CA1153521A - Method for the production of a reinforced endless toothed belt of synthetic plastics material having a minus tolerance of the belt circumferential length - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

The method for the production of an endless reinforced toothed belt of synthetic plastics material, the circumferential length in the untensioned condition is to have a predetermined minus tolerance in relation to an operationally tensioned intended circumference having the exact tooth pitch, firstly produces on a moulding wheel and a tensioner wheel a helically wound wire coil with fixed wire ends, the moulding wheel and tensioner wheel hav-ing an interaxial distance at which the wire coil has the minus tolerance from the intended circumference. Then the wound wire coil is tensioned with elastic stretching of the wire turns and enlarged to the intended circumference by enlargement of the interaxial distance to the intended distance. Then with the mould-ing wheel and a moulding belt a closed mould cavity is formed and by injection of synthetic plastics material into the mould cavity beginning a synthetic plastics strand of toothed-belt form is produced into which the wire coil is embedded in the mould cavity.
With one revolution of the wire coil the synthetic plastics strand issuing from the mould cavity end is conducted back around the tensioner wheel into the mould cavity beginning and in the mould cavity the beginning of the synthetic plastics strand is cast with its end. Next the intended distance is shortened again and the finished reinforced toothed belt is removed from the moulding wheel and tensioner wheel, the elastically stretched wire coil relaxing and contracting the finished toothed belt to the belt circumferential length with the minus tolerance from the intended circumference.

Description

1153S2~

The present invention relates to a method for the pro-duction of an endless toothed belt of synthetic plastics material or the like extrudable material, reinforced by a wire insert extending in the circumferential direction ofthe belt, with a minus tolerance of the belt circumferential length when the toothed ens~0~ d belt is in the _trctchcd condition.
Endless synthetic plastics toothed belts may have dif-ferent circumferential lengths and contain a reinforcing insert in the form of an embedded wire coil extending uninterrup-tedly around in the circumferential direction can be produced with the method disclosed in German Patent Specification No. 2,526,691.
The apparatus for this method comprises a moulding wheel and a tensioner wheel, both of which have a circumference profiled in the manner of gear wheels. The distance between the moulding wheel axis and the tensioner wheel axis is variable so that the circumferential length of the toothed belt to be produced can be varied by even multiples of its tootll pitch. The moulding wheel is surrounded over a part of its circumference of gear wheel profile by a covering which over this circumferential part, together with the mo~ldiny wheel, forms an arcuate mould cavity having a closed side edge and an open side edge. A synthetic plastics material and a reinforcing wire are introduced simul-taneously into the commencement of the mould cavity at its closed side edge, in order to form in the mould cavity a narrower synthetic plastics strand of toothed belt type with embedded reinforcing wire. The consolidated strand issuing from the end of the mould cavity is conducted around the tensioner wheel and reintroduced into the mould cavity with lateral offsetting beside the point of introduction of synthetic plastics material and reinforcing wire. By continuous introduction of synthetic plas-tics material and reinforcing wire into the mould cavity and con-tinuing conducting of the formed reinforced strand around the ~53~iZl moulding wlleel and tensioner wheel, an inwardly toothed flexible hose with embedded wire coil is formed from the turns of the strand fused with one another in the mould cavity. The flexible hose closes the open lateral edge of the mould cavity and issues from the mould cavity continuously at this lateral edge. Toothed belts with the desired belt width are cut from the hose. The shaping of the synthetic plastics toothed belt in the form of the hose thus takes place together and simultaneously with the wind-ing of the reinforcing wire on moulding wheel and tensioner wheel, 0 that is to say simultaneously with the formation of the wire coil.
The toothing of the moulding wheel shapes the desired tooth pro-file of the toothed belt to be produced and has a tooth pitch which corresponds to the intended tooth pitch of the finished toothed belt. ~ith regard to this intended tooth pitch, in the production of an endless toothed belt running around the moulding wheel and tensioner wheel, the injection operation and the shap-ing of the synthetic plastics strand must ta~e place with an intended distance between moulding wheel axis and tensioner wheel axis which depends upon the tooth pitch to be produced. The toothed belt which can be produced with this method consequently in the finished, untensioned condition possess the intended tooth pitch necessary for operational co-operation with toothed wheels and a circumferential length of the reinforcing insert which cor-responds to the circumferential length of the wire coil determined and fixed in the winding of the reinforcing wire and simultaneous injection of the toothed synthetic p]astics strand by the intended interaxial distance of moulding wheel and tensioner wheel.
However, in practice, a toothed belt in operation with toothed wheels does not run untensioned, but must have a specific belt tension. By reason of the belt tension the reinforcing insert of the toothed belt stretches elastically and increases its circumference. This again means that the tooth pitch of the 1153SZ~

