JPH02163506A - Compressed screw having superior fatigue characteristics - Google Patents

Abstract

PURPOSE:To improve the fatigue characteristics of a screw so as to lengthen its fatigue life by gradually cutting and reducing part of the contact face of a screw of a compression load applied side in a direction of compression load to gradually increase a contact area. CONSTITUTION:Both ends 14, 15 of a body 10 and side plates 16, 17 are threadedly attached. A female screw 20 threadedly engaged with the male screw 19 of a side plate 16 is formed inside the end of the vessel body 10. A portion from the male screw ridge FS1 of the side plate 16 having a pitch P to the male screw ridge FS10 is re-machined by a pitch P1 larger than the Pitch P and one part of a face CF contact with the female screw ridge MS of the F1-F10 side of each of the male screw increasingly cut. The contact width FW of the male screw ridges FS1-S10 is gradually increased in a direction A2 of compression load, according to it, an area contact with a female screw MS is gradually increased. Thus, the fatigue characteristics of the screw is improved to extend its fatigue life.

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to a spring that receives a compressive load and is used in places where the load fluctuates rapidly. This relates to compression materials with excellent fatigue properties that are used in a wide range of areas.

Conventional technology For example, an accumulator as a chamber device divides the inside of a container body into a gas chamber and a liquid chamber by a bracket, and closes both ends of the chamber with a side plate, and also sets a flag in response to fluctuations in fluid pressure in a fluid circuit. The container body is compressed to provide a pulsation absorption function and a shock absorption function, and 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 internal pressure increases overnight and the L side plate is pressed outward, the load on the screw in the axial and circumferential directions, the so-called fluctuating load, changes from the minimum load to the maximum load. Although this load is repeatedly applied over a range of , this load is not shared evenly by each thread, but varies greatly in the direction of the tensile force.

As a result, stress concentration occurs at the bottom of the tip of the female ring, which receives a large tensile back shape, and it breaks from there.

Therefore, in order to solve this problem, we developed a patented "E-J joint with reduced fatigue characteristics using a tapered external thread" (US Pat. No. 4,189,975, Japanese Patent Publication No. 5
6-53 (see No. 151) may be used.

As shown in FIG.
6.8 A test accumulator was manufactured in which the height h of the screw threads n17 to I]11 was acidified according to the above-mentioned patent, and the triangular screws were The conventional accumulator used in the same standard f3.
and seal diameter (1104m+n, internal pressure p =
O~313 kg, cm2, frequency 2.5
Under the conditions of 1-12, the load sharing ratio and fatigue of each pile of each Ayumtota were investigated.

As a result, we found out whether the load sharing ratio is better for the test accumulator or the bCC pear-shaped accumulator), but the fatigue life is shorter for the test accumulator or the conventional accumulator. In the test accumulator, the top part 2 has the highest load sharing ratio.
At the second thread m2 from m, the ratio is ], 8,
5 r6, be In the next type A/A accumulator, the rate is 219° at the first threaded ridge from the tip, and the fatigue life is 560° in the conventional type accumulator.
times, and in the test accumulator it was 380,000 times.

Normally, the fatigue life of a screw increases when the load sharing ratio of the screw threads decreases, but in the above test accumulator,
Fatigue, on the other hand, shortened lives.

Therefore, when we investigated the cause, we found that during the maximum bending moment applied to each female root f, a peak bending moment 1~ is applied to the second female root f2 of the female thread tip 2e.
It was found that the moment amplitude of the song reached its maximum, and destruction occurred from there. That is, when a load is applied to the male thread 4 in the direction of arrow P, each thread f m of the female thread becomes a cantilever beam that receives a shared load on the lower surface, and the female thread f Ill
The peak height f h can be seen as a span that affects the magnitude of the bending moment.

Therefore, if the thread height fh is applied uniformly, if the shared load on each thread is not applied uniformly, the larger the shared load, the larger the peak bending moment I will be. The moment amplitude also reaches its maximum, making it easier to break.

Therefore, the flower that occurs at the bottom of the female thread of the accumulator for the bCC pear-shaped accumulator test σ) maximum surface i-
I calculated 1 moment using the formula below.

