Process for the injection molding of pneumatic tires having symmetrical parts of similar physical characteristics

A process and apparatus are provided for injection molding a pneumatic tire having corresponding symmetrical parts such as the sidewalls of the tire which are geometrical symmetrical and have substantially the same physical characteristics. The process involves providing a feed stream of suitable plastic or elastomeric compound such as rubber, separating the feed stream into intermediate streams and remixing the intermediate stream before injection into the mold. The compound is injected into the mold cavities at uniformly spaced points along at least one of the annular zones of the cavity. The feed stream is preferably separated into two streams, one of which comes primarily from the outer portion of the stream and the other predominantly from near the center of the stream and then these streams are intermixed to provide a stream which is substantially uniform in composition throughout. Similarly prepared streams are injected into the two parts of the mold cavity which form a pair of symmetrical parts of the tire such as the two sidewalls. An apparatus for dividing a feed stream into the intermediate streams and mixing them to form a stream for injection into the mold cavities is also provided.

This invention relates to a process for the injection molding of pneumatic 
tires. 
The invention is particularly applicable to pneumatic tires for motor 
vehicles in which different compositions are used for making different 
parts of the tire; i.e., tires in which the crown is made of one 
composition and the sidewalls are made from a different composition. The 
invention is particularly important for the molding of the sidewalls of a 
tire. Hence, it will be described herein with reference to such molding, 
but it may be used gnerally for the molding of any tire portions which are 
mirror images of one another relative to the median plane of the tire, 
i.e., to the tire plane of symmetry perpendicular to the wheel asis. 
There must be perfect physical symmetry (isotropy) between the portions 
which are geometrically symmetrical in a pneumatic tire. In other words, 
it is not sufficient that the mold cavity, and hence the mass of injected 
material, possesses the required geometrical symmetries, in particular, 
when it comprises two portions which are mirror images of one another 
relative to the median plane of the tire. It is also necessary that the 
physical properties of the geometrical symmetrical parts be substantially 
the same as regards internal stresses, deformations, degree of 
vulcanization, mechanical properties of the material and the like. 
Otherwise, the molded body will not have the desired symmetry when it is 
demolded, when it is inflated or when it is subjected to stresses. 
Therefore, in the following description of the present invention a 
distinction will be made between the geometrical symmetry and the physical 
symmetry, it being obvious that the lack of symmetry of physical 
properties may and generally does give rise, at one time or another, 
during the life of the tire, to a lack of geometrical symmetry, even if 
such symmetry did exist initially. 
Injection molding of tires, especially of tires having parts made from 
different compositions is a substantially new process in the art. Although 
proposals for the injection molding of pneumatic tires have already been 
described in the technical literature, these proposals do not deal with 
and do not resolve the problem of the physical symmetry of the tire and do 
not produce a tire having such symmetry. In any case, these proposals 
generally relate to the injection molding of tires made of only one 
composition and which, moreover, do not usually contain natural or 
synthetic rubber. On the other hand, the injected molded tire is made from 
plastic materials which have substantially different physical properties 
from those of natural or synthetic rubber. 
A process is described in French patent specification No. 1,508,135 which, 
in general and in theory, may be utilized for the molding of tires from 
two different compositions. In accordance with the disclosed process, the 
sidewalls are molded first and then, after having substituted the 
necessary mold part, the tread is molded. However, the tire produced by 
such a process from two different compositions would not be entirely 
satisfactory because its properties would be substantially uneven. The 
faults would be particularly significant if the sidewalls were molded from 
natural rubber compounds. This is especially true if the tire has the 
configuration of the tire described in Italian patent specification No. 
928.502 and U.S. Pat. No. 3,805,868 granted Apr. 23, 1974. 
The invention will now be described with particular reference to tires of 
the type described in U.S. Pat. No. 3,805,868 but it is to be understood 
that it is adaptable for other types of motor vehicle tires. A tire of the 
type described has two sidewalls extending away from one another from the 
respective beads to the respective zones of connection to the crown. The 
sidewalls are substantially convex inwardly when in a deflated condition 
and are still convex, though less markedly, when in an inflated condition. 
The crown is outwardly convex and acts as a tread in the central portion 
thereof where it normally comes into contact with the ground. The crown is 
reinforced by means of a suitable annular, substantially inextensible 
reinforcement member which is generally made of a textile material. In 
U.S. patent application Ser. No. 596,409 filed July 16, 1975 now Pat. No. 
4,088,523, a single stage process has been described which is suitable for 
the molding of a tire of this type. 
Although the present description is made with reference to a two-stage 
process, i.e., a process in which the sidewalls and the crown are molded 
in two different stages, the present invention may be applied also to a 
single stage process of the type described in the earlier application Ser. 
No. 596,409. 
Thus, the main object of the present invention is to provide a process of 
making a pneumatic tire by injection molding in which every part, 
especially the sidewalls, has an excellent symmetry, both geometrically 
and physically. A more specific object of the invention is to provide a 
method for making a tire by injection molding which produces sidewalls 
made of a rubber compound, particularly a natural rubber compound, which 
are both physically and geometrically symmetrical.

