The present invention relates to a segmented annular tread
mold for curing an annular ring tread, according to the pre-characterizing part
of claim 1.
Background of the Invention
In the making and curing of tire treads or tire tread and
belt assemblies, it has been a common practice to wrap one or more layers of an
uncured elastomer such as rubber, with or without reinforcements, such as metal
cord reinforced plies or fabric and the like about a cylindrical core. The cylindrical
core was selected to have a diameter equal to the desired inside diameter, the cylindrical
core, with the elastomeric layers attached is generally placed in the center of
a cylindrical core of a larger segmented cylinder, which larger segmented cylinder
can include mold faces with desired tread patterns on the interior surface thereof,
the diameter of the larger segmented cylinder is reduced until it properly contacts
the material wrapped about the inner core apparatus and the entire apparatus is
heated. The outer mold face segmented cylinder can, of course, be constantly heated
but it is more difficult to heat the inner core about which the rubber is wrapped.
As a result, premature curing might then take place. US-A- 4,207,052 on which the
pre-characterizing part of claim 1 is based, shows a plurality of inner segments
which fit together to form a generally cylindrical mold face surface to form the
inner surface of the tread belt along with a means for retracting said plurality
of inner segments toward the axis of said inner cylinder and a means for heating
said segments. Additionally, the apparatus included a plurality of outer segments
which fit together to form an inner generally cylindrical mold face surface of an
outer cylinder, said outer cylinder being coaxial with said inner cylinder and of
equal lengths therewith along with the means for retracting the plurality of outer
segments away from the common axis of said cylinders and a means for heating said
plurality of outer segments. The apparatus further included a pair of rings for
sealing said inner cylinder to said outer cylinder at the ends thereof, at least
one of said sealing rings being removable so that an uncured tire tread or track
belt could be positionable between said plurality of inner segments and said plurality
of outer segments wherein said plurality of inner segments was retracted toward
said common axis and said plurality of outer segments is retracted away from said
In the prior art it was common for the radially retractable
segments to have curved or arcuate shapes with vertically extending edges or sides.
The outer segments could move inwardly and create an annular ring for forming the
outer tread surface including the tread lugs. The inner segments would move sequentially
radially outwardly in an alternating pattern wherein every other inner tread segment
would be extended and then every other retracted inner tread segment could be then
extended outwardly thereby forming a ring in the fully extended position thereby
providing a mold that would cure the tread belt assembly over a period of time.
This time was considered the mold cure cycle. Each radially outer segment and each
radially inner segment had edges that were generally vertically extending and parallel
to the common axis of both the inner and outer segments. Upon curing the tread the
inner segments would then be retracted such that the inner surface of the molded
tread could be separated from the first radially inward moving segments while the
adjacent inner segments held in the closed position would retrain the tread belt
assembly within the tread forming outer segments. Once the first radially inner
segments had been moved inwardly, the second set of radially inner segments could
be moved inwardly thereby releasing the entire inner surface of the tread. Thereafter
the outer tread forming segments could be moved radially outwardly thereby releasing
the tread belt assembly from the mold in its entirety. As the tread is removed from
the outer segments a device would be used to lift the cured tread belt assembly
from the mold.
In this type of prior art tread belt assembly molding the
radially inner tread forming surface had equal sized tread segments generally with
vertical extending edges that extended generally parallel to the axis of the mold
rings when in the closed position. Similarly, the outer segments also had vertically
extending or generally parallel side faces such that when the mold closed these
faces would abut forming a tight joint between the segments. In principle the above-referenced
prior art mold as described in US-A- 4,207,052 works generally well for fairly large
tread belt assemblies. However, the application of the forces when one closes the
inner segments and outer segments of such a mold is such that all movement works
in a radial direction increasing the amount of pressure on the radially inward segments
Some examples of prior art segmented mold can be found
in EP-A-1295702, US-A- 2,381,395 and EP-A- 1260351.
It has been an objective of the present invention to provide
a tread belt mold that would provide improved stability of both the inner and outer
segments as the tread belt assemblies being cured such that a uniformity of curing
pressure can be insured around the entire 360° circumference.
