CA1063760A - Method of and mold for retreading pneumatic tires - Google Patents

Abstract

METHOD OF AND MOLD FOR RETREADING
PNEUMATIC TIRES
ABSTRACT OF THE DISCLOSURE: A resilient mold and a method for retreading tires using such mold which has an inner face of a normal, unstretched diameter which is smaller than the outer diameter of a tire tread. The mold is in the shape of a ring and has, on its inner side or face, an embossing pattern which applies a tread design to a vulcanizable rubber band previously applied to a tire body. The ring mold is first expanded and then fitted over the tire body and the so-applied vulcanizable band and, thereafter, the ring mold is allowed to contract responsive to its inherent tension.
The ring mold, thus fitted over the tread band, is centered on the body while the tire is rotated. This whole unit is then heated to a temperature which converts the tread band into a plastic form and embosses the tread design from the ring mold onto the tread band, which is vulcanized and bonded to the tire body. The air between the mold and the band may be evacuated and the mold may be subjected to ex-ternal pressure to assist in embossing the mold pattern in the tread band. The mold inner face is shaped so as to con-fine the tread band between such face and the tire body.

Description

This invention relates to the art of applylng rubber treads to tires, and more particularly, to methocls of re-treading used pneumatic tire bodies with a full circle camelback or tread of new rubber.
Two systems are often used for ~etreading tires.
- One system uses a metal mold to apply a vulcanizable rubber tread band, frequently called a camelback regardless of whether the outer surface -thereof is curved or straight in cross-section, to a carcass or a tire body while simultane-ously embossing and vulcanizing it. The other system be-gins with a previously embossed and vulcanized tread band which is bonded to the carcass or tire body in a heated `
pressure vessel.
- The first of these systems uses a rigid, toroidal metal mold or cavity which opens to receive the tire body and then closes to process the retread and design. If the tire body is very carefully placed in a perfect position within the mold, there are no problems. E~owever, if the tire `~
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- body is not properly placed, the retread will be asymmetrical.
Accordingly, the existing system for embossing and vulcanizing ~ retread camelbacks in rigid metal molds entails a risk of - deformation of the tire. ~
; After the mold is closed, the tire body usually is ;
subjected to internal pressure during vulcanization. If the internal size of the mold is the same as the unstretche~
- size of the final tire there usually is little stretching of :-the tire body, but many different molds are required to per-mit retreading of the many different tire sizes. The in-- ternal size of the mold can be such that it may be used for a few different tire body diameters, thereby reducing the

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number of molds required, but for smaller body diameters the material of -the tire is exposed to a substantial stress through pressure and extension during vulcanization in the rigid mold. Furthermore, the newer radial tires are sub-stantially inextensible in the ~adial direction and, there-fore, a different mold for each tire size is almost always necessary to provide the desired retreading. Accordingly, . .
when using this system, it is necessary to have a great num~

- ber of molds to accommodate different tire diameters.
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The second of the systems mentioned above, in a first step, uses hydraulic presses with flat metallic molds to vulcanize the tread band and then in a second step uses a . . I .
heated pressure vessel to bond, by means of a vulcanizable rubber interlayer or an adhesive, the prevulcanized tread band to the tire body. This system eliminates the deforma~

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tion of the tire' however, it also greatly increases the ~- working operations~ The tread band has to be prevulcanized . ~. .
and embossed in special vulcanizers. Thereafter, the en-gagement surfaces of the tire body and the tread band must be suitably cleaned, roughened, and coated with a rubber ~i adhesive and a vulcanizable rubber interlayer which bonds .

' the tread band to the tire body. This method also has the ~;
,:-disadvantage that the retreaded tires have different outside .~ diameters. The thickness of the tread band is the same, hut the initial tire body diameter varies, dependent on make , and the number of ply or cord layers~ If two tires with different diameters are used on the same vehicle, treads tend to wear unequally and rapidly~
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~ Accordingly, an ob3ect of the present invention is ~
r ,','~ ' to provide new and improved tire retreading methods.
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Another object is to eliminate expensive and rigid ,.