Hereinafter, the expression "symmetrical parts" of the tire will be used to 
indicate any two portions of the tire which have to be mirror images of 
one another relative to the "median plane" of the tire (therewith being 
meant the plane which, when the tire is mounted, coincides with the plane 
of symmetry of the rim perpendicular to the axis of the wheel); and each 
of those portions, taken separately, will be referred to as a "symmetrical 
portion". Such symmetrical parts may be well defined components of the 
tire, such as, for example, the sidewalls (the word "sidewall", as used 
herein, is intended to include the bead) or parts of the sidewalls, well 
defined parts, such as the beads or any portion thereof, such as, for 
instance, portions made of a material different from that of the other 
portions of the sidewalls. The symmetrical parts may be also the two 
halves of the crown which are arranged on opposite sides of the median 
plane, or portions of the crown which are symmetrical relative to the 
plane and are made of a material different from that of the other 
portions. 
The process provided by the present invention is characterized in that a 
primary fluid supply of compound is generated, that the mold cavities 
which correspond to symmetrical parts are filled from that supply with 
fluid molding compound by means of a plurality of injection streams which 
penetrate into each one of the parts through openings which are uniformly 
spaced on at least one annular zone, and that the injected streams are 
formed partly by an "outer" compound and partly by an "inner" compound of 
the supply stream in practically equal proportions for all of the 
injection streams. 
In order to render more clearly the present description and the annexed 
claims it is convenient at this point to explain the meaning of some of 
the terms used and which will be used herein. 
The molding fluid compound is obtained, by means known in the art and which 
do not need to be described herein, through kneading, mastication, 
fluidification, pressurizing operations, which are well known per se. In 
this way, a feeding flow or supply stream of fluid compound to be injected 
is produced, which flow is fed to the mold through one pipe or conduit 
whose axis generally coincides, at least at the end portion, with the axis 
of symmetry of the mold. It is also possible to utilize two or more 
feeding pipes or conduits: for example, two pipes whose axes coincide, in 
the end portion, with the axis of symmetry of the mold and which are 
arranged in opposed relationship on the same axis at the two sides of the 
mold. In these cases, all the material flowing through the two or more 
feeding pipes will be considered totally as a single stream included in 
the expression "feed stream". 
The mold cavities corresponding to any pair of the symmetrical parts, even 
if the mold constitutes a mechanical unit, are considered as distinct, 
inasmuch as compound does not pass from one to the other. 
According to the invention, when the symmetrical parts are the sidewalls, 
the compound is introduced separately into the mold cavities of each 
sidewall, preferably from the region of the bead, so as to render the 
injection itself perfectly symmetrical with respect to the axis of the 
mold and as uniform as possible, minimizing the necessity of having the 
injected streams spread out in a fan-shaped fashion from the zone of the 
bead to the zone of connection of the sidewall to the crown which has a 
greater diameter. In each sidewall cavity, each injection opening is 
ideally annular, but practically it is not convenient to provide one or 
more true annular openings, and one contents himself with providing at 
least one plurality of sufficiently and uniformly spaced openings, each of 
which forms a segment of the annular opening or of one of them, so that 
everything takes place as though the injection were made into one or more 
annular openings, portions of which, uniformly spaced, had been closed. 
Thus, a plurality of real injection openings located along at least one 
annular zone is obtained for each sidewall and at each of these openings 
there is an injected stream which enters the mold through the opening 
itself. 
Analogous consideration may be made in respect of symmetrical parts other 
than sidewalls. If such parts are the beads, the injection openings will 
remain in the position as said before; if they are different portions of 
the sidewalls, they will be correspondingly displaced. If the symmetrical 
parts are the two halves of the crown, it is preferable to inject the 
compound from two series of openings disposed on two annular zones located 
at the two shoulders of the crown, from which the streams of compound will 
converge to meet each other on the median plane. An analogous arrangement 
will be used for injecting symmetrical portions of the crown which do not 
form the whole crown, by arranging the injection openings in a different 
position depending on the circumstances. 
The most simple way of carrying out the injection molding would be that of 
dividing the supply stream of compound into the various injection streams 
relative to one or the other of each pair of symmetrical parts, taking 
care that the cross-sections of the paths are uniform so that each stream 
has the same volume which is indispensable for the regularity of the 
injection. 
However, unexpectedly, by acting in this way one does not obtain a tire 
having a perfect physical symmetry. 
Not even the perfect symmetry of the molding apparatus with respect to the 
median plane of the tire insures the physical symmetry of the latter. It 
would seem that, if the apparatus is symmetrical, any local characteristic 
of a part should be reproduced at the symmetrical point of the 
corresponding part and that in this way the physical symmetry of the 
geometrically symmetrical parts should be achieved. But experience teaches 
that it is not so. The molding process of a pneumatic tire is so delicate 
that even in case of having avoided the dissymetries which may be called 
systematic dissymmetries, i.e., due to the geometry of the apparatus and 
therefore visually identifiable and even the rheological dissymmetries, 
which are very difficult to eliminate completely, consisting in harmful 
delivery differences, the desired result is not achieved with certainty, 
obviously because of accidental, casual and eventually variable 
dissymmetries which cannot be determined quantitatively and corrected, 
neither can they be generically identified in a reliable way. The present 
invention, instead, allows one to obtain an excellent physical symmetry of 
the tire in spite of the presence of these non-identifiable factors; and 
as will be seen, when carrying out the process according to the present 
invention it is not even necessary to have a strict geometrical symmetry 
of the apparatus. It is possible, for example, to feed the compound to the 
zone of the mold at only one side of the same, which is very advantageous 
both from the structural and the operational point of view. 
