US2155437A

US2155437A - Tube drawing method

Info

Publication number: US2155437A
Application number: US168572A
Authority: US
Inventors: Herr Charles Miller; George E Nighthart
Original assignee: Aluminum Company of America
Current assignee: Howmet Aerospace Inc
Priority date: 1937-10-12
Filing date: 1937-10-12
Publication date: 1939-04-25
Anticipated expiration: 1956-04-25

Description

April 25, 1939. T. MCORE ET AL 2,155,437

TUBE DRAWING METHOD Filed Oct. 12, 195'? I 2g 2% INVENTORS, mw

TTORNEY.

Patented Apr. 25, 1939 UNITED STATES PATENT OFFICE 2,155,437 TUBE DRAWING METHOD Company of America,

Vania a corporation of Pennsyl- Application October 12, 1937, Serial No. 168,572

4 Claims.

This invention relates to an improved method and means for drawing tubing, and particularly for drawing relatively long and relatively thinwalled metal tubing of relatively small diameter.

Broadly, it is an object of the present invention to provide an improved method of and means for drawing material of the above described character. A more specific object is to provide means which can more readily be brought into cooperative relationship with the tubing to effect a reduction of gauge and thickness while maintaining a uniform outside diameter over substantially the entire length of the tube. Another object is the provision of a method and means for maintaining a film of lubricant within the interior of the tubing being drawn, to facilitate subse-v quent drawing operations.

Other objects will. be apparent from the following description of the invention .in tion with the drawing, in which:

Fig. 1 shows the tubing and the drawing tools prior to the beginning of the drawing operation, with the die in section and a portion of the tube 'broken away; and Fig. 2 shows the relative positions of the tools and tubing after the drawing operation is started.

In the usual commercial methods of drawing tubing, metal is initially formed into a hollow cylindrical blank which is subsequently reduced in diameter and gauge by successive passes through drawing dies having tapered or conical apertures progressively decreasing in diameter to the desired external diameter of the tube. During the drawing operation the interior of the tube is in contact with a mandrel corresponding to the desired interior diameter of the tube, and positioned interiorly of the drawing die. The mandrel may be of uniform diameter and of a length equal to the length of the tubing, or may take the form of a bulb fixed to the end of a long rod. In the latter case, the rod is anchored at one end of the drawing bench and is of a length sufficient to position the enlarged portion or bulb within the aperture of the drawing die during the drawing operation.

The customary method of operation with this type of mechanism is to first swage or collapse one end of the tube to be drawn to a size which will permit its entry into the draw die aperture. The bulb or mandrel is then threaded into the opposite end of the tube until the endof the mandrel or bulb is substantially in contact with the swaged end, which is then inserted in the die aperture. If a mandrel having a uniform diameter throughout its length is used, the tubconnecing is usually pushed through the die by some suitable mechanism operating on the opposite end of the mandrel, and if a, bulb mandrel is used, the swaged end is gripped by suitable gripping means and the tubing is pulled through the die.

By utilizing the type of mechanism illustrated in the attached drawing, the laborious threading operation may be eliminated. In this form of mechanism, we provide a loose or unattached mandrel or bulb I formed to provide a bearing surface 2 having a diameter equal to the desired inside diameter of the tubing 3. The die 4 is provided with an aperture having a bearing surface 5, of a diameter substantially equal to the desired outside diameter of the tubing, and a flared entry surface 6, substantially as shown. The enlarged portion of the mandrel I has a diameter greater than the diameter of. the bearing surface 5 of the die, to insure that the mandrel will not be drawn through the die during the drawing operation.

' In the drawing operation, the mandrel is placed in the end of the tube a short distance from its end, and the end of the tube is swaged down, as shown, or otherwise reduced, to a diameter which will permit of its insertion in the die. The end of the tube is gripped by means of the tongs 8, which are then actuated by a draw ing bench mechanism, not shown, to pull the tube through the die and over the mandrel I up into position within the die illustrated in Fig. 2 To insure that the mandrel i will be brought into its proper position in the die, the tube 3 is provided with an indentation 9 near the position of the end of the mandrel away from the swaged 'end of the tube. This indentation will force the mandrel into the die aperture and will subse quently be effaced as the drawing operation proceeds.

If the exterior surface of the mandrel conforms closely with the configuration of the flared surface 601. the die, it has been found that upon attempting to draw a tube, the friction between the tube and the surfaces of the mandrel and die is usually too great. As a result, the tube is not reduced in diameter and gauge as intended, but becomes wedged tightly in the drawing tools and generally breaks under the tensile force applied to effect the drawing operation. However, if the mandrel is so shaped as to provide contact with the tube over only a portion of its length, the friction may be reduced to an extent which permits the drawing operation to be successfully performed. This reduction of contact area is suitably effected by forming the mandrel with a relieved area ill. The entering tubing is thus in contact with the enlarged portion of the mandrel as indicated at H and the surface 6 of the die, and is reduced to gauge upon passing through the opening defined by the mandrel surface 2 and the die surface 5.

