The method of rolling billets and bars on flat rolls without grooves is also known as flat roll rolling, rounded rectangular rolling, or grooveless rolling.
Billet, square steel, and round steel are generally rolled on rolls arranged with various pass shapes. However, this rolling method consumes a large number of rolls and reserves, and changes the rolls frequently, which not only seriously affects the productivity of the rolling mill, but also increases the production cost. For this reason, many countries in the world have studied the use of non-grooved flat rolls to replace all grooved rolls in the roughing and intermediate rolling mills in the production of billets and simple section steels for non-pass rolling, and only the finishing mills still use the conventional pass rolling method rolled and achieved results.
At the end of the 20th century, no-pass rolling was successively performed on the bar rolling mill of Brocken Hill (BHP) in Australia, the wire rolling mill of Laclede in the United States, and the billet rolling mill of Mizushima Plant in Japan. Industrial trials were made and were successful. Since the 1980s, countries such as Japan and China have made progress in theoretical research and practical application. The no-pass rolling method of bars and billets successfully researched by Japan’s Kawasaki Steel Company has been put into industrial production and is being popularized and applied in the rolling production of small and medium-sized steel mills in some countries in the world. Passless rolling is replacing conventional pass rolling more widely. Passless rolling technology can be used not only for rolling carbon steel, but also for rolling alloy steel; not only for billet production but also for rolling square steel, round steel, and wire rod; It is widely used in billet mills as well as in the various bar and wire rod mills such as compact mills, semi-continuous mills, tandem mills, and continuous mills.
Compared with the traditional pass rolling method, the non-pass rolling method has the following advantages:
(1) Energy-saving. The use of no-pass rolling can significantly improve the operation rate of the rolling mill, thereby reducing the downtime and reducing the fuel consumption of the heating furnace by 6%; Small, there is no effect of the force of the groove sidewall on the rolling piece and the effect of the roll diameter difference around the rolling groove on the friction force caused by the rolling piece, so the rolling force is reduced by 5%~10% compared with the conventional pass rolling. Save about 7% of electricity.
(2) The finished product is of good quality. Passless rolling can avoid the quality defects caused by the dislocation of the roll and the guide device, rolling offset, and overfilling during pass rolling; passless rolling can cause the metal to flow laterally, which is conducive to surface renewal, thus making Defects such as hairlines and cracks on the surface are reduced and the surface layer changes uniformly, which is very important for products requiring uniform distribution of the decarburized layer; there is no speed difference on the working surface of the roll, and the relative sliding on the contact surface between the metal and the roll is higher than that of pass rolling. The time is much smaller, so there is no grinding debris from the rolls to press on the surface of the rolling stock, which is particularly beneficial for the production of wire rods as wire drawing blanks. Because the wear debris pressed on the surface of the rolling piece is the main cause of the filament breaking. Due to the improved quality of the wire rod, the production capacity of the filament drawing machine can be increased by 6% and the cost can be reduced by 5.5%.
(3) High yield and save metal. During the passless rolling, the deformation of the rolling piece is uniform, so the length of the defects formed at the head and tail of the rolling piece is greatly reduced. Since the length of the cutting head and tail is significantly reduced, the yield can be increased by 0.4%~1.0%; the guide plate and the guard plate are simple in the non-pass rolling, their installation and adjustment requirements are not strict, and the rolling movement of the rolls The deformation of the workpiece has no effect, so the intermediate rolling scrap caused by the card steel and other reasons is also reduced accordingly; due to the uniform deformation, the percentage of the rolling stock without internal defects is also higher than that of the conventional pass rolling method. Therefore, significant effects of improving yield and saving metal can be obtained.
(4) Save rolls and simplify roll repairs. The diameter of the rolls used in non-pass rolling is smaller than that used in conventional pass rolling, and the difference is twice the depth of the groove, thereby reducing the weight of the rolls; in flat roll rolling, because there is no roll ring, the roll body is The utilization rate of the length can be increased by 20%~30%; the working diameter of the roll at the contact point between the rolled piece and the roll is the same, there is no roll diameter difference formed by the groove, and there is no roll surface speed difference in the width direction of the rolled piece, and the wear of the roll is greatly reduced. And it is more uniform, the amount of roll repair is significantly reduced, and the life of the roll is increased by 3 to 6 times; since the non-porous roll can be applied to various specifications of products, the same roll can be applied to different stands. The reserve of the rolls is greatly reduced (about 1/3), which greatly simplifies the management of the rolls; because the flat rolls are not grooved, the labor and cost of roll processing are reduced.
(5) Improve the production capacity of rolling mills and reduce labor intensity, labor volume, and production costs. In the case of no-pass rolling, due to the large commonality of the rolls, it is often not necessary to change the rolls when changing the rolled products, and the adjustment of the rolling mill is relatively simple so that the downtime of the rolling mill can be reduced by 37%; The requirements are not strict, the guide plate and the guard plate are simple and easy to adjust, which greatly shortens the roll changing time; during rolling, there are fewer jamming and intermediate rolling scrap accidents, and less time to deal with accidents. Therefore, the operation rate of the rolling mill is greatly improved, thereby significantly improving the production capacity of the rolling mill. In addition, due to the large deformation of the passless rolling pass, the rolling pass can be reduced, and the rolling rhythm time can be shortened, which is also one of the main reasons for the increase in the rolling mill output.
There are still the following problems to be solved in the application of no-pass rolling:
(1) Because no-pass rolling does not have side walls to clamp the rolling piece, it is easy to cause out of square, and it is impossible to continue rolling in severe cases;
(2) Because The corners of the rolled pieces are repeatedly rolled without grooves, so they are relatively sharp and may cause folding defects;
(3) On a continuous rolling mill composed of horizontal roll stands, the two stands need to be twisted and turned. When the rolling piece contacts the guide device, it is prone to scratches, and continuous rolling can cause folding defects;
(4) To make the non-porous rolling used in actual production, it is necessary to design rolling procedures and guide devices to prevent stripping. The design of this guide device should be able to prevent the front and rear ends of the rolling piece from bending, twisting out of square deformation, and scratching the surface of the rolling piece;
(5) A turning device that can stably twist the rolling piece should be installed between the continuous horizontal stands. The main design points of the no-pass rolling are to make the rolling stock stable between the two rolls, the rolling stock will not be overturned or twisted, and the diagonal difference of the rolling stock cross-section or the inclination of the side of the rolling stock cross-section. The degree does not exceed a certain limit value. Therefore, it is necessary to accurately determine the cross-sectional shape, size, and deformation parameters of the rolling stock, and at the same time determine the difference between the distance between the guide plates in the direction of the roll entrance and the width of the rolling stock at the entrance. In the case of non-pass rolling, the entrance guide plate plays a decisive role in the stability of the rolling stock entering the rolls and rolling between the rolls, and the gap value between the entrance guide plate and the entrance rolling piece must be reasonably determined.