EP0081700A1

EP0081700A1 - Spin forming

Info

Publication number: EP0081700A1
Application number: EP82110719A
Authority: EP
Inventors: David Alan Bivans
Original assignee: Air Products and Chemicals Inc
Current assignee: Air Products and Chemicals Inc
Priority date: 1981-11-20
Filing date: 1982-11-19
Publication date: 1983-06-22

Abstract

Controlling the temperature of an aluminum-pre-form during spin forming so that the physical properties of the metal are not adversely affected by the temperature changes which occur during the spin forming.

A conventional apparatus may be used to which means are added for cooling the work by a cooled gas or liquid cryogen, while other parts of the work are being heated by a torch and spin formed.

Description

TECHNICAL FIELD

This invention relates to spin forming of metals. More particularly it relates to the process by which pressure vessels are formed by spin forming ends and necks on tubes and to the means of carrying out the process.

BACKGROUND OF THE PRIOR ART

Spin forming is a highly developed art as evidenced by the following United States Patents describing representable apparatuses at least parts of which may be used in the practice of the present invention:
and many others of a similar nature.
In spin forming metals and alloys the working process produces a considerable amount of heat and causes the temperature of the material being processed to rise, not only in the portion of the work which is being acted on by the tool, but in other portions of the workpiece to which such heat is conducted. This may adversely affect the physical properties of the resulting article when metals or alloys affected by the temperature changes encountered are being processed.

BRIEF SUMMARY OF THE INVENTION

The principal object of this invention is to provide a process and apparatus which avoids the adverse effects of the heating which is incidental to the spin forming of the ends and necks on tubes intended to be used for seamless metal tanks, gas bottles, pressure vessels and the like.
Another object of this invention is to provide a method and apparatus for producing such vessels from tubular stock, rapidly and with uniform properties.
Essentially the present invention resides in controlling the temperature of a heat sensitive metal such as aluminum alloy 6061 during spin forming so that the physical properties of the unworked portions of the metal are unaffected by the temperature changes which occur during spin forming and so that the worked portions of the metal have desired dimensions and physical properties.
In the process a conventional torch is used to preheat the work and then as the work is further heated it is simultaneously cooled by a cool gas or a liquid cryogen such as carbon dioxide, nitrogen, helium, argon, or any other gas which can provide the desired cooling action without adversely affecting the surface properties of the part being spun.
Briefly summarized the process involves the following steps:

1. A tube or pipe is inserted into a chuck which permits the work to be rotated, the tube being inserted into the chuck so that up to about one half the length of the tube is held by the jaws of the chuck and the remainder of the tube is available to be shaped;
2. Spinning the tube at any appropriate speed, while directing a torch or other heating means toward the portion of the tube to be shaped, e.g. the end of the tube, so as to heat the tube rapidly to a desired working temperature and simultaneously therewith, directing a stream of fluid coolant onto the exterior of the tube so as to maintain the temperature of the tube between the end being heated and shaped and the end held in the chuck below some predetermined temperature depending on the specific metal being worked;
3. Shaping the end of the tube while continuing to heat and cool selected portions of the tube until the desired dome shape is produced;
4. Discontinuing the application of heat to the tube; and finally
5. Rapidly quenching the entire dome shaped end.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing objects and others will be pointed out or will be apparent from the detailed description which follows taken in conjunction with the drawings forming a part of this application in which:

Figures 1-8 are schematic views showing the spin forming of a light weight pressure vessel at various stages of the process.

