GB1570853A - Mehtod and apparatus for the injection moulding of pneumatic tyres - Google Patents

Description

(54) METH()D AND APPARATUS FOR THE iNJECTION MOULDING OF PNEUMATIC TYRES (71) We INDUSTRIE PIRELLI SpA an Italian Companv of Centro Pirelli. Piazza Duca d Aosta No. 3. Milan. Italv. do hereby declare the invention for which we prav that a patent may be granted to us. and the method by which it is to be performed. to be particularly described in and bv the following statement: This invention relates to a process and apparatus for the injection moulding of pneumatic tyres.

The invention is particularly applicable to pneumatic tyres made of differentiated compounds of natural or synthetic rubber. i.e.

tyres in which the crown is made of a compound different from that of the sidewalls. and has a particular importance in the moulding of the sidewalls. wherefore it will be described herein with reference to such moulding. but it may be generally used for the moulding of tyre portions which are mirror images of one another relative to the median circumferential plane of the tyre.

perpendicular to the tyre axis.

In the case of pneumatic tyres there must be a perfect physical symmetry (isotropy) between the portions which are geometrical- lv svmmetrical. In other words. it is not sufficient that the mould cavitv. and hence the mass of injected material. possesses the required geometrical symmetries. in partiocular. in the case concerned. that it comprises two portions which are mirror images of one another relating to the median plane of the tyre. but it is necessary that such asymmetry is substantially maintained also for the physical properties. i.e. that the geometrically symmetrical portions be symmetrical also as regards internal stresses.

deformations. degree of vulcanisation, mechanical properties of the material. and so on. Otherwise. the moulded bodv nvill not have the desired symmetry when rcmoved from the mould. or when being inflated. or when subject to stress. Therefore. in the following description of the present invention a distinction will be made between the geometrical symmetry and the physical symmetrv. it being obvious that the lack of physical symmetry may and generally does give rise, at one time or another in the tyre's life. to a lack of geometrical symmetry, even if such symmetry does exist initially.

Injection moulding of tyres, especially of tyres made of different compounds, is a substantially new process in the art.

Although proposals for the injection moulding of pneumatic tvres 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 tyre and do not allow the obtaining of such symmetry. In any case, these proposals generally relate to the injection moulding of tyres made of non-differentiated compounds which. moreover, generally do not comprise natural or synthetic rubber, but comprise plastics materials which from the point of view of physical properties are markedly different from natural or svnthetic rubber.

In French Patent Specification no.

1.508.135 there is described a process which. generally and in theory, may be utilised also for the moulding of tyres made of different compounds. and consists in that first the sidewalls are moulded and then, after having substituted the mould part which has to be substituted, the tread is moulded. However, should one trv to use that process. in accordance with what is described in said patent specification and with what is known in the art, for the moulding of a pneumatic tyre made of different rubber compounds, no satisfactory results would be obtained and, on the contrary. the resulting tyre would have serious unevennesses. I'he faults would be particularly significant if the sidewalls were moulded from natural rubber compounds.

This case is of particular interest for the type of tyre described in previous patents granted to the Applicant. as for instance in Italian Patent Specification No. C)3X,503.

The invention will now be described with particular reference to tyres of the type described in the above-mentioned patent of the Applicant. without however being exelusively limited to it. A tyre of this type comprises two sidewalls extending away from one another from the respective heads to the respective zones of connection to the crown, being markedly convex inwards when in the deflated condition and still convex. though Icss markedly, when in the inflated condition, as well as a convex crown acting as a tread in the central portion.

where the tyre normallv comes into contact with the ground. which is reinforced bv a suitable breaker structure or reinforcement generally made of a textile material and being annular in shape and substantially inextensible.

An object of the present invention is to obtain. in a pneumatic tyre manufactured bv injection moulding. a sufficient symmetry.

both geometrical and physical. of every part of the tyre. in particular the sidewalls.

One object of the present invention is to obtain said symmetry in injection moulded tyres in which the sidewalls are made of a rubber compound and particularly of a natural rubber compound.

Hereinafter. the expression svmmetrical parts" of the tvre will be used to indicate any two portions of the tyre which are mirror images of one another on opposite sides of the median circumferential plane of the tyre perpendicular to the axis of the tvre. Each of said portions. taken separate ly. will be referred to as a svmmetrical portion". Such symmetrical parts may be well defined components of the tyre. 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 whatever. for instance portions made of a material different from that of other portions of the sidewalls: or also two halves of the cn-)wn arranged on opposite sides of the median plane. or portions of the crown which are svmmetrical relative to said plane and are made of a material different from that of the other portion(s).

