FI59551C - FREQUENCY REQUIREMENT FOR FRAMING OF PNEUMATIC SHEET - Google Patents

Description

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Ma IJ UTLAGGNI NGSSKRIFT J 70 o 1 'S * ^ (51) K ».ik? / I« .a.3 B 29 H 17/00 FINLAND — FINLAND (* D PtMnttltatkMnut - Ptt * fttan »eknin | 109 3 / 7 3 (22) Htk «mi« pftlv <—Afweknlnpdif 06.0U.73 * (23) Alkupllv · —GiM | h «ttdt | 06.0U.73 (41) Tullut) ulklMk * l - Gratings aftamll | 07.10.73 _ t i (44) Date of departure and date of issue. - -

Patents and registries '' AiwWcan uttagd och utUkriftM pubimnd 29.05.8l (32) (33) (31) Pyydetty ocuoUtaui — Boglrd prlorltat 06.0U. 72

Engianti-England (GB) 15707/72 Proven-Styrkt (71) Dunlop Limited, Dunlop House, Larder Street, St. James's, London SW1Y 6QR, England-England (GB) (72) Eric Holroyd, High Legh Park, Ne ^ r Knutsford, Cheshire, Anthony Gerald Goodfellow, Maghull, Near Liverpool, Lancashire, James Neil McGlashen, Winstanley, Near Wigan, Lancashire, England-England (GB) (7U) Oy Jalo Ant-Wuorinen Ab (5U) Method and apparatus for pneumatic tire The present invention relates to a method for manufacturing a pneumatic tire by casting, which ring comprises heel thickenings, sidewalls and a wear part. The features of the method appear from the appended claim 1.

The pneumatic tire is manufactured according to the invention in three parts, comprising two side walls and a tread part. Kan thickening core pieces can be incorporated into the side walls together with rubber base thickening pieces and cord or Textile or other side wall reinforcements which, if desired, can be placed in the mold cavity prior to casting the side walls. The tread may similarly include a buffer piece or other type of reinforcement, which may be, for example, a textile cord fabric, a steel cord fabric, or a high modulus polymeric wave that may be assembled or preformed around the core body prior to casting the tread portion.

If desired, one or more parts of the ring may be provided with a reinforcement extending beyond this part of the ring. The ring part is cast so that a free reinforcing strip is protruded from it. The free reinforcing strip is kept out of the way when the associated ring portion is brought into contact with the adjacent ring portion and is then pressed into contact with an adjacent ring portion to form a portion extending over the joint before the rubber is vulcanized.

The rubber can be any of your elastomeric, crosslinkable polymeric solids, for example, natural rubber, butyl rubber, SBR, neoprene, ethylene-propylene rubber, and nitrile rubber, or a mixture thereof. The type of rubber used will, of course, depend on the desired properties of the finished tire, and the selection and combination of a suitable rubber for each special purpose is well known in the rubber art.

Although the rubber should be substantially unvulcanized when used to form parts of the tire, it is most convenient to subject it to a certain treatment before molding to destroy its "vibrancy" (memory). A suitable treatment may be, for example, grinding, pressing or other mechanical or thermal treatment, but it must not initiate the vulcanization of the rubber. In other words, although a certain amount of energy has been introduced into the rubber, it is nevertheless substantially unvulcanized when used to cast tire parts.

This can be arranged provided that special attention is paid to the dependence of the rheometric value of the vulcanization rate on the temperature of the rubber compound used. In general, these values form a curve with a plateau at the beginning where the vulcanization rate is very low, followed by a rapid increase in the vulcanization rate when a certain temperature, the "threshold" temperature is reached. In the present invention, where the rubber compound has such a curve, the temperature of the compound is preferably kept below the threshold temperature throughout the processing, casting and joining steps, and is then heated above this temperature when vulcanization is performed.

The mold or molds used to form the parts are pressurized by introducing compressed air or some other suitable gas, for example nitrogen. It is most suitable that the pressure 2 is at least 0.35 kg / cm, but considerably higher pressures can be used if desired.

