GB2118492A - Inner tube and apparatus for its manufacture - Google Patents

Abstract

The inner tube 1 has a right- cylindrical portion 3 whose axis of symmetry is coincident with that of the toroidal body. The inflation valve for the tube is mounted in the portion 3 with the result that the mounting is more secure than in conventional inner tubes because said portion has only one radius of curvature. The apparatus for making the inner tube comprises half-moulds 15,16 closeable around a core 17 to define a cavity into which elastomeric material is injected, said core and one of said half-moulds having facing surfaces which are right-cylindrical and coaxial with the mould as a whole. The inflation valve 4 is mounted, before closing the half-moulds onto the core, in one half- mould 16 in such a manner that the injected elastomeric material (in filling said cavity) flows around one end of the valve. <IMAGE>

Description

SPECIFICATION Inner tube and apparatus for its manufacture The present invention relates to an inner tube for pneumatic tyres and the like, and to an apparatus for manufacturing the inner tube.

Inner tubes to be used in pneumatic tyres for vehicle wheels (and, more generally, inflatable hollow bodies able to impart by inflation a more or less permanent shape to an article having flexible walls) have been known for many years. Conventional inner tubes to be used in tyres are hollow toroidal bodies having circular sections in planes passing through the axis of symmetry of said toroidal body and are provided with valves for admitting air under pressure into the interiors of said bodies and for allowing it to escape therefrom. Said valves are mounted in a hole formed therefor in the tube wall and the connection between the valve and the tube is carried out by means of adhesive agents applied between the outer surface of the tube and a support of elastomeric material carried by the valve base.

Said conventional inner tubes, during their introduction into the tyres, can give rise to difficulties and drawbacks, particularly if the operation is effected without care and precision by the operator in charge of the work. Firstly, during the fitting of the tube into the tyre, the latter is already assembled on a vehicle wheel rim and, in the course of introducing the tube between the tyre and the rim, twists can be imparted to the tube; these, if not eliminated during inflation of the tube, will lead to trapped folds in the tube wall and these in turn will or may lead to unexpected (sudden) ruptures of the tube. The result is rapid deflation of the tyre and this is potentially very dangerous because it may take place during travel of the vehicle.

Secondly, a permanent and tight anchorage of the valve to the tube wall cannot always be guaranteed and it will be obvious that this drawback will occur every time the union of the valve and the tube is not carried out in an accurate and correct manner. The consequence of this is a large amount of production waste and also a product which is not quite reliable (in particular after prolonged use) because it often happens that, after a certain time of operation of a tyre provided with an inner tube, it is possible to note in the tyre a tendency for the tyre to deflate slowly due to the air leakage which takes place at the union between the valve and the tube.

The present invention aims at providing an inner tube which is free from the above-discussed disadvantages and to provide an apparatus for manufacturing inner tubes according to the invention.

According to a first aspect, the present invention consists in an inner tube for pneumatic tyres which comprises a hollowtoroidal body of cross-linked elastomeric material and a valve, fast with said hollow toroidal body, for admitting air to the tyre and for releasing it therefrom, said hollow toroidal body comprises a cylindrical portion, whose axis of symmetry coincides with the axis of symmetry of the toroidal body.

According to a second aspect, the present invention consists in an apparatus for the manufacture of inner tubes, characterized in that it comprises two half-moulds and a core which can be associated or detached with respect to them, a part of the outer surface of the core having a shape complementary to that of the surfaces of the two half-moulds facing thereto, so as to define with said half-moulds a pair of substantially annular cavities, complementary to each other, and to originate therefore a hollow toroidal body, one of the half-moulds and the core surface facing thereto having substantially cylindrical coaxial surfaces, ducts being provided in the core to supply elastomeric material to the cavities defined between the half-moulds and the core, means for detaching the half-moulds from the core, means for removing the core from the space existing between the two half-moulds, means for mutually approaching the two half-moulds by placing their edges into reciprocal and direct contact, means for admitting fluid under pressure into the closed cavity defined between the two half-moulds and means for curing the elastomeric material being also provided.

