US3919875A

US3919875A - Method of and apparatus for making high pressure tube bends, especially for the chemical industry

Info

Publication number: US3919875A
Application number: US496121A
Authority: US
Inventors: Radko Maev; Cestmir Zacek; Petr Janak; Jan Strecha; Josef Duzy; Ludek Lucak
Original assignee: KRALOVOPOLSKA STROJIRNA NARODNI PODNIK
Current assignee: KRALOVOPOLSKA STROJIRNA NARODNI PODNIK
Priority date: 1974-08-09
Filing date: 1974-08-09
Publication date: 1975-11-18
Anticipated expiration: 1992-11-18

Abstract

Method of and apparatus for producing tube bends for high pressure and high temperature use. A seamless tube is hot bent whereby to provide a semi-finished product, such semi-finished product is then filled with sand and tamped it in place. The method then proceeds with closing the ends of the thus sandfilled semi-finished product with lids, again heating the thus prepared semi-finished product to bending temperature, and the thrusting the heated semi-finished product downwardly through a female die by an aligned male die, whereby to produce a tube bend of oval form the longer axis of which is parallel to the bending axis of the semi-finished product and has a length which is 3 to 4 percent longer than its shorter axis. Thereafter the covers and sand are removed from the product, and after again heating the thus formed product calibrating it so as to change the oval cross-section thereof into a section which is circular in crosssection.

Description

United States Patent 1191 Maev et al.

[ 5] Nov. 18, 1975 i 1 METHOD OF AND APPARATUS FOR MAKING HIGH PRESSURE TUBE BENDS, ESPECIALLY FOR THE CHEMICAL INDUSTRY [75] Inventors: Radko Maev; Cestmir Zacek; Petr Janak; Jan Strecha, all of Brno; Josef Duzy; Ludek Lucak, both of Ostrava, all of Czechoslovakia [73] Assignee: Kralovopolska strojirna, narodni podnik, Bmo-Kralovo Pole, Czechoslovakia [22] Filed: Aug. 9, 1974 [21] Appl. No.: 496,121

3328996 7/l967 Pin et al 72/369 Primary E.\'aminer-Lowell A. Larson ABSTRACT Method of and apparatus for producing tube bends for high pressure and high temperature use. A seamless tube is hot bent whereby to provide a semi-finished product, such semi-finished product is then filled with sand and tamped it in place. The method then proceeds with closing the ends of the thus sand-filled semi-finished product with lids, again heating the thus prepared semi-finished product to bending tempera' ture, and the thrusting the heated semi-finished product downwardly through a female die by an aligned male die, whereby to produce a tube bend of oval form the longer axis of which is parallel to the bending axis of the semi-finished product and has a length which is 3 to 4 percent longer than its shorter axis.

Thereafter the covers and sand are removed from the product, and after again heating the thus formed prod uct calibrating it so as to change the oval cross-section thereof into a section which is circular in crosssection.

3 Claims, 2 Drawing Figures US. Patent Nov. 18, 1975 METHOD OF AND APPARATUS FOR MAKING HIGH PRESSURE TUBE BENDS, ESPECIALLY FOR THE CHEMICAL INDUSTRY This invention relates to the production of tube bends or elbows, which are adapted for use under high pressure and/or high temperatures, by forming them from straight seamless tubes of carbon or alloy steels. Such tube bends are employed in very substantial quantitles in the chemical industry.

Tube bends of this kind are presently manufactured from forged pieces in tube form or from rolled seamless tubes, the processing of which is done eccentrically with a consequent strength decrease of the bending zone of the outer wall of the bends caused by the bending process. The tube is tamped full of sand and is then bent by a bending machine or in a press with assistance of different tools. The eccentric tube working is, however, severe and costly; such bending often causes the cross-section of the passage through the elbow to be narrowed, thus causing an irregular weakness of the wall and an undesirable oval shape, the bending radius and the distance between the tube ends being unpredictable.

The above mentioned disadvantages of the prior art methods and apparatus for making tube bends are overcome by the method of and apparatus for manu facturing tube elbows in accordance with the invention.

A particular object of the invention is the provision of a method of producing elbows from straight seamless tubes, from which a semi-finished product is made by hot-bending the cross-section of which at the same time receives an oval shape, the longer axis of the oval semifinished product, which is parallel to thebending axis, being 3 to 4 percent longer than the shorter axis. The semi-finished product is then tamped full with sand, both ends of the product are closed with suitable covers, and after being heated to the desired bending temperature, is bent while keeping its oval shaped crosssection. At the end of such bending, the covers are removed from the ends of the product and the sand is removed therefrom. The elbow is again heated and is calibrated by being worked between shaped dies having a cavity of the desired shape formed between them, such calibration further deforming the metal of the tube bend so that its cross-section and the cross-section of the passage therethrough are made circular.

