The invention relates to a method of manufacture and a building drum
for a breaker belt for a vehicle tyre comprising an essentially cylindrical steel
ply assembly which is covered by a textile band arrangement.
Prior art methods comprise the winding of a textile band, notably
a nylon band, over the steel plies, preferably in the form of a strip which is
wound helically around the steel plies. In this known method the textile band
arrangement is wound over the steel belting which has been assembled on a flat
drum to give a planar cross section
It is an object of the present invention to improve such methods
such that the breaker can safely resist higher loads.
According one aspect of the present invention a method of manufacture
for a breaker for a radial tyre comprises steel reinforcement plies covered by
a textile bandage or cord comprising helically winding a textile strip of bandage
over steel belt plies, characterised in that the steel reinforcement plies are
bulged radially outwards in the axially central or crown regions before winding
on of the textile strip.
The steel-textile breaker assembly resulting from this method undergoes
a higher extension in the circumferential direction in the region of the tyre
shoulders when it is expanded in the completed green tyre into the heated mould
with the result that the breaker has improved properties giving improved high
speed tyre performance and better long-term structural performance.
Further, in a vehicle tyre made in accordance with the method of
the invention, the breaker has a regular or more uniform extension over the cross
section of the tyre, i.e. from one tyre shoulder across the top or centre of the
tyre to the other tyre shoulder.
By using the method of the invention it is possible to save material
fro the textile band, in particular the use of lower filament or cord size and/or
lower filament or cord density, without affecting the performance at high speed
of the finished tyre.
Another aspect of the invention provides a breaker belt assembling
drum for manufacturing the breaker which comprises a plurality of drum segments
arranged to form a circular ring characterised by first drum segments which are
flat in the axial direction of the drum and second drum segments which are curved
or bulged in the axial direction of the drum, flat drum segments being movable
from a rest position to a first outward radial position in which the radially
outer surfaces of the flat drum segments are located on the same circumference
as the radially outmost central regions of the bulged drum segments and the bulged
drum segments are movable to a second position located radially outwards of the
Because the first drum segments are flat in the axial direction and
the second drum segments are bulged or curved in the axial direction the different
radial movements of the first and the second drum segments provide a belt assembling
drum which allows, in a first position in which the first flat drum segments provide
the outer periphery of the drum, to apply the steel belt plies, and which allows,
in a second position located radially farther outwardly in which the second bulged
drum segments determine the outer periphery of the drum, to wind the textile band
onto the steel belting which is deformed into a curved shape.
Preferably the bulged drum segments are arranged around the circumference
of the drum alternately with the flat drum segments.
The centres of curvature of the bulge of the second drum segments
may be arranged essentially on a centre circumferential line with respect to the
axial width of the drum to provide a symmetrical curved deformation of the steel
belting, in which the bulge or curvature of the bulged drum segment occurs not
only in the axial direction but in addition to the circumferential direction and
the drum segments which are horizontal in the axial direction are also curved
in the circumferential direction. By this arrangement a rounder belt structure
is achieved, i.e. a structure of smoother curvature.
Furthermore the centres of curvature of the bulge of each individual
bulged drum segment can be disposed on a straight line, whereby the finishing
of the bulged drum segments is simplified. If the drum segments manufactured in
this manner are made short in the circumferential direction and short drum segments
are accordingly distributed close to each other over the circumference, a more
homogeneous, essentially circular-shaped circumferential form for the steel belting
is also obtained.
The invention will now be explained in more details in connection
with an example and with reference to the drawings, in which:
- Figure 1 is a cross section through a belt structure achieved with the method
of the invention;
- Figure 2 is a schematic side view of a belt assembling drum of the invention;
- Figure 3 is a sectional view of a flat drum segment;
- Figure 4 is a sectional view of a bulged drum segment; and
- Figure 5 is a detail of Figure 2 showing the bulged drum segments outwardly
A belt structure of a steel belted radial tyre for a passenger car
is illustrated in Figure 1 and comprises two steel belt plies or layers 11,12
whose steel cords cross each other. The belt layers 11,12 are covered by a textile
band 13 which is wound in a helix on the steel ply 12. This is a nylon band having
for example a width of 10mm wound with the side edges of the textile band either
terminated at an obtuse angle at the side edges of the steel belt structure or
overlapping outwardly in the axial direction. The belt structure comprising the
two steel layers 11,12 and the textile band 13 is in this case slightly bulged
or curved in cross section.
Figure 2 shows schematically the circular-shaped arrangement of drum
segments 21,22 of a belt assembling drum 2. First flat drum segments 21 and second
curved or bulged drum segments 22 are arranged alternately around the drum. The
flat drum segments 21 have at their outer circumference in the axial direction
a substantially flat surface 23. They may be slightly curved in the circumferential
direction in correspondence with the envelope circle of the belt assembling drum
Figure 3 shows a section through a flat drum segment 21 in a plane
extending through the axis of the belt assembling drum 2. The upper sectional
edge of the outer plane 23 extends parallel to the axis of the belt assembling
The curved drum segments 22 have axially outer edges 25,25&min; between
which the radially outer surface bulges outwardly radially from the centre of
the drum segment 22 and forms a central region 24.
In Figure 5 is shown a detail of the belt assembling drum schematically
illustrated in Figure 2, in which the bulged drum segments 22 are displaced in
a radially outwardly offset position with respect to the flat drum segment 21.
In the position illustrated in Figure 2, all drum segments 21,22 lie in a common
circumferential line, such that the maximum circumference 20 envelops both the
flat drum segments 21 and the bulged drum segments 22.
The steel belt plies or layers are applied in turn by wrapping onto
the belt assembling drum in this first position of the drum segment. The steel
belting 11,12 then lie flat on the flat drum segments 21. The steel belting can
also contact the central regions 24 of the bulged drum segment 22 which are arranged
therebetween or the drum segment 22 can be positioned radially inwardly at such
a distance that in this position there is no contact of the steel belting with
the bulged drum segments 22.
After the steel belting 11, 12 has been assembled onto the belt assembling
drum 2, the bulged drum segments 22 are displaced outwardly until their radially
outer surfaces extend at least partly radially beyond the circumferential line
20, whereby the regions 24 of the bulged drum segments 22 provide the envelope
of the circumferential line 26 having a larger diameter in the centre and in the
axial cross section a bulge or convexity.
In Figure 5 the bulged drum segments 22 are displaced outwardly over
such a distance that their axial outer edges 25 are displaced radially outwardly
exactly as far as the outer surfaces 23 of the flat drum segments 21.
The outward displacement of the bulged drum segments 22 radially
outwardly beyond the circumferential line 20 which carries the steel plies 11,22
deforms the steel plies into a convex or crown shape. The textile band can then
be helically wound on the curved steel plies 11 and 12.
The resultant breaker assembly has a predetermined curvature as shown
in Figure 1. The tyre building can then be completed by expanding or shaping a
tyre carcass into the breaker sub-assembly in the conventional way, applying a
tyre tread strip and if necessary separate sidewalls and consolidating the assembly.
The resulting green tyre contains a curved or convex cross section breaker package
in which, most importantly, the bandage strip winding length for each turn is
set to match the curvature.
The green tyre is then passed to a vulcanisation/moulding machine
where the tyre is expanded into a patterned mould and subjected to heat and pressure
to cure it. In the mould the breaker and strip wound bandage are expanded and
the tensions applied to the components provide the results required in the finished