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molds heretofore used for retreading tires.
Yet ano-ther object is to save costs by eliminatiny many operations which ~ere heretofore necessary for retread-ing tires with prevulcanized tread bands such as the use of presses, grinding and trimming machines.
A further object is to p;rovide an inexpensive re-silient mold for retreading tires which may be used for re-treading tire bodies which have different sizes within a re-latively wide range and which do not require radial extension - 10 of the bodies during retreading.
In ~eeping with an aspect of the invention, these and other objects are accomplished by providing an elastic mold which may be snapped over an unvulcanized camelback - tire band previously attached to a tire body. The elastic band may be centered on the tire body while it is turning.
Then, the entixe unit (elastic mold, camelback and tire body) may be heat treated to vulcanize the camelback and emboss the tread design thereon.
~ccording to a broad aspect of the present invention, `
there is provided a method of treading tires comprising the ;
steps of fitting a vulcanizable cameLback tread band over a tire body, expanding over said band and tire body a resilient matrix ring mold having an internal embossing negative pattern which applies a tread design to said band, said ring mold having an inner diameter which is smaller than the diameter of :
the tire with said tread band over the tire, when the mold is `
in an unexpanded condition, allowing the expanded matrix ring - mold to contract, responsive to its own inherent tension, over the tread band on the tire body, and heating the matrix ring ` 30 mold, tire, and tread band to a temperature which converts the tread band into a plastic form, embosses the tread design from the matrix ring mold onto the tread band, and vulcanizes the ~ - 4 -`' ' 7 ~
tread band onto the tire body.
According to a further broad aspect of the presentinvention, there is provided a resil:ient, stretchable mold for - embossing a pattern in unvulcanized rubber on the peripheral ~:
surface of a supporting body, salcl mold having the shape of a generally circular, continuous band having an inner face ex-tending around and facing the axis o~ said band, said band . having a pair of lips of at least a prede-termined radial dimen--sion extending from said inner face toward said axis and having a plurality of spaced, pattern forming projections of a radial .
-. dimension less than said predetermined radial dimension on said . inner face intermediate said lips and extending toward said .. axis, and wherein a plurality of said projections are arranged -. in a plurality of circumferentially extending, axially spaced r rows, wherein said inner face between said rows and in cross- .
section being substantially flat and wherein the radial thick- :
ness of said band between said rows is greater than the thick-. ness of said band radially outward of said rows.
. Reference may be made to the following specification . . ~
and the accompanying drawings describing and showing pre~erred ~-.: embodiments of the invention, wherein~

. Fig. 1 is a transverse, axial, cross-sectional ~ ~:
. ,:- ', .. view of an elastic mold constructed according to the inven-tion and showing the mold as being stretched around a tire --~- body with the tread rubber thereon, .
;-. Fig. 2 is a cross-sectional view similar to Fig. 1 showing the elastic mold in its contracted molding position, .
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.. Fig. 3 is a schematic, axial view of the stretched . elastic mold and the tire body shown in Fig. 1 .. , ~ .
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' Fig. 4 is a view similar to Fig. 3 of the con-tracted elastic mold and the tire body shown in Fig. 2, Fig. 5 is a perspective view of the elastic mold;
Fig. 6 is a cross-sectional view similar to Fig. 2 ;~
showing the elastic mold and tire body with a superimposed rubber diaphragm, ,r Fig. 7 is a fragmentary, cross-sectional view, similar to Fig. 6, of a modified embodiment of the invention e in which the mold contains re-enforcing wires and in which an internal bladder is used during vulcanizing, i - ,. . .
Fig. 8 is a fragmentary, cross-sectional view, ;
~- similar to Fig. 7, of a modified embodiment of the invention in which a sealing ring and a tube-like bladder are used .
during vulcanizing; and 3'- Fig. 9 is a fragmentary, cross-sectional view, similar to Fig. 7, of a modified embodiment of the invention in which the air removal holes in the mold are formed by hollow metal pins, one of the mold lips has rib forming re-cesses, and a centering groove is provided.
In accordance with a preferred embodiment of the ii:. .
invention, as illustrated in Figs. 1-4, a tire body 2 which ;~
is to be retreaded is first treaded on its radially out-ward surface, in a conventional manner, such as by grinding, ~-, . . .
etc., to provide a tread rubber receiving surface. A tread layer on band 1 of unvulcanized rubber, without the tread pattern thereon, is then placed around the tire body 2 in contact with such prepared surface, such as by winding one ~;,' ~ , . ~ .
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or more ribbons of such rubber therearouncl, forming a band o~ rubber of the proper size and placiny it therearound.
The thickness of the band 1 is selected rela~ive to the diameter of the tire body 2 so tha-t the outside diameter Oe the retreaded tire will be uniform and standard.
- Thereafter, an elas-tic mold or embossing ring 9 having tread pattern projections 10 on its inner side or ~- face 3 and treated on its inner face 3 with an anti-adhesive agent, is stretched radially, as indicated by the arrows 12, and placed around the tire body 2 and treadbandl as shown in Fig. 1 and is then released permitting the mold 9 to contract, as indicated by the arrows 13, and assume the posi- -tion shown in Fig. 2, i.e., with the projections 10 engaging the tread ban 1 and usually, penetrating into the band 1.
~ The mold or ring 9 must be sufficiently resilient in an out-- wardly radial direction to permit it to be stretched around the treadbandl, and it must withstand the vulcanizing heat subsequently applied without deforming. Therefore, a suitable high temperature elastic rubber or similar material is used to make the ring mold 9. In one embodiment actually used, the vulcanizing temperature of the rubber of the band 1 was about 100C. and the rubber of the mold or ring 9 vulcanized at about 150 -180C., and was otherwise resistant ~ to heat.
`- The projections 10 on the inner face 3 of the .
` mold 9 form an embossing tread pattern, that is, they form ,~ grooves, etc. in the tread band 1 and the pattern may be any desired pattern. The mold 9 also has a pair of radially inwardly extending lips 9" and 9"' at axially opposite edges 6 and 7 thereof for purposes hereinafter described. When -,; , . .
s expanded or stretched (Figs. 1 and 3), the smallest inner ~ - 6 -,. :; :

