GB2213749A - Forming convolutions in metal cylinder - Google Patents

Abstract

A metal bellows is formed from a metal cylinder (15) by urging an inner rotating forming tool (17) outwardly to stretch and bend the material of the cylinder. As the material distorts, the bending action results in a reduction in length of the cylinder. Outer rotatable forming tools (20, 21) engage the cylinder (15) on either side of the inner forming tool (17) and are mounted on actuators (24, 25) so that during the process the outer forming tools are moved toward one another as indicated by arrows (B). This movement is synchronized with the distortion of the cylinder (15) so as to allow for its reduction in length. The outer forming tools (20, 21) may commence movement towards one another when the inner forming tool (17) has completed 75% or more of its total outward movement. Adjustable mountings (24', 25') enable the outer forming tools (20, 21) to be moved towards or away from drums (11, 12) supporting the cylinder (15). <IMAGE>

Description

FORMING CONVOLUTIONS.

This invention relates to forming convolutions in sheet metal cylinders, for instance for making metal bellows, and extends to a method of forming convolutions, an apparatus for using the method and to the product made by this method.

The invention provides a method of forming a convolution in a metal cylinder comprising the steps of mounting the cylinder with freedom to rotate, urging an inner rotating forming tool radially outwardly against the inner circumference of the cylinder and continuing radially outward movement of the inner forming tool as the material of the cylinder distorts to form a convolution, while a pair of outer rotatable forming tools maintain radiallY inward pressure on the cylinder at points either side of the convolution, and moving the outer forming tools toward one another during the outward movement of the inner tool so that the movements of the inner and outer forming tools co-ordinate to aid and allow stretching and bending of the cylinder material to form the convolution.

It will be appreciated that when a convolution is formed the material of the cylinder is both stretched and bent, the bending action resulting in a reduction in the length of the cylinder. The movement of the outer tool is calculated to allow for the necessary movement of the cylinder as it reduces in length, maintaining the cylinder in position for the inner forming tool to continue shaping the convolution without interruption.

The invention is particularly relevant to deep convolutions where the reduction in cylinder length is most marked. Deep convolutions are defined as those in which the depth of the convolution is between 20 mm and 75 mm.

According to another aspect, the invention provides apparatus for carrying out the method set forth above, comprising means for rotatably supporting a metal cylinder, an inner forming tool adapted both to rotate and to be moved radially-outwardly against the inner circumference of the cylinder, a pair of outer forming tools adapted to exert radiallyinwardly directed pressure on the cylinder at points either side of the inner tool, and means for moving the outer forming tools toward and apart from one another.

There may be automatic means for synchonizing the radiallyoutward motion of the inner tool and the movement of the outer tools toward one another. The outer tools may commence their movement after the inner tool, for instance after the inner tool has completed the major part (e.g. 75%) of its movement.

The outer forming tools may be mounted to rotate freely with the cylinder.

According to another aspect, the invention provides a bellows formed by the method or the apparatus described above.

For forming bellows in which a series of convolutions are to be made, the apparatus may include means for indexing the cylinder along to allow convolutions to be formed at appropriate positions.

A specific embodiment of the invention is shown in the accompanying drawing, in which: Figure 1 is a diagrammatic representation of a bellows forming machine at the start of a convolution forming operation, and Figure 2 is a scrap view of part of the machine of Figure 1 showing a formed convolution.

Referring first to Figure 1, a pair of spaced, co-axial support drums (11, 12) are mounted for free rotation on bearings (13) or V support rollers with eccentric mountings. A cylindrical workpiece (15) is supported on the outer surfaces of the drums, bridging the gap between them. The workpiece is of metal, for instance steel or stainless steel. In the gap between the support drums an inner forming rolling tool (17) is supported on a mounting (18), whereby radially outwardly directed pressure may be exerted as shown by arrow A. The position of mounting (18) may be moved radially outwardly or inwardly by mechanical, hydraulic or pneumatic means (not shown). Mounting (18) also carries a drive mechanism (19) for rotating the tool (17). It will be seen that radial movement of mounting (18) carries the tool (17) outward through the gap between drums (11, 12).

On the outer circumference of the workpiece run two more rolling tools (20, 21). These rotate freely on bearings (22, 23) and are mounted on actuators (24, 25) so that the tools can be moved toward one another as indicated by arrow B along a path parallel to the axis of the drums (11, 12). The actuators (24, 25) are in turn mounted on adjustable mountings(24', 25') whereby the tools (20, 21) may be moved toward or away from drums (11, 12).

A control unit is connected to actuators (24, 25), adjustable mountings (24', 25'), mounting (18) and drive (19) so as to co-ordinate their operation, as described hereinafter.

Figure 1 shows the beginning of a convolution forming operation.

