GB2028183A - Method and apparatus for forming a helical gear pump or motor rotor - Google Patents

Abstract

A helical gear pump or motor rotor is formed from a tubular workpiece 11 by feeding the workpiece progressively and bending it to the desired helical gear form. This can be achieved by intermittently and axially feeding the workpiece 11 and pressing it laterally with a deforming member 18 at a location downstream of the position 12 of clamping between intermittent feeds and turns. Alternatively, the workpiece can be fed continuously between first and second pairs of parallel rollers, one pair having its axes angled with respect to those of the other pair, the rollers of a pair having concavities which together form the cross-section of the workpiece. <IMAGE>

Description

SPECIFICATION Method and apparatus for forming a helical gear pump or motor rotor The present invention relates to a method and apparatus for forming a helical gear pump or motor rotor.

Conventionally, such rotors have been formed by turning the rotor from solid stock on a lathe. This is an extremely complex and expensive operation, particularly if the rotors are of considerable axial length. Such long rotors, having a large pitch, have been developed in particular for helical gear motors, which can, for example, be used for driving well drills, being driven by mud under pressure. In recent years it has been proposed to form the rotors of helical gear pumps and motors by deforming a tubular workpiece.

This is achieved by feeding the workpiece between three die members having a female profile corresponding to the male helical gear form. The die members have a frusto-conical external surface, and are moved axially in a press having cooperating frusto-conical surfaces, so that the die members are pressed onto the workpiece. This method, however, is quite unsuitable for rotors having a large pitch, because the cost of the die members and the press would be prohibitive.

It is now proposed, according to the present invention, to provide a method of forming a rotor for a helical gear pump or motor by progressively bending a tubular workpiece to the desired helical gear form.

In a preferred method, the workpiece is fed intermittently axially and is turned intermittently about its axis, it is clamped and is pressed laterally by a deforming member at a location downstream of the position of clamp ing between the intermittent feeds and turns.

Advantageously, an anvil having a female profile approximately corresponding to that of a portion of the finished rotor, is mounted at a location opposite to that of the deforming member, the latter bending the workpiece against the profile of the anvil.

The above method is particularly simple and inexpensive. It enables the workpiece to be formed to the desired helical gear form rapidly and, by making minor adjustments, it is possible to compensate for any variations in the material of the workpiece. While the apparatus for carrying out the invention is relatively small, it is capable of forming a very long rotor, for example 5 metres or more, and producing a rotor with a large pitch, e.g. 1.5 metres.

The deforming member preferably has a recess in the face abutting the workpiece, the recess conforming to the external shape of the workpiece. The deforming member is advantageously pivotably mounted on a hydraulic ram which produces the force to bend the workpiece.

In order to produce the correct helical gear form, the workpiece is axially fed forward, for each pitch, by n integers and is turned at each integer by 360 n For example it may be fed forward by 90 integers being turned by 4" each time.

The amount at which the workpiece is bent at each occurrence, will usually be very slightly greater than the amount of the final product, because the metal of the workpiece will spring back very slightly after the bending operation. This can be taken into account and a gauge can be provided on the anvil which is engaged by the workpiece at the end of the bending operation and it is then determined to stop the bending operation.

The invention also provides apparatus for producing a helical gear pump or motor rotor, said apparatus comprising, means for intermittently feeding a tubular workpiece axially and for turning it intermittently about its axis, means for clamping the workpiece between intermittent feeds and means for pressing the workpiece laterally including a deforming member positioned at a location downstream of the position of clamping.

It is also contemplated that the bending operation could be achieved in a continuous manner by feeding the workpiece axially, and at the same time turning it about its axis, between a first pair of parallel rollers and a second pair of parallel rollers having their axes angled with respect to those of the first pair, the rollers of a pair having concavities which together form the cross-section of the workpiece. Desirably there is a further pair of similar rollers upstream of the first pair and having its axes parallel to those of the first pair, the further and first pairs holding the upstream portion of the workpiece straight.

In order that the invention may more readily be understood, the following description is given, merely by way of example, reference being made to the accompanying drawings in which: Figure 1 is a perspective view of a rotor of a helical gear pump or motor; Figure 2 is a perspective view illustrating the method of forming the rotor of Fig. 1 according to the invention; Figure 3 illustrates four schematic views, showing the positions of the deforming member at the beginning of the deforming operation on the left, and at the end of the deforming operation on the right; and Figure 4 is a sketch showing the relationship between the helical pitch length A of the tube per pitch, the circumference B, the helix angle CL and the pitch P itself.

Fig. 1 shows a rotor 10 in which the helical gear form has a pitch P, the diameter of the rotor at any given point along its axial length being "d". This is referred to as the minor diameter. The major diameter "D" is the total diameter swept by the rotor which has an eccentricity ''e''.

Referring to Fig. 2, there is illustrated the method of the present invention. A workpiece 11 is initially clamped in a releasable clamp arrangement 1 2. This releasable clamp arrangement may be mounted on a lathe bed and the workpiece itself may also be clamped in a suitable indexing chuck 1 3. This chuck may be provided with 90 equally circumferentially spaced detents, at 4" intervals. The chuck may be also connected to the lead screw of the lathe so that it can be fed forward in integers which are th 90 of the pitch P of the rotor to be formed, these integers being set off on a scale 14 adjacent the chuck.

Forming one part of the releasable clamp 1 2 is an anvil member 1 5 which is provided on its face with a clamping recess 16, of semi-circular cross-section, this widening out into a female profile portion 1 7 having a profile approximately corresponding to that of a portion of the final rotor form.

