JPH0223746B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a piston head coated with fluororesin suitable for use in hydropneumatic equipment such as air cylinders and hydraulic cylinders, particularly for shock absorbers, 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 into contact with the cylinder tube, and a piston ring made of copper alloy or the like or a metal A short cylindrical ring made by winding a strip coated with low-friction plastic is fitted onto the back metal.

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

In addition, 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 to have dimensions close to the dimensions of the piston head to which it is to be applied, so if the diameter of the piston head differs, a mold with dimensions that match it will be required. do.

Furthermore, in order to cope with thermal expansion of the plastic coating layer due to heat generated during use, the piston head of 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 a so-called tight fit condition.

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 is 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.

This U.S. patent provides the above-mentioned voids to address this problem, but the presence of these voids often causes the gas trapped within the voids to expand, causing the adhesion of the plastic adhesion layer to deteriorate. This creates a new problem of harming sexuality.

(Problems to be Solved by the Invention) The present invention solves the above-mentioned problems of noise in the prior art, problems in obtaining a cup-shaped plastic molded product, problems in adhesion of the adhesion layer, and problems in clearance. It was made to solve the
Take the following solution.

(Means for solving the problem) That is, a heat-shrinkable fluororesin tube is heat-shrinked on the piston head body to form a resin adhesion layer, and the adhesion layer is formed on at least one end surface of the head body. The present invention provides a piston head coated with a fluorine resin formed by folding a layer radially outward and uniformly expanding the diameter of the folded periphery to form a lip that seals fluid, and a method for manufacturing the same. .

In addition to the above-mentioned PTFE, the fluorocarbon resin tube used in the present invention is made of tetrafluoroethylene hexapropylene copolymer (FEP) and these fluorocarbon resins as main components, and is filled with reinforcing fillers and lubricating fillers. Those containing agents etc. are used.

FEP has a slightly inferior coefficient of friction and heat resistance compared to PTFE, but it has excellent wear resistance.

Fluorine resin heat-shrinkable tubes can be 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 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 the inflated 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 dimensions. To be precise, it contracts in the radial direction and expands in the length direction.

Although this expansion/contraction ratio can be changed depending on the expansion processing conditions, it is easy to handle a material having an expansion/contraction ratio of about 20 to 30%.

The advantage of using this heat-shrinkable fluorocarbon resin tube to attach the piston head is that it is not necessary to strictly select the diameter of the tube according to the diameter of the piston head body, and it can be used at various shrinkage rates within the above-mentioned shrinkage ratio range. It can be used for attaching head bodies of different diameters, and there is no loss when removing material.

Further, the wall thickness of the tube can be easily varied from a thin thickness preferable for this type of deposition, for example around 0.3 mm, to a thickness of 1 mm or more if necessary.

First, a heat-shrinkable fluorine resin tube is fitted onto the piston head body taking into account the amount of heat shrinkage. As mentioned above, when heated, the tube contracts in the radial direction but expands in the length direction, so it is cut to a predetermined length in consideration of this expansion.

If a lip part is provided on both end faces of the piston head body, or if a lip part is provided only on one end face but the other end face needs to be covered with an adhesive layer, it is necessary to The length of the tube is determined in advance so that it is longer than the height of the head body in the horizontal direction.

If this is not necessary and a lip portion is provided only on one end surface, the cutting length of the tube is determined in relation to the amount of stretching of the adhered resin during sizing, although this also relates to the subsequent sizing process.

The tube thus cut to a predetermined length is fitted onto the head main body, both are placed on a stand, and the whole is placed in a heating furnace for heat shrinking treatment.

The heat treatment temperature is 340 to 370℃ when PTFE is used as the fluorine resin, and 250 to 370℃ when FEP is used.
The temperature is 300°C and the treatment time is 3 to 10 minutes.

The adhesive layer that is heat-shrinked and adhered to the head body is
Since the adhesion is not perfect and there are variations in dimensional accuracy and roundness in the radial direction, sizing is performed using a heated mold to eliminate this.

