JPH01224510A - Screw with difference in pitch excellent in fatigue property - Google Patents

Abstract

PURPOSE:To prolong fatigue lifetime in a screw used in such a part where a load remarkably fluctuates as an accumulator by setting pitches of a screw receiving a tensile load smaller than those of the other screw. CONSTITUTION:A male screw 19 has larger pitches than those of a female screw 20. Therefore, when a fluctuating load is applied on the screwed screws, the first thread Fs10 and others on the side where the threads come into contact with each other receive the load in order, and at last a thread Fs1 on the other end receives a charge load, thereby resulting in averaging bending moment generated in the respective bottoms of the threads irrespective of change in screwing or fastening positions. Therefore, the smaller peak bending moment generated in the thread bottoms in comparison with that in a conventional screw can enhance the fatigue property as well as prolong the fatigue lifetime.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to screws that receive tensile loads and are used in places such as accumulators and cylinders where loads fluctuate rapidly. This relates to screws with .

BACKGROUND ART For example, an accumulator as a flow 14Ca device uses a bladder to partition the inside of a container body into a gas chamber and a liquid chamber, and closes both ends of the chamber with side plates, and expands and contracts the bladder in response to fluctuations in fluid pressure in a fluid circuit. Although it functions as a pulsation absorber and a shock absorber, parallel screws are used as means for fixing the container body and the side plate.

Problem to be Solved by the Invention By the way, when the pressure inside the accumulator increases and the side plate is pressed outward, the R load in the axial and circumferential directions, the so-called variable load, falls within the range of 0 to the maximum load. Although this load is repeatedly applied, each screw thread does not share it evenly, but is largely biased in the direction of the tensile force.

As a result, stress concentration occurs at the root of the female screw tip, which is subjected to a large tensile load, and fracture occurs from there.

Therefore, in order to solve this problem, we applied the already patented ``Threaded joint with excellent fatigue characteristics using a tapered external thread'' (U.S. Patent No. 4 N9975, Japanese Patent Publication No. 56
-53651) may be used.

As shown in FIG.
The external thread 4 is formed with a thread m7 according to the above-mentioned patent.
A test accumulator was manufactured in which the peak height h was gradually reduced by ~ml, and a conventional accumulator using the triangular screw in the standard state was manufactured, and the seal diameter d = 1.
The load sharing ratio and fatigue life of each screw thread of each accumulator were investigated under the conditions of 0.04 mm, internal pressure p=o ~ 3 kg/C112, and frequency 2.5 H2.

As a result, the load sharing ratio was more averaged in the test accumulator than in the conventional accumulator, but the fatigue life of the test accumulator was shorter than that of the conventional accumulator.

Incidentally, in the test accumulator, the thread with the highest load sharing ratio is the second thread m2 from the tip 2m,
The rate is 18.5%, and in the conventional accumulator, the rate is 21% for the first screw out from the tip.
In addition, the fatigue life of the conventional accumulator is 560.0.
00 times, and in the test accumulator it was 380.000 times.

Normally, when the load sharing ratio of the screw threads decreases, the life of the screw increases due to fatigue, but in the above test accumulator,
On the other hand, the fatigue life was shortened.

When we investigated the cause of this, we found that during the bending moment applied to each female thread root f, the maximum bending moment was applied to the second root f2 of the thread tip 2e, and the fracture occurred from there. , when the male thread 4 is pressed in the direction of arrow Y, each thread fm of the female thread becomes a cantilever beam that receives a shared load on the lower surface, and the height f h of the female thread fm is equal to the bending moment. It can be seen as a span that affects the size.

Therefore, even if the thread height fh is made uniform, if the shared load of each screw thread is not made equal, the larger the shared load, the greater the bending moment and the easier it will be to break.

Therefore, the bending moment per unit that occurs at the root of the female thread of the conventional accumulator and the test accumulator is
The results were calculated from the load sharing ratio and the thread height as shown in Figure 4.

In this figure, A is a conventional accumulator, B is
The test accumulator is shown, and the screw tip 2e of the test accumulator B has a 13
．． A peak bending moment PB of 5 kgmm/wr■ occurs, and that moment PB is equal to the peak bending moment P A = I+, 4k of conventional accumulator A.
It was found that the screw was larger than g/g, and as a result, the screw was susceptible to fatigue failure.

In view of the above circumstances, it is an object of the present invention to improve the fatigue characteristics of screws and extend their fatigue life.

Means for Solving the Problems The present invention attempts to solve the above problems by making the pitch of the screw that receives a tensile load smaller than the pitch of the other screw in screws that are screwed together and that receive a varying load. It is something.

When a fluctuating load is applied to the threaded screw due to the applied load fluctuation, the end of the screw that receives the tensile load first, that is,
The full load is applied to the first thread on the side where the threads are in contact with each other.

However, this thread deforms within its elastic limits and the load is shared by the next thread.

In general, the relationship between the elongation and force of steel is proportional within the elastic limit, so the pitch of the screws that receive the compressive load can be increased to account for the amount of elongation of the load bones that is safe to apply to each screw thread. .

The load that cannot be shared by this screw-out is transferred to the next screw thread, and the load shared by this screw thread is also the same as that of the above-mentioned screw thread.

In this way, the total load applied to the screw is divided by the amount of deformation corresponding to the pitch difference in order from the first screw thread, and the load is finally shared by the screw thread at the other end.

Therefore, the bending moment generated at each thread root is averaged, and the peak bending moment is greatly reduced.

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the accompanying drawings, in which the same reference numerals have the same names and functions.