toothed belt becomes greater than the or.iginal intended tooth pitch present in the untensioned belt condition, with which the toothed belt can be produced only in the known method.
Moreover the toothed belt should possess the desired belt ten-sion and mesh satisfactorily with the intended tooth pitch with toothed wheels, even when in practice a plus tolerance or a minus tolerance is used in the interaxial distance of the toothed wheels and correspondingly the requisite circum-ferenti.al length of the toothed belt and of its reinforcing insert differs from that circumferential length which was de-termined by the intended interaxial distance bet~een the mould-ing wheel and the tensioner wheel in the production of the toothed belt. This intended distance in this method, in view of the intended tooth pitch to be produced, cannot be increas-ed or reduced by fractions of the intended tooth pitch.
Thus the problem exists of producing an endless rein-forced toothed belt so that in the unstressed belt the rein-forcing insert lying in the neutral belt cross-sectional plane has a predetermined minus tolerance in the circumferential length and the tooth pitch is smaller than the intended pitch, so that in the subsequent operationally stressed condition, stretched elastically by the minus tolerance, the toothed belt possesses both the desired belt tension and the necessary in-tended tooth pitch.
According to the present invention there is provided a method of producing an endless toothed belt which is made of synthetic plastics material or similar extrudable material and is reinforced by a wire insert which extends in the cir-cumferential direction of said belt and exists with a minus tolerance of the belt circumferential len~th when said belt is in the unstretched state, sai.d method co~prising the steps of: providing a molding wheel, the circumference of which is 1~53SZ~
provided with an annular depression which is profiled in a gear wheel manner and corresponds in cross section to the cross section of the belt to ~e produced, covering means associated with said molding wheel and being placeable upon a portion of the circumference thereof for closing said depression in the region of this portion to form an arcuate mold cavity; provid-ing a tensioning wheel locatable at a variable distance from said molding wheel and having a circumference profiled in a gear wheel manner; providing a wire coil helically wound from a reinforcing wire; placing said wire coil on said molding wheel and said tensioning wheel after setting the interaxial distance between said molding wheel and said tensioning wheel below the intended distance in such a way that the circumfer-ential length of said wire coil is smaller by a predetermined minus tolerance than the intended circumferential length of said wire insert in the belt to be produced when the latter is in its tensioned state; fixing said wire coil in position to prevent receding of any portion thereof in the circumfer-ential direction of said coil; increasing the interaxial dis-tance between said molding wheel and said tensioning wheelto the intended distance to increase the circumference of said wire coil, accompanied by elastic stretching of the turns of said wire coil, to the intended circumferential length to thus place said wire coil in a tensioned state; closing said depression with said covering means to form said mold cavity;
turning said wire coil through one revolution by rotating said molding wheel and said tensioning wheel; introducing synthetic plastics material or similar extrudable material into the beginning of said mold cavity throughout said wire coil revolu-3Q tion to form a material strand; fusing the beginning of saidmaterial strand with the end thereof as said strand ~eginning starts to reenter the beg~nning of said mold cavity at the , ~

~lS35Zl conclusion of said wire coil revolution; hardening said mater-ial; shortening the interaxial distance between said molding wheel and said tensioning wEleel to relax the embedding rein-forcing insert and thereby contract the finished endless toothed ~elt; and axially stripping said endless belt from said molding wheel and said tensioning wheel.
Thus the method of the present invention includes the following steps:
Firstly a wire coil wound helically from a reinforc-ing wire is applied to a moulding wheel, the circumferenceof which - 4a 11535~1 is formed with an annular depression profiled in a gear wheel manner, corresponding in cross-section to the toothed belt cross-section to be produced, with which there is associated a cover-ing which can he laid upon a part of the mould wheel circumference and in this region closes the depression to form an arcuate mould cavity, and upon a tensioner wheel of variable distance from the moulding wheel, with circumference profiled in gear wheel manner, the interaxial distance of moulding wheel and tensioner wheel being set below the intended distance in such a way that the cir-cumferential length of the wire coil is smaller by a predeter-mined minus tolerance than the intended circumferential length of the wire insert in the toothed belt to be produced, when in its tensioned condition.
After fixing of the two wire ends of the wire coil against receding in their circumferential direction, then the circumference of the wire coil is increased, with elastic stretch-ing of the turns of the wi.re coil, to the intended circumferen-tial length by increasing of the interaxial distance of moulding wheel and tensioner wheel to the intended distance.
With the wire coil in the tensioned condition and the mould cavity closed, the wire coil is turned through one revolu-tion by rotation of moulding wheel and tensioner wheel and from the beginning to the end of this revolution the synthetic plastics material is introduced into the beginning of the mould cavity and the beginning of the synthetic plastics strand re-entering the mould cavity commencement is fused with its end and then the dis-tance between mould wheel and tensioner wheel is shortened and the finished endless toothed belt, contracting by relaxation of the embedded reinforcing insert, is stripped axially from the mould wheel and tensioner wheel.
Thus in the method according to the invention there occurs initially only the formation of the complete wire coil :llS3SZ~