One embodiment of each of the two aspects of the present invention will now be described, only by way of non-limiting example, with reference to the accompanying drawings, in which: Figure 1 shows in perspective view an inner tube according to the invention; Figure 2 is a sectional view, on an enlarged scale, taken on the line ll-ll of Figure 1; Figure 3 is a sectional view, on enlarged scale, of a detail of an inner tube according to the invention; Figure 4 is a diagrammatic section of an apparatus, including a core, according to the invention; and Figure 5 is a diagrammatic section of the apparatus of Figure 4 from which the core has been omitted.

According to the general inventive idea, in an inner tube according to the present invention, a portion of the toroidal body thereof is cylindrical and has its axis of symmetry coincident with the axis of symmetry of the toroidal body. Moreover, still according to said general inventive idea, said tube is provided with a valve whose base is embedded in the elastomeric material forming the tube wall and consequently becomes an integral part of the tube wall.

Said general inventive idea further comprises an apparatus adapted to manufacture the inner tubes described in the preceding paragraph.

Referring to Figures 1,2 and 3, there is illustrated an inner tube which is constituted by a toroidal body 1 of cross-linked elastomeric material and which has an axis of symmetry 2. A portion 3 of the body 1 is cylindrical and the axis of symmetry of said cylindrical portion coincides with the axis of symmetry 2 of the toroidal body.

More particularly, the cylindrical portion 3 has a diameter smaller than that of the whole toroidal body and, therefore, it has such a position that, once the inner tube is fitted into a tyre which has been already mounted on the rim of a vehicle wheel, it will automatically assume the position in which it is in contact with the respective surface of the rim flange of the vehicle wheel.

Moreover, on the mid-circumferential plane or median line of the cylindrical portion 3, there is a valve 4 whose base is embedded in the elastomeric material forming the wall of the inner tube. Figure 3 represents, on an enlarged scale in order to facilitate understanding of the constructional details, the zone of union between the base of the valve 4 and the elastomeric material forming the wall of the inner tube. It will be seen that the valve 4 has a stem 5 which is provided with a through-duct 6 and which, at or near its end intended to be joined to the inner tube, has a portion 7 of reduced diameter, whereby an annular groove 8 is formed. The valve stem 5 is made of metallic material and a body 10 of elastomeric material is fast with said end of the stem in which the groove 8 is formed.

Said body 10 has a frusto-conical shape and has its greater base 11 at the same level as that of the end 12 of the valve stem 5. The smaller base 13 of said body 10 is joined to a cylindrical member 9 which is therefore an extension of said body. The right cylindrical outer surface of the member 9 merges into the sloping or inclined surface 14 of the body 10.

The elastomeric material forming the body 10 and the member 9 is such as to ensure a good anchorage or bond with the elastomeric material constituting the inner tube; preferably it contains butyl rubber. A generally preferred formulation of said elastomeric material, indicated only by way of example, is as follows: - butyl rubber 100 parts by weight -stearicacid 1.5 -zinc oxide 5 " " " - N 550 black 50 - paraffin oil 20 -tetramethylthiuramdisulphide 1 " - mercaptobenzothiazole 1 " - sulphur 1.7 " The elastomeric material forming the inner tube encircles said outer surfaces of the member 9 and of the body 10 and, only by way of example, the elastomeric material forming the inner tube may be of the following formulation:: - butyl rubber 100 parts by weight -zinc oxide 5 D D D -stearicacid 0.5 - magnesium oxide 20 - N 550 black 15 " - N 762 black 35 " " " - aromatic oil 5 D 11 - precipitated silica 15 - mercaptobenzothiazole 0.8 " -tetramethylthiuramdisulphide 1. " " " -sulphur 2 An inner tube according to one aspect of the present invention is manufactured by means of an apparatus which is diagrammatically represented in Figures 4 and 5 and which constitutes the other aspect of the present invention. As can be seen in Figure 4, said apparatus comprises two half-moulds 15 and 16 between which a core 17 is interposed. The half-mould 15 has an annular form and its face directed towards the core 17 is so shaped as to present an annular surface 18 corresponding to a certain part of the outer surface of the eventual inner tube. Likewise, the half-mould 16 has an annular form and its face directed towards the core 17 is so shaped as to present an annular surface corresponding to the remaining part of the outer surface of the eventual inner tube.

Obviously, both the half-mould 15 and the half-mould 16 have flat edges on the profile of their surfaces corresponding to the portions of outer surfaces of the inner tubes to be produced; said edges can be placed into mutual contact to close the mould.

