JPH0155828B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a piston head coated with fluororesin and a method for manufacturing the same.

[Prior Art] Conventionally, in a piston-cylinder type shock absorber, a ring-shaped groove is bored on the outer diameter surface of the head where the piston head slides on the cylinder tube, and a piston ring made of copper alloy or a metal backing is inserted into the groove. A short cylindrical ring formed by winding a strip coated with low-friction plastic is fitted onto the cylindrical ring.

In devices using these rings, the ring slightly moves in the axial direction of the head within the groove, causing a problem of the hitting noise generated at that time.

Furthermore, in order to ensure smooth sliding contact between the piston head and the cylinder tube, there is also an embodiment in which low-friction plastic is directly coated on the outer diameter surface of the head.

For example, the technology disclosed in U.S. Pat. No. 3,212,411 involves fitting a thin cup-shaped polytetrafluoroethylene resin (PTFE) to cover the end surface and outer diameter surface of the piston head. The product is then press-fitted into a heated sizing mold to adhere to the outer diameter surface and measure the dimensions.

The cup-shaped plastic molded product used in this technology must be made with dimensions close to the dimensions of the piston head to which it is to be attached, so if the diameter of the piston head is different, a mold with a size that matches it must be made. I need.

Furthermore, in order to cope with the thermal expansion of the plastic coating layer due to the heat generated during use, the piston head in this technology is described as having a partial gap between the plastic coating layer and the outer diameter surface of the head. There is.

The effect of this gap is that when the plastic adhesion layer expands and comes into contact with the cylinder tube, the plastic escapes into the gap, thereby preventing the piston head and cylinder tube from fitting together.
The purpose is to prevent an interference fit.

In general, for piston heads coated with this type of plastic, maintaining a constant clearance with the cylinder tube ensures fluid sealing within a certain range and prevents variations in damping force. , and is necessary to keep the sliding resistance constant.

If the clearance becomes zero or if the piston head is press-fitted into the cylinder tube, this will not only significantly impede the sliding properties but also hasten the wear of the adhered layer.

In this U.S. patent, the above-mentioned voids are provided to address this problem, but the presence of these voids often causes the gas within the voids to expand, impairing the adhesion of the plastic adhesion layer. There is a problem.

The present invention has been made to solve these problems of the prior art.

That is, a heat-shrinkable fluorine resin tube is adhered to the outer diameter surface of the piston head body to form a low-friction sliding surface, and an adhesive layer made of the tube is attached to one end of the head body in the axial direction. A piston coated with fluororesin, characterized in that the diameter expands uniformly from the outer peripheral surface to form a lip part, and the lip part slides into contact with the cylinder tube to seal the fluid sealed therein. The present invention provides a head and a method for manufacturing the same.

In addition to the above-mentioned PTFE, the fluororesin tube used in the present invention is made of tetrafluoroethylene hexafluoropropylene copolymer (FEP). FEP
is slightly inferior to PTFE in friction coefficient and heat resistance, but superior in wear resistance.

The fluorine resin heat-shrinkable tube is manufactured, for example, by the technique disclosed in Belgian Patent No. 564359 (1958). This technology can be summarized as follows.

That is, a fluorine resin tube with a predetermined diameter is inserted into a metal cylinder with a diameter larger than the diameter of the tube, the tube opening is closed, the whole is heated, and pressurized gas is sent into the tube. When the tube is inflated and then cooled while maintaining this pressurized state, the tube is cooled while maintaining its expanded state. It maintains this shape even after the pressure inside the tube is released, and its dimensions do not change at room temperature. However, when this tube is heated to the temperature used during the expansion process, the tube returns to its original size.

To be precise, it contracts in the radial direction and expands in the length direction. This expansion/contraction ratio can be changed depending on the expansion processing conditions, but a value of about 20 to 30% is easy to handle.

The advantage of using this heat-shrinkable fluorine resin tube for attaching the piston head is that there is no need to strictly select the diameter of the tube in accordance with the diameter of the piston head body; It can be used for attaching head bodies with a diameter of 100 mm, and there is almost no loss when removing material.