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diameter of the mold 9 is larger than the ou-ter diameter of i the vulcanizable tread band 1 on the tire body 2. On its `- outer slde, equatorial to the -tread, the mold 9 has a full- ;
~ circle projection bead or circumferential fin 11, which "~ serves as a centering index when the ring is placed over the tire body 2 and tread band 1, just before the vulcanization ,, step. Preferably, the tire is rotated, on any suitable supporting mechanism (not shown) while the bead or fin 11 ;~ is inspected or measured for trueness of its position. Al-.~ . - 10 though the unvulcanized rubber of the tread band 1 may be relatively stiff, it is formable and during the centering of the mold 9 with the aid of the fin 11, the mold 9 con-~: tinues to contract, responsive to its own inherent tension.
'~ In any event, it is contracted to the extent permitted by ,....................................................................... .
~" the tread band 1 by the time that the centering steps are com-pleted. Thus, the mold 9 presses radially inwardly, in the direction of the arrows 13, against the unvulcanized tread band 1 and the tire body 2. ~-The unit comprising the tire body 2, the rubber -camelback layer 1 and the ring mold 9 is thereafter placed ~; in a heated tank, using either gas or liquid as a heat ;,; transfer medium. In the hereinbefore cited example of camel-.: :
,;- back rubber which vulcanizes at a low temperature, such as 100C., the heated tank temperature will usually be about 100C.
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While so heated, the rubber layer 1 is changed rom a low plastic condition into a high plastic condition~
In this highly plastic state during the vulcanization pro-cess, the inherent tension of the ring mold 9 causes it to press against the layer 1 and transfers and embosses the profile of its tread pattern projections 10 into the rubber :, ~: ' ~ .:

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layer 1. The elastic pressure of the ring mold 9 is directed radially toward the tread area of the enclosed tire body to accomplish the corresponding embossing process. Preferably, ~ -the plastic condition of the rubber camelback layer 1 is main- `
tained, as long as possible, through a slow temperature in-crease of suitably selected rubber mixtures, so that the em-bossing pressure exerted by the ring mold 9 will not have to be high, and so that the profiles of the projections 10 on the inner face of the ring mold which are deformable under pressure, are not deformed. Also, suitable holes, similar to those described hereinafter, may be formed in the ring mold 9 to enable an escape of air entrapped between the inner face of the mold 9 and the tlre body 2.
The embossing part of the retread operation is con-` cluded during the early part of the vulcanization process.
Later, because of the vulcanization, the rubber layer changes from its plastic condition to a stable elastic condition.
After the completion of the vulcanization process, the pattern of the tread has become stable and finished. The ring mold 9 is then stretched and removed from the tire, which is now re-treaded, and such ring mold 9 is ready for re-use in the re-treading of another tire body.
~ Although ~a rubber, or other elastomer, having a ^~
,- vulcanizing temperature the same as or only slightly higher than that of the rubber of the tread band 1 could be used for the mold 9, and, in fact, the rubber could be the same ,, .-. , ~ forlboth, the mold 9 tends to lose its elasticity after a ~ ~
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~: few uses thereof if it has a vulcanizing temperature close !i to that of the band 1. Accordingly, it is preferable to use i 30 a rubber for the mold 9 which has a vulcanizing temperature (degrees C) at least 20% higher than the w lcanizing ~ ~ .

