JPS6263012A - Equalizing external thread forming die - Google Patents

Abstract

PURPOSE:To secure such an external thread that its thread surface pressure at the time of screw-down becomes equalized, by manufacturing such a die as making the specified angle smaller than a standard angle so as to cause a flank angle on a load thread surface of an internal thread to come into contact with a crest angle part of the external thread at the time of no-load. CONSTITUTION:A cutting edge angle of a die 3 is formed so as to cause a flank angle of an external thread 1 adjoining the side of a load thread surface 2a of an internal thread 2 having a thread ridge of a standard angle to become a range of 28 deg.00'-26 deg.25'. When the external thread 1 formed with this angle and the internal thread 2 having the standard thread ridge are screwed down tight with each other, distribution of contact surface pressure between thread surfaces is equalized, thus excellent in fitting, preventing a torque radius from decreasing and, what is more, such an effect that makes their engagement hard come loose is brought about. In this connection, it may be acceptable if a plate or round die for thread rolling is, in addition to a metalcutting die.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a die for forming a male thread, particularly a die for forming a pressure-equalizing male thread so that the load screw blood pressure is equalized during tightening. Regarding.

(Prior art and its problems) The flank angle of the threads of bolts, nuts, etc. that are used for fastening purposes is set at 30 degrees for both male and female threads for standard metric threads, and both are geometrically Conventionally, it was common knowledge that the threads should be at the same angle.However, when the threads are tightened to a negative angle, the threads of male threads are more likely to be elastically deformed than the threads of internal threads due to the difference in three-dimensional shape. ,
The blood pressure generated between the load thread surfaces is not equal, and the load always acts biased toward the root of the male thread. As a result, fitting is lost, the torque radius becomes smaller, and there is a tendency for the material to loosen easily.

FIG. 5 shows the shape of the thread of a standard metric thread. In this case, the flank angle of both the male thread 1 and the female thread 2 is 30 degrees, and in the silent state, the grapple screw 1 and the female thread 2 are in contact with each other on their thread surfaces. When a load is applied to the threads due to tightening, each thread deforms elastically. 6 and 7 show cross sections of the external thread 1 and the Jlll thread 2. In each figure, the circumference length of the root of the screw thread held at a certain angle 0 is AB for male thread 1, and AB for female thread 2.
In the case of , it is CD, and naturally the relationship AB < CD holds. Therefore, when the threads are separately loaded with the same load, the elastic deformation of the thread of male thread 1 is larger than that of the thread of female thread 2, so the load is The fall of the thread due to this is larger for male thread 1. When the thread surfaces of the male thread 1 and the female thread 2 are elastically deformed while being in contact with each other, the center of action of the load moves to the side with a smaller radius to achieve balance. Therefore, the distribution of contact surface pressure between the threads is not uniform, and the pressure is biased towards the root 1a of the male thread 1. This condition impairs the conformability of the thread at the contact surface and reduces the torque radius when the nut loosens and rotates, resulting in a tendency for loosening and sizing.

[Purpose of the invention]

The present invention focuses on the above-mentioned drawbacks of the prior art, and forms an equal pressure male screw having threads that are difficult to loosen by contacting the female screw thread with equal pressure to uniform the distribution of contact surface pressure and preventing a decrease in torque radius. It was created with the purpose of providing dice for

[Summary of the invention]

In order to achieve the above object, the die according to the present invention is designed such that the flank angle of the load thread surface of the male thread that fits into the female thread having the standard angle thread is set at a different angle than the standard angle so that the flank angle of the loaded thread surface of the male thread comes into contact with the crest corner of the male thread when no load is applied. It is characterized by having a cutting edge angle corresponding to this so that the required angle is small.

(Embodiments of the Invention) The present invention will be described below with reference to embodiments shown in FIGS. 1 to 4, using the same reference numerals for parts common to those in FIG.

Fig. 1 shows a side surface of a die for thread cutting, and Fig. 2 shows a cross section of its cutting edge. The flank angle of the male screw 1 in contact with the side is 30° as shown in the third diagram.
It is formed with a cutting edge angle that is a slightly smaller value (-α).

This (-12)+7) value is in the range of 2°Oo' to 3°35', preferably in the range of 2°00' to 3°00'.

A male thread 1 and a female thread 2 of the standard thread are thus formed.
When screwed together, the distribution of contact surface pressure between the screw surfaces is uniform, resulting in good conformability, preventing the torque radius from decreasing, and making it difficult to loosen.

The table below shows the results of a tightening test between a bolt with a male thread formed by the die of the present invention and a nut with a standard thread.

In the table above, "Bolt A" has α of 2°00', "Bolt B" has α of 3°35', and "r Bolt C" has α of 5°25'.
This is the case.

Bolts A and B both leave considerable residual torque even when the "standard bolt" is completely loosened, and bolt C has the opposite effect. This is thought to be because the color increase of α to 5°25' prevented a good fit with the nut. Therefore, the value of α that achieves the object of the present invention is preferably within the range of 2'00' to 3°35'.

In addition to cutting dies, the dies to which the present invention is applied may be plate dies for rolling or round dies.

〔Effect of the invention〕

As explained above, the pressure-equalizing male thread forming die according to the present invention has a standard angle so that the flank angle of the load thread surface of the male thread that fits into the female thread having the standard angle thread is in contact at each part of the crest of the male thread when no load is applied. In order to obtain the desired color and size, the corresponding cutting edge angle is set to the right. Therefore, when the male thread formed by this and the standard female thread are screwed together and tightened, the surface of the loaded thread surface at the time of tightening load. pressure can be equalized,
This makes it possible to increase the torque radius and provide a screw that is less likely to loosen.

[Brief explanation of the drawing]

Fig. 1 is a side view of a thread cutting die as an example of a pressure equalizing thread forming die according to the present invention, Fig. 2 is a front view of the cutting edge thereof, and Fig. 3 is a tllFi side view of the same cutting blade. FIG. 4 is a sectional view of the screwed state of the male thread obtained by the die of the present invention and the standard female thread, FIG. 5 is an explanatory diagram of the screwed state of the standard screw, FIGS. 6 and 7 is a cross-sectional view of a male thread and a female thread, and is a diagram for explaining the difference in elastic deformation of the thread. DESCRIPTION OF SYMBOLS 1... Male thread, 1a... Bottom of male thread, 2... Female thread, 2a... Load thread surface of female thread, 3... Die, 3a... Cutting edge. - Tewaichi Neichi Masade 1 Indication of matter f1 1985 Patent Application No. 202695 2 Name of the invention Pressure equalization M Company 4 Agent 8 Contents of amendment (1) The third line from the bottom of page 4 of the specification of the application “This (-α
)” should be corrected to “this value of α”. (2) Same as above, page 5, line 7, ``fastening'' is corrected to ``14 movement''. (3) On page 6, line 7 of the same page, ``color increase'' is corrected to ``color decrease.'' (4) In the third line from the bottom of the same page on fii, ``Each part of own loss'' is corrected to ``Corner of the summit.'' (5) On page 7, line 6, "For equalizing pressure thread forming" is corrected to "For equalizing pressure male thread forming."

Claims (1)

[Claims] 1. The flank angle of the load thread surface of the male screw that fits into the female screw having a standard angle thread is set to a required angle smaller than the standard angle so that the flank angle of the load thread surface of the male screw comes into contact with the crest corner of the male screw when no load is applied. A die for forming an equal pressure male thread, characterized by having a cutting edge angle corresponding to this. 2. The pressure-equalizing male thread forming die according to claim 1, wherein the amount of reduction in the cutting edge angle is in the range of approximately 2°00' to 3°35'.