Technical field

The present application relates to a lock washer adapted to be used with a bolt and nut arrangement.

Background

Washers are normally used for distributing the load of a threaded fastener, such as a screw or nut. Loosening of bolts and nuts is a known problem, especially when subjected to vibration. To prevent such loosening washers having locking effect are used between the bolt and/or nut and the workpiece. A test, called Junker test, is a mechanical test to determine the point at which a bolted joint loses its preload when subjected to shear loading caused by transverse vibration. The Junker Test is the established method used for analyzing the self-loosening behavior of secured and unsecured threaded fasteners under transverse loading conditions by vibration testing, test methodology is described in international standard DIN 25201 (-4).

A known locking system, known as Nord-Lock washers, comprises a pair of washers that have cams on one side and radial teeth on the opposite side. The cam angle is greater than the thread pitch, thereby a wedge effect is created by the cams, preventing the bolt from rotating loose. Several different designs of the Nord-Lock type washers are known, all of which have the same basic function, variations of such locking washers are described in US 4134438 and US 2014/0377032.

There are some disadvantages related to the Nord-Lock system as this type of washer must be used in pairs to provide a working arrangement. Thus, there is a risk of incorrect positioning of the lock washer pair during assembly of these types of fasteners. The opposing cam surfaces must be positioned correctly for locking engagement, and wrongly positioning of a lock washer relative to the associated cam surface of another washer may prevent the locking effect, thus allowing the fastener to loosen and separate from the work piece.

US 4377361 discloses a reversible lock washer having oppositely disposed cam surfaces adapted for use in combination with a threaded fastener. However this lock washer is not universal as it has to be used in combination with a fastener having at least one matching cam surface. Other known methods for securing bolt and nut are chemical locking means. There are some disadvantages related to these locking methods e.g. that it is not possible to optically observe that the product functions and it may be affected by chemicals. Thus the use of a chemical locking system may be associated with uncertainty in some applications.

The present invention provides a reversible lock washer having a locking effect between a fastener, such as a bolt and nut, and the workpiece or connecting part. The present lock washer is essentially symmetrically formed, thus the lock washer can be randomly positioned and the risk of incorrect mounting is essentially eliminated. The inventive lock washer is universal and can be used with any type of bolt and nut assembly.

Further, the present lock washer is not influenced by chemicals. In demanding environments the lock washer may be manufactured in materials withstanding such conditions, while maintaining the locking effect.

These and other advantages with the present invention will become evident in the following description.

Summary of invention

The present invention is defined in the accompanying claim 1.

According to the present invention a lock washer adapted for use with a bolt and nut arrangement is provided, the lock washer comprises an annular shaped washer body having a central opening therein, defining an inner peripheral edge and an outer peripheral edge, and oppositely arranged engaging surfaces, wherein the height of the inner peripheral edge and the height of the outer peripheral edge differs, and the highest of the peripheral edge is provided with a circumferential slot, thereby defining two essentially equally shaped lips, which provide an axial force when loaded by the tightening of the bolt and/or nut.

The annular shaped washer body is essentially symmetrical around a horizontal plane.

The annular shaped washer body is produced as a one piece product in solid material.

The cross-section of the washer body (cross-section of half the lock washer body, from the inner peripheral edge to the outer peripheral edge) has a tapered shape defined by the two oppositely arranged engaging surfaces, where the two oppositely engaging surface are inclined relative to the horizontal plane, and the inner peripheral edge and the outer peripheral edge, where the inner peripheral edge and the outer peripheral edge are essentially vertical relative to the horizontal plane.

The shape of the slot in the cross-section of the washer body has essentially a V-shape, the V-shape of the slot is defined by two sidewalls, where the sidewalls are inclined relative to the horizontal plane, and extends into the washer body in a distance from the highest peripheral edge.

In an embodiment the outer peripheral edge is higher than the inner peripheral edge. In another embodiment the inner peripheral edge is higher than the outer peripheral edge. The highest peripheral edge may be from 2-30 % higher than the lowest peripheral edge. The height difference may in some embodiments be 5-20 %, for instance 5-15 %. In an embodiment the height difference is about 10 %.

The two lips defined by the slot and the two oppositely arranged engaging surfaces are elastically deformable in order to be compressed and forced towards each other when the lock washer is loaded by tensioning the nut and/or bolt. The compression of the two lips results in an axial spring force between a workpiece and the bolt and/or nut, providing a locking effect.