The mold temperature in the sizing process should be lower than the temperature in the heat shrinking process, and in the case of PTFE,
250-340℃, 200-250℃ for FEP.
If the temperature is too high, bends and wrinkles will occur in the stretched portion, which will be described later, and this will significantly impede the formation of the lip portion.

In the present invention, the sizing process involves perfecting the adhesion of the adhesive layer to the outer diameter surface of the head main body, measuring the dimensions of the adhesive layer in the radial direction, and stretching the adhesive resin layer. The feature is that it allows you to do the following.

In addition, when providing lip portions on both end surfaces of the head body, or when providing a resin adhesion layer on one end surface, it is important to form the lip portion or adhesion layer on one end surface in this sizing process. Has characteristics.

In the present invention, the lip portion provided on the end surface of the head main body is formed by bending the adhesion layer provided on the outer diameter surface of the head main body radially inward to apply it to the end surface, and then folding it back to cover the end surface. It is formed by overlapping and adhering to the adherend layer and expanding the diameter of the peripheral edge.

The lip formed in this way can, for example, touch the edge of the adhesion layer provided on the outer diameter surface of the head body.
Compared to the configuration where the diameter is expanded from the outer diameter surface to create a lip part, the influence of the fluid on the adhered layer can be reduced, so problems such as peeling of the adhered layer are almost completely eliminated. It also has an excellent sealing function.

Like the piston in an air cylinder,
When both end faces are used alternately as the pressure side, a piston head with lip parts on both end faces is used, but when pressure is applied to the damping side like a shock absorber,
A type in which a lip portion is provided only on one end surface is used.

Below, a method for manufacturing a resin-coated piston head using this heat-shrinkable fluororesin tube will be explained with reference to examples.

(Embodiment) FIG. 1 is a perspective view showing an embodiment of a piston head having a lip portion on one end surface and coated with the fluorine resin of the present invention.

FIG. 2 is a perspective view showing another embodiment of a piston head coated with the fluorine resin of the present invention and having lip portions on both end faces.

FIG. 3 is an enlarged longitudinal cross-sectional partial view of FIG. 1.

In the figure, 1 is a fluorine resin coating layer, 2 is a piston head body, 3 is an outer diameter surface of the head body, and 4 is a piston head body.
is one end face thereof, and 5 is the other end face. 6 and 7 are ring-shaped grooves provided on each end face.

1a is a fluorine resin adhesion layer applied to the outer diameter surface 3 of the head body, 1b is an adhesion layer applied to one end face 4, and 1c is an adhesion layer applied to the other end face 5. ,
1d is a lip portion formed by folding back the adherend layer 1b and expanding its peripheral edge.

The adhering layers 1b and 1c on each end face are:
The ring-shaped grooves 6 and 7 are filled with resin constituting the adhesion layer and locked, ensuring adhesion on the end faces.

4 to 10 show the method of manufacturing the piston head shown in FIG. 1 in the order of steps.

FIG. 4 is a longitudinal sectional view showing a state in which a heat-shrinkable fluororesin tube PTFE indicated by 1' is fitted onto the head main body 2.

In this embodiment, since the adhesion layer 1c is provided on the end surface 5 of the head body, the head body 2 is placed upside down on the stand 8, and the tube 1' during the heat shrinking treatment is placed upside down. This is intended to cause expansion in the length direction of the end surface 5 to occur on the end face 5 side.

In the figure, 9 is a hole into which a piston rod, which will be described later, is fitted, and 10 is an orifice.

Then, as shown in the longitudinal cross-sectional view in FIG. 5, the whole was placed in a heating furnace 11 and treated at 350° C. for 5 minutes to shrink the tube 1' and adhere it to the outer diameter surface 3 of the head body. . 1c' is a protrusion of the adhered layer that bulges in the axial direction during the treatment. This protrusion 1c' covers the end surface 5 of the head body and covers the adhesion layer 1c.
It has sufficient length to form a

FIG. 6 is a longitudinal cross-sectional view of the mold and head in the sizing process, where 12 is the sizing mold, 13 is the receiving mold, and 14 is the pressing mold, and the temperature of the mold is 300°C.