DETAILED DESCRIPTION OF THE DRAWINGS

The invention will be better understood by reference to the drawings which illustrate schematically a preferred sequence of operations.
Figure 1 shows a fragment of a tube or pipe 10 mounted in a hollow chuck 12 for rotation about its axis 14. Chuck 12 is provided with conventional clamping means (not shown) to grip the tube or pipe 10. The extent to which the tube or pipe is inserted into the chuck depends on the length of the tube or pipe, the speed at which it is to be rotated, whether it is given additional support, and other factors which may be readily ascertained by anyone practicing this process as evidenced by the patents noted above. The free end of the pipe 18 actually extends a considerable distance from chuck 12.
Figure 2 shows the apparatus during the preheating step. As shown, a forming tool, in this instance a rotating wheel 16, is shown adjacent the end 18 of pipe 10. Means 20 are provided for supporting wheel 16 so that it may be advanced along the axis 14 of pipe 10 and toward and away from axis 14, such means being known in the art and forming no part of the present invention. Preheating of the end 18 of pipe 10 is by means of one or more torches 21 directed toward the end of the pipe and disposed between the end of the pipe and chuck 12. The amount of preheating is monitored by an optical pyrometer 22 directed toward the portion of the pipe which is being preheated. Pyrometer 22 detects the temperature of the pipe and signals the result to a temperature gauge 24, which is connected to a control means 30, whereby the fuel fed to one or more torches 21 from a supply 36 by a valve 34 is controlled by controller 30 so as to produce a desired temperature in the work, for example an aluminum alloy tube 10 might be preheated to a temperature of about 350°F and from 350°F to a temperature of 650° - 750°F within an interval of 1 to 2 minutes after being placed in the chuck.
Also shown in Figure 2 is a means for applying coolant to the pipe or tube 10 including a coolant discharge tube 38 connected to a coolant supply 46 which is controlled by a valve 42 which is actuated by a controller 32. An optical pyrometer 22' actuates controller 32. Temperature gauge 26 is provided to permit the operator to visually check on the temperatures of the workpiece adjacent to chuck 12.
A further quenching means is shown in Figure 2, namely pipe 40 connected to coolant supply 46 through a valve 44. Valve 44 is controlled by optical pyrometer 22 and controller 30. At the stage of the process shown in Figure 2 coolant is being discharged by pipe 38 but not by pipe 40.
Figure 3 shows the first phase of dome formation in which the end of the pipe, now at a temperature of 650° - 750°C is nosed in while rotating, by moving the spinning wheel 16 into contact with the preheated end 18 of pipe 10. This step takes about 15 seconds.
Figure 4 shows the next phase of dome formation in which the end of tube 10 is almost closed. This step takes about 30 seconds, and is effected while the pipe temperature is maintained between 650°F and 750°F.
Figures 5 and 6 schematically show the formation of the neck on the pipe, by suitable movement of the spin forming wheel 16 while maintaining coolant through pipe 38 and heating through torch 21, so that the tube at the chuck mouth is maintained at a temperature below about 350°F and the portion of the tube being formed into a neck is maintained at about 650°F - 750°F; the operation in Figure 5 taking about 30 seconds while that in Figure 6 talking about 15 seconds.
Figure 7 illustrates the rapid quenching step which follows completion of the neck formation. Torch 21 has been extinguished and coolant is now applied by both pipe 40 and pipe 38. Spin forming wheel 16 has been withdrawn from the work. Rapid quenching reduces the temperature of the work to about 350°F in from about 60-90 seconds.
Final cooling to less than 150°F is shown in Figure 8, after which the dome ended pipe is removed from chuck 12.
In this example tube 10 is an aluminum tube originally supplied as an extrusion with a temper of T-6 and consisting of alloy 6061 which has a nominal analysis of 0.8/1.2 Mg, 0.4/0.8 Si, 0.15/0.35 Cr, 0.15/0.40 Cu, and the balance aluminum. Obviously for other grades of aluminum alloy and for other nonferrous or ferrous alloys such as stainless steels other parameters of temperature will apply.
Figure 2 illustrates a preferred cooling system for insuring that the work does not lose its temper, or deteriorate physically as a result of the heating by torch and the heating due to the working incidental to the shaping of the dome on the tube. However it is also possible to supplement the externally produced cooling by the use of a coolant introduced through the chuck into the interior of the pipe 10. This would appear to be especially desirable in spin forming thicker tubes and to supplement the quenching step so that quenching can be accomplished in a minimum of time.
As a result of controlling the temperature of the work during spin forming, the physical properties existing in the tube prior to spin forming are not adversely affected by the temperature changes which the tube experiences during spin forming and consequently the end product can be used in the construction of light weight gas cylinders for storing cryogenic gases at high pressures and low temperatures where such properties are essential.
By practice of this invention overaging and embrittlement of the aluminum alloy in the dome region of the spin formed article are avoided. The cooling depends on the temperatures reached at various stages of the spin forming, and may be either continuous or intermittent. Because of the use of cryogenic coolants such as liquid C0₂ the cooling is sufficiently rapid to produce a uniform crystalline profile across the dome wall, which is not possible with relatively thick walled workpieces employing air cooling or water cooling.
In the sequence for spinning aluminum tubes illustrated in Figures 1-8, tubes having thicknesses between 0.375" and 0.500", outside diameters of 15.7" to 20.1" and lengths of approximately four feet were spun with the chuck rotated at between 150 and 200 rpm according to the following schedule:
Obviously other schedules would apply to other aluminum alloys and other metals such as steels.
It will be appreciated that the drawings are for purposes of illustration only and are not to scale. In the apparatus in which the invention was practiced, gas fired torch 21 heats a region 12-15" in width adjacent the end of tube 10 and pipe 38 applies coolant to the portion of th6 pipe extending up to about 18 inches from the chuck 12.
Having now described a preferred embodiment of my invention it is not intended that it be limited in any way except as may be required by the appended claims.

