Sealing nut and method of making same

A sealing nut has an annular heat stabilized nylon sealing insert retained within a recess in a metallic nut body by a coined collar on the nut body. The sealing insert is initially formed symmetrical about a transverse median plane to enable bidirectional assembly into the nut body recess, and undergoes dynamic preloading when the collar is coined onto the periphery of the insert. When installed onto a threaded shaft extending from a bearing surface so that the coined collar is torqued against the bearing surface, the sealing insert forms a fluid-tight seal between the threaded shaft and a threaded bore in the bearing surface through which the threaded shaft extends. The nut body and sealing insert facilitate reduced manufacturing costs while enabling re-use without significant loss in sealing properties.

BACKGROUND OF THE INVENTION 
The present invention relates to sealing nuts, and more particularly to a 
novel sealing nut having a nut body and sealing insert which provide 
improved performance and cost reduction over prior sealing nuts. 
Sealing nuts are known which employ a nut body having a recess adjacent one 
end in which a sealing insert is retained, and wherein an internally 
threaded bore through the nut body and insert enable mounting of the 
sealing nut on a threaded shaft. In one prior sealing nut, such as 
disclosed in U.S. Pat. No. 4,019,550 which is owned by the assignee of the 
present invention and incorporated herein by reference, a coined annular 
lip on the nut body retains the sealing insert within the nut body recess. 
As the nut is threaded onto a threaded shaft, the annular lip is caused to 
engage a bearing surface through which the threaded shaft extends so that 
a protrusion or crown of the insert is compressed into sealing relation 
with the threaded shaft. Such sealing nuts find particular application as 
high pressure hydraulic sealing nuts but may also be utilized with equal 
efficiency in other applications. Other prior sealing nuts are described 
in U.S. Pat. No. 4,019,550 and their shortcomings discussed. 
The various features enumerated for the sealing nut disclosed in U.S. Pat. 
No. 4,019,550 apply equally to the sealing nut of the present invention. 
In this respect, the sealing nut of the present invention provides 
metal-to-metal contact of the nut body against the bearing surface through 
which the threaded shaft extends so that the sealing insert flows into 
sealing engagement with the threaded shaft; both the nut body and sealing 
insert are tapped with a continuous axial thread; the sealing nut is 
reusable without significant loss of sealing ability; and the nut can 
withstand high pressures without leakage. In addition, the sealing nut of 
the present invention lends itself to significantly reduced manufacturing 
costs. For example, most prior sealing nuts employ relatively expensive 
manufacturing techniques wherein the nut body is made by cold forming. A 
shortcoming of this technique is that close dimensional tolerances are 
difficult to achieve. Also, the prior sealing inserts have been made by 
injection molding techniques requiring movement of die members in both 
horizontal (X) and vertical (Y) axes during the injection process, thus 
requiring more costly dies with resulting increased manufacturing costs. 
One of the primary objects of the present invention is to provide a novel 
improved sealing nut which includes a nut body having an annular sealing 
insert retained within a recess adjacent one end of the nut body, the nut 
body and sealing insert enabling reduced manufacturing costs while 
facilitating high pressure sealing of a threaded shaft extending from a 
bearing surface against which the sealing nut is engaged. 
A more particular object of the present invention is to provide a novel 
sealing nut having a nut body which receives an annular sealing insert, 
and wherein the insert is bidirectionally insertable into a recess in the 
nut body and retained therein by an annular collar formed over the insert 
in a manner to dynamically preload the sealing insert with resulting 
greater fluid tight sealing about a threaded shaft on which the nut is 
mounted. 
In carrying out the present invention, a metallic nut body is formed with a 
polygonal first end defining external wrench flats and having an axial 
bore, and an annular wall or collar adjacent an opposite end which defines 
an internal generally cylindrical recess concentric with the axial bore. A 
generally donut shaped insert made of a high impact resilient resin 
material is inserted into the recess. The annular wall or collar of the 
nut body is formed, as by coining, over the insert in a manner to 
mechanically encapsulate and dynamically preload the insert such that the 
insert undergoes a cross-sectional twisting action or partial inversion 
which causes the outer end of a cylindrical axial bore in the insert to 
increase slightly in diameter, and the diameter of the inner end of the 
insert bore to decrease. A uniform thread bore is formed axially through 
the nut body and sealing insert to facilitate mounting onto a threaded 
shaft. In installing the sealing nut, the nut body is torqued against a 
bearing surface through which the threaded shaft projects so that the 
coined annular wall or collar engages the bearing surface and the sealing 
insert is further dynamically compressed into fluid tight relation with 
the threaded shaft. 