The applicants have found, as a result of careful studies and experiments, 
that it is not sufficient to simply divide the feed supply of compound 
into many injection streams of the same volume, but it is also necessary 
to carry out a further operation which may be referred to as 
"equalization". In this way, each injected stream contains a part of the 
outer zone or strata of the stream of compound and a part of the inner 
zone or strata of the feed supply of compound, in proportions which are 
practically equal for all of the secondary streams. 
In any liquid vein flowing in a pipe or conduit there is an outer zone, 
i.e., a zone situated near the walls of the pipe or conduit and an axial 
or inner zone, i.e., a zone which is situated around the axis of the pipe 
or conduit. Obviously, the distinction between the two zones is not a 
sharp distinction, because between the clearly inner strata and the 
clearly outer strata there are intermediate strata. Thus, expressions such 
as "outer compound" and "inner compound", in this case, are to be 
considered as being approximate. That is, they are intended to indicate, 
respectively, the parts of the stream compound which are situated nearer 
to the walls of the conduit and the parts which are situated nearer to the 
central axis, and the separation between the two parts is arbitrary and 
need not be defined for the comprehension and accomplishment of the 
present invention. When the feed supply of compound is distributed in a 
plurality of pipes or conduits, as "outer compound" and "inner compound" 
are considered, respectively, the complex of the outer compounds and that 
of the inner compounds of the various pipes or conduits. 
It is believed that the surprising technical effect of the present 
invention, thanks to which it has been possible to obtain pneumatic tires 
having a perfect physical symmetry, which are not obtainable by prior art 
techniques, may be explained by the following considerations, which, 
however, are given by way of suggestion and illustration and not for any 
binding effect and which are in no way determinant for the definition and 
accomplishment of the invention. 
In a stream of material having the rheological properties of a compound 
used for injection molding and in particular, in the compounds which are 
especially of interest herein, containing natural rubber, the behavior of 
the speed in a cross-section has not the usual parabolic diagram which is 
associated, for example, with the viscous flow of water or similar 
liquids. The linear speed increases rather suddenly with departure from 
the walls and reaches fairly soon a value which is then maintained 
practically constant throughout the axial zone of the fluid vein. 
Correspondingly, very substantial slidings take place between adjacent 
strata in the outer zone and practically no sliding in the axial zone. The 
deformation work corresponding to such slidings produces a very 
considerable and unavoidable temperature difference between the outer and 
the axial zones of the stream. It can be said that the temperature is 
higher where the derivative of the speed of the flow of compound in a 
radial direction is higher and the value of said derivative reflects the 
"outer" or "axial" character of each particle of the flowing compound. 
When a feed stream is divided into a plurality of injection streams, some 
of which are intended to fill the cavity of a part, while the other 
injection streams are intended to fill the cavity of the part which is 
symmetrical to the former, obvious geometrical reasons cause the material 
coming from the outer zone of the feed stream to be predominantly present 
in some injection streams, particularly in those relative to one part, 
while the material coming from the axial zone is predominantly present in 
other injection streams, particularly in those relative to the other part. 
Applicants believe that this uneven distribution of the material of the 
outer and the axial compound in the feed stream may chiefly be ascribed to 
the physical assymmetry which is found especially between the sidewalls 
and/or between different zones of each sidewall when the injection is 
carried out according to the known technique, even if all the precautions 
suggested by the technique or which may be provided by a person skilled in 
the art are taken to insure the absolute uniformity of the streams. 
It is to be noted, however, that physical dissymmetries may arise even in 
those conditions in which the geometry of the apparatus would indicate 
that globally the quantities of the axial and outer compounds fed to two 
symmetrical parts should be equal. It can be supposed that even in these 
cases there is an interference of accidental temperature variations or 
eventually other non-identifiable causes which determine a physical 
asymmetry and which are compensated by the equalization of each injection 
stream. 
Although, as said before, it is necessary that the portions of outer 
compound and axial compound of the feed stream be present is substantially 
constant proportions in the injection streams intended to give rise to 
symmetrical parts, it is obviously not possible to make sure that the 
proportions of axial and outer compounds be exactly the same, nor is it 
necessary to ascertain such condition, because when the desired physical 
symmetry has been achieved, it is obvious that any variation of the 
proportions which remains becomes negligible. This is what is meant by the 
expression "proportions practically equal for all of the injection steams" 
of the outer and inner compounds. 
According to one characteristic of the invention, the equalization of the 
composition of the injection streams is achieved by forming from the feed 
stream a plurality of intermediate streams and by combining again these 
intermediate streams in such a way as to obtain from them, in the end, 
sufficiently uniform injection streams. 
According to a preferred characteristic of the invention, some of the 
intermediate streams are predominantly outer ones and some are 
predominantly axial ones, and they are combined again in such a way that 
each injection stream has a quantity of predominantly outer stream 
substantially equal to the quantity of the predominantly axial stream. 