P n = ” Hn
- Average catching height of the first b of the N thread that is subjected to tension, w n = Shared load of the N thread, Sn - Length from the midpoint of the contact width of the thread of the N thread that is subjected to tension to the bottom of the valley, It is.

The results were as shown in FIG.

In this figure, A is a conventional accumulator, B is
The test accumulator is shown, but from the top thread 2e of the test accumulator B, there is a 13
．． A peak bending moment per unit PB of 5 kgmn/in occurs, and the moment l-P B is greater than the peak bending moment per unit l-P A = 11.4 kg order/in of the conventional accumulator l\. As a result, the bending moment l-amplitude was also large, making it clear that 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 that are subjected to compressive loads.

Means for Solving the Problems This invention provides that in screws that are screwed together and that are subjected to variable loads, the screw on the side that receives the compressive load has a portion of the contact surface near the bottom of each screw at the end of the screw that is subjected to the compressive load. The above objective is achieved by gradually increasing the contact area between the screw and the screw that is engaged with the screw and receives tension by making the recess gradually smaller in the direction of the screw.

For example, when a 1-way male thread and a threaded female thread are subjected to a tensile load, a compressive load is applied to the thread, or even if the height of each thread thread is the same, the contact width gradually increases in the direction of the compressive load. So,
The contact area gradually increases accordingly. Therefore, if the contact area of the first thread with the first thread 1" that receives a compressive load is small relative to the transmitted load to be shared, the thread will undergo plastic deformation and deformation within the limit, and the deformation within the elastic limit will occur. (J load is carried by the receiver, and other loads are transferred to the next thread.

In addition, if the contact area of the screw is large relative to the transmitted load to be shared, the screw will deform within its elastic limit, and the load will be carried by the amount of deformation within the elastic limit, and the rest of the load will be transferred to the next screw thread. be transferred.

In this way, even if there is an adjustment error in the contact area of each female screw, the load shared by each female screw is uniformly distributed.

The maximum moment per unit of each screw root is 1~
can be averaged, the peak bending moment per unit that is biased toward the threaded end can be greatly reduced, and the bending moment I
-Since the amplitude is also small, the strength is maintained within a range where fatigue failure does not occur.

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 sectional view of the accumulator Ace. The inside of the container body 10 is partitioned into a gas chamber 12 and a liquid wood chamber 13 by a bladder 11, and both ends 14 of the body 10 are partitioned into a gas chamber 12 and a liquid wood chamber 13.
15 is closed by side plates 16.17.

Both ends 14, 15 of the main body 10 and the side plate 1617 are screwed together, and the threaded portion S is formed as shown in FIG.

That is, inside the end 14 of the container book (4c10) there is a side plate 1.
A female thread 20 is formed which screws into the male thread 19 of No. 6.

This male thread] 9 is provided with ten male threads FS, and each thread is formed to have a standard height. From the male thread FS of the side plate 16 with pitch P to the male thread FSlo, reprocess it with a pitch P1 larger than the pitch P, and make one of the contact surfaces CF with the female thread MS on the side of each male thread F+ to. Cut out the section gradually.

When the side plate 16 is reprocessed in this way, the line 21 connecting the upper ends of the contact surfaces CF of each male thread FSz to becomes parallel to the center line C, and the line 21 connecting the lower ends thereof becomes parallel.
2 has a tapered shape, and the intersecting angle between the line 21 and the line 22 is γ, which is preferably within 10 degrees.

The male thread FS processed in this way, the contact width F of ~1o
W gradually increases in the compressive load direction A2, and the contact area with the female screw MS also gradually increases. Pitch P at this time
The relationship between P and the recursive bit P (the detailed explanation of the system is omitted, but it can be expressed by the following calculation formula.

r'1=Pcos7 jcos7+5in7+;an(
α−γ) (In this equation, α represents the intersection angle between the line 21 and the contact surface CF.

Using this calculation formula, the rework pitch P can be calculated easily and accurately.

As an example, pitch P = 2, γ = 3° α = 60°
The reworked pitch P = 2,062 for the pigeon coop.

Each thread height ML of the female thread 20 is formed to a standard height. Incidentally, 25 is a C-shaped stopper for preventing the screw from being pressed onto the collar and tool.

Next, the one-way motion 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.
Compress in the direction.

Therefore, each threaded screw has a shared load W1 1
It costs 0.

