GB2087504A - Lock washer - Google Patents

Abstract

A lock washer has raised portions (2), with plateau-like tops (4) concavely curved to form scraper edges (5), formed on its annular surfaces. <IMAGE>

Description

SPECIFICATION A lock washer The present invention concerns a lock washer provided with annular side surfaces having raised portions and depressions.

Previously, lock washers of this kind have had on the annular side surfaces either a plurality of circular concentrically arranged grooves (see for example German GM 8002314) arranged close to one another and radially extending channels (see for example the leaflet of The Philadelphia Steel and Wire Corporation January 1977 page 18) or channels inclined or in a crossed arrangement extending over the annular side surfaces (see for example German GM 1814398). In all the constructions, it is common for toothiike or gridlike raised portions to be formed by the grooves or channels, having a substantially triangular cross-section the apices of which must dig into the pressure transmitting surfaces of the nuts, scres or base members for increasing the retaining forces against loosening by rotation.

Whereas the desired effect can be obtained with soft nut or bolt material, problems are produced with higher grade nut or bolt materials.

Thus, especially with high strength nut or bolt materials, the points or burrs of the raised portions on the lock washers are more or less squashed flat on tightening so that the desired effect of these points or burrs biting into the pressure transmitting surfaces of the nut or bolt is not achieved or only to a slight extent.

The result of this is a relatively low security against automatic loosening under dynamic loads transverse to the bolt axis. Thus, frequently more expensive and labour intensive security against automatic loosening has been recommended (for example bolts with ratchet teeth, adhesives or the like) especially with high strength bolts.

It is an object of the present invention to provide a lock washer provided with annular side surfaces of a completely novel structure which guarantees a greater security against loosening than with previous lock washers of this kind even with bolted connections of high strength material.

This object is achieved in accordance with the invention in that each of the raised portions has a plateau-like top the plateau surface of which is concavely curved at least in the circumferential direction of the lock washer for the formation of scraper edges in the region of the edges of the plateau.

With the spring ring of the type in accordance with the invention, points or burrs are not provided for digging into the respective adjacent pressure transmitting surfaces on tightening. Furthermore, only scraper edges are provided the effective edges of which cannot be squashed flat or truncated during a tightening operation due to the protective arrangement inthe region of the edges of the plateau. The result of this is that the sharpness and effectiveness of the scraper edges is not impaired by the tightening operation. Also, the opposing surfaces of the threaded connection are cleanly scraped by the scraper edges during a tightening operation so that they receive an increased frictional value against unscrewing.

Thus, not only does the resistance of the increased frictional force between the plateau surface and the counter surface on the threaded connection act against a torque in the unscrewing direction, but so does the scraping resistance of the scraper edges.

Experiments have shown that an improved retention against unscrewing is not only achieved with crude forms of lock washers in accordance with the invention but also with crudely lubricated forms provided with rust protective coatings.

Lock washers of the type in accordance with the invention are relatively cheap to produce. The new form prevents a notch effect with a higher danger of rupturing at the cross section of the material of the lock washer.

Advantageous further developments of a spring washer of the type in accordance with the invention are provided by claims 2 to 7.

In a preferred embodiment of the invention, the raised portions are made like an embankment. In this embodiment, these embankment-like raised portions extend in a straight line or on an arc from the inner edge to the outer edge of each annular side surface. Due to the arrangement of raised portions extending and returning in a circumferential direction and lying close to one another, a grid like structure with rhombic depressions between the embankment-like raised portions is produced. With this embodiment, the angle of the sloping region of the depression directly adjacent to the scraper edge is equal to or less than 144" with respect to the plateau area.

The height of the raised portions amounts to substantially a 1 50 ,um and the depth of curvature at the plateau like top amounts to at least 5 4m.

The pitch of the raised portions in a circumferential direction can amount to 0.5 to 1.0 mm, corresponding to a centre-to-centre value Ra = 10 - 25 ym, according to the desired area component of all the plateau areas to the entire area.

Experiments have shown that the arrangement in accordance with the invention is suitable both for lock washers according to B DIN 127 and for lock washers according to A DIN 128 as well as other standards for securing high strength screw threads.

For the further explanation and for the better understanding, an embodiment of the invention is described in detail in the following with reference to the accompanying drawings.

Figure 1 shows a partial plan view on an enlarged scale of a lock washer of the type in accordance with the invention; and Figure 2 shows a section on the plane Il-Il in Figure 1 likewise to an enlarged scale.

The partial section of a lock washer illustrated in the figures is provided with raised portions 2 and depressions 3 on each of its annular side surfaces 1.

As can be seen from Figure 1, the raised portions 2 in the present embodiment are made embankment-like wherein they extend arcuately from the inner edge to the outer edge of each annular side surface.