The expressions "predominantly outer stream" and "predominantly axial 
stream", as used hereinbelow and in the annexed claims relate exclusively, 
unless specifically stated otherwise, identify the outer and the axial or 
inner portion of the feed stream. That is, "predominantly outer" is any 
stream which contains predominantly or only a material coming from the 
outer zone of the feed stream, and "predominantly axial" is any stream 
which contains predominantly or only a material coming from the axial zone 
of the feed stream. Since it is not possible to obtain absolutely axial or 
outer streams, the word "predominantly" is always implied even where 
simply axial or outer streams are mentioned. 
Further preferred and more particular embodiments of the invention are 
characterized by the presence of one of the following characteristics or 
of more than one of them in combination: 
(a) both the predominantly outer streams and the predominantly axial 
streams are in number equal to the number of the injection streams for 
each symmetrical part of the tire; 
(b) each predominantly outer stream is combined with a predominantly axial 
stream to form a combined stream, to form an injection stream for one 
symmetrical part of the tire and an injection stream for the other 
corresponding symmetrical part; 
(c) the feed stream is subdivided into pairs of predominantly axial and 
outer intermediate streams; or it is subdivided into a plurality of 
streams which will be called "secondary streams" to distinguish them from 
the stream from which derive and which will then be referred to as 
"primary stream", said secondary feed streams containing outer and axial 
compounds in the same proportions as the primary flow, but with a 
different spatial distribution apt to facilitate the separation into 
predominantly outer and predominantly axial intermediate streams; 
(d) the secondary feed streams and/or the predominantly outer and the 
predominantly axial streams and/or the combined intermediate streams 
and/or the injection streams have a rectangular cross-section; 
(e) each pair of predominantly axis are predominantly outer streams is 
inverted before the streams and joined to one another to form a combined 
stream, it being thereby meant that the streams exchange their position, 
for example, relative to the plane of mirror image symmetry of the tire, 
so as to bring the innermost strata of the ones to be adjacent to the 
outermost strata of the others; 
(f) the axis of the mold is vertical, i.e., the tire is molded in a 
horizontal position, and the secondary feed streams and the intermediate 
streams run in a substantially radial direction with respect to the mold; 
(g) the predominantly outer and predominantly axial streams which are 
directed radially as said before, are diverted in such a way that the 
predominantly axial streams will occupy the plane which previously was 
occupied by the predominantly outer streams and vice versa and the streams 
are then joined, so that form a predominantly outer and a predominantly 
axial stream a combined stream is generated which runs in a substantially 
radial direction relative to the mold, from each of the combined streams 
there being derived (upwards and downwards if the axis of the mold is 
vertical) two injection streams for two symmetrical parts. 
It is also an object of the present invention to provide a molding 
apparatus for pneumatic tires which is suitable for carrying out the 
process provided by the invention and which comprises, in combination with 
a mold having cavities capable of producing symmetrical parts of the tire 
having the desired geometrical characteristics, at least one conduit for 
feeding the fluid molding compound, a plurality of injection conduits for 
introducing the compound into the two cavities of the mold, the conduits 
associated with each mold cavity leading into it through openings which 
are uniformly spaced on at least one annular zone, means for drawing 
intermediate streams from the feed conduit, and means for combining again 
the intermediate streams and for feeding to the injection conduits 
sufficiently uniform streams of mixture. 
According to a preferred characteristic of the invention, the means for 
drawing intermediate streams comprises means for drawing predominantly 
axial streams and predominantly outer streams. 
According to another preferred characteristic of the invention, the means 
for combining again the intermediate streams comprises means for imparting 
to the mixture to be fed to the injection conduits a sufficient uniformity 
of temperature. 
According to another preferred characteristic of the invention, the means 
for combining again the intermediate streams are such as to give rise to 
substantially equal deliveries of predominantly axial and predominantly 
outer streams. 
According to a further preferred characteristic of the invention, the means 
for combining the intermediate streams comprises means for bringing the 
innermost strata, i.e., those which were situated in the inner portion of 
the feeding conduit, to be adjacent to the outermost strata, i.e., to 
those which were situated in the outer portion in the feed conduit. 
In a further preferred embodiment of the invention, the symmetrical parts 
are the sidewalls of the tire and the annular zones are situated at the 
beads. 
In another preferred embodiment of the invention, the means for originating 
the outer stream of material and the axial stream of material from the 
feeding conduit to the injection conduits comprises first offtake conduits 
located so as to receive the predominantly outer streams of compound and 
second offtake conduits located so as to receive predominantly axial 
compound streams, said offtake conduits joining each other in such a way 
as to form from at least one offtake conduit of outer compound and at 
least one offtake conduit of axial compound a combined conduit, the 
combined conduit feeding at least one injection conduit. 