The workpiece (15) is loaded onto the drums (11, 12) with that portion where a convolution is to be formed bridging the gap between the drums.

Actuators (24, 25) are set so that there is a predetermined distance between the outer tools (20, 21). The adjustable mountings (24', 25') are then located to a predetermined clearance from the workpiece.

Mounting (18) is urged toward the workpiece so that the tool (17) exerts pressure on the inner surface of the workpiece where it bridges the gap and causes initial stretching of the workpiece (shown to an exaggerated degree in Figure 1). The rotational drive (19) is then caused to start the rotation of rolling tool (17). As the rolling tool rotates, while exerting pressure on the workpiece, rotational drive is imparted to the workpiece by friction, so that the workpiece itself starts rotating, carrying drums (11, 12) with it. The rotation of the workpiece is also imparted to the two outer rolling tools (20, 21).

Thus a spinning motion is set up, with tool (17) pressing on the inner surface while tools (20, 21) hold the workpiece at locations spaced either side of tool (17). The outer circumference of rolling tool (17) is curved to facilitate the stretching of the workpiece over it. While the spinning rotation continues, the mounting (18) is moved slowly in the direction of arrow A (i.e. radially-outwardly) so that the pressure on the workpiece is maintained while the workpiece stretches and is formed into a convolution. When the tool (17) has reached a predetermined radial position (typically 75% or more of its total movement), the control unit (29) starts to operate the actuators (24, 25) so that the outer tools (20, 21) are moved linearly toward one another at a predetermined rate.The outer movement of rolling tool (17) is continued smoothly at the same time, synchronized with the linear movement of the outer tools, until the full convolution is formed as seen in Figure 2. At this point, the two outer tools are adjacent the outer sides of the formed convolution.

Mountings (24', 25') then withdraw the tools (20, 21) from the workpiece, tool (17) is retracted, and the workpiece is free to be moved along the drums for another convolution to be formed if required.

A bellows may comprise one convolution or a series, depending on the flexibility needed.

It will be seen that the inner diameter of the workpiece remains substantially constant, change being prevented by drums (11, 12). All the forming action takes place by expansion from this initial diameter.

The convolution is formed partly by stretching the material, partly by bending it. It will be understood that in bending the material into a convolution, the length of the workpiece is substantially shortened.

The linear motion of the outer tools (20,.21) allows and aids this shortening action while the convolution is being formed, without the need to stop the process and reset the tools.

The relationship between the depth of the convolution, the rate of radially outer movement of the inner tool and the linear motion of the outer tools may be determined by trial and error. Typically, for a stainless steel workpiece of diameter 1,000 rtrn and thickness 0.91 ms a deep convolution of depth 50 mm is fully formed in 45 seconds in a single process using the machine described above.

The movements described above may be powered mechanically, hydraulically or pneumatically and may be fully automated.

Claims (9)

CLAIMS:

1. A method of forming a convolution in a metal cylinder comprising the steps of mounting the cylinder with freedom to rotate, urging an inner rotating forming tool radially outwardly against the inner circumference of the cylinder and continuing radially outward movement of the inner forming tool as the material of the cylinder distorts to form a convolution, while a pair of outer rotatable forming tools maintain radially inward pressure on the cylinder at points either side of the convolution, and moving the outer tools toward one another during the outward movement of the inner tool so that the movements of the inner and outer forming tools are co-ordinated to aid and allow stretching and bending of the cylinder material to form the convolution.

2. A method as claimed in claim 1, wherein said step of moving the outer forming tools toward one another is commenced after the outward movement of the inner tool.

3. A method as claimed in claim 2, wherein said step of moving the outer forming tools toward one another is commenced when the inner tool has completed 75% or more of its total outward movement.

4. A method as claimed in any of claims 1 to 3, wherein said outer forming tools are moved toward one another until they lie adjacent the formed convolution.

5. A method of forming a convolution in a metal cylinder substantially as described hereinbefore with reference to the accompanying drawings.

6. Apparatus for carrying out the method of any of claims 1 to 5, comprising means for rotatably supporting a metal cylinder, an inner forming tool adapted both to rotate and to be moved radially outwardly against the inner circumference of the cylinder, a pair of outer forming tools adapted to exert radially inwardly directed pressure on the cylinder at points either side of the inner tool and means for moving the outer forming tools toward and apart from one another.

7. Apparatus as claimed in claim 6, wherein said means for rotatably supporting the metal cylinder comprises a pair of co-axial support drums spaced apart to leave a gap for said inner forming tool to move in.

8. Apparatus as claimed in claim 6 or claim 7, wherein the movements of the inner forming tool and the pair of outer forming tools are synchronized by automatic control means.

9. Apparatus for forming a convolution in a metal cylinder substantially as described hereinbefore with reference to the accopanying drawings.