Plastic article or earthenware shaping or treating: apparatus – Product or preform repair or restoring means – Tire recapping – rebeading or sidewall replacing means
Reexamination Certificate
2001-09-19
2003-08-19
Mackey, James P. (Department: 1722)
Plastic article or earthenware shaping or treating: apparatus
Product or preform repair or restoring means
Tire recapping, rebeading or sidewall replacing means
C425S024000, C425S039000
Reexamination Certificate
active
06607373
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention concerns a resilient mold for treads, designed notably for methods of treading vulcanized tire carcasses. These methods are generally applied today in retreading, but, of course, everything to be stated below is applicable to the treading of new tire carcasses.
There are two main types of retreading methods, one, commonly called “cold retreading,” consisting of using a precured tread that is placed on a carcass ready to be retreaded, and then curing the assembly by using heating means such as an oven; the other method, called “hot retreading,” consists of placing a crude rubber tread, notably, in the form of sheets, strips or sections, on a carcass ready to be retreaded and then curing the assembly in a mold.
These hot retreading methods are applied, in particular, to the retreading of large-sized tires, such as tires intended for trucks, farm machinery, construction equipment, etc., for which problems of handling and warping of treads render their use difficult in a precured form. The invention lies within the area of hot retreading.
Among the hot retreading methods, U.S. Pat. No. 4,053,265 describes a method which consists of using a resilient ring mold containing lateral wings, preferably made of rubber, designed to make possible the molding and vulcanization of the tread. This resilient mold is placed on the tire carcass to be retreaded, which has been previously covered with a crude rubber tread, the mold-carcass assembly then being totally enveloped by a membrane ensuring tightness. This assembly in then placed in an oven for curing after creation of a vacuum in the membrane.
In order to place the resilient mold on the tread, it is stretched and, maintaining it in a stretched position, the carcass covered with said tread is placed inside and the mold is then left to be compressed on the tread.
In general, for this operation, the tools used grip the wings of the resilient mold, followed by a radial rebound of the latter, resulting in stretching of the entire mold and, therefore, its increase in diameter. However, this operation raises numerous difficulties. In fact, said stretching acts more on the wings and peripheral edges of the mold than on its center zone, which creates a heterogeneous distribution of deformation of the mold and subjects it to intense strains. Furthermore, to enable the central zone of the mold to adopt a diameter greater than that of the crude rubber tread, it is necessary to exert a very considerable stress on the wings of the mold, which can cause the threshold of elasticity of the wings of the mold to be exceeded, give rise to tears and, in addition, not necessarily suffice for the transmission of tensile force on the wings to result in stretching of the center zone of the mold.
This phenomenon also has consequences on the tire itself on mold stripping. In fact, insofar as the center zone of the mold is not directly stretched, there are difficulties of mold stripping in the center of the cured tread. Thus, it is not then possible with this type of mold to carry out the retreading of a tire casing whose H/W shape ratio is high, H being the height of the tire casing mounted on the rim and inflated to its working pressure and W being the maximum width of the casing.
Furthermore, following placement of the tire casing inside the mold, the latter is left to be compressed on the tread, without making it possible to check whether the bottom of the sculpture made in the crude rubber tread leaves a sufficient thickness of rubbery compound in relation to the tire carcass or leaves too great a thickness.
SUMMARY OF THE INVENTION
The invention concerns a resilient mold which makes it possible to overcome these problems.
More particularly, the invention relates to a resilient ring mold designed to ensure the molding of a crude rubber tread covering a vulcanized tire carcass, being made of a rubbery material, in which provision is made for limiting its diameter in compression.
The invention also concerns an apparatus for molding a tread on a tire carcass, comprising a resilient ring mold according to the invention, which also embraces a mounting rim for the tire carcass to be treaded and two resilient flanges intended to cover respectively the outer surface of the tire casing constituted by said carcass and a crude rubber tread covering it, lying between a bead of said casing and the peripheral edge of the corresponding mold.
The choice of radial and axial directions for the retreading means as well as for the tire relates below to the axes generally used as reference in the tire, the axial direction corresponding to a direction parallel to the axis of rotation of the tire casing, and the radial planes being planes containing a radius of the tire casing and passing through said axis of rotation.
Other characteristics and advantages of the invention will appear on reading a working example of a resilient mold according to the invention, with reference to the attached drawings.
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U.S. patent application Ser. No. 09/956,154, by Chamoy, filed Sep. 19, 2001.
Mackey James P.
Michelin & Recherche et Technique S.A.
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