JPH04369534A - Method and apparatus for shaping green tire - Google Patents

Abstract

PURPOSE:To prevent the biting of the rubber of a green tire and to enhance tire uniformity by suppressing a sudden increase in the internal pressure of a bladder accompanied by mold clamping at the time of the shaping of the green tire and keeping shaping pressure almost constant. CONSTITUTION:Inert gas such as nitrogen gas is supplied to the bladder 54 arranged in the green tire 52 within a mold 50 to expand the bladder 54 and the green tire is shaped. At this time, the inert gas is discharged from the bladder corresponding to an increase in the internal pressure of the bladder accompanied by mold clamping to keep shaping pressure almost constant.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] This invention prepares the shape of a green tire before vulcanization molding, prevents rubber from chewing when the mold is closed, and improves the shape of the mold, the green tire, and the green tire and bladder. The present invention relates to a method and apparatus for shaping a green tire that suppresses the occurrence of air traps between the tires and improves the uniformity of the molded tire.

0002

[Prior Art] Before green tires are vulcanized and molded, a so-called shaping operation is performed with the main purpose of adjusting the shape of the tire itself and making it easier to fit into the inner shape of the mold. is customary.

[0003] This work, as schematically shown in FIG.
First, the mold 10, that is, the upper mold 1, is opened along the mating surfaces.
A green tire 12 to be vulcanized and molded is placed in a space defined by the lower die 10b and the green tire 12, and a bladder 14 disposed inside the green tire 12 is supplied from a supply source 16 through a supply pipe 18. The green tire 12 is inflated with an inert gas such as nitrogen gas, and the green tire 12 is expanded from the inside to the outside to form a shape similar to the inner surface of the mold, and then the upper and lower molds 10a and 10b are closed. At the same time, by applying a higher shaping pressure to the bladder 14, the shape of the green tire 12 is made such that the entire green tire 12 is easily brought into close contact with the mold 10.

Then, the three-way valve 20 provided in the supply pipe 18 is switched to supply a higher pressure vulcanizing medium such as steam or nitrogen gas from a vulcanizing medium supply source (not shown) to further inflate the bladder 14. The green tire 12 after the shaping work is pressed almost uniformly onto the entire inner surface of the mold 10, while being heated from the outside by the heated mold 10 to vulcanize and mold it into a molded tire of a predetermined shape.

The supply pipe 18 is provided with a three-way valve 2 for switching the flow of inert gas and vulcanizing medium to the bladder 14.
0, a valve means 22 for setting the pressure of the inert gas from the supply source 16 to a predetermined pressure, and a valve means 22 for allowing the inert gas at the predetermined pressure to flow toward the bladder, while allowing the inert gas to flow in the opposite direction. Check valves 24 for blocking the flow are sequentially arranged between the supply source 16 and the three-way valve 20, and by opening and closing the three-way valve 20, inert gas or vulcanizing medium is supplied to the bladder 14. It can be supplied as appropriate. On the other hand, Bladder 1
Another three-way valve 28 is attached to the discharge pipe 26 connected to 4, and by opening and closing this three-way valve 28, the inert gas and vulcanizing medium can be appropriately discharged from inside the bladder. .

[0006]

[Problems to be Solved by the Invention] However, in such a conventional technique, since the inflated green tire 12 is pinched by the closing movement of the upper and lower molds, the volume in the bladder space decreases, and as shown in FIG. As shown by P in 4(b),
As the internal pressure of the bladder 14 rapidly increases, the green tire to be shaped undergoes local deformation, and a portion of the green tire pressed from the inside by the bladder gets caught in the dividing surface of the mold, and furthermore, It is known that the uniformity of sulfur-molded tires deteriorates. For this reason, an orifice 29 is provided in the discharge pipe 26 to keep the primary shaping pressure constant and to continuously increase the shaping pressure as shown by the broken line in the same figure. A method has also been proposed in which the inert gas is discharged from the bladder 14 while suppressing the decrease in the bladder internal pressure while alleviating the sudden increase in the pressure.

However, since the opening area of the orifice 29 is constant, the inert gas cannot be discharged quickly in response to changes in the bladder internal pressure caused by the slowness of the mold clamping operation. Since the mold clamping operation must be performed in relation to the orifice 29, the mold clamping time uniquely determines the shaping operation time, which poses a problem in that it is difficult to shorten the production cycle. In other words, if you are trying to shorten the shaping work time,
As the bladder internal pressure increases rapidly with mold clamping, the problems of rubber chewing and uniformity mentioned above become unavoidable.On the other hand, if an orifice with a large opening area is used, the bladder internal pressure tends to decrease; Another problem arises in that it is difficult to perform a satisfactory shaping operation.

[0008] In addition, the discharge pipe 26 is
It is conceivable to open the three-way valve 28 and allow the inert gas to be discharged from the bladder through the exhaust pipe 30, thereby suppressing the rapid increase in internal pressure and maintaining the internal pressure almost constant. It is difficult to quickly adjust the valve opening of the three-way valve in response to rapid changes in bladder internal pressure due to tightening, and the above-mentioned problem has not yet been solved.