In an embodiment at least one of the oppositely arranged engaging surfaces is provided with friction means. The friction means may be radial protrusions or grooves in the engaging surfaces. The protrusions may be serrate/saw shaped, cam shaped, wave shaped, tooth shaped or ridges. In another embodiment both engaging surfaces are provided with a plurality of said friction means. The plurality of friction means should be essentially equally spaced.

The locking washer can be made from a material chosen from the group; metals, metal alloys, plastic materials, ceramic materials and composite materials. The metal may be chosen from the group; a steel alloy, a stainless steel alloy, a duplex stainless steel alloy, a spring steel alloy, an aluminium alloy, a bronze alloy, a brass alloy, titanium, nickel or any metal or suitable alloy.

In an embodiment the outer diameter of the locking washer (engagement surface) corresponds to the diameter of the loading surface of the associated bolt head or nut. The locking washer is universal and may be adapted for use with any dimensions of bolt and/or nut, which may be according to the DIN 938 standard, DIN 125, ISO 7089 or any other standards for such fasteners.

Brief description of drawings

Figure 1 Illustrates a planar view the lock washer annular body.

Figure 2 Illustrates a vertical cross section through the center of the lock washer. Figure 3 Illustrates a side view of the lock washer.

Figure 4 Illustrates a vertical cross section of the lock washer through A-B.

Figure 5 Illustrates a vertical cross section of the lock washer through A-B without any tension force.

Figure 6: Illustrates a vertical cross section of the lock washer through A-B under tensioning, by e.g. a not shown tightened bolt and nut assembly.

Figure 7: Illustrates a different embodiment of the lock washer.

Figure 8: Shows an embodiment of the lock washer having friction means on the engagement surfaces.

Figure 9: Shows another type of friction means.

Figure 10: Illustrates different profiles of the friction means on the engagement surface.

Detailed description

Referring to FIG. 1-5, it is illustrated a locking washer generally indicated 1, which is adapted for use with a bolt and nut fastener arrangement (not shown). The locking washer comprises an annular shaped washer body 2 having a central opening, and oppositely arranged engaging surfaces 7, T generally facing/engaging a bolt, nut or a workpiece when in use. The thickness/height C of the inner peripheral edge 5 and the thickness/height D of the outer peripheral edge 6 differ such that the cross-section of the washer body (half washer body) shows a tapered form. The cross-section of the annular body thus shows a symmetrical tapered form which is of concave or convex type. The thickest/highest of the peripheral edges is provided with a circumferential slot 4, thereby defining two lips 8, 8' . The two lips 8, 8' are essentially equally shaped. The annular shaped body 2 is essentially symmetrical around a horizontal plane (illustrated by the dashed line in FIG. 2), and the circumferential slot 4 is located in the symmetrical plane. See also FIG. 3, which illustrates a side view of the lock washer.

Throughout the description and in the claims the term essential, e.g. essential symmetrical and essentially equally shaped, should be understood as including deviations from the exact meaning of these terms (e.g. exact symmetrical and exact equally shaped), which may rise during the manufacture process.

In the present context the terms "locking washer" and "lock washer" are used interchangeably, both of which should be understood as denoting the present invention. The lock washer according to the present invention may also be referred to as a "locking spring washer" or a "spring washer", as an axial spring force is generated when the lock washer is loaded by a tensioning force. All of the aforementioned terms should be considered to denote the present invention unless it is explicitly stated otherwise.

In the present context the term "slot" should be understood to include the terms "groove", "cut" and "slit", all of which should be understood as denoting the circumferential slot 4.

In the present text we have used the terms "height" and "thickness" interchangeably when describing the structural design of the locking washer. Both of the aforementioned terms should be considered to have the same meaning unless it is explicitly stated otherwise.

