JPS605459B2 - How to make pneumatic tires - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method for manufacturing pneumatic tires.

The present invention provides a method for manufacturing a pneumatic tire having beads, sidewalls, and a tread portion, the tire being first formed into at least two parts, each part being molded with unvulcanized rubber in a mold cavity. molded and provided with fixing protrusions to maintain said part in the desired part of the mold, the mold being pressurized and opened when molding at least the sidewalls, and then each part of the tire being placed in the mold in which it is held. are brought into contact with each other and bonded together under heat and pressure.

Preferably, the pneumatic tire is manufactured in at least three sections having two sidewalls and a tread section. The bead core, along with the rubber bead top and cord or fabric or other sidewall reinforcement, may be placed within the sidewall and, if desired, placed in the mold space prior to forming the sidewall. Similarly, the tread portion may have placards or other reinforcements, such as cord fabrics, steel cord fabrics, or high modulus polymeric materials, which are assembled or preformed around the core prior to formation of the tread portion. be able to. If desired, reinforcement may be provided in one or more portions of the tire extending from that portion of the tire.

The tire section is formed with free reinforcement extending therefrom. This free reinforcing piece is held out of the way, and at the same time the tire part associated with this reinforcing piece is brought into contact with the adjacent tire part, and then the joining points of the two parts are brought into contact before the rubber is added. Pressed into contact with adjacent tire portions in a connecting manner. Rubber can be any type of elastomeric cross-linked polymer material, such as natural rubber, butyl rubber, styrene-butadiene rubber,
It may be neoprene, ethylene-propylene rubber, nitrile rubber or mixtures thereof.

The type of rubber used will of course depend on the desired properties of the finished tire, and the selection and formulation of the appropriate rubber for a particular purpose is a procedure well known in the rubber art. Rubber must be substantially unvulcanized when used to form parts of a tire, but its "nerve" or "memory effect" (m
It is preferable to add some amount of processing to the rubber prior to the forming step to eliminate emory.

Suitable processing may be carried out, for example by milling, extrusion or other mechanical or thermal treatment, but should not be carried out to such an extent that the rubber begins its hardening cycle. In other words, although the rubber may have received a certain amount of energy, the rubber still needs to be substantially unvulcanized when used to form parts of a tire. This can be accomplished by paying careful attention to the rheometer curve of cure rate versus temperature of the rubber compound used.

Generally, this curve is one that exhibits an initial flattening of the cure rate, followed by a rapid acceleration of the cure rate once a certain temperature, or "limit" temperature, is reached. In the present invention, where the compounded rubber has this kind of curve, the temperature of the compounded rubber is always kept below this critical temperature throughout the processing, molding and post-assembly stages, and then heated above this temperature when carrying out curing. preferable. The molds used to form each section may conveniently be pressurized by introducing compressed air or other suitable gas, such as nitrogen.

Pressure to at least 0.35 k9/carp (5 p.s.i.) is preferred, but significantly higher pressures may be used if desired. The pressurized gas is divided into equal parts of the mold space (equ
It is usually convenient to pressurize the mold by filling it over the mold.

However, if a male mold is used in conjunction with the mold space, in some applications it is advantageous to introduce the gas through the male mold, such as its pole. Pressurization of the mold should be started before opening the mold for the various parts of the tire and maintained until the parts have been joined and cooled or cured (if desired, each part can be cured after being joined). may be cooled before completion).

Pressure serves to prevent gas from escaping from the warm rubber compound after molding, and also works with fixing protrusions, especially when molding side walls, to hold the molded part in the correct part of the mold and join it. It acts so that it is carried out.

It has been recognized that the escape of gases from warm compound rubber is particularly undesirable as it can cause unsightly holes in the surface of the molded tire part and can also make the finished product riddled with holes, resulting in structural defects in the tire during use. There is. In another embodiment, the invention comprises at least two mold spaces and an apparatus for forming a molded part of a rubber pneumatic tire in these spaces, the mold spaces being provided with a groove for a locking projection. an apparatus for preventing movement of the halves and for pre-processing the rubber without substantially curing it before it is formed; and an apparatus for pressurizing the mold with a gas;
A molding device is provided having a device for collecting mold spaces that holds sections of a tire so as to join the sections together.