around moulding wheel and tensioner wheel wi-th an interaxial distance of moulding wheel and tensioner wheel falliny short by a prede-termined amount of the intended distance. The injection operation, that is the actual production and shaping of the synthetic plastics toothed belt takes place only after subsequent tensioning of the wire coil to the zero tolerance in the circum-ferential length, with the wire coil in an initially -tensioned condition corresponding to the subsequent desired operational belt tension, and with the intended interaxial distance between moulding wheel and tensioner wheel necessary for the intended tooth pitch to be produced. Since the wire coil is initially wound with normal slackness with the predetermined minus toler-ance in the circumferential length and then the finally would wire coil is tensioned as a whole, a uniform tension occurs in all wire turns of the wire coil. After termination of the production of the belt the initially tensioned wire coil goes back into the untensioned condition and in doing so contracts the synthetic plastics material. In the untensioned condition then the finished toothed belt has a neutral circumferential lenyth which iS less by the minus tolerance predetermined in production than the intended circumferential length, and also a tooth pitch falling short of the intended tooth pitch. When the toothed belt is tensioned in operation and stretched by the minus tolerance to the intended circumferential length, the toothed belt has both the desired operational belt tension and again the intended tooth pitch necessary fol exact meshing with gear wheels.
The wire coil can be prefabricated with the minus tolerance in the circumferential length on a separate winding reel and then laid upon moulding wheel and tensioner wheel with the aid of auxiliary clips which hold the turns of the wire coil together in the distance as wound. ln this case the two ends of the wire coil can be secured detachably on the winding reel llS3521 in a web-type lock which is transferred together with the wire coil on to the moulding wheel and inserted into a tooth groove of the moulding wheel in order to hold the wire ends fast in the elastic tensioning of the wire coil. This lock, insertable into a tooth groove of the moulding wheel, can then at the same time be formed as filler piece in such a way that it co-operates in sealing manner with the moulding belt and closes the mould cavity in sealing manner at the beginning of the injection operation in the direction of rotation of the moulding wheel. After the emer-gence of the lock from the mould cavity the end of the latter isclosed by the solidified synthetic plastics materi`al and the lock can be removed from the wire coil. The separate prefabrication of the wire coil makes it possible that during the further process-ing of a wire coil transferred on to moulding wheel and tensioner wheel the next wire coil can already be prefabricated on thé
winding reel for the next toothed belt to be produced. Thè wire coil can also be wound directly on moulding wheel and tensioner wheel, as will be described below by reference to the illustrated example of embodiment. Here the procedure in accordance with the invention, using a mould cavity having an open lateral edge, also permits of intermittently producing a hose from which toothed belts can be cut with the desired belt width. In this case for example the initial section of a wire coil can be wound and the initial section of the hose can be injected with this initial section of the wire coil in the tensioned condition. Then with the interaxial distance of moulding wheel and tensioner wheel shortened again, whereby the initial section of the hose is firstly slackened, the next section of the wire coil is wound, the initial section of the hose travelling out of the open side edge of the mould cavity. The wound next section of the wire coil is then tensioned, the edye of the initial section of the hose adjoining the next section of the wire coil likewise being tensioned again, 11535;~1 and during the surrounding of the next wire coil sectlon by injection this initial section edge closes the open side edge of the mould cavity and at the same time is fused together with the next section of the hose.
The present invention will be further illustrated diagrammatically by way of the accompanying drawings, wherein:
Figure l is a lateral elevation of an apparatus for carrying out the method according to one embodiment of the present invention;
Figure 2 is a plan view of a part of the apparatus according to Figure l;
Figures 3 to 5 show the apparatus according to Figure l in different stages of the toothed belt shaping, from the beginning to the end of the injection operation.
Thè apparatus comprises a moulding wheel l and a ten-sioner wheel 2. According to the belt cross-section and the tooth profile of the toothed belt to be produced the moulding wheel 1 possesses an annular depression with teeth 4 and tooth gaps 5 between lateral shoulders 3. The tensioner wheel 2 also possesses corresponding teeth 6. On the tip surfaces of the teeth 4 of the moulding wheel l there are arranqed narrow flange-like winding noses 7 which support the reinforcing insert of the toothed belt, formed by a wire coil 12, in its production at a specific radial distance from the tip surfaces of the teeth 4, on the one hand so that the turns of the wire coil can be enveloped completely with synthetic plastics material subsequently, except for the nearly punctiform support point, and on the other hand so that the - 7a -~LlS3S2~
reinforcing insert lies exactly in the neutral cross-section plane of the toothed belt to be produced. The teeth 6 of the tensioner wheel 2 are expediently also provided with similar winding noses 7. So that the turns of the wire coil 12 have uniform distances from one another and do not shift laterally in the injection of the toothed belt, the winding noses 7 are provided with notches ~ (Figure 2), into which the turns of the wire coil place themselves. The annular depression of the mould-ing wheel 1 is closable to form an arcuate mould cavity by a covering co-operating with a part of the circumference of the moulding wheel. This covering consists of an endless moulding belt 10 conducted over rollers 9, which belt can be laid in seal-ing manner upon the shoulders 3 of the moulding wheel 1 and lifted away from the moulding wheel 1. By means of a heating and cool-lng apparatus 11 the mould cavity can be heated at its initial region and cooled at its end region to promote the synthetic plastics injection operation. The interaxial distance between moulding wheel 1 and tensioner wheel 2 is variable so that end-less toothed belts can be produced with difference desired cir-cumferential lengths.
Firstly the wire coil 12 is formed on the mouldingwheel 1 and the tensioner wheel 2 by normal slack winding o-E a reinforcing wire. The interaxial distance of moulding wheel 1 and tensioner wheel 2, which must have the intended value B for the synthetic plastics injection operation with regard to the intended tooth pitch to be produced (Figure 1), is here reduced to the distance A in such a way that in winding the wire coil 12 receives a circumference which is less by a predetermined minus tolerance than the intended circumference of the wire insert of coil form in the toothed belt to be produced when the latter is tensioned and stretched to the desired operational belt tension.
In order to fix the ends of the wire coil against receding in the l~S3S;~
circumferential direction of the wire coil when the wire coil is tensioned in the course of the toothed belt production according to the invention, by way of example the wire ends can be connected with the adjacent turn of the wire coil by solder joints 13 and 14 (Figure 2). The production of the wire coil 12 with the inter-axial distance A can then take place as follows. All notches 8 of the winding noses 7 lie on circles, as may be seen from Figure