In accordance with one aspect of the present invention there is provided a process for the injection moulding of pneumatic tyres from rubber-based compounds. characterised in that it comprises forming a primary feeding flow of an injectable tyre moulding compound. obtaining from said primary feeding flow a pluralitv of first intermeditte flows predominantfv formed from the outer region of said primary feeding flow and another plurality of second intermediate flows predominantly formed from the central region of said primary feeding flow. combining at least one of said first intermediate flows with at least one of said second intermediate flows to form a combined flow, drawing from said combined flow a plurality of injection flows and filling each of two mould cavities corresponding to any pair, of symmetrical parts of a tyre with moulding compound of said injection flows.

The fluid moulding compound is obtained, bv means known in the art and which do not need to be described herein, through kneading, mastication. fluidification. and pressurising operations. which are well-known per se. In this way. a primary feeding flow of fluid compound to be injected is produced.

The mould cavities corresponding to any pair of symmetrical parts of a tyre, even if the mould constitutes a mechanical unit, are considered as distinct, inasmuch as there is not a passage of compound from one to the other.

According to a preferred embodiment of the invention. when the symmetrical parts are the sidewalls, the compound is introduced separately into the sidewall cavities, preferably from the region of the bead, so as to render the injection itself svmmetrical with respect to the axis of the mould and as uniform as possible. minimising the necessity of having the injection flows spreading 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 oneself with providing a plurality of uniformly spaced openings, each of which forms a segment of said annular opening or one of them, so that everything takes place as though the injection were made into said one or more annular openings. portions of which. uniformlv spaced, have been closed.

Thus. a plurality of injection openings located along at least one annular zone is obtained for each sidewall. and at each of these openings there is an injection flow which enters the mould through the opening itself.

Analogous considerations may be made in respect of symmetrical parts other than sidewalls. If such parts are the beads. the injection openings will remain in the positions previously described. If they are different portions of the sidewalls, they will be correspondingly displaced. If the svmmetrical parts are two halves of the crown. it is preferable to inject the compound from two series of openings disposed in two annular zones located at the two shoulders of the crown. from which the flows of compound will converge to meet each other at the mediall plane. An analogous arrangement will he 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.

Vhe most simple wav of carrving out the injection moulding would be that of dividing the feeding flow into the various injection flows relative to one or the other of each pair of symmetneal parts. taking care that the cross sections of the paths be uniform so that each flow has the same capacity. as is indispensable for the regularity of the injec- tion.

However. unexpectedly. by acting in this wsy one does not obtain a tyre having perfect physical symmetry.

Not even perfect symmetry of the moulding apparatus with respect to the median plane of the tyre ensures the physical symmetry of the latter. It could seem that if the apparatus is svmmetrical. 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 symmetrical parts should be achieved. But experience teaches that it is not so. The moulding process of a pneumatic tvre is so delicate that even having avoided the lack of symmetry which may be called systeniatic dissynietry. i.e.

what is due to the zeometrv ot tlie nppiratus and therefore visuallv identifiable. and even the rheological dissmmetries. which are very difficult to eliminate completely. consistine in harmful delivery differences. the desired result is not achieved with certainty.

obviously because of accidental. casual and eventually variable dissvmmetries which cannot be determined qujntitively and corrected. neither can they be generically identified in a reliable wav. The present invention. instead. allows one to obtain an excellent physical symmetry of the tyre in spite of the preseiice of said non identifiable factors: and as will be seen. when carrying out the process according to the present invention it is not even necessarv to have a strict geometrical symmetry of the apparatus. and it is possible for example to feed the compound to the zone of the mould at only one side of the same. which is verv advantageous both from the structural and operational point of view.

The Applicants have found. as a result of careful studies and experiments. that it is not sufficient to simpl',' divide the feeding flow into manx injection flows of the same capacity. hut it is necessary to calrv out a further operation which may be referred to as ''equalization''. by means of which each injection flow contains compound both from an outer region and from an inner region of the feeding flow. preferably in practically equal proportions.

In any liquid flowing in and filling a pipe or conduit there is an outer zone, i.e. a zone situated near the wall of the pipe or conduit, and an inner zone, i.e. a zone which is situated around the axis of the pipe or conduit. Obviously. the distinction between said 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 approximatc. i.e. intended to indicate, respectively, the parts of the compound which are situated nearer to the wall of the conduit and the parts which are situated nearer to the axis. and the separation between the two parts is arbitrary.