A second objective of the present invention is to provide
a way in which the radially outer mold segments can be provided with improved structural
integrity wherein the parting line between circumferentially adjacent segments extends
across the tread lug forming depressions within the outer segments thereby avoiding
thin ribs within the groove forming section of the mold to as large an extent as
Summary of the Invention
The invention relates to an annular mold for curing an
annular ring tread according to claim 1.
Particular embodiments of the invention are the subject
of the dependent claims.
The radially outer segments have inclined laterally extending
edges relative to the axial direction of the mold while the circumferentially extending
axially outer edges are perpendicular to the axial direction of the mold. Preferably,
the inclined laterally extending edges are inclined at least 5°, more preferably
10° relative to the axial direction. In the preferred embodiment the mold has
12 outer segments, each segment being of an arc length of 30°.
In one aspect of the invention, the radially outer segments
each have a pair of obtuse angles &agr; and a pair of acute angles &bgr;. The
sum of &agr; and &bgr; equal 180°, the sum of the pairs of &agr; and
&bgr; equal 360°.
In another aspect of the invention, the mold when placed
in a closed position has an annular shape, the outer segments forming an annular
ring radially outward of the ring formed by the radially inner segments. The annular
mold has an axis and a midcircumferential center plane perpendicular to the axis.
Preferably, the mold has a plurality of radially movable outer segments each movable
outer segment being an arcuate parallelogram having pairs of obtuse included angles
&agr; and acute included angles &bgr; relative to the axis of the mold. The
outer segments when closed form an annular ring of arcuately adjacent parallelograms.
Preferably each axially outer segment has two inclined axially extending edges or
surfaces. The inclined axially extending edges or surfaces are inclined relative
to the axial direction. Furthermore, the arcuate circumferentially extending axially
outer edges of the tread forming outer segments are preferably perpendicular to
the axis of the mold. The combination of inner segments and outer segments provide
a structurally improved mold design such that the arcuately shaped axially extending
inclined outer edge surfaces extend beyond the radially inner segments such that
the axially outer segments press against and have an inward force extending across
one full axially inner segment and portions of two axially outer segments.
Preferably, the axially inclined edge surfaces of the outer
segments extend across tread element forming depressions in each of the outer segments
wherein the outer segments form circumferentially offset tread elements with respect
to the mid-circumferential center plane of the mold and the linearly axially inclined
surfaces extend nonparallel to the axis of the mold across circumferentially offset
tread forming depressions within the outer segment. The tread element forming depressions
can be elongated tread bars extending axially inwardly from the lateral edges of
the mold toward the tread centerline. Furthermore, the tread element forming depression
can include a circumferentially centered continuous rib forming depression. When
the inclined edge surfaces extend across these tread element and rib forming depressions
this insures that the parting line between the axially adjacent outer segments lie
in a radially outer surface of the tread elements and do not lie within the groove
forming ribs of the outer tread forming segment. This insures that the parting lines
do not create weak thin projecting rib portions as is commonly found in single pitched
"Circumferential" means lines or directions extending along
the perimeter of the surface of the annular tread perpendicular to the axial direction.
"Cord" means one of the reinforcement strands of which
the plies in the track are comprised.
"Equatorial plane (EP)" means the plane perpendicular to
the track's axis of rotation and passing through the center of its tread.
"Footprint" means the contact patch or area of contact
of the tread with a flat surface under load and pressure.
"Lateral" and "laterally" means lines or directions that
are parallel to the axis of rotation of the tire (also "axial").
"Ply," means a continuous layer of rubber-coated parallel
"Radial" and "radially" means directions extending radially
toward or away from the axis of rotation of the track.
"Zero-degree wires" means at least one layer of parallel
cords &usually metal wire), underlying the tread, unanchored to the bead, spiraling
circumferentially around the tread, and having cord angles in the range from 0 degrees
to 5 degrees with respect to the equatorial plane of the tire.