The invention also includes the apparatus for carrying out the above method, such apparatus including a rod or mandrel which has a straight portion of circular cross-section at the entering end thereof, the other end of the rod being in the form of a hood of oval cross-section having its longer axis parallel to the bending axis of the semi-finished product and 3 4 percent longer than its shorter axis. A section of straight seamless tube is telescoped over the entering, straight circular portion of the rod after being heated to a suitable heating temperature and it is thrust down the length of the rod and around the hook thereon so as to form a curved, semifinished product with a radius of bending somewhat greater than that desired in the finished product, and with the passage through the semi-finished form of oval shaped corresponding to the shape of the cross section of the hook or the mandrel.

The above-referred to apparatus further comprises a female die with rounded workpiece-engaging surfaces, the shortest distance between which is the sum of a distance from a mid-axis of the semi-finished piece and the opposite outer surfaces thereof. The apparatus further comprises a male die or presser element by which the semi-finished product is thrust through the female die in engagement with the working surfaces thereof, the center line of the passage through the workpiece then lying at equal distances between the opposed surfaces of the elbow cross-section. The working surfaces of the female die and the working surfaces of the pressure element are formed in such manner that upon thrusting the piece through the female die the workpiece is formed to be oval in cross-section with its longer axis parallel to the bending axis of the elbow and 3 to 4 percent longer than the shorter axis thereof.

The invention has among its objects the provision of an apparatus which has the capability of making high pressure tube bends from straight seamless tubes. It permits bends to be made with relatively small and simple apparatus, such tube bends having walls of high strength and a passage of circular cross-section.

In the drawing attached hereto there is shown an example of the apparatus of the invention in shcematic form.

In the Drawings:

FIG. 1 is a view in longitudinal section through a first part of such apparatus, the apparatus being shown after it has formed a seamless tube section into an intermediate or semi-finished tube bend product; and

FIG. 2 is a view in vertical section of female and male dies for further bending the intermediate product shown in FIG. 1 so as to reduce the radius of bending of such product.

The apparatus of FIG. 1 consists of a rod or mandrel 1 in circular cross-section, on one end of which there is affixed a fixed lock 2. On its other end rod 1 it has the form of a hook 3, which, as can be seen from FIG. 1, is bent to a circular form which the semi-finished product 4 is to take. The hook 3 is furthermore so formed that it gradually changes from a circular cross-section at its entering end to an oval-shaped cross-section at its mid and exit portions, the longer axis of the cross-section of the semi-finished product 4 being parallel to the bending axis and 3 to 4 percent longer than the shorter axis of such cross-section.

On rod 1 there exists a pressure part 5, which is moved by an apparatus (not shown) in the direction of the arrow. On rod 1 there are affixed several straight seamless tubes 6; rod 1 with the serially disposed tubes are led through a heating oven, not shown in the drawings. The tube bends 4 are discharged from the bending mandrel after passing end 3 thereof.

FIG. 2 shows the clearly recognizable semi-finished product 4, which is tamped full with sand, and sealed by covers 7 on both ends and is put into the female die 8 on a frame 9. Above die 8 there is situated a pressure element 10. In the frame 9 below die 8 there is illustrated an elbow 11, which already has attained the necessary bending radius.

The rounded working surfaces 12 of the female die 8 are so designed, that the smallest distance between them are equal to the elbow middle line distance (11 respectively 13) and to the elbow cross-sectional diameter.

Furthermore, the working surfaces 12 of the female die 8 and the working surfaces 14 of the pressure element 10 are formed in such a way that while lowering the pressure element 10 into the female die 8 each hollow space created shows a transverse oval cross-sea 3 tion, the longer axis of which is parallel to the elbowbending axis and is 3 to 4 percent longer than its shorter axis.

The method of production and the function of the apparatus are as follows:

Onto the rod 1, which first has to be unclamped from lock 2 and removed from pressure part 5, a number of tubes 6 are affixed, whereby they are pushed through the pressure part after mandrel 1 has again been affixed to lock 2. Now the heating oven is turned on. As soon as the temperature has reached the necessary temperature, the pressure part 5 is thrust to the left. Pressure is being applied to the front part of the tube 6, which is then transferred over to the hook 3, whereby the tube is guided along the hook 3 and through continuous heating is bent and formed in such a way that the semi-finished product 4 is created, product 4 having an oval-shaped cross-section.

Thereafter the semi-finished product 4 is filled with sand, closed on both ends with covers 7, heated in an oven, and put into the female die 8. By means of the pressure element 10 pressure is applied to the semi-finished product 4, whereby the rounded working surfaces 12 of the female die 8 and the working surfaces 14 of the pressure element deform the semi-finished product 4 in such a way that the bending radius is decreased in the desired way and an elbow 11 is created with an oval cross-section.

Finally, after removal of covers 7 and, respectively, sand and after renewed heating, elbow 11 is calibrated by being formed again in a hydraulic press with the application of a calibration-apparatus. Such calibration hollow space determins the final form of the finished elbow, which cross-section is circular. In such calibration the outer wall of the elbow, which has experienced a decrease in strength in its bending zone due to the formation conducted in the female die 8, is thickened without renewed sand filling and tamping.