The differentiated height between the inner peripheral edge 5 and the outer peripheral edge 6, and the circumferential slot 4 extending a distance E into the washer body 2 from the highest peripheral edge, thereby defining two lips 8, 8' on either side of the slot 4, have the effect that when the bolt is tightened the lips 8, 8' are compressed towards each other, and thereby creating an axial spring force, illustrated in FIG. 6. The axial force created by the lock washer when tightening the bolt provides a tensioning force between the bolt/nut fastening assembly and the workpiece, thus giving a spring locking effect which prevents loosening of the bolt and/or nut due to e.g. vibrations. The applied load on the lock washer when the bolt and/or nut is tightened must be less than the yield point of the annular washer structure, i.e. below the upper limit of forces that can be applied without permanent deforming the washer structure. By maintaining the tensioning force on the washer lower than the yield point, i.e. in the elastically deforming range, the axial spring force will be sustained, providing a locking and secure fastening of the bolt and nut arrangement.

The axial force created by the loading of the lock washer depends on e.g. the depth E and width G of the slot 4, the thickness F of the lips 8, 8', the height difference (Ηι+Η ₂ ) between the inner and outer peripheral edges, the material in which the locking washer is produced and the compression force provided by the tightening of the bolt and/or nut. The slot 4 in the peripheral edge may extend into the washer body 2 up to about 80% of the distance A-B (shown as distance E) between the inner peripheral edge 5 and the outer peripheral edge 6. In some embodiments the distance E of the slot 4 is up to 70% of the distance A-B, for instance up to 60% or 50 %. In some embodiments the depth of the slot 4 is even less, e.g. 40 % or 30 % of the distance A-B. In order to provide a sufficient axial spring force by the compression of the two lips 8, 8', the slot 4 should not be too shallow. Therefore the distance E should be at least 20 % into the washer body 2. The part of the washer body which is not provided with the slot is solid material.

As seen in e.g. FIG. 2, 4 and 5, which illustrates a vertical cross-section 3 of the washer body 2 through A-B, the side walls of the slot 4 are inclined defining a slight tapered profile of the slot 4. The slot 4 illustrated in the drawings is V-shaped, having an essential acute angle a in the inner end of the slot 4 (see FIG. 5). By essential acute angle it should be noted that the point where the inclined sidewalls of the slot 4 meets in the innermost end of the slot, may have a slight roundness due to the production process. However, the profile of the slot is essential V-shaped, which should be considered to be different from e.g. a U-shaped profile. The width of the slot opening (distance G) in the peripheral edge is larger than the height difference (Hi + H ₂ ) between the outer peripheral edge 6 and the inner peripheral edge 5. This feature is achieved by forming the sidewalls of the slot 4 with a higher inclination angle compared to the inclination angle of the engaging surfaces 7, 7' . In the preferred embodiment, the lock washer is essentially symmetrical about a horizontal plane, and Hi will be equal to H ₂ .

Referring to FIG. 6, which depicts the locking washer loaded by tensioning a bolt and/or nut (not shown), it is illustrated by the broken lines that the tensioning force, by the action of tightening the bolt and/or nut, causes the two lips 8, 8' to be compressed towards each other. This is further illustrated by a smaller angle α', a smaller width of the slot opening (distance G') and a smaller peripheral edge height D' . As the lock washer is compressed by the tightening of the bolt/nut, the height difference (H'i+H' ₂ ) will become less compared to the unloaded state. In some embodiments the height D' will be close to the height C, thus the washer takes a more flat structure without being permanently deformed, but it should be noted that the height D' should always be larger than the height C. Due to the tapered form of the lock washer and the non-flexible solid part of the lock washer, which is not bent by the tensioning force, a small space is created into which the steel (or other material) of the bolt and/or nut and/or workpiece will be pulled/drawn by the tensioning force created when the bolt and/or nut is tightened. This force which elastically deforms the material pulled into the said space provides an additional locking force of the loch washer to the workpiece and bolt/nut. As described above, the compression of lips 8, 8' generates an axial force acting upon the bolt and/or nut and the workpiece in a locking manner.

FIG. 1-6 and 8 illustrate an embodiment of the lock washer wherein the outer peripheral edge is higher than the inner peripheral edge, thus in this embodiment the slot 4 is provided in the outer peripheral edge. The height difference (Hi + ¾) between the outer peripheral edge and the inner peripheral edge may be from 2-30 %. The proper height difference will depend on e.g. the flexibility and hardness of the material, as well as the desired axial spring force in a specific application of the lock washer. A flexible material like e.g. plastic or a soft metal will tolerate a larger height difference, compared to a hard material with lower flexibility.

