GB2062791A

GB2062791A - Torque featured screw thread

Info

Publication number: GB2062791A
Application number: GB7938457A
Authority: GB
Original assignee: HATFIELD AUTOMATICS Ltd
Current assignee: HATFIELD AUTOMATICS Ltd
Priority date: 1979-11-06
Filing date: 1979-11-06
Publication date: 1981-05-28
Also published as: GB2062791B; ES254546Y; ES254546U; DE3041371A1; DE3041371C2

Abstract

A screw has a cylindrical portion 13 with a plastics insert 14 to provide a torque feature. As shown both metal portion 13 and insert 14 are threaded and the screw is used as an idler adjusting screw for a carburettor. In a second embodiment (Fig. 2 not shown) the plastics insert is unthreaded. In a third embodiment (Fig. 3 not shown) the plastics insert constitutes the entire threaded surface of the screw. <IMAGE>

Description

SPECIFICATION Torque featured screw thread The present invention relates to torque screw arrangements in which it is required that a screw is really adjustable to a desired position but remains in that position when the adjustment has finished.

In prior art arrangements it is known to provide a torque feature by applying a coating of powder to part of a screw thread. When the coated thread engages another thread resistance to relative rotation increases and, to continue screwing, it is necessary to apply increased torque. The prior art arrangement suffers from the disadvantage that the life of the coating is short, because it is stripped from the screw by repeated adjustment, and so is not reusable. Furthermore, where the screw thread is exposed to harmful environments it is possible for the coating to be damaged.

In accordance with the present invention there is provided a torque screw member which comprises a generally cylindrical metal part having a plastics insert extending along part or all of its cylindrical surface, the cylindrical surface of the member being threaded along at least a substantial part of its length.

The present invention will now be described by way of the example only with reference to the accompanying drawings of which; Fig. 1 shows a partially-sectioned view of a first embodiment of a torque screw member in accordance with the present invention; Fig. 2 shows a partially-sectioned view of a second embodiment of the invention; and Fig. 3 shows a partially-sectioned view of a third embodiment of the invention.

Referring to Fig. 1 of the drawings there is shown a carburettor idler adjusting screw 10 having a torque feature. This type of screw is often called a "set screw". The screw comprises a head 12, a threaded cylindrical portion 13, a stepped shank portion 1 5 and an end portion 16. All the above mentioned parts are integrally formed of metal. An annular groove 17 is formed in cylindrical portion 13, in which is provided a threaded plastics insert 14 which extends.

completely around the circumference of portion 13. The insert 14 is preferably of nylon applied by an injection moulding process. In Fig. 1 the thread of the nylon insert is indicated in broken lines.

In use the screw 10 is mounted in a female threaded portion of a carburettor with the end portion 1 6 projecting into a passageway for fuel and/or air. It is so arranged that the plastics insert 14 engages the female thread when end portion 1 6 lies in its operating range of positions. Thus when end portion 16 is adjusted to one of these positions, by screwing head 12, the torque screw member is held in this adjusted position by the relatively high frictional engagement between the threads.

An advantage of the above embodiment is that by appropriate selection of the plastics material a very accurate degree of torque may be introduced into the screws member over a wide range, depending upon the required application. In addition by selecting the size and shape of the threads on the plastics insert with respect to those on the metal portion there is provided a further method of consistently controlling the torque over a very close tolerance band. Furthermore the plastics material may be selected to withstand exposure to harmful environments; for example a grade of nylon may be chosen which is resistant to petrol, oil, water and/or gases etc., as well as heat.

Fig. 2 shows a second embodiment of the invention in which there is provided an unthreaded plastics insert 18. By appropriate selection of the hardness of the plastics material and the depth to which it fills annular groove 17 the degree of the torque provided may be adjusted. It may be arranged that when the torque screw member is first inserted in its corresponding female member a thread is cut in the plastics insert 18 by the thread of the female member.

Fig. 3 shows a third embodiment in which a plastics sleeve 1 9 is provided along the entire length of portion 13, so that all the threads are provided by the plastics material. The threads are shown in broken lines in the Figure. This embodiment provides a relatively high torque feature throughout its entire range of movement.

