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April 16, 1963 P. BILLEN ET AL 3,085,684 EXTRUDED TUBES AND CABLE SHEATHS Filed Oct. 24, 1957 mg. I IN l/EN TO ITS LZ 817/ ?Haezbd elem 3,085,684 Patented Apr. 16, 1963 2 present invention is more especially concerned with the ex trusion of aluminium and aluminium alloys. The method 3,085,684 EXTRUDED TUBES AND CABLE SHEATHS proposed by the present invention is based on the earlier method of preventing, by means of the relative displace ment of mandrel and die, the development of the annular Peter Billen, Leverkusen-Kuppersteg, Ernst Emmerich, Cologne-Bruck, Walter Haendeler, Dusseldorf, and Willi Linnerz, Dusseldorf-Ellen‘, Germany, assignors to Schloemann Aktiengesellschaft, Dusseldorf, Germany Filed Oct. 24, 1957, Ser. No. 692,230 2 Claims. (Cl. 207-10) markings known as “bamboo rings” on extruded tubes and cable sheaths of aluminium or other metals which are subjected to cooling immediately they leave the die, the said earlier method consisting in displacing the tools to The invention relates to a method, by the relative dis 10 increase the size of the annular extrusion ori?ce when the pressure drops and to reduce the size of the ori?ce placement of mandrel and die, of preventing the develop when pressure is re-applied. The method now proposed ment of the annular markings known as “bamboo rings” by the present invention, in which the adjustment of the on extruded tubes and cable sheaths which are cooled tools to increase the size of the annular ori?ce is effected immediately they leave the die. According to an earlier proposal (German patent application Sch 14,000 Ila/7b, of November 20', 1953, which issued as Patent No. 1,012,892; U.S. application Ser. No. 460,961, which issued as Patent No. 2,828,859 on April 1, 1958, of October 7, 15 before the standstill period begins, is primarily distin guished from the aforementioned earlier proposal by the fact that it is performed in a gradual manner in proportion with the gradual contraction of the annular ori?ce due to the cooling of the die. At the same time the simultaneous 1954; British Patent No. 765,367, published Jan. 9, 1957) contraction of the annular ori?ce due to the gradual drop the normal velocity of extrusion is gradually reduced to in the pressure can likewise be taken into consideration nil in such a way that during the standstill period the (as proposed in German patent application Sch 14,000 cooling cable sheath and the tube-forming tools will at lb/ 7b, U.S. patent application Ser. No. 460,961, and no time assume temperatures likely to injure the insula ‘British Patent No. 765,367). Another feature of the in vtion of the cable. As the temperature and the speed of extrusion go down, the die will necessarily contract and 25 vention is that the tools are displaced in the sense of reducing the size of the ori?ce before the press is re reduce the size of the annular ori?ce through which the started at the end of a standstill period. The amount of sheath is extruded, so that the thickness of the wall of the displacement is preferably calculated to allow for the tube will slowly diminish. Moreover, the gradual reduc ‘degree of thermal contraction of the extruded material tion of the normal velocity of extrusion involves a concomitant reduction in pressure. The drop in pressure 30 which is within the region of the die during the standstill period of the press. Allowance may also be made for affects the pressure inside the extrusion chamber behind contraction due to the pressure drop that precedes the the ori?ce of the die. Consequently there is some recovery standstill period of the press. from the longitudinal elastic strain imposed by the normal Yet another feature of the invention is that the further pressure of extrusion, and this recovery likewise affects the extrusion chamber itself. Hence, the thermal varia 35 adjustment of the tools in the sense of reducing the size of the ori?ce until they have resumed the position which tion of the size of the annular ori?ce due to the change corresponds with normal extrusion velocity after the in the temperature will be modi?ed by an elastic varia press is re-started is gradually performed approximately tion due to the changing extrusion pressure and the conse in proportion with the increase in the size of the extru quent ?uctuation of the load on the tools. The magni tude of this elastic variation depends upon the amplitude 40 sion ori?ce due to the die again heating up. The accompanying drawings are axial sections of parts of the pressure ?uctuation that occurs in the space con— of three extruded aluminium cable sheaths showing the taining the tools. If the pressure of extrusion is abruptly inequalities (bamboo rings) in the conformation of the relaxed, then a pronounced annular depression will form sheaths at the points which correspond with the standstill on the extruded tube, known as a “bamboo ring.” If the drop in pressure is gradual, then the resultant marking will 45 