Furthermore, the tube can be easily made thin enough for this type of deposition, for example around 0.3 mm.

Below, a method for manufacturing a piston head using this heat-shrinkable fluororesin tube will be described in detail.

First, this tube is cut into a predetermined length, taking into account contraction in the radial direction and expansion in the length direction, and the tube is fitted into the piston head body. FIG. 1 shows this state, where 1a is a heat-shrinkable fluororesin tube, and 2 is a piston head body.

The piston head body 2 is made of iron-based sintered alloy, etc., and 3 is a hole into which a piston rod (described later) is fitted, 4 is an orifice, 5 is an outer diameter surface of the piston head body, and 6 is an outer diameter surface 5. It is an annular groove provided in. This annular groove 6 is provided on the outer diameter surface of the piston head in the vicinity of the lip portion, which will be described later, to ensure that the coating layer made of the fluororesin tube is adhered to the outer diameter surface of the head body.

Then, the whole is heated in a heating atmosphere.
For PTFE, at an ambient temperature of 340-370℃,
In the case of FEP, each sample is held at an ambient temperature of 250 to 300°C for 3 to 10 minutes. Fluorine resin tube 1
shrinks and adheres to the outer diameter surface 5 of the head body 2.

FIG. 2 shows this state, where 1b is an adhesion layer and 7 is a heating furnace.

Fluorine resin adhesion layer 1b thus obtained
The adhesive layer 1b is not in perfect contact with the outer diameter surface of the head body, and the outer diameter dimension of the adhesion layer 1b is not accurate. Incidentally, the annular groove 6 on the outer diameter surface of the head body
A gap 8 remains with the adherend layer 1b somewhat inserted therein.

Therefore, sizing is performed in the next step. FIGS. 3 and 4 show the sizing process, where 9 is a sizing mold and 10 is a press mold. The sizing mold 9 should be 250 to 340℃ when using PTFE, and 200 to 250℃ when using FEP.
In both cases, the temperature is lower than the ambient temperature applied to the shrinkage treatment.

When the piston head with a fluorine resin coating layer is pushed into the sizing receiving die 9, a pressing force is applied to the coating layer in the radial direction, and the resin constituting the coating layer is pushed in the opposite direction to the pushing direction. Causes plastic flow of the material.

Through this process, the thickness of the adhered layer is slightly reduced,
and an axial extension occurs at the end of the piston head opposite to the direction of indentation. At the same time, the adhesion layer is brought into close contact with the outer diameter surface of the head. Incidentally, in FIG. 4, the void 8 in the annular groove that remained at the time of heat contraction in FIG. 2 is filled by the plastic flow of the resin and no longer exists.

11 is a stretched portion of the fluororesin adhesion layer. As already mentioned, the temperature of the sizing mold should be lower than the heat shrinkage temperature.
This is necessary in order to form the stretched portion 11 soundly.If the temperature in the sizing process is higher than the temperature in the shrinkage process, the stretched portion 11 will be bent or wrinkled, which will seriously hinder the formation of the subsequent lip. This creates difficulties and makes it impossible to form the desired lip.

FIG. 5 shows the lip forming step, which is carried out under almost the same heating conditions as sizing.

Reference numeral 12 denotes a lip forming receiving mold which has the same cavity dimensions as the sizing receiving mold 9, but has an inclined surface 13 for forming the lip and an enlarged diameter portion 14 connected thereto. Reference numeral 15 denotes a press mold, which has a slope 1 on its peripheral edge opposite to the slope 13 of the receiving mold.
6, and the above-mentioned extending portion 11 has the slope 1
3 and 16, the diameter of the adherend layer is uniformly expanded from the outer circumferential surface of the adherend layer 1b, and a lip portion 17 is formed at the peripheral edge portion having a larger diameter than the peripheral edge portion of the adherend layer 1b.

FIG. 6 shows the lip portion 1 obtained in this way.
7 is a perspective view of a piston head H coated with a fluorine resin having a diameter of 7.

