Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
  • B21B—ROLLING OF METAL
  • B21B17/00—Tube-rolling by rollers of which the axes are arranged essentially perpendicular to the axis of the work, e.g. "axial" tube-rolling
  • B21B17/14—Tube-rolling by rollers of which the axes are arranged essentially perpendicular to the axis of the work, e.g. "axial" tube-rolling without mandrel, e.g. stretch-reducing mills

Definitions

• the force which is exerted by a roller on the tube in the direction of rolling that is the force which is applied to effect the tension basically depends on the frictional forces in the region of the contact surface between the roller and the tube. These frictional forces are influenced by the ratio of the peripheral speed of the roller to the speed at which the tube passes through. This ratio is different at the individual peripheral points of the tube, since the roller radius at the individual peripheral points of the tube which are in contact with a roller, is also different, whilst the roller angular velocity remains the same. It may therefore be the case that the peripheral speeds of the roller at all the peripheral points of the tube which come into contact with a specific roller, are greater or smaller than the speed at which the tube passes through.
• peripheral speeds of a roller it is also possible for the peripheral speeds of a roller to be greater at certain peripheral points of the tube and to be The distance of these points from the axis of rotation of the roller is designated as the rolling radius.
• the peripheral speed, which is calculated from the rolling radius and the roller angular velocity is therefore the same as the speed at which the tube passes through.
• R represents the rolling radius
• D the outer diameter of the tube
• WD the ideal roller diameter, which is equal to double the distance between the axis of rotation of the roller and the longitudinal axis of the tube.
• R A (WD 00) (Formula II)
• 0 represents a factor for determining the rolling radius. It has the value 1 when the rolling radius is identical to the roller radius in the region of the groove base.
• the value of 0 becomes greater than 1. If, however, the peripheral speed of the roller at each of these peripheral points is smaller than the speed at which the tube passes through, then the value of c becomes less than 1 and assumes a maximum value of 0.5 for a three-roller pass, i.e., the pass of a stand having three rollers whose axes are at to one another.
• the maximum force exerted by the roller on the tube is in the opposite direction to the direction of rolling, whereas in the case of a c value of l or more, the maximum force exerted by the roller on the tube is in the direction of rolling.
• the value of c in the case of a threeroller pass is approximately 0.9, depending on the ratio of roller diameter to tube diameter and also on the reduction in diameter. The precise value is produced from the equilibrium of forces between the tube and the roller. If the tube hasentered all the stands of the rolling mill, which may, for example, number 24, then the tension is built up e.g., in the first four to six passes or sizing gaps. If the maximum possible tractive forces are utilized, the c values e. g., of the three-roller pass rolling mill, are approximately 0.5 or less. The last sizing gaps, e.g.
• K F K K passes of the rolling mill and with the leading and trailing end portions of the tube beyond or in front of the rolling mill.
• these ratios are no longer correct when each of the end portions of the tube passes through the rolling mill.
• those passes which roll the leading longitudinal portions of the tube always serve to reduce the tension.
• the 0 values of these passes would always have to be 1 or more for the maximum possible tension to be applied. If the leading portion of the tube in question is elongated to a lesser degree than the middle portion of the tube, for the initially mentioned reasons, then a point in the region of the leading portion of the tube passes a specific point on the rolling mill at a lower speed than a point in the region of the middle portion of the tube.
• the thickened end portions are, for example, approximately 2.2 to 2.5m long.
• this is only possible in the case of individually driven stands with which it is difficult to maintain the predetermined speeds during the steady state.
• the cost of individually driven stands, including the control and regulating devices is very high and they are more susceptible to trouble than the above-mentioned group drive having fixed speed sequences, which drive is constantly able to maintain the predetermined speeds.
• the object of the invention is to shorten the length of the thickened end portions even further and to lower the proportion of scrap during the reducing rolling of tubes correspondingly.
• the tube in the region of those passes of the rolling mill which are at the front when viewed in the direction of rolling and which build up the tension, preferably in the region of the first to sixth passes, during the entry of the leading end portion of the tube into and the exit of the trailing end portion of the tube from this region, the tube is acted upon, at least in the respective penultimate pass which builds up the tension, by a maximum tractive force, which is limited only by the transmission capacity of the frictional forces between the rollers of the pass and the tube.
• maximum tractive force in only one of the front passes represents a substantial intensification of the tension in the tube in this part of the rolling mill and thus a shortening of the 'thickened end portions of the tube.
• maximum tractive force is also to be exerted on the tube in several or in all the other front passes which build up the tension.
• the invention includes a rolling mill for carrying out the method according to the invention, wherein the speeds of the rollers are predetermined and are kept substantially constant during rolling, and wherein in the region of those passes of the rolling mill which are at the front when viewed in the direction of rolling and which build up the tension, preferably in the region of the first to sixth passes, the roller speed of the first pass of the rolling mill is determined in accordance with a 0 value equal to or smaller than 0.35, which fixes the rolling radius of the rollers, and the roller speed of the pass following on the last pass of those passes which build up the tension, is determined in accordance with a e value of 1.0 or over.
