Lock washer

Corrosion, loosening, safety and reusability problems incurred with prior art lock washers are eliminated in a lock washer having a planar washer body (6) formed of a thin sheet of resilient metal. A central aperture (12) is located in the body (6) and is adapted to receive the shank (24) of a bolt which a nut (22) is to be attached and locked. A lock fold (8) is formed in the body (6) radially outward of the central aperture (12). The lock fold (8) has a radially inward facing curved edge (18) displaced to one side of the plane of the body (6). The edge (18) is transverse to the radius of the body (6) and a lock fold (8) resiliently, lockingly engages with a flat of the nut.

FIELD OF THE INVENTION 
This invention relates to a lock washer, and more particularly, to a lock 
washer that will positively retain a nut, is not susceptible to corrosion 
problems, omits a free edge that can get caught on clothing and be 
permanently deformed, and which is readily releasable as well as reusable. 
BACKGROUND OF THE INVENTION 
Lock washers are commonly used in many different fields. As a consequence, 
there are large varieties of lock washer configurations that have evolved 
over the years for use in specific environments. Many have detriments of 
one sort or another associated with their use. 
For example, it is not unusual to provide lock washers that include a sharp 
edge or point displaced from the body of the washer so as to dig in or 
gouge one or both of the nut that is being locked and the surface to which 
the nut is applied. While these types of lock washers work well for their 
intended purpose in many environments, they are not satisfactory where 
corrosion presents a problem. More particularly, where such lock washers 
are used after a protective coating has been applied to one or the other 
of the components to be joined, the gouging action provided by the sharp 
edge will always penetrate the coating if a good locked joint is to be 
obtained. As a result, the protective coating is no longer continuous and 
moisture or other corrosive substances may penetrate the joint with 
corrosion resulting. 
Other lock washers include lock tabs which are displaced from the plane of 
the body of the washer and which have flat, free edges which are adapted 
to abut a flat of the nut to be locked. See, for example, U.S. Pat. No. 
1,349,404 issued Aug. 10, 1920 to Blake. In this construction, a plurality 
of lock tabs greater in number than the number of flats on the nut to be 
locked is provided and all project away from the plane of the washer to be 
located about the periphery of the nut. While these types of lock washers 
work well in terms of providing the desired locking function, it is 
difficult to loosen the locked nut and reuse of the lock washer may be a 
problem. 
Typically, such lock washers are made of a resilient metal and each of the 
lock tabs requires a force of 8-10 lbs. to depress the same back into the 
plane of the base of the washer. It is necessary to displace each tab back 
into the plane of the base of the washer to move it out of interfering 
relation with the flats of the nut if the nut is to be loosened. 
When a number of the tabs are present as in Blake and other constructions, 
the total force involved may be 65-80 lbs. While such a force may be 
applied axially through the use of a socket wrench, where it is necessary 
to loosen the nut with a box end or open end wrench, the average user of 
such a tool is incapable of applying such a force over the lever arm 
represented by the length of the wrench, making removal difficult, if not 
impossible. 
Furthermore, such constructions are extremely difficult to loosen with an 
open end wrench even if the force of the locked tabs can be overcome. 
Specifically, an open end wrench, by reason of its open ended geometry, 
will typically be incapable of depressing all of the lock tabs which in 
turn means that one or more lock tabs will spring into locking position in 
abutment with the flat of the nut, preventing its rotation. 
If, in such a situation, rotation of the nut is forced, then the lock 
washer will be permanently distorted and cannot be reused. 
French patent document 1,394,517 issued Feb. 22, 1965 to Bruhwiler, et al., 
provides a means of at least overcoming potential corrosion problems 
through the use of a locating tab on the body of the lock washer which may 
be received in a notch or recess in the surface to which the lock washer 
is applied to prevent the lock washer from rotating. However, Bruhwiler 
continues to employ a large number of lock tabs that require substantial 
force to displace into the plane of the washer body and which prevent 
ready loosening of the nut with a tool such as an open end wrench. 
Furthermore, the pointed lock tabs of Bruhwiler may hinder loosening of 
the nut in that they may have a tendency to dig into the sides of the 
loosening tool and hinder its rotation. When such occurs, to the extent 
the rotation is forced, then the lock tabs are permanently deformed and 
the Bruhwiler lock washer cannot be reused. 
The present invention is directed to overcoming one or more of the above 
problems. 
SUMMARY OF THE INVENTION 
It is the principal object of the invention to provide a new and improved 
lock washer. More specifically, it is an object of the invention to 
provide a lock washer whose installation does not cause corrosion 
problems; which, when installed, does not require the application of undue 
force in order to depress locking folds; which is reusable; which 
minimizes nut vibration and can be economically manufactured in low 
volume. 