2. A reinforcing wire is fed to the moulding wheel 1 so that it always runs beside the right moulding wheel shoulder 3 in Figure 2 into the first circle of notches. The beginning of the wire is firstly brought back, after conducting around the tensioner wheel 2, to the second circle of notches and connected by the first solder joint 13 with the wire lying in the first circle of notches.
Then the moulding wheel 1 and tensioner wheel 2 are rotated, whereby the wire commencement held fast by the first solder joint 13 at the interval of the notch circles runs of its own accord into the third and further notch circles until the wire commence-ment arrives for example in the penultimate notch circle beside the left moulding wheel shoulder 3 in Figure 2. The wire end of the wound wire coil 12 is then connected by the final solder joint 14 with the adjacent wire turn. In place of soldering of the wire ends to the coil other suitable measures can be applied to prevent yielding of the coil ends in the coil circumferential direction in the tensioning of the wound wire coil. For lateral guidance of the wire coil turns on the winding noses 7 in place of the notches 8 a comb-type guide piece can be provided which is arranged on the side co-operating with the moulding wheel of a nozzle mouthpiece of a synthetic plastics extruder which is to be connected to the beginning of the mould cavity.
The wire coil 12 wound with the minus tolerance in cir-cumferential length is then -tensioned by enlargement of the inter-axial distance of moulding wheel 1 and tensioner wheel 2 to the 1153SZl intended distance B, wi~h elastic stretching of the turns, and enlarged in circumference to the intended circumference which the reinforcing insert has in the finished toothed belt at the desired operational belt tension. In this controllahle tensioning of the entire wire coil after the winding operation a uniform tension occurs in all turns. With the wire coil 12 in this condition tensioned to the zero tolerance in circumferential length now the mould cavity is closed by approach of the moulding belt 10 to the moulding wheel 1 (Figure 3). Furthermore, a mouthpiece 15 of an extruder, co-operating in sealing manner with the mould-ing wheel and the moulding belt, is attached to the beginning of the mould cavity and now the injection of the synthetic plastics material into the beginning of the mould cavity is commenced. So that the mould cavity is closed in the direction of rotation of the moulding wheel at the beginning of the injection operation and an injection pressure necessary for the complete filling of the mould cavity can be applied, before the windiny of the wire coil around moulding wheel and tensioner wheel a filler piece 16 was insertPd into a tooth gap S of the moulding wheel 1, which filler piece protrudes from the tooth gap and co-operates in sealing manner with the moulding belt 10 and possesses slottings 17 (Figure 2) into which the turns of the wire coil fit. This filler piece 16 can also be formed as a lock in which the ends of the wire coil are held fast by means of clamping screws or the like, for example if the wire coil is prefabricated on a separate winding reel and laid from this together with the lock upon the moulding wheel and the tensioner wheel. At the beginning of the injection operation the plasticised synthetic plastics material is introduced into the cavity between the nozzle mouthpiece 15 and the filler piece 16. The injection operation and the shaping of the toothed belt take place with the intended distance B