,,-temperature of the rubber used for the band 1, thereby pro-viding uniform characteristics ~or each use thereof, better resistance to carburizing and hence, degeneration, and longer life. There are, of course, many elastomers or rubbers known ;
to those skilled in the art, and the selecting of a suitable elastomer or rubber for the mold 9 when the rubber for the band 1 has been determined is readily accomplished by those skilled in the art. For example, when the rubber of the band 1 is o-f the type generally used in the art, namely, natural or synthetic rubber, the mold 9 may be made from butyl, chloro- `;~
butyl or silicone rubber~
The preferred characteristics for the mold 9 may be .i ~.
generally stated as follows:
(1) The elastomer from which it i3 made has a vulcanization temperature which is at least 20% higher than that of the rubber for the band 1 ~`~

and which is relatively constant, (2) The hardness and stiffness of the pro-` jections 10 and the elasticity of the mold 9 is '' ~ . ' , 2C such as to permit the embossing of small or thin tread grooves, ; (3) The heat conductivity of the elastomer should be relatively high to aid in distributing - the vulcanizing heat and known types of additives may be used to increase the heat conductivity thereof,

(4) The stretchability and resiliency should be such that it can be stretched from a normal diameter, approximately the outer diameter of the tire body 2, to a diameter greater than the outer - 30 diameter of the unvulcanized tread band 1 on the tire body 2, and thereafter, contract to such normal _ 9 _ :

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diameter without damage, such as tears or cracks, and such stretching and contracting should be re-peatable many -times,

(5) If the tread pattern embossing pressure r is to be supplied only by the inherent contracting forces of the mold 9, it should be relatively thick in cross-section ~see Fig. 1), whereas with the ap-plication of external pressure, as described herein-after, the cross-section may be relatively thin (see Fig. 6),

(6) The normal diameter of the mold 9 should be such that the inside thereof is completely filled by the rubber of the band 1 and the projections 10 are fully seated before the mold 9 is fully contracted and hence, while it is still applying pressure to the band 1. However, the normal diameter should not be small enough to apply a pressure which forces ~
rubber of the band 1 from under the mold 9, at the ~ -lips 9" and 9"', during the wlcanization step, s-~ 20 ~7) If it is desired to use the mold 9 for making retreaded tires of different diameters, the stretchability should be such as to permit the mold 9 to be stretched over the largest diameter tire body ~ ;
and tread band to be processed and yet should have a ~ ~
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~- normal diameter and hence, resilience, as set forth in Paragraph (6) hereinbefore.
~r~r~ With respect to the hardness and stiffness of the projections 10 mentioned in Paragraph (2) hereinbefore, it ~-~ is preferred khat the mold 9 be unitary and of the same ` 30 material throughout, in order to simpliy its manufacture and reduce its cost. However, if desired, the mold 9 can be ~' - 10 - ~, ~" ~, ~

~ 3 made of dif~erent materials at different parts as long as the desired stretchability and resiliency is retained. For example, the projections 10, or some of them, may be circumferentially discontinuous and may be formed of a relative stiff and hard rubber or may be metal inserts in the rubber body of the mold 9.
It will be observed from the drawings that the axially opposite edges 6 and 7 of the mold 9 have a pair of radially inwardly extending, circumferentially continuous, lips 9" and 9"',which extend from the surface 3 by a distance greater than ` 10 the radial dimension of the projections 10. As mentioned here-inbefore, the unvulcanized rubber tread band 1 becomes rela-tively soft and plastic during the vulcanizing step, and the main purpose of the lips 9" and 9"' is to confine the rubber ~ of the band 1 at its sides during such vulcanizing step. The - lips 9" and 9"' also aid in centering the mold 9 wi-th respect to the tire body 2, the lips 9" and 9"' having a radial dimen-sion such that they engage the tire body 2 at least when the mold 9 has fully contracted. Preferably, the radial dimension of the lips 9" and 9"' from the surface 3 is slightly greater than the radial dimension of the projections 10 plus the radial dimension of the band 1 so that the lips 9" and 9"' engage - the tire body before the mold is fully contracted, and the ~-inner faces 4 and 5 thereof are divergent, as shown, ~o as ~ to increase the pressure of the lips 9" and 9"' against the -~ tire body 2 as the mold 9 contracts and so as to provide ;
tapered sides for the band 1. Preferably, also, the minimum distance between the lips 9" and 9"', i.e., the points of inter~section thereof with the inner face 3, is less than the width of the prepared surface of the tire body 2 to which the band 1 is to be applied and radially innermost portions of -i the faces 4 and 5 are spaced apart by a distance greater -than ';
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such width to assist in centering of the mold 9 with respectto the tire body 2. Pre~erably, the lips 9" and 9"' are cir-cumferentially continuous, but, if desired, each lip may be formed by a plurality of circumferential segments which are closely spaced, contacting or overlapping at the segment ends when the mold is in its contracted state. Although the inner faces 4 and 5 have been shown as smooth, they may have tread pattern projections thereon. Also, although it is preferred that the lips 9" and 9"' be integral with the mold 9, the lips 9" and 9"' may be separate rings of an inner diameter which will cause them 'co engage the side walls of the tire body 2 and of an outer diameter which will cause them to engage the body of the mold 9 when it is fully contracted but without pre-venting such contraction.
Accordingly, the preferred embodiment of the mold 9 of the invention is made of a resilient and stretchable elas-i~ tomeric material and is in the shape of a generally circular, continuous band having an inner face 3 extending around and facing the axis of the band and a pair of axially opposite . '~
edges 6 and 7. The band has integral therewith a pair of sub-~stantially circumferentially continuous axially spaced lips -9" and 9"' at the edges 6 and 7 and extending from said face 3 toward said axis and has a plurality of spaced tread pattern projections 10 on said inner face 3 intermediate said lips ~ -~ 9" and 9"' and extending toward said axis. When the mold 9 3- is unstretched, the inner diameters of the face 3 and the pro-jections 10 are less than the outer diameter of the tread kand land the inner diameter of the lips 9" and 9"' is less than the inner diameter of said tread band 1. The projections 10 have a radial dimension from the face 3 less than the ~ radial dimension of the tread band 1, and the mold 9 is 5.-~ stretchable to a size such that the inner diameter of at least ~: :