Due to the swaging operation and the gripping action of the tongs, particularly when drawing light gauge and small diameter material, the end of the tube is virtually sealed. If the mandrel i is solid, it is apparent that upon pulling the tubing through the die a vacuum will be set up in the space 12 bounded by the tube wall, the swaged end of the tube, and the one face of the mandrel. It has been found that the vacuum caused by this drawing operation results in the production of tubing having a diameter less than that which would be produced by the same tools if air were allowed ingress into the space l2, and may result in the production of material which varies in diameter along its length. This latter eifect obtains when the seal formed by the swaged end is not perfect and some air leaks through the swaged end, relieving the vacuum from time to time. These fluctuations of the air pressure withinthe tube are reflected by corresponding variations in the diameter of the tubing produced. If the tubing is of extremely thin gauge, the pressure diiferential at high drawing speeds is sometimes suflicient to cause a partial collapse of the tube wall, produced longitudinally extending wrinkles in the tube.

The vacuum thus formed could be relieved, of course, by puncturing the tube at a point between the swaged end and the die, but this results in a substantial weakening of the tubes resistance to the tensile stresses occasioned by the drawing operation. It has been found preferable to provide an opening l3 through the bulb to eliminate the differential pressure.

In addition to performing this function, the opening IS in the bulb serves another purpose. It is necessary, in cold drawing operations, to keep the surfaces of the tubing well lubricated where they pass through the die or over the bulb. When the tubing is of relatively large internal diameter, it is not difflcult to get oil or other lubricating material into the interior of the tube so as to cover the entire interior surface, but in smaller diameter tubing, the lubricant can be introduced only by pressure. If the mandrel is solid and the tube pulled through the die, the lubricant will be wiped out by the drawing operation, but when the mandrel is provided, as shown, with a relatively small diameter hole extending through its length, the lubricant will be wiped back until it reaches a level above the opening in the mandrel. The difference between atmospheric pressure and the pressure occurring in the space l2 causes the lubricant to flow through the opening in the mandrel, depositing the lubricant on the interior surface of the tube which has already passed through the die, thus lubricating the interior of .the tube for a succeeding drawing operation.

What is claimed is:

1. The method of drawing tubing which includes positioning a loose mandrel inwardly from the end of a tube, swaging the tube end, inserting the swaged end in a drawing die having a flared entry surface; indenting the tube at a point inwardly from the end. of the 'mandrel opposite the swaged end ofthe tube, gripping the end of the tube and pulling said tube through said die until a portion of the mandrel adapted to define the internal diameter of the tube is in cooperative relationship with a portion of the die adapted to define the periphery of the tube, stopping the further entry of the mandrel into the die opening by contact of a. limited area of an enlarged portion of said mandrel with the tube within the flared entry of the die, and continuing to draw the tube around the mandrel and through the die while relieving the vacuum formed between the gripped end of the tube and the mandrel by an aperture extending through said mandrel.

2. The method of drawing tubing which includes positioning a loose mandrel inwardly from the end of a tube, swaging the tube end until substantially sealed to the passage of air therethrough, inserting the swaged end in a drawing die, indenting the tube at a point past the end of the mandrel farthest removed from the swaged end of the tube, gripping the swaged end of the tube, pulling said tube and mandrel throughsaid die until a portion of the mandrel adapted to define the internal diameter of the tube is in cooperative relationship with a portion of the die adapted to define the external diameter of the tube, arresting the entry of themandrel into the die opening, continuing to draw the tube over the mandrel and through the die, and utilizing the air pressure differential existing on opposite sides of said mandrel to force lubricant into the portion of the tube reduced by the drawing operation through an aperture extending through said mandrel.

3. The method of drawing tubing which includes positioning a loose mandrel inwardly from the end of a tube, swaging the tube end, inserting the swaged end in a drawing die having a flared entry surface, gripping the end of the tube and pulling said tube and mandrel through said die until a portion of the mandrel adapted to define the internal diameter of the tube is in cooperative relationship with a portion of the die adapted to define the external diameter of the tube,

the die opening by contact of a limited area of an enlarged portion of said mandrel with the tube within the flared entry of the die, and continuing to draw the tube over the mandrel and through the die while relieving the vacuum formed between the gripped end of the tube and the mandrel by .an aperture extending through said mandrel.

4. The method of drawing tubing which includes positioning a loose mandrel inwardly from the end of a tube, swaging the tube end, inserting the swaged end in a drawing die, gripping the end of the tube and thereby sealing the tube against the ingress of air through the swaged end,

pulling said tube through said die until a portion of the mandrel adapted to deflne the internal diameter of the tube is in cooperative relationship with a portion of the die adapted to define the periphery of the tube, arresting the movement of the mandrel into the die opening, continuing to draw the tube over the mandrel and through the die, and utilizing the air pressure differential existing on opposite sides of said mandrel to force lubricant into the portion of,

the tube reduced by the drawing operation through an aperture extending through said mandrel.

CHARLES MILLER HERE, Administrator of the Estate of Theodore Moore,

Deceased. I

GEORGE E. NIGHIHART.

- preventing the further entry of the mandrel into