The parts of the tire may be shaped within the mold space in any convenient manner.

For example, female mold forming, vacuum forming, and combinations of both techniques can be used for the sheet material. A male mold is used to force the sheet into the mold space, and vacuum forming removes air from the mold space to create a partial vacuum between the sheet and the forming surface of the mold, causing the sheet to This is a method of taking the form of a type space. Furthermore, molding can be carried out by compression molding, transfer molding or injection molding techniques. As a device for preprocessing rubber before molding, it is convenient to use the injection screw of an injection molding device or the transfer action of transfer molding.

A combination of both of the above techniques can be used to feed the transfer chamber with a relatively low temperature screw. For this reason, compression molding alone is not applicable to the method of the present invention, but may be used if the rubber can be "worked" to the desired extent before being placed in the compression mold. The locking projections are shaped to resist movement of the respective tire section within the mold, for example due to deflation of the tire section or removal of the male mold when the male mold is used.

The locking projection also allows the compressed gas entering the mold during pressurization to pass over the lip and over the surface of the molded half that is peeled away from its corresponding mold part, but between the tire part and this tire part. It is preferable that the shape is such that it does not come between the molding space and the wall of the molding space that holds the molding space. If this latter is not done, it is by no means desirable, as it may result in bubbles or similar defects in the product, resulting in a highly unsatisfactory product, and resulting in lifting of the tire part from the molding space in which it is to be held. A particularly convenient form of the fixing projection is one in which a thicker part is connected to one half of the article by a thinner part. Examples of suitable locking projections are shown in FIGS. 1, 2 and 3 of the accompanying drawings and will be described in more detail below. If the tire is to be molded in three parts, preferably the tread part with the breaker assembly, and two side walls, the molding of all parts, i.e. the side walls and the tread part, is carried out with special fastening projections as described above. It can also be carried out using a pressurizing mold.

Instead of the above, when molding the step part, the part of the tread pattern molded on the tread part can be used to act as a fixing protrusion, and similarly, the mold in which the tread part is molded can be folded. Alternatively, it may be a flat ring holding a packing piece of cured non-adhesive rubber to form the inner contour of the tread ring, for example. In the former case the tread mold can remain inside the tread part until after the joining stage, and in the latter case the tread mold ring can be slid laterally out of the tread part before the joining stage. Pressurization of the tread mold is not necessarily necessary;
rix) and to prevent gas from escaping from the molded warm tread rubber.

The method of the invention allows pre-vulcanized tire parts to be formed and then joined without causing damage.

If these unvulcanized portions are formed without going through the steps of the present invention, these unvulcanized portions are susceptible to damage and deflection. For example, unvulcanized portions tend to stick to the male mold when it is removed, resulting in unsatisfactory molding. The method of the invention, as will be explained in more detail below, overcomes these difficulties and makes it possible to obtain satisfactory, fault-free tires from substantially unvulcanized parts. Traditional methods of molding tires in two or more sections typically required at least partial vulcanization of at least one of the sections to prevent damage.

These partially vulcanized parts cannot be satisfactorily joined together without the use of an adhesive. The present invention eliminates all these difficulties and extra steps. Another advantage is that the parts of the tire can be joined together with a relatively low degree of interference, i.e. to form the desired article, since the parts of the tire are brought together by the parts of the mold before their curing has begun. It is.

The amount of interference is adjusted by carefully monitoring the amount of rubber in each part of the tire. This ensures that the mating surfaces of the parts of the tire held by each part of the mold fit tightly when the parts of the mold are assembled. Too much rubber can create areas of undesirable wall thickness in the joint area, which can prevent proper formation of the joint and result in an unacceptable product. you will be able to understand. As mentioned above, when unvulcanized rubber parts are molded,
There is a strong tendency for unvulcanized rubber parts to become deflected or damaged before they can be joined together, e.g. uncured rubber parts tend to stick to the male mold when it is removed. There is.

