DESCRIPTION

The present invention relates to a bush with a quick-screwing action.

It is known in the technical sector of metal fittings that there exists the need to provide metal bushes with an internal threading designed to allow the joining together of parts, such as panels and the like which must be fastened in various ways.

Although effective, the known bushes nevertheless have functional drawbacks arising from their form which results in a slow speed of insertion and a limited tensile strength, said drawback constituting a major defect in particular if the bushes are inserted in low-density and/or small-thickness materials.

The technical problem which is posed, therefore, is that of providing a bush which overcomes, or at least limits, the aforementioned technical drawbacks. In connection with this problem it is also required that the bush should have small dimensions, be easy and inexpensive to produce and be able to be easily installed very rapidly using normal standardized means.

These results are obtained according to the present invention by a bush according to the characteristic features of Claim 1.

Further details may be obtained from the following description of a non limiting example of embodiment of the subject of the present invention provided with reference to the attached drawings in which:

Figure 1 : shows a perspective view of a bush according to the present invention;

Figure 2: shows a top plan view of the bush according to Fig. 1 ; Figure 3: shows a half-view/half cross-section along the plane indicated by

Ill-Ill in Fig. 2;

Figure 4: shows a cross-section of the enlarged detail of the threading of the bush according to the invention.

As shown and assuming solely for the sake of easier description without any limiting meaning a pair of reference axes extending respectively in a longitudinal direction X-X, coinciding for convenience with the axis of the bush, and transverse/radial direction Y-Y perpendicular to the first direction, as well as a top part "S" corresponding to the operating part of the bush and a bottom part "I" opposite to the top part, an example of a bush according to the invention comprises:

- a substantially cylindrical hollow body 10 with a top end face integral with:

- a substantially frustoconical hollow head 11 with an outer larger base 11a, comprising an annular edge 11 b, and a smaller base 11 b connected to the cylindrical body 10 by a crown 11c inclined towards the axis of the bush body;

- a threading 12 formed on the outer side surface 10a of the body 10;

- a female thread 13 formed on the inner side surface 10b of the body 10. Advantageously, the frustoconical head 11 had an inner cavity with a polygonal profile 14. Preferably the polygonal profile is obtained by means of the superimposition of two hexagons, the second one of which is rotated through a predefined angle, preferably of between 25° and 35°, and more preferably 30°, relative to the first one; this allows easier screwing for insertion of the bush, which may be performed using both a special spanner and a standard hex key. Preferred embodiments of the bush are provided with:

- an outer threading 12 with an asymmetrical profile, preferably defined by a wide angle a of inclination of the bottom side of the thread relative to a plane parallel to the transverse direction Y-Y and a small angle b of inclination of the top side of the thread relative to a plane parallel to the transverse direction Y-Y.

The thread 12 preferably has an asymmetrical profile with:

- an angle a of inclination of the bottom side of the thread relative to a plane parallel to the transverse direction Y-Y ranging between 35° and 45°, and preferably between 38°and 42°; and/or

- an angle b of inclination of the top side of the thread relative to a plane parallel to the transverse direction Y-Y ranging between 4° and 10°, and preferably between 5.5° and 8°.

The wide angle a of the bottom profile allows fast and easier screwing of the bush which may be synergically combined with the polygonal profile of the head, while the small upper angle b results in an increased resistance to axial forces of extraction of the bush, which is particularly useful for low- density materials.

The Applicant has surprisingly discovered that the speed and ease of screwing may be improved in particular by an angle a of between 35° and 45°, preferably between 38°and 42°, which in combination with an angle b of inclination of between 4° and 10°, preferably between 5.5° and 8°, also allows the resistive force of the bush to be maintained once the bush is mounted. The asymmetrical profile described above therefore results in a bush which offers maximum ease of screwing together with an excellent resistance to the axial extraction forces.

The cylindrical body generally has an axial length of between 8.5 mm and 12, preferably between 9 mm and 10.5 mm.

Preferably the bush is made of metal with a low carbon content.

Preferably, the bush is produced by means of a low-cost rolling operation.

It is therefore clear how the particular characteristics of the form and threading of the bush according to the invention are such as to allow fast screwing thereof, a high extraction resistance and therefore high resistance also in panels with a small thickness and/or low material density, as well as a high mechanical resistance to deformation.

In addition to the above, the bush according to the invention gives rise to further advantages: the particular angles of the sides of the threading allow in fact insertion also by means of pressure instead of by screwing; moreover, the particular frustoconical form of the head with a polygonal operating surface allows coplanar insertion of the bush inside the panel without the need for prior counterboring of the material, since the counterbore is in fact automatically formed during insertion.

Although described in connection with a number of embodiments and a number of preferred examples of implementation of the invention, it is understood that the scope of protection of the present patent is determined solely by the claims below.