GB2068494A

GB2068494A - Spring washers

Info

Publication number: GB2068494A
Application number: GB8102711A
Authority: GB
Original assignee: HEDTMANN WILHELM KG
Current assignee: HEDTMANN WILHELM KG
Priority date: 1980-01-30
Filing date: 1981-01-29
Publication date: 1981-08-12
Also published as: NL8100341A; GB2068494B; ES498772A0; SE449907B; ATA595780A; ES8201696A1; SE8100463L; AT377836B; IT8119158A0; CH651116A5; IT1135056B; FR2481767B1; NL187868C; FR2481767A1

Abstract

A spring washer comprises an upper and a lower operative face and tooth-like projections on those faces. The projections may extend at an angle to the respective radius of the washer, such as extending helically. A method of making the spring washer comprises rolling or drawing a circular cross-section wire of spring steel, bronze or stainless steel into a wire of trapezoidal cross-section, forming the narrow face (1) into a concave, or a peaked shape, rolling or stamping the non-parallel faces (2) with projections, and finally bending the wire into a ring shape, with the concave, or peaked face innermost to form a ring-shaped spring washer. During bending the work is supported on the narrow concave or peaked face, avoiding deformation of the ridged operative faces. <IMAGE>

Description

SPECIFICATION Spring washers The invention relates to spring washers. Known spring washers are standardised, for example, in DIN 127, 128,7980 and/or 43699. They are usually made of spring steel and are used as locking elements for locking screws, nuts or bolts etc. against rotation.

However, their locking effect is limited as they tend to work loose and to twist off. Vibration tests have proved that neither spring washers, toothed discs, fan discs, retaining plates nor castellated nuts with split pins in combination with tempered screws are suitable as locking elements.

Spring washers conventionally have smooth surfaces and are consequently subjected, during loading, to movement relative to screws, nuts and/or workpieces, said relative movement leading to loosening of the connection. Toothed discs, that is to say closed annular discs which are thin-walled and are not resilient, are stamped out of steels of lower strength than spring steel and are not comparable with spring washers in their effect. Fan discs, that is to say annularly closed discs with notched, bent, radial spring lugs can be made only from very thin material and are therefore not suitable for locking screws.

Other known locking elements comprise screws which have a toothed undersurface to their head.

However, these have the fundamental disadvantage that a high degree of hardening of this toothed face or of the rest of the screw is not possible, since the tooth faces would tend to break off.

In conclusion, it may be established that none of the known elements for locking screws against rotation meet the requirements fully. Either there is provided a spring washer of thick cross-section with smooth contact faces which cannot be made grippable by economically viable means (stamping or the like) or a toothed disc can be used, which, though having grippabie contact faces, is not resilient and does not have a sufficient crosssectional thickness, or fan discs are used, which, although they are resilient in parts, can have only very thin cross-sections and, consequently, are not sufficiently prestressable, or, finally, screws with toothing on the underside of the head can be used, but spring steel cannot be employed with economic justification as starting material and, consequently, sacrificing strength of the teeth and a good spring force.

It is an object of the present invention to provide a spring washer which acts as a good locking element for screws, bolts etc.

According to one aspect of the invention there ic provided a spring washer comprising an upper and a lower, operative, face and tooth-like projections provided on the upper and lower faces.

The projections are suitably regularly spaced over the operative faces and each projection may extend at an angle to the respective radius of the washer, such as being helically extending.

Alternatively, the projections may be disposed on the faces in a reticular pattern.

The radially inner face of the washer may be concave, since, if the washer is to be formed from a wire into an annulus, the operative faces having the projections ought not to bear against the forming tool since this could damage the projections, so that the concave inner face serves to centre and guide the wire on the forming tool.

The tooth may be sharp-edged and/or undercut.

In another embodiment, the projections on the upper and lower operative faces comprise a plurality of circularly extending concentric corrugations, the ridges of which project above the said faces and the grooves of which are recessed below the faces, and impressed into the said operative faces are radially extending channels spaced a short distance from one another, the channels reducing the height of the ridges at least as far back as the said faces. The ridges may project approximately 0.15 mm above the operative faces, while the grooves are not recessed below these faces by the same amount.