between moulding wheel axis and tensioner wheel axis necessary 11535Zl with regard to the intended tooth pitch of -the toothed belt to be produced. During the rotation of moulding wheel ancl tensioner wheel the syntlletic plastics ma-terial introduced in the liquid state consoliciates and the end of the mould cavity is closed by the issuing strand of synthetic plastics material. The wire commencement and the wire end of the wire coil are anchored in the consolidated synthetic plastics strand, so that after the emer-gence from the mould cavity (~igure 4) the filler piece 16 can be removed from the wire coil 12. The commencement of the syn-thetic plastics strand or of the moulded toothed belt is conductedaround the tensioner wheel 2 and drawn by the wire coil 12 into the commencement of the mould cavity so that the co~lmencement and the end of the synthetic plastics strand are cast to one another and the shaplng of the endless toothed belt is terminated on rotation of the wire coil 12 by one revolution. During this one revolution the wire coil shifts axially on the moulding wheel and the tensioner wheel by one turn pitch of the wire coil. This turn pitch, that is the distance between two turns of the wire coil, as a rule in reinforced toothed belts is so small, for example of the order of magnitude of about 1 mm, that the lateral shift of the commencement of the synthetic plastics strand oceurring by only this slight amount is of no importance and the commencement of the synthetic plasties strand can readily be reintroduced or drawn into the commencement of the mould cavity for the casting with the end of the synthetic plastics strand. In order to facili-tate the fusing together of the beginning and end of the synthetic plastics strand in the beginning of the mould cavity, the beginning of the synthetic plastics strand can be pre-heated and softened shortly before its re-entry into the mould cavity by suitable 3U heater devices, whereby the reintroduction of the beginning of the synthetic plastics strand, laterally staggered by one turn pitch into the mould cavity is also facilitated. The nozzle mouthpiece 15 possesses an u~per part 18 (Figure 5) which co-operates in sealing manner with the moulding belt 10, and a lower part 19 which closes that clear cross-section of the mould cavity commencement which corresponds to the cross-section of the bac~
of the toothed belt. In the rotation of the moulding wheel 1 the lower part 19 always co-operates in sealing manner with at least one moulding wheel tooth 4 so that no synthetic plastics material can escape backwards through the moulding wheel tooth gaps 5.
This lower part 19 of the nozzle mouthpiece 15 is made retractable and the injection passage of the nozzle mouthpiece 15, conducted through the upper part 18 and the lower part 19, is preferably blocked by retraction of this lower part 19, in order to block off further inflow of synthetic plastics material into the beginning of the mould cavity when the lower part 19 is in the retracted position. Shortly before the re-introduction of the commencement of the synthetic plastics strand into the mould cavity the lower part 19 of tlle nozzle mouthpiece 15 is retracted so that the belt back of the commencement of the synthetic plas-tics strand can be introduced into the beginning of the mould ~0 cavity. After the entry of the beginning of the synthetic plas-tics strand into the mould cavity firstly the beginning of the strand is seamlessly fused with the end of the strand by heating by means of the device 11 and then the connection is consolidated by cooling by means of tlle device 11. Next the distance between between moulding wheel axis and tensioner wheel axis is shortened and the finished endless toothed belt whicll then contracts by relaxation of the reinforcing insert 12 to the belt circumferen-tial length with the minus tolerance, is taken from moulaing wheel and tensioner wheel. The edges of the finished toothed belt can then be finished by clean cutting away, for example also in order to remove the initial solder joint 13 and final solder joint 1~.
The finishea toothed belt contains a reinforcing insert of coil 11535Zl form uninterrupted in the circumferential direction and terminat~
ing at the two belt edges. R toothed belt ring with narrower desired belt width can be cu-t off by a cut in the circumferential direction which severs the wire coil at one point.