It is believed that in a flow of material having the rheological properties of a compound for injection moulding. and in particular in compounds which are especially of interest herein. containing natural rubber, the behaviour of the speed in a cross-section has not the usual parabolic curve 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 central region of the fluid flow. Correspondingly. very marked slidings take place between adjacent strata in the outer zone and practically no sliding in the central zone. The deformation work corresponding to such slidings produces a very considerable and unavoidable temperature difference between the outer and the central zone of the flow. It can be said that the temperature is higher where the derivative of the speed of the flow of compound in a radical direction is higher, and the value of said derivative reflects the "outer" or "central" character of each particle of the flowing compound. When a feeding flow is divided into a plurality of injection flows. obvious geometrical reasons cause the material coming from the outer zone of the feeding flow to be prevailingly represent in some injection flows. while the material coming from the central zone is prevailingly present in other injection flows.

Applicants believe that this uneven distribution of the material of the outer and the central compound in the feeding flow may chieflv be ascribed to the physical assymmetre 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 said technique or which may be provided bv a person skilled in the art are taken to ensure the absolute uniformitv of the flows.

It is to be noted, however. that physical dissvmmetries may arise even in those con editions in which the geometrv of the apparatus would indicate that the quantities of the central 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 eventuallv other non identifiable causes which determine a physical assymmetry and which are compensated by the equalization of each injection flow.

According to a preferred method of performing the invention. the equalization of the composition of the injection flows is achieved by forming from the feeding flow a plurality of intermediate flows and bv com binding again these intermediate flows in such a wav as to obtain from them. in the end. sufficiently uniform injection flows.

Preferably some of said intermediate flows are prevailingly of outer compound and some are prevailingly of central compound and they are combined again in such a wav that each injection flow comprises a quantitv of prevailingly outer compound substantially equal to the quantitv of the prevailingly central compound.

The expressions "prevailingly outer compound" and "prevailingly central compound". as used hereinbelow relate exclu lively. unless specifical indications to the contrary are given. to the outer and the central portion of the feeding flow.

In accordance with another aspect of the invention there is provided an apparatus for the injection moulding of pneumatic tyres from rubbensed compounds comprising. in conibination with a mould provided with syninietrical cavities arranged to mould svmnietrical parts of the tyre. at least one feeding conduit for a primary feeding flow of moulding compound. means for drawing from said feeding conduit. a plurality of first and second intermediate flows respectively of compound from an outer region and from a central region of the primary feeding flow, means to join said first and second interme- diate flows to form a plurality of combined flows. means for drawing from said combined flows a plurality of injection flows and a corresponding plurality of injection conduits tor feeding said injection flows into said synimetncal parts of the mould. said injection conduits associated with the mould cavities leading into them through corresponding openings suitablv spaced around the mould.

The means to join the intermediate flows preferably comprises means for imparting to the compound to be fed to the injection conduits a substintially uniform tcmpera- ture.

The means to join the intermediate flows is preferably such as to impart substantially equal delivery capacities to the first and second intermediate flows.

The means to join the intermediate flows may be arranged to join compound from an innermost region of the primary feeding flow with compound from an outermost region of the primary feeding flow in one of the combined flows.

The symmetrical cavities may be for moulding the sidewalls of the tyre and the openings may be in the regions of the mould cavities where the beads of the tyre are moulded.

The means for drawing from said feeding conduit a plurality of first and second intermediate flows may comprise first offtake conduits located in such a wav as to receive compound primarily from a central region of the feeding conduit and second offtake conduits located in such a wav as to receive compound primarily from an outer region of the feeding conduit, said first and second offtake conduits being then joined together to form at least one common offtake conduit for compound from the outer region of the feeding conduit and at least one common offtake conduit for compound from the central region of the feeding conduit. a combined conduit obtaining compound from both the said common offtake conduit and feeding at least one injection conduit.

Preferred embodiments of the invention will now be described with reference to the accompanying drawings. in which: Figure 1 is a diagrammatic plan view of apparatus according to one embodiment of the invention: Figure 2 is an enlarged. partial crosssectional view taken along line 2-2 of Figure 1. with parts shown in elevation; Fi, res 3 and 4 are perspective views of a detail (equalization device) according to two embodiments of the invention: Figitre 5 is a diagrammatic representation of rheological phenomena which occur during the moulding of a tyre: Figure 6 is a representation, similar to that of Figure 2. of apparatus according to another embodiment of the invention: Figities 7 and 7A are. respectively. a plan view and a cross-sectional view, similar to those of Figures 1 and 2. of a modification of the apparatus shown in Figures 1 and 2, provided with means for moulding the crown of the tyre: Figure 8 is a plan view. similar to that of Figure 1. of a further embodiment of the invention. and Fi,glzre 9 is a cross-sectional view of the apparatus of Figure 8. taken along the line 9-9 of Figure 8.

Referring now to Figures 1 and 2. in an emmbodiment of the invention in which the symmetrical parts to be moulded are the sidewalls of the tyre. the mould for moulding the sidewalls is indicated generally by reference numeral 10. Reference numerals '3-'3' indicate the two cavities of the mould. It has to be noted that throughout the present description and in the claims, when the word "cavitv" is used. reference is made to the cavities which define the configuration of symmetrical parts, for the moulding of which the present invention is used.

