JPH02145724A - Metallic bellows and manufacture of same bellows - Google Patents

Abstract

PURPOSE:To increase the value of hardness in the title bellows by age-hardening and to increase their repeated stress by subjecting metallic bellow obtd. by subjecting a stainless steel tube to plastic working into the shape of bellows to low temp. annealing. CONSTITUTION:The elements of bellows formed by cylindrical material constituted of stainless steel into the shape of bellows by plastic working are welded in the direction of a axis and connected, or are integrally formed to form a main body 40 of bellows. After the integral forming or welding, the above main body 40 of bellows is subjected to low temp. annealing treatment. Then, metallic bellows 15 and 16 contained so as to be freely expandable in the direction of the axis in housings 11 and 12 and partitioning liquid 21 and 23 and air 20 and 22 in the housings 11 and 12 can be obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a metal bellows built into, for example, a vehicle suspension system, various gas springs, or an accumulator, and a method for manufacturing the bellows.

[Prior art] For example, Japanese Patent Application Laid-open No. 63-46908 (Japanese Patent Application No. 61-1
A fluid-filled suspension system for a vehicle such as that disclosed in Japanese Patent No. 91263) is provided with an air chamber filled with compressed gas and a liquid chamber filled with air. Bellows are used to separate gas and oil. From the viewpoint of gas barrier properties, a bellows made of a thin metal plate is suitable for this bellows. This bellows expands and contracts in the axial direction.

Metal bellows built into a vehicle suspension system are made of a thin metal plate made of stainless steel, for example. For example, austenitic stainless steel (JIS, 5US
304) is shown in the S-N diagram (J I
S, B8243), it is known that there is a certain relationship between repeated stress and the number of repetitions. This also applies to metals other than austenitic stainless steel.

In other words, metal bellows will eventually break if it exceeds its durability under a certain stress, but S
-N diagram, the higher the repeated stress for the same number of repetitions, the higher the durability.

In addition, the stress σ generated in the bellows due to expansion and contraction of the bellows and pressure load during use of the bellows is expressed by the following formula 1% (1), where σ: stress (kgf / mm2)
t: Plate thickness (mm) δ: Expanded melon
(tnts >b: 1/2 of pitch
(Second) h: Height of the peak (1/2 of the difference between the inner diameter and outer diameter) (mm) N:
Twice the number of peaks P・Design pressure (k, gf/(to)2)E
:Young's modulus (kgf/11ta2)
The specification of the bellows for the required number of durability is determined by the relationship between the above-mentioned S-N diagram and the stress σ when the bellows is used.

[Problems to be Solved by the Invention] Suspension devices, gas springs, accumulators, etc. that incorporate metal bellows as described above are becoming more and more compact due to increased loads, increased gas filling pressures, and demands for compactness.
In the future, they will be used under increasingly harsh conditions. For this reason, there has recently been a demand for metal bellows that are more durable (higher stress for the same number of repetitions in the S-N diagram) than traditional metal bellows. Furthermore, in addition to the demand for miniaturization, we have also improved pressure resistance (TP-800σ
B t2/h2. In order to improve reliability and reliability (TP: pressure resistance, σB: tensile strength of material), thick bellows may be required while satisfying durability.

However, conventional metal bellows have not been able to meet these strict requirements.

Accordingly, an object of the present invention is to provide a metal bellows made by plastic working that has excellent durability.

The metal bellows according to the present invention, which was developed to achieve the second object, is housed inside a housing so as to be expandable and contractible in the axial direction, and partitions the liquid and gas inside the housing. This metal bellows has a bellows body which is integrally formed by plastic working or has bellows elements formed by plastic working connected by welding in the axial direction. The main body is characterized by being subjected to low-temperature annealing treatment after the above-mentioned plastic working or the above-mentioned welding.

Further, the method for manufacturing a metal bellows according to the present invention is characterized in that a cylindrical material made of stainless steel is formed into a pipe with a predetermined thickness, and is formed into a bellows shape by plastic working, and then low-temperature annealing is performed. The temperature of low temperature annealing is 300~500℃
One hour is approximately 5 to 60 minutes, but depending on the material, the heating time may be outside this range. The annealing atmosphere may be air or a bright annealing atmosphere.