According to a further aspect of the invention there is provided a method of making a spring washer according to said one aspect of the invention, the method comprising forming the projections on the surface of elongate stock material, then bending the stock material into a ring and cutting off the washer from the rest of the elongate stock material.

Suitably, the cross-section of the elongate stock material is profiled, and the teeth formed thereon, by rolling.

Alternatively the cross-section of the stock material is profiled by rolling and the teeth are formed thereon by intermittent stamping.

Preferably, in such a method, wire made of spring steel of circular cross-section is profiled into wire having a substantially symmetrical trapezoidal cross-section forming, on the two opposite, non-parallel faces of the wire of trapezoidal cross-section, longitudinal corrugations, the ridges of which project above the said two faces of the wire and the grooves of which are recessed relative to these faces, shaping, simultaneously or in a subsequent step, the narrow face of the trapezoidal wire into two mutually angled surfaces intersecting in a circularly extending peak, thus providing the narrow face with a cross-section which is substantially the two equal length sides of an isosceles triangle, pressing into the two opposite, non-parallel faces transverse, parallel channels spaced a short distance from one another, at least the ridges of the longitudinal corrugations. being pressed back where the channels are, bending the wire into the shape of a ring, the narrow face of the trapezoidal wire becoming innermost on bending so that the wire becomes of rectangular cross-section, during bending the wire being supported and guided on the two surfaces forming the narrow face of the wire and supported and guided on the outer face of the wire, the outer face being that opposite the narrow face, and cutting the wire to length.

In such a method, suitably the forming of the corrugations and shaping of the narrow face of the wire are effected in a common drawing operation.

The channels are suitably impressed only as far as the original side faces of the wire, so that the core material merely undergoes a slight deformation. In this way, the ridges of the corrugations are broken into short lengths, preferably regularly, so that short ridges form in sections.

A hardened spring washer, in accordance with the invention and consisting of spring steel, has projedting peaks of a short length and width which have a suitable hardness, corresponding to the hardened spring steel, to guarantee an intimate contact between the underside of the screw head or the nut and the workpiece. The pre-stressing force- is available because of the spring action of the spring washer and is adjustable.

This prestressing force is also maintained during loading, since automatic twisting of the spring washer is prevented by the peaks of the grooves.

It is absolutely essential to provide corrugations which project, so that the channels are impressible transversely to the longitudinal direction of the corrugations with an economical expenditure of force. By means of the ridges of the corrugations, and form lock can be achieved, in addition to the force-locking connection, since the relatively softer material of the workpiece or of the screw or nut is plastically deformable by the ridges.

A feature which is advantageous for the manufacture of the spring washer is that the narrow face of the wire is peaked, so that it has an approximately triangular face in cross-section.

Thus during the bending of the wire the narrow face of the trapezium which will later constitute the inner face, or, of the spring washer, and the face opposite thereto can be guided on the forming tool, so as not to damage the corrugations and/or channels.

The finished spring washer may then be hardened in a known way.

Since the spring steel wire frequently has, in its state as supplied, a marginal decarburisation of up to 0.2 mm, as a result of which places of varying softness occur in the teeth, the finished spring rings are recarburised, so that a uniform strenth is obtained into the very peaks of the teeth.

The final product thus obtained is pre eminently suitable as a lock against screw, bolt etc. rotation and its production can be carried out very economically and efficiently.

Embodiments of the present invention will now be described, by way of example, only and with reference to the accompanying drawings, in which: Figures 1 to 4 illustrate successive stages in a method of making a spring washer according to the invention; Figure 5 shows a plan veiw of a spring washer according to the invention; Figure 6 shows a side elevation of the spring washer shown in Figure 1; Figure 7 to 12 illustrates successive stages in a method of making an alternative embodiment of a spring washer according to the invention, Figure 11 showing a longitudinal section along the line Xl Xl in Figure 10; Figure 13 shows a plan view of a spring washer made by the method illustrated by Figures 7 to 12; Figure 14 shows a side elevation of the spring washer of Figure 13; and Figure 1 5 shows a view of a two-layer spring washer.

