Method and mould for the manufacture of a plastic sole for shoes

Abstract

A method for the manufacture, by molding of a plastics sole with exchangeable gripper elements, for sports shoes, in which the gripper elements are so located in recesses of the mold, before introducing the fluid plastic material into the mold, that plastic material is cast directly round the threaded extensions of the gripper elements or round holder inserts into which the gripper elements have already been screwed. This saves the subsequent screwing-in of the gripper elements or the provision of additional holder elements for the holder inserts. In addition, a sports shoe with a plastic outsole and gripper elements is disclosed, the outsole of which has annular projections which project into annular grooves on the support face of the gripper element which faces the outsole. This makes it possible to lengthen the thread and hold the gripper element more securely without causing additional weight.

Description

The present invention relates to a method for the manufacture of a plastic sole for shoes, especially sports shoes, with exchangeable screw-on gripper elements, by moulding. The invention further relates to a mould for carrying out this method and to gripper elements for use in the method.

It has been known for a considerable time to manufacture plastic outsoles of sports shoes, especially of football boots and track shoes, by moulding, wherein, preferably, the soles are moulded directly onto the ready-lasted shoe upper. In order to hold exchangeable gripper elements which themselves consist of plastic, for example the studs of football boots, metal holding inserts, in the form of threaded sleeves with adjoining projections, are moulded directly into the plastic outsoles and the gripper elements (studs) are provided with corresponding metal screw inserts. The metal inserts in the sole and in the gripper elements ensure the requisite hold and at the same time the requisite resistance to breaking-off or shearing-off when the sports shoes are used.

However, the provision of the holding inserts in the sole and in the gripper elements themselves not only increases the cost of manufacture of the known shoe soles but also their weight. In addition, it was always necessary to take special precautions to locate the holding inserts in the mould in such a way that the inserts occupy the desired position in the finished plastic sole.

Sports shoes with plastic outsoles have also already been proposed in which gripper elements of plastic are fixed without any metal inserts. However, with these outsoles, projections -- to which the gripper elements are fixed -- must be provided at the fixing position of the gripper elements, in order to provide a greater length of thread and take account of the lower strength of the plastic thread. This causes an undesirable stiffening of the sole and increased weight.

According to the invention there is provided a method for the manufacture of a plastics material outsole for shoes, especially sports shoes, with exchangeable gripper elements having screw-threaded extensions, said method comprising locating the screw-threaded gripper elements in a mould, and thereafter introducing plastic material directly round the screw-threaded extensions to mould the sole.

The invention thus dispenses with metal inserts in the sole and in the gripper elements and also with large projections on the sole, from which the gripper elements extend. This leads -- due to the omission of the metal or additional plastic -- to a not inconsiderable saving in weight, which can be of the order of magnitude of 30 to 40 g, depending on the number of gripper elements. The gripper elements and the plastic sole are preferably manufactured of different materials, in such a way that the material of the gripper elements is not impaired at the temperatures at which the sole is cast and also does not bond to the material of the sole. Suitably, the sole consists, as hitherto, of an elastic plastic, for example nylon, whilst the gripper elements are manufactured from styrene or the like.

As a result of suitably choosing the material of the sole and of the gripper elements, the exchangeability of the gripper elements is in no way impaired, in spite of direct moulding round the threaded extensions, because a bond is not formed between the two materials. The gripper elements can accordingly, just as before, be unscrewed, by means of tools, from the sole after the sole has been moulded round them, and be replaced by other elements. The strength also does not suffer since the threaded plastic extensions can be made of substantially greater diameter than hitherto without misgivings as to a possible increase in weight. This has been avoided in the case of metallic threaded inserts in order to keep the weight as low as possible. A particularly advantageous embodiment furthermore provides that the gripper elements have a recess in their support face, by which they rest against the underside of the sole and transfer the stud or spike pressure, and that the gripper elements are located with this support face either flush with, or projecting from, the corresponding surface of the mould cavity. This produces a corresponding ring-shaped shoulder on the outsole within and/or around the periphery of the support face of the gripper element, which can transfer very substantial shear forces. Furthermore, this increases the thread length without having to tolerate additional weight in the form of projections, since the ring-shaped shoulder is accommodated in the interior of the gripper element itself.

Before introduction into the mould, the gripper elements can be treated with a release agent, which further improves their detachability from the sole. A particularly advantageous embodiment of the method furthermore provides that -- as is already in itself known -- the plastic sole is moulded directly onto the ready-lasted upper, so that after the moulding method a finished complete shoe is obtained. This results in a substantial simplification of the production since the gripper elements no longer have to be screwed into the soles in a separate working step, and results in a corresponding saving in machinery.