Although the invention is illustrated and described with reference to one preferred embodiment thereof, it is to be expressly understood that it is in no way limited to the disclosure of such a preferred embodiment, but is capable of numerous modifications within the scope of the appended claims.

What is claimed is:

1. Method of producing tube bends for high pressure and high temperature use, comprising hot bending a seamless tube whereby to provide a semi-finished generally U-shaped product having legs disposed angularly with respect to each other, filling such semi-finished product with sand and tamping it in place, closing the ends of the thus sand-filled semi-finished product with lids, again heating the thus prepared semi-finished product to bending temperature, and then thrusting the heated semi-finished product downwardly through a female die by an aligned male die, whereby to reduce the angle between the legs of the product and to produce a tube bend of oval form the longer axis of which is parallel to the bending axis of the semi-finished product and has a length which is 3 to 4 percent longer than its shorter axis, thereafter removing the covers from the product and the sand from within it and, after again heating the thus formed product, calibrating it so as to change the oval cross-section thereof into a section which is circular in cross-section.

2. Apparatus for producing tube bends for high pressure and high temperature use, comprising a mandrel with a bent hook-shaped end and a straight portion leading to such hook shape end, means for attaching the end of the straight portion of the mandrel to a fixed support, a tube-thrusting element which is telescoped over the straight end portion of the mandrel after a seamless tube has been telescoped over the mandrel, and means to thrust the tube-thrusting member to force the tube into engagement with and along the curved end portion of the mandrel, the straight portion of the mandrel being circular in cross-section, the tube entering end of the curved portion thereof changing gradually in cross-section from circular to oval, the long axis of such oval cross-section. being parallel to the bending axis and from 3 to 4 percent longer than the shorter axis thereof.

3. Apparatus for producing tube bends for high pressure and high temperature use, comprising a female die with opposed rounded working surfaces, the smallest distance between the opposed working surfaces of the die being equal to the distance between the outer side surfaces of parallel confronting portions of a still further finished tube bend, and a male die for thrusting the semi-finished product through the female die, the male die having working surfaces with an outer rounded portion and two spaced parallel longitudinal portions, the distance between the spaced longitudinal portions of the male die being equal to the desired distance between the inner confronting surfaces of the straight portions of the still further finished tube bend product, the working surfaces of the female die and the working surfaces of the male die being formed in such manner that the tube bend product which has been forced through the female die by the male die is of oval crosssection, such cross-section having its longer axis parallel to the bending axis of the tube bend and from 3 to 4 percent longer than its shorter axis.

Claims

1. Method of producing tube bends for high pressure and high temperature use, comprising hot bending a seamless tube whereby to provide a semi-finished generally U-shaped product having legs disposed angularly with respect to each other, filling such semifinished product with sand and tamping it in place, closing the ends of the thus sand-filled semi-finished product with lids, again heating the thus prepared semi-finished product to bending temperature, and then thrusting the heated semi-finished product downwardly through a female die by an aligned male die, whereby to reduce the angle between the legs of the product and to produce a tube bend of oval form the longer axis of which is parallel to the bending axis of the semi-finished product and has a length which is 3 to 4 percent longer than its shorter axis, thereafter removing the covers from the product and the sand from within it and, after again heating the thus formed product, calibrating it so as to change the oval cross-section thereof into a section which is circular in cross-section.

2. Apparatus for producing tube bends for high pressure and high temperature use, comprising a mandrel with a bent hook-shaped end and a straight portion leading to such Hook shape end, means for attaching the end of the straight portion of the mandrel to a fixed support, a tube-thrusting element which is telescoped over the straight end portion of the mandrel after a seamless tube has been telescoped over the mandrel, and means to thrust the tube-thrusting member to force the tube into engagement with and along the curved end portion of the mandrel, the straight portion of the mandrel being circular in cross-section, the tube entering end of the curved portion thereof changing gradually in cross-section from circular to oval, the long axis of such oval cross-section being parallel to the bending axis and from 3 to 4 percent longer than the shorter axis thereof.

3. Apparatus for producing tube bends for high pressure and high temperature use, comprising a female die with opposed rounded working surfaces, the smallest distance between the opposed working surfaces of the die being equal to the distance between the outer side surfaces of parallel confronting portions of a still further finished tube bend, and a male die for thrusting the semi-finished product through the female die, the male die having working surfaces with an outer rounded portion and two spaced parallel longitudinal portions, the distance between the spaced longitudinal portions of the male die being equal to the desired distance between the inner confronting surfaces of the straight portions of the still further finished tube bend product, the working surfaces of the female die and the working surfaces of the male die being formed in such manner that the tube bend product which has been forced through the female die by the male die is of oval cross-section, such cross-section having its longer axis parallel to the bending axis of the tube bend and from 3 to 4 percent longer than its shorter axis.