A feature of the sealing nut in accordance with the invention lies in the 
utilization of an annular nylon sealing insert which is generally 
symmetrical about a median plane transverse to the axis of the insert. 
This enables the insert to be bidirectionally inserted into the recess in 
the nut body. The insert undergoes a cross-sectional twisting action or 
partial inversion as the annular wall or collar of the nut body is formed 
over and compressed against the insert. This causes an outwardly facing 
end of the insert to be stretched outwardly and the inwardly facing end of 
the insert to be compressed inwardly adjacent an axial bore through the 
annular insert. This action dynamically preloads the insert and causes it 
to fill any voids in the nut body recess. An internal thread is then 
formed in the axial bore of the nut body and sealing insert. 
Typical sealing nuts of the type employing sealing inserts encapsulated 
within a nut body require that the sealing insert engage at least a 
three-pitch length of the threaded shaft on which the nut is installed. A 
significant advantage of the sealing nut in accordance with the present 
invention is that for most applications the sealing insert forms a very 
effective liquid tight seal while engaging approximately a single-pitch 
length of the threaded shaft, thus requiring a significantly reduced 
volume of sealing insert material over prior sealing nuts. 
Another feature of the sealing nut in accordance with the invention lies in 
pre-loading the sealing insert by forming the annular wall or collar of 
the nut body over the insert so as to compress the insert and stretch its 
outer exposed surface in a manner to inhibit shear and abrasion of the 
insert as it engages the runout area of a tapped bore in a bearing surface 
from which a threaded shaft extends during installation of the nut onto 
and removal from the threaded shaft. 
Further objects, features and advantages of the sealing nut of the present 
invention will become apparent from the following detailed description of 
the invention taken in conjunction with the accompanying drawing wherein 
like reference numbers designate like elements throughout the several 
views.

DETAILED DESCRIPTION 
Referring now to the drawing, a sealing nut constructed in accordance with 
the present invention is indicated generally at 10 in FIG. 1. Briefly, the 
sealing nut 10 includes a metallic nut body 12 having a sealing insert 14 
made of a relatively tough nylon or resinous material retained within a 
recess in the nut body. The sealing nut 10 is adapted to be threaded onto 
a threaded shaft, a fragmentary portion of which is indicated at 16 in 
FIG. 6, and brought into engagement with a bearing surface 18a of a body 
18 having a threaded bore 18b through which the threaded shaft 16 extends. 
The body 18 may comprise a metallic housing or other structure such that 
the threaded bore 18b is exposed to a pressurized fluid. As will become 
more apparent from the following description, the sealing nut 10 is 
threaded onto shaft 16 to engage the bearing surface 18a in metal-to-metal 
contact and effect a fluid-tight seal between shaft 16 and the runout at 
the intersection of the threaded bore 18b with the bearing surface. 
The nut body 12 is preferably made of a non-corrosive metallic material, 
such as a suitable strength stainless steel, and may be formed by 
conventional screw machine techniques to enable close tolerance 
manufacture of the nut body. The nut body has an external polygonal 
circumferential surface 22 adjacent one end which, in the illustrated 
embodiment, comprises a hexagonal surface defining wrench flats for 
engagement with a spanner or wrench. The upper and lower peripheral 
margins of the hexagonal surface 22 are preferably chamfered, as indicated 
at 22a and 22b, in accordance with conventional practice. The nut body 12 
is initially formed with a cylindrical axial bore 24 which intersects a 
planar outer end surface 22c at a chamfer 24a. The bore 24 will later be 
taped. 