The head obtained through the heat shrinking step shown in FIG. 5 is allowed to cool slightly, the upper and lower end surfaces are returned to their original positions, and the head is press-fitted into a mold with the protrusion 1c' side of the adherent layer facing down.

In this sizing process, the adhesion layer 1a is
3, the adhesive layer 1a receives a radially inward pressing force and causes plastic flow of the resin in the direction opposite to the press-fitting direction, so that the thickness of the adhered layer 1a is slightly reduced.

Before the head with the adhesive layer reaches the bottom of the receiving mold, the protruding portion 1c' of the adhesive layer comes into contact with the bottom of the receiving mold and is bent inward in the radial direction, and as the press-fitting by the pressing mold continues, the protrusion 1c' of the adhesive layer is bent. The end is brought into close contact with the end surface 5 of the head body under pressure in the axial direction, and an adhesion layer 1c is formed there. At this time, the bent end is tightly filled into the ring-shaped groove 7 provided on the end face of the head body and is locked there.

On the other hand, plastic flow of the resin that occurs in the direction opposite to the press-fitting direction in this sizing process is caused by the plastic flow of the adhered layer 1a.
axially upward stretching. 15 is
This stretched portion is shown. The length of the extending portion 15 is such that it is bent onto the end surface 4 of the head main body, as will be described later.
Then, it is folded back and expanded in diameter, and the end face adhesive layer 1 is placed there.
The length is sufficient to form the lip portion 1d.

The length of this extended portion 15 is determined by the restoring force in the longitudinal direction remaining in the adherend layer 1a, the size of the drawing margin at the time of press-fitting into the receiving mold, and the sizing temperature.

As already mentioned, the temperature of the mold in the sizing process is lower than the heat shrinkage temperature in the previous process, but this is necessary in order to form the stretched portion 15 in a sound manner. If the height is increased, bends and wrinkles will occur in the stretched portion 15, making it extremely difficult to form a lip portion in a subsequent process.

FIG. 6 shows a longitudinal section of the member at the time when the formation of the adhesion layer on one end face of the head body and the formation of the extension portion on the other end face side are completed.

FIGS. 7 to 10 are partial views showing the positional relationship between the press mold and the receiving mold and the longitudinal cross-sectional structure of the workpiece in the lip forming step.

Reference numeral 16 designates a receiving mold, and the receiving mold 13 used in the sizing process may be used as is, or a separate mold having the same cavity dimensions may be used.

17 is a pressing mold, 18 is an outer diameter portion that fits into the cavity of the receiving mold, 19 is a peripheral step portion, 20 is a reduced diameter portion, 2
1 is an end face part, and 22 is a reduced diameter part 20 and an end face part 2.
It is a convex curved surface portion connecting 1 to 1.

When the press mold 17 descends, the peripheral stepped portion 19 of the press mold comes into contact with the end of the extending portion 15 and presses it in the axial direction.
A substantially central portion of the extending portion 15 is bent inward in the radial direction. FIG. 8 is a partial vertical cross-sectional view of the mold and workpiece showing this state.

As the pressing die 17 further descends, the portion below the center of the extending portion 15 is attached to the upper end surface 4 of the head body, and the portion above the center is folded back radially outward and placed on the upper end surface. The end face adhesive layer 1b is formed by overlapping and adhering to the adhesive layer.

FIG. 9 is a partial vertical cross-sectional view of the mold and workpiece showing this state. The ring-shaped groove 6 has an adhesion layer 1b.
The folded peripheral edge portion 23 of the adherend layer 1b has the same diameter as the adherend layer 1a.

Outer diameter adhesion layer 1a in the above sizing process
The pressing force at the time of dimensioning varies depending on the height and area of the adhered layer portion, the drawing margin, and the sizing temperature, but an axial pressing force of approximately 50 to 200 kg/cm ² is sufficient. In the present invention, when applying PTFE to a head body having an outer diameter of 30 mm, a height of 10 mm, and an end surface area of 3 cm ² , good results have been obtained with a pressing force of 100 kg/cm ² .