The core 17 has a disc-like form and its faces directed towards the half-moulds 15 and 16 have correspondingly shaped surfaces similar to those of said half-moulds. In particular, the face 20 directed towards the half-mould 15 has a surface 21 corresponding in shape to the surface 18 of the half-mould 15, but of smaller radius, thereby forming an annular cavity 22. Likewise the face 23 directed towards the half-mould 16 has a surface 24 corresponding in shape to the surface 19 of the half-mould 16, but of smaller radius, thereby forming an annular cavity 25. The cavities 22 and 25 form respective parts of the eventual inner tube.

An important feature is that a part of the surface of the core 17 directed towards the half-mould 16 and a part of the surface of the half-mould 16 directed towards the core 17 must be rectilinear and parallel to each other in order to define a right-cylindrical portion 26 of the annular cavity 25, said portion 26 being coaxial with the axis of symmetry of the half-moulds 15 and 16 and also being nearer to said axis than all of the other portions of said cavities 22, 25.

Moreover, a through-hole 27, intended to encircle the stem of an inner tube is formed in the wall of the half-mould 16 in register with the portion 26.

The core 17 comprises a plurality of through-ducts 28 and 29, of which the duct 28 has one of its ends opening into the cavity 25 and of which the duct 29 has one of its ends opening into the cavity 22; the respective other ends of the ducts 28,29 are in communication with a recess 30 provided in the central part of the core 17 and intended to be connected to an injection device (not shown) by means of which elastomeric material can be supplied at high pressure to the cavities 22,25. It is to be noted that the opening of the duct 28 into the cavity 25 is offset circumferentially of the core with respect to the opening of the duct 29 into the cavity 22.

The walls of the half-moulds 15 and 16 are further provided with closed recesses (now shown) which are in communication with the outside through holes formed in said walls and used for the supply of fluids (namely, a cold fluid and a hot fluid) to the half-moulds. The cold fluid is sent before and during the supply of the elastomeric material to the annular cavities 22, 25 whereas the hot fluid is sent after the direct mutual joining of said half-moulds 15 and 16, said hot fluid being the curing medium for said elastomeric material.

. Lastly, the half-moulds 15 and 16 are associated with the platens of a press (not shown) operable to move said half-moulds towards or away from each other and towards or away from the core 17; other means (also not shown but of a conventional type known to a skilled technician in this field) are provided for interposing the core 17 between the half-moulds 15 and 16 and for removing it therefrom.

The operation of the apparatus described above is as follows: The stem 5 of a valve 4 is at first inserted in the through-hole 27 in the half-mould 16 in such a way that the body 10 of elastomeric material provided at said one end of the stem 5 lies within the portion 26 of the cavity 25 of the half-mould 16. Then the half-moulds 15, 16 and the core 17 are brought together in order to obtain the configuration shown in Figure 4. Elastomeric material is injected, by means of an extrusion head which is not shown but which is housed in the recess 30, in order to fill the cavities 22,25. During this injection step, a cold fluid is circulated through the half-moulds.

At this juncture, the press which is operable to move the two half-moulds 15 and 16 away from the core 17 is actuated and, during said movement, the elastomeric material which has filled the cavities 22,25 remains surprisingly adherent to said half-moulds. Now, the core 17 is removed from its position between said half-moulds which remain, therefore, directly facing each other. Thereafter, the press to whose platens are connected the half-moulds 15, 16 is actuated again in order to move the two half-moulds towards and into direct mutual contact with one another as shown in Figure 5.

At the end of this latter operation, a hollow toroidal body 31 of uncured elastomeric material is present in the half-moulds because the union of the edges of the two annular inner tube portions formed between the half-moulds and the core has already taken place.

Now, a fluid (for instance, air) under pressure is admitted into the interior of the hollow toroidal body through the valve 4 and the hot fluid, (for instance, steam) is admitted into the cavities in the half-moulds in order to effect cure of the elastomeric material.

When the curing of the elastomeric material is complete, firstly the valve 4 is connected to the ambient atmosphere in order to release the pressure existing in the inner tube 31 and the press is actuated again to move the half-moulds 15,16 away from one another in order to allow the removal of the completed inner tube 31.