In other particularly preferred embodiments of the invention, the apparatus 
possesses one of the following characteristics or more than one of them in 
combination: 
(a) both the first and the second offtake conduits are in number equal to 
the number of the injection conduits for each symmetrical part of the 
tire; 
(b) each first offtake conduit is connected to a second combined conduit 
from which there are formed an injection conduit for one symmetrical part 
of the tire and an injection conduit for the respective second symmetrical 
portion; 
(c) from the feeding conduit, or from each feeding conduit, there are 
directly derived the offtake conduits, those which receive predominantly 
outer compound being derived upstream of the others with respect to the 
direction of the feed stream; or from each primary feed conduit there are 
derived a plurality of conduits which will be referred to as "secondary 
conduits" to distinguish them from the other conduits, which will then be 
referred to as "primary conduits", the secondary conduits being 
distributed symmetrically relative to the respective primary conduit, and 
each of them being divided into at least one first and one second offtake 
conduit; 
(d) the secondary feeding conduits and/or the offtake conduits and/or the 
combined conduits and/or the injection conduits have a rectangular 
cross-section; 
(e) each pair of first and second offtake conduits is inverted before the 
members of the pair are joined together to form a combined conduit; by 
this is meant that they are exchanged in their position, for example, with 
respect to the plane of mirror image symmetry of the tire, so as to bring 
the more intermediate strata of the compound flowing through one of them 
to be adjacent to the outermost strata of the compound which flows through 
the other; 
(f) the axis of the mold is vertical, i.e., the tire is molded in a 
horizontal position, the primary feeding conduit or conduits extend, at 
least at the end portion, along said axis, and the secondary feeding 
conduits, the first and the second offtake conduits and the combined 
conduits extend in a substantially radial direction with respect to the 
mold and symmetrically with respect of the axis of the latter; 
(g) the first and second offtake conduits which extend radially as said 
before, are diverted in such a way that the second conduits will be 
located in the plane in which previously were located the first conduits, 
and vice versa, and said conduits are then joined together, so that from 
one pair of them a combined conduit is obtained which extends in a 
substantially radial direction with respect to the mold, from each of said 
combined conduits there being derived (upwardly and downwardly if the axis 
of the mold is vertical) two injection conduits for the two cavities of 
the mold. 
The molding operation, although being more easily carried out with the axis 
of the mold in a vertical position, may also be carried out with the axis 
of the mold in a horizontal position, inasmuch as the perturbation effects 
of the gravity are not notable in an operation of this kind. Hence, should 
the axis of the mold be disposed horizontally, nothing essential would 
have to be changed in the examples which will be described hereinbelow, 
and therefore these examples apply to this case as well. 
Referring now to FIGS. 1 and 2, one embodiment of the invention in which 
the symmetrical parts to be molded are the sidewalls of the tire is 
illustrated. The mold for molding the sidewalls is indicated generally by 
reference numeral 10. Reference numerals 23-23' indicate the two cavities 
of the mold. It has to be noted that throughout the present description 
and in the claims, when the word "cavity" is used, reference is made to 
the cavities which define the configuration of the symmetrical parts under 
consideration, for the molding of which the present invention is applied. 
Other cavities which may be present in the mold, and for example, the 
cavity relating to the crown (when the invention is not applied also to 
the molding of the crown) are not taken into consideration and are not 
included in the expression "cavity of the mold". 
In the description of this embodiment, it is proposed to mold first the 
sidewalls and then to substitute those parts of the mold which are 
required for molding the tread for the ones used in molding the sidewalls. 
This, however, as said before, does not represent a limitation of the 
invention, since it is possible, without departing from the scope of the 
invention, to mold the various parts of the tire not only in the way 
described herein, but also by a single operation, or by successive 
operations, but without any substitution of parts of the mold. On the 
contrary, the embodiment of the invention which will be described first is 
particularly suitable to be used for the simultaneous molding of all of 
the parts of the tire, with suitable modifications of the mold, as will be 
better explained later with reference to FIG. 7. 
The primary feed conduit, through which flows the primary feed stream, is 
indicated by reference numeral 11. As can be seen from FIG. 1, conduit 11 
is disposed on side only of the plane S-S of mirror image symmetry of the 
sidewalls, which is indicated in FIG. 2. 
The primary feed conduit 11 is subdivided into a number of secondary 
conduits 12, which are only diagrammatically shown in FIG. 1 and which are 
arranged symmetrically relative to the axis of the mold, which axis is 
also the axis of the primary feed conduit 11 and is indicated by reference 
letters A--A (FIG. 2) in the example shown. The secondary conduits 12 may 
be very short or even completely omitted, as will be shown in FIG. 4. In 
this embodiment, eight injection conduits are used. Eight injection points 
are shown diagrammatically at 13 or 13' in the upper and lower sidewall 
respectively. It has to be pointed out that this embodiment is described 
while assuming that the mold is horizontal and the axis A--A is vertical, 
but, as said in the introduction to the present description, no 
substantial change would be required if the position of the whole assembly 
were rotated by any angle, even by an angle of 90.degree., in which case 
FIG. 1 would represent a vertical side elevational view and the plane of 
FIG. 2 would become a vertical plane. 
It has to be pointed out as well that in this embodiment, the axes of the 
secondary conduits 12 lie in the plane S--S and, as will be seen later, 
the equalization device 14 is approximately symmetrical relative to said 
plane. It would, however, be possible, although not desirable, to displace 
the parts perpendicularly to plane S--S at one side or at the other, and 
in other cases the conduits and the equalization device 14 may be inclined 
with respect to the plane S--S, as in the case shown in FIG. 7, or be 
suitably diverted. 