periods of the press. The sheath shown in FIGURE 1 is produced without any displacement of the extrusion not be pronounced. Whereas rapid cooling causes the tools and therefore exhibits the development of a pro diameter of the die to become smaller by radial contrac nounced bamboo ring. In the production of the sheath tion and hence entails a reduction in the wall thickness shown in FIGURE 2 the size of the annular extrusion of the cable sheath, the withdrawal of heat from the tool ori?ce was increased as the pressure fell at the end of the head by the cooling of the tube when the standstill periods extrusion stage before the standstill period began and it are long causes a shrinkage of mandrel and die also in the was reduced again when pressure was re-applied. FIG axial direction. This axial shrinkage involves an enlarge URE 3 illustrates the method of controlling the extrusion ment of the annular extrusion ori?ce and hence tends to ori?ce as proposed by the present invention. thicken the wall section of the extended tube. In the method illustrated in FIGURE 1 the pressure It has already been disclosed that the depression which of extrusion is gradually reduced before the point 1, forms part of the bamboo ring and which is due to elastic which corresponds with the standstill period, is reached, changes in the size of the extrusion ori?ce at the end of a ‘ so that the wall thickness “d” of the extruded sheath will pressure period can be prevented from forming by a likewise diminish from the left to the right towards displacement of the mandrel, i.e. by an adjustment of point '1. During the standstill period the die cools and the size of the ori?ce, i.e. a variation of the distance 'therefore radially contracts, thus pressing a bamboo between mandrel and die. The object taken in view by the ring, in the form of a notch-like annular groove, into the present invention is to eliminate the eifect of changes in the size of the extrusion ori?ce due to causes that had > wall of the sheath. For re-starting the press a high pres not heretofore been considered, namely those due to ' sure is then applied, which causes the size of the ori?ce extruding aluminium, the temperature ?uctuation that tube wall slowly increases to assume its original value “d” at about the point 3. The resultant confonnation of changes in temperature. When extruding lead sheaths 65 to increase and the tube wall to thicken abruptly at the point 2. During the ensuing pressure stage the tempera these temperature variations do not produce considerable ture of the die gradually rises and the thickness of the and particularly troublesome changes. However, when must be controlled covers a range of several hundred degrees C. and this is rapidly traversed owing to the high rate of cooling the process requires, which therefore pro duces very sensible thermal shrinkage effects. Hence the the wall, as shown in FIGURE 1, is therefore non-uni form and unsatisfactory. In the method illustrated in FIGURE 2, which is an 3,085,684. ' A. 3 improvement on that of FIGURE 1, the wall thickness likewise gradually diminishes from its normal value “d” on the left to a smaller value “til” at the standstill point 4- owing to the gradual pressure drop during this period. However, when the press stops, at the point 4, the tools are adjusted in the sense of increasing the width of the ori?ce. This adjustment therefore compensates the im pending reduction in wall thickness due to the contrac tion of the die. When the press is re-started, at the point 5, the pressure of the extruded material rises again and may not always be as pronounced as shown in the draw ings, the individual sections are nevertheless easily detect able when the cable sheath has been completed. Since in actual practice it is very rarely possible by ad justing the tool to compensate with entire precision shrinkage due to changes in temperature as well as elastic changes due to fluctuations in pressure, it is preferred in making the adjustments to be somewhat generous in the positive direction i.e. in the sense of an increase in the thickness of the sheath wall beyond its thickness in other regions, and at points 7 and 11 not to effect the adjust the thickness of the wall tends to increase, but this is now ment abruptly but gradually whilst the sheath still slow compensated by a readjustment of the tools, in the sense ly moves through the die. A small and uniform tem of decreasing the ori?ce, at point 6. In other words, the porary increase in the wall thickness throughout the con tools are ?rst displaced, at the point 4, to increase the ori?ce, and they are then readjusted, at the point 16, to re 15 trolled length of the cable is an advantage when, as is frequently necessary, the standstill periods are long, be duce the ori?ce. This method is better than the method cause the increase will then offset the effect of metal illustrated in FIGURE 1, because there is now no abrupt lurgical changes due to cooling, which would otherwise