The slot 4 may be formed either in the outer peripheral edge 6 or in the inner peripheral edge 5. In FIG. 7 an embodiment is shown wherein the inner peripheral edge is higher than the outer peripheral edge. Thus in the embodiment illustrated in FIG. 7 the slot 4 is located in the circumference of the inner peripheral edge 5. This embodiment works the same way as the ones described above where the circumferential slot is provided in the outer peripheral edge, thus the above described embodiments with regards to dimensions of the lock washer, depth of slot and height differences also applies for the embodiment shown in FIG. 7.

One or both of the engaging surfaces 7,7' may be provided with friction means. The frictions means may be radial protrusions formed on the engaging surfaces 7,7' . The protrusions on the opposing engagement surfaces 7,7' may be serrate shaped, saw tooth shaped, cam shaped, wave shaped, tooth shaped, or similar, generally illustrated in FIG. 10. The friction means may also be formed by providing radial grooves in the surface. The examples of shapes/profiles shown in FIG. 10 should only be considered as illustrative and not be regarded as limiting for the invention. The actual shape of the friction means may vary widely within the generally illustrated shapes. It should also be noted that the friction means may have other shapes/profiles. The friction means should be equally spaced on the engaging surface. As an axial spring force is generated by the two lips 8, 8' when the lock washer is loaded by the fastener means, e.g. bolt and nut, the friction means will bite into the associated surface, e.g. bolt head, nut and/or surface member on work piece. The friction means together with the axial force from the compressed lips 8, 8' provide a continuing locking action of the fastening assembly by effectively resisting turning of the bolt and/or nut. FIG. 8 shows an embodiment wherein the lock washer has friction means on the opposing engagement surfaces 7, 7' . FIG. 9 shows friction means having a saw tooth shape. It should be noted that the friction means are not mandatory for achieving a spring locking effect by the use of the present lock washer.

The lock washer according to the present invention may be produced in a wide range of materials from metals, plastic materials, ceramic materials and composite materials, e.g. ceramic matrix composites (CMCs), metal composites, plastic composites, ceramic- metal composites etc. The above materials may generally have different properties in strengths/hardness, brittleness, corrosion resistance, galvanic corrosion, ductility, etc. In addition, some materials may have coatings or platings to enhance e.g. corrosion resistance. Metals suitable for the present lock washer may be selected among the metals commonly used for fasteners such as bolts, screws, nuts and washers. Such metals range from common steel to titanium, and to other metals and metal alloys like aluminium, bronze alloys or brass alloys.

Steel is in general the most common fastener material. Steel may have various surface treatments such as zinc plating, galvanization and chrome plating. Steel fasteners are commonly available in different grades, referring to type of alloy and properties (e.g. hardness, strength, corrosion resistance). In demanding or special application of the lock washer stainless steel or other suitable metal or alloy may be required, e.g. duplex stainless steel, silicon bronze, brass, titanium or aluminium. The metal for the manufacture of the present lock washer may generally be chosen from the group consisting of a steel alloy, a stainless steel alloy, a duplex stainless steel alloy, a spring steel alloy, an aluminium alloy, a bronze alloy and a brass alloy. It should be noted that other metals and alloys may also be used in the manufacture of the lock washer, e.g. titanium, nickel and the alloys of such metals.

In some applications the washer must be manufactured in a material having relatively low hardness. Such material requirement may arise when joining work pieces of easily deformable material, like soft metals or plastic materials. In applications involving high temperature or special corrosive conditions lock washer manufactured of ceramic or composite material may be required. The present lock washer may be manufactured by cold forming processes. Cold forming is a common term for metal working products, e.g. steel, into semi-finished or finished goods at relatively low temperatures. The cold forming method allows a high production rate at a relative low cost. Cold formed goods are manufactured by working metal billet, bar or sheet using stamping, machining, rolling, cutting, forging or pressing forming it into a product. The present lock washer may also be produced by additive manufacturing methods.

The methods for manufacturing the present lock washer in plastic, ceramic or composite materials may include cutting, stamping, machining, grinding, additive manufacturing, casting and moulding technics, drilling and other known forming methods for such materials.

Having described preferred embodiments of the invention it will be apparent to those skilled in the art that other embodiments incorporating the concepts may be used. These and other examples of the invention illustrated above and in the accompanying drawings are intended by way of example only and the actual scope of the invention is to be determined from the following claims.