A carcass ply is applied around the outer surface of a building drum that has a diameter larger than the fitting diameter of a tyre. Coaxially engaged around each end flaps is an annular anchoring structure defining the suitable diameter. A pair of sidewalls is manufactured by laying of a continuous elongated element in the form of approached coils on the carcass sleeve. An outer sleeve, which has at least one belt structure associated with a tread band, is coaxially centered around the carcass sleeve. Through axial approaching of two halves forming the building drum, the carcass sleeve is shaped into a toroidal configuration to determine the application of same against a radially internal surface of the outer sleeve.
Difficulties that occur in progress:
The construction of the “overlying sidewall” offers more reliability as in the sidewall/tread interface and involves construction complications in the tyre manufacturing process. Similarly, the “underlying sidewall” is easier to manufacture, but reliability is critical between the apex of the sidewall and the tread band where, use and ageing of the tyre, undesirable separations can also occur.
Excellent quality of a product can be achieved by carrying out the whole manufacture of the green tyre without removing the carcass structure from the building drum. The problem of avoiding transportation of a carcass sleeve and reducing deformations of the tyre being processed, particularly during the shaping step can also occur.
The sidewalls are manufactured as a semi-finished product of one piece construction and then laid on the not yet shaped carcass sleeve tyre. It must be submitted to critical stretching actions during the developing step. Above all of the radially outermost regions where the sidewall, formed initially to the laying diameter, should reach a diameter substantially equal to that of the outer sleeve. This stretching action can involve undesirable stresses on the carcass structure.
Even the problem of obtaining an optimal junction without structural and covering discontinuities within the radially external flaps of sidewalls and the axially outer portions of the tread band.
How to deal with these problems?
The problems mentioned above can easily be solved by providing a suitable building step for the sidewalls. In this sidewalls can be directly formed on a carcass sleeve of cylindrical shape through the assembly of primary components and more precisely by winding up at least one continuous elongated element of elastomeric material.
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