SYSTEM FOR HOLDING AND TIGHTENING SCREWS

Abstract: New system for holding and tightening screws, comprising a screw head with a mortise hole (1) which is bevelled in the screw axis and is provided with a plurality of lugs (2) and corresponding circular sections (3), a tip (4) of a screw-driver or tightening tool with a plurality of wings (5) corresponding to the number of lugs and a tooling set intended to obtain said mortise (1) in the screw head and said tip (4) of screw-driver or tightening tool.

Description: The present invention relates to a new system for holding and fastening screws designed to achieve a quick and safety coupling between a screw and a screwdriver or fastening tool, with practically no chance that the screw could be accidentally removed from the screwdriver or fastening tool, as well as for improving the torque transmission without the need of additional efforts for maintaining said coupling, thus making it easy the coupling operations with screws, particulary during automatic assembly operations carried out by means off electrical screwdrivers with torque regulation in the case of robotized machines at industrial facilities, as well as for specific manual applications. An object of the present invention is a system comprising a screw head provided with a mortise hole having a tapered configuration and a circular cross section and provided with one or more lugs projected towards the screw longitudinal axis, the circular shaped walls of said mortise hole forming a conic angle with respect to the screw longitudinal axis, and the screw front lugs walls forming a conic angle with respect to said longitudinal axis. The specific tapered configuration of the mortise hole shaped in the screw head, in accordance with the screwdriver or fastening tool head tip represents significant advantages with respect to known to the art systems like: a) a housing produced by the lateral wedge effect of lugs allowing for a reliable gradually increasing pressure coupling between the screw and screwdriver or fastening tool; b) a wider contact surface area between screw head and screwdriver or fastening tool head tip, this improved area contact producing a more uniform distribution of mechanical stresses and lesser wear in the screw head as well as in the screwdriver or fastening tool head tip; c) a saving in cost of material used for the manufacture of the screws as compared with "philips" or "pozidriv" screws of the art; d) providing for a total safety when screwing in and out the screws with no needs for additional efforts thus avoiding errors in the fastening torque; e) a higher efficiency and a longer useful life of the mortise dies and screwdrivers and fastening tools; and, f) easiness for making screw connections in places of difficult access. As it has been described herein before, the mortise hole made in the screw head has a circular cross section having a number of lugs preferably comprised between two and six, projected towards the screw longitudinal axis. The cross area of said mortise hole decreases gradually downwards along the screw longitudinal axis, the width of lugs also decreasing. The sections of the mortise hole located between each two lugs present a circular form with a predetermined conic angle, this angle keeping a constant value non-dependant from the number and thickness of said lugs, the front faces of said lugs forming an angle with respect to the screw longitudinal axis, said angle changing in correspondance with the screw nominal diameter, and the side faces of said lugs forming an angle with respect to the screw longitudinal axis. This configuration of the system according to the invention provides important advantages in comparison with the systems of the state of the art, and therefore the system of the present invention represents a specially novel system for applications in which a safety coupling between screw and screwdriver or fastening tool is required as it is the case of robotized systems or manual applications with a difficult access to the screwed connections. The Applicant has found that the system for holding and fastening screws of the invention prevents the operator from having to apply an axial force when screwing in the screw of the invention. In manual operations that effort results specially tedious in case of installations of difficult access. Background of the Invention The conventional screws known in the art, apart from the head shape and the recesses made in the heads for the insertion of the screwdriver head, have the inconvenience that the screw often get loose this causing a time waste and damages to the said screws. This problem is more relevant in the case of industrial robotized applications since the screws and the screwing tool are handled by automatic machines so it is essential to have an easy and safety coupling between said screw and tool. There exist previous attempts related to the present invention. In particular Pat. US-2,445,525 discloses a coupling system between screw and screwdriver, the screw head having an axial slot with a number of fins of identical cross area separated by triangular cross spaces, with a screwdrive head matching said screw head; the recess penetrates