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one of the lips 9" and 9"', and hence, of the projections 10, is at least equal to the outer diameter of the tread band 1 In one method of making the ring mold 9, a new or unused retread tire can be used as a form. First, a layer o~
any suitable high temperature, vulcanizable rubber of the desired thickness is placed over the patterned tread surface of the new or unused tire form, which preferably is pretreated with an anti-adhesive agent. Thereafter, this layer, while ~ :.
-~ on the form, is vulcanized under both pressure and suitable high temperature. Thus, the resilient rubber layer is inter~
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nally embossed with a negative contour of the tread pattern ;~

on the tire which is used as a form and may be used as the mold . :
9 The best results of creating said negative contour are ~- obtained when the tire with the unvulcanized rubber layer i:-~ thereon is inserted into a flexible tubular rubber envelope : ~ :
~ which covers the tire on its entire surface. The air from the , ~ open space between the tire body, rubber layer and tubular : ' .
i envelope is evacuated by suction and the assembly is exposed to heat and pressure in a ~hamber. Preferably, a tubular , 20- envelope as is described in United States Patent ~o. 2,966,936 ~
is used for manufacturing the ring mold 9. Other methods of ~ -using envelopes as known from the art of retreading may be ,~ utilized as well.
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Any air entrapped between the rubber layer and the ;

~ form tire is evacuated through radially extending holes which ,~ :
~ are made in the body of the tire form at the deepest parts of i -:: ..
~- the tread pattern. These holes are similar to the holes 15 ~ shown in Fig. 6 except that they extend through the body of ;- the tire form instead of through the mold 9'~

When required, the embossing pressure of the ring mold 9 may be augmented by any suitable means for applying ~; - 13 -~,,;. , .