Starting from a metal wire of round cross section (Figure 1), an approximately trapezoidal profile is produced (Figure 2), for example by drawing or rolling. If the finished spring washer is to have a rectangular cross sectional form, the initial trapezoidal profiling is conventional and necessary.

The profiled wire is further shaped, for example in a further drawing or rolling operation, so that the narrow face 1 of the wire of trapezoidal cross section is concave. This will eventually form the inner surface of the spring washer. The concave face 1 could instead be made simultaneously with the profiling of the wire to give it the trapezoidal cross-section.

The two opposite, non-parallel faces 2 of the wire of trapezoidal cross-section are then toothed.

These faces will form the upper and the lower faces, i.e. the operative faces, of the spring washer. The toothed faces 2 are formed either by rolling continuously or by stamping intermittently to form diagonal teeth (Figure 4) or teeth arranged in a reticular pattern (Figure 5).

The shaped and toothed wire is introduced into a forming tool which forms and separates the spring washer from the wire in a known way. The separating operation can be carried out by cutting and is done optionally simultaneously with the above mentioned stamping operation forforming g toothed faces 2. The wire is guided in the forming tool, as shown schematically in Figure 4, by means of two guides 3, 4, which, without damaging the toothed faces of the washer, engage the concave face 1 and that face of the wire opposite thereto, i.e. the outer face.

A finished spring washer is shown in Figures 5 and 6. A spring washer with the teeth of the toothed faces 2 being disposed in a recticular pattern is shown in Figure 5. The toothed faces 2 can have rounded teeth, but preferably have sharp-edged teeth. It is because of the operative faces of the spring washer i.e. its upper and lower faces being toothed that the spring washer is suitable as an element for locking a screw against rotational movement.

The spring washer according to the invention can be made of any suitable material.

Starting from a wire of round cross-section and made of spring steel (Figure 7), an approximately trapezoidal profile is first made (Figure 8) by means of a drawing operation. This procedure is known and ensures that the finished spring washer will have a rectangular cross-section.

Of course, during the shaping of the wire to form a spring washer, the inner face is compressed and the outer face stretched, so that, in fact, the wire forming the final washer has a rectangular crosssection. The trapezoidal profile (Figure 8) is shaped, preferably in a further drawing operation, so that the previously narrow face 11 of the wire of trapezoidal cross-sections is formed into a peaked face 12 which is triangular in crosssection, while continuous longitudinal corrugations 13, in the preferred embodiment three such corrugations 1 3, per face, are formed on the two opposite, non-parallel side faces of the wire of trapezoidal cross-section.To give an idea of the sizes concerned, it may mentioned that, for a wire having trapezoidal cross-section dimensions as follows: centre length, i.e. width between the non-parallel sides taken mid-way between the parallel sides, of 2 mm, a base side, i.e. longer parallel side, of length 2.22 mm, a top side, i.e. shorter parallel side, of length 1.92 mm and a height i.e. spacing between the parallel sides, of 3.42 mm, the ridges 14 of the corrugations project by 0.15 mm above the core, or original side face of the trapezium, while the grooves 1 5 are not set back by the same amount, but are plane-parallel. The corrugation spacing is 0.7 mm in this case and the radius between the ridges 14 and grooves 1 5 is 0.3 mm.

If the wire is profiled as shown in Figure 9, the wire runs through a tool which impresses into the profiled side faces transversely extending channels 1 6 which are spaced and close to one another, for example 0.3 mm, and which cut the ridges 14 of the corrugations 1 3 at least as far back as the core level, preferably rather deeper in the case of simultaneous channel formation in the core.

The wire thus ready-profiled is introduced into a forming tool which forms and separates the spring washer from the rest of the wire in a conventional way.

