The invention further relates to a rivet.

BACKGROUND TO THE INVENTION The uses of rivets with a rivet head include joining together two or more components, e. g. members to form a chassis for a truck. A shank of a rivet is intended to run through a hole in each component, the rivet being intended to be deformed inter alia by said deforming force being applied, in the direction of the rivet shank, to the upper portion of the rivet head. The rivet head is thus deformed and pressed against the component which is situated nearest to the rivet head, with radial displacement of material of the surface of the rivet head's underside facing towards the component.

Rivets whose head comprises a planar lower surface running perpendicular to the rivet shank are known.

Also known, from SE patent specification No. 504 121, are rivets comprising a planar lower surface which runs perpendicular to the rivet shank and is of substantially radial extent closest to the rivet shank, and comprising a chamfered peripheral portion adjacent to the upper side.

Today, said components are often subjected to some form of surface treatment. In both cases of known rivets there is an obvious risk of the surface treatment being damaged due to friction between the planar lower surface of the rivet head and such surface coating at the time of deformation of the rivet head when the latter, being

subjected to high pressure and radial displacement of material, abuts against the surface coating.

This is particularly serious in the case of the first kind of rivets mentioned, which have a relatively acute-angled peripheral edge. Even if in the case of the second kind of rivets an attempt is made to alleviate this effect by peripheral chamfering, there is a substantially planar contact surface exerting strong radial friction forces on the surface coating.

Damage to the surface coating is of course undesirable and may give rise of said components.

SUMMARY OF THE INVENTION The object of the present invention is to provide a rivet head which eliminates the problems associated with known rivet designs.

This object is achieved with rivet heads and rivets of the kind specified in the attached independent claims. Thus a rivet head according to the invention comprises a lower portion which has a lower surface intended to project beyond the shell surface of the rivet shank, substantially the whole of which lower surface is arranged to form an angle of more than 90° with the centreline of the rivet shank. Large friction forces are thereby prevented because there is, on average, a small contact surface relative to the component concerned, while at the same time the peripheral portion of the lower surface is not brought into damaging contact with said component during a riveting process.

Further advantages are achieved with features according to the respective dependent patent claims. According to a preferred embodiment, said lower surface thus has an arcuate configuration whereby said angle increases substantially continuously towards the periphery of the lower surface. This accentuates the fact that during said deformation of the rivet head the lower surface is successively rolled/pressed against

the component concerned and thus comes gently into contact with the surface of the component.

BRIEF DESCRIPTION OF THE DRAWINGS The invention is described below in more detail with respect to embodiments illustrated by the attached drawing, in which - Fig. 1 depicts schematically an axial section through a known rivet inserted for riveting, and an example of damaged surface coating adjacent to the rivet head, - Fig. 2 depicts schematically an axial section through a first embodiment of a rivet according to the invention, inserted for riveting, - Fig. 3 depicts schematically the first embodiment of a rivet according to the invention, viewed perpendicular to its axial direction, and - Fig. 4 depicts schematically a detail according to Fig. 3 of, inter alia, the arcuate lower surface of the rivet head, viewed as in Fig. 3.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT Fig. 1 depicts damage in the form of a crease 1 in relevant surface coating 1', a crease formed by, inter alia, friction forces of the kind described in the introduction.

Figs. 2 to 4 depict a rivet 2 and a rivet head 3 which in several ways resemble known rivets but also exhibit substantial differences. The rivet head 3 is arranged to be supported by and to connect to a rivet shank 4 and comprises an upper portion 5 to which a deforming force F is intended to be applied and a lower portion 6 from which the rivet shank is intended to extend.

The rivet thus arranged is intended to join together at least two components 7,8, e. g. two surface-treated chassis components for a truck.

The lower portion has a lower surface 10 which projects beyond the shell surface 9 of the rivet shank and substantially the whole (i. e. at least almost the whole surface) forms an angle v > 90° with the centreline 11 of the rivet shank.

According to preferred embodiments, the lower surface has an arcuate configuration whereby said angle increases substantially continuously towards the periphery 6'of the lower surface, as shown in Figs. 2 to 4.

In addition, it is preferable that the lower surface substantially has a ball-like configuration and thus substantially has, in axial section, the shape of part of a circle, a circular arc. In such cases, it is often preferable that the radius of curvature of the ball surface or circular arc corresponds to at least 1.5 times the rivet shank diameter or equivalent.

It is further preferable that the lower surface is arranged to extend in towards the rivet shank substantially perpendicular to the centreline of the rivet shank.

The function of the rivet head and the rivet according to the invention have probably been substantially indicated above.

The substantially angled and/or, as preferred, arcuate configuration of the whole lower surface means that during the intended deformation of the rivet head the lower surface is arranged to be successively rolled/pressed against the relevant component's preferably surface-treated upper side and hence to come gently into contact with said upper side, resulting in an, on average, small contact surface preventing large friction forces, while at the same time the peripheral portion of the lower surface is not brought into damaging contact with said upper side during the riveting process.

The shape of the lower surface, especially the magnitude of the angling/radius of curvature, is adapted to the rivet head's shape in other respects and volume, so that the process described is achieved.

The invention has been described above in connection with preferred embodiments. A multiplicity of embodiments and minor changes and additions may of course be conceived without departing from the fundamental idea of the invention.

Thus the angled lower surface of the rivet head may conceivably be substantially non- arcuate or arcuate or a combination of arcuate and non-arcuate surface, e. g. so that it comprises an outer portion corresponding to the shell surface of a truncated cone and an arcuate inner portion connecting to the latter.

It is usually preferable that the rivet according to the invention be in a known manner axially symmetrical with a generally domed configuration of the rivet head and a substantially cylindrical shape of the rivet shank.

A rivet according to the invention is preferably made of steel and in one piece.

Embodiments are nevertheless conceivable whereby the rivet head is manufactured separately.