In this embodiment first the sidewalls are moulded and then parts of the mould are substitured to mould the tread.

The primary feeding conduit. through which flows the primary feeding flow. is indicated by reference numeral 11. As can be seen from Figure 2 said conduit is disposed on one side only of the plane S-S of mirror image symmetry of the sidewalls, which is indicated in Figure 2.

The primary feeding conduit 11 is subdivided into a number of secondarv conduits 12. which are only diagrammaticallv shown in Figure I and which are arranged symmetricallv relative to the axis of the mould, which axis is also the axis of the primary feeding conduit 11 and is indicated by reference letters A-A (Figure 21 ) in the example shown. Said secondarv conduits may be very short or even completely omitted. as, will lie shown in Figure 4. In this emhodiment. the secondary conduits are eight in number. and there are also eight injection points diagrammatically shown at 13 or 13' in the upper and lower sidewall respectively. It has to be pointed out that this embodiment is described supposing that the mould is horizontal and the axis A-A is vertical. but. as said in the introduction to the present description. no substantial change would arise if the position of the whole assembly were rotated by any angle.

even by an angle of C)O'. in which case Figure ] would represent a vertical side elevational view and the plane of Figure ' would becoiiie a vertical plane.

In this embodiment the axes of the secondary conduits lie in the plane S-S.

As alreadv said before. the assemblv of the injection points at which the mould 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 cir cumstances and is so established as to obtain the desired injection uniformity all along the circular development of the sidewalls.

Each secondar',, conduit 12 terminates at cqualizatir,n device 14 which will be letter described liter and whose position is only diagranini'itically indicated by rectangles shown in dashed lines in Figure 1 and in Figure 2. In the equalization device 14 the secondary feeding conduits 12 are each divided into a first and a second offtake conduit, in which flow a prevailingly outer and a prevailingly axial compound respectively, and which will be better illustrated later. Each pair of offtake conduits join together to form a combined conduit 15 which. in turn. is divided into injection conduits 15 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 Figure 1).

In the embodiment shown, the primary feeding conduit 11 has a circular crosssection, as shown at 17, and the secondary feeding conduits, 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 crosssections could be used.

In Figure 2 there is diagrammatically shown in a cross-sectional view one half of the mould, the other half, which is symmetrical. being omitted. In this example, the mould 10 is subdivided into two halves 20 and 21 and comprises a core 22. This latter, together with the half 2(). defines cavities 23-23'. into which the compound will be injected. The half 21 will be substituted later. for moulding the crown. The compound is introduced into the cavities 23-23' from the injection points 13-13' through injection conduits 24-24'.

An embodiment of the equalized device 14 is shown in a perspective view in Figure 3. Each secondary feeding 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 moulding arrangement which is being illustrated above the second. First conduit 30 is directed downwards, and the second conduit 31 is directed upwards. as shown at 32 and 33 respectively. and these conduits exchange their respective positions, so that the second is now 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.

Figure 4 shows a secondary embodiment of the equalization device. In this embodiment. secondary conduits 12. which, as already said previouslv. may have any desired length. are completely missing. Directlv branched from the feeding conduit 11 are the first and the second offtake conduits for the outer and the axial compounds respectivelv. which offtake conduits are indicated in the Figure by reference numerals 40 and 41 respectively. They are directed downwards and upwards respectivelv (looking at the device as it is shown in the Figure), as indicated at 42 and 43. and their position is exehinged by. so to sav. invcrting the flows, and in the position achieved after the inversion they are indicated by reference numerals 4()' and 41'. The inverted conduits 40' and 4.1' are then joined together to form the combined conduits 15. It can be seen that the tauter compound conduits are branched from the feeding conduit upstream of those for the axial compound relative to the flow direction of the compound towards the mould. which direction is from the top to the bottom in the Figure.

It is clear. and it will be better understood with reference to Figure 5, that in Figures 3 and 4 the outermost strata of the outer compound conduits 3() and 4(). are situated.

after the reversal. adjacent the innermost strata of the axial compound conduits 31 and 41.

It is not necessarv that the cross-section of the primary feeding conduit should be circular. and if it were not. the eeometrv of the secondary conduits andior the offtake conduits, as well as their number. could be suitablv varied to adapt them to the different cross-section of the feeding conduit.

It is also not necessary that the other conduits have a rectangular cross-section.

The geometrv of the various parts could be arranged to suit the change of the crosssection. without any difficultv. The number of the conduits mav also varv in anv case.