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additional pressures, which are directed radially against the mold 9.
Preferably, pressure of a fluid or gaseous vulcan-izing medium is used in connection with a superimposed rubber diaphragm to apply an auxiliary embossing pressure to the assembly, Fig. 6 shows how this method is carried out in practice. The tire body 2 with an unvulcanized rubber band or layer 1 and matrix ring or ring mold 9 7 iS covered with a resilient rubber diaphragm 14. This diaphragm 14 also covers, with sealing, a surface portion of the tire body 2 which extends beyond the lips 9" and 9"' of the ring mold 9'.
The ring mold 9' is provided with radially extending holes 15 and the rubber diaphragm 14 is provided with a suc-tion valve 16. By means of a suction pump (not shown), connected to this valve 16, entrapped air can be evacuated from the spaces between the inner side of the ring mold 9' and the outer side of the tread band 1 and between the outer side of the ring mold 9' and the inner side of the rubber diaphragm 14. Those surfaces of the ring mold 9', which are directed radially outwards, can be roughened or suitably pat-- terned to allow the passage of air from the holes 15 to the suction valve 16.
- In order to facilitate the application of the -ring mold 9' and the rubber diaphragm 14 onto -the tire body 2 provided with the tread band 1 and to have the first two ele-ments positioned in controlled relation to each other, they are preferably bonded together at the lateral edges 18 and 19 `
of the ring mold 9'. The rubber diaphragm 14 thereby will -i accompany the ring mold 9' when this is expanded and contracted.
In order to assist, in this case, in the centering of the matrix pattern projections 10 in relation to the tire - 14 - ;-, ~0~;~7~
body 2, the rubber diaphragm 14 and not, as before, the ring ` mold 9, is provided with a full-circle projection bead or , circumferential fin 17.
, The entire assembly including the tire body 2 with the tread band 1, the ring mold 9' and the rubber diaphragm 14 is introduced into a conventional pressure vessel (not shown~, to which a heated fluid or gaseous vulcanizing medium is then supplied under proper pressure, thereby applying pres-sure to the rubber diaphragm 14 and thus, onto the ring mold :~
9~, such pressure being in addition to the contracting forces ~t of the mold 9'. During this vulcanizing process, the pressure iS increased slowly.
In order to achieve a true print of the pattern of projections 10 on the rubber band or layer 1, when using such ~ an additional pressure, the ring mold 9' should be designed as ~;
,~- is shown in Fig. 6. As shown therein, the thickness of the ~ ring mold 9', seen transversely, varies such that it is largest ~
in the middle between two neighboring projections 10 of the pattern and is decreased from the middle in both directions towards these projections 10. Such a shape eliminates the ~ risks that the shape of the tread band 1 of the vulcanized ; tire will be concave between these two projections, the addi-- tional thickness preventing bulging of the mold 9' intermediate . ........................................................................ .
:~ the rows of projections 10. Thus, through the design mentioned hereinbefore, the resistance to bending will be the largest in `
the middle between the rows of projections 10, where the lar-gest bending moment is generated by the additional pressure. -~
*-` The bending of the mold 9' between the rows of projections 10 ` thereby will be minimized, which is essential for a true tread print.
When using an additional pressure as is described in connection with Fig. 6, it is possible to dimansion the ring ~- - 15 -:~ '.. :
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7~ 9 mold 9' to be -thinner, as it is not necessary for the ring - mold 9' to have such a large inherent tension. The air en-trapped between the tire band 1 and the ring mold 9' is evacuated to insure a good duplication or printing of the tread design. If the entrapped air were allowed to remain, it would be compressed to deface the tread and thereby result in an unsatisfactory imprinting of it into the embossed tire ~- band 1.
The embodiment of the invention shown in Fig. 7 is similar to the embodiment in Fig. 6, except that the mold 20 corresponding to the mold 9' has a plurality of circumferen-tially spaced, axially extending rods or pins 21 therein and the interior of the body 2 is covered by an internal diaphragm 22. The pins 21, which are relatively rigid, aid in preventing bending of the mold 20, intermediate the rows of projections 10 ~ `
for the purposes described hereinbefore.
It sometimes happens that a tire body 2 to be re-~ treaded has holes extending from the interior thereof to the 5~ surface thereof to which the tread band is applied due to naiL
punctures, etc. Such holes may make it difficult to remove air ~ by way of the suction valve 16 and, in addition, steam is ofte~
t ' used as the vulcanizing heat medium. In the latter case, water -can seep through such holes into contact with the underside ~ of the tread band 1 creating voids between the tread band 1 f~ and the tire body 2. For these reasons, it may be desirable to employ an internal, fluid-impexmeable diaphragm 22 which s~ covers the interior of the body 2 and extends around the out-'~ side thereof and into contact with the diaphragm 14 during the . .
removal of air by way of the valve 16 and the vulcanization of the tread band 1.
~, Fig. 8 shows an embodiment similar to the embodiments '' in Figs. 6 and 7, except that in Fig. 8 the internal diaphragm .~ .
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22 is replaced by an inflatable bladder 23 supported inter- ;
nally by a ring 24, such bladder 23 and ring 2~D" serving the same purposes as the internal diaphra~m 22 and also serving to aid in maintaining the desired shape of the body 2 during vul-canizing. Fig. 8 also shows a pair of 0-rings 25 and 26, which may be of vulcanized or unvulcanized rubber, between the ~;~
diaphragm 14 and the side walls of the body 2 to assist in pro-viding a fluid seal between the diaphragm 14 and the body 2.
Fig. 9 shows an embodiment similar to the embodirnents in Figs. 6-8, except that the mold 27 has been modified to include hollow metal pegs or pins 28, rib forming recesses 29 and 30, and a centering groove 31. The metal pins 28, which are embedded in the mold 27, provide the holes 15 described hereinbefore and may be incorporated in the mold 27 during ~ -vulcanization thereof or inserted therein after vulcanization thereof. ~ ~
The groove 31 in the rib 32 integral with the mold -, -: .
27 may be used in centering the mold 27 with respect to the body 2. Thus, a roller ~not shown) properly mounted with res~
pect to a rotatable support for the body 2 may ride in the ~-' groove 31 as the body 2 is rotated, causing the rib 31, and ~
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hence, the mold 27, to center properly with respect to the ~- ~
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; body 2.
~-~ Because of the presence of the rib 3~, the diaphragm ~`
14 may be made in two parts 14' and 14", sealed in any desired manner at their edges 33 and 34 to the mold 27 and connected ~;- to two suction valves 16 and 16'.
In some cases, it is desirable for decorative pur- ;
poses to apply one or more ribs to the side wall, or to both side walls of a tire body 2 being retreaded. In such cases, a ; lip, such as the lip 27', or both lips, may be provided with '- - 17 -,., ' ., ~ ;, .