The nut body 12 has an annular wall or collar 28 formed integral with the 
polygonal end 22 concentric with the center axis of bore 24. The annular 
wall or collar 28 defines the outer annular margin of a generally 
cylindrical internal recess 30 having a generally transverse planar base 
surface 32 intersected by bore 24. The base surface 32 may have a slight 
frusto-conical concavity, such as a conical angle of approximately 
10.degree. relative to the base of the cone. The annular wall 28 has an 
outer diameter slightly less than the diameter of a circle internally 
tangent to the hexagonal wrench surface 22. 
The sealing insert 14 has an annular generally donut or torus ring shape 
which is of uniform cross-sectional configuration about its full 
circumference. The sealing insert is molded independently of the nut body 
12 and has upper and lower convex arcuate surfaces 36a and 36b which 
intersect an annular cylindrical outer peripheral surface 38. The sealing 
insert is formed with an axial cylindrical bore 40 having a diameter 
approximately equal to the diameter of the bore 24 in nut body 12. 
The sealing insert 14 is preferably molded from a relatively tough, stiff 
yet resilient, high impact, high durometer, slippery resin material, such 
as nylon. A sealing insert material which finds particular use in high 
pressure hydraulic applications and is characterized as a heat 
stabilized-lubricated 66 nylon is commercially available under the trade 
name "Zytel ST801" by E.I. Du Pont de Nemours. This material is heat 
retardant to a temperature of approximately 105.degree. C., and exhibits 
stiffness and memory characteristics that make it particularly suitable 
for the sealing nut 10. The lubricant may be a silicone which assists in 
removal of the sealing insert from a mold and reduces friction during 
installation and removal of the sealing nut 10. 
The sealing insert 14 is symmetrical about a median plane transverse to the 
axis of the bore 40, thereby enabling bidirectional insertion within the 
recess 30; that is, the sealing insert can to be assembled into the recess 
30 without regard to which convex outer surface 36a or 36b engages the 
base surface 32 of the recess. The diameter of the outer cylindrical 
surface 38 on the sealing insert is approximately equal to the diameter of 
the inner surface 28a of the annular wall 28 of nut body 12. 
As aforedescribed, the sealing nut body 12 may be made by conventional 
screw machine techniques which facilitate economical manufacture of the 
sealing nut. For example, the nut body 12 may be made from bar stock 
having a hexagonal or other polygonal peripheral surface 22 by rotating a 
length of the bar stock about its longitudinal axis while cutting radially 
into the bar stock sufficiently to form an external cylindrical surface 
28b contiguous to the polygonal surface portion of the bar stock. The 
polygonal surface portion will thus define one end of the nut body and the 
cylindrical surface will have a planar end surface defining a second or 
opposite end of the nut body. The cylindrical recess 30 is then formed 
internally of and concentric with the external cylindrical surface 28b so 
as to define an annular wall peripherally of said recess. The axial 
cylindrical bore 24 is then formed in the bar stock to extend the length 
of the nut body and intersect the recess 30 which is formed with a 
diameter greater than the axial bore and with the generally planar base 
surface 32 transverse to the longitudinal axis of the axial bore. 
In assembling the nut body 12 and sealing insert 14, the sealing insert is 
placed within the recess 30 so that either of the convex outer surfaces 
36a and 36b engages the recess base surface 32. In the relaxed state of 
insert 14, an annular void will be created between the sealing insert and 
the recess base 32. After placing the sealing insert within the recess 30, 
the annular wall or collar 28 of the nut body 12, which has an axial 
length less than the axial thickness of the sealing insert 14 as measured 
at the bore 40, is formed, as by coining, over the outer peripheral 
portion of the sealing insert so as to form a retaining lip, as indicated 
at 28c, which mechanically encapsulates the sealing insert in the nut 
body. As the outer end of annular wall 28 is formed over the outer 
periphery of the sealing insert 14, the sealing insert undergoes a dynamic 
preloading caused by the coined end of the annular wall compressing the 
sealing insert to effect a cross-sectional twisting or partial inversion 
action of the insert generally about a circular centerline centrally of 
the annular insert. Simultaneously, the sealing insert is compressed 
sufficiently to fill any voids between the insert and the recess base 
surface 32 so that the insert fully engages the annular base surface and 
the inner surface 28a of the annular wall 28. 