Nor is it necessary the offtake conduits to be arranged two by two, and thus. for instance in the embodiment shown in Figure 3. from each secondary conduit 12 there could be derived more than one outer compound conduit and more than one axial compound conduit.

Also the course of the conduits could be varied within wide limits. Thus. in Figures 3 and 4 there have been shown offtake conduits which extend in planes parallel to each other and to the median plane of the mould.

and the reversal of the conduits is carried out by bending them twice practically at right angles.

It has alreadv 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. llowever, in carrying out the process according to the invention it would also lie possible to deliberately augnient the preseiice of both types of compound in each offtake conduit by giving the conduits such a configuration.

with respect to those from which they derive, that each of them contains part of a true outer compound and part 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 relatively uniformity of temperatures. or more exactly to attenuation of the temperature differences. through the phenomena which will be better understood with reference to Figure 5.

The effect of the equalization device is diagrammatically shown in Figure 5. In this Figure it is supposed that the device has the arrangement shown in Figure 3. The curve composed of the two halves 50-51 indicates the temperature diagram of the compound in the conduit 11. relative to a zero assumed arbitrarilv and indicated at 52. Therefore.

the cross hatched areas indicate the curves of the temperatures. When from the primarv feeding conduit 11 there is branched to the right-hand side the secondary conduit 12 and to the left-hand side the symmetrical secondary conduit 12a. onlv the half 51 of the compound moves into the conduit 12, as shown in the Figure. while the symmetrical half 50 moves onto the conduit 12a. If we consider the centreline plane P-P, which is a horizontal plane when carrving out the moulding with a vertical axis mould. the temperature of the part of compound which is siutated above said plane and thus will flow through the first offtake conduit for prevailingly outer flow. is indicated bv the diagram shown by simple hatching 54. while the temperature of the prevailinglv axial compound which will flow through the second offtake conduit is indicated in the cross-hatched diagram 55. The equalization device shown in Figure 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 bv the areas 55' and 54'. The temperature diagram is now indicated by the curves 51 ' and SI" which represent respectively the lower and the upper half of the compound 51 shown adjacent the offtake conduit. Thus, in this conduit. at the centreline plane P-P, which in the embodiment shown in Figures 1 and 2 coincides with the plane S-S. but could 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, respectivelv. Thus. an equalization is achieved, a kind of laminar mixing. if it mav be so described, of the adjacent compounds, so that the real temperature diagram. though not being rectilinear, has much less marked variations. as shown by dashed line 56. At this point. the temperature of the compound is sufficientlv uniform to allow deriving from the combined conduit 15 the two injection conduits 16 and 16' (Figure 2). inasmuch as in these conduits there are present compounds having temperatures fairly near to one another and hence a moulding unifor mitt.

Should conduits 17. I'a be missing. as in the embodiment of Figure 4, nothing would change in what has just been expounded.

Diagrams 54 and 55 would still represent the trend of the temperatures in each pair of offtalic conduits. as conduits 40-41 directly bninched from conduit 11 in Figure A.

It has alreadv ticen pointed out that the cross-sections of the pipes. their particular course. the wav 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 feeding conduit there could be provided two. situated along the axis of the mould - be it horizontal or vertical - and in opposed relationship to one another. Such situation is shown in Figure 6. similar to Figure 2. where reference numeral h() generally indicates the mould and reference numerals 61 and 61' indicate the two primary feeding conduits.

Each of these two conduits is divided into a plurality of secondary feeding 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 bv joining each conduit ó. to a conduit 64 and each conduit (.3' to a conduit 64'. Alternatively, however 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 wav, two combined conduits (r5-65' are obtained. which may be made to lead to the one and to the other sidewall respectively. at the respective injection points 66-(('. or the conduits 65-65' man be joined together to form a conduit.

and this latter may then be divided into two injection conduits of each said sidewall.

although such anangement is not particular ly advantageous. or four conduits 63-64-63'- 64' may lie 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 thcn are obvious.

In Figures 7 and 7A there is shown an appreciable variation of the embodiment shown in Figures I and 2. which differs from this latter in that instead of a single primary feeding conduit. three of such conduits are provided. Figures 7 and 7A are. respectively. a plan view and a diagrammatic partial cross-sectional view of a device for moulding simultaneously, or almost simultaneous ly. the sidewalls and the tread. In this case, there are provided two primary feeding conduits 71 and 71' for moulding the sidewalls, a primary conduit 79 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 feeding conduits 71 and 71' allows also the provision of the primary conduit 72, without having to change parts of the mould or to substitute the latter for carrying out the moulding of the tread.

Even if the moulding of the tread, effected through the mould portions 73 and 74 and the injection conduits 76. would not be carried out simultaneously with the moulding of the sidewalls, the possibility of having in place the feeding conduits for the tread without being compelled to effect displacements or substitution of conduits. still represents an operational advantage.