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the necessary number of circumferential recesses, such as the recesses 29 and 30, for receiving and forming unvuLcanized ~. rubber 1' extending from the tread band 1 downwardly to the $` recesses 29 and 30 or merely applied to the portion of side wall of the body 2 adjacent to the recesses 29 and 30, the thickness of the rubber 1' being sufficient to at least fill . such recesses 29 and 30. Such rubber 1' will assist in sealing the diaphragm part 14' to the side wall during air removal and vulcanizing of the tread band 1.
:.ç 10 Those skilled in the art will readily perceive modi- :
ficiations which fall within the scope and the spirit of the ~` invention. Therefore, the appended claims are to be construed broadly enough to cover all equivalent structures.

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Claims (26)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:-

1. A method of treading tires comprising the steps of:
(a) fitting a vulcanizable camelback tread band over a tire body, (b) expanding over said band and tire body a resilient matrix ring mold having an internal embossing negative pattern which applies a tread design to said band, said ring mold hav-ing an inner diameter which is smaller than the diameter of the tire with said tread band over the tire, when the mold is in an unexpanded condition, (c) allowing the expanded matrix ring mold to contract, responsive to its own inherent tension, over the tread band on the tire body, and (d) heating the matrix ring mold, tire, and tread band to a temperature which converts the tread band into a plastic form, embosses the tread design from the matrix ring mold onto the tread band, and vulcanizes the tread band onto the tire body.

2. The method of claim 1 wherein step (c) includes the further step of centering the matrix ring mold on the tire by visually inspecting an equatorial bead on the mold while the tire rotates.

3. The method of claim 1 and the preliminary steps of making said matrix ring mold by placing a band of vulcanizable material over the tread of a tire form and heating said ban and tire form under pressure to form and vulcanize said nega-tively embossed pattern of the tread of said tire form into said matrix ring mold.

4. The method of claim 3 and the further preliminary step of forming holes in said tire form to enable an escape of entrapped air in said vulcanizable band while said matrix ring mold is being made.

5. The method of claim 3 wherein said band of vulcaniz-able material has a first characteristic temperature at which vulcanizing occurs and the camelback tread band has a second characteristic temperature at which vulcanizing occurs, said first characteristic temperature being higher than said second characteristic temperature.

6. The method of claim 5 wherein said second character-istic temperature is approximately two-thirds of said first characteristic temperature.

7. The method of claim 1 wherein step (a) comprises the further step of selecting a camelback having a thickness rela-tive to the diameter of said tire body which causes the com-bination of said camelback and tire body to have a standard diameter.

8. A method of retreading tires, comprising the steps of:
(a) applying a vulcanizable rubber tread band to a tire body, (b) expanding a resilient combined compressing and embos-sing matrix ring mold over said tread band for applying an in-wardly directed radial pressure thereto, said matrix ring mold having on its inner side an embossing pattern and having an inner diameter which in the normal unstretched condition of said ring mold is smaller than the outer diameter of said tire body including the applied tread band, (c) allowing the stretched matrix ring mold to contract around said tread band and said tire body responsive to its own inherent tension, and (d) heating under pressure said tire body, tread band and the attached matrix ring mold so that said tread band is simul-taneously softened, embossed and vulcanized under the embossing pressure exerted at least partly through the inherent tension of said matrix ring mold.

9. The method according to claim 8 wherein the matrix ring mold comprises heat resisting material having properties for embossing said tread band when heated without being deformed and the added step of maintaining the heat applied during said step (d) long enough for said tread band to reach and maintain a plastic condition during a period which embosses the tread band under the pressure applied by contraction of said matrix ring mold to emboss said tread band while avoiding deformation of the embossing pattern in said matrix ring mold.

10. The method of claim 9 and the preliminary steps of:
(a1) forming holes in a tire form used to make said matrix ring mold to enable an escape of entrapped air while said matrix ring mold is being made, (a2) making said matrix ring mold by placing a band of high temperature vulcanizable material over the tread of said tire form and heating said material and tire form under pressure to form and vulcanize said inner embossing pattern of the tread of said tire form into said matrix ring mold, (a3) selecting said rubber tread band with a thickness relative to the diameter of said tire body which causes the combination of said band and tire body to have a standard dia-meter, step (b) includes the further step (b1) wherein said band of vulcanizable material is selected from a class of materials having a first characteristic temperature at which vulcanizing occurs, and the tread band is selected from a class of rubber having a second characteristic temperature at which vulcanizing occurs, said first characteristic temperature being higher than said second characteristic temperature, and step (c) includes the further step (c1) of centering the matrix ring mold on the tire by inspecting an equatorial bead on the outside of the mold while the tire rotates, and while the matrix ring mold contracts.