Normally, it is most convenient to subject the mold to pressure by supplying a pressurized gas through a circumferential circle of mold cavities. However, if patrice moldings are used in connection with the mold cavities, it may in certain cases be advantageous to introduce gas through the patriot moldings, for example their poles.

The pressurization of the molds is started before the molds for the different parts of the tire are opened and is maintained 59551 3 preferably until the parts are joined together or either cooled or vulcanized (if desired, the parts can be cooled after joining before the vulcanisation is completed). The purpose of the pressure is to prevent gas from escaping from the warm compound after casting, which pressure, especially when casting the side walls, cooperates with the latch strip to hold the casting in the right part of the mold to perform the joining. It should be noted that the removal of gas from the warm compound is particularly disadvantageous because it causes ugly pitting on the surface of the molded ring groove and porosity in the finished product, which can lead to breakage of the ring structure in use.

The invention also relates to a casting apparatus for manufacturing a tire, the apparatus comprising a tread cavity delimited by the mold parts, and two sidewall castings delimited by the mold parts, devices for pretreating rubber substantially unvulcanized, devices for feeding rubber into the mold cavities and The characteristics of the apparatus appear from the appended claim 5.

The casting of the ring parts in the mold cavities can be performed in any conventional manner. For example, internal stud casting, vacuum casting, or various combinations of these two methods can be used for sheet materials. In addition, casting can be performed by compression, die or injection molding techniques.

The device for pre-treating the rubber prior to molding may suitably be an injection mold compression screw or a transfer movement in the die mold. A combination of these methods can be used, in which the rubber is fed into the die space by means of a relatively low temperature screw. For this reason, injection molding alone is not recommended for the process of the invention, but may be satisfactory if the rubber can be "processed" to the desired degree before it is fed into the die.

The latch strips are shaped so as to resist the movement of the ring parts in the mold, for example due to shrinkage or removal of the patric pieces when the latter are used. The latch strip is also preferably shaped to ensure that the pressurized gas flowing into the mold during pressurization flows over the edge of the strip onto the surface of the mold half from which the respective ring portion is removed but does not flow between the ring portion and the mold cavity wall. The latter is highly undesirable because it causes blistering or similar defects in the preparation and can lead to the ring part rising up from the mold cavity which should support it.

A particularly preferred shape of the latch strip is one which comprises a thicker part which is connected to the half of the preparation by means of a thinner part. Examples of suitable latch strips are shown in Figures 1, 2 and 3 of the accompanying drawing and are described in more detail below.

According to the invention, the tire is cast in three parts, comprising a tread which optionally includes a buffer part and two side walls, whereby all parts, i. sidewalls and tread surface, casting can be performed using a special latch strip and mold pressure as described above. Alternatively, when casting the tread portion, a portion of the tread pattern of the tread portion may act as a latch strip, and similarly the mold portion to which the tread portion is cast may be collapsible or alternatively be a flat ring that may support a sealing strip and be vulcanized non-stick rubber. to shape the inner profile of the ring. In the former case, the tread shaping body may remain inside the tread portion after the joining step, and in the latter case, the tread shaping ring may be pulled out of the tread portion before the joining step.

Pressurizing the tread mold is not essential, but may be advantageous in maintaining a close connection between the tread portion and the tread matrix to prevent gas from escaping from the hot molded tread rubber.

The method according to the invention makes it possible to cast unvulcanized tire parts and to join them without the risk of damage. If these unvulcanized parts were cast without the steps of this invention, they would be very susceptible to damage and displacement. Thus, for example, unvulcanized parts would tend to adhere to the patric molds when the latter are removed, which would lead to unsatisfactory casting. The method of the invention overcomes these difficulties as described in more detail below and allows the production of satisfactory, undamaged 59551 5 tires from substantially unvulcanized parts. Previous methods of casting rings in two or more parts have usually required partial vulcanization of at least one part to avoid damage. These partially vulcanized and parts cannot be joined together satisfactorily unless an adhesive is used. The present invention eliminates all these difficulties and additional steps.

