Expanded – threaded – driven – headed – tool-deformed – or locked-thr – Threaded fastener locked to a discreet structure – Nut – and means to engage substructure on its opposite faces...
Reexamination Certificate
2000-06-29
2001-11-13
Wilson, Neill (Department: 3627)
Expanded, threaded, driven, headed, tool-deformed, or locked-thr
Threaded fastener locked to a discreet structure
Nut, and means to engage substructure on its opposite faces...
C411S060200, C411S508000
Reexamination Certificate
active
06315510
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a screw grommet (or plug) used for fastening panels together and to a method for manufacturing such a plug.
DESCRIPTION OF THE RELATED ART
Generally plugs are connection elements which are pushed or pressed into preformed holes in order to connect two components by friction or wedging.
For fastening screws in bores of a component there are known various forms of plug which vary depending on the nature and the material of the component and/or of the screw. For fastening screws in through-bores in sheet material, in particular metal sheet, so-called grommets are known. These consist usually of plastic. They are inserted into the through-bore where they are prepositioned by way of a slight press fit and/or by way of saw-tooth-shaped projections on their outer contour. Subsequently a screw is screwed into a fastening bore in the grommet, the fastening bore being orientated in the plugging direction, wherein usually the thread of the screw digs into a corresponding contour of the walling of the fastening bore. With this the screw widens the grommet or plug sticking in the bore, by which means a rigid friction and/or positive fit connection to the wall of the bore arises. A component which is to be fastened to the surface of the metal sheet is then held under the head of the screw and via the screw and the grommet is rigidly connected to the surface of the metal sheet.
Such a fastening is particularly applied in the construction of automobiles in order for example to fasten bumper strips or number plate holders to the car body or to attach wheel housing shells in the wheel guard.
In order to ensure corrosion protection it is necessary that after the attachment of the grommet and of the screw, moisture may no longer penetrate into the inner side of the metal sheet. For this usually sealing rings are applied which must be preassembled with the grommet or the through-bore, or sealing masses are attached at suitable locations before the assembly of the grommet. This is particularly disadvantageous with the large scale production in automobile construction since every additional assembly step, thus also the attachment of seals, causes additional costs.
SUMMARY OF THE INVENTION
It is the object of the invention to supply a plug for fastening a screw in a through-bore of a sheet material, in particularly metal sheet, and a method for its manufacture which seals the through-bore when the screw is fastened.
According to the invention this object is achieved by a plug for fastening a screw in a through-bore of a sheet material, in particular a metal sheet which has a plug body dimensioned to be insertable into the throughbore, and a fastening bore, for receiving a screw, which is orientated in the direction of plugging. Preferably accordingly the plug body extends elongately around the fastening bore and is preferably cylindrical, e.g. circularly cylindrical, or tapers somewhat towards its tip. According to the invention a sealing collar extends radially outwards around the plug body and on plugging the plug into the through-bore serves as an abutment. The sealing collar comprises an annular, e.g. circular annular sealing surface which is orientated in the direction of plugging and sealingly cooperates with the surface of the edge of the metal sheet through-bore when the sealing collar abuts here on insertion of the plug into the through-bore. Preferably the fastening bore in the plug body is a blind hole whose wall has an uninterrupted surface and integrally connects to the sealing surface. This has the effect that the plug completely sealingly closes the through-bore as soon as the sealing surface completely occludes with the edge of the through-bore.
Preferably the sealing surface is a sealing lip which projects in the plugging direction axially from the sealing collar and sealingly forms possible unevenness of the surface of the edge of the through-bore. This also permits the use of the plugs with metal sheets of thickness which are different within certain limits.
Preferably at least the sealing surface of the sealing collar is formed of a softer plastic than the plug body. By way of this these two elements of the plug according to the invention meet their respective demands particularly well: the hard plastic of the plug body may ensure the demanded strength and stiffness for a secure connection of the metal sheet to the screw, whilst the soft plastic may be flexibly adapted to the surface of the metal sheet and thus seals particularly well.
Preferably such a plug is manufactured by way of a method according to the invention, in which firstly the plug body of the first, hard plastic is injection moulded in the known manner in a first mould, the plug body is then applied into a second mould in which the sealing collar of the soft, second plastic is injection moulded around the plug body. The second plastic is preferably an elastomer.
An alternative method according to the invention envisages the plug body to be manufactured from the first hard plastic with the sealing collar of the second, soft plastic simultaneously in a suitable known 2-component tool of a suitable injection molding machine.
The plug body comprises on its outer contour preferably saw-tooth-shaped projections which in the plugging direction axially in front of the sealing collar are arranged uniformly distributed on the circumference of the sealing body and whose inclination in the plugging direction runs flatly so that on inserting the plug they slide through the through-bore without great resistance, the other flank however being so steep that the plug, i.e. under bias of the sealing lip does not press itself out of the through-bore. The plug may according to the invention also comprise more than one set of saw-tooth-shaped projections, wherein the sets then are arranged at different distances from the sealing collar in order to be able to use the plugs with metal sheets of still differing metal sheet thicknesses.
REFERENCES:
patent: 4948314 (1990-08-01), Kurosaki
patent: 5269640 (1993-12-01), Jonishi et al.
patent: 5294225 (1994-03-01), Kazino et al.
patent: 5340257 (1994-08-01), Morassutti
patent: 2902123 (1980-03-01), None
patent: 441691 (1991-08-01), None
patent: 26717248 (1988-12-01), None
Rehberg Karsten
Sturies Jens
ITW-Ateco G.m.b.H.
Lowe Hauptman & Gilman & Berner LLP
Wilson Neill
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