Figures 8 and 9 show in a plan view and in a cross-sectional view along line 9-9, a further embodiment of the invention. In this embodiment. a mould. indicated generally by reference numeral 81. is fed through two opposed priiiiary 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 feeding conduits 82-82' (which may be omitted): and by reversal of said offtake conduits, in equalization devices which may be like those described previously. the combined conduits 85-85' and the injection conduits 15-15' for the two halves of the mould are obtained. It is to be noted that the word "half" is not intended to indicate here. nor in relation to the previous embodiments. and anyhow does not necessarily indicate, separable parts of the mould. but simply portions which are symmetrical relative to the median plane.

Up to this point, this embodiment corresponds to that shown in Figure 6, in relation to the modification of this latter in which each conduit 63 is joined together with the correspondiiig conduit 64 and each conduit 63' is joined together with the corresponding conduit 64'. For the sake of simplicity, in Figure 8 there is indicated by full lines the assembly comprising a secondary feeding 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 said assembly is indicated generally by reference num eral 84-84', the assemblies 84' relating to the conduit 11' being indicated by dashed lines, for the sake of claritv of representation.

Instead. in Figure 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 Figure 6. each of the combined conduits derived from the one or the other of the primarv feeding conduits ll-ll'. feeds both mould halves. it being divided into two injection conduits 15-15'. in a way analogous to that shown in Figure 2. Each primary feeding conduit 11-11' feeds, through the injection conduits deriving from it. one halve of the injection points 13 of one mould half. and half of the injection points 13' of the other mould half. To make this possible, the offtake and the injection conduits deriving from each primary conduit ll-ll' are rotated. with respect to those depriving from the other primary conduit. bv 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 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 l l-l l ' a kind of spidershaped structure. having four arms in the embodiment under consideration. the two structures being angularly shifted bv 45o.

Conduits X'-X3'. devices X3-X3' and conduits 85-85' are not parallel to the median plane of the mould. as in the precediiig embodiments. but are convenientlv inclined.

It will be clear that the invention may be applied to any tyre structure when the same is manufactured. wholly or mainly by injection moulding. Thus. the invention may be applied also to tvres which have a convex tional structure and which work with side walls under tension. for example conventional radial tyres. as well as to tyres having the configuratlon illustrated in the foregoing embodiments or a different configuration.

whether they are conventional or not. which are provided with any reinforcement whatever in the sidewalls.

WHAT WE CLAIM IS: 1. A process for the iniection moulding of pneumatic tyres. from rubber-based compounds. characterised in that it comprises forming a primary feeding flow of an inject ahle tyre moulding compound. obtaining from said primary feeding flow a plurality of first intermediate flows predoniinantly formed from the outer region of said prim ary feeding flow and another plurality of second intermcriiate flows prcdominantly formed from the central region of said primary feeding flow, combining at least one of said first intermediate flows with at least one of said second intermediate flows to form a combined flow. drawing from said combined flow a plurality of injection flows.

and filling each of two mould cavities corresponding to any pair of symmetrical parts of a tyre with moulding compound of said injection flows.

2. A process according to claim 1 characterised in that each injection flow comprises a volume of compound from the outer region of the primary feeding flow which is substantially equal to the volume of compound from the central region of said primary feeding flow.

3. A process according to claim 2 characterised in that said first and second intermediate flows are joined in such a wav that the resulting combined flow will have a substantially uniform temperature.

4. A process according to claim 1 characterised in that the combination of one of said first intermediate flows with one of said second intermediate flows is carried out by putting into contact the outermost zone of the volume of compound from said outer region with the innermost zone of the volume of compound from said central region.

5. A process according to any one of the preceding claims. characterised in that the first and second intermediate flows are equal in number to the injection flows for each symmetrical part of the tyre.

6. A process according to any one of the preceding claims characterised in that the primary feeding flow is subdivided into a plurality of secondary feeding flows, said secondary feeding flows containing substantially equal portions of compound from the outer region and from the central region of said primary feeding flow but in an altered spatial arrangement to facilitate the separation of said primary feeding flow into said first and second intermediate flows.

7. A process according to claim 6 characterised in that said primary feeding flow has a circular cross-section and the secondary feeding flows, the intermediate flows, the combined flows and the injection flows have a rectangular cross-section.

8. A process according to claim 6 characterised in that the axis of the primary feeding flow. at least in its end portion, is vertically disposed and the secondary feeding flows and the intermediate flows extend in a substantially radial direction relative to the tyre mould.

