Expanded – threaded – driven – headed – tool-deformed – or locked-thr – Threaded fastener locked to a discreet structure – Nut – and means to engage substructure on its opposite faces...
Reexamination Certificate
1999-09-09
2001-01-09
Wilson, Neill (Department: 3627)
Expanded, threaded, driven, headed, tool-deformed, or locked-thr
Threaded fastener locked to a discreet structure
Nut, and means to engage substructure on its opposite faces...
C411S438000
Reexamination Certificate
active
06171040
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a thread insert having a detachable tongue which is screwed into a hole formed in a work for providing a female thread on the inner surface of the hole.
2. Description of Related Art
Thread inserts are helical parts used for forming a female thread on the inner surface of a hole formed in a work which is made of a material having relatively low hardness such as plastics or aluminum.
FIGS.
20
-
22
illustrate an example of conventional thread inserts. This thread insert is formed by winding a metal wire in a helical shape, and a male screw
31
and a female screw
32
are respectively formed on the outer and the inner surfaces of the helical wire. At the front end of the helical wire, a first coil portion
33
having a smaller diameter is formed so that the thread insert can be smoothly screwed into a hole from the side of the first coil portion
33
.
A detachable tongue
34
is formed at the front end of the first coil portion
33
so as to extend toward the center of the first coil portion
33
, and a notch
35
is formed on the wire by cutting between the first coil portion
33
and the tongue
34
for facilitating the detachment of the tongue
34
.
When the thread insert is used, the detachable tongue
34
is grasped by a tool (not shown) inserted through the thread insert, and the thread insert is screwed into a hole of a work by the tool. Then, the detachable tongue
34
is pushed by an another tool inserted through the screwed insert, and the tongue
34
is detached by breaking the wire at the notch
35
. After detaching the tongue
34
, it is possible to screw a bolt into the insert beyond the length of the insert.
In order to extract the insert screwed in the work, as shown in
FIG. 23
, a detachment tool
37
is pushed into the back end portion
36
of the thread insert so that a pair of cutting edges
39
of the tool
37
bite in the inner thread
32
of the insert. Then, the tool
37
is rotated so as to unscrew the insert from the work.
However, the above thread insert has the following drawbacks. That is, the above thread insert cannot be extracted unless the special detachment tool
37
having cutting edges is used. Furthermore, if the pushing force of the detachment tool
37
is too weak, the tool
37
does not form notches
38
having a sufficient depth, and it is not possible to rotate the thread insert by the tool
37
. In contrast, if the pushing force of the detachment tool
37
is too strong, the tool
37
enlarges the diameter of the thread insert, and the risk will arise that the inner surface of the hole will be damaged. Should the inner surface of the hole be damaged, it becomes necessary to re-tap the hole in order to attach a new thread insert in the same hole, and the new thread insert must be larger than the original one if the inner diameter of the hole is enlarged by re-tapping. Therefore, the operation of the detachment tool
37
is not easy and requires the skill of an expert.
Additionally, because the notch
35
is formed on the front surface of the wire as shown in
FIG. 21
, when the tongue
34
is pushed by the tool inserted through the thread insert, a crack generates from the back surface
35
a
opposite to the notch
35
. However, the back surface
35
a
is smooth, stress generated by pushing the tongue
34
does not concentrate on a single point in the wire, and breaking the wire requires large load.
Furthermore, because the back end
36
of the insert is flat, when the thread insert is unscrewed, the edge
36
a
of the back end
36
scrapes the inner surface of the hole. The scraping by the back edge
36
a
not only increases the rotational resistance of the insert, but also increases the risk that the inner surface of the hole will be damaged.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a thread insert which can be easily extracted without a special tool and the skill of an expert.
In order to accomplish the above object, the thread insert comprises a helical body having a front end portion and a back end portion, and a detachable tongue connected to the front end portion of the helical body, wherein at least one engaging notch is formed in the back end portion of the helical body.
In the thread insert of the present invention, by inserting a general tool such as a minus driver (flathead screwdriver) into the engaging notch, it is possible to firmly rotate the thread insert screwed in a work, and it is possible to easily extract the thread insert without the skill of an expert. The back end portion may have a pair of the engaging notches formed at an interval of 180 on the inner surface of the back end portion.
The helical body may comprise a female thread formed on an inner surface of the helical body, and a male thread formed on an outer surface of the helical body. Furthermore, the detachable tongue may have a circular portion having an outer diameter which is smaller than that of the helical body.
It is another object of the present invention to facilitate the detachment of the detachable tongue after the insert is screwed into a work. In order to accomplish this object, at least one cutting notch may be formed between the front end portion of the helical body and the detachable tongue on at least one of a surface facing toward the back end portion and a surface facing toward a center axis of the helical body.
In this case, when the detachable tongue is pushed ahead, stress will concentrate at the bottom of the cutting notch, and a crack will generate from the bottom of the cutting notch. Therefore, it is possible to facilitate the cutting of the detachable notch. The cutting notch may have a “V” cross section, and may be formed between the front end portion of the helical body and the circular portion of the detachable tongue.
The back end portion may have a back end face chamfered at an outer side of the helical body. In this case, because the back end portion does not scrape the inner surface of the insert when the thread insert is unscrewed, it is possible to prevent the damage of the inner surface of the hole in which the thread insert was screwed. The back end surface of the back end portion additionally may have a flat face perpendicular to an outer surface of the helical body, and the whole circumferential edge of the flat face may be chamfered.
Furthermore, the engaging notch may have a tool contact surface which intersects with the inner surface of the helical body at substantially a right angle or an acute angle, and further which faces toward the clockwise direction. In this case, the rotational force applied to an unscrewing tool can be effectively transmitted to the engaging notches.
REFERENCES:
patent: 2371674 (1945-03-01), Caminez
patent: 123064 (1947-01-01), None
patent: 0 140 812 B1 (1988-03-01), None
Kato Spring Works Co., Ltd.
Scully Scott Murphy & Presser
Wilson Neill
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