It is also an object of the invention to provide a lock washer with a body 
having a continuous uninterrupted edge about lock folds thereon, so that 
when the lock folds resiliently, lockingly engage with a flat of the nut, 
the continuous uninterrupted edge is such that clothing or other objects 
cannot be caught or snagged on the lock folds. 
It is also an object of the invention to provide a lock washer that is 
susceptible to use in a large variety of environments, including in 
aircraft environments, and does not require the use of labor intensive and 
non-reusable safety wire. It is a further object to provide such a lock 
washer that when installed, is free from sharp edges that could cause 
tearing of apparel that might come in contact therewith. 
It is also an object of the invention to provide a lock washer that will 
not mar the surface of the item being fastened, as the lock washer will be 
prevented from rotating with respect to said item being fastened. 
It is also an object of the invention to provide a lock washer of the type 
having locked folds that will not stick or gouge into the underside of a 
loosening tool. 
It is also an object of the invention to provide a lock washer that is such 
that if the clamping load is lost, the lock washer is such as to minimize 
nut motion to resist the effects of shock and vibration. 
An exemplary embodiment of the invention achieves one or more of the above 
objects in a lock washer for use with a nut having n flats where n is an 
integer equal to 4, 5 or 6. The lock washer includes a generally planar 
washer body formed of a thin sheet of resilient metal. A central aperture 
is located in the body and is capable of receiving the shank of a bolt to 
which the nut is to be attached and locked. A lock fold located radially 
outwardly of the central aperture is displaced to one side of the plane of 
the body at a point on the perimeter of the body spaced from the central 
aperture a distance greater than the spacing of a flat on the nut from the 
central aperture. The lock fold resiliently and lockingly engages with a 
flat of the nut thereby preventing the nut from loosening. The washer body 
has a continuous uninterrupted edge thereby avoiding the use of a free 
edge on which clothing or other objects may catch or snag. 
In a preferred embodiment, the generally planar washer body is circular. 
In a preferred embodiment, the lock washer further includes a key 
protruding from the perimeter of the aperture opening and displaced as to 
one side of the plane of said washer body thereof opposite the lock fold. 
The key engages with the keyway of a bolt to keep the lock washer from 
rotating with respect to the shank of the bolt or the like, and prevents 
marring of the surface in any manner. 
In one embodiment, two opposed points on the perimeter of the body are 
spaced a distance greater than that between two opposed flats on the nut, 
to define at least two opposed resilient lock folds. Each of the two lock 
folds are formed in the body radially outwardly from the aperture opening, 
and are displaced to one side of the plane of the washer body to 
resiliently and releasably engage with two corresponding flats of the nut 
to hold the nut in a locked position. 
In one embodiment of the invention, according to another facet thereof, 
there is provided a lock washer having a generally planar, circular washer 
body with a central aperture as defined before. A key protrudes from the 
perimeter of the aperture opening and is displaced as to one side of the 
plane of the washer body, opposite the lock folds. Four equally angularly 
spaced points on the perimeter of the body define four resilient lock 
folds, opposed ones of the lock folds being spaced a distance greater than 
the spacing between two opposed flats on the nut. The lock folds are all 
formed in the body radially outward of the aperture opening, and curved to 
one side of the plane of said body from the plane of the washer body to 
engage with corresponding flats of the nut to secure the nut in a locked 
position.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to FIGS. 1-4, inclusive, a first embodiment of the invention will 
be described in detail. The lock washer includes a ring-like body, 
generally designated 6, formed from a thin sheet of resilient, metallic 
material. Preferably, tempered stainless steel sheet having a thickness of 
0.013"-0.017" is employed. As best seen in FIG. 2, the body 6 is planar 
except for four lock folds 8, 9, 10 and 11. The lock folds 8, 9, 10 and 11 
are equally angularly spaced about the periphery of the body 6 which is to 
say they are at 90.degree. to each other. 
The body 6 includes a central aperture 12 which is generally circular. As 
will be appreciated by those with ordinary skill in the art, the diameter 
of the central aperture 12 will be just slightly greater than the diameter 
of the shank of the bolt whose nut is to be locked. 
The four lock folds 8, 9, 10 and 11 are defined by four bend lines 14, 15, 
16 and 17, respectively, which are located radially outward of the central 
aperture 12. The respective folds 8, 9, 10 and 11 are bent on the lines 
14, 15, 16 and 17 from the plane of the body 6 to one side thereof at an 
acute angle that typically will be in the range of 40.degree.-60.degree.. 
