GB2045133A

GB2045133A - Thread rolling dies

Info

Publication number: GB2045133A
Application number: GB7942779A
Authority: GB
Original assignee: Ingramatic SpA
Current assignee: Ingramatic SpA
Priority date: 1979-03-30
Filing date: 1979-12-12
Publication date: 1980-10-29

Abstract

Screws having a thread formation with two starts of different depth are rolled between threading dies provided with protuberances for pointing the screws. Relatively reciprocating dies, or a roll and concave platen, may be used. Each screw is given a point of substantially conical configuration with a terminal thread thereon. <IMAGE>

Description

SPECIFICATION Tool for producing screws comprising a thread with two starts of different depths, and the screw produced The invention relates to a tool for producing screws comprising a thread and two starts of different depths, and the screw produced.

In producing screws comprising a thread with two starts of different depths, a tool is used at the present time consisting of a mobile part and a fixed part which, on their opposite facing surfaces, comprise grooves having a cross-section which at the exit end of the respective fixed and mobile parts is equal to the cross-section of the two thread starts.

The screws produced by the aforesaid tool at the moment comprise a point of pyramid configuration, normally known as a nail point, which has of necessity to be made first, i.e. the thread is prepared on a screw blank which already has the said nail point preformed thereon.

This leads to a screw which is not always weil received by the user, because in order to drive it in it is necessary to exert an initial thrust for inserting the nail point into the material into which the screw is to be screwed.

The present invention sets out to obviate the aforesaid drawbacks by providing a tool for producing screws comprising a thread with two starts of different depths, which leads to a point of conical configuration, with the terminal thread on the point, which therefore offers improved penetration into the material and in particular does not require any initial thrust for driving in the point, the point being driven in in a manner which can be defined as "gentle" and constant with the screwing-in of the thread.

Within that general aim, it is possible to arrange that the tool according to the invention comprises a thread with two starts of different depths, which can be easily fitted to traditional machines, and which does not require any lengthening of the machining stages, although leading to a product of improved quality.

It is further possible to arrange that the tool, according to this invention, enables a high quality product to be produced by cold rolling.

According to one aspect of this invention, there is provided a tool for producing screws comprising a thread with two starts of different depths, comprising a fixed part and a mobile part which oppose each other, and which on their mutually facing surfaces comprise grooves for constructing the two starts of different depths, wherein at the mutual exit ends of said fixed part and said mobile part there are provided protuberances which rise from said surfaces and approach each other so as to come into extreme proximity, said protuberances being arranged to form, on the screw being machined, a point of substantially conical configuration with the terminal thread on the point.

Further characteristics and advantages will be more apparent from the detailed description of a tool for machining screws comprising a thread with two starts of different depths, illustrated by way of non-limiting example in the accompanying drawings in which: Figure 1 shows the tool according to the invention, comprising a pair of flat chasers; Figure 2 is a section on the line ll-ll of Figure 1; Figure 3 is a section on the line Ill-Ill of Figure 1; Figure 4 is a section on the line IV-IV of Figure 1; Figure 5 is a diagrammatic view of the tool constituted by an annular part and a sector part; Figure 6 is a plan development of the annular part of Figure 5; Figure 7 is a plan development of the sector part of Figure 5; Figure 8 is a section on the line VIII-VIII of Figure 7; Figure 9 is a section on the line IX-IX of Figure 7;; Figure 10 is a section on the line X-X of Figure 7; Figure 11 is a diagrammatic view of the screw produced; and Figure 12 shows the screw point to an enlarged scale.

With reference to the said figures, the tool for producing screws comprising a thread with two starts of different depths, according to the invention, is constituted by a fixed part and a mobile part which respectively comprise a fixed flat chaser indicated by 1 and a mobile flat chaser indicated by 2, which on their opposing facing surfaces comprise a plurality of grooves for producing the two starts of different depths. More precisely, the grooves comprise grooves 3 for producing the start of greater depth, and grooves 4 for producing the start of lesser depth.

Advantageously, the grooves are formed in such a manner as to obtain uniform filling, for which purpose the cross-section of the groove 3 for forming the thread of greater depth has an angle between the sides of the groove at the entry end of the respective fixed and mobile plates 1 and 2 which is greater than the angle formed by the same groove at the exit end. This is done in order to provide uniform filling of the grooves, so as to obtain machining precision on the finished product.

The special characteristic of the tool according to the invention is the fact that a protuberance 10 is provided on the respective machining surfaces of the plates 1 and 2 towards their exit ends, this protuberance emerging laterally beyond the region initially comprising the grooves, and rising above the surface itself, so as to reach a position of extreme proximity to the surface provided on the facing part.

This variation in cross-section, which is better illustrated in Figures 3 and 4, makes it possible to form a screw 30 having a point 31 of conical configuration, this point being directly formed during the rolling for producing the thread on the screw.

