Method of producing a spliceless annular tread cap

Abstract: A method of producing a spliceless annular tread cap (2), whereby a portion (23) of an extruded tube (21) of green elastomeric material is fed inside an annular body (8), the inner annular surface (17) of which presents a diameter approximately equal to but no smaller than the outside diameter of the tubular portion (23), and negatively reproduces the pattern of the finished tread cap (2); the tubular portion (23) being expanded and calendered against the inner surface (17) of the annular body (8) by means of a roller (34) moved into a position coplanar with and eccentric in relation to the annular body (8).

Description: The present invention relates to a method of producing a spliceless annular tread cap. In particular, the presente invention relates to a method of producing a spliceless annular tread cap and of the type disclosed in GB-A-2 133 357, that is a method comprising the stages of feeding a tubular spliceless portion of green elastomeric material inside an annular body, an inner annular surface of which presents a diameter approximately equal to but no smaller than an outside diameter of the tubular portion, and negatively reproduces the pattern of the finished tread cap; fitting the tubular portion inside the annular body; and expanding the tubular portion against the inner surface of the annular body. In the aforementioned GB-A-2 133 357, the tubular portion is expanded statically against the inner surface of the tubular body by applying static pressure from the inside and vacuum from the outside, and by heating the tubular body to 80-100°C. In actual use, static expansion of the aforementioned tubular portion led to the production of unaccurate tread patters, and the heating of the tubular body to a temperature of 80-100°C involved a pre-curing of the tread cap which, though very good in principle, requires a very strict and expensive control of the timing of the whole tire forming process and of the following curing process in order to avoid overcuring. It is an object of the present invention to provide a method enabling a spliceless annular tread cap to be produced easily, cheaply, and to a relatively high degree of accuracy. According to the present invention, there is provided a method of producing a spliceless annular tread cap, the method comprising the stages of feeding a tubular spliceless portion of green elastomeric material inside an annular body, an inner annular surface of which presents a diameter approximately equal to but no smaller than an outside diameter of the tubular portion, and negatively reproduces the pattern of the finished tread cap; fitting the tubular portion inside the annular body; and expanding the tubular portion against the inner surface of the annular body; the method being characterized in that the tubular portion is fitted inside the annular body about a roller coplanar with and eccentric in relation to said annular body; the tubular portion being expanded by rolling the roller along the inner surface of the annular body, so as to radially calender the tubular portion against the inner surface of the annular body. The invention will now be described by way of example with reference to the accompanying drawings, in which: Fig.1 shows a schematic view in perspective of a system for producing a spliceless tread cap using the method according to the present invention; Fig.s 2 and 3 show larger-scale cross sections of a detail in Fig.1 in two different operating positions. Number 1 in Fig.1 indicates a system for producing a spliceless annular tread cap 2 (Fig.3). As shown in Fig.3, tread cap 2 presents an outwardly-convex, substantially barrel-shaped outer surface 3 having grooves 4 defining the tread pattern; and an inwardly-concave, substantially barrel-shaped inner surface 5 coaxial with surface 3. As shown in Fig.1, system 1 comprises a forming unit 6 in turn comprising a frame 7, and an annular forming body 8 supported on frame 7 via the interposition of at least two supporting and assembly rollers 9, one of which is connected to the output shaft 10 of a motor 11, so as to rotate at a given constant speed about its axis 12. As shown more clearly in Fig.s 2 and 3, annular body 8 comprises a cylindrical ring 13 having a substantially rectangular axial half section, and defined internally by a cylindrical surface 14 having a central annular rib 15, the opposite axial ends of which define two annular axial shoulders 16. Rib 15 is defined internally by an annular surface 17 constituting the inner surface of annular body 8 and having a substantially barrel-shaped axial half section mating with surface 3 of tread cap 2. Surface 17 is coaxial with axis 18 of annular body 8, and negatively reproduces the central portion of outer surface 3 of tread cap 2. System 1 also comprises an extrusion unit 19 having an annular die 20 for producing a continuous tube 21 of elastomeric material. As it comes out of die 20, tube 21 is cut, by a cutting device 22 between units 6 and 19, into tubular portions 23, the length of which is approximately equal to and normally no smaller than the width of rib 15; the outside diameter of which is approximately equal to but no larger than the minimum inside diameter of rib 15; and the thickness of which is greater than that of tread cap 2. System 1 also comprises a calendering unit 24 arranged facing extrusion unit 19 on the opposite side of unit 6. Unit 24 comprises a base 25 on which is mounted a first slide 26 moved back and forth, by an actuating device not shown, in direction 27 parallel to axes 12 and 18. Slide 26 comprises uprights 28, between which is mounted a second slide 29 moved back and forth, by an actuating device not shown, in direction 30 perpendicular to direction 27 and substantially radial in relation to axis 18. Slide 29 is fitted with a rotary shaft 31 having its axis 32 parallel to axis 18. Shaft 31 is connected at one end to a motor 33 supported on slide 29, and is fitted on the other end with a calendering roller 34, which is rotated by motor 33 about axis 32 in the same direction as annular body 8, and at a surface speed substantially equal to the inner surface speed of annular body 8. Roller 34 also moves radially, in direction 30, to and from an idle position substantially coaxial with axis 18; and axially, in direction 27, between a backup position outside annular body 8, and a forward position inside and coplanar with annular body 8. Roller 34 presents an outwardly-convex, substantially barrel-shaped outer surface 35 having an axial half section so shaped as to mate with that of surface 5. Surface 35 presents a maximum outside diameter smaller than the inside diameter of tube 21, and is defined axially by two flanges 36, each rolling against cylindrical inner surface 14 of ring 13 and respective shoulder 16, so as to define, with shoulder 16, a cutter for cutting off tread cap 2 any excess elastomeric material expelled during calendering from the chamber defined between surfaces 17 and 35 at the instantaneous contact zone between roller 34 and annular body 8. As regards the diameter of roller 34, which must obviously always be smaller than the inside diameter of tube 21, experience has shown that the best results are obtained when the diameter of roller 34 is at least 70% that of surface 17. In actual use, portion 23 is fed inside annular body 8 with which it is arranged substantially coaxial when detached from the rest of tube 21 (Fig.2). At this point, slide 26 is moved in direction 27 towards annular body 8, so as to insert roller 34 inside both annular body 8 and tubular portion 23, and into a position wherein roller 34 is substantially coaxial with annular body 8 (Fig.2). Slide 29 is then moved in direction 30 to position roller 34 eccentrically in relation to annular body 8 (Fig.3), with flanges 36 contacting surface 14, and portion 23 pressed between surfaces 17 and 35. Annular body 8 is then rotated about axis 18, and roller 34 about eccentric axis 32, so as to substantially roll surface 35 over surface 17, and so expand portion 23 against surface 17, and, at the same time, calender portion 23 between surfaces 17 and 35 to produce a totally spliceless tread cap 2.