In addition, a pressing force of 200 to 500 kg/cm ² is preferable when forming the end face adhesion layers 1b and 1c, and in the case of the above-mentioned adhesion area, a pressing force of 300 kg/cm ² (maintained for about 10 to 20 seconds) is good. We are getting results.

FIG. 10 is a vertical cross-sectional partial view of the mold and the workpiece, showing the step of expanding the diameter of the folded peripheral edge of the end face adhesive layer to form a lip portion. The temperature of the mold is approximately the same as that during the sizing process.

24 is a receiving mold, 25 is a cavity of the receiving mold and has a diameter approximately equal to the outer diameter of the head main body having the adherent layer 1a, 26 is a stepped portion expanding outward in the radial direction, and 27 is a cavity that is connected to the cavity 25. A concave curved surface portion connects to the stepped portion 26, and 28 is an enlarged diameter portion.

29 is a press mold, 30 is an outer diameter portion that fits tightly into the enlarged diameter portion 28 of the receiving mold, 31 is a peripheral step, 32 is an end surface, and 33 is a convex connecting the peripheral step 31 and the end surface 32. It is a curved surface.

By lowering the press die 29, the diameter of the folded peripheral edge 23 of the adherend layer is expanded to form a lip portion 1d.

In this lip part forming step, the lip part 1d can be obtained by heating an appropriate press die and pressing it against the adherend layer 1b to expand the diameter of the peripheral edge part 23 without using the receiving die 24. The advantage of using a mold and a mold is that by changing the radius of curvature of the concave curved surface portion 27 and the convex curved surface portion 33, not only can the wall thickness of the lip portion 1d be made thinner, but also that the lip can be made with good dimensional accuracy. Can be done.

In the above embodiment drawings, a method for manufacturing a piston head having a lip portion only on one end surface of the head body has been described, but as shown in FIG. ,
By configuring the bottom of the receiving mold in the sizing process shown in FIG. 6 like the pressing mold 17 in FIG. 7, a folded adhesive layer can be provided on the lower end surface 5 of the head main body 2. The folded periphery is the 10th
By enlarging the diameter in the manner shown in the figure, a piston head is obtained which also has a lip on the lower end surface 5 of the head body.

FIG. 11 is a longitudinal sectional view showing an example of a shock absorber incorporating the piston head of the present invention shown in FIG. 1, in which H is the piston head of the present invention, C is the cylinder tube, and P is the outer cylinder, R is the piston rod, and O is oil.

(Effects of the Invention) As explained above, the piston head coated with the heat-shrinkable fluororesin tube of the present invention has high adhesion strength, and at least one end surface of the head body is coated on the outer diameter surface. Since it has a folded and folded adherend layer that is integrated with the adherend layer and a lip part whose diameter is enlarged around the folded periphery, the lip part has great strength against sliding and fluid pressure, and its sealing function is exclusive. Since it rests on this lip, there is no need to be very careful about the clearance between the head outer diameter surface coating layer and the cylinder tube, and the operation is smooth and no rattling noise is generated.