into the screw threaded body, thus affecting to the mechanical resistance and useful life of the screw; on the other hand, no specific conic angle values were established, on the contrary said conic angles being stated in the case of the present invention. Pat. US-2,239,440 discloses a coupling system between screw and screwdriver, but such recess configuration provides no possibility for having an easy and safety coupling between the screw and screwdriver. Pat. US-2,592,462 discloses a coupling system between screw and screwdriver, the screw head also having a wide enough cross like recess adapted to any type of screwdriver, thus having no possibility for an easy and safety coupling between screw and screwdriver. Moreover, document GB-A-148246 discloses a screw head formation by means of a punch which presses against the screw head and produces a conical recess having ridges and grooves on its lateral surface. However, due to the way this formation process is carried out, there is a rather limited wedge effect as the tool tip contacts the bottom surface of the recess in the screw head as it completely fills the die cavity. Therefore, none of the aforementioned patents describes an easy and safety coupling between the screw and screwdriver with the screwdrive head having an specific configuration precisely fitted to a screw head mortise hole, as it is in the case of the present invention. Description of the invention. The system for holding and fastening screws according to the present invention comprises the feateures of claim 1. Said mortise hole lugs act by a grip fastening torque provided by means of a contact with the screwdriver or fastening tool head splines for transmitting said fastening torque; said mortise lugs-spline contact providing a significant larger faces contact area thanks to which the mechanical stresses beared by the screw head are considerably smaller than for the kown screws of the art. Furthermore, thanks to the mortise hole punching practiced into the screw head of the system according to the invention a contact concurrence conic angle is produced thus ensuring, by means of the obtained side faces wedge effect, a quick and safety coupling between screw and screwdriver or fastening tool thus with practically no need for exerting any pressure along the screw longitudinal axis, as it normally happens in the case of known screws of the art; and, at the same time, thanks to said coupling safety, the wearings on the screw and screwdriver or fastening tool heads are considerably reduced thus preventing errors for obtaining the predetermined torque. It is convenient to indicate that for screw heads with mortise holes having four lugs, apart from the specific screwdrivers or fastening tools, standard "philips" or "pozidriv" type screwdrivers could be used, whereas for a different number of lugs it will be essential to use the screwdriver or fastening tool. The Applicant has carried out the corresponding mechanical tests for different number of lugs, for different α conic angles of said lugs, and for different β conic angles of said circular section, said angles being in correspondance with the practiced depth of the mortise hole of the screw head. Furthermore, all these above-mentioned parameters were related to different screw head outside diameters and their corresponding screw nominal diameters. Based on the tests carried out by the Applicant, the preferred values for the different parameters which determine the design of the mortise hole of the present invention, practiced on the screw head, have been established as follows: a) For mortise holes having from two to five lugs, the lug conic angle α is comprised at the angle range between 5 to 12.5 degrees, preferably between 7.5 to 11.5 degrees; the circular section conic angle β is comprised at the range values between 20 to 30 degrees, preferably between 23 to 23.5 degrees; the mortise hole bottom conicity A is comprised at the range between 25 to 35 degrees, preferably between 28 to 29 degrees; the C angle formed by lug side faces is comprised at the range between 15 to 35 degrees, preferably between 30 to 30,5 degrees; the distance D is comprised at the length range between 0.5 mms to 7 mms, preferably between 0.65 mms to 6.5 mms; the distance d is comprised at the range values between 0.8 mms and 9 mms, preferably between 0.9 mms and 8.2 mms; and the distance e is comprised at the range between 0.2 mms to 4 mms, preferably between 0 27 to 4.0 mms. In no case the depth of the mortise hole should affect the mechanical resistance of the screw. The undercuttings in the screwdrive or fastening tool head tip must match the lugs of said screw head mortise hole and the wings of said scredriver or fastening tool head tip must match the sections between said two adjacent lugs of the screw head mortise hole. Description of Drawings A set of drawings is attached herein with reference to preferred examples of practical embodiments of the present invention: Figure 1 shows a plan view of the system of the invention made in the screw head, for a preferred embodiment comprising three lugs (2) with the corresponding intermediate spaces or circular sections (3); Figures 2 to 4 show cross sections