Another advantage is that since the ring parts are joined together by means of the mold parts before the vulcanization has started, they will be suitable for joining together, i. the desired preparation can be formulated with relatively little interference. The degree of interference is adjusted by adjusting the amount of rubber fed to the tire parts to ensure that the surfaces of the tire parts to be joined together, which are supported by the mold parts, come into close contact with each other when the mold pieces are joined together. It is obvious that excessive interference during the formation of the joints can lead to an unsatisfactory product, since excessive interference in this context can cause an excessive increase in the thickness of the walls in the plant area.

As mentioned above, when casting unvulcanized rubber parts, there is a very strong tendency for the parts to move or tear before they can be joined together and, for example, they tend to adhere to the patric molds when the latter are removed. Therefore, the functional devices of the present invention, i. latch strips to hold the halves in the corresponding cavities are very important. This technique can be further developed by coating the part of the mold from which the cast unvulcanized ring part is removed with a suitable non-stick material, for example poly (tetrafluoroethylene), and roughening the part of the mold supporting the ring part. Roughening can be performed, for example, by blasting.

The invention is illustrated by way of example only with reference to the accompanying drawing, in which Figures 1, 2 and 3 show cross-sections of suitably shaped latch strips and Figure 4 schematically a method and apparatus for manufacturing a pneumatic tire.

In Figure 1, the molded ring portion 20 (shown schematically) is formed with a latch strip 21. Salpaliuskassa 21 has a cut surface 22 which is inclined in such a way that the gas under pressure which is fed to the mold in the direction of arrow A, to change the direction of the cut surfaces of the above, and therefore have between the molded part and the self-6 59 551 mold surface, i. the tendency of the gas to enter the surface 26 of the molded part, i. between the outer surface of the finished product and the surface of the mold itself is effectively reduced.

Figure 2 shows a latch strip shaped in another way. This strip is connected to the molded ring part 20 by means of a narrow casting part and neck 23. This narrow part 23 facilitates the finishing of the finished casting product. The strip is also then provided with an inclined surface 22 for controlling the gas flow.

Figure 3 shows a particularly suitable type of latch strip. It has all the characteristics of the strip of Figure 2, but forms a small angle X ° with the normal of the casting part. X ° may suitably be up to 45 °. In this way, the two latch strips are prevented from joining together when the parts are joined together along the surface 24.

The joining of both latch strips can cause undesired joint deformation.

Figure 4 schematically shows the operating steps of a method and an apparatus for manufacturing a tire. Fig. 4a shows the casting of the side walls of the tire and the joining of the side walls to the tread, and Fig. 4b shows the casting of the tread part. As shown in Fig. A, in step A, the side wall units 30 are placed on different sides of the center plate 31. The plate 31 is provided with circular protrusions 32 and the side wall units are provided with a corresponding groove 33 with a slightly greater depth.

The plate 31 is provided with channels 34 leading from the inlet 35 leading from the screw injector to the plate surface by the center line of the annular protrusions and the side wall units 30 including channels 42 leading from the groove 33 to the casting surface 3b.

During the manufacturing process, the side wall units 30 are connected to the plate 31 so that the protrusion 32 cooperates with the groove 33 to form a transfer chamber and the rubber is compressed through the channels 34 to fill the chamber thus formed. The pieces 36 and the base thicknesses 37 are placed on the casting surfaces 36 of the side wall units.

In step B, a pair of die-cast plates 39 provided with casting surfaces 40 are placed tightly against the sidewall units 30 to form sidewall casting cavities 41. The rubber is then pressed into the die by pressure from the transfer chamber through the channels 42 into the side wall casting cavities 41 ·

The casting plates 39 are provided with latch strips (not shown) located at the casting surfaces 40.

7 59551

In step C, the mold or mold-containing space is subjected to pressure and the casting plates 39 are lifted off the sidewall units 30. Slabs 39 effectively prevent air from entering between the cast sidewall and surface 40 supported by tiles.