Furthermore, both the start of greater depth 32 and the start of lesser depth 33 preferably die out at a point close to but spaced apart from the vertex of the conical point formed on the screw.

With reference to Figures 5 to 10, the tool according to the invention is constituted by a mobile part 20 of annular or roller configuration, and a fixed part 21 shaped as a circumferential sector.

As shown in Figures 6 and 7, the respective parts 20 and 21 are provided with grooves analogous to those described heretofore, and thus indicated with the same reference numerals. tlowever, preferably the part of annular configuration is provided with more than one set of grooves also having the same characteristics as heretofore described, and in parti cular comprising at their respective exit ends protu berances 10 which approach each other to reach a state of extreme proximity, so as to form said conical point-31 on a screw 30 comprising a thread with two starts of different depths, and which the terminal thread on the point.

With particular reference to Figures 11 and 12, the screw according to the invention, indicated overall by the reference numeral 30, is constituted by a shank 34 comprising at one end a head indicated by 35, which can be of any shape according to require ments.

At the opposite end to the head, the shank 34 defines a substantially conical point 31. The angle at the vertex, and consequently the length of the conical point 31, is made as small as possible so as to obtain a point of greater length, but obviously compatible with the necessary mechanical strength of the material constituting the screw.

Said shank 34 is provided with a thread with two starts of different depths, namely a first start 33 of lesser depth and a second start 32 of greater -depth than the first start 33.

Said starts 32 and 33 terminate at the point, and in this respect are formed such that they die out before the vertex of the conical point, such that as the screw is being -inserted into the material into which the screw is to be screwed, there do not arise two points of contact which, because of the rotation of the screw during its insertion, could create a moment by virtue of the two spaced-apart points of contact, which would tend to displace the point of application of the screw.

As shown in -detail in Figure 12, the second start 32 terminates in extreme proximityto the vertex of the conical point, but spaced apart therefrom so that the user is always certain that when pressing in the screwforthe purpose of screwing it down, only a single point will bite into the material, and thus no moment will arise which couldtend to displace the point of application of the screw.

The first start'33 terminates preferably, but not necessarily, at the major base of point Df concial configuration.

From.the aforegoing description, it can beseen that the invention attains the proposed objects, and in particular the fact of having provided said protu- berances on the respective fixed and mobile parts means that by means of a single machining operation, both the thread with two starts of different depths and conical pointwith terminal thread are obtained, so giving a product of improved quality and more acceptable to the user. In practice the materials used can be chosen at will according to requirements, provided they are compatible with the specific use, as can the dimensions and contingent shapes.

Claims

1. Atool for producing screws comprising a thread with two starts of different depths, comprising a fixed part and a mobile part which oppose each other, and which on their mutually facing surfaces comprise grooves for constructing the two starts of different depths, wherein at the mutual exit ends of said fixed part and said mobile part there are provided protuberances which rise from said surfaces and approach each other so as to come into extreme proximity, said protuberances being arranged to form, on the screw being machined, a point of substantially conical configuration with the terminal thread on the point.

2. Atool for producing screws comprising a thread with two starts of different depths, as claimed in the preceding Claim, wherein said protuberances emerge laterally from the longitudinal development of the region comprising the grooves provided on said mutually facing surfaces for forming said thread.

3. A tool for producing screws comprising a thread with two starts of different depths, as claimed inthe preceding Claims, wherein said fixed part and said mobile part are constituted respectively by a mobile flat chaser and a fixed flat chaser which face and oppose each other.

4. A tool for producing screws comprising a thread with two starts of different depths, as claimed in the preceding Claims, wherein said fixed part and said mobile part are constituted respectively by a fixed annular sector and a rotating annular element or roller comprising an outer surface conjugate with that surface of said fixed -sector which faces the lateral surface of said mobile annular element.

5. A screw comprising a thread with two starts and produced by the tool as claimed in the preceding Claims, comprising a shank which at one end defines the screw head and at the other end defines a point of substantially conical configuration, said shank being provided with a thread with two starts of different depths which terminate in proximity to said point.

6. A screw comprising a thread with two starts, as claimed in the preceding Claim, wherein one of said starts of said thread ends in extreme proximity to the vertex of said substantially conical point, while the other of said starts ends in proximity to the base of said substantially conical point.

7. A screw comprising a thread with two starts, as claimed in the preceding Claim. wherein the thread start of greater depth ends in proximity to the vertex of said point.

8. Atool for producing screws comprising a thread with two starts of different depths, substantially as herein described with reference to the accompanying drawings.

9. A screw comprising a thread with two starts, substantially as herein described with reference to the accompanying drawings.

10. Any novel element, or combination of elements, herein described and/or shown in the accompanying drawings, irrespective of whether the present Claim is within the scope of, or relates to the same invention as, any of the preceding Claims.