It may be arranged that the size and/or shape of the threads vary along the length of portion 13 so that there are provided regions of low and high torque.

The plastics insert may extend for any desired length along the cylindrical portion 13 from one thread, or even part of a thread, to the entire length as shown in Fig. 3. In addition a plurality of plastics inserts may be provided along portion 13, and to satisfy particular torque requirements, these inserts may be of different materials.

Moreover one or more of the inserts may be unthreaded, as shown in Fig. 2.

In further modifications the plastics inserts extend around only a part of the circumference to cylindrical portion 13. By varying the proportion of the circumference covered by the plastics inserts, additional control of the amount of torque is achieved.

Any dimension of screw thread up to 1 inch diameter can be manufactured with the inbuilt torque feature, or any standard screw can be adapted and given a torque loading to any specified requirement.

The torque screw members of the present invention are not limited to use in carburettors, but may be employed in set screw arrangements, and especially in set screw arrangements, where it is desired to retain a screw member in an adjusted position.

In particular, the embodiment of Figure 3 can be employed in electrical devices with advantage, when a conductor (the portion 13) is also insulated by the threaded sleeve from the member in which it is fitted.

Claims

1. A torque screw member which comprises a generally cylindrical metal part having a plastics member extending along part or all of its cylindrical surface, the cylindrical surface of the screw member being threaded along at least a substantial part of its length.

2. A torque screw member accordingto Claim 1, wherein the cylindrical metal part and the plastics member are both threaded.

3. A torque screw member according to Claim 1, wherein the cylindrical metal part is threaded and the plastics member is unthreaded.

4. A torque screw member according to Claim 1, wherein the cylindrical metal part is unthreaded and the plastics member is threaded.

5. A torque screw member according to any preceding claim wherein the plastics member extends around the entire circumference of the cylindrical metal part.

6. A torque screw member according to any of claims 1 to 4 wherein the plastics member extends around only a part of the circumference of the cylindrical metal part.

7. A torque screw member according to any preceding Claim, wherein the plastics member is made of nylon.

8. A torque screw member according to any preceding Claim, wherein a plurality of plastics members are provided in the cylindrical metal part.

9. A torque screw member according to Claim 8, wherein the plastics members are of different materials.

10. A torque screw member according to any preceding Claim, wherein the cylindrical metal part is provided with one or more grooves and the plastics member or members are provided as inserts in said groove(s).

11. A torque screw member substantially as herein described with reference to the accompanying drawings.

12. A method of manufacturing a torque screw member which comprises providing a generally cylindrical metal part with a plastics insert by an injection moulding process, the plastics insert being provided so that it extends along an axially central region of the cylindrical surface of the metal part, the cylindrical surface of the screw member being threaded along at least a substantial part of its length.

12. A carburettor having as an idler adjusting screw a torque screw member according to any preceding claim.

New claims or amendments to claims filed on 23rd October, 1980.

Superseded claims 1-12.

New or amended claims: 1-12.

1. A torque screw member which comprises a generally cylindrical metal part having a plastics insert extending along an axially central region of its cylindrical surface and around substantially all of its circumference, the cylindrical surface of the screw member being threaded along at least a substantial part of the its length.

2. A torque screw member according to Claim 1, wherein the cylindrical metal part is threaded and the plastics insert are both threaded.

3. A torque screw member according to Claim 1, wherein the cylindrical metal part is threaded and the plastics insert is unthreaded.

4. A torque screw member according to Claim 1, wherein the cylindrical metal part is unthreaded and the plastics insert is threaded.

5. A torque screw member according to any preceding claim wherein the plastics insert extends around the entire circumference of the cylindrical metal part.

6. A torque screw member according to any preceding claim, wherein the plastics insert is made of nylon.

7. A torque screw member according to any preceding claim, wherein a plurality of plastics inserts are provided in the cylindrical metal part.

8. A torque screw member according to Claim 7, wherein the plastics inserts are of different materials.

9. A torque screw member according to any preceding claim, wherein the or each insert is an injection-moulded insert.

10. A torque screw member substantially as herein described with reference to the accompanying drawings.

1 A carburettor having as an idler adjusting screw a torque screw member according to any preceding claim.