CA1135650A

CA1135650A - Conveyor belting incorporating aromatic polyamide traction bearers, and a method for producing the same

Info

Publication number: CA1135650A
Application number: CA000350686A
Authority: CA
Inventors: Heinz Gerdes; Hugo Heeke; Karl-Gunther Blattermann
Original assignee: Conrad Scholtz AG
Current assignee: Conrad Scholtz AG
Priority date: 1979-05-02
Filing date: 1980-04-25
Publication date: 1982-11-16
Also published as: GB2048773A; GB2048773B; JPS55156111A; DE2917756A1

Abstract

ABSTRACT OF THE DISCLOSURE

The invention relates to a conveyor belt incorporating longitudinally extending traction bearers made of an aromatic polyamide, and has for its object to reduce the risk of damaging the bearers by accid-ental incision when, during splicing, the elastomeric material of the belt is cut to expose the bearers.
In one embodiment, the bearers are sheathed in a material which is a different colour to that of the basic material of the belt, thus rendering the bearers readily indentifiable. Additionally or alter-natively, the bearers may be protected by incision-resistant elongate elements, for example metal cables, wound around and/or disposed between and extending parallel to, the bearers.

Description

~1356SO

BACKG~OUND OF THE INVENTION
_ The invention relates to conveyor belting o~ elas-tomeric material comprising several separate longitudinally extending traction bearers or element3 in the ~orm of ropes, cables or other tendons o~ aromatic polyamide, the latter being referred to in abbreviated ~orm as aramide.
~ he st~ucture of a conveyor belt of this type is analogous to that of a conventional steel cable con-veyor belt, wherein the separate traction bearers are normally arranged in a single layer in the neutral por-tion or plane o~ the conveyor belt. ~he difference ismerely that the traction bearers are not made to steel but are specifically o~ aramide. As is known, thi9 is a plastics material which, like steel, possesses relat-ively high strength and low extensibility, but which may be damaged very easily by incisions.
This susceptibility to incisions raises problems during preparation o~ a conventional belt joint in which the ends o~ the traction bearers are o~erlapped in steps, i.e. interleaved, whereafter they are vulcanised in the belt again, e.g. as apparent ~rom German Standard Speci~ication DI~ 229131. During this preparation, the individual traction bearers must be uncovered along a specific length of the conveyor belt, and this is e~fec-ted by manually cutting down into, and removing, the surrounding elastomeric material, which is usually a rubber, by mean~ o~ a cu~ting tool. Since steel cables are practioally incision-proo~, thi~ uncovering operation doe~ not give rise to problems when applied to conventional steel cable conveyor belts.
~owever, in the case o~ conveyor belts incorporating ~135650 aramide traction bearers or ropes, the problem of achieving an appropriate belt joint arises because of the said susceptibility of aramide to incision. The application of the known essentially proven joint tends to be outweighed, in the case of aramide traction bearers, by the considerable risk that these bearers may accidentally be nicked whilst being uncovered during preparation of the joint section, and may thereby be permanently damaged to an extent that the tensile strength of the finished joint is inadequate.
The invention is based on the problem of devising a conveyor belt of the type incorporating aramide traction bearers, by means of which it is possible to achieve a satisfactory belt joint in a comparatively uncomplicated manner.
SUMMARY OF THE INVENTION
The subject invention is a conveyor belt of elasto-meric material, including separate traction bearers extending generally longitudinally of the belt and comprising ropes or cables of an aromatic polyamide (aramide) and means extending along and embedded within the belt in association with the traction bearers, arranged and adapted to reduce the risk of accidental incision of the traction bearers during incision of the elastomeric material of the belt to expose the traction bearers preparatory to splicing of the belting. The means extending along and embedded within the belt in association with the traction bearers comprises protective elements of a material resistant to cutting, extending along the outside of each traction bearer and leaving part of the outside of each traction bearer free for direct bonding of the elastomeric material with the traction bearer.

3~

Advantageously, in a conveyor belt of the subject invention, each aramide traction bearer is individually sheathed in a protective element in the form of cancellated or open-work structure of incision-proof or-resistant material, e.g. polyester,or preferably of metal.
Alternatively, at least one flexible longitudinal element of incision-proof or-resistant material may be instal-led beside and parallel to each aramide traction bearer.