As already said before, the assembly of the injection points at which the 
mold is provided with inlet openings, substitutes the ideal annular slot 
along which the injection should be carried out, and the number of the 
chosen points depends upon the circumstances and is so established as to 
obtain the desired injection uniformity all along the circular development 
of the sidewalls. 
Each secondary conduit 12 terminates with an equalization device 14 which 
will be better described later and whose position is only diagrammatically 
indicated by rectangles shown in dashed lines in FIG. 1 and in FIG. 2. In 
the equalization device 14 the secondary feed conduits 12 are each divided 
into a first and a second offtake conduit, in which a predominantly outer 
and a predominantly axial compound flow, respectively, and which will be 
better illustrated later. At the end of the equalization device 14 each 
pair of offtake conduits join together to form a combined conduit 15 
which, in turn, is divided into injection conduits 16 and 16' for the two 
sidewalls, in the present case the upper sidewall and the lower sidewall 
(the passage from the first mentioned conduit to the second conduits not 
being visible in FIG. 1). 
In the embodiment shown, the primary feeding conduit 11 has a circular 
cross-section, as shown at 17, and the secondary feed conduits 12, as well 
as all the successive conduits, have a rectangular cross-section (said 
expression including also the case of a square cross-section), as shown 
diagrammatically at 18. If desired, also other cross-sections may be used. 
In FIG. 2 there is diagrammatically shown in a cross-sectional view 
one-half of the mold, the other half, which is perfectly symmetrical, 
being omitted. On the other hand, the structure of the mold does not form 
part of the invention, the structure depending, instead, on the structure 
of the particular tire, and a diagrammatical example of it is given herein 
for the sake of clarity only. In this example, the mold 10 is subdivided 
into two halves 20 and 21 and comprises a core 22. This latter, together 
with the half 20, defines the cavities 23-23', into which the compound 
will be injected. The half 21 will be substituted later, for molding the 
crown. The compound is introduced into the cavities 23-23' from the 
injection points 13-13' through the injection conduits 24-24'. 
An embodiment of the equalization device 14 is shown in a perspective view 
in FIG. 3. Each secondary feed conduit 12 is subdivided into a first and a 
second offtake conduit, indicated by reference numerals 30 and 31 
respectively, in the first of which flows the outer compound, while in the 
second flows the axial compound, the first being disposed, in the vertical 
axis molding arrangement which is being illustrated, above the second. 
First conduit 30 is bent downwards, and the second conduit 31 is bent 
upwards, as shown at 32 and 33, respectively, and these conduits exchange 
their respective positions, so that the second results now in being 
situated above the first (the two conduits being indicated in the drawing, 
in this new position, by reference numerals 30' and 31', respectively) and 
finally join together to form a combined conduit 15. 
FIG. 4 shows a second embodiment of the equalization device. In this 
embodiment, secondary conduits 12, which, as already said previously, may 
have any desired length, are completely missing. Directly branched from 
the feed conduit 11 are the first and the second offtake conduits for the 
outer and the axial compounds, respectively, which offtake conduits are 
indicated in the Figure by reference numerals 40 and 41, respectively. 
They are bent downwards and upwards, respectively (looking at the device 
as it is shown in the figure), as indicated at 42 and 43, and their 
position is exchanged by, so to say, inverting the flows, and in the 
position achieved after the inversion, they are indicated by reference 
numerals 40' and 41'. The inverted conduits 40' and 41' are then joined 
together to form the combined conduits 15. It can be seen that the outer 
compound conduits are branched from the feed conduit upstream of those for 
the axial compound relative to the flow direction of the compound towards 
the mold, which direction is from the top to the bottom in the figure. 
It is clear, and it will be better understood with reference to FIG. 5, 
that in FIGS. 3 and 4 the outermost strata (i.e., those situated in the 
uppermost part of the figures) of the outer compound conduits 30 and 40, 
are situated, after the reversal, adjacent the innermost strata (i.e., 
those situated in the lowermost part of the figure) of the axial compound 
conduits 31 and 4l. 
It is not necessary that the cross-section of the primary feed conduit be 
round, and if it were not, the geometry of the secondary conduits and/or 
the offtake conduits, as well as their number, could be suitably varied to 
adapt them to the different cross-section of the feed conduit. 
Also not necessary is that the other conduits have a rectangular 
cross-section, and also in such a case the geometry of the various parts 
may be arranged to suit the change of the cross-section, without any 
difficulty. The number of the conduits may also vary in any case. Nor is 
it necessary that the offtake conduits be arranged two by two, and thus, 
for instance, in the embodiment shown in FIG. 3, from each secondary 
conduit 12 there may be derived more than one outer compound conduit and 
more than one axial compound conduit. 
Also, the course of the conduits may be varied within ample limits. Thus, 
in FIGS. 3 and 4, there have been shown offtake conduits which extend in 
planes parallel to each other and to the median plane of the mold, and the 
reversal of the conduits is carried out by bending them twice practically 
at right angles. None of these geometrical particularities is necessary 
and all of them can be amply modified. 