reduction in wall thickness as at 1 in FIGURE 1, but rather a short increase in thickness. The further course of the extrusion process from point 6 corresponds with that shown in FIGURE 1, and the original wall thickness d will therefore be re-established. In the method now proposed by the present invention, which is illustrated in FIGURE 3, the pressure again gradually diminishes from the left to the standstill point adversely affect the ?exural properties of the cable. What is claimed is: 1. A method of controlling the thickness of a sheath or tube of aluminium or other metal produced in an ex trusion press in which the thickness is determined by the distance between one end of the mandrel and the end face of the die aperture and in which the extruded prod uct is cooled immediately after leaving the die, compris sion. The e?ect of cooling would therefore be to dimin ing the steps of reducing the extrusion pressure gradual ish the wall thickness accordingly. However, according ly when a stoppage is to be effected, progressively adjust to the invention it is proposed to counteract this gradual ing the relative axial spacing of the mandrel and die from decrease from the very beginning by displacing the tools 30 the beginning of the reduction in pressure and during its at the point 7, where the reduction of pressure begins in continuance to the extent necessary to compensate for with a concomitant reduction in the velocity of extru the sense of progressively increasing the ori?ce so that the wall thickness will not actually diminish at all but the reduction in the annular gap that would otherwise re sult from the variation of the load on the mandrel and will maintain its original value “d” until the standstill die caused by the changing extrusion pressure, continu point is reached, or may even be slightly increased. Dur 35 ing the adjusting of the mandrel and ‘die to compensate ing the standstill period of the press, which begins at point 8 the tools are re-adjusted at the point 9 for the further enlargement of the extrusion ori?ce to compen sate for the thermal contraction of the die. During the for the reduction in the annular gap that would other wise be caused by the cooling and consequent contraction of the die, and progressively re-adjusting the mandrel and die when extrusion is resumed, to the extent neces possibly prolonged standstill period the extrusion ma 40 sary to compensate for the thermal and elastic expan terial in the vicinity of the ori?ce will cool so that, rough sion of the die resulting from the increase in temperature ly expressed, it will lie between the tools with play, thus and pressure. tending to give rise to a sudden considerable increase in wall thickness when pressure is re-applied. To prevent this from happening it is proposed by the invention to re-adjust the tools at the point 10 during the standstill period in the sense of reducing the ori?ce. When pressure is resumed at the end of a prolonged period of standstill the increase in wall thickness, in dicated at points 9 and 10, will therefore be only slight ' (wall thickness greater than or equal to d) and this is then compensated up to point 11 by the further adjust ment of the tools to constrict the ori?ce, thus at the same time continuously compensating the increase in wall thickness that will be caused by the rise in the tempera ture of the die, and therefore operating to maintain the wall thickness d. Hence, besides preventing the develop ment of depressions, the present invention will also re duce any undesirable thickening of the wall. If the ad justment of the tools is skillfully controlled and per 60 formed, any thickening of the wall may even be entire ly avoided. However, whenever such thickening does oc cur, the transitions will not be abrupt, a factor which will tend to impart to the tube or sheath a much greater flexural strength on the bending machine than when changes in wall thickness are well de?ned and abrupt. Although the variations in the thickness of the walls 2. A method of controlling the thickness of a sheath or tube of aluminium or other metal produced in an ex trusion press as claimed in claim 1, further comprising the step of reducing the size of the extrusion gap before the press is re-started after a standstill period to the ex tent necessary to compensate for the thermal contrac tion of the cooling extrusion material in the vicinity of the die during the stand-still period. References Cited in the ?le of this patent UNITED STATES PATENTS 2,131,173 Greenall ____________ __ Sept. 27, 1938 2,177,681 2,782,920 Anderson ____________ __ Oct. 31, 1939 Norman ____________ .._ Feb. 26, 1957 2,828,859 Emmerich ____________ .._ Apr. 1, 1958 380,037 Great Britain _________ __ Sept. 8, 1932 876,573 France ______________ __ Oct. 10, 1942 909,332 Germany ____________ __ Apr. 15, 1954 FOREIGN PATENTS OTHER REFERENCES “Advanced Fluid Mechanics,” vol. 1, by R. C. Binder, Prentice-Hall, Inc., Englewood Cliffs, N.J., @ 1958, pp. 263-271.