Brief Description of the Drawings
The invention will be better understood by reference to
the drawings when like numbers denote like parts throughout and wherein:
Detailed Description of the Invention
- Figure 1 illustrates a top view of a mold according to the prior art for curing
a tire tread and tread belt assembly;
- Figure 2 is a partial view of the prior art mold showing the lower links;
- Figure 3 is a cross-sectional view of the prior art mold outer segment of Figure1;
- Figure 4 is a top view of the mold segments according to the present invention
illustrated in a full open position;
- Figure 4A is a cross-sectional view, taken along lines 4A of Figure 4, showing
the outer segment and the inner segment.
- Figure 5, Figure 6 and Figure 7 are top views of the inner and outer mold segments
wherein in Figure 5 a first set of inner segments is extended radially outwardly;
in Figure 6 a second set of inner segments is extended radially outwardly, and in
Figure 7 the outer segments are retracted radially inwardly as the mold is shown
in a fully closed position;
- Figure 7A is a cross-sectional view taken along lines 7A-7A of Figure 7 showing
an inner segment and outer segment in the mold closed position;
- Figure 8 is a plan view of the outer segment and the tread forming inner surface
of the outer segment;
- Figure 9 is a cross-sectional view taken along lines 9-9 of Figure 8;
- Figure 10 is a plan view of the radially outer surface of the outer segment;
- Figure 11 is a top view of the outer segment;
- Figure 12 is a perspective schematic view of the outer segments;
- Figure 13 is a partial view of the molded tread belt.
Prior art tire tread and track belt curing apparatus 10
shown generally in Figures 1, 2 and 3 details the structure of said prior art apparatus
10. The apparatus 10 included an inner cylinder 12 formed of a first set of a plurality
of inner segments 14, a second set of a plurality of inner segments 16 which act
as slave segments which are carried forward by the movement of the first set of
inner segments 14, which segments 14 are powered. Thus, the first set of segments
14 and the second set of segments 16 fit together in alternating sequence to form
the inner cylinder 12. It is necessary that the inner cylinder 12 be completely
continuous. That is, gaps cannot be left between adjacent inner segments 14 and
16, and a proper mechanical arrangement must be provided to give an easy and smooth
working mechanism whereby the first plurality of inner segments 14 and the second
plurality of inner segments 16 can be easily retracted and advanced to form the
continuous inner cylinder 12.
Retraction of the first set of segments 14 proceeds via
action of a first plurality of links 20 under the impetus of an elevation cylinder
22 which is moved upwardly or downwardly under the impetus of a first hydraulic
cylinder. The first hydraulic cylinder acts between a frame and the elevation cylinder
to cause the elevation cylinder 22 to move upwardly or downwardly as guided by a
centering slide which forms a part of the frame. As will be most apparent from Fig.
2, there is a second plurality of links 30 aligned below the first plurality of
links 20 in one-to-one relation therewith so as to provide an even pulling or pushing
force upon the tops and bottoms of the first set of inner segments 14 and upon the
second set of inner segments 16. Each of the links 20 is pivoted at a plurality
of first pivots 32 to the elevation cylinder 22. In the embodiment illustrated,
the elevation cylinder 22 is at its lowermost position under the impetus of the
hydraulic cylinder which is substantially fully retracted and in that position each
of the first plurality of links 20 and the second plurality of links 30 is substantially
horizontal thus holding the first powered set of segments 14 in their outwardly
expanded position to form the continuous inner cylinder 12.
Referring now once again most particularly to Figs. 1 and
2, there is illustrated therein some detail the structure and operation of the outer
cylinder 44. Briefly, the outer cylinder 44 comprises a plurality of outer segments
106, each of which is retractable outwardly under the impetus of a respective one
of a plurality of outer hydraulic cylinders 108, with each of the plurality of outer
segments 106 being generally carried by a rod 110 of a respective one of the outer
hydraulic cylinders 108, and with each of the segments of the plurality of outer
segments 106 being slidingly held and positioned between a respective guide supported
by the frame. For a more detailed description of the prior art structure reference
to US-A- 4,207,052 should be made.