Since a heat-shrinkable fluorocarbon resin tube is used to provide the fluorocarbon resin adhesion layer, there is no need to strictly select the diameter of the tube according to the diameter of the piston head body, and the shrinkage rate can be adjusted within the range. It has many practical advantages, such as being able to adhere to head bodies of various diameters within the tube, eliminating the loss of material during material removal, being able to use thin-walled tubes, and being able to easily obtain such thin-walled tubes. It has a great effect.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing an embodiment of a piston head coated with the fluorine resin of the present invention having a lip portion on one end surface, and FIG. FIG. 3 is a perspective view showing another embodiment of a piston head coated with resin. Figure 3 shows
FIG. 2 is an enlarged longitudinal cross-sectional partial view of FIG. 1; Figures 4 to 10 show the manufacturing method of the piston head shown in Figure 1 in the order of steps, and Figure 4 shows the state in which a heat-shrinkable fluorine resin tube is fitted into the piston head body. Fig. 5 is a longitudinal cross-sectional view of the head main body and the tube showing the heat shrinking process, and Fig. 6 is a longitudinal cross-sectional view of the head main body and the adhesion layer showing the heat shrinking process, and Fig. 6 shows the mold and workpiece at the time of completion of sizing in the sizing process. FIGS. 7 to 10 are vertical cross-sectional partial views of the mold and the workpiece in the lip forming step. FIG. 11 is a longitudinal sectional view showing an example of a shock absorber incorporating the piston head of the present invention shown in FIG. 1. 1, 1a, 1b, 1c...fluororesin adhesion layer, 1
c'...Protrusion part, 1d...Rip part, 1'...Heat-shrinkable fluorine resin tube, 2...Piston head body,
4, 5... End face, 6, 7... Ring-shaped groove, 11...
Heating furnace, 12...Sizing mold, 15...Stretching part, 1
6... Receiving die, 17... Pushing die, 18... Outer diameter part, 19...
Peripheral step part, 20... Reduced diameter part, 21... End face part, 22...
Convex curved surface part, 23... Folded peripheral edge part, 24... Lip part forming receiving mold, 25... Cavity, 26... Step part, 2
7... Concave curved surface part, 28... Expanded diameter part, 29... Lip part forming mold, 30... Outer diameter part, 31... Peripheral step part, 32...
End surface portion, 33...Convex curved surface portion, H...Piston head,
C...Cylinder tube, R...Piston rod,
O...Oil.

Claims (1)

[Claims] 1. A heat-shrinkable fluororesin tube is heat-shrinked on the piston head body to form a resin adhesion layer, and the adhesion layer is placed radially outward on at least one end surface of the head body. A piston head coated with fluororesin, characterized in that it is folded back and the diameter of the folded periphery is uniformly expanded 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 heat-shrink the tube and attaching it to the outer diameter surface of the head; The head body is press-fitted into a sizing mold to apply a radially inward pressing force to the adherend layer to ensure adhesion and to determine its dimensions, and at the same time generates plastic flow in the adherend layer on the outer diameter surface of the head body and press-fits. Stretching the adherend layer in the opposite direction, pressing the stretched portion in the axial direction using a heated mold to bend approximately the center of the stretched portion inward in the radial direction into a bent shape; The lower part is applied to the upper end surface of the head main body, and the upper part from the center is folded radially outward to overlap and adhere tightly to the adhesion layer on the upper end surface, and then the periphery of the folded extension part is A piston coated with fluorine resin, characterized in that it consists of the above-mentioned steps of pressing in the axial direction using a heated mold to uniformly expand the diameter to form a lip that seals the fluid. Head manufacturing method. 3. 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, and extending the axis from the end surface of the head. Providing a protruding part that bulges in the direction, press-fitting the protruding part downward into a heated sizing mold, applying a pressing force radially inward to the adhered layer to ensure adhesion and its size. At the same time, the protruding part is pressed in the axial direction, and the approximately central part of the protruding part is bent radially inward in a bent shape, and the part above the center of the protruding part is attached to the lower end surface of the head body, and the center The lower portion is folded radially outward to overlap and adhere tightly to the adhesive layer on the lower end surface, and in this sizing process, at the same time, plastic flow is generated in the adhesive layer on the outer diameter surface of the head body to improve the pressure in the press-fit direction. Stretching the adherend layer to the opposite side, and then pressing the stretched portion in the axial direction using a heated mold to bend approximately the center of the stretched portion inward in the radial direction into a waist-fold shape, The lower part is attached to the upper end surface of the head body, and the upper part from the center is folded radially outward to overlap and adhere tightly to the adhesive layer on the upper end surface.In this way, the upper and lower end surfaces of the head body are The method is characterized by comprising the above-mentioned steps of pressing the peripheral edge of the folded portion formed in the mold in the axial direction using a heated mold to uniformly expand the diameter to form a lip portion that seals fluid. A method for manufacturing a piston head coated with fluorine resin.