FI57227C - FOERFARANDE FOER FRAMSTAELLNING AV ETT RINGFORMIGT UPPBLAOSBART FOEREMAOL - Google Patents

Description

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England-England (GB) 385U2 / 72 (71) Dunlop Limited, Dunlop House, Ryder Street, St. James's, London, S.W.l, England-England (GB) (72) Eric Holroyd, High Legh Park, Nr. Knutsford, Cheshire, Anthony Gerald Goodfellow, Maghull, no. Liverpool, Lancashire, James Neil McGlashen, Winstanley, no. The present invention relates to a method for casting tires from a flowable, non-vulcanized, non-vulcanized, non-vulcanized material. , but not exclusively, for tire inner tubes, and is an improvement or variation of the invention disclosed in English Patent 1,367,084.

Patent 1,367,084 discloses a method for molding a hollow rubber body, in which the body is first formed in two halves, each part being molded in a matrix mold cavity from unvulcanized rubber, the halves provided with a latch strip to prevent the halves from moving, then pressed by heat and pressure.

According to the present invention, there is provided a method of casting an annular pressurizable body, e.g., an inner ring of a tire, wherein the body is first made in two halves, by heat and pressure.

The method is characterized in that the halves are cast in a cross-sectional shape flattened in the joint plane of the halves relative to the final shape of the body and that the halves are joined together in this state and that the product is removed from the original mold and pressurized to its final dimensions in a larger mold. after which the final vulcanization is carried out.

The present invention makes it possible to produce many different pieces in a casting press in which only one could be made if the final mold were cast.

The molded parts are thus preferably inner rings of rings having an annular shape in the plane. In this case, several rings can be placed inside each other in the same mold concentrically, e.g. for simultaneous casting of three rings, for example having approximately elliptical cross-sections but different inner diameters, instead of casting one tube of circular cross-section.

Thus, in the manufacture of inner tubes for tires, for example, three rings can be cast at the same time, for example. The inner diameter of the ring when cast is preferably the same as the corresponding size of the inner ring of circular cross-section, whereby the circumferential length of the cross-section of the ring is the same as that of the corresponding circular ring.

If desired, the larger mold may have a larger inner diameter and than the original mold, in which case the part will be stretched in the larger mold. In this way, pieces with different sizes and inner diameters can be produced in the first mold, whereby the second mold in which the final vulcanization takes place can be relatively light in construction to withstand the pressure of the tire.

The rubber can be any elastomeric, crosslinkable, polymeric material such as natural rubber, butyl rubber, SBR, neoprene, ethylene-propylene rubber and nitrite rubber. The type of rubber used will, of course, depend on the desired properties of the finished product and the selection of a suitable rubber for any particular purpose is well known in the art of rubber technology.

Although the rubber must be substantially unvulcanized when used to form halves, it is appropriate to subject it to a certain treatment 3 57227 prior to the shaping steps to destroy its "viability" or "memory". A suitable treatment may be, for example, grinding, extrusion or other mechanical treatment or heat treatment, but it must not initiate the vulcanization process of the rubber. In other words, although the rubber is preferably provided with a certain amount of energy and is warm, it is still substantially unvulcanized when used to form halves.

This is possible due to the temperature dependence of the rheometry value of the vulcanization rate for most rubber compounds. The rheometry curve has an initial plateau where the vulcanization rate remains very low as the temperature rises to a threshold temperature where the vulcanization rate begins to increase rapidly. Therefore, in the present invention, care must be taken not to treat the spent rubber to such an extent that the threshold temperature is reached. The molded halves are joined as soon as possible after they have been shaped, while the rubber is still in a processed but unvulcanized state.

The mold or molds used to cast the halves are preferably pressurized by supplying compressed air or another suitable gas, e.g. nitrogen. It is suitable to use a pressure of at least 0.35 kg / cm, but considerably higher pressures can be used if desired. The gas pressure is generally capable of acting in two respects: it is fed into the mold at a point such that gas cannot flow between the molded half and the surface of the matrix mold cavity, the latch strip being shaped to provide a gas tight seal around the matrix mold cavity. The gas pressure then holds the molded half against the surface of the matrix mold when the mold is opened. The gas pressure also resists the tendency of the warm rubber to gasify when the mold is opened. Gassing is caused by the evaporation of moisture in the rubber when the mold is opened and results in unwanted porosity in the rubber and poor surface finish.

If desired, the cavity of the initial mold need not be circular in plane, but may be corrugated or otherwise tortuous in shape so that a ring having a larger diameter than the outer diameter of the cavity of the mold is cast. Such a ring is removed from the original mold after the halves have been joined together, but before the vulcanization is complete and pressurized in a suitably sized circular mold in which the vulcanization is completed.

If desired, the valves can be cast into suitable halves of the tire when casting the halves.

57227

The invention will now be described in detail by way of example with reference to the accompanying drawing, in which Figure 1 shows an inner ring made in a first step according to the invention; Figure 2 shows an inner ring having the same inner diameter but a circular cross-section; Fig. 3 shows three inner rings nested in which valves have been cast and which have been manufactured in accordance with the first step of the invention; Figures 4 and 5 show inner rings of corresponding size in cross-sectional views, one for comparison being one circular in cross section and the other substantially elliptical in shape; Figures 6 and 7 show possible non-circular shapes to which the inner rings according to the present invention can be cast in the first step.

As shown in Fig. 1, the ring 1 according to the present invention is in the first stage cast in a flat cross-section, the outer diameter of which is considerably smaller than that of a ring of circular cross-section (see Fig. 2) having the same inner diameter. The compressed air supply valve 2 is located in the second ring half and the circumferential seam lines 3, 4 run along the central circumferential line of the pipe in both the inner and outer walls.

The radial width r of a ring of flat cross-section is therefore also considerably smaller than the radial width 'r' of a ring of circular cross-section having the same cross-sectional circumference. This is shown schematically in Figures 4 and 5.

It is clear that the axial width a of a ring with a flat cross-section is greater than the axial width 'a' of a tube of circular cross-section having the same inner diameter and circumferential circumferential length (see Figs. 4 and 5). However, this width is not of great importance, because the most expensive factor in the casting process is now the the required clamp diameter is required. The factor affected by the axial width a of the tire is the impact depth of the mold. This depth can be reduced, if desired, by selecting a flattened cross-section when casting the ring halves to a W-shape instead of a U-shape, as described above, or otherwise wavy.

Figure 1 shows how a plurality of flattened rings can be nested in a mold having the same outer diameter.

Claims (8)

A process for producing an annular inflatable article, e.g. the inner ring of a tire, according to which the article is first manufactured as two halves, which halves are formed of uncured rubber in a matrix mold and provided with a readout to prevent the halves from being displaced, which form is pressurized and the halves of the article are seamed and joined together. with each other under heat and pressure, characterized in that the halves are formed into such a shape on the cross-section, which in the connecting plane of the halves is flattened in relation to the final shape of the article and that the halves in this state are combined and that the product is removed from the original before the final curing. the mold and inflated to its final format in a larger mold, where the final curing is then carried out. Method according to claim 1, characterized in that such a larger mold is used, the inner diameter of which is larger than in the original mold. 3. A method according to claim 1 or 2, characterized in that several articles are placed concentrically within each other.