The manufacturing can then be repeated after the core 17 has been inserted between the half-moulds and after having inserted a new valve 4 in the through-hole 27 in the wall of the half-mould 16; subsequently, the press is again actuated in order to bring the half-moulds 15,16 into contact with the core 17 (Figure 4).

From the above description, it can be easily understood that an inner tu be according to the present invention and an apparatus for the manufacture of said inner tubes are able to achieve the proposed aims. In fact, creating an inner tube which is formed by a toroidal body having (in section) a configuration comprising a cylindrical portion which is so disposed as, in use, to be in contact with the flange of a rim for vehicle wheel rim is able to confer on said inner tube a resistance to deformations which may occur in consequence of twist stresses which may arise during the fitting of the inner tube between the tyre and the wheel rim. Said resistance is due to the presence of moulded corners where the wall of the inner tube (seen in section in Figure 2) passes from a rectilinear configuration to a circular configuration.The resistance of the inner tube to said deformations due to twist stresses presents the latter from leading to folds in the inner tube wall, and consequently eliminates all of the aforementioned risks due to the presence of said folds.

Moreover, the connection of the valve (which is necessary for the inflation of the inner tube inside the tyre) in a part of said tube having only one bending radius facilitates the creation of a satisfactory or adequate union betwen the valve base and the inner tube and this, in turn, permits the elimination (or at least the reduction) of the danger of an inadequate anchorage between said elements.

Furthermore, the fact that the connection of the valve to the inner tube is actually carried out during the formation of the inner tube wall and the fact that the frusto-conical and right-cylindrical outer surfaces of the body 10 and member 9 of the valve base provide large surface areas for contact and union with the elastomeric material of the innertube mean that the mechanical connection between said elements is improved and provides considerable long-term stability of the anchorage. In fact, because the surfaces of the union between the inner tube walls and the valve base are arranged as described above, the stresses which might be originated in said zones during use of the tyre facilitate the union itself, and the risk of production waste due to the possible filling of the valve with the elastomeric material is avoided.

Lastly, by means of the apparatus according to one aspect of the invention, it is possible to make inner tubes whose walls have a thickness which is variable at will.

Claims (9)

1. An inner tube for pneumatic tyres which comprises a hollow toroidal body of cross-linked elastomeric material and a valve fast with said body, for admitting air to the same and for releasing it therefrom, said body comprising a cylindrical portion whose axis of symmetry coincides with the axis of symmetry of the toroidal body.

2. An inner tube as claimed in Claim 1, wherein said valve is connected to the cylindrical wall portion of the body and has a valve base of elastomeric material whose bottom surface constitutes a portion of the internal surface of the inner tube.

3. An inner tube as claimed in Claim 1 or Claim 2, wherein said valve base has a frusto-conical shape of which the greater (larger diameter) base constitutes a portion of the internal surface of the inner tube.

4. An apparatus for manufacturing inner tubes which comprises two half-moulds and a core which can be moved towards or away from said half-moulds; parts of the outer surface of the core having respective shapes complementary to those of the surfaces of the two half-moulds facing them, thereby defining with said half-moulds a pair of substantially annular cavities which are complementary to each other for the purpose of forming a hollow toroidal body; one of the half-moulds and the respective facing core surface having substantially cylindrical coaxial surfaces; ducts being provided in the core to supply elastomeric material to the annular cavities defined between the half-moulds and the core; means for moving the half-moulds away from the core; means for removing the core from the space between the two spaced half-moulds; means for moving the two half-moulds towards one another in order to place their edges into reciprocal and direct contact; means for supplying a fluid under pressure into the closed cavity defined inter alia between the two half-moulds; and means for curing said elastomeric material.

5. An apparatus as claimed in Claim 4, wherein a through-opening for supporting the body of an inner tube valve is provided in that wall of said one half-mould which has a cylindrical surface.

6. An apparatus as claimed in Claim 4 or Claim 5, wherein the ducts for the supply of said elastomeric material have their ends opening into a respective cavity offset with respect to one another circumferentially of the apparatus.

7. An inner tube constructed, arranged and adapted to operate substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

8. An apparatus for manufacturing inner tubes, constructed arranged and adapted to operate substantially as hereinbefore described with reference to and as illustrated in Figures 4 and 5 of the accompanying drawings.

9. Any features of novelty, taken singly or in combination, of the embodiments of the invention hereinbefore described with reference to the accompanying drawings.