Therefore, the positive measures mentioned above, namely the fixing projections provided by the invention to hold each half in its respective mold space, are of great importance. This technique is achieved by coating the part of the mold that is to be removed from the molded unsulfurized tire part with a suitable non-stick material, such as polytetrafluorethylene, and the part of the mold in which the tire part is held. It can be further assisted by turning it into a lees surface. The surface roughening can be carried out, for example, by shot blasting. Embodiments of the present invention will be described below with reference to the accompanying drawings.

A protrusion 21 is formed on a molded tire portion 20 (shown schematically) in FIG.

The protrusion 21 has a cutting surface 22, and since this cutting surface is inclined, pressurized gas introduced into the mold in the direction of arrow A is refracted beyond the cutting surface, thereby forming the mold. The tendency for gas to enter between the part and the surface of the mold itself, i.e. between the surface 28, i.e. the outside of the finished product of the molded part and the surface of the mold itself, is effectively reduced. do. FIG. 2 shows protrusions of different shapes. This protrusion is connected to the two molded tire parts by a narrow molded portion or neck 23. This narrow section 23 facilitates cutting out the finished molded product. Furthermore, the protrusion has a cutout surface 22 that prevents gas from flowing into the mold. FIG. 3 shows a particular preferred type of protrusion.

This protrusion has all the characteristics of the protrusion of FIG. 2, but is formed at a small angle Xo with the perpendicular to the molded part. For convenience, Xo can be set up to 45o. This allows the two protrusions to partially overlap the surface 24.
prevents them from being joined together when they are joined together. 2
If two protrusions join together, undesirable deformation of the joint may occur.

Figures 4a and 4b schematically illustrate the stages of operation of the method and apparatus for manufacturing a tire, with Figure 4a showing the forming of the tire sidewall and joining of the sidewall to the tread, and Figure 4b showing the forming of the tread portion. show.

Fig. 5a shows the closed state of the mold before forming the tire sidewall, and Fig. 5b shows the state in which the mold is opened by pressurized gas after forming the sidewall. A pair of sidewall molds 30 are assembled on either side of the central platen 31 as shown in step (A).

The platen 31 has an annular ridge 32 and each sidewall molding has a corresponding groove 33 of slightly greater depth. Platen 3
1 has a passageway 34 extending from an inlet 35 connected to the screw injector to the surface of the platen in the center of the annular ridge, each sidewall mold body 30 forming from a groove 33 a part of the mold space for the tire sidewall. It has a passageway 42 extending to a molding surface 36 configured to do so. In operation, the sidewall 30 is assembled adjacent the platen 31 and cooperates with the groove 33 to form the ridge 3.
2 forms a transfer chamber, and rubber is injected through passage 34 to fill the formed transfer chamber.

The pead 37 assembled with the top 38 is placed in position on the molding surface 36 of the sidewall. In step (B), a pair of molding press platens 39 having molding surfaces 40 are brought into close contact with the sidewall bodies 301 to form a sidewall molding space 41 . Pressure is then applied by the molding press to force the rubber from the transfer chamber through the passageway 42 into the sidewall molding space 41. Each molding platen 39 has protruding grooves adjacent to the molding surface (FIG. 5a).

In step (C) the mold or the chamber containing the mold is pressurized and the forming press platen 39 is lifted from the side wall 30.

Providing protrusion grooves in platen 39 effectively prevents air from entering between the molded sidewall and surface 40;
As the platen assists in holding the mold, the molded sidewall is lifted away from the sidewall body and carried on the press platen (Figure 5b). The side walls 30 and center platen 31 are then moved and ready to be used again in step (A).

In step (D), the breaker assembly is assembled into mold 43.

In step (E), the mold 43 is pressed against a pair of press platens 44 and 4.
The breaker mold 43 and the concentric ring 46 are vertically attached between the breaker 5 and the breaker mold 43.

The tread ring 46 carries a tread pattern on its inner surface, and the ring 46, the breaker mold 43 on which the breaker assembly is assembled, and the upper press platen 45 together provide a space for forming the tread portion of the tire. Determine. The inclined surface 47 is provided on the mold 43 and also on the upper platen 4.
A surface 48 corresponding to 5 is provided so that the tread portion has an inclined side surface for joining with a mating surface on the molded side wall. Ring 46 is screw injection device 49
The rubber forming the tread portion is injected into the tread forming space formed radially outwardly of the breaker assembly.