Opposed ones of the bend lines 14, 16 and 15, 17 are parallel to one 
another and are spaced a distance just slightly greater than the spacing 
between opposed flats on the nut to be locked, the distance also being 
less than that between opposed points on the nut to be locked. 
It will be readily appreciated from FIG. 3 that the folds 8 and 10 or the 
folds 9 and 11 need not always be diametrically opposite one another. If 
the nut with which the washer is to be used is a five sided nut, the 
opposed lock folds will not be directly opposite one another. 
Turning to FIGS. 3 and 4, specifically, a nut generally designated 22, has 
been applied to the shank, generally designated 24, of a bolt, which is 
impaled through an aperture 26 in a metal panel 28 or the like. As can be 
seen, the nut 22 is a hex nut which is to say it has six, equally 
angularly spaced flats 30 as is well known although the nut 22 could have 
only four or five flats 30 if desired. Adjacent flats 30 are separated by 
points 32. The nut 22 sandwiches the body 6 of the lock washer against the 
panel 28 such that the lock folds 8, 9, 10 and 11 extend away from the 
panel 28. As can be appreciated from FIGS. 3 and 4, the lock folds 9 and 
11, due to their inherent resilience, are displaced from the plane of the 
body 6 and are in substantial abutment with corresponding ones of the 
flats of the nut 30 along a substantial portion of the length thereof. As 
a consequence, rotation of the nut 22 is blocked by the lock folds 9 and 
11 to prevent the same from loosening. At this point in time, the lock 
folds 8 and 10 underlie opposed points 32 and are depressed into the plane 
of the body 6 where they do not appreciably resist rotation of the nut 22 
except in the case where the clamping load is lost. If the nut 22 is to be 
further tightened on the shank 24, the points 32 will cam the lock folds 9 
and 11 back down into the plane of the body 6 to allow such tightening. At 
the same time, when the point 32 depressing the tab 8 passes past the end 
of the bend line 14 thereof, the tab 8 will spring up to abut one of the 
flats 30 and resist rotation unless, of course, held down by a tool or the 
like. A similar action will occur at the lock tab 10. 
When it is desired to loosen the nut 22, a tool such as a socket wrench, an 
open wrench or a box wrench, is applied to the nut and a small force 
applied to the same along the axis of the shank 24. Since, when using a 
lock washer according to the invention, the nut is always holding down 
some or all of the lock folds 8, 9, 10 and 11, fewer tabs need to be 
depressed to loosen the nut. This in turn means that significantly less 
force is required to depress said lock folds back into the plane of the 
washer body in order to loosen the nut. This is in contrast with the great 
amount of force (65 lbs.-80 lbs.) required in some prior art 
constructions, and makes washers made according to the invention 
substantially easier to use in terms of loosening the nut. 
Because so little force is required to depress one or more of the lock 
folds 8 or 10, it will readily be appreciated that there is no need to 
force the rotation of the nut 22 against any of the folds to permanently 
deform the same. Additionally, because the washer body maintains a 
continuous uninterrupted edge, the possibility of permanently deforming 
the fold with either the point 32 of the nut 22 or some other external 
force (such as clothing or other objects that may be caught on a free edge 
contained in some prior art) is substantially reduced. Consequently, a 
lock washer made according to the invention is readily reusable and easily 
maintains its integrity. 
It will also be appreciated that the embodiment of FIGS. 1-4, through the 
use of a planar body 6, does not gouge or penetrate either the nut or the 
panel 28. As a consequence, corrosion producing sites are avoided. 
Furthermore, sharp points are avoided throughout. 
The lock washer may further include a key 34 protruding radially inward 
from the perimeter of the aperture opening 12. The key 34 is displaced as 
to one side of the plane of the washer body 6 thereof opposite the side to 
which the lock folds 8, 9, 10, and 11 are displaced. When displaced, the 
key 34 will engage with a keyway 35 of the shank 24 of the bolt or in a 
bushing or the like. This engagement will keep the lock washer from 
rotating with respect to the shank 24 of the bolt and prevent marring of 
the panel. 
From the foregoing, it will be readily appreciated that a lock washer made 
according to this invention is highly advantageous in that it completely 
eliminates the generation of corrosion sites, is readily and easily 
loosened intentionally through the use of standard tools such as open end 
wrenches, eliminates vibratory motion of the nut when clamp load is lost, 
and is reusable. The absence of exposed edges or points is highly 
desirable to prevent safety hazards in many environments and the lock 
washer provides a positive lock without any need for safety wire or the 
like.