9. A process according to claim X characterised in that the flows extend in a radial direction are diverted so that flows predomi nantly of compound from central regions of previous flows come to lie in a plane in

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (1)

1. **WARNING** start of CLMS field may overlap end of DESC **.

   eral 84-84', the assemblies 84' relating to the conduit 11' being indicated by dashed lines, for the sake of claritv of representation.

   Instead. in Figure 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 Figure 6. each of the combined conduits derived from the one or the other of the primarv feeding conduits ll-ll'. feeds both mould halves. it being divided into two injection conduits 15-15'. in a way analogous to that shown in Figure 2. Each primary feeding conduit 11-11' feeds, through the injection conduits deriving from it. one halve of the injection points 13 of one mould half. and half of the injection points 13' of the other mould half. To make this possible, the offtake and the injection conduits deriving from each primary conduit ll-ll' are rotated. with respect to those depriving from the other primary conduit. bv 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 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 l l-l l ' a kind of spidershaped structure. having four arms in the embodiment under consideration. the two structures being angularly shifted bv 45o.

   Conduits X'-X3'. devices X3-X3' and conduits 85-85' are not parallel to the median plane of the mould. as in the precediiig embodiments. but are convenientlv inclined.

   It will be clear that the invention may be applied to any tyre structure when the same is manufactured. wholly or mainly by injection moulding. Thus. the invention may be applied also to tvres which have a convex tional structure and which work with side walls under tension. for example conventional radial tyres. as well as to tyres having the configuratlon illustrated in the foregoing embodiments or a different configuration.

   whether they are conventional or not. which are provided with any reinforcement whatever in the sidewalls.

   WHAT WE CLAIM IS:

   1. A process for the iniection moulding of pneumatic tyres. from rubber-based compounds. characterised in that it comprises forming a primary feeding flow of an inject ahle tyre moulding compound. obtaining from said primary feeding flow a plurality of first intermediate flows predoniinantly formed from the outer region of said prim ary feeding flow and another plurality of second intermcriiate flows prcdominantly formed from the central region of said primary feeding flow, combining at least one of said first intermediate flows with at least one of said second intermediate flows to form a combined flow. drawing from said combined flow a plurality of injection flows.

   and filling each of two mould cavities corresponding to any pair of symmetrical parts of a tyre with moulding compound of said injection flows.

   2. A process according to claim 1 characterised in that each injection flow comprises a volume of compound from the outer region of the primary feeding flow which is substantially equal to the volume of compound from the central region of said primary feeding flow.

   3. A process according to claim 2 characterised in that said first and second intermediate flows are joined in such a wav that the resulting combined flow will have a substantially uniform temperature.

   4. A process according to claim 1 characterised in that the combination of one of said first intermediate flows with one of said second intermediate flows is carried out by putting into contact the outermost zone of the volume of compound from said outer region with the innermost zone of the volume of compound from said central region.

   5. A process according to any one of the preceding claims. characterised in that the first and second intermediate flows are equal in number to the injection flows for each symmetrical part of the tyre.

   6. A process according to any one of the preceding claims characterised in that the primary feeding flow is subdivided into a plurality of secondary feeding flows, said secondary feeding flows containing substantially equal portions of compound from the outer region and from the central region of said primary feeding flow but in an altered spatial arrangement to facilitate the separation of said primary feeding flow into said first and second intermediate flows.

   7. A process according to claim 6 characterised in that said primary feeding flow has a circular cross-section and the secondary feeding flows, the intermediate flows, the combined flows and the injection flows have a rectangular cross-section.

   8. A process according to claim 6 characterised in that the axis of the primary feeding flow. at least in its end portion, is vertically disposed and the secondary feeding flows and the intermediate flows extend in a substantially radial direction relative to the tyre mould.

   9. A process according to claim X characterised in that the flows extend in a radial direction are diverted so that flows predomi nantly of compound from central regions of previous flows come to lie in a plane in

   which flows predominantlv of compound from outer regions of previous flows were lying. and vice versa, and said flows are then joined together. so that a combined flow is generated which extends in a substantially radial direction with respect to the mould, from each of said combined flows there being derived injection flows for the symmetrical parts of the tyre.

   1(j. An apparatus ' for the injection moulding of pneumatic tyres from rubberised compounds comprising, in combination with a mould provided with symmetric- al cavities ranged to mould symmetrical parts of a tyre. at least one feeding conduit for a primary feeding flow of moulding compound. menus for dr'iwing from said feeding conduit. a plurality of first and second intermediate flows respectively of compound from an outer region and from a central region of the primary feeding flow.

   means to join said first and second intermediate flows to form a plurality of combined flows. means for drawing from said combined flows a plurality of injection flows and a corresponding plurality of injection conduits for feeding said injection flows into said symmetrical parts of the mould. said injection conduits associated with the mould cavities leading into them through corres ponging openings suitabl spaced around the mould.