A conveyor belt incorporating aramide traction bearers and embodying the present invention enables the tried and tested belt joint, comprising traction bearers laid side-by-side in a stepped or interleaved manner and re-vul-canised into the belt, to be applied to a conveyor belt of this type without any substantial risk of damage to the traction bearers during preparation of the joint portion.
In the case of a conveyor belt in which at least one flexible generally longitudinal protective element is arranged beside and generally parallel to each traction bearer, this reduction of the risk of damage to the traction bearers may be achieved by a belt construction wherein the traction bearers and the generally parallel longitudinal elements are disposed generally in a common plane and are embedded in a core stratum of elastomeric material embedded in the elastomeric material of the belt, the core stratum having visual characteristics discernable from those of the elastomeric material of the belt.
The sheathing of the traction bearers in a particular elastomer or plastics material may, however, be troublesome from the point of view of its production technique. Care must be taken, moreover, to ensure a satisfactory bond between the sheathing elastomer or plastics material and the elastomeric material of the actual conveyor belt. These limitations are avoided inthe case of the conveyor belt structure wherein each traction bearer is indivldually sheathed in a protective eler.~ent in the form of a cancellated structure. The preferably metallic cancellated or open-work structure mandatorily prevents damage to the traction bearers upon being cut out of the elastomeric material of the conveyor belt. This means that the known belt embodying the present invention, for example a conveyor belt having aramide traction bearers sheathed in metal cancellated structures, by the same technique and procedure as adopted for steel cable conveyor belts.
It is to be understood that the term "cancellated structure" used in the ensuing specification and appended claims is to be construed as encompassing apertured or open-work structures or the like which do not enclose the individual traction bearers over their entire area, but which have one or more interstices or openings uncovering the underlying traction bearer. These interstices or openings should, in practice, be sufficiently large to allow satisfactory penetration by the elastomeric material of the conveyor belt so that the latter material may form a direct bonded joint with the actual traction bearer-whilst not being so large as to leave wide areas of the traction bearer uncovered, in which the latter is exposed to the risk of damage by conventional cutting tools during preparation of the joint portion.

- ~
_ ~ _ The sheathing of the traction bearers in cancellated structures, for example metal structures, has the substantial additional advantage that the bond between the elastomeric material of the conveyor belt and the aramide traction bearers, which intrinsically is not particularly satisfactory, is improved suhstantially by the cancellated metal structures. The _ _ \
, - 4a -113~6~0 bond which is obtainable, e.g. between rubber and gal-vanised steel, is actually distinctly stronger than that between rubber and aramide, even if the latter is impregnated to promote adhesion. Galvanised steel is preferably employed as the metal for the cancellated structures, because its processing in conjunction with rubber or an analogous elastomeric material is satis.actorily controllable, particularly in respect of the bond to be obtained.
In a preferred embodiment of the invention, each cancellated structure comprises at least one elongate or longitudinal element, in the form of a wire, strand or the like, which is helically wound around, and extends longitudinally of, its associated traction bearer. The additional production cost for traction bearers wound in this manner is very low, because the helical winding may be applied simult-aneously with the actual production of the traction bearers, and by the same techniques used for this purpose. At the same time, the requirements regard-ing rubber penetration as well as protection against damage by incisions may be optimised by appropriate selection of the spacing, in the axial direction of the traction bearer or belt, between, i.e. the pitch of, the individual turns of the elongate element.
An embodiment in which the elongate elements wound around the rope-like traction bearers lie in the helically extending depressions between the strand~ of the traction bearer and partially project beyond the periphery of the traction bearer~ Preferably by half their diameter, proved to be particularly advan-tageous in th~s respect. In thi~ embodiment~ the elon-gate elements consequently have the same length and ~13S6SO

direction of twist as the externally situated strand~
of the rope constituting the traction bearer. The production of the sheathed traction bearer is thereby rendered particularly uncomplicated. Furthermore, because of their partial seating in the natural or inherent depressions of the actual traction bearer, the elongate elements adhere or locate particularly well relative to the same.
Another embodiment of a traction bearer wound with an elongate element makes allowances 7 to a special degree, for the different expansions of the materials of the elongate elements and of the aramide. In the embodiment, an elongate element, i.e. of steel, is helically wound around a rope-like aramide traction bearer with a lay or length of twist which is smaller i.e. a finer pitch, than that of the traction bearer.
Even though it is extremely small, the elongation of aramide material is nevertheless two or three times greater than that of steel. In the said embodiment, the steel elongate element has a greater structural elongation than the aramide rope because of the smaller length of twist (finer pitch) of the elongate element as compared to the actual aramide rope, thereby bal-ancing the lesser elongation of the material (steel) of the elongate element. This prevents overloading and damage to the elongate element upon tensioning the con-veyor belt, or when the belt is running around drums or rolls.
~o provide satisfactory access to the aramide of the tra~tion bearer for the elastomeric material of ~he conveyor belt, the unobstructed spacing, in the axial direction of the traction bearer or belt, between the turns of the elongate element advantageousl~
.:

~13565;U

corresponds approximately to its width in this axial direction, i.e. the diameter of the elongate element.
In an earlier mentioned aspect of the invention, the aramide traction bearers are protected against damage by incisions by means of the flexible elongate or longitudinal elements embedded in the elastomeric material of the conveyor belt so as to extend generally parallel to the traction bearers, said elements consisting, for example, of steel or polyester cords. Upon cutting or excising the aramide traction bearers from the elastomeric material, the cutting tool is guided along the incision-proof longitudinal elements, thereby preventing the tool from accidental cutting into the aramide traotion bearers. However, this protection is mainly effective only in the case of generally vertical cuts if,, to simplify matters, longitudinal elements are only installed which lie in the plane of the traction bearers, that is between the latter. In order to achieve protection in this case in respect of generally horizontal cuts, recourse may additionally be had to the aforementioned first aspect of the ihvention, i.e. the core stratum of the conveyor belt wherein the traction bearers are normally embedded, may be endowed with a colour differing from that of the two covering layers or strata of the conveyor belt.
Alternatively, a loose complementary protective layer comprising transversely extending elements may also be installed above and below the stratum of the traction bearers.
The incorporation of complementary longitudinal elements between the traction bearers in accordance with the aforementioned third aspect of the invention has .re ~13SFi~

the additional substantial advantage that the mutual spacing between the traction bearers in the transverse direction may be maintained much more precisely an~
evenly during production than without longitudinal elements. ~ateral "drifting" o~ the traction bearers during vulcanisation in the then softened elastomeric material is ef~ectively impossible, par-ticularly if so many longitudi~al elements are in-corporated that the gaps between the traction bearers are largely filled. In this case, it is even possible to produce the conveyor belt - deviating from the conventional production method which utilises traction individually applied to the traction bearers - on calendering machines as in the case of a fabric conveyor belt, i~ the traction bearers and longitudinal elements are held together by individual, mutually longitudinally spaced, transverse elements, which are interwoven with the traction bearers and the longitudinal elements. To this end, the longitudinal spacing and the sizes o~ the transver~e elements are such that they play a part during production only, whereas the properties o~ the finished conveyor belt remain largely unaffected.
The objective that they should no-t substantially alter the overall action of the conveyor belt ~uring operation also applies to the longitudinal elements.
Their diameter is consequently no greater than that required to assure the protective ~unction. In order that they are not subject to substantial tensile stre-sses, apart from the traction bearers, and cannotthereby be destroyed in certain circumstances, the longitudinal elements are appropriately embedded, largely free o~ initial stress, in the elastomeric 113565~

material of the conveyor belt. Alternately or additionally, the longitudinal elements may consist of a material, e.g.
polyester, of such nature that they have a higher degree of elongation than the aramide traction bearers.
An arrangement of the longitudinal elements in which they are, in each case, installed in pairs between adjacent traction bearers, proved to be particularly appropriate. In this case, each traction bearer is protected on either side by one longitudinal element against damage by incisions, and in addition, a satisfactory assurance against "drifting"
of the traction bearers during vulcanisation of the conveyor belt is also obtained.
If structure of the conveyor belt having flexible, longitudinal protective elements arranged beside and parallel to the traction bearers is produced in the manner of a conventional steel cable conveyor belt with individually tensioned traction bearers and if a grid, e.gO a guide comb, is used to establish a particular transverse position of the traction bearers, the longitudinal elements may advantageously also be incorporated in the belt structure by means of a grid or the like, the application of interwoven transverse elements then being superfluous.
BRIEF DESCRIPTION OF THE DRAWINGS
In order that the invention may be more readily understood, reference will now be made to the accompanying drawings which illustrate diagrammatically three embodiments of the invention. In the drawings:-Fig. 1 is a transverse cross-section through a first embodiment of conveyor belt having traction bearers of aramide;
Fig. 2 is a transverse cross-section, on an enlarged scale, through one of the traction bearers of the conveyor _ g _ ~

1135~5~

belt shown in ~igure l;
Fig. 3 is a side view o~ the traction bearer shown in Figure 2;
Fig. 4 i9 a side view o~ an alternative ~orm of traction bearer;
Fig. 5 is a fragmentary transverse cross-section through a second embodiment of conveyor belt; and ~ ig. 6 is a cross-section through a third embod-iment of conveyor belt.
The conveyor belt illustrated in Figure 1 basically - comprises several separate traction bearers 1, each extending ln the longitudinal direction of the conveyor belt. These traction bearers are mutually transversely ~paced in a common plane, and are embedded in a core stratum 2 of elastomeric material, namely a rubber in this embodiment. The core stratum 2 is enclosed or embedded in upper and lower covering layers 3 and 4 respectively, and edge portions 5, all formed integrally from a rubber having a different composition to that of the core stratum 2. The upper covering layer 3 is on the load-conveying or carrying side of the core stratum 2, whilst the lower covering layer 4 is on the running or supported side o~ the core stratum 2. The traction bearers 1 consist of ropes or cables of an aro-matic polyamide or aramide.
One of the mutually identical traction bearercables 1 is illustrated in detail in Figures 2 and 3.
It comprise~ seven primary strands or cables 11, each built up from a plurality of, for example seven~multi-filament or ~ thread secondary strands or cables, thefilaments or threads o~ which are of aramide. The pri-mary cables 11 are laid up with their particular direc-tion and length of twist depending on the required prop-erties of the traction bearer cable 1. In this embodi-ment, six outer cables are situated around the periphery 113S~

