Expanded – threaded – driven – headed – tool-deformed – or locked-thr – Internally threaded fastener element – e.g. – nut – etc. – Thread structure
Reexamination Certificate
1999-05-25
2002-08-27
Estremsky, Gary (Department: 3627)
Expanded, threaded, driven, headed, tool-deformed, or locked-thr
Internally threaded fastener element, e.g., nut, etc.
Thread structure
C470S025000
Reexamination Certificate
active
06439818
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a nut and an intermediate product therefor, and more particularly, it relates to the structures of a nut having a concave lead-in shape suitable for internal threading with a rolled tap and an intermediate product therefor.
2. Description of the Prior Art
In general, a nut is internally threaded with the so-called cutting tap
52
shown in
FIGS. 13A and 13B
. In this threading with the cutting tap
52
, the inner peripheral surface of a prepared hole of an unthreaded intermediate product
51
for a nut is cut to form roots of a female screw threading while discharging chips through grooves
52
a
of the cutting tap
52
shown in FIG.
13
A. In such internal threading with the cutting tap
52
, the crest diameter of the worked female screw threading coincides with the inner diameter d of the unthreaded prepared hole and hence the accuracy of the female screw threading shape can be relatively readily ensured. However, parts of the chips tend to remain in the worked female screw threading to bite into a male screw engaging with the female screw threading and disadvantageously hinder proper fastening.
In order to solve such a problem, a nut is increasingly internally threaded with a rolled tap causing no chips.
FIGS. 14A and 14B
show a rolled tap
53
threading an intermediate product
51
for a nut. In such internal threading with a rolled tap
53
, a female screw threading is formed not by cutting but by plastic working. In other words, the inner peripheral surface of a prepared hole of the intermediate product
51
for a nut is depressed for forming roots of the female screw threading while the material extruded from the depressed portions is raised to form crests. The crest diameter of the worked female screw threading is smaller than the inner diameter d of the prepared hole of the unthreaded intermediate product
51
.
However, such conventional internal threading of the nut with a rolled tap has the following problem:
In general, an internally threaded screw hole of a nut is provided on its opening end with a tapered concave lead-in, called a countersink in general, in order to guide the forward end of a bolt engaging with the nut or facilitating discharge of chips resulting from internal threading with a tap.
FIG. 15A
shows an unthreaded intermediate product
131
for a nut provided with a concave lead-in
31
a
having such a shape, to be internally threaded with a rolled tap
53
from the side of the lead thread
31
a
. As a consequence of internal threading with the rolled tap
53
, a nut
31
provided with a female screw threading having a concave portion CP
1
or CP
2
in each thread is formed as shown in FIG.
15
B. When the rolled tap
53
is screwed into the intermediate product
131
from the side of the concave lead-in
31
a
, the material is plastically deformed along thick arrows appearing in
FIG. 16
, showing a detailed area enclosed with a circle XVI in
FIG. 15B
in an enlarged manner, in the vicinity of the concave lead-in
31
a
. Thus, roots of the rolled tap
53
cannot be completely filled up with the material but crests of the threads of the formed female screw threading are disadvantageously depressed with concave portions or depression CP
1
and CP
2
. In particular, the root of the rolled tap
53
for forming a thread
31
b
adjacent to the concave lead-in
31
a
cannot be sufficiently filled up with the material in general due to the tapered shape of the concave lead-in
31
a
. Thus, the thread
31
b
has a lower height a larger depression or concave portion CP
1
than the remaining threads.
When a bolt
32
is to engage with the nut
31
internally threaded with the rolled tap
53
in the aforementioned manner from the side of the concave lead-in
31
a
as shown in
FIG. 17A
, a thread on the forward end of the bolt
32
hits against the depression on the crest of the thread
31
b
of the nut
31
adjacent to the concave lead-in
31
a
to cause the so-called cross-thread, as shown in a part enclosed with a circle A in FIG.
17
B. Consequently, the bolt
32
incorrectly engages with the nut
31
, to result in an improper fastening state.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a nut having a concave lead-in shape causing no cross-thread in engagement with a bolt also when the is internally threaded with a rolled tap.
In order to attain the aforementioned object, a nut according to a first aspect of the present invention consists of integral metal material and has a female screw threading formed in a screw hole opening substantially perpendicularly to an end surface of one end, and a concave lead-in defining an opening end of the screw hole for the end surface has a concavely depressed shape along the overall periphery thereof.
In a preferred embodiment, the concave lead-in includes a concave bent or curved portion in an arbitrary longitudinal section including the central axis of the screw hole. The concave lead-in preferably has such a shape that the concave bent portion is continuously combined with a linear tapered portion, and in this case, the concave bent portion further preferably starts from the inner peripheral side of the opening end to be continuous with the linear tapered portion on an outer prescribed position.
A nut according to a second aspect of the present invention comprises a shaft portion and a flange portion outwardly extending from a first end of the shaft portion, consisting of integral metal material. The shaft portion is in the form of a hollow cylinder, has a portion slated or adopted for caulking in a second end opposite to the first end and is formed with a female screw threading on the inner peripheral surface excluding the portion slated for caulking. The portion slated for caulking has an inner diameter larger than that of the portion formed with the female screw threading, and a concave lead-in defining an end of the portion of the shaft portion formed with the female screw threading adjacent to the portion slated for caulking has a concavely depressed shape along the overall periphery. In this nut, the present invention is applied to the so-called rivet type tee nut having a predeterminate caulked portion, and the shape of the portion formed with the female screw threading is common to the nut according to the first aspect of the present invention.
The present invention includes an unthreaded intermediate product for a nut consisting of integral metal material and having a screw hole opening substantially perpendicularly to an end surface of one end, slated for internal threading with a rolled tap at least in a prescribed region, and a concave lead-in defining an end of the prescribed region of the screw hole slated for internal threading has a concavely depressed shape along the overall periphery.
The nut according to the first or second aspect of the present invention is formed by working a female screw threading in the screw hole of such an intermediate product for a nut with a rolled tap. In the intermediate product for a nut according to the present invention, the concavely depressed shape of the concave lead-in is preferably so formed that the crest of a thread of the female screw threading adjacent to the concave lead-in has no concave groove but a convex shape and particularly a line edge crest formed along an intersection of the two sloping flanks of the screw thread ridge. Consequently, no concave groove is formed on the crest of the thread of the female screw adjacent to the lead thread when the intermediate product is threaded with the rolled tap, whereby it is possible to prevent such an inconvenient phenomenon that a thread on the forward end of a bolt engaging with the nut hits against the thread of the female screw threading to cause cross-thread. Further, the nut maintains such a characteristic of the countersink that the diameter of the concave lead-in enlarges toward the opening end, whereby the female screw threading can be worked without damaging the function of the counte
Estremsky Gary
Fasse W. F.
Fasse W. G.
Nagayama Electronic Industry Co. Ltd.
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