A particular feature of this tool is that, as illustrated schematically in Figure 12, three guides 17, 18, 19 are provided, which, without being able to crush the profiled side faces, engage on the inner face 12 and the outer side.

The finished hardened spring washer is shown in Figures 13 and 14.

Here, the corrugations 13 extend in concentric circles and the channels 1 6 in a radial direction.

Figure 1 5 illustrates a double spring washer which is also according to the invention, and comprises two helical turns.

Claims

1. A spring washer comprising an upper and a lower, operative, face and tooth-like projections provided on the upper and lower faces.

2. A spring washer as claimed in Claim 1, in which the projections are regularly spaced over the operative faces.

3. A spring washer as claimed in Claim 1 or Claim 2, in which the projections extend across the said faces, each projection being disposed at an angle to the respective radius of the spring washer.

4. A spring washer as claimed in any of the preceding claims, in which the projections extend helically across the operative faces.

5. A spring washer as claimed in Claim 1 or Claim 2, in which the projections are disposed on the faces in a reticular pattern.

6. A spring washer as claimed in any of the preceding claims, comprising a radially inner face which is concave.

7. A spring washer as claimed in any of the preceding claims, in which the projections have sharp edges.

8. A spring washer as claimed in any of the preceding claims, in which the projections are undercut.

9. A spring washer as claimed in any of Claims 1 to 3, in which the projections on the upper and lower, operative, faces comprise a plurality of circularly extending concentric corrugations, the ridges of which project above the said faces and the grooves of which are recessed below the faces, and impressed into the said operative faces are radially extending channels spaced a short distance from one andther, the channels reducing the height of the ridges at least as far back as the said faces.

10. A spring washer as claimed in Claim 9, comprising a radially inner face which comprises two mutualiy angled surfaces intersecting in a circularly extending peak.

11. A spring washer as claimed in Claim 9 or 10, in which the ridges of the corrugations project approximately 0.15 mm above the operative faces and the grooves are not recessed below the operative faces by the same amount.

12. A spring washer as claimed in any of the preceding claims, in which the spring washer is made from spring steel, bronze or stainless steel.

13. A method of making a spring washer as claimed in any of Claims 1 to 12, comprising forming the projections on the surface of elongate stock material, then bending the stock material into a ring and cutting off the washer from the rest of the elongate stock material.

14. A method as claimed in Claim 13, in which the cross-section of the elongate stock material is profiled, and the teeth formed thereon, by rolling.

1 5. A method as claimed in Claim 13, in which the cross-section of the stock material is profiled by rolling and the teeth are formed thereon by intermittent stamping.

1 6. A method of making a spring washer as claimed in any of Claims 9 to 11, wherein wire made of spring steel of circular cross-section is profiled into wire having a substantially symmetrical trapezoidal cross-section, forming on the two opposite, non-parallel faces of the wire of trapezoidal cross-section, longitudinal corrugations, the ridges of which project above the said two faces of the wire and the grooves of which are recessed relative to these faces, shaping simultaneously or in a subsequent step, the narrow face of the trapezoidal wire into two mutually angled surfaces intersecting in a circularly extending peak, thus providing the narrow face with a cross-section with is substantially the two equal length sides of an isosceles triangle, pressing into the two opposite, non-parallel faces transverse parallel channels spaced a short distance from one another, at least the ridges of the longitudinal corrugations being pressed back where the channels are, bending the wire into the shape of a ring, the narrow face of the trapezoidal wire becoming innermost on bending so that the wire becomes of rectangular cross-section, during bending the wire being supported and guided on the two surfaces forming the narrow face of the wire and supported and guided on the outer face of the wire, the outer face being that opposite the narrow face, and cutting the wire to length.

17. A method as claimed in Claim 16, in which forming of the corrugations and shaping of the narrow face of the wire are effected in a common drawing operation.

1 8. A spring washer substantially as hereinbefore described, with reference to and as illustrated in the accompanying drawings.

19. A method of making a spring washer substantially as hereinbefore described, with reference to and as illustrated in the accompanying drawings.