Method and apparatus for manufacturing a tyre tread and a tyre

Abstract

A method of manufacturing an agricultural tyre (1) with deep cross-lugs (6), comprising the steps of: (a) proving a tyre case (2) and tread belts (3); (b) applying rubber blocks (206) onto tread belts (3), each of such rubber blocks (206) being arranged to make a respective lug (6) of the final tread (4); (c) winding a rubber ribbon (200) above said rubber blocks (206) so as to completely enclose said rubber blocks (206); (d) curing the rubber blocks (206) together with the wound ribbon (200) in a curing mould (105) negatively reproducing a desired pattern of the tread (4).

Claims

1. A method of making a tire tread on a tire casing, the tread comprising a tread base and a number of lugs, each of which projects upwards from the tread base and extends substantially crosswise to a travelling direction of the tire, the method comprising the steps of: (a) providing a tire casing and tread belts; (b) arranging a plurality of rubber blocks directly onto said tread belts, each of said rubber blocks being configured to make a respective lug of the final tread; (c) winding a rubber ribbon about said rubber blocks and tread belts arranged onto a drum so as to shield said rubber blocks; and (d) curing said rubber blocks together with said wound ribbon in a curing mould negatively reproducing a desired pattern of the tread.

2. The method according to claim 1, wherein each of said blocks has an inner wall and an outer wall substantially parallel to one another.

3. The method according to claim 1, wherein said rubber blocks are made of a different rubber compound or mixture with respect to said ribbon.

4. The method according to claim 1, wherein said step (b) includes a step of heating to join the rubber blocks and the tread belts.

5. The method according to claim 1, wherein said step (b) provides assembling said rubber blocks onto said tread belts directly onto a construction drum.

6. The method according to claim 1, wherein, in said step (b), each of said rubber blocks is arranged with an outer wall located at a shoulder of the tread to be formed and an inner wall opposite the outer wall and located in a central area of the tread to be formed.

7. The method according to claim 1, wherein, before said step (b), there are provided further steps of: extruding or calendering a continuous rubber strip having a cross-section corresponding to transversal section of said rubber blocks; cutting rubber blocks off said continuous rubber strip, preferably by an inclined crosswise cut.

8. The method according to claim 1, which is a method of regenerating used tire treads.

9. The method according to claim 1, wherein said tire is an agricultural tire.

10. The method according to claim 1, wherein, in said step (c), each of said rubber blocks is arranged so as to extend from a shoulder portion to a portion at a distance from the tire centerline or from a shoulder portion to a portion beyond the tire centerline.

11. The method according to claim 1, wherein said step (c) is performed onto a TAM (Tire Assembly Machine) drum, onto a TAM server or offline.

12. The method according to claim 1, wherein said tire is an agricultural pneumatic tire.

13. The method according to claim 1, wherein said step (c) includes winding the rubber ribbon directly onto a portion of the tread belts.

Description

SHORT DESCRIPTION OF THE DRAWINGS

(1) Reference will be made to the figures of the annexed drawing, wherein:

(2) FIGS. 1 and 2 relate to an exemplary agricultural tyre which can be manufactured by a preferred embodiment of the method according the present invention, such figures showing a perspective front view and a partial cross-sectional view according to an axial plane of said tyre, respectively;

(3) FIG. 3 shows a schematic representation of a sequence of manufacturing steps according to the aforementioned preferred embodiment of the method;

(4) FIG. 3A shows a perspective view of a block or bar used in the method of FIG. 3;

(5) FIG. 3B shows a perspective frontal view of an intermediate product having a tyre case, tyre belts or plies and bars or blocks applied thereon according to the method of FIG. 3, which intermediate product is being formed onto a drum;

(6) FIG. 3C shows a perspective frontal view of a subsequent intermediate product having also a tread ribbon applied onto the bars according to the method of FIG. 3;

(7) FIG. 3D shows a perspective frontal view of a final intermediate product ready for a moulding step according to the method of FIG. 3; and

(8) FIG. 4 shows a preferred embodiment of an exemplary cross-sectional profile of the bar of FIG. 3A.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

(9) With reference to FIGS. 1 and 2, an agricultural tyre 1 has a central axis of rotation A. A rolling direction of tyre 1 is denoted by 7.

(10) Tyre 1 comprises a toroidal casing 2, which extends about a central axis of rotation A and supports tread belts, or plies, 3 wound about casing 2.