However, if this shared load W is too large, the threads will undergo elastic deformation and plastic deformation, causing the force pitch to change, and the actual load that each thread can handle will be
The tensioning range of the deformation within the elastic limit is lifted, and the other loads are transferred to the next thread.

In this way, the actual load shared by each thread is regulated by the contact area of the thread, and therefore the average load of the thread is regulated by the contact area of the thread.
Applying height, immediately, midpoint 1' of contact width FW (+ to
If the contact area gradually decreases in the direction in which the tension load is received, that is, in the direction of the arrow A1, the contact area also gradually decreases in the same direction, so that the shared load that each thread receives is 1 h on average.

In addition, as mentioned above, since the contact height ML gradually decreases in the direction of arrow A1, the span (average caught height H+ to) that affects the magnitude of the bending moment
The length also gradually decreases in the same direction.

In other words, the peak bending moment per unit L- generated at the thread root of the female thread tip E1, that is, each thread root E+
Since the maximum bending moment per unit applied to +a is also reduced, the maximum bending moment per unit of each Mewaji valley bottom E+to is reduced by 1 h on average.

As a result, the amplitude of the bending moment applied to the root of each screw is on average 1 hi, resulting in a screw that is subject to compression with poor liquid sealing properties.

Incidentally, an accumulator using the screw according to the present invention was manufactured (
Ya, under the same row C1 as in the above experiment, the bottom of the valley fl-10
When the maximum bending moment per unit and the fatigue life of the screw were investigated, the maximum bending moment per unit was as shown in curve C in Figure 3, and the peak bending moment per unit was l-P C is 5.7 Kg, n+m
/mm, and the fatigue life is: 10. QOo, 0
1) 4 O groups"2, which is more than 20 times that of conventional accumulators.

Although the above-mentioned embodiments have been described with respect to Japanese screw threads, it goes without saying that the present invention can also be applied to various types of screws, such as square screws, round screws, trapezoid screws, etc.

Also, the female thread receives a compressive load f! '! 11 sleeping characters,
For example, when the angle is 1~, as shown in FIG. , arrow [1A2 direction, the contact area between the nut 50 and the pole I-51 screwed together is gradually increased by making the holes smaller and smaller.

In this case, regardless of the screwing position of the nut 50 with the bolt 51, the contact width, in other words, the contact area, always increases gradually in the back direction, so the shared load is always 1 on average.
This results in excellent fatigue properties.

In FIG. 4, 52 indicates a fixture.

Effects of the Invention In the screw receiving a compressive load according to the present invention, as described in ``2'' below, the screw on the side receiving the compressive load has a portion of the contact surface near the bottom of each screw at the end thereof subjected to the compressive load. Since the contact area between the thread and the thread that receives tension is gradually increased by making the cracks smaller and smaller in the direction, the shared load of each thread is averaged, and the maximum bending moment per unit at the bottom of each groove is also averaged 1. Hi.

Therefore, since the peak bending moment per unit and the bending moment l-amplitude generated at the edge are reduced compared to the conventional example, the fatigue characteristics are improved and the fatigue life is extended.

[Brief explanation of the drawing]

1 is a diagram showing an embodiment of the present invention. FIG. 2 is an enlarged sectional view of the threaded portion, FIG. 2 is a vertical sectional view of the accumulator, and FIG. A diagram showing the relationship, FIG. 4 is a longitudinal sectional view showing another embodiment,
FIG. 5 is a diagram showing a part of an enlarged sectional view of a conventional example. 19 ... Male thread 20 ... Female thread CF ... Contact surface FW ... Contact width El ... Female thread tip A2 ... Compressive load direction

Claims (3)

[Claims] (1) In a threaded screw that is subjected to a fluctuating load, the screw on the side that receives a compressive load causes a part of the contact surface near the root of each thread at the end of the screw to gradually become smaller in the direction of the compressive load. A screw that is subjected to compression and has excellent fatigue properties, characterized by a gradual increase in the contact area between the screw and the threaded screw that receives tension. (2) The thread that receives compression and has excellent fatigue properties according to claim 1, wherein the thread on the side that receives compression load is a female thread. (3) A screw receiving compression having excellent fatigue properties according to claim 1, wherein the thread on the side receiving the compressive load is a male thread.