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Mill roll technology

mill roll technology( both in Chinese and english)
2014-05-09 12:44:27


一、(Introduction roll)
  Rolls and roller bearings are important components in a rolling mill. In the rolling process, roll to metal direct contact with the rolling. Rolls cause the rolled metal to deform plastically. Various types of roller bearings supporting the rolls.
Roll Category: By rolling mill can be divided into panels and the steel mill roll mill roll two categories steel mill roll body roll is a rolling groove, according to steel rolling process of arranging and size of pass
1.1 Composition Roll
composed of the roll body roll, roll neck and the axis of the first of three parts. Roll neck bearings mounted in bearing and pressure through the device to pass a few rolling force. Connected to the shaft head and shaft connection, passing the rolling torque.
shaft there are three main forms: Plum shaft, cardan shaft with keyway or cylindrical shaft. Easy processing of the commonly used axis head with the platform.
1.2 Roll dimensions

basic dimensions of the roll the name of parameters including roll diameter, barrel length, diameter and roll neck roll neck length.
1.2.1  Nominal diameter and roll barrel length
A、Nominal diameter of roll
1.4。nominal roll diameter, the main parameters of both the rolling mill, roll size is the main parameter. When the roll diameter is determined, other parameters of the roll by the strength, stiffness, or structural limits are also identified. Roll steel mill is a hole in the body. Typically, the steel mill to the center distance as the gear housing nominal roll diameter, roll a groove diameter larger than its nominal working diameter. In order to avoid too deep groove cut into the slot, the roll diameter and work on behalf of the ratio of the diameter does not exceed 1.4.。Work roll diameter based on the maximum bite into the roll angle α and to determine the strength requirements.
B、 Barrel length。Roll with a hole in the body depends on the length of pass configuration, the roll of the bending strength and stiffness. Therefore, the rough mill longer barrel roll in order to configure a sufficient number of pass; and finishing mill roll mill roll products in particular the shorter barrel, so that roll stiffness can be strengthened to improve the accuracy of product size

1.2.2  Roll neck diameter and length。roll neck diameter and length of roller bearings in the form and work load related. Radial roller bearings due to size restrictions, roll neck diameter is much smaller than the diameter of the barrel. Therefore, the transition barrel roll at the neck and is often the worst place to roll intensity. As long as conditions allow, roll neck and roll neck diameter of the fillet and roll the body larger r should be selected.
1.3 Roll roll surface hardness of the material and
1.3.1  Used roller material :roll materials commonly used:
1、Alloy forged steel
2、alloy cast steel
3、Cast iron. Can be divided into ordinary cast iron cast iron, alloy cast iron and ductile iron. Casting roll, the use of a different mold, you can get different hardness cast iron roll. Therefore, it is semi-chilled rolls, chilled rolls and indefinite chill roll of the points:
1)HS≥50。1) semi-chilled roll. Roll no obvious white surface layer, the roll surface hardness of HS ≥ 50.
2)HS≥60。2) chill roll. Clear white surface layer, the center is gray layer, the middle layer of hemp mouth, roll surface hardness of HS ≥ 60.
3)HS≥65。3) indefinite chill roll. The surface layer is white, but gray layer of white layer and no clear boundaries between the roller surface hardness HS ≥ 65.。Cast iron roll hardness, surface smooth, wear simple and cheap manufacturing process. The disadvantage is that strength than steel
1.3.2  1.3.2 Selection of materials and roll roll surface hardness
Roll the choice of materials and work characteristics and damage roll form are closely related.
                 Steel mill roll and have a larger impact force load, should have sufficient strength and hardness of the roll surface can be placed on second.Roughing mill roll should be chosen by special soft annealed pearlite ductile iron rolls, the hardness should be lower, usually select the hardness HS38 ~ 42. If the resistance is a major problem, then select slightly higher hardness of the HS45 ~ HS48 more appropriate.
       Group selected in the rolling mill roll mill set the hardness to be thicker high, the hardness value of up to HS67, material to pearlite or bainite ductile cast iron as well. If the needle used centrifugal casting ductile iron roll the best. The slit rolling mill group in the practical effect of high-chromium roll better.
          Finishing mill roll selected for the centrifugal casting ductile iron needle roller or high-speed steel roll. High speed steel roll working layer of high hardness, can reach HS80 ~ 85, has good wear resistance and thermal crack resistance, hot roll surface crack does not appear, generally do not spalling.
         