Claims

1. An apparatus for spin forming the ends of a metal tube or pipe which comprises: -

a rotatable chuck adapted to receive support and grip one end of said tube for rotation;

a tool mounted to engage the end of said tube;

means to heat a portion of said tube to a temperature at which it is deformable by said tool; and

means to maintain those portions of the tube which are not being worked on at a temperature below the temperature at which the physical properties of the metal are adversely affected.

2. The apparatus of Claim 1 wherein the means to maintain the temperature is a means for supplying a fluid coolant to said tube.

3. The apparatus of Claim 2 wherein said means supplies said coolant to the exterior of said tube.

4. The apparatus of Claim 2 including means to sense the temperature of that portion of the tube which is to be maintained below the temperature at which the physical properties of the metal are adversely affected.

5. The apparatus of Claim 4 including in addition means to control the operation of the means to supply fluid coolant, in response to the temperature sensed by the temperature sensing means.

6. The apparatus of Claim 2 wherein the fluid coolant is a cooled gas or a liquid cryogen.

_7. The apparatus of Claim 6 wherein the fluid coolant is selected from the group consisting of carbon dioxide, nitrogen, helium, argon and other gases which are inert to the surface of the metal being spin formed.

8. The apparatus of Claim 1 including means to sense the temperature of the portion of the tube which is being heated and means to control the means to heat that portion of the tube.

9. The apparatus of Claim 1 including means to quench the tube after it has been spin formed.

10. In a process for spin forming a shaped end onto a heated tube in which one end of the tube is inserted into a rotatable chuck and the other end of the tube is heated to a temperature at which it is spin formed by a tool, the improvement which comprises maintaining the temperature of the unworked portion of the tube below a temperature at which the physical properties of the tube would be adversely affected.

ll. The process of Claim 10 in which the temperature is maintained below the temperature at which the physical properties of the metal are adversely affected by means of a fluid coolant selected from the group consisting of carbon dioxide, nitrogen, helium, argon and other gases which are inert to the surface of the metal being spin formed.

12. The process of Claim 10 wherein the tube is an aluminum alloy.

13. The process of Claim 12 wherein the metal is heated to a temperature of about 650 - 750°F for spin forming and the balance of the tube is maintained at a temperature below about 350°F.

14. The process of Claim 10 including the step of quenching the metal of said tube after it has been spin formed.