A dashed line 52 extending vertically through the molded portion 51 shown in FIG. 4b indicates the seam between the tread portion and the breaker assembly. In step (F), after molding, press platens 44 and 45 are disengaged from the molded tread portions and air pressure is introduced into the mold.

The breaker mold 43 is removed and the ring 46 is separated from the injector 49. Since the tread portion carried by the ring 46 serves as a fastening projection itself, there is no need to provide a separate fastening projection for the tread portion of the tire.
In all stages described up to this point, the rubber has been processed by a screw injection machine to a temperature at which it can be molded.
However, it will be appreciated that there is a temperature below which an appreciable rate of cure begins.

This temperature is determined by the shape of the cure rate versus temperature rheometer curve for the rubber compound used. Generally, these curves exhibit an initial plateau where the cure rate remains very low, but once a certain temperature or "critical temperature" is reached, the cure rate begins to increase rapidly. We have found that by careful control and planning of each step (A) through (F), all of these steps are performed while keeping the rubber below critical temperatures. Different rubbers can be applied to different parts of the tire if their rheometer curves indicate that the temperature is sufficient to cure these rubbers together at such a high temperature as to provide a suitable bond between the rubbers. You can use those rubbers. Each stage (A),
(B) and (C) are each stage (○), (E) and (F
) can be done at the same time, and in step (G) ring 46
The tread portions held by the treads are placed between the forming press platens 39 which hold the sidewalls.

As the forming press platen moves up to the ring 46, the side wall and the tread portion come into contact along the annular face.
At this stage, the rubber is still warm, but below the critical temperature. Here the temperature is raised to cure the hitherto unvulcanized rubber. If desired, internal gas pressure, such as air or steam, may be introduced into the mold at this stage to press the tire firmly against the molding surface during curing. Finally, the mold platens are separated again, the cured tire is removed from the mold, and the projections are cut away.

If desired, the tread portion of the tire may be formed with a concave inner surface so that it joins more smoothly with the contour of the sidewall.In this case, the mold 43 in which the tread portion is formed may be foldable. Alternatively, it may be coated with a molded surface ring, such as hardened ethylene propylene rubber.

This rubber allows removal of the cylindrical mold and is then easily peeled away from the interior of the tread. Furthermore, the angle and position of the joint between the tread portion and the side wall need not be as shown, the primary requirement being that the joint be placed on the tread ring 46 during closure of the platen 39 in step (G). The parts must be placed in such a position that they can be pressed together or peeled off.

[Brief explanation of drawings]

1, 2 and 3 are cross-sectional views of a suitably shaped fixing protrusion according to an embodiment of the present invention, and FIGS. 4a, 4b, 5a and 5b are sectional views of a pneumatic tire. 1 is a schematic diagram of the equipment used for manufacturing. 20... Tire portion, 21... Protrusion, 30...
Side wall mold body, 37... Bead, 39... Molding press platen, 43... Mold, 44, 45... Press platen, 46
...Tread ring. Figure 1 Figure 2 Figure 3 Figure 5a Figure 5b Figure 4○ Figure 4b

Claims (1)

[Claims] 1 molding at least two separate completely unvulcanized tire parts from completely unvulcanized rubber in respective molds, opening said mold with said tire parts still in a completely unvulcanized state, and Collecting the tire sections while they are still completely unvulcanized and applying heat and pressure to join the tire sections together and cure the beads and sidewalls to form the finished tire. A method for manufacturing a pneumatic tire having a tread portion, wherein a mold for forming a tire portion having at least a side wall of the tire is opened in an atmosphere of pressurized gas, and said tire portion enters said pressurized gas into said mold. integrally molded with an air-tight locking projection having a shape to ensure that gas is deflected to one side of the completely unvulcanized tire part, so that the completely unvulcanized tire part It is peeled off from one part of the mold and remains stuck to the other part of the mold, and the completely unvulcanized tire part is removed by the other part of the mold to which it is stuck. A method for manufacturing a pneumatic tire, characterized by joining.