A particular advantage of the method according to the invention is that gripper elements which must occupy a certain orientation or angular position relative to the longitudinal direction of the sole, as in the case, for example, with the ridge-like or pyramidal gripper elements of track shoes, can very simply be fixed to the outsole in this orientation of the elements. It only requires the gripper elements to be located appropriately in the mould whereas hitherto the position of the threads, both in the sole and in the gripper element, had to be matched very accurately to one another, or compensation by corresponding spacers was necessary.

When using plastic holder inserts, special measures to support the holder inserts in the mould are no longer required because the gripper elements themselves, which remain in the finished moulded outsole, serve as a support for the holder inserts. The gripper elements, for example football studs, which are screwed into the holder inserts, merely have to be inserted in recesses provided in the mould, without requiring special setting work and additional removal of supports. It is a particular advantage here that the position of the holder inserts in the plastic sole which is to be manufactured can be determined by screwing the gripper elements more or less deeply into the holder inserts.

The method of the present invention is of particular importance because in football, in recent years, a noticeable transition from the previous relatively hard plastic outsole to a soft outsole has been noticeable and as a result it has been necessary to resort increasingly to moulding-in of holder inserts since the softer plastic material does not possess sufficient strength for holding screw-type gripper elements securely.

The mold for carrying out the method according to the invention differs from the known molds only in that recesses for receiving the gripper elements are provided in the face of the mold cavity which forms the underside of the sole. Hence, it is possible to adapt any known mold to the method according to the invention, without a substantial increase in cost. At the same time it is possible to match the recesses to the maximum size of gripper elements which occurs and then to hold smaller gripper elements by means of separately inserting support rings. These support rings are at the same time intended to fulfil a certain sealing function to prevent the fluid plastic material of the sole from entering the recesses.

In order that the invention is more fully understood, the following description is given, merely by way of example, reference being made to the accompanying drawings, in which:

FIG. 1 is a schematic section, in the longitudinal direction of the sole, through the lower part of a mold according to the invention, with a shoe mounted thereon, and further shows, for simplicity, two different embodiments of gripper elements on one sole;

FIG. 2 is a side elevation of a holder insert made of plastic, into which a football boot stud has already been screwed and which can be embedded by molding, by the method according to the invention, in the outsole of a football boot;

FIGS. 2a and 2b are plan views of different embodiments of the plastic holder inserts according to FIG. 2; and

FIG. 3 shows a further modified embodiment of a plastic holder insert according to FIG. 2, constructed to receive two gripper elements.

As indicated, FIG. 1 is a section, in the longitudinal direction of the sole, through the lower part of a mould 1, on which a ready-lasted upper 2 of a football boot is mounted, in such a way as to create a mould cavity 3 which corresponds precisely to the dimensions of the outsole which is to be attached by injection moulding to the upper 2. The drawing shows a situation in which plastic material, for example nylon, has already been injected into the mould cavity 3 and forms the outsole. The lower part 1 of the mould has, in its base, which defines the mould cavity 3 and moulds the underside of the outsole, recesses 4, 5 which serve to receive studs 6, 7.

The recesses 4, 5 and the studs 6, 7 inserted therein are of two different embodiments. The stud 6, shown on the left of the drawing, has in its part which projects from the sole, the customary slightly concavely-domed truncated cone shape of the known football studs. From its support face 8, by which it rests against the underside of the outsole, protrudes an integrally moulded threaded extension 9, which projects beyond the support face 8 by an amount precisely equal to the thickness of the sole and hence comes to rest, when the mould is closed, against the insole, which is not shown, of the shoe upper 2. The support face 8 has a circular groove 10, extending directly from the threaded extension 9, and the radially outer flank of this groove is conical.

The recess 4 matches the outer face of the stud 6 precisely, so that the support face 8 of this stud lies flush with the base surface of the lower part 1 of the mould. In the embodiment shown on the right of the drawing, the recess 5 is stepped and receives a support ring 11, the inner face of which matches the outer shape of the stud 7. The dimensions of the recess 5 are matched to the largest embodiment of the stud 7 which occurs, adaptation to smaller sizes of studs being effected through appropriate dimensioning of the support ring 11. The support ring 11 is conical on its outer face in order to exert a good sealing effect to prevent the entry of plastic material into the recess 5.

The stud 7 is so located in the support ring 11, that is to say the internal diameter of the support ring 11 is such, that the support face 8' is not flush with the base surface of the lower part 1 of the mould but instead is about 0.5 mm above it. The support face 8' can also be provided with a circular groove 10. The outer edge of the support face 8' is cylindrical at least to a height which corresponds to the amount by which the support face 8' lies above the base surface of the lower part of the mould.

