GB2028949A

GB2028949A - Protectors for Screwthreads

Info

Publication number: GB2028949A
Application number: GB7835494A
Authority: GB
Original assignee: MERCOL RUBBER Ltd
Current assignee: MERCOL RUBBER Ltd
Priority date: 1978-09-04
Filing date: 1978-09-04
Publication date: 1980-03-12

Abstract

A screwthread protector moulded from synthetic plastics comprises radial projections or "pips" 14 constituting an interrupted helical thread for engaging the screwthread to be protected. The radial projections 14 extend in axial rows. <IMAGE>

Description

SPECIFICATION Protectors for Screwthreadg The invention relates to protectors made of plastics materials for screwthreads and has for its object to provide an improvement therein.

It is known to apply synthetic plastics materials in the liquid or plastic state to exposed screwthreads so that when they dry they form a tough protective skin which protects the screwthread from damage but which can easily be stripped off when the screwthread is to be used. However, it is also known to provide preformed thread protectors which can be applied to screwthreads and removed (possibly for re-use) when the screwthreads are to be used. Such preformed thread protectors can of course be made a tight push fit over the threads which are to be protected or can be more positively secured, for example by being screwthreaded so that they can be screwed onto or off the screwthread to be protected.

The production of thread protectors of the preformed screwthreaded kind is difficult because most synthetic plastics materials shrink considerably after being moulded so that it is necessary to take such shrinkage into account when manufacturing the moulds in which they are to be made. This is not difficult so far as diameters and component lengths are concerned but is very difficult when cutting a screwthread since screw cutting lathes, and indeed taps and dies, can cut given standard sizes of screwthreads but are not generally available for cutting sizes say 10% greater in diameter than a standard size (with a similarly greater percentage lead).

According to one aspect of the invention, there is provided a protector made of a synthetic plastics material for protecting the screwthread of a screwthreaded component, the protector being provided with a plurality of thread elements constituted by radial projections or "pips" for engaging the screwthread to be protected, each projection or "pip" being of a size and shape such that it can seat itself between a pair of adjacent threads of the screwthread, and the arrangement of projections or "pips" being such that they are arranged on an imaginery helix having the same lead angle as that of the screwthread to be protected. Each projection or "pip" will preferably be of generally frusto-conical form with a rounded tip for engaging the space between a pair of adjacent threads.The projections or "pips" may be arranged in axially extending rows, the rows of projections or "pips" preferably being at leat three in number.

According to another aspect of the invention, there is provided a method of making a synthetic plastics protector for protecting the screwthread of a screwthreaded component, the method including the step of making a mould to produce a moulding of cylindrical or cup-like shape, and the step of forming respective cavities in the mould for the forming of the projections or "pips" required on the moulding at spacings such that the projections or "pips" will engage spaces between adjacent threads of the screwthreaded component, the axial spacing of the cavities in the mould being greater than the required axial spacing of the projections or "pips" in the finished component by a factor equal to the rate of shrinkage of the synthetic plastics material which is to be used for the moulding of the protector.

In order that the invention may be fully understood and readily carried into effect, the same will now be described, by way of example only, with reference to the accompanying drawings, of which:~ Fig. 1 is a part-sectional side view of a screwthread protector embodying the invention, and Fig. 2 is a view in the direction of arrow 2 in Fig. 1.

Referring now to the drawings, the screwthread protector there illustrated has a body 10 of generally cylindrical shape with a closed end 12 and is provided with a plurality of inwardly projecting "pips" 14. The inwardly projecting "pips" are arranged in four circumferentially spaced rows, there being three such "pips" in each row. In axial section, that is to say as shown in Fig. 1, each "pip" 14 has a shape conforming to the thread profile with which it is to be engaged.

In the finished screwthread protector, the spacing of the "pips" in each row, and their disposition with respect to the "pips" in the other rows, is such that the protector can be applied to the screwthread which it is to protect with a screwing action in the manner of a nut. In other words, the "pips" 14 are located on an imaginery helix of the same diameter and lead as that of the screwthread which is to be protected from damage. However, it will be understood that to compensate for the shrinkage which takes place on cooling of the synthetic plastics material, not only must the diameter of the mould cavity in which the protectors are produced be greater than that of the finished protector by an appropriate percentage, but also that the axial spacing of the "pips" in each row must be greater than finally required by that same percentage.

This is not difficult to arrange (but it will be understood that it would be very difficult to arrange for a completely moulded thread to have a non-standard lead). It is a very simple matter to determine the shrinkage rate of the synthetic plastics material which is to be used, and to make the mould with all its appropriate dimensions increased in that same proportion. It has been found that the thread elements constituted by the radial projections or "pips" are sufficiently resilient as to allow the moulded component to be detached from the mould core by being forced off it.

Various modifications may be made without departing from the scope of the invention. For example, it will be understood that, if prepared, the rows of projections or "pips" could be only three in number; alternatively, if preferred, they could be greater than four in number. It will also be understood that instead of being in the nature of small "pips" as illustrated in the drawings, the thread elements could be elements each extending a short distance along the imaginery helix, that is, for example, being say two or three times greater in length than in width. The invention is not only applicable to a thread protector for protecting an external screwthread but to a protector for protecting an internal thread.

Claims

1. A protector made of a synthetic plastics material for protecting the screwthread of a screwthreaded component, the protector being provided with a plurality of thread elements constituted by radial projections or "pips" for engaging the screwthread to be protected, each projection or "pip" being of a size and shape such that it can seat itself between a pair of adjacent threads of the screwthread, and the arrangement of projections or "pips" being such that they are arranged on an imaginary helix having the same lead angle as that of the screwthread to be protected.

2. A protector according to claim 1, in which each projection or "pip" is of generally frustoconical form with a rounded tip for engaging the space between a pair of adjacent threads.

3. A protector according to either one of the preceding claims, in which the projections or "pips" are arranged in axially extending rows, the rows of projections or "pips" being at least three in number.

4. A method of making a synthetic plastics protector for protecting the screwthread of a screwthread component, the method including the step of making a mould to produce a moulding of cylindrical or cup-iike shape, and the step of forming respective cavities in the mould for the forming of the projections or "pips" required on the moulding at spacings such that the projections or "pips" will engage spaces between adjacent threads of the screwthreaded component, the axial spacing of the cavities in the mould being greater than the required axial spacing of the projections or "pips" in the finished component by a factor equal to the rate of shrinkage of the synthetic plastics material which is to be used for the moulding of the protector.

5. A protector constructed, arranged and adapted to be used substantially as hereinbefore described with reference to and as illustrated by the accompanying drawings.

6. A method of making a synthetic plastics protector substantially as hereinbefore described.