The present invention has been made in view of these problems, and provides a green tire shaping method and apparatus capable of suppressing the rapid increase in bladder internal pressure associated with mold clamping and keeping shaping pressure almost constant. The purpose is to provide

0010

[Means for Solving the Problems] In order to achieve this object, in the method of the present invention, an inert gas such as nitrogen gas is supplied to a bladder placed in a green tire in a mold to inflate the bladder. , when shaping a green tire, an inert gas is discharged in response to an increase in pressure inside the bladder due to mold clamping, and the shaping pressure is maintained almost constant.

In the apparatus of the present invention, in particular, the inert gas is supplied from the bladder to the supply pipe for supplying the inert gas to the bladder in response to an increase in the pressure inside the bladder due to the clamping of the mold. Valve means are provided for venting and for shutting off the supply of inert gas from the source to the bladder to maintain the shaping pressure substantially constant. In addition, when the valve means is attached to the supply pipe, it is preferable that the valve means is capable of reducing the supply pressure of inert gas from the supply source to a predetermined pressure. It is preferable to provide a strainer to remove impurities contained in the inert gas discharged from the bladder.

0012

[Operation] According to the present invention, the supply pipe is provided with a valve means that cuts off the supply of inert gas to the bladder in response to changes in the internal pressure of the bladder due to mold clamping, while allowing its discharge from within the bladder. Therefore, even if the bladder is pressed during the mold clamping operation, the internal pressure can be maintained substantially constant. Note that by disposing a strainer in the piping section between the valve means and the bladder, the operation of the valve means is ensured by removing the green tire or foreign matter attached thereto.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the drawings. FIG. 1 is a diagram showing a shaping apparatus to which the method of the present invention is applied, in which an upper mold 50a and a lower mold 50b of a mold 50 are shown.
The green tire 52 is opened and closed along the dividing plane, and the green tire 52 is accommodated in the space defined by the upper and lower molds. on the other hand,
The bladder 54 located inside the green tire 52 is
The green tire 52 is inflated by being supplied with an inert gas through a supply pipe 58 connected to a supply source 56 of an inert gas such as nitrogen gas, and the green tire 52 is expanded from the inside to the outside to form a mold. Shape close to the inner surface. Next, upper mold and lower mold 5
By applying a higher shaping pressure to the bladder 54 via the supply pipe 58 while closing the green tire 52, the shaping operation is completed by making the green tire 52 into a shape that makes it easier to adhere to the mold 50 as a whole.

When the shaping operation is completed, the three-way valve 60 provided in the supply pipe 58 is switched to supply a higher pressure vulcanizing medium such as steam or nitrogen gas to the bladder 14 from a vulcanizing medium supply source (not shown). Similar to the prior art, the green tire 52 is pressed almost uniformly onto the entire inner surface of the mold 50, and heated from the outside using the heated mold 50 to vulcanize and mold it into a predetermined shape. In addition, bladder 5
The inert gas and the vulcanizing medium are discharged from the inside of the chamber 4 by opening and closing a three-way valve 64 attached to a discharge pipe 62 connected thereto.

In this embodiment, a valve means 66 is provided in the supply pipe for supplying inert gas into the bladder. This valve means 66 is capable of discharging inert gas from within the bladder in response to an increase in pressure within the bladder due to mold clamping, and is capable of cutting off the supply of inert gas from its source to the bladder. For example, the control valve shown in FIG. 2 can be used.

The control valve 66 is capable of causing fluid to flow down in the direction indicated by the arrow in the figure along a flow path communicating from the input section 68 to the output section 70, and a valve seat 72 formed in the flow path
The valve body 74 is arranged so as to be able to come into contact with the first
It has a configuration in which it is held movable relative to a diaphragm 76 and is pressed by a second diaphragm 78 that receives a signal pressure Ps, so that the valve body 74 is pushed down by the difference between the signal pressure Ps and the source pressure P of the fluid. At , fluid at a predetermined pressure P is brought from the output section 70 . When the output pressure P exceeds a predetermined value, the output pressure pushes up the first diaphragm 76 through the suction pipe 80, presses the valve body 74 against the valve seat 72, and blocks the flow path. As the output pressure increases further,
The valve body 74 pushes up the relief valve 84 against the spring 82 provided on the second diaphragm, bringing the relief valve 84 into communication with the discharge hole 86, allowing fluid to be discharged. Therefore, the output pressure P can be maintained at approximately a predetermined pressure.

