GB2026642A - Inserts e.g. Screw Sockets - Google Patents

Abstract

An insert for insertion in a hole in parent material and retention therein by means of serrations (4) thereon, the serrations being radially outwardly tapered and undercut to form forwardly acting cutting or broaching edges e.g. edges (9) to facilitate entry of the insert into and its retention within said hole. The insert may have a threaded bore 2, or projecting stud. The insert is particularly useful for installation in materials, such as thermo-setting plastics materials, which are hard and brittle. <IMAGE>

Description

SPECIFICATION Press-in Insert This invention related to inserts of the kind having a serrated or similarly formed exterior to provide a plurality of projections for retention of the insert in a hole therefor in parent material and which are installed in position of use in the hole by relative axial movement of the insert and material. Such inserts are usually, but not necessarily, provided with a threaded bore or shank for receiving a threaded member such as a screw or nut, as appropriate, and are widely used, for example, in components of plastics material.

Although conventional inserts of the aforesaid kind are generally suitable for use with thermoplastic materials which are relatively soft during reception of the insert, some have been found to be unsatisfactory when used with materials such as thermosetting plastics which are hard and brittle during reception of the insert, tending to crack and often failing to provide adequate retention of the insert.

An object of the present invention is to provide an insert of the aforesaid kind which has an improved performance in use with materials, such as thermosetting plastics which are relatively hard during reception of the insert.

According to the invention, there is provided an insert of the kind referred to wherein the serrations are radially outwardly tapered and undercut to provide forwardly acting cutting or broaching edges.

The invention will now be described, by way of example, with reference to the accompanying drawings in which: Figure 1 is a perspective view of one form of the insert of the invention, Figure 2 is a view of the rear end of the insert of Figure 1, Figure 3 is a cross-section along the line 3-3 of Figure 2, and Figure 4 is a view of the insert of Figures 1 to 3 from the leading end opposite to that shown in Figure 2.

The insert in the drawings comprises a basically cylindrical body 1, as of brass for example, having a threaded bore 2 for receiving a screw, normally when the insert is embedded in parent material. An intermediate portion 3 of the external periphery ofthe body 1 is formed with a number of circunferentially extending axially spaced rows of serrations or teeth 4, two rows being present in the embodiment shown, although this may be varied from a single row to as many as are required. Extending beyond the intermediate portion 3 in the intended leading direction of the insert is a plain portion 5 of reduced diameter, terminating in an external lip 6 of forwardly tapering annular form for facilitating the centering of the insert upon its introduction into a hole in parent material, as will be described.

Extending beyond the intermediate portion 3 in the intended trailing direction of the insert is an end portion having a series of elongate longitudinally extending radially outwardly tapering flutes or splines 7, the leading end portions 8 of which are forwardly tapering and terminating adjacent the rear extremities of the adjacent serrations 4. As shown, the flutes or splines are equal in number to the serrations in a circumferential direction and each flute or spline is circumferentially aligned with a respective one of the adjacent serrations. Again, the same number of serrations is provided in each circumferential row and respective serrations in adjacent rows are circumferentially aligned. The serrations and splines thus form axially extending rows, as will be seen from Figure 1.

Each serration 4 is in the form of a radially extending tooth which tapers in a radially outward direction to form a sharp edge 9 as will be seen from Figure 1. Each tooth is undercut to provide an intended leading face composed of a surface 10 extending radially inwardly from the edge 9, and an oblique surface 11 joining the radially inner edge of the surface 10 to the root of the forwardly adjacent tooth. It will be seen that the surfaces 11 of the leading teeth are somewhat foreshortened so as to increase the length of the plain portion 5 for a given length of insert. This facilitates gripping the insert around the portion 5 for subsequent turning operations, such as the threading of the bore 2.

Together with the edge 9, the edges 14 (Figure 4) of the tooth 4 defining the surface 10 constitute cutting edges to facilitate entry of the insert into and its retention within a hole in a body of parent material. The intended trailing surface 12 of the tooth extends generally radially from the root of the tooth to the edge 9 and is shown rounded in the region 1 3 adjacent the edge 9 to remove the cutting edges which would otherwise be present although such cutting edges can be retained. In either case the insert has considerable resistance to removal or pull out from a hole once inserted therein.

