GB2204475A

GB2204475A - Reinforcing plastic heels

Info

Publication number: GB2204475A
Application number: GB08711367A
Authority: GB
Inventors: Michael T Buller
Original assignee: BULLER PLASTICS Ltd
Current assignee: BULLER PLASTICS Ltd
Priority date: 1987-05-14
Filing date: 1987-05-14
Publication date: 1988-11-16
Anticipated expiration: 2007-05-14
Also published as: GB8711367D0; GB2204475B

Abstract

A roll pin for reinforcing the heel of a shoe has a constant internal diameter (A) and an external diameter which varies from a minimum at the toppiece end (2) to a maximum at a point (3) approximately 30mm from the toppiece end. The heel pin improves the strength of the heel by providing additional reinforcement in the critical zone 30-50mm from the toppiece end where breakage is most likely to occur. At the same time, the increased outside diameter at the heel seat end improves fatigue resistance of the heel. <IMAGE>

Description

REINFORCING PLASTIC HEELS The present invention is concerned with reinforcing plastic heels, and more particularly is concerned with a reinforcing pin to be incorporated in plastic heels, and to plastic heels incorporating such pins.

Heels for shoes are commonly moulded from plastics material. If a slender heel is required it is common to incorporate within the heel a reinforcing member. Commonly, the reinforcing member is in the form of a roll pin having a constant inside diameter and a constant larger, outside diameter. Such roll pins are commonly available engineering items, and can be obtained at low cost from a number of sources. The roll pin is commonly located in the mould cavity prior to moulding such that one end of the roll pin extends to that end of the heel which is lowermost in use (known as a toppiece end). By locating the roll pin in this manner the hollow centre of the roll pin is exposed at the toppiece end after moulding, and the heel tip (known as the toppiece) can be attached to the heel by furnishing the toppiece with a peg which is an interference fit in the hollow centre of the roll pin.The combination of low cost, ready availability, and ease of toppiece attachment has made the roll pin a very common and successful form of heel reinforcement.

However, tests have shown that in the case of heels which fail through breakage, the breakage usually occurs at a height of between 30mm and 50mm from the toppiece end, according to the height of the heel. It would appear that increasing the strength of the reinforcing member in this region will help to resist breakage.

However, because commercially available roll pins have a uniform wall thickness, if it is desired to increase the wall thickness in the 30-50mm zone from the toppiece it is necessary to increase the wall thickness along the entire length of the pin. If one wishes to maintain an inside diameter for the roll pin which is large enough to facilitate toppiece mounting, increasing the wall thickness implies an increase in outside diameter.

This in itself is undesirable since in very slender heels (in which the breakage problem is liable to be greatest) it is desirable to keep the outside diameter of the pin to a minimum at the toppiece end in order to permit an adequate covering of plastics material surrounding the pin at the toppiece end.

We have now found that the desired increase in strength at 30-50mm from the toppiece end can be obtained by using a roll pin having a tapering wall thickness over at least the zone of the pin adjacent the toppiece end.

Accordingly, one aspect of the present invention provides a roll pin for reinforcing a heel, the wall thickness of the roll pin increasing from a minimum at the toppiece end of the roll pin towards the other end of the roll pin.

With such a pin, the inside diameter can be maintained at the value at present used, and accordingly existing toppieces can be fixed in conventional manner.

Further, the outside diameter of the roll pin at the toppiece end can be maintained at the conventional diameter enabling the heel to be moulded with a very slender toppiece end. The increase in wall thickness provides the required added strength in the critical 30-50mm breakage zone.

In a particularly preferred embodiment of the invention the inside diameter of the roll pin is maintained constant, and the outside diameter increases from the toppiece end towards the other end of the pin, at least over part of the length of the pin. In this case, the pin has a larger outside diameter at the end of the pin opposite the toppiece end (known as the heel seat end). A heel pin of this design has been found to give surprisingly good fatigue resistance test results. This is believed to be attributable to the fact that the larger outside diameter of the heel pin at the heel seat end is better supported by the moulded plastics material of the heel than the relatively small diameter heel pins at present used.This improved support tends to prevent the heel seat end of the roll pin tearing through the plastics material of the heel during fatigue loading, thereby improving the overall strength of the heel.

In a particularly preferred embodiment of the invention the inside diameter of the roll pin is constant over its entire length and the outside diameter increases from a minimum at the toppiece end to a maximum value approximately 30mm from the toppiece end, and thereafter the outside diameter is constant throughout the remaining length of the pin. Such a pin has been found to provide dramatically improved resistance to fatigue failure, as compared with a conventional roll pin having the same inside and outside diameters along the entire length of the pin.

The invention will be better understood from the following description of a preferred embodiment thereof, given by way of example only, reference being had to the accompanying drawing wherein: the single Figure illustrates in axial cross-section a preferred embodiment of reinforcing pin according to the present invention.

The reinforcing pin 1 as shown in the drawing is in the form of a roll pin having a constant internal diameter A and a wall thickness which increases from a minimum B at the toppiece end 2 of the pin to a maximum C at a point 3 located approximately 30mm from the toppiece end 2. From the point 3 to the heel seat end 4 of the pin the wall thickness is constant.

In the preferred embodiment of the invention the internal diameter A has a value of 2819mm, which is the standard internal diameter used in roll pins presently used in the shoe making industry. Accordingly, conventional toppieces can be fitted to the new reinforcing pin. The wall thickness B at the toppiece end is, in the preferred embodiment, 0.8mm, which is the normal wall thickness of a roll pin as used at present in slender moulded heels. The wall thickness preferably increases uniformly from the minimum B to the maximum C, which in the preferred embodiment is 1.5mm.

With the pin described above and illustrated in the drawing the total outside diameter at the toppiece end is 4.6mm, as is conventional at the present time. However, in the zone 30mm-50mm from the toppiece end, where breakage of conventional roll pins normally occurs, the outside diameter is 5.8mm, and the wall thickness is nearly twice that at the toppiece end.

Accordingly, the illustrated pin is substantially stronger in the 30-50mm zone than conventional roll pins having the same dimensions as the toppiece end. Further, the total outside diameter of the pin at the heel seat end (5.8mm) is significantly larger than the 4.6mm outside diameter which would be present in a conventional cylindrical roll pin. It has been found that this increase in outside diameter at the heel seat end improves pin retention within the heel and overall heel strength since the transverse loading applied by the pin to the plastics material of the heel is better supported over the larger projected area of the proposed pin.

Claims

1. A roll pin for reinforcing a heel, the wall thickness of the roll pin increasing from a minimum at the toppiece end of the roll pin towards the other end of the roll pin.

2. A roll pin according to claim 1 wherein the inside diameter of the roll pin is constant throughout the length of the roll pin.

3. A roll pin according to claim 1 or claim 2 wherein the outside diameter of the roll pin increases from a minimum at the toppiece end to a maximum value intermediate the toppiece end and the heel seat end.

4. A roll pin according to claim 3 wherein the outside diameter of the roll pin is constant from the point at which the outside diameter reaches a maximum value to the heel seat end of the pin.

5. A roll pin according to claim 3 or claim 4 wherein the outside diameter of the roll pin reaches a maximum not more than 30mm from the toppiece end of the roll pin.

6. A roll pin for reinforcing a heel, substantially as hereinbefore described with reference to the accompanying drawing.

7. A heel incorporating a reinforcing roll pin according to any preceding claim.