Note: Descriptions are shown in the official language in which they were submitted.
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BRIEF SUMMARY OF THE INVENTION .
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It is a purpose of this invention to provide a nut
having wedge ramp type threads with a prevailing torque
feature.
The invention accomplishes this purpose by means of
a design to which the diameter of the internal wedge ramp
threads at the top of the nut is reduced to impose a resis-
tance to threading of a bolt in the nut.
Thus, the present invention may be seen as providing
a nut of the prevailin~ torque type comprising a body having
a through aperture and an outer wrenching periphery coaxial
with the aperture, the body having a top at one end of the
aperture and a bottom including a bearing surface at the
other end of the aperture, the body being internally threaded
along the length of the aperture with helical threads having
wedge ramp roots sized for en~agement by the crests of exter-
nal threads of a male member passing through the aperture,
an upper portion of the body adjacent the top being deformed
.~ radially inwardly and on a taper with respect to the axis of
the aperture to reduce the width of an upper portion of the
aperture and the diameter of the threads in the upper portion,
.~ the aperture and threads between the upper portion and the
bottom being of substantially uniform diameter and larger than '.
the thread and aperture diameter in the upper portion, the
taper serving to make the wedge ramp roots in the upper por-
tion closer to parallel to.the axis of the aperture than are
the wedge ramp roots in the substantially uniform diameter
. portion of the aperture, the crests of the external threads
on the male member being initially engageable with the wedge
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ramps at the top oE -the nut so as to place subs-tantially
the entire portion of the male member wi~thin the aperture
;. of the nut in tension when a load is placed on the bearing
surface thereof~
` Furthermore, the present invention ma~ be definecl as
a nut of the pre~ailing torque type comprising a body having
a through aperture and an outer wrenching periphery coaxial
with the aperture, the body having a top at one end of the
aperture and a bot-tom a-t -the other end of the aperture in-
~luding a bearing surface, the aperture including a uniformportion extending from the bearing surface to an intermediate
axial level of the body and a tapered portion extending from
the uniform portion toward the top of the body, the uniform
portion having substantially uniform cross sections alon~ its
length and the tapered portion having cross sections decreas-
ing in at least one direction with distance from the bearing
surface, the body being internally threaded along the length
of the aperture with wedge ramp type threads, the threads
having wedge ramp roots in the uniform portion that make angles
of about 30 with respect to the axis of the aperture and in
the tapered portion make angles less than 30 with respect to
the axis in accordance with the taper o~ the tapered portion,
the wedge ramp roots being engageable by the crests of exter-
.~ nal threads on a male member threaded into the aperture,
the crests of the external threads on the male member being
initially engageable with the wedge ramps at the top of the nut
so as to place substantially the entire portion of the male
: member within the aperture of the nut in tension when a load
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is placed on the bearing surface thereof.
DESCRIPT:[ON OF THE DRAWINGS
Figure 1 is a side elevation, partly broken away, of
a nut embodying the invention;
Figure 2 is a top elevation of the nut of Figure l;
Figure 3 is a bottom elevation of the nut of Figure l;
and
Figure 4 is an enlarged view, partly in sec-tion of the
nut of Figure 1 assembled on a bolt and pressing against a
workpiece~
DESCRIPTION OF THE INVENTION
; The nut 1 comprises a body 3 formed of suitable material,
such as s-teel, and having an outer periphery 5 and an inner
aperture 7 that is coaxial with the outer periphery. The body
3 has a top 9
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and 2 hOttOnl 11, including annular bearing surface 13, and the
aperture extends through the body between the top and bottom.
The body 3 is provided with intcrnal thrcads 15 of the wedge ramp
type and these define the aperture 7 The body 3 is also provided
with suitable external wrenching surfaces symmetrical with the
axis, such as the twelve point configuration illustrated on the outer
periphery 5. It will be understood that the invention may be used
with other nut body designs than the presently preferred embodi-
ment that is illustrated.