Second, roller bearings Introduction
2.1 Characteristics of the work roll bearings
        Rolling mill roller bearing is an important base of work components. Since the various mill structure and working conditions vary greatly, and must use different types of bearings. And general purpose bearing, roller bearing oil the following characteristics:
(1) a large workload. The barrel roll diameter should be ensuring the strength and bearing dimensions should not exceed the minimum diameter of the barrel, roll diameter and relatively short length, so the roll neck is exposed to a large unit load. Usually borne by roller bearing unit pressure than the general purpose bearings 2 to 4 times higher, even higher, while the pv value (bearing units of the product of pressure and line speed) is the common bearing 3 to 20 times.
2) The large difference in operating speed. Different mill operating speed varies greatly. The mill at different speeds, use different forms of bearings

(3) working environment. A variety of hot rolling machine, roll to be cooled with water, and there is squama splash. Therefore, bearing the seal of the proposed higher requirements.
2.2 Types of roller bearings
   The main types of roller bearings are rolling bearings and sliding bearings.
   Roller bearings are mainly used on double row spherical roller bearings, four-row tapered roller bearings and multi-row cylindrical roller bearings. The rigid bearing, friction coefficient is small, but the impact of poor performance, size large. But after improving on the bearing material, is used in rolling bearings can meet requirements of the current commonly used mill for the rolling bearing.
2.3 Rolling
     Determine the characteristics of rolling mill on its use. As in the radial roller bearing size is limited to conditions under a lot of rolling force, so the rolling mill using a multi-column multi-roller bearings. The bearing has a smaller radial size and good impact resistance. There are double row spherical roller bearings, four row tapered roller bearings and multi-row cylindrical roller bearings. The first two can be both radial force and axial force; third, although to additional axial thrust bearing, but its radial size is small, large carrying capacity, allowing high speed, which in recent years, high-speed, heavy contains extensive use of the rolling mill.
Third, technology use and maintenance of roll
3.1 Replacement and adjustment of roll
       In steel rolling, when the roller is worn or replacement of product variety to a certain extent, the roll should be replaced, especially the work rolls. Roll changing work includes demolition of the old roll, install the new roll and other accessories, post-roll mill for the corresponding parameters to be adjusted. For rolling roll is one of the important activities of the production process, and production line operating rates and product quality related. Roll changing the length of occupancy, depending on preparations for pre-roll, roll change when the roll changing labor organizations and operators to participate in technical proficiency.
3.1.1 reduce roll change time, improve the quality of change roll
       Roll changing in many cases takes a lot of time, to a certain extent, affect the output of rolled products increased. Only improve the roll changing speed to further enhance the productivity of rolling. With the development of market economy, less bulk and more specifications, market demand, and greatly increased the frequency of roll exchange. To this end, reduce roll change time, improve the quality of roll changing, is to improve the operating rate and reduce waste rolling review, to increase production is one important means.
          In order to improve efficiency and quality of work, should vigorously promote the standardization work on preparations for pre-roll, roll change when the change of labor organizing and participating in staff roll process analysis, process flow analysis, path analysis, operational analysis, action analysis, skill analysis. Lay the machine serviced from the child, lifting crane to remove the roller cover every aspect. Each test, repeated operation, the rationality of its action to simplifying your, tally up the roll change operation method. This approach typically incorporated into the "production operating procedure" in the.
3.2 Roll Maintenance
         Roll a direct impact on the quality of the production process. Production can be correctly and effectively to maximize rational use of effective protection to maintain and roll, not only can improve production efficiency, improve product quality can also be stable, thus reducing production costs, create the best results

3.2.1 improvement of rolling process, to extend the life cycle of hot rolling mill roll
         In the rolling process, the products, improve accuracy, the production rate was higher on the roll also made use of a higher demand. If the roll surface appears rough, peeling off the roll surface, scratches and other defects, will not only affect the surface quality of products, and even disrupt the production of rhythm, reduced productivity, increased production costs. Therefore, the improvement of rolling process and rolling technology to improve the performance of roll, roll to extend the life cycle, has become the manufacturing plant research and research projects.
 3.2.1.1 Roll the life cycle
        Roll roll life cycle is a measure of an important indicator of performance is an important rolling production management content. It not only reflects the situation of rolling production to organize, but also related to the rolling mill roll production to consumption and production costs. Roll the life cycle of destruction by way of roll by roll roll changing time to decide. Roller mill for two cases:
         The first plan for roll, that roll wear and according to product quality, combined with the rolling roll tonnage or rolling miles, there are plans to roll from the mill to replace the down, the repair mode.
         roll, that roll for a variety of accidents, such as the heap of steel, roll off, roll surface peeling, scratches and other causes of non-normal roll change.
          Roll from the roll-on roll to change a life cycle is completed. Analysis of roll process life cycle factors, we must roll damage resulting from the analysis of the causes of these problems in order to find a solution.
3.2.1.2 failure mode and analysis of roll
1) The roll wear
       Roll wear is the most common failure mode for roll, which is rolled by the work roll and backup roll and work roll and the friction caused between. In the production process, work roll for a long time in a hot environment, the roller surface produces a layer of dense, brittle but wear the oxide film. Good dense oxide film can not only extend the life cycle of the roll, but also can improve the surface quality of products. However, in the rolling process, because roll surface oxide film to withstand periodic alternating stress, prolonged stress will roll surface fatigue, fatigue limit is reached after the work roll and the rolling friction between the generated under the action of strong shear stress, the roll surface oxide film began to fall, so that the roll surface becomes rough. At this time the situation should be based on the roll surface roughness reasonable arrangements for roll, to avoid impact on surface quality of workpiece.