FIG. 2 shows a holder insert 21 into which a football stud 22 has been screwed. In the arrangement shown, these two parts are inserted into a recess of a mould -- which is not shown -- in such a way that the edge 23 of the stud 22 is flush with the edge of the recess. If now fluid plastic material is forced into the mould, the material flows into all the interspaces between the holder insert 21 and the stud 22 and fills these. Hence, in the finished outsole, the holder insert is embedded in, and fixed by, plastic material. The location of the holder inserts 21 in the mould proves very simple because the height position relative to the stud 22 is fixed by first screwing in the stud and all that is necessary before the moulding is to insert the stud 22 in the desired position of the holder insert 21 into the recess provided in the mould. On the other hand, special setting in respect of height is no longer necessary.

FIGS. 2a and 2b show plan views of different embodiments of the holder insert 21 shown in FIG. 2. The notches 24 or perforations 25 provided respectively at the edge or in the edge zone serve to permit the plastic material to flow more easily through to the other side of the holder insert, so that the latter is firmly enclosed by plastic material. The holder inserts according to FIGS. 2a and 2b are preferably so arranged in the outsole that their longitudinal direction matches the main direction of stress of the particular gripper element. This produces a longer lever arm which effects a more uniform distribution of forces.

The holder insert 26 according to FIG. 3 is constructed to receive two gripper elements and extends -- in the finished outsole -- transversely to the longitudinal direction of the outsole. With this design it is directly possible, if desired, to locate the holder insert at an angle to the outsole, that is to say to locate it in such a way that it is more deeply embedded in the sole in the region of one gripper element than in the region of the other gripper element.

The holder inserts shown in the drawings consist of plastic, preferably of a hard grade of nylon or of PVC. When using plastic holder inserts, a soft transition from the softer areas of the sole to the areas in which the holder inserts are located is achieved, so that painful pressure points can be avoided. This can also be controlled additionally by giving the holder inserts an asymmetrical shape relative to the fixing position of the gripper elements. This asymmetrical shape can also be selected in relation to the principal stresses on the particular gripper element which is to be held.

The method according to the invention, in accordance with FIG. 1, is carried out as follows:

First, studs 6 or 7 are inserted in the recesses 4 or 5 of the lower part 1 of the mould. The studs 6, 7 can first be treated with release agent at their threaded extensions 9. Thereafter, a ready-lasted shoe upper is mounted on the mould so that the insole rests against the free end faces of the threaded extensions 9. Fluid plastic material is then injected into the mould cavity 3 thus formed. The plastic material flows round the threaded extensions 9 and -- in the case of the stud 7 -- also round the cylindrical part of the outer surface of the stud. In addition, the material penetrates into the circular groove 10 and fills the latter. In this way, ring-shaped shoulders which correspond to the grooves 10 or the cylindrical outer surface of the stud 7 are created in the outsole and these shoulders absorb by far the greatest part of the shear stresses which arise when using the shoe and therefore prevent the threaded extensions 9 from breaking off or shearing off. After the plastic material has hardened, the finished complete football boot can be taken from the mould. Since the plastic material of the studs 6, 7 differs from that of the outsole, the studs can, if required, be unscrewed by applying tools to key faces which are not shown, and be replaced by other studs.

The method in conjunction with the holder inserts according to FIGS. 2, 2a, 2b and 3 takes place correspondingly, except that the holder inserts are screwed onto the gripper elements before the latter are inserted into the mould.

Claims

I claim:

1. A method for the manufacture of a plastic material outsole for shoes, especially sports shoes, with exchangeable screw-in gripper elements, having screw-threaded extensions, said method comprising the steps of locating the screw-threaded gripper elements in a mold cavity and thereafter introducing plastic material directly round the screw-threaded extensions.

2. A method as claimed in claim 1 and further comprising treating the threaded extensions with a release agent before being inserted in the mold.

3. A method as claimed in claim 1, wherein the plastic sole is molded directly onto a ready-lasted upper.

4. A method as claimed in claim 1, wherein the length of the threaded extensions of the gripper elements is chosen to be equal to the thickness of the sole.

5. A method as claimed in claim 1, wherein each gripper element has a support face and a recess in each support face from which the screw-threaded extension projects and is located with this support face flush with the corresponding face of the mold cavity.

6. A method as claimed in claim 1, wherein each gripper element has a support face and is located with its support face projecting a relatively small distance from the corresponding face of the mold cavity.