of the system of the invention exposed on Figure 1, showing the conic angles α, β, A and C; Figure 5 shows a screwdriver or fastening tool head tip (4) matching the system of the invention shown on Figure 1; Figure 6 shows two cross sections of the screwdriver or fastening tool head tip (4) with the corresponding fins (5); Figures 7 and 8 show a punching mortise die for the conformation of the screw head mortise hole shown on Figure 1; Figure 9 shows a plan view of the mortise hole (1) made on the screw head for a preferred embodiment comprising four lugs (2) with the corresponding circular sections (3). Figures 10 to 12 show the cross sections of the screw head exposed on Figure 9, showing the conic angles α, β, A and C; Figure 13 shows a screwdriver or fastening tool head tip (4), matching the screw head exposed on Figure 9; Figures 15 and 16 show a punching mortise die for the conformation of the screw head mortise hole exposed on Figure 9. Preferred Embodiments of the Invention One preferred embodiment of the invention, as shown in Figures 1 to 8, relates to the case in which the mortise hole (1) made on the screw head comprises three lugs (2). For this case, the conic α angle of lugs (2) will be comprised between 7.5 to 7.75 degrees, or 9 5 to 9.75 degrees, or 10.5 to 10.75 degrees depending on the lug (2) type; the conic β angle of circular sections will be comprised between 23 to 23.5 degrees; and the A angle of the mortise hole bottom will be comprised between 28 to 29 degrees. The lug (2) width at decreases towards the screw longitudinal axis proportionally to the corresponding fastening torque each radius point, said width value e varying from 0.4/0.42 mms to 3.05/3.09 mms according to the corresponding lug type. The C angle is comprised between 30 and 30.5 degrees. The distance D varies from 0.65/0.68 mms to 5.85/5.89 mms according to the corresponding lug type. The diameter d varies from 0.9/0.95 to 8.0/8.1 mms according to the corresponding lug type. Another preferred embodiment of the invention, as shown in Figures 9 to 16, corresponds to the case in which the mortise hole (1) practiced on the screw head comprises four lugs (2). For this case, the α, β, A and C angles mantain the same said angles values as those was stated for the precedent embodiment comprising three lugs (2). The lug (2) width decreases towards the screw longitudinal axis proportionally to the corresponding fastening torque at each radius point. The said width value e varies from 0.35/0.37 mms to 2.7/2.74 mms according to the corresponding lug type. The distance D varies from 0.7/0.73 mms to 6.0/6.04 mms according to the corresponding lug type. The diameter d varies from 0.9/0.95 to 8.8/10.0 mms according to the corresponding lug type. These preferred embodiments are not limitative with respect to the production and use of screw-screwdriver systems and/or the corresponding matching tools for the cases wherein it is convenient to employ a number of lugs below three or above four, as long as the design parameters as set in the attached claims, in particular the fundamental conic angles, are maintained, so that the system could operate under the stated conditions of safety and mechanical resistance.

Claims: System for holding and fastening screws designed to provide a quick and safety coupling between the screw head and the screwdriver or fastening tool head tip, the system comprising a screw head having a mortise hole (1) with a tapered configuration, depth lesser than screw thickness, along the screw longitudinal axis, and having a circular cross section with a number of lugs (2) projecting towards said screw longitudinal axis and a corresponding number of circular sections (3), characterized in that the conic angle α of lugs (2) front face is comprised at the angle range values between 5 to 15 degrees; and in that the conic angle β of circular section walls (3) located between two adjacent lugs (2) is comprised at the range values between 20 to 30 degrees; and in that the angle C of lugs (2) side walls is comprised at the range values between 15 to 35 degrees; said contact conic values thus ensuring a face wedge effect that provides a quick and safety coupling between lugs screw and splines screwdriver or fastening tool. System for holding and fastening screws according to claim 1, characterized in that the suitable screwdriver or fastening tool head tip (4) matches the corresponding screw head mortise hole (1), said screwdriver or fastening tool head tip (4) having a definite shape and a number of fins (5) both according to the corresponding number of lugs (2) of said screw head mortise hole (1). System for holding and fastening screws according to the precedent claims 1 and 2, characterized in that the conformation of the mortise hole (1) on said screw head presents a definite configuration made by the application of a punching mortise die in a cold conformation process.

Inventors: CASINO LORITE FRANCISCO, CASINO SANTISO FRANCISCO, MARIN SANCHEZ LUIS, CASINO LORITE, FRANCISCO, CASINO SANTISO, FRANCISCO, MARIN SANCHEZ, LUIS
Applicants: CASINO Y MARIN CASMAR S L, CASINO Y MARIN CASMAR S.L.
Application year: 1999
Main classification: F16B23
IPC codes: F16B23, B25B15