The roll surface cracks
        In rolling, the roll surface cracks is also a common roll defects. Roller surface cracks usually as a result of local material adverse roll, rolling caused by uneven cooling. In the normal rolling process, roll the body temperature is usually 50 ~ 90 ℃, in contact with the rolling surface of roller rack instantaneous temperature differences ranging up to 600 ~ 800 ℃. The roll surface in contact with the rolling, high temperature by the moment, the surface expansion due to rapid temperature rises, sub-surface temperature due to heat restrictions remain the same. Surface, subsurface tensile stress generated each other, the surface showed a higher compressive stress. When rolling, roll out and when the role by the cooling water, the surface temperature down quickly and contraction, so that the surface compressive stress into tensile stress state. Roll each one revolution, and its surface to carry out a tension and compression stress cycle, repeated many times resulting in tension and compression fatigue surface and then roll thermal fatigue crack generation. For the roughing mill, the good mill roll surface cracks can improve the biting conditions, but if the finished product roll finishing cracks to the finished product will reflect the surface of the defect, resulting in finished surface spider veins occur periodically, once surface defects found in finished products must be immediately roll change, in order to avoid more waste.

3) roller surface spalling
       Roll in roll spalling failure mode is also more common. In addition to roll their own factors (such as the Ministry of internal quality roll evenly with the grain size of inclusions or roller displacement, etc.) influence, but also to roll in rolling process is directly related to the force. In the rolling process, the work roll in complex gravitational state, both between the work roll and the rolling contact stress, but also work roll and the rolling contact or work roll cooling thermal stress, the stress will roll surface fatigue. When the fatigue strength more than the allowable value, it is likely to cause spalling of the roll surface. On the other hand, if the roll during rolling to a larger extent of the roll surface crack did not roll changing in time, these cracks will roll deep in the way of expansion by fatigue, developed to a certain extent will lead to the roll surface spalling

4) roll-off
        Damage in all the way roll, roll off the greatest impact on production. Although the incidence and rate of roll-off is not much, but its roll wear and handling due to roll off the difficulty and length of time sufficient to produce the rhythm of the production costs and tremendous impact. In the production process, resulting in broken roll a number of factors, in addition to roll their own factors, such as roll material, heat treatment or processing techniques, which do not meet the requirements, the production process roll inadequate cooling or cooling uneven roll by the first heat at first cold rolling system of low temperature steel, pressure overload or due process of rolling overload caused by the irrational arrangements and so on, are likely to result in broken roller mill, so roll scrapped.
5) The roller surface scratches
         In the production process, the roll surface scratches generally caused by the following factors: inadequate maintenance of equipment, rolling mill imports and exports of Guide guide guide guide and guard roller rolling groove and contacts, resulting in rolling tanks roll surface scratches.
3.2.1.3 extended roll life cycle approach
      Extended roll life cycle methods are:

      (1) rolling to develop a reasonable plan. In the production process, the preparation of a reasonable plan for improving rolling performance roll, roll to extend the life cycle is essential. Unreasonable if the rolling planning, not only the use of performance not roll into full play, but will produce a great impact. Therefore, in the preparation of rolling plans, must be rolling in detail the varieties, specifications, etc., in general, the preparation of the rolling plan should have the following principles:
          1) reasonable for hot rolling mill roll. Hot roll roll and pressed to pay attention to rhythm control, and adjust the roll cooling water, to ensure the production of roll surface layer of the proper and uniform thickness of oxide film
        2) The roll gap adjustment. Determine the quality of roll gap adjustment is based on: rolling smooth, rolling size pass shape rolling reduction amount of the normal and uniform distribution
        2) a reasonable load distribution. Reasonable load distribution is the key to achieving stability in rolling. Load distribution during the mill, they need to follow the "second flow equal" principle, but also to ensure uniform load distribution, to avoid the rolling force is too large or individual rack rolling overload, which caused damage to the roller.

     3) to confirm the normal roll into the cooling water. In production, roll cooling water on the use of a large roll. Roll cooling water into bad, will accelerate the roll wear and roll surface oxide peeling, or even off roll, roll to shorten the life cycle. Therefore, in the production must be strengthened on the roll cooling nozzles management to ensure roll cooling water pressure normal, filters and cooling nozzle without clogging, nozzle angle normal, water enough to make roller temperature control within a certain range, to ensure that roll the normal use.
     4) increase the level of process operation. In production, many factors restricting stable production. Improper operation of production or intervention if the process is not timely, it may cause heap steel mill accident, which caused damage to the roll. Therefore, raising the level of process operation, reduce troubles, but also extend the life cycle of a roll effective way.
3.2.1.4 Summary
        Roll the life cycle of destruction by way of roll, roll roll destruction and is closely linked to technology. Only by constantly improving technology and rolling rolling technology, to effectively compensate for various factors on the adverse effects of roll, roll to improve performance, extend the life cycle of the roll.