11. The method according to claim 8 wherein the outside of said matrix ring mold is provided with a full-circle equatorial projection, and the added step of centering said matrix ring mold on said tire body by rotating the tire while checking the trueness of the equatorial projection.

12. The method according to claim 8, and the added step of molding said matrix ring mold over a new or an unused retread tire form by applying a layer of high temperature vulcanizable rubber to the tread side of said tire form and vulcanizing the high temperature layer under pressure and heat, thereby embos-sing a negative impression of the tread on the tire form into said high temperature rubber.

13. A method of treading tires comprising the steps of:
(a) fitting a vulcanizable camelback tread band over a tire body, (b) expanding over said band and tire body a resilient matrix ring mold and outside said matrix ring mold a resilient rubber diaphragm, said matrix ring mold having an internal em-bossing negative pattern which applies a tread design to said band, said ring mold having an inner diameter which is smaller than the diameter of the tire with said tread hand over the tire, when the mold is in an unexpanded condition, (c) allowing said expanded matrix ring mold and said expanded rubber diaphragm to contract responsive to their own inherent tension, (c) heating the rubber diaphragm, matrix ring mold, tire and tread band in a pressure medium having a temperature which converts the tread band into a plastic form, embosses the tread design from the matrix ring mold onto the tread band, and vul-canizes the tread band onto the tire body.

14. The method of claim 13 wherein said rubber diaphragm is bonded to lateral edges of said matrix ring mold.

15. The method of claim 13 wherein said matrix ring mold is provided with radially extending holes, and suction pump means connected to said rubber diaphragm for evacuating through said holes the air entrapped between said matrix ring mold and said tread band.

16. The method of claim 13 wherein said matrix ring mold is transversely made with different thickness which thickness is greater in the middle between two neighboring projections of said embossing pattern than adjacent said projections.

17. The method of claim 13 wherein step (c) includes the further step of centering the rubber diaphragm and the matrix ring mold on the tire by visually inspecting an equatorial bead on the rubber diaphragm while the tire rotates.

18. A resilient, stretchable mold for embossing a pattern in unvulcanized rubber on the peripheral surface of a supporting body, said mold having the shape of a generally circular, con-tinuous band having an inner face extending around and facing the axis of said band, said band having a pair of lips of at least a predetermined radial dimension extending from said inner face toward said axis and having a plurality of spaced, pattern forming projections of a radial dimension less than said pre-determined radial dimension on said inner face intermediate said lips and extending toward said axis, and wherein a plur-ality of said projections are arranged in a plurality of cir-cumferentially extending, axially spaced rows, wherein said inner face between said rows and in cross-section being substan-tially flat and wherein the radial thickness of said band bet-ween said rows is greater than the thickness of said band rad-ially outward of said rows.

19. A mold as set forth in claim 18, wherein at least said band and said lips are made of elastomeric material and wherein said lips are respectively at axially opposite edges of said band.

20. A mold as set forth in claim 18, wherein said band also has an outer face extending around and facing away from said axis and has a plurality of holes extending from said inner face at portions thereof intermediate said projections to said outer face to permit the passage of air from said inner face to said outer face.

21. A mold as set forth in claim 20, further comprising a fluid impenetrable diaphragm extending over said outer face and alongside said lips, said diaphragm being bonded to said band at axially opposite edge portions thereof and circumferen-tially of the latter, and a valve in said diaphragm for with-drawing air from between said diaphragm and said outer surface and through said holes.

22. A mold as set forth in claim 21, wherein said dia-phragm has an outwardly extending, circumferential fin thereon intermediate the axially opposite sides thereof.

23. A mold as set forth in claim 21, wherein said band has an outwardly extending circumferential rib thereon which extends outwardly of said diaphragm, said rib having an out-wardly opening, circumferential groove therein.

24. A mold as set forth in claim 20, further comprising a plurality of pins each having an opening therein extending from one end to the other thereof, each pin being mounted in one of said holes with its ends respectively at said inner and outer faces.

25. A mold as set forth in claim 18, further comprising a plurality of axially extending, circumferentially discontinuous reinforcing means in said band at the portions thereof inter-mediate said rows.

26. A mold as set forth in claim 18, wherein at least one of said lips has an inner surface facing the other of said lips and wherein said inner surface of said one lip has a circumfer-entially extending, rib-forming recess therein.