[Function] Metal bellows that are subjected to low-temperature annealing after being plastically worked into a bellows shape have a higher hardness (HV) value due to the effect of age hardening, and also have a higher hardness (HV) value under the same stress conditions than bellows that are not subjected to low-temperature annealing. If the number of repetitions is the same, the number of repetitions will increase, and if the number of repetitions is the same, it will be possible to increase the repetition stress. Figure 7 shows stainless steel
These are the durability test results when low-temperature annealing was performed on 4 thin plates at 400°C and 500°C, and the durability was significantly improved compared to the one without low-temperature annealing.

[Embodiment] An embodiment of the present invention will be described below with reference to FIGS. 1 to 6.

The fluid-filled vehicle suspension system 10 shown in FIG.
It includes a first housing 11 and a second housing 12. Inside each housing 1.1.12, an inner cylinder 13
, 14 and metal bellows 15 and 16 are provided concentrically with the housings 1x and 12, respectively. Further, a mouth rad 17 is inserted into the first housing 11 so as to be movable in the axial direction.

The inside of the first housing 11 is partitioned into an air chamber 20 and a liquid chamber 21 by the bellows 15. Also, the second
The inside of the housing 12 is also partitioned into an air chamber 22 and a liquid chamber 23 by a bellows 6. The air chambers 20 and 22 are filled with an inert gas such as nitrogen at a predetermined pressure.

The sealing pressure of the gas is set to such a high pressure that the vertical load applied to the rod 17 can be supported only by the repulsive force of the gas. Therefore, the pressure in the air chambers 20 and 22 acts in a direction that causes the rod 17 to protrude from the housing 11. The illustrated lower end of the housing 1 is connected to, for example, an axle-side member via a mounting part 25.

The upper end side of the rod 17 in the drawing is a mount insulator 2.
For example, it is connected to a member on the vehicle body side via 6.

A damping force generation mechanism 3 provided at the lower end of the rod 17 in the drawing
0 is equipped with a well-known plate valve or a rotary type valve body 31, and by rotating this valve body 31 by a predetermined angle by a motor 32, the orifice opening amount, that is, the damping force can be changed. It has also become.

The liquid chamber 21 in the first housing 11 and the liquid chamber 23 in the second housing 12 can communicate with each other via the communication portions 33, 34. A valve mechanism 35 is located in the middle of the flow section 34.
is provided, and by opening and closing this valve mechanism 35, the gas spring constant can be changed.

The metal bellows 15, 16 differ in size but have a common structure. Each bellows 15, 16 has a bellows body 40 that is expandable and retractable in the axial direction of the housing 11, 12, respectively.
and a bellows cap 41 air- and liquid-tightly attached to one end side of the bellows main body 40.

The bellows body 40 is formed into a bellows shape by plastic working a thin metal plate such as austenitic stainless steel, and has a crest 42 with a U-shaped cross section and a valley with an inverted U-shape, as partially shown in FIG. The portions 43 and parallel portions 44 are formed alternately at a shade pitch.

When the bellows main body 40 contracts within the housing 11, 12 beyond a certain limit, the bellows cap 41 fits into the open end of the inner cylinder 13 (or 14) in a fluid-tight manner, as shown by the solid line in FIG. When the bellows body 40 is extended, the bellows cap 41 is expanded as shown by the two-dot chain line in FIG.
is separated from the open end of the inner cylinder 13 (or 14).

In the suspension system 10 of this embodiment, which incorporates metal bellows 15 and 16, when the a-rad 1f moves in the direction in which the rod 1 is pushed into the housing 11, the air chamber opens in accordance with the increased amount of pushing of the rod 7. Since the volumes of 20 and 22 decrease, the bellows body 40 extends in the axial direction. Conversely, when the rod [7] moves in the direction of coming out of the housing 11, the air chambers 20, 2
As the volume of the bellows 2 increases, the bellows body 40 contracts.