Mounted opposite the anvil 15, is a swivel block deformer member 1 8 which is carried by a knuckle joint illustrated schematically at 1 9 on a hydraulic ram 20.

In order to rigidify the arrangement, the ram 20 and the anvil 1 5 are connected by the lathe bed at the bottom, and by a bridge at the top, these members not being shown in the drawing for the sake of clarity.

The front edge of the deforming member 1 8 is provided with a semi-cylindrical recess 21 to conform approximately to the shape of the workpiece 11.

In operation, the workpiece is introduced into the clamp 12, so that a portion of it projects beyond the clamp and overlies the female profile on the anvil. The ram is then operated and this causes the tubular workpiece to be bent against the profile.

The ram is then released, the workpiece moved forward by one integer on the scale 14 and is rotated by one detent position on the chuck 1 3 and the clamp 1 2 is then moved to the clamping position. The ram is once again operated and the whole procedure is repeated until the whole of the workpiece has been bent to the desired helical gear form.

It can be seen in Fig. 3 how the knuckle joint 1 9 enables the deforming member 1 8 to swivel to the correct angle to push the workpiece in the desired way to take up the anvil profile form.

A feeler gauge (not shown) is mounted on the far side of the anvil, as seen in Fig. 2, and this is used to detect when the workpiece has been bent the desired amount against the anvil. As soon as this happens, of course, a control signal is sent to the hydraulic ram 20 to instruct the ram to cease to apply the pressure; the workpiece can then be moved both axially and rotationally, after releasing the clamp.

It will be appreciated that the workpiece will spring back slightly, after this has taken place.

The amount of spring back will depend on the material and dimensions of the workpiece.

Tests can be carried out on a particular metal tubular stock to determine the correct amount of deformation and the correct profile form of the anvil to give the desired helical gear shape. If this is wrong, then it can be changed very easily and quickly at little expense and so one can achieve very rapidly a satisfactory helical gear form of the correct dimensions.

Since the workpiece is only being bent, in essence, the diameter of the original workpiece will be substantially identical with the minor diameter of the finished rotor. This makes the calculations necessary to achieve the desired result much easier than in previously known deformation methods. Since the workpiece is made from tubular stock, there is a great saving in materials and furthermore there are certain advantages in having a tubular rotor particularly when the rotor is used as a mud motor rotor.

Claims (16)

1. A method of forming a rotor for a helical gear pump or motor comprising progressively bending a tubular workpiece to the desired helical gear form.

2. A method according to claim 1, comprising the steps of feeding the workpiece intermittently axially and turning it intermittently about its axis, clamping the workpiece and pressing it laterally by using a deforming member at a location downstream of the position of clamping between the intermittent feeds and turns.

3. A method according to claim 2, wherein a female profile approximately corresponding to that of a portion of the finished rotor is mounted at a location opposite to that of the deforming member, the deforming member bending the workpiece against the profile of the anvil.

4. A method according to claim 2 or 3, wherein the deforming member has a recess in the face abutting the workpiece, the recess conforming to the external shape of the workpiece.

5. A method according to claim 2, 3 or 4, wherein the deforming member is pivotably mounted on a hydraulic ram which produces the force to bend the workpiece.

6. A method according to claim 2, 3, 4 or 5, wherein the workpiece is fed at axially forward, for each pitch of the finished workpiece, by n integers and is turned, at each integer, by 360 n

7. A method according to claim 6, wherein the workpiece is bent at each occurrence of bending, by an amount which is slightly greater than the amount of the final product, and the workpiece is allowed to spring back after each bending operation.

8. A method according to claim 1, wherein the workpiece is fed continuously axially and is continuously turned about its axis, between a first pair of parallel rollers and a second pair of parallel rollers having their axes angled with respect to those of the first pair, the rollers of a pair having concavities which together form a cross-section of the workpiece.

9. A method according to claim 8, wherein a further pair of similar rollers are provided upstream of the first pair and the rollers of said further pair have their axes parallel to those of the first pair, the further and first pairs holding the upstream portion of the workpiece straight.

10. A method of forming a helical gear pump or motor rotor, substantially as hereinbefore described, with reference to and as illustrated in the accompanying drawings.

11. A helical gear pump or motor rotor produced by the method of any preceding claim.

1 2. Apparatus for producing a helical gear pump or motor rotor, said apparatus comprising, means for intermittently feeding a tubular workpiece axially and for turning it intermittently about its axis, means for clamping the workpiece between intermittent feeds and means for pressing the workpiece laterally including a deforming member positioned at a location downstream of the position of clamp ing.

1 3. Apparatus according to claim 12, wherein an anvil having a female profile approximately corresponding to that of a portion of the finished rotor is mounted at a location opposite to that of said deforming member, whereby the deforming member may bend the workpiece against the profile of the anvil.

1 4. Apparatus according to claim 1 2 or 13, wherein the deforming member has a recess in the face abutting the workpiece, said recess conforming to the external shape of the workpiece.

15. Apparatus according to claim 14, wherein a gauge is provided on the anvil, at a location to be engaged by the workpiece at the end of the bending operation.

16. Apparatus according to any one of claims 1 2 to 15, wherein the deforming member is pivotally mounted on a hydraulic ram which produces the necessary force to bend the workpiece.

1 7. Apparatus for forming a helical gear pump or motor rotor, substantially as hereinbefore described, with reference to and as illustrated in the accompanying drawings.