It has already been pointed out that a complete separation between an outer 
compound and an axial one is not possible and that each offtake conduit 
contains at least parts of a compound which may be considered as 
intermediate between the outer compound and the axial one. However, in 
carrying out the process according to the invention it would also be 
possible to deliberately augment the presence of both types of compound in 
each offtake conduit and thus impart to the conduits such a configuration, 
with respect to those from which they derive, that each of them contains 
parts of a true outer compound and parts of a true axial compound provided 
that, in the end, the quantities of outer and axial compounds are balanced 
in the various injection conduits and that preferably the equalization 
operation leads to a relative uniformity of the temperatures, or more 
exactly to a marked attenuation of the temperature differences, through 
the phenomena which will be better understood with reference to FIG. 5. 
The effect of the equalization device is diagrammatically shown in FIG. 5. 
In this Figure, it is assumed that the device will have the configuration 
shown in FIG. 3, but nothing substantial is changed when the device has a 
different configuration. The curve composed of the two halves 50-51 
indicates the temperature diagram of the compound in the pipe 11, relative 
to a zero assumed arbitrarily and indicated at 52. Therefore, the hatch 
indicates the arc of the diagram of the temperatures. When from the 
primary feed conduit 11 there is branched to the right-hand side, the 
secondary conduit 12 and to the left-hand side, the symmetrical conduit 
12a, only the half 51 of the diagram moves onto the conduit 12, as shown 
in the figure, while the symmetrical half 50 moves onto the conduit 12a 
and such movement is not shown, for the sake of simplicity. If we consider 
the centerline plane P--P, which is a horizontal plane when carrying out 
the molding with a vertical axis mold, the temperature of the part of the 
compound which is situated above the plane and thus will flow through the 
first offtake conduit for a predominantly outer flow, is indicated by the 
diagram shown with a simple hatch 54, while the temperature of the 
predominantly axial compound which will flow through the second offtake 
conduit is indicated in the cross-hatched diagram 55. The equalization 
device shown in FIG. 3 brings about the reversal of the two compounds and, 
consequently, of the respective temperature areas in the combined conduit 
15, as indicated in the figure by the areas 55' and 54'. The temperature 
diagram is now indicated by the curves 51' and 51" which represent 
respectively the lower and the upper half of the curve 51 shown adjacent 
to the offtake conduit. Thus, in this conduit, at the centerline plane 
P--P, which in the embodiment shown in FIGS. 1 and 2 coincides with the 
plane S--S, but may be different, there are in contact with one another 
two portions of compound having the minimum and the maximum temperature 
respectively, i.e., outermost and innermost strata, respectively. Thus, an 
equalization, a kind of laminar mixing, if it may be said so, of the 
adjacent compounds occurs, so that the real temperature diagram is not the 
one defined by lines 51' and 51", but a diagram which though not being 
rectilinear has much less marked variations, as shown by dashed line 56. 
At this point, the temperature of the compound is sufficiently uniform to 
allow deriving from the combined conduit 15 the two injection conduits 16 
and 16' (FIG. 2), inasmuch as in these conduits there are present 
compounds having temperatures which are fairly near to one another and 
hence a molding uniformity. 
Should conduits 12, 12a be missing, as in the embodiment of FIG. 4, nothing 
would change in what has just been said; diagrams 54 and 55 would still 
represent the trend of the temperatures in each pair of offtake conduits, 
as conduits 40-4l directly branched from conduit 11 in FIG. 4. 
It has already been pointed out that the cross-sections of the pipes, their 
particular course, the way in which the equalization is accomplished, and 
so on, could be modified without departing from the scope of the 
invention. Some modifications which are immediately obvious are the 
following: 
Instead of a single primary feed conduit there may be provided two, 
situated along the axis of the mold, either horizontal or vertical, and in 
opposed relationship to one another. Such situation is shown in FIG. 6, 
similar to FIG. 2, where reference numeral 60 generally indicates the mold 
and reference numerals 61 and 61' indicate the two primary feed conduits. 
Each of these two conduits is divided into a plurality of secondary feed 
conduits 62-62' and each of these latter is divided into a first offtake 
conduit 63-63' and a second offtake conduit 64-64'. At this point the 
equalization may be carried out by joining each conduit 63 to a conduit 64 
and each conduit 63' to a conduit 64'. However, alternatively, it is also 
possible, as shown in the figure, to join each first offtake conduit, for 
example 63, relative to one sidewall, with the second offtake conduit 64' 
which is relative to the other sidewall and is situated in the same 
angular position, and thus join together each conduit 64 and a 
corresponding conduit 63'. In this way, two combined conduits 65-65' are 
obtained, which may be made to lead to the one and to the other sidewall, 
respectively, at the respective injection points 66-66', or the conduits 
65-65' may be joined together to form a conduit, and this latter may then 
be divided into two injection conduits of each sidewall, although such 
arrangement is not particularly advantageous; or four conduits 
63-64-63'-64' may be joined together to form a single combined conduit, 
from which there may be then obtained two injection conduits for the two 
sidewalls. These alternative possibilities are not represented, since they 
are obvious. 
In FIGS. 7 and 7A there is shown an appreciable variation of the embodiment 
shown in FIGS. 1 and 2, which differs from this latter in that instead of 
a single primary feed conduit, three of such conduits are provided. FIGS. 