Since one respective row of the embankmentlike raised portions extends arcuately in a circumferential direction of the spring washer and the other row returns arcuately, a grid like pattern is produced in which the depressions 3 surrounded on all sides by raised portions have a substantially rhombic shape. A substantially triangular shape is provided for the respective depressions only partially surrounded by raised portions and opening respectively towards the inner edge or outer edge of the annular side surface.

As can be seen from Figure 2, the raised portions 2 have a substantially trapezoidal cross section. Moreover, the plateau like top of each raised portion is provided with a concavely curved plateau surface 4. In the present tested embodiment, the height of the raised portions amounts to approximately 150 ,rm and the depth curvature to approximately 20 ym.

Due to the concavely curved plateau area 4 and the trapezoidal cross section of the raised portions 2, scraper edges 5 are provided in the region of the edges of the plateau, the angle of which measured between the sloping region of the depression 3 directly adjacent to the scraper edge, and the plateau area 4 is in the present embodiment equal to or less than 1440.

If a lock washer fashioned in the described manner is inserted, for example, between a base member and a nut or bolt in the usual manner, then, due to their protected arrangement in the region of the edge of the plateau top 5 the raised portions, cannot be squeezed together, truncated or turned over during the tightening operation. The result is, that the sharpness and effectiveness of the scraper edges is not impaired by the tightening operation. Also during the tightening operation, the counter area of the threaded connection is scraped clean by the scraper edges so that it receives an increased degree of friction against unscrewing. Thus, not only does the resistance of the increased frictional force between the plateau area and the counter surface on the threaded connection act against a torque in the unscrewing direction but so does the scraping resistance of the scraper edges.

In other words: due to the scraping effect during tightening, the hard counter surface of the bolts or nuts is cleaned and embedded so that the degree of friction of the specifically smaller top of the raised portions is increased. Due to this effect, the tightening torque is increased in comparison to lock washers with smooth surfaces to a desired force on the threaded connection. However, a higher loosening torque at a ratio with respect to the tightening torque better than 0.8 during static tests is produced automatically. Tests have shown that with metric threads the loosening torque using spring washers in accordance with the invention is equal to or greater than 80% of the tightening torque. When using normal lock washers, this value normally lies below 8G%.

During dynamic tests with a screw connection vibration test stand unscrewing torques were produced after 3000 load changes which were in the ratio of 0.9 to 1.75 with respect to the tightening torque depending on the surface protective arrangement and variations in the height of the raised portions and indeed with screws of efficiencies 8.8 and 1 0.9.

For pre-stressing forces N according to VDl 2230/77 Table 1 below 0.125 yG, clamping torques Nm below MK 0.16 were encountered.

This corresponds to an increase in tightening torque by 15%.

Claims (12)

1. A lock washer having annular side surfaces provided with raised portions and depressions, characterised in that, each of the raised portions has a plateau-like top the plateau surface of which is concavely curved in cross section at least in the peripheral direction of the lock washer for the formation of scraper edges in the region of the edges of the plateau.

2. A lock washer according to claim 1, characterised in that, the area component of all the plateau areas on one annular side amounts to at least 35% to 55% of the total annular side surface.

3. A lock washer according to claim 1, characterised in that, the angle of the sloping region of the depression directly adjacent to the scraper edge is equal to or less than 1440 with respect to the plateau area.

4. A lock washer according to claim 1, characterised in that, the height of the raised portions amounts to between 90 ,um and 1 50 ym but is not greater than 5% of the thickness of the washer.

5. A lock washer according to claim 2, characterised in that, the pitch of the raised portions in the circumferential direction amounts to substantially 0.5 to 1.0 mm corresponsing to a rough centre-to-centre value Ra = 1 0-25 ,um.

6. A lock washer according to claim 1, characterised in that, the depth of the curvature of the plateau area amounts to at least 5 ,um.

7. A lock washer according to one or more of the preceding claims, characterised in that, the cross section of the raised portions in the upper region of the circumferential direction and in a radial direction is substantially rectangular and/or trapezoidal.

8. A lock washer according to one or more of the preceding claims, characterised in that, the raised portions are made like embankments and extend from the inner edge to the outer edge of each annular side surface.

9. A lock washer according to claim 8, characterised in that, the embankment-like raised portion include an angle of clearly less or more than 900 with respect to a tangent to the washer.

10. A lock washer according to claim 8, characterised in that, the embankment-like raised portions extend in straight line or in an arc.

11. A lock washer according to claim 9 or 10, characterised in that, the embankment-like raised portions cross in the form of a grid.

12. A lock washer substantially as herein described with reference to the accompanying drawings.