   II. An apparatus as claimed in claim 10.

   wherein the means to join the intermediate flows comprises means for imparting to the compound to be fed to the injection conduits a substantially uniform temperature.

   12. An apparatus as claimed in claim 1() or claim 11. wherein the means to join the interiiediate flows is such as to impart substantilly equal delivery capacities to the first and second intermediate flows.

   13. An apparatus as claimed in any one of claims 1()-13. wherein the means tc; join the interniediate flows is arranged to join conipound from an innermost region of the primary feeding flow with compound from an outermost region of the primary feeding flow in one of the combined flows.

   14. An apparatus as claimed in any one of claims 1(1-I 3. wherein the symmetneal cavities are for moulding the sidewalls of the tyre and wherein the openings are in the regions of the mould cavities where the beads of the tyre are moulded.

   IS. An apparatus as claimed in any one of claims 1(1-14. wherein the meals for drawing from said feeding conduit a plural itv of first and second intermedi'ite flows ctimplises first offtalse conduits located in such a way as to recei',-e compound primari lv from a central region of the feeding conduit and second offtake conduits located in such a wav as to receive compound primarily from an outer region of the feeding conduit, said first and second offtake conduits being then joined together to form at least one common offtake conduit for compound from the outer region of the feeding conduit and at least one common offtake conduit for compound from the central region of the feeding conduit, a combined conduit obtaining compound from both the said common offtake conduit and feeding at least one injection conduit.

   16. An apparatus according to any one of claims 10-15. characterised in that from each primary feeding conduit there are derived a plurality of secondary feeding conduits, said secondary conduits being distributed symmetrically with respect to the primary conduit from which they derive, and each of them dividing into at least one first and one second offtake conduit.

   17. An apparatus according to claim 16 characterised in that the primary feeding conduits have a circular cross-section and the secondary feeding conduits and/or the combined conduits and/or the injection conduits have a rectangular cross-section.

   18. An apparatus as claimed in claim 16 or claim 17. characterized in that each pair of first and second offtake conduits is reversed before said conduits of said pair are joined together to frirm a combined conduit. so as to bring the innermost strata of the compound which flows in one of them to be adjacent to the outermost strata of the compound which flows in the other one.

   19. An apparatus according to any one of claims 16-18. characterized in that the axis of the mould is vertical, the primary feeding conduits extend. at least at their end portions, 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 mould. symmetrically with respect to the axis of the latter, 20. An apparatus according to claim 19 characterized in that the first and the second offtake conduits extending radially are diverted in such a wav that the second offtake conduits come to lie in the plane in which previouslv were lying the first offtake con duits, and zsice zeissle and said conduits are then joined together. so that from a pair of them a combined conduit is formed which extends in a substantially radial direction.

   with respect to the mould. from each of said combined conduits there being derived injection conduits for the two cavities of the mould.

   21. An apparatus according to any one of claims 16-20 characterized in that a single primary feeding conduit extends, at least in its end portion. along the axis of the mould and on one side of the plane of mirror image symmetry of the cavities which define symmetrical parts of the tyre. and that each combined conduit is obtained bv joining together one first and one second offtake conduit which derive from the same secon darv feeding conduit.

   ". An apparatus according to any one of claims 16-20, characterized in that it comprises two primary feeding conduits extending. at least in their end portions along the axis of the mould on both sides of the plane of mirror image symmetry of the cavities which define svmmetrical parts of the tyre, and that each combined flow is obtained by joining together a first and a second offtake conduit which derive, throuh a secondarv feeding conduit. from the same primary feeding conduit.

   23. An apparatus according to any one of claims 16-20 characterized in that it comprises two primary feeding conduits extending, at least in their end portions, along the axis of the mould and on both sides of the plane of mirror image symmetry of the cavities which define the sidewalls of the tyre, and that each combined flow is obtained hv joining together a first offtake conduit derived, through a secondary feeding conduit. from one of the primary feeding conduits, and a second offtake conduit derived. through a secondary feeding conduit. from the other primary feeding conduit.

   24. An apparatus according to any one of claims 16-20. characterized in that it comprises two primary feeding conduits, each of which feeds. through a plurality of offtake conduits. combined conduits and injection conduits. one half of the injection openings of each cavitv of the mould.

   '5. An apparatus according to claim 24 wherein the offtake conduits and the combined conduits extend along their axes which are inclined relative to the median plane of the mould.

   26. An apparatus for the injection moulding of pneumatic tyres from rubber based compounds. substantially as described hereinabove with reference to Figures 1. ' and 3. Figures 1. 2 and 4. Figures 6. 7 nd 7A or Figures X and 9 of the accompanying drawings.