It is recommended anyway to do not exceed 1 ÷ 1,2 mm. Further dressing must remove totally any crack present on the barrel (cracks could originate spallings). Tests through Eddy Currents (and eventually through UT too) permit to verify the presence of cracks. In case of surface free from defects, after elimination of wear, normally a further dressing of 0,5 ÷ 1 mm on diameter permit to obtain a suitable surface of the roll for next use. The aim of increment of trip duration must be pursued anyway for each specific mill, for each specific kind of roll, and for each kind of rolled steel. Remarks : on the basis of our experience, it is possible to avoid the complete removal of firecracking network if it is uniform distributed on the barrel surface and if it is very small in size.
F ig. 6
F ig. 5
new back-up and work rolls
worn work rolls and new back-up rolls
立辊轧制形成的板坯狗骨头形状 会增加板带边部轧制时的应力。 结合层区域因此处于高疲劳，在 轧辊寿命的最后阶段（工作层消 worn back-up and work rolls 耗了50-70%后），每个换辊周期 之后,都要用超声波检测结合层， 特别是检查位于轧制区域边部的 结合层。 © 2009 Innse Cilindri – All Rights Reserved
F ig. 5 F ig. 5
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These tests can permit to take under control these areas as far the possible formation of misbondings due to fatigue for the heavy rolling conditions. To limit the problem of misbonding during the use (normally more frequent in second part of roll life) rolls are normally cast with increased shell thickness at scrap diameter up to 25 mm.
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这些检测可控制在这些区域由于轧制周期过长产生的疲劳而可 能引起的结合不良。为了避免在使用过程中产生结合不良（通 常更频繁地出现在轧辊寿命的后半部分），通常轧辊浇铸时要 增加工作层的厚度,其增加的直径厚度超出报废直径可达25毫米。 工作层厚度 为了避免芯部残余应力过大，主要是在新的高合金材质（半高 速钢和高速钢）上，工作层厚度的增加一定要受到限制。比方 说，直径1200mm的高速钢轧辊在厚度较薄的地方工作层厚度不 能超过145mm。 实际上，这些轧辊（由于立式离心铸造的缘故）辊身有可能存 在15-20mm的厚度差，因而轧辊铸造底部的厚度会达到165mm： 这是工作层厚度的上限。
Fig. 5
new back-up and work rolls
Fig. 6
worn work rolls and new back-up rolls
worn back-up and work rolls Fig. 5 Fig. 5
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FLAT ROLLING ROUGHING STANDS WORK ROLL APPLICATIONS 热轧板带轧机粗轧工作辊的使用
Nov. 2009 09年11月 年 月
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1Baidu Nhomakorabea
ROUGHING MILL WORK ROLLS粗轧工作辊 粗轧工作辊
SHELL THICKNESS The increment of shell thickness, mainly for new high alloyed grades (semi HSS and HSS), should be anyway limited in order to avoid the creation of excessive values of residual stresses in the core. For instance, HSS rolls with diameter 1200 mm should have a maximum total shell thickness of 145 mm in the part with lower thickness. In fact for these rolls (due to the vertical centrifugation) it is possible to have a difference in thickness through the barrel length of 15 ÷ 20 mm, and consequently a shell thickness of 165 mm in the bottom part of the casting : this value is considered as the limit.
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INCREMENT OF TRIP DURATION is the main aim for work rolls of roughing stands. In the last years there was a continuous increment rolling campaigns. Presently the target is to reach and to exceed 50.000 tons in Carbon Steel rolling with 5/7 passes in reversing stands. Of course, the aims of increment of rolling campaigns must be pursued paying strong attention to avoid rolling accidents (in particular risks of spalling of barrel edges). In fact, excessive values of work roll wear, together with the back-up roll wear, could cause too high values of stresses in the zones closed to the barrel edges, as shown hereunder. The formation of dog bone profile of the slab by the Edger can increase these values of stress in correspondence of the strip edges Being the bonding area subjected to high fatigue, it is opportune to make, mainly in the last part of the roll life (after 50 ÷ 70 % of shell consumption), after each trip, UT tests of the bonding area, taking care in particular of the area of rolling edge.
MAIM AIMS主要目标: increment of mill productivity through : 通过以下方法增加产量 - increment of trip duration - 增加轧制周期 - reduction of roll changes - 减少换辊次数 MAIN PROBLEMS : 主要问题： - wear resistance - 耐磨性 - bar surface quality –辊面质量 - slippage tendency - 打滑趋势 - firecrack resistance - 抗热裂纹性 EVOLUTION OF ROLL QUALITY :轧辊质量的评估 Carbon Steel rolling :碳钢轧制： Hi Cr Steel 高铬钢 semi HSS (HSS) 半高速钢 （高速钢） Stainless Steel rolling :不锈钢轧制 Hi Cr Steel 高铬钢 HSS 高速钢 REMARKS : 备注 The change of roll grade into well developed grade permits to get better results as far wear resistance, but it is necessary to pay attention in using, to avoid risks of spallings connected with higher values of residual compressive stresses of the shell using more alloyed grades 轧辊材质的改进提高了轧辊的耐磨性，但我们在使用中必须注意避免剥落的风险, 这 是因为工作层中添加更多的合金材料使得残余压应力变大。