The side wall unit 30 and the center plate 31 are then removed and are again ready for step A.

In step D, the buffer layer is formed on the shaping body 43.

In step E, the shaping piece 43 is pressed between two pressing plates 44 and 45 together with a ring 46 which is concentric with the shaping piece. The inner surface of the ring 46 has a tread pattern and the ring 46, the shaping piece 43 and the upper compression plate 45 together define a casting cavity for the tread portion of the tire. The shaping body 43 is provided with a sloping surface 47 and the top plate 45 is provided with a corresponding surface 40 so that sloping side surfaces are formed in the tread portion, which are connected to the respective surfaces of the cast side walls.

The tire 46 is provided with channels 50 leading from the screw clamping unit 49 to the inner surface of the tire, and the rubber forming the tread is thus injected into the mold cavity.

In step F, the casting plates 44 and 45 are removed from the molded tread portion after casting by supplying compressed air to the mold. The bumper shaping member 43 is removed and the ring 46 is removed from the injection unit 49.

It is obvious that in all the steps described so far, the treatment with a screw press has raised the temperature of the rubber to a point where it can be cast, but it is below the temperature at which no significant vulcanization begins. This temperature depends on the shape of the rheometric curve which indicates the vulcanization ratio to the temperature of the rubber compound used. These curves usually have an initial plateau where the vulcanization rate remains very low, but when a certain temperature, the "threshold temperature", is reached, the vulcanization rate rises rapidly. It has been found that by carefully controlling and designing steps A-F, all of these can be performed so that the rubber temperature remains below the threshold temperature. Different grades of rubber may be used in different parts of a tire 8 59551 provided that their rheometric curves are sufficiently similar to allow them to cure at one elevated temperature so that the joints between them become strong enough.

Steps A, B and C may be performed simultaneously with steps D, E and F, and in step G, the tread portion supported by the tread ring 46 is interposed between the casting plates 39 supporting the side walls. The casting plates are raised for the tread ring so that the side walls and the tread portion contact each other along the annular sloping surfaces. At this point, the rubber is still warm, but below the threshold temperature. The temperature is now raised to vulcanize the hitherto unvulcanized rubber. If desired, pressurized air or steam can be fed into the mold at this stage to press the tire tightly against the casting surfaces during vulcanization.

Finally, the casting plates are separated again, the vulcanized ring is removed from the mold and the casting strips are cut off.

If desired, the tread portion of the tire may be made with a concave inner surface to align more evenly with the contour of the sidewall. In this case, the molding 43 on which the tread portion is cast may be collapsible or covered with a shaped spacer ring made, for example, of vulcanized ethylene-propylene rubber, which allows the cylindrical molding to be removed and which is then ready to be removed from inside the tread.

The oblique angle and position of the joints between the tread portion and the sidewalls need not be as shown in the drawing, but it is essential that the joint be positioned so that the portions can be pressed together when the plates 39 are pressed onto the tread ring 46 in step G.

Claims (5)

A method of manufacturing by casting a pneumatic tire comprising beads, sidewalls and a tread, characterized in that a) the vulcanizable but unvulcanized rubber is subjected to a treatment sufficient to destroy its nerve but not to initiate the vulcanization process ; b) the tire is made of the above-mentioned rubber in at least three separate parts comprising a tread portion and two-sided wall parts, by forcing said rubber into annular, limited-shaped hollows, a portion of each of the above-mentioned side wall molding-limiting molds being provided with for forming a gas-tight reading strip which facilitates retention of the formed sidewall portions of said mold part at the opening of the mold? c) opening the molds of the tire portions, at least opening the molds for molding the sidewall portions to open in an atmosphere under pressure such that gas under pressure flows between the mold portions of the sidewalls and of the gas-tight reading strips is prevented from passing behind the formed tire sidewalls; and then in a manner known per se: d) the mold parts which support the tire parts are joined together so that said tire mold parts and said tire parts come into contact; e) the tire parts are joined by heating under gas pressure. A method according to claim 1, characterized in that one or more parts of the tire are provided with a