Each of the outer cylinders 108 is held by an outer ring
portion 114 of the frame to form a continuous cylindrical ring as shown in Figure
3. The outer segments 106 each contain a portion 109 of the tread pattern for the
tread belt or track assembly. Each portion of the outer segments 106 has a pair
of vertical ends 107 that are radially parallel to the axis of the prior art mold
Accordingly, each outer segment 106 when viewed from the
top has a circumferentially extending arcuately shaped top and bottom that are equal
in length and aligned.
This prior art mold design required the segment parting
lines at the ends 107 to cross over the groove forming ribs 111 of the tread forming
outer segments 106 and the outer cylinder 44 and the inner cylinder 12 would sandwich
the tread belt assembly in between the inner cylinder 12 and outer cylinder 44 causing
a compression on the assembly. The segments were heated with steam passing through
passages in the mold to cure the tread belt assembly.
Each inner segment 14, 16 and each outer segment 106 is
held in abutting relation to the circumferentially adjacent segment. The outer segments
106 inwardly press radially against the tread and the inner segments 14, 16. During
curing the retention of the segments in a fully closed position is critical.
The present invention as illustrated in Figures 4 through
11 shows an improved mold curing apparatus for tread belt assemblies. As in the
prior art design, inner segments of the present invention are employed that advance
and retract in an alternating sequence. The first set of inner segments 120A are
arcuately shaped with the abutting edges 122 flared outwardly as shown. The second
set of segments 120B have the abutting edges 121 flared inwardly as illustrated,
thus when the first set of inner segments 120A is extended to a closed molding position
as shown in Figure 5, the second set of inner segments can wedge the abutting edges
121 against the surfaces of the abutting edges 122 of the first inner segments 122
forming the inner ring as shown in Figure 6.
Once the tread belt assembly is securely positioned onto
the expanded inner segments the mold can close wherein the outer segments can be
moved radially inwardly as shown in Figure 7.
As shown in Figures 4A and 7A the movement of the radially
outer segments 130 inwardly closes the space 150 between the cylinder formed by
the inner segments 120A and the outer segments 120B.
The tread forming outer segments 130 press into the tread
rubber forcing the tread rubber to move into the tread forming depressions. The
groove forming ribs 155 on the mold surface 151 first engage the uncured rubber
and push into the rubber. This movement requires a large amount of force but care
must be exercised not to move the outer segments 130 too quickly into the tread
belt so as to distort the underlying cord reinforcements or to close too slowly
as to permit large amounts of rubber to get entrapped between the adjacent outer
segments 130 in the area commonly referred to as the mold parting lines or to prematurely
cure the rubber.
Preferably the uncured tread belt 2 can be contoured to
facilitate displacement of the tread rubber into the mold. As shown for mold 10
in Figure 3 the rubber was thicker in the center and then thinner at the lateral
edges. As shown, the first tread belt, formed from a mold according to the present
invention, had a circumference of 11.132 m (438.25 inches) and a diameter of 3.543
m (139.5 inches). In cross section at the center tread belt assembly had a thickness
of 15.75 cm (6.2 inches) that tapered to about 13.72 cm (5.4 inches) at the lateral
edges. This is very complimentary to the tread forming outer segments contoured
lateral edges and insures the tread rubber uniformly flows toward the lateral edges.
The heated mold then cures at a pressure of about 27.6 bar (400 psi) for several
hours. The tread belt as shown in Figure 12 weighs over 2041 kg (4500 pounds).