The insert of the invention is particularly suitable for use in relatively hard parent material such as metal, wood and especially thermosetting plastics materials, although it may be used with thermo-plastic materials if desired. The insert is normally installed in hard material by pushing it into a hole of suitable diameter and depth in the appropriate material.The relative movement required between the insert and material for insertion of the insert may be obtained by axially moving either relative to the other, or by moving both of them. -- - - This first step in the insertion of the insert is to offer up the leading end to the hole, which has a diameter such that the insert may be freely received within the hole until the edge of the hole is contacted by the surfaces 11 of the forward teeth 4 at locations approximately mid-way along those surfaces when considered axially.Although the hole is thus of slightly larger diameter than the lip 6, the latter nevertheless minimises the tendency of the insert to rock during initial insertion thereof and provides an approximate axial alignment action which is continued more accurately by the surfaces 11 of the forward teeth when they contact the edge of the hole.

As the insert is pressed further into the hole, the forward teeth 4 commence a cutting or broaching action at their edges 14 adjacent the sharp edges 9 and form grooves in the wall of the hole as insertion progresses. Material removed by this action is accommodated forwardly of the teeth against the surfaces 10 and 11 and possibly in the space around the reduced diameter portion 5. It is found that due to slight outward yielding of the parent material, the depth of cut made by the forward teeth is less than the full radial extent of the cutting edges of these teeth and a further cut is made by the rear set of teeth 4 as insertion progresses, the radial extent of the actual cutting edges of these further teeth may be equal to that of the forward teeth (as shown) or of greater or lesser radial extent for cutting within the grooves made by the latter.Material removed by the second teeth is accommodated against the surfaces 10 and 11 of the rear teeth and behind the surfaces 1 2 of the forward teeth.

It will be seen that the axial length of the edges 9 is relatively small compared with the distance between the surfaces 12 of the forward teeth and the surfaces 10 of the rear teeth so as to provide a relatively large waste receiving space between the teeth. Again, slight yielding of the material occurs during this second cutting operation and this means that both sets of teeth, after cutting, are subject to some resilient gripping force by the wall of the hole for axial retention of the insert, but the force is not sufficiently large to burst or crack the material. Final movement of the insert to its fully inserted position brings the splines 7 into the grooves formed by the teeth to resist rotation of the insert within the material. Some further yielding of the material preferably takes place during such insertion of the splines.

The insert of the invention may take many forms alternative to the embodiment described above. For example, it would be possible to provide additional cutting edges similar to those on the teeth 4 on the forward end portion of the splines 7. Again, it would be possible to provide successive rows of teeth of different radial extent.

One example is the provision of two or more axially successive forward rows of teeth having the same diameter and two or more axially successive rear rows at a larger diameter, the rearmost row possibly being formed on the forward portions of the splines 7. In general, the number of rows of teeth may be varied as desired according to the length of the insert and other requirements. It is preferred to use straight axially extending splines, of the kind described since this provides the smallest possible crosssection perpendicular to the cutting edges of the teeth and this, in turn, reduces the pressure required for insertion of the insert in the parent material. It may, however, be possible to arrange the rows of teeth, including the splines, in a slightly helical configuration. Although the teeth are shown and described are of zero rake in the forward direction, it may be preferred to depart from this in some circumstances and provide a slight positive or negative rake.

It will be appreciated that the insert of the invention may be of female form, of which an example is described, or may alternatively be provided with a male projection which may be threaded or plain according to requirements.

It will be further noted that the teeth 4 themselves provide resistance to rotation of the insert once inserted and although the splines 7 are desirable for additional security, they may not be necessary, particularly when the axial dimension of the insert is small.

Claims (6)

Claims

1. An insert of the kind referred to wherein the serrations are radially outwardly tapered and undercut to provide forwardly acting cutting or broaching edges.

2. An insert according to claim 1 wherein the radially innermost extremity of the undercut meets a surface which is radially inclined towards the body.

3. An insert according to claim 1 or 2 wherein successive serrations in a direction away from the forward end of the insert are of the same or different radial extent.

4. An insert according to any of the preceding claims wherein the serrations are arranged in linear rows in the longitudinal and peripheral directions.

5. An insert according to claim 4 wherein a rearmost portion is provided with longitudinal flutes aligned respectively with said linear rows of serrations.

6. An insert of the kind referred to substantially as herein described with reference to the accompanying drawings.