Claims: A method of producing a spliceless annular tread cap (2), the method comprising the stages of feeding a tubular spliceless portion (23) of green elastomeric material inside an annular body (8), an inner annular surface (17) of which presents a diameter approximately equal to but no smaller than an outside diameter of the tubular portion (23), and negatively reproduces the pattern of the finished tread cap (2); fitting the tubular portion (23) inside the annular body (8); and expanding the tubular portion (23) against the inner surface (17) of the annular body (8); the method being characterized in that the tubular portion (23) is fitted inside the annular body (8) about a roller (34) coplanar with and eccentric in relation to said annular body (8); the tubular portion being expanded by rolling the roller (34) along the inner surface (17) of the annular body (8), so as to radially calender the tubular portion (23) against the inner surface (17) of the annular body (8). A method as claimed in Claim 1, characterised by the fact that it comprises stages consisting in extruding a continuous tube (21) of elastomeric material; and feeding said tube (21) directly inside said annular body (8); said tube (21) being cut into said tubular portions (23) by a cutting device (22) adjacent to said annular body (8). A method as claimed in Claim 1 or 2, characterised by the fact that each said portion (23) presents a length approximately equal to but no smaller than the length of said inner surface (17) of said annular body (8), and a thickness greater than that of said annular tread cap (2). A method as claimed in any one of the foregoing Claims, characterised by the fact that said roller (34) is rolled over said inner surface (17) of said annular body (8), for calendering said tubular portion (23) against said inner surface (17) of said annular body (8), by rotating said annular body (8) in a given direction about a first axis (18), and by rotating said roller (34) about a second axis (32) eccentric in relation to said first axis (18), in the same direction as said annular body (8), and at a surface speed substantially equal to the inner surface speed of said annular body (8). A method as claimed in any one of the foregoing Claims, characterised by the fact that it also comprises a further stage consisting in removing from said tread cap (2) any excess material of said tubular portion (23) via cutting means (16, 36) defined by said annular body (8) and said roller (34). A method as claimed in any one of the foregoing Claims, characterised by the fact that the outside diameter of said roller (34) is equal to at least 70% of the diameter of said inner surface (17) of said annular body (8).

Inventors: SIEGENTHALER KARL J, SIEGENTHALER, KARL J.
Applicants: BRIDGESTONE CORP, BRIDGESTONE CORPORATION
Application year: 1992
Main classification: B29D30
IPC codes: B60C11, B29C69, B29D30, B29K21, B29C43