Plastic and nonmetallic article shaping or treating: processes – Direct application of fluid pressure differential to... – Producing toroidal work
Reexamination Certificate
1999-07-30
2001-12-25
Vargot, Mathieu D. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Direct application of fluid pressure differential to...
Producing toroidal work
C156S110100, C156S414000, C264S326000, C425S044000, C425S049000
Reexamination Certificate
active
06332999
ABSTRACT:
The present invention relates to a method for moulding and curing tyres for vehicle wheels, comprising the following steps: disposing a tire being worked on a toroidal support having an outer surface the shape of which matches that of an inner surface of the tire itself; closing the tire and the toroidal support in a moulding cavity defined by a vulcanization mould, said moulding cavity having walls conforming in shape to an outer surface of the tire when vulcanization has been completed; pressing the tire with its outer surface against the moulding cavity walls; administering heat to the tire being worked in order to cause a molecular cross-linking of same.
The present invention also relates to an apparatus for moulding and curing tires for vehicle wheels, comprising: a toroidal support arranged to engage a tire being worked, said toroidal support having an outer surface the shape of which matches that of an inner surface of the tire; a vulcanization mould arranged to receive the toroidal support carrying the tire being worked within a moulding cavity having walls conforming in shape to an outer surface of the tire when vulcanization has been completed; pressing means for pressing the outer surface of the tire against the moulding cavity walls; heating means for transmitting heat to the tire closed between the moulding cavity and the toroidal support.
In a tire production cycle it is provided that, subsequently to a manufacturing process in which the different tire components are made and/or assembled together, a moulding and curing process is carried out which aims at stabilizing the tire structure according to a desired geometric conformation, usually characterized by a particular tread pattern.
For the purpose, the tire is closed in a moulding cavity internally defined by a vulcanization mould and conforming in shape to the geometric configuration of the outer surfaces of the tire to be obtained.
In one of the most widely spread moulding methods it is provided that a vulcanization bladder of elastomer material filled with steam and/or another high-temperature and high-pressure fluid should be inflated within the tire closed in the moulding cavity. In this way, the tire is conveniently pushed against the inner walls of the moulding cavity and stabilized to the geometric conformation imposed to it, following the molecular cross-linking undergone by the elastomer material of which it is made, due to a supply of heat transmitted by the fluid through the bladder and by the mould walls.
Also known are moulding methods in which, instead of the inflatable vulcanization bladder, a rigid toroidal support is arranged within the tire, the shape of which matches that of the inner surface of the tire to be obtained.
Such a method is described in the European patent EP 242 840 for example, in which a rigid toroidal support is employed for imposing the final shape and sizes to the tire closed in the mould. In accordance with that which is described in this patent, the different coefficient of thermal expansion between the metallic toroidal support and the raw elastomer material of which the tire is made is utilized for achieving a suitable moulding pressure.
In conclusion, the assembly of the parts forming the mould and the toroidal support defines a closed interspace in the moulding cavity, which substantially has a shape conforming to the whole geometric configuration of the tire. In this way, both the outer surfaces and the inner surfaces of the tire are maintained in contact with rigid portions of the moulding and curing apparatus. In other words, all the apparatus parts intended to set up the final tire geometry are rigid parts, in contact with the methods using the inflatable vulcanization bladder which, as known, constitutes a deformable part of the mould.
It is however to point out that, at the present state of the art, both methods, i.e. that employing the inflatable vulcanization bladder and that employing a rigid toroidal support during tire vulcanization, have some problems.
With reference to the methods employing the inflatable bladder, it is in fact to note that the bladder deformability can easily give rise to geometric and/or structural imperfections in the tire, due to possible distortions to which the bladder itself may be submitted, owing to an unbalanced expansion and/or to friction phenomena generated between the outer surfaces of the bladder and the inner surfaces of the raw tire. Taking into account the fact that the bladder also has the task of locking the tire beads against the corresponding portions of the mould, the bladder deformability makes it difficult to achieve sufficient bead-locking pressures. Therefore an undesired out-of-alignment positioning of the beads relative to the geometric axis of the tire can occur, which will give rise to distortion of the whole tire structure. An insufficient bead-locking pressure, in addition, can give origin to formation of burr at the beads themselves, due to escape of elastomer material between the bladder and mould, above all at the starting instants of the curing process.
The vulcanization bladder needs use of great amounts of steam, due to the requirements of filling the whole inner volume of the bladder inflated in the mould cavity, and in addition it constitutes an obstacle to heat transmission to the tire by said steam.
On the other hand, use of a rigid toroidal support instead of the inflatable vulcanization bladder makes it necessary to carry out a very precise, and also very difficult, checking of the volumes of the material used in manufacturing the tire.
Furthermore, it is not presently possible to impose an appropriate radial and/or circumferential expansion to the tire, for achieving desired preloading effects in the reinforcing structures employed in manufacturing said tire.
Even with the aid of the rigid toroidal support, in addition, it is somewhat difficult to obtain a correct and efficient heat transmission to the inside of the tire.
The Applicant has envisaged the possibility of achieving important improvements in the processes for moulding and curing a tire with the aid of a rigid toroidal support, by carrying out admission of a heating fluid and/or another fluid under pressure, in accordance with the present invention, to an interspace defined between the inner surface of the tire and the outer surface of the toroidal support itself.
In particular, the invention relates to a method of moulding and curing tires for vehicle wheels, characterized in that said pressing step takes place by admission of a fluid under pressure (or pressurized fluid) to at least one fluid-diffusion interspace created between the outer surface of the toroidal support and the inner surface of the tire.
In more detail, the pressing step preferably takes place concurrently with an expansion imposed to the tire by effect of admitting fluid under pressure to the diffusion interspace.
Said radial expansion preferably involves an increase in the tire circumference included between 1.5% and 3.5%, measured at an equatorial plane of the tire itself.
The diffusion interspace, preferably having a size included between 3 mm and 14 mm, measured between the inner surface of the tire and the outer surface of the toroidal support at least at one equatorial plane of the tire itself, can be advantageously created following expansion of the tire.
In a preferential embodiment, admission of fluid under pressure takes place through feeding channels formed in the toroidal support and opening onto the outer surface of said support.
In addition, it is preferably provided that during admission of fluid under pressure the tire should be sealingly engaged at its inner circumferential edges between the moulding cavity walls and the outer surface of the toroidal support, for hermetically delimiting the diffusion interspace at the inner circumferential edges of the tire itself.
Advantageously, heat administration preferably takes place by admission of a heating fluid to said diffusion interspace.
This heating fluid may constitute, or at least may be part o
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Pirelli Pneumatici S.p.A.
Vargot Mathieu D.
LandOfFree
Method and apparatus for moulding and curing tires for... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and apparatus for moulding and curing tires for..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for moulding and curing tires for... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2593899