The piston head H of the present invention has its sealing function exclusively in the lip portion 17, so there is no need to pay particular attention to the clearance between the outer circumferential surface of the head and the inner circumferential surface of the cylinder tube, and the thermal expansion of the head is taken into account. All you have to do is set the clearance.

When this piston head is assembled into a shock absorber, the lip portion 17 is positioned on the side of the piston where damping is applied.

FIG. 7 is a longitudinal sectional view showing an example of a shock absorber incorporating the piston head of the present invention.
In the figure, H is the piston head of the present invention, C is the cylinder tube, P is the outer cylinder, R is the piston rod, and O is oil.

FIG. 8 is a partially enlarged longitudinal sectional view showing the state of sliding contact between the piston head H and the cylinder tube C in FIG. There is a considerable clearance L between the outer peripheral surface of the head and the inner peripheral surface of the tube.

〔Effect of the invention〕

As explained above, the piston head coated with the fluorocarbon resin of the present invention can be used by being incorporated into equipment consisting of a piston and cylinder, such as a shock absorber, and operates smoothly, without rattling noise, and with a smooth lip. Since it has a part, it has an excellent sealing function and exhibits a good damping effect, and has many other effects.

[Brief explanation of drawings]

FIGS. 1 to 5 show a process for manufacturing a piston head in which a heat-shrinkable fluororesin tube is adhered to a piston head body, and a lip portion is formed by an extended portion of the adhered layer. Fig. 1 is a vertical cross-sectional view of the piston head body with a heat-shrinkable fluorocarbon resin tube fitted over the piston head body, and Fig. 2 is a longitudinal cross-sectional view of the piston head body with a heat-shrinkable fluorocarbon resin tube fitted thereon, and Fig. 2 shows a heat-shrinkable fluororesin tube fitted onto the piston head body. FIG. 3 is a vertical cross-sectional view of the head with an adhesive layer and the sizing mold, showing the head with an adhesive layer in a state in which sizing is started; FIG. FIG. 5 is a vertical cross-sectional view of the head and the sizing mold showing a state in which sizing has been completed, and FIG. 5 is a vertical cross-sectional view of the head and the lip forming mold showing the lip forming step. FIG. 6 is a perspective view showing one embodiment of the piston head of the present invention, FIG. 7 is a longitudinal sectional view showing an example of a shock absorber incorporating the piston head of the present invention, and FIG. FIG. 3 is a partially enlarged longitudinal cross-sectional view showing a state of sliding contact between the piston head and the cylinder tube in the figure. 1a...Heat-shrinkable fluororesin tube, 1b
...Adhesion layer made of heat-shrinkable fluororesin, 2...
... Piston head main body, 5 ... Outer diameter surface, 6 ... Annular groove, 7 ... Heating furnace, 9 ... Sizing receiving mold, 10 ... Sizing press mold, 11 ... Extension part,
12... Lip part forming receiving mold, 15... Lip part forming press mold, 17... Lip part, H... Piston head.

Claims (1)

[Scope of Claims] 1. A heat-shrinkable fluorine resin tube is adhered to the outer diameter surface of the piston head body to form a low-friction sliding surface, and the tube is attached at one end in the axial direction of the head body. A piston head coated with a fluorine resin, characterized in that the coated layer is uniformly expanded in diameter from its outer peripheral surface to form a lip that seals fluid. 2. Fitting a heat-shrinkable fluorine resin tube onto the outer diameter surface of the piston head body; heating the entire tube to shrink the tube and attaching it to the outer diameter surface of the head body; The adhesive layer is pushed into a sizing mold with a radial direction applied to the adherend layer to ensure adhesion, and the dimensions of the adherend layer are determined. Stretching in the axial direction at the end of the head body on the opposite side, and then pressing the stretched part in the axial direction of the head body to uniformly expand the diameter from the outer circumferential surface of the adherend to form a lip part. A method of manufacturing a piston head coated with a fluororesin comprising the above steps.