FIG. 2 is a longitudinal cross-sectional view of the accumulator ACC, in which the interior of the container body 10 is partitioned into a gas chamber 12 and a liquid chamber 13 by a bladder 11, and both ends 14.
15 is closed by side plates 16.17.

Both ends 14.15 and side plates 16.17 of this main body 10 are
The threaded portion S is formed as shown in FIG. 1.

That is, inside the end 14 of the container body 10.

A female thread 20 is formed to be screwed into the male thread 19 of the side plate 16.

This female thread 20 with a pitch pf is provided with ten female threads FS formed at the same height, and the female thread thread F
The parts where S contacts the thread MS of the male thread, the so-called contact surfaces i'jjFW of the female thread, are the same, but this contact surface [FW is the size at which the thread FS can deform within the elastic limit. It is formed.

The thread roots f1 to flO are formed in an arc shape, and the radius fr thereof is 0°1 to 0.18 times the pitch.

The male thread 19 is formed to have a larger pitch than the pitch p of the female thread 20, and its ten threads MS have the same height mh.

In this way, since the screws 19 and 20 with different pitches are screwed together, the first screw thread F S , o and the screw thread M S , on one end portion 20B of the screw are in contact with each other. , other threads FS9-. , MS9-, and the comrades do not come into contact with each other, and a gap α is created between them.

In addition, 25 is a stopper for preventing screwing in more than necessary, and C is a center line.

Next, the operation of this embodiment will be explained.

When the hydraulic pressure in the hydraulic circuit 30 fluctuates and liquid is pressurized into the accumulator ACC from the supply/discharge port 23, the bladder 11 is compressed and the pressure in the gas chamber 12 increases, causing the side plate 16 to move as shown by arrow A2.
Press in the direction.

Therefore, the male screw 19 is also pushed in the same direction, and first,
Female thread F S at end 20B where threads are in contact with each other
The full load is applied to to, but if this load is too large, the screw threads F S and o stop receiving the load equivalent to the deformation within the elastic limit.

In this way, the extra load that cannot be shared by the female thread FSto is transferred to the next female thread FS9. Then, the screw expands and the threads FS9 and MS9 come into contact, eliminating the gap α, and the female thread FS9 is connected to the thread FS9.
The load is shared in the same manner as in 10, and the excess load is transferred to the next female thread FS8.8 In this way, the female threads FS8-... , MS8-,
contact and the gap α disappears, resulting in the state shown in Fig. 3.

At this time, since the contact heights of all threads FS+ or r are the same, no matter how the screw tightening position changes, the load actually shared by each thread FS+ +a is approximately equal, and the root of each thread The bending moment generated in fl-IQ is also approximately equal.

Therefore, the peak bending moment PC per unit generated at the thread root f of the female thread 20 is reduced to a greater extent than that of the conventional accumulator, so that the fatigue life can be extended.

In addition, an accumulator using the screw according to the present invention was manufactured, and the bending moment generated at the root of the female thread fl-IQ and the fatigue life of the screw were investigated under the same conditions as in the above experiment. As shown in curve C, the peak bending moment pc is 5.7Kg, mm/
+am, and the fatigue life is 10,000.000
This is more than 20 times that of conventional accumulators.

Further, as shown in FIG. 5, the entire thread FS of the screw,
-,. - Contact height Lh, for example, 75 of the thread height
You can trim the peak to a height of %.

When an accumulator using this screw was manufactured and the bending moment generated at the root of the female thread fl-10 was investigated under the same conditions as in the above experiment, the curve was as shown in Figure 4, and the peak bending moment PD was 4. ,5 mm
/am, which was better than the accumulator of the previous example.

In the above embodiment, a case has been described in which the pitch of the female thread is smaller than the pitch of the male thread, but it goes without saying that the pitch of the male thread may be smaller than the pitch of the female thread.

It goes without saying that the present invention is applicable not only to triangular threads but also to square threads, round threads, trapezoidal threads, etc.

Effects of the Invention In this invention, since the pitch of the screw receiving the tensile load is smaller than the pitch of the other screw, when a fluctuating load is applied to the threaded screws, the thread receiving the tensile load first changes. One end, that is, the first thread on the side where the threads are in contact with each other receives a load in sequence, and finally the thread on the other end receives a shared load.

At this time, each thread can only share the load by the difference in elastic limit, thread, and pitch, and since the thread contact heights are the same, the bending that occurs at the thread root of each thread The moments are also averaged and become approximately equal regardless of changes in the screwing position and tightening position.

Therefore, the peak bending moment generated at the root of the thread is reduced compared to the conventional example, resulting in improved fatigue characteristics and longer fatigue life.

[Brief Description of the Drawings] Figures 1 to 5 are diagrams showing embodiments of the present invention.
The figure is an enlarged vertical cross-sectional view, and is an enlarged view of the threaded part in Fig. 2. Fig. 2 is a longitudinal cross-sectional view of the accumulator. Fig. 3 is an enlarged sectional view showing another state of Fig. 1. Fig. 4 5 is an enlarged view showing another embodiment and corresponds to FIG. 1, and FIG. 6 is a partially enlarged sectional view of the conventional example. Figure 19 Male thread 20 Female thread FS Female thread thread L Contact height MS Male thread 1) f Female thread pitch pm Male thread pitch

Claims (1)

[Claims] A screw with a pitch difference that has excellent fatigue properties, in which the pitch of the thread that receives a tensile load is smaller than the pitch of the other thread, in screws that are threaded together and that receive a fluctuating load.