(11) Tyre 1 comprises a tread, globally denoted by 4, arranged about casing 2 and over belts 3 according to a toroidal configuration. Tread 4 comprises a tread base 5, which completely covers casing 2 and belts 3, and a plurality of lugs 6. Lugs 6 project upwards (i.e. extend radially outwards) from tread base 5 and are arranged substantially crosswise with respect to a tyre travelling direction.

(12) Typically, lugs 6 are arranged symmetrically about axis of rotation A.

(13) In the present embodiment, each lug 6 curves from a centreline C of tyre 1 to a corresponding shoulder and has a cross-sectional shape tapering away from tread base 5.

(14) Each lug 6 has a lateral portion 8 at a shoulder of tyre 1 and a central portion 9 located in the central area of tyre 1. In the present embodiment, each lug 6 is thinner at central portion 9 and thicker at lateral portion 8. In the example provided, central portion 9 of each lug 6 has a greater curvature than lateral portion 8 (lateral portion 8 may also be assumed to be substantially straight).

(15) As will be explained in detail shortly, tread base 5 is obtained by a moulding and curing process from a rubber ribbon blank. Each lug 6 is obtained by the same mounding and curing process as a superimposition of said rubber ribbon blank with a respective block or bar.

(16) The manufacturing method described below allows tread base 5 to be of substantially constant thickness.

(17) The manufacturing method of tyre 1 is shown schematically in FIGS. 3 and 3A to 3D.

(18) In particular, casing 2 can be produced, in a conventional mode, on a building unit 101 and subsequently mounted onto a building drum 102 of a Tyre Assembly Machine (TAM).

(19) Upon building drum 102, tread belts 3 are applied onto casing 2.

(20) In a conventional unit 103, tread rubber is mixed and extruded (or calandered) into a strip 260.

(21) In the same or in a separate unit 104, extruded (or calandered) strip 260 is cut into green tread bars (or blocks or elements) 206 (FIG. 3A). Each bar 206 has an inner portion 209 corresponding to central portion 9 of final lug 6 and an outer portion 208 corresponding to lateral portion 8 of final lug 6.

(22) Tread belts 3 and tread bars 206 can assembled together directly onto drum 102, or they can be joined beforehand (i.e. “off-line”) and subsequently placed on TAM and assembled with casing 2 and belts 3.

(23) Bars 206 are lied upon belts 3 according to a selected arrangement and predetermined relative angles (FIG. 3B).

(24) Bars 206 can be joined to belts 3 according to several processes, e.g. by heating, by interposition of chemical compounds or by any other known method for increasing rubber stitching and tackiness properties.

(25) Subsequently, a tread ribbon 200 is would onto bars 206 lied upon drum 102 (FIG. 3C). To this aim, tread rubber is mixed and extruded (or calandered) in a green tread ribbon 200, for example in the same unit 103 mentioned above. Ribbon 200 can be applied by a Ribbon Tread Applicator 106, already known per se in the relevant field.

(26) Thereafter, the tyre to be built is removed from drum 102 (FIG. 3D) and placed in a mould 105, wherein vulcanization (also using a press) takes place according to conventional means and modes.

(27) Strip 260 and/or ribbon 200 can also be manufactured in advance and stored in coils.

(28) With reference to FIGS. 3A and 4, it will be appreciated that dimensions and shape of strip 260 and bars 206 are not equal to the mould lug: they may have a lower height and a wider base, eventually by defining almost same volume. Similarly, sharp outermost edges can be avoided.

(29) Still with reference to FIG. 3A, each bar 206 can have a constant cross-section, preferably with a cut angle α (and bare angle γ as well) common for the two end cross-sections. In this way, the cutting operation is simplified and rubber wastes are avoided.

(30) Generally speaking, the manufacturing method according to the present disclosure is simplified with respect to the prior art. In particular, preparation and winding of tread ribbon 200 is easier than manufacturing and arranging tread blank below blocks according to the known methods.

(31) It will be appreciated that the above method avoids the need for assembling tread blank and bars. In fact, application of bars 206 on tread plies 3 is done before application of ribbon 200.

(32) As already pointed out, the method disclosed allows an important reduction of excess rubber for the tread base with respect to the prior art.

(33) Application of lubricants or other additives upon the semi-manufactured tread before vulcanization to favour air flow and rubber detachment is possible.

(34) It will be appreciated that the method of the invention can be used either to build a new tyre or to regenerate the tread of a used one.

(35) The present invention has been described so far with reference to preferred embodiments. It is intended that there may be other embodiments which refer to the same inventive concept and fall within the scope of the following claims.