Referring to FIG. 6, as the outer edge portion 28c of the annular wall or 
collar 28 is coined or rolled radially inwardly and downwardly onto the 
adjacent opposing surface 36a or 36b of the sealing insert 14, the sealing 
insert undergoes a dynamic preloading wherein the upper region of the 
insert adjacent bore 40 is stretched generally radially or arcuately 
outwardly, as depicted by surface line 40a. This is believed to cause the 
outer exposed surface of the sealing nut to become more resistant to shear 
and abrasion when the exposed insert surface engages a bearing surface 
peripherally of a threaded shaft on which the sealing nut is mounted, as 
will be described. Simultaneously, the initial dynamic preloading of the 
insert causes the annular region of the insert peripherally of bore 40 and 
adjacent the recess base surface 32 to be compressed generally radially 
inwardly, as represented by the surface line 40b. With the collar lip 28c 
thus formed onto the sealing insert as illustrated in FIGS. 1 and 6, the 
upper outwardly facing surface 36a of the sealing insert extends above or 
outwardly from a plane tangent to the uppermost surface of the coined wall 
or collar 28. It will be understood that the terms "upper", "lower", 
"upwardly", "downwardly" and "overlying" and the like as used herein 
describe the sealing nut characteristics as depicted in the various views. 
Such terms may require opposite directional definitions when the sealing 
nut or its components are considered when rotated 180.degree. in the plane 
of the paper on which they are illustrated. 
After assembling the insert within the recess 30 and coining the upper edge 
portion of the annular wall or collar 38 onto the sealing insert as 
described, a tap is run through the nut body bore 24 and axially aligned 
bore 40 of the retained sealing insert so as to form a continuous uniform 
internal thread axially through the sealing nut, as indicated at 42 in 
FIGS. 1 and 6. 
In use, it is intended that the sealing nut 10 be threaded onto a threaded 
shaft, such as indicated at 16 in FIG. 7, so as to form a fluid tight seal 
between the threaded shaft and the threaded bore 18b in the body 18. The 
internal thread 42 in the nut body and sealing insert is formed to enable 
the sealing nut to spin freely along the length of the threaded shaft 
until the outwardly extending surface 36a of the sealing insert engages 
the bearing surface 18a. The sealing nut is then torqued farther onto 
shaft 16 to engage the outermost surface of the coined wall 28 in 
metal-to-metal contact with the bearing surface 18a. During such torquing 
of the sealing nut, the sealing insert 14 undergoes further compression 
and dynamic loading which causes the sealing insert to be compressed 
radially inwardly about the external thread on the threaded shaft 16. At 
this point, the sealing nut may be torqued more tightly against the 
bearing surface 18a by a wrench or other suitable tool so that the sealing 
insert undergoes cold flow and is forced into the thread of shaft 16 about 
at least a one-pitch length of the shaft adjacent the bearing surface 18a, 
and into a countersink 18c formed at the intersection of threaded bore 18b 
with the bearing surface 18a. The sealing insert will also be compressed 
into the runout formed at the intersection of the threaded bore 18b with 
the countersink surface 18c. 
By preloading the sealing insert 14 within the nut body recess 30 through 
coining of the annular wall 28, taken with the configuration of the 
sealing insert 14, any void or cavity space within the recess 30 is 
eliminated so that all compressive energy created by tightening the 
sealing nut against the bearing surface 18 causes the sealing insert to be 
more strongly compressed against the outer thread of the threaded shaft 16 
in sealing relation therewith. The toughness characteristics of the 
sealing insert enable the sealing nut 10 to be removed from the threaded 
shaft 16 and re-applied without significant loss of sealing properties. 
Thus, in accordance with the present invention, a reusable sealing nut 
having improved sealing properties is provided wherein the nut body may be 
readily formed by conventional high volume screw machine techniques, and 
the annular sealing insert may be assembled into the nut body recess 
bidirectionally; that, is without concern for which outer annular surface 
of the sealing insert serves as the inner surface engaging the base 
surface 32 of recess 30. 
While a preferred embodiment of the sealing nut and its method of 
manufacture in accordance with the present invention have been illustrated 
and described, it will be understood to those skilled in the art that 
changes and modifications may be made therein without the departing from 
the invention in its broader aspects. Various features of the invention 
are defined in the following claims.