Therefore, if this control valve 66 is attached to the supply pipe between the inert gas supply source 56 and the three-way valve 60 and an appropriate signal pressure Ps is applied to the second diaphragm 78,
The inert gas at the pressure P0 supplied from the supply source 56 is reduced to a predetermined pressure P. On the other hand, when the output supplied to the bladder 54 exceeds a predetermined pressure, the inert gas from the supply source side is blocked, and the bladder 54 is
4 increases further, the relief valve 84 is pushed up by the increased pressure, and the inert gas is discharged from the discharge hole 86. Therefore, Bladder 54
The applied pressure is maintained almost constant, ensuring good shaping work. Of course, the control valve applicable to the present invention is not limited to this.

By the way, in consideration of the fact that the inert gas applied to the bladder 54 may contain impurities such as deteriorated rubber on the inside of the bladder, in this embodiment, the control valve 66 and The piping section between the bladder 54, i.e.
A strainer 8 is installed in the piping between the control valve 66 and the three-way valve 60.
0 to prevent the operation of the control valve 66 from being impaired by these impurities.

In addition, in this embodiment, by installing the control valve 66 between the inert gas supply source 56 and the bladder 54, the bladder 54 is closed during mold clamping as in the conventional example shown in FIG. It is possible to eliminate the need for a check valve that prevents backflow of inert gas due to an increase in internal pressure. On the other hand, with the removal of the check valve, the three-way valve 60 was removed during the vulcanization process.
If there is a risk that the vulcanizing medium, such as high-pressure steam or nitrogen gas, supplied to the bladder 54 via the strainer 80 and the three-way valve 6 may leak from the three-way valve toward the control valve,
It is preferable to provide, for example, a switching valve 88 between the three-way valve 60 and the strainer 80, which allows inert gas to flow into the bladder while suppressing the flow of the vulcanizing medium from the three-way valve 60 toward the strainer 80.

Of course, valve means are disposed in the discharge pipe 62 for discharging the inert gas from the bladder 54, ie downstream of the three-way valve 64 for discharging the vulcanizing medium from within the bladder.
A valve that can discharge inert gas from inside the bladder in response to an increase in the pressure inside the bladder due to mold clamping, and a valve that is installed in the supply pipe and can shut off the supply of inert gas from that source to the bladder. The valve may be provided with a valve.

Incidentally, FIG. 4 shows the change in bladder internal pressure when shaping a green tire for a truck bus using the device shown in FIG. 1 to which the present invention is applied and the conventional device shown in FIG. 3. , uniformity of invented tires and conventional tires obtained by vulcanization molding,
That is, the following table shows the results of examining the radial reaction force (RFV) and the presence or absence of protruding rubber on the dividing surface of the mold.

[0022]The uniformity of the tire is an index evaluation based on that of a conventional tire as 100.
The smaller the index, the better the uniformity. In addition, the presence or absence of protruding rubber was visually inspected. It can be seen that according to the present invention, fluctuations in shaping pressure are small, there is no occurrence of extruded rubber, and tire uniformity is improved.

[0023]

Thus, according to the present invention, even during the green tire shaping process, especially during the mold clamping work, the bladder internal pressure is maintained almost constant, and the green tire can be shaped almost along the inner surface of the mold. By uniformly inflating the tire and suppressing a sudden increase in shaping pressure, there is no protruding rubber during mold clamping, and the tire has good uniformity after vulcanization molding.
Tire performance can be improved. In addition, the mold clamping time can be shortened, which greatly contributes to improving productivity.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing a shaping device according to the present invention.

FIG. 2 is an explanatory diagram showing a control valve suitable for application to the apparatus shown in FIG. 1;

FIG. 3 is a schematic diagram showing a conventional shaping device.

FIG. 4(a) is an explanatory diagram showing how the shaping pressure changes with the mold clamping operation when the present invention is applied, and (b) is an explanatory diagram showing how the shaping pressure changes when the conventional device is used. FIG. 3 is an explanatory diagram showing how shaping pressure changes during tightening work.

[Explanation of symbols]

50 Mold 52 Green tire 54 Bladder 56 Source of supply 58 Supply pipe 60 Three-way valve 62 Discharge pipe 64 Three-way valve 66 Control valve 80 Strainer 88 Switching valve

Claims (1)

[Scope of Claims] [Claim l] When shaping the green tire by supplying an inert gas such as nitrogen gas to a bladder placed inside the green tire in the mold, A green tire shaping method characterized by discharging an inert gas from the bladder in response to an increase in bladder pressure accompanying tightening, and maintaining shaping pressure almost constant. 2. In an apparatus for shaping a green tire by supplying an inert gas such as nitrogen gas from a source to a bladder disposed inside a green tire in a mold to inflate the bladder, the bladder is inert. Inert gas is discharged from the bladder to the gas supply pipe in response to the increase in pressure inside the bladder due to mold clamping, and
A shaping device for a green tire, characterized in that a valve means capable of cutting off the supply of inert gas from a supply source to a bladder is provided to maintain shaping pressure substantially constant. 3. The valve means is attached to the supply pipe, and the piping section between the valve means and the bladder is provided with a strainer for removing impurities contained in the inert gas discharged from the bladder. green tire shaping equipment.