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Claims (3)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE

PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method of producing an endless toothed belt which is made of synthetic plastics material or similar extrud-able material and is reinforced by a wire insert which extends in the circumferential direction of said belt and exists with a minus tolerance of the belt circumferential length when said belt is in the unstretched state, said method comprising the steps of: providing a molding wheel, the circumference of which is provided with an annular depression which is profiled in a gear wheel manner and corresponds in cross section to the cross section of the belt to be produced, covering means associated with said molding wheel and being placeable upon a portion of the circumference thereof for closing said depres-sion in the region of this portion to form an arcuate mold cavity; providing a tensioning wheel locatable at a variable distance from said molding wheel and having a circumference profiled in a gear wheel manner; providing a wire coil helical-ly wound from a reinforcing wire; placing said wire coil on said molding wheel and said tensioning wheel after setting the interaxial distance between said molding wheel and said ten-sioning wheel below the intended distance in such a way that the circumferential length of said wire coil is smaller by a predetermined minus tolerance than the intended circumferen-tial length of said wire insert in the belt to be produced when the latter is in its tensioned state; fixing said wire coil in position to prevent receding of any portion thereof in the circumferential direction of said coil; increasing the interaxial distance between said molding wheel and said ten-sioning wheel to the intended distance to increase the circum-ference of said wire coil, accompanied by elastic stretching of the turns of said wire coil, to the intended circumferential length to thus place said wire coil in a tensioned state;
closing said depression with said covering means to form said mold cavity; turning said wire coil through one revolution by rotating said molding wheel and said tensioning wheel; intro-ducing synthetic plastics material or similar extrudable mater-ial into the beginning of said mold cavity throughout said wire coil revolution to form a material strand; fusing the beginning of said material strand with the end thereof as said strand beginning starts to reenter the beginning of said mold cavity at the conclusion of said wire coil revolution; harden-ing said material; shortening the interaxial distance between said molding wheel and said tensioning wheel to relax the embedding reinforcing insert and thereby contract the finished endless toothed belt; and axially stripping said endless belt from said molding wheel and said tensioning wheel.

2. A method according to claim 1, which includes the steps of: prewinding said wire coil, with said minus tol-erance in the circumferential length thereof, on a winding reel which can provide different winding circumferences; fix-ing the length of said wire coil with at least one detachable lock which corresponds in cross section and length to a tooth of the toothed belt to be produced, and is removable from said reel; removing said wire coil and lock from said reel;
placing said wire coil on said molding wheel and said tension-ing wheel by inserting said lock into a gap between teeth on the circumference of said molding wheel at the beginning of said mold cavity prior to said step of increasing said inter-axial distance; after said closing step, sealingly connecting an extrusion nozzle at the beginning of said mold cavity for introducing said material thereto between said nozzle and said lock; and after starting said introducing step, and prior to completion of said wire coil revolution, removing said lock from said wire coil.

3. A method according to claim 2, which includes the steps of providing an extruder with a mouthpiece, provid-ing said mouthpiece with a portion which during said closing step sealingly cooperates with said covering means and said molding wheel at the beginning of said mold cavity, after com-pletion of said introduction step and prior to said fusing step, bringing the beginning of said material strand to said mouthpiece, retracting that portion of said mouthpiece which cooperates with said molding wheel, opening that cross section-al part of said mold cavity which corresponds to the cross section of the back of the toothed belt to be produced, and introducing the beginning of said material strand into said mold cavity in such a way that its back surface sealingly co-operates with said retracted mouthpiece portion.