The helical wedge ramp threads 15 are preferably of
the configuration shown, though dimensional and angular variations
~re within the broad purview of the invention. Such threads are
illustrated in U. S, Patent No. 4, 076, 064. Each thread comprises
a lead ilank 17 and a following Ilank 19 and a root in the form of
- , . ;
a wedge ramp 21 In the preferred and illustrated embodiment where- ~
in the threads 15 are to mate with standard e~ternal threads 23 on
a bolt 25, the flanks 17 and 19 make angles of about 30 to an imag-
inary plane normal to the axis of the aperture 7 and the wedge ramp
21 is snbstarltially normal to the lead flank 17.
In accordancc with the invention, the aperture 7 has a
lower section 7a that is of uniform circular cross section or diam-
eter and an upper section 7b ~Yhich is inwardly taperecl. The threads
î5 are in both sections; hence~ the threads in section 7b and, in
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particular, the wedge ramps 21 thereof, are of gradnallyijdècreasing
widfh at least alon~ one or more radii of the aperture. Therefore, as
seen bcst in Figure 4, the arrangement of aperture sectiolls 7a and
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7b will enable a bolt 25 to be free spinning with respect to the nut
until its threads 23 enter the tapered sectiGn 7b and encounter ~qedge
ramps 21 ha~,ing a diameter less than tlleir major diameter. At
this point the bolt threads 21 will encounter resistance from the
nut to provide prevailing torque. Continued application oI torque
to the assembly of nut 1 and bolt 25 will cause the nut body adjacent
aperture section 7b to elastically dilate; and, when the bearing
surface 13 engages the workpiece 27, tension in the bolt and elongation
thereof will enable the bolt threads 23 to ride down the wedge ramps
21. Figure ~ shows the beginning of substantial pressure between
the nut and the workpiece, and as bolt load increases still more
the bolt threads 23 will come in contact with the wedge ramps 21 in
the lower aperture section 7a. Continued application of torque will
cause the bolt threads to ride Eurther and further down the wedge
15 . ramps toward the iollowing Elanks 19 to align the parts, take up
clearances, and powerfully resi~st unintentional loosening.
The tapered aperture section 7b in cornbination with
the wedge ramps 21 provide the assembly with substantial resistance
~o loosening under vibratory loads of any kind. All of ~he threads ~-
15 are preferably formed in one operation and on the same diameters,
i. c. in an aperture 7 of constant uniform circular cross section.
The nut body 3, preferably, is subsequently deformed by the appli-
cation of radial inward pressure on its upper portion. This may be
alollg a diameter to form an oval but is preferably at three equi-
angularly spaced points 29. If the nut is made of steel or equivaient
materials, the application of sufficient squeeze pre.ssure will per-
manently deform the nut body into substantially the shape shown in
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I~igurc 2, it bein~, recognized that ]~i~urc 1 and l~i$~urc 4 are p;lrli;ll
cross sections along a plane through poin~ 2~. Thus, tllc al~crturc
7b may be regarded as a tapered trilobular cross section while the
lower ~ection 7a remains substantially circular as shown in ~igure
3. When the tapered section 7b is formed after the aperture has
been threaded, the wedge rarnps 21 in the section 7b will be ben
inwardly, i. e~, toward the vertical, by an angle corresponding to
an angle of taper. This has the effect of bringing the wedge ramp
angle closer to the vertical (i. e. axial) and of increasing the friction
between mating threads. :
While the mcthod just described for forming the taper
is presently preferred, it is within the broad purview of the invention
to provicle the aperture 7 with a tapered upper section 7b by other
methods. Tapers OI this type in nuts having ordinary V or standard
thl ~ ads are known in the fastener inaustry, and nuts witll locking
action provided by inwardly squeezed two or three point shapes on
6tandard thread sections are comTnercially available. Thus, known
r ethods of form.ng the taper may be employed, i~ desired, in using
the invention.
~0 lVlodificatio~ls in the specific structure described may
be made without departing from the spirit and scope of the invention.
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