• c values which hitherto would have been regarded as unrealistic may for the first time be selected for the first passes of the rolling mill.
• a e value of less than 0.5 in the first pass of the rolling mill signifies, in the case of a three-roller pass, that the rolling radius is greater than the distance between the axis of rotation of the roller and that portion of working surface of the roller which is furthest away from said axis, and thus that a particularly high relative speed is selected between the tube and the roller.
• the relative speed in the front passes is, in respect of the amount, still substantially lower than the speed which is produced anyway in the latter passes, e.g., in the twentieth to twenty-fourth stands.
• the increased wear in the region of the front stands is in fact so small, as compared with normal wear, that it can be neglected, so that nothing conflicts with the reduction in the method according to the invention of the e value in the first pass.
• the invention can be used in rolling mills having individual drives for the stands as well as in those having group drive.
• the speeds, which are predetermined in accordance with the invention are to be kept constant regardless of how far the tube has entered the rolling mill, an expensive individual drive, which is susceptible to trouble in respect of regulation, is superfluous and the group drive is to be recommended, since it is possible with this drive to maintain precisely the determined speeds.
• the thickened end portions are shortened from 2.2 to 2.5m in conventional individually driven rolling mills to approximately 1.8 to 2m with a group driven rolling mill according to the invention.
• the invention which when selecting the roller speeds in the front passes, takes into account and commences from the non-steady state of the entry of the leading end portion of the tube into or the exit of the end portion of the tube from the rolling mill, can be varied in quite diverse ways.
• the roller speed of the penultimate pass of those which build up the tension is determined in accordance with a value of approximately 0.5. It is also advisable to select the roller speeds of the individual front passes of the rolling mill in accordance with c values, which are always greater than 0 values of the respective preceding pass.
• roller speeds of the second pass up to the last pass of those which build up the tension in accordance with c values which linearly increase from a value equal to or smaller then 0.35 and a value equal to or greater than 1.
• c values which linearly increase from a value equal to or smaller then 0.35 and a value equal to or greater than 1.
• the invention which is clarified above using the example of a stretch-reducing rolling mill with three rollers per pass, can also be used analogously with rolling mills having a different number of rollers per pass, although in this case different c values are produced.
• a method of rolling tubes under tension in a multipass stretch-reducing rolling mill in which, during the entry of the leading end portion of the tube into and the exit of the trailing end portionof the tube from the region of those passes of the rolling mill which are at the entry end when viewed in the direction of rolling and which build up the tension subjecting the tube, at least in the respective penultimate pass of those passes which build up the tension, to a maximum tractive force, which is limited only by the transmission capacity of the frictional forces between the rollers and the tube and is created by causing the relevant peripheral speed of the rollers in such passes at each point of contact surface between the rollers and the tube to be greater than the speed of the tube passing through said rollers.
• a rolling mill having multiple passes, each pass including three-rollers for rolling tubes under tension, which mill is so adapted that the speeds of the rollers are pre-determined and are substantially maintained during rolling, in which in the region of those passes which are at the front when viewed in the direction of rolling and which serve to build up the tension, the roller speed of the first pass of the rolling mill is determined in accordance with a c value equal-to or smaller than.0.35, which fixes the rolling radius of the rollers, and the roller speed of the pass following the last of the passeswhich serve to build up the tension is determined in accordance with a c value of 1.0 or over, said 0 value being determined from the formula R 'WDC'D) where R represents rolling radius, D the outer diameter of the tube and WD the ideal roller diameter.
• roller speeds of the individual passes in the entry region of the rolling mill are selected in accordance with c values, which in every case are greater than the c values of the respective preceding passes.
• roller speeds of the second pass up to the last pass of those passes which serve to build up the tension are determined in accordance with c values which linearly increase from a value equal to or smaller than 0.35 to a value equal to or greater than 1.
• roller speeds of the second pass up to the last pass of those passes which serve to build up the tension are determined in accordance with c values which linearly increase from a value in excess of 0.35 to a value equal to or greater than 1.
• roller speeds of the second pass up to the last pass of those passes which serve to build up the tension are determined in accordance with 0 values which linearly increase from a value in excess of 0.35 to a value equal to or greater than 1.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Control Of Metal Rolling (AREA)
• Reduction Rolling/Reduction Stand/Operation Of Reduction Machine (AREA)
• Metal Rolling (AREA)

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• 1973
  • 1973-09-24 DE DE2347891A patent/DE2347891C2/de not_active Expired
• 1974
  • 1974-09-17 US US506844A patent/US3919872A/en not_active Expired - Lifetime
  • 1974-09-20 GB GB41026/74A patent/GB1487614A/en not_active Expired
  • 1974-09-20 JP JP49107861A patent/JPS5059258A/ja active Pending
  • 1974-09-24 FR FR7432191A patent/FR2244574B3/fr not_active Expired
• 1975
  • 1975-12-20 DE DE2557707A patent/DE2557707C2/de not_active Expired
• 1976
  • 1976-12-10 AT AT918376A patent/AT359956B/de not_active IP Right Cessation
  • 1976-12-14 US US05/750,374 patent/US4086800A/en not_active Expired - Lifetime
  • 1976-12-16 GB GB52481/76A patent/GB1563920A/en not_active Expired
  • 1976-12-17 JP JP51151003A patent/JPS5277868A/ja active Pending
  • 1976-12-20 FR FR7638346A patent/FR2335275A2/fr active Granted

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