Screw and method of its manufacture

Abstract

A screw includes a barrel-shaped central pin is surrounded by a cylindrical bore having a conical bottom The cylindrical insert is seated in the cylindrical bore. The top surface of the central pin is lowered below the top surface of the head. The walls of the pin (4) are convex towards the insert. Manufacturing the screw includes producing the threaded part with the head with the cylindrical recess with the cone-shaped bottom. The cylindrical insert terminates at one end with a bevel with an inclination angle of =10-30. The insert is introduced into the cylindrical recess. The upper part of the insert protruding from head of the screw is pre-shaped. The pin is upset using an appropriate tool and simultaneously the top surface of the pin is lowered below the top surface of the head.

Claims

1. A screw comprising: a threaded part; a head extending from the threaded part, the head having a cylindrical bore and a barrel-shaped central pin surrounded by the cylindrical bore; and a cylindrical insert made of copper aluminium, copper alloy, or aluminium alloy and having an axial through hole, a top surface and grooves on the top surface, the insert being permanently seated in the cylindrical bore, wherein a top surface of the central pin is lowered by a distance from 0.1 mm to 0.6 mm below a top surface of the head.

2. The screw according to claim 1, wherein a radially outer surface of the cylindrical bore is parallel to an axis of the screw.

3. The screw according to claim 1, wherein a bottom of the cylindrical bore has the form of a circular sector with a radius of R from 0.8 L to 1.2 L, where L is equal to a difference between a diameter of the cylindrical bore and a diameter of the central pin.

4. The screw according to claim 1, wherein the top surface of the central pin has a concave shape.

5. The screw according to claim 1, wherein the walls of the central pin are convex towards the insert.

6. The screw according to claim 1, wherein the cylindrical bore is defined by a conical bottom with an inclination angle of from 10 to 30.

7. The screw according to claim 1, wherein the grooves are disposed concentrically with an axis of the screw.

Description

DESCRIPTION OF THE DRAWINGS

(1) The aspects of the disclosed embodiments will be presented in more detail with reference to exemplary embodiments presented in the drawing, where:

(2) FIG. 1 depicts the cross-section and top view of the screw;

(3) FIG. 2 presents detail A indicated in FIG. 1;

(4) FIG. 3 depicts the cross-section of the cylindrical insert;

(5) FIG. 4 presents the cross-section of the cylindrical insert with flange;

(6) FIGS. 5 to 8 illustrate the consecutive phases of manufacturing the screw using plastic forming method; and

(7) FIG. 9 presents the screw in an alternative version which has the bottom with the radius R and parallel outer surfaces of the bore.

DETAILED DESCRIPTION

Example 1

(8) Using known methods of plastic working and machining, the threaded part 1 is produced together with the head 2 in which the cylindrical recess 3 with a cone-shaped bottom having the inclination angle of =20 surrounding the cylindrical central pin 4, and where the surface of the head 2 and the surface of the pin 4 are coplanar. In a separate machining operation the cylindrical insert 5 with the axial through hole is produced from a copper alloy, the said insert terminating at one end with a bevel with an inclination angle of =20 and having the inner diameter and outer diameter corresponding to the respective diameters of the cylindrical recess 3 in the head 2. Next, in operation A the insert 5 is introduced into the cylindrical recess 3. Then in operation B the upper part of the insert 5 is pre-shaped which protrudes above screw head 2. Further, in one plastic working operation C, the pin 4 is upset using an appropriate tool, the top surface of the pin 4 is lowered below the top surface of head 2 and the final shape of the upper part of the insert 5 is formed together with grooves 6 recessed in the top surface concentrically with the screw axis.

(9) The screw produced in this method has the cylindrical copper alloy insert 5 permanently seated in the head 2 with top surface of central pin 4 lowered by d=0.3 mm below the surface of the head 2.

Example 2

(10) An identical screw is produced using the method described in Example 1, but the insert 5 is made of aluminium alloy and provided with a flange 7.

Example 3

(11) Using known methods of plastic working or machining, the threaded part 1 is produced together with the head 2 in which the cylindrical recess 3 is provided, surrounding the cylindrical central pin 4, the said recess having the bottom in the form of a quadrant sector with the radius R between 1.2 L and 0.8 L, and where the surface of the head 2 and the surface of the pin 4 are coplanar. Moreover, the top surface of the pin 4 has a concave shape. In a separate machining or plastic working operation, the cylindrical insert 5 is produced from copper alloy, the said insert having the inner diameter and outer diameter corresponding to the respective diameters of the cylindrical recess 3 in the screw head. Next, in operation A the insert 5 is introduced into the cylindrical recess 3. Then in operation B the upper part of the insert 5 is pre-shaped which protrudes above the screw head 2. Further, in one plastic working operation C, the pin 4 is upset using an appropriate tool, and simultaneously the top concave plane of the pin 4 is lowered below the top surface of head 2 and, as a result, the walls of the pin 4 slightly draw aside towards the insert 5 and the final shape of the upper part of the insert 5 is formed together with grooves 6 recessed in the top surface concentrically with the screw axis.