Further, the movement of the rod 17 is attenuated by the flow of water through the damping force generating mechanism 30. Therefore, this suspension device 1
0 serves both as a suspension gas spring and as a shock absorber. Since the metal bellows 15, 16 have excellent gas barrier properties and are also excellent in oil resistance, they can completely separate oil and gas within each housing 11, 12.

The bellows body 40 is manufactured through a manufacturing process schematically illustrated in FIG.

First, in the pipe-making process, a stainless steel plate with a desired thickness is formed into a cylindrical shape. Note that a commercially available stainless steel seamless pipe may be used instead of pipe making.

Next, the cylindrical material is thinned by spinning to a predetermined bellows thickness. The final thickness is, for example, around 0.1 to 0.3 mm, depending on the pressure resistance and material required for the bellows body 40.

Thicknesses other than those listed above may be used depending on mechanical strength, etc.

Next, it is formed into a desired bellows shape by plastic working such as bulge working. The bellows body 40 has 1 over its entire length.
Although it may be integrally molded from a cylindrical material, as shown in FIG. The entire circumference of the part) may be welded. Alternatively, two or more bellows elements with multiple peaks and valleys may be axially welded. In either case, the bellows element 50 is plastically worked into a predetermined shape (a shape with peaks and valleys) before welding.

"The bellows body 40 after biped plastic processing or welding,
Perform low temperature annealing treatment. Annealing temperature is 300 to 50
The holding time at 0° C. is preferably 5 to 60 minutes, but may be other than this depending on the material. In this example, annealing was performed in air at 470° C. for 60 minutes. However, it may be carried out in a bright annealing atmosphere.

Stainless steel bellows body 40 annealed at low temperature
In addition to removing harmful residual stress generated during bellows forming and welding, durability is improved through age hardening after plastic working.

Table 1 below shows the durability of the bellows before and after low-temperature annealing for two types of bellows sizes (mountain diameter D = 55 m).
These are the results of an investigation of bellows A with a peak diameter of D-41 mm and a bellows B with a peak diameter of D-62 and a valley diameter of 44 am. The test conditions were: average stress σm-21.5kgf
/mm2. Amplitude stress σa-±35 kgf/mm2 The annealing conditions for both A and B are 470°C x 60 minutes in the air.

Table 1. The test results (indicated by the number of breakages, X104) in FIG. 5 are for the bellows A described above (diameter D = 55 mm).

These are the results of investigating changes in hardness before and after annealing with respect to the valley diameter d-4 fmm). FIG. 6 shows the change in hardness in bellows B (peak diameter D=62 mm, valley diameter d-44+cm). The influence of age hardening was observed in both bellows A and B.

Note that the metal bellows of the present invention is not limited to vehicle suspension systems.
The present invention can be similarly applied to bellows that need to partition liquid and gas contained in a housing, such as various gas springs, hydraulic dampers, accumulators, etc.

[Effects of the Invention] As described above, according to the present invention, the durability of the metal bellows, which undergoes repeated axial expansion and contraction operations, can be significantly improved.

[Brief explanation of the drawing]

Fig. 1 is a process explanatory diagram showing one embodiment of the method of the present invention;
The figure is a sectional view showing a part of the bellows main body, FIG. 3 is a sectional view showing an example of a bellows element, FIG. 4 is a longitudinal sectional view of a suspension device equipped with a metal bellows, and FIGS. 5 and 6 are respectively 7 is a diagram showing changes in hardness due to low-temperature annealing, FIG. 7 is an S-N diagram showing changes in durability due to low-temperature annealing, and FIG. 8 is an S-N diagram showing durability of stainless steel. 10... Vehicle suspension system, 15 16... Metal bellows.

Claims (2)

[Claims] (1) A metal bellows that is accommodated inside the housing so as to be expandable and contractible in the axial direction and is used to partition the liquid and gas within the housing, and the metal bellows may be integrally formed by plastic working or A metal comprising a bellows body in which bellows elements formed by plastic working are axially connected by welding, and the bellows body is subjected to low-temperature annealing treatment after the plastic working or the welding. Bellows. (2) A method for producing metal bellows, which comprises forming a cylindrical material made of stainless steel into a pipe of a predetermined thickness into a bellows shape by plastic working, and then subjecting it to low-temperature annealing.