As illustrated, the outer segments 130 number twelve. This
number can be larger or smaller depending on the tread belt size. Each outer segment
130 extends circumferentially in an arc of 30°. Unlike the prior art, however,
this 30° arcuate parallelogram is inclined at an angle &thgr; relative to
an axial direction. As illustrated the outer segments 130 are inclined such that
&thgr; is about 10°. Accordingly, the top of the outer segment 130 is shifted
right 10° as the bottom is shifted toward the left 10° relative to the
mold centerline. This effectively means that the outer segment 130 spans circumferentially
about 50° from top to bottom. This inclination &thgr; is preferably 5°
As the mold closes each outer segment 130 can align with
at least two inner segments 120A, 120B. Preferably each outer segment can align
with one full inner segment 120A or 120B and portions of two other inner segments
120A or 120B when the mold is fully closed. In this design the pressure exerted
by the closing of the outer segments 130 is absorbed more efficiently, particularly
the second set of wedge shaped inner segments 120A or 120B receive mechanical support
in that at least one, preferably both, inner segments 120A of the first set or the
second set are partially aligned with an inclined parallelogram shaped outer segment
130 in an alternating pattern. This means that the inner ring can resist the tendency
to open more effectively than if the segments 130 were all vertically formed as
in the prior art.
This shifting of the tread forming outer segments 130 to
form an inclined parallelogram is ideally designed to enhance the structural integrity
of the mold.
As shown in Figure 8 each groove forming rib 155 of the
mold outer segments 130 are attached using threaded fasteners 160. As a result of
the use of the inclined parallelogram design each rib 155 is fully positioned inside
the parting lines formed by the ends 135, 136. In prior art designs having vertical
sides at the parting line, shown in Fig. 3, portions of the ribs 111 may lie on
or cross these parting lines. To make the tread these groove forming ribs 109, 111
would be cut leaving thin rib portions that would abut when the outer segments 106
closed. The present invention's use of inclined parallelograms insures the groove
forming ribs 155 never cross the parting lines formed by the ends 135, 136. As shown
six such groove forming ribs 155 are attached to each mold outer segment 130, three
ribs 155 on each tread half.
With reference to the end surfaces and edges 135, 136 or
135A, 136A, or 135B, 136B of the outer segments 130 are inclined relative to the
axis at an angle &thgr; of 10° and are oriented radially inwardly. In other
words in the embodiment shown having 12 equal sized arcuate parallelograms of an
arc length of 30° each radially extending edge surface 135, 136 is inclined
at 15° radially from a midpoint of the edges circumferentially as measured
in any axial location across the mold face to intersect the mold axis. It is important
to note that the calculations for compound angles on the parallelogram shaped outer
segment 130 is actually more complex. The angle of the segment at the edge 135A,
136A of the end 135, 136 at or on the tread forming surface 150 is best defined
by a tangent plane C on the tread surface in which the edge line 135A, 136A lies,
the angle being defined by the formula Tan C = (Tan A) (Cos B), or in this case
the angle A is the 10° inclination previously noted as &thgr; and the Cos
B is the 15° inclination as shown in Fig. 12. Thus, the Tan C = 0.1703 and
the angle C = Tan-(0.1703), C being 9.666° at edge 135A, 136A at
the inner surface 150. The angle D of the end surface 135, 136 can be defined as
a line lying in a plane tangent to the end surface 135, 136, thus the Tan D = Tan
B x Cos A or Tan 15° x Cos 10°, thus D = Tan-(0.26388), D being
As illustrated in Figure 10 the outer segments at the opposite
ends 135B, 136B on the end surface 135, 136 have chamfers 138, 139. These chamfers
138, 139 do not interfere with the edges 135A and 136A on the tread forming surface
150 which naturally must not have any gaps when closed. The closing of the parallelograms
of these segments is greatly enhanced by using the chamfers 138, 139.
As further illustrated each mold outer segment 30 may include
a top or bottom plate 131, 132 for forming the side of the tread belt as illustrated.
Assuming a top plate 131 is used on each outer segment 130 then a corresponding
bottom plate 132 could be affixed to the inner mold segment 120A, 120B as an alternative.
Both the inner segments 120A, 120B and the outer segments
130 have steam or fluid passages 128 for passing heated fluids to maintain the cure
temperature of the mold at a temperature below 204°C typically. In addition,
a thermal insulating block 127, 137 may be used adjacent the portion of the segments
having the heat passages 128 to force the heat to move toward the molding surfaces
150 and away from the cylinder mechanisms.
As shown in Figure 13 a partial view of the molded tread
2 has the parting lines 4 shown diagonally extending across the tread and at the
tread lugs 3.