7 and 7A are, respectively, a diagrammatic cross-sectional view taken 
along a plane normal to the axis of the mold and a diagrammatic partial 
cross-sectional view of a device for molding simultaneously, or almost 
simultaneously, the sidewalls and the tread. In this case, there are 
provided two primary feeding conduits 71 and 71' for molding the 
sidewalls, a primary conduit 72 for the supply of the compound for the 
tread, secondary injection conduits 75 for the sidewalls and secondary 
injection conduits 76 for the tread. In this embodiment, the location of 
the two primary feed conduits 71 and 71' allows also the provision of the 
primary conduit 72, without having to change parts of the mold or to 
substitute the latter for carrying out the molding of the tread. Even if 
the molding of the tread, effected through the mold portions 73 and 74 and 
the injection conduits 76, would not be carried out simultaneously with 
the molding of the sidewalls, the possibility of having in place the feed 
conduits for the tread without being compelled to effect displacements or 
substitution of conduits, still represents an operational advantage. 
FIGS. 8 and 9 show in a plan view and in a cross-sectional view along 
half-planes 9--9--9, respectively, a further embodiment of the invention. 
In this embodiment, a mold, indicated generally by reference numeral 81, 
is fed through two opposed primary conduits 11-11'. Branched from each of 
these latter are a number of offtake conduits for the outer and the axial 
compounds, with the interposition, in the particular embodiment shown, of 
secondary feed conduits 82-82' (which may be omitted); and by reversal of 
the offtake conduits, in equalization devices which may be like those 
described previously, the combined conduits 85-85' and the like injection 
conduits 15-15' for the two halves of the mold are obtained. It is to be 
noted that the word "halves" is not intended to indicate here, nor in 
relation to the previous embodiments, and anyhow does not necessarily 
indicate, separable parts of the molds, but simply portions which are 
symmetrical relative to the median plane. 
Up to this point, this embodiment corresponds to that shown in FIG. 6, in 
relation to the modification of this latter in which each conduit 63 is 
joined together with the corresponding conduit 64 and each conduit 63' is 
joined together with the corresponding conduit 64'. For the sake of 
simplicity, in FIG. 8 there is indicated by full lines the assembly 
comprising a secondary feed conduit, an equalization device with the 
respective offtake conduits, one of which is intended for the outer 
compound and the other for the axial compound, and the resulting combined 
conduit; and the assembly is indicated generally by reference numeral 
84-84', the assemblies 84' relating to the conduit 11' being indicated by 
dashed lines, for the sake of clarity of the representation. Instead, in 
FIG. 9, the equalization devices are omitted, these devices being similar 
to those already shown and being located in the zones 83-83'. 
Unlike the embodiment shown in FIG. 6, each of the combined conduits 
derived from the one or the other of the primary feed conduits 11-11', 
feeds both mold halves, it being divided into two injection conduits 
15-15', in a way analogous to that shown in FIG. 2. Each primary feed 
conduit 11-11' feeds, through the injection conduits deriving from it, one 
half of the injection points 13 of one mold half, and half of the 
injection points 13' of the other mold half. To make this possible, the 
offtake and the injection conduits deriving from each primary conduit 
11-11' are rotated, with respect to those deriving from the other primary 
conduit, by an angle equal to the angle which separates each injection 
point from the adjacent one. Thus, if the injection points are, for 
instance, eight in number, each primary conduit 11-11' originates four 
secondary conduits (which may be missing), four pairs of one offtake 
conduit for the outer compound and one offtake conduit for the axial 
compound, four equalization devices, four combined conduits and four pairs 
of injection conduits. Thus, there is created for each primary conduit 
11-11' a kind of spider-shaped structure, having four arms in the 
hypothesis under consideration, the two structures being angularly 
shifted, in the hypothesis under consideration, by 45.degree.. Conduits 
82-82', devices 83-83' and conduits 85-85' are not parallel to the median 
plane of the mold, as in the preceding embodiments, but are conveniently 
inclined. 
The invention has been described in relation to embodiments given by way of 
illustrative example only, and many variations and modifications may be 
introduced without departing from the scope of the invention. 
In particular, it is clear that the invention may be applied to any tire 
structure when the same is manufactured, wholly or for the important part 
of it, by injection molding. Thus, the invention may be applied also to 
tires which have a conventional structure and which work with sidewalls 
under tension, for example, conventional radial tires, as well as to tires 
having the configuration illustrated in the foregoing embodiments or a 
different configuration, whether they are conventional or not, which are 
provided with any reinforcement whatever also in the sidewalls. Since the 
invention is essentially directed to the feeding of the fluid molding 
compound to the mold, it is obvious that its suitableness and usefulness 
cannot be excluded by factors internal to the mold, such as particular 
mold configurations or the presence of inserts of any type, such as 
reinforcements disposed within the mold for being incorporated into the 
molded tire. 
Although the invention is described in detail for the purpose of 
illustration, it is to be understood that such detail is solely for that 
purpose and that variations can be made therein by those skilled in the 
art without departing from the spirit and scope of the invention except as 
it may be limited by the claims.