of the seventh cable a~ viewed in cros~-section. The traction bearer cable 1 consequen-tly has six generally wedge-~ection grooves or depres~ion~ 12 extending helically around its periphery between the six outer aramide cables 11. Six strands, for example multi-strand cables 16, of ~alvanised steel which, in the direction of the h~ical depres~ions, are wound helically and tightly around the actual traction bearer cable, are inserted in the depressions 12. The diameter of the steel cables 16 i~ smaller than that of the aramide cables 11 and is selected so that the steel cable~ 16 project by approximately one half of their diameter beyond the periphery of the actual traction bearer ca~æ 1, indicated by the dash-dotted line 1~.
~ igure 4 shows a traction bearer rope or cable 1' in an alternative embodiment. This cable 1', as in the previous embodiment, comprises seven twisted ara-mide ~trands or cables 11'. These are, however, wound in helical or coil form with a single steel ~trand or cable 16'. The steel cable 16' is applied tightly with a length of twist which is distinctly smaller (i.e. a finer pitch~ than that of the aramide cables 11', and is æo selected that the unobstructed spacing longitudinally of the cable 1' between the individual windings or turns of the steel cable 16' corresponds approximately to the diameter of the latter. The direction of twist of the steel cable 16' is opposite to that of the aramide cable 11'.
During manufacture of the conveyor belt, the rope or cable 1 or 1' already wound with a comple-mentary steel strand or cable 16 or ~' at the rope mill ia processed like a normal aramide traction bearer lackin~ ~teel strands, the rubber of the core stratum 2 113S6~0 being suitable for forming a direct bond, both with the aramide ~trands or cables ll over a part of their sur-faces, and with each steel cable 16 or 16' firmly seated thereon, If it is necessary to uncover a part of the length of the traction bearer cables 1 or 1' to join conveyor bel~ ends and thus complete the con-veyor belt, this may al~o be performed by mean~ of methods and tools common to steel cable conveyor belts, without risk of damage to the aramide~traction bearers.
This is because the latter bearers are effectively protected against damage due to incisions by the can-cellated structure which is proof against inci~ions and is formed by the steel cables 16 or 16' wound aro~nd said bearers.
The conveyor belt shown in ~igure 5 has a struc-ture analogous to that of Figure 1. Its traction beare-r rop~sor cables 1" are not,however~sheathed in a can-cellated metal structure, but, in each case, are individ-- ually sheathed by a layer 6 of an elastomer which adhere3 to the strands or cables 11' formed of aramide filament3 or threads, the layers 6 being in turn, surr-ounded by the rubber of the oore stratum 2". The elas-tomeric layer 6, applied for example by ~xtrusion, has a colour differing clearly from that of the other elas-tomeric material of the conveyor belt and, for example,may be produced in transparent form if the conveyor belt is made of a black rubber. Upon uncovering the traction bearer cables 1", the elastomeric layer 6 then provide~ an indication of the posi~ion of the cables 1" wi-thin the conveyor belt, with reference to which it i8 pos~ible to avoid damage by incisions to the traction bearer cables.
The conveyor belt shown in ~igure 6 is also constructed in an analogous manner to that of ~igure 1.

113S~

Its aramide traction bearer ropes or cables 21 are not, however, sheathed by longitudinal elements but are embedded direct in the core stratum 22 of the conveyor belt. To identify the plane in which the traction 5 bearer cables 21 are situated, the elastomeric material of the core stratum 22 has a colour clearly differing from that of the elastomeric material of the covering layers 23 and 24 and of the edg~ portions 25. Spaced from and parallel to the traction bearer cables 21 10 are flexible longitudinal elements in the form of steel cords 26 which are embedded in the core stratum 22. In this embodiment, two steel cords 26 are situated between each pair of adjacent traction bearer cable~ 21. The steel cords 26 are all identical to each other and have 15 a small diameter in relation to that of the traction bearer cables 21, for example, a diameter o~ lesæ than one half of that of the traction bearer cables. In contrast to the traction bearer cables, the steel cords 26 are embedded in the elastomeric material of the core 20 stratum 22 whilst being largely free of initial stress.
Transverse elements 27 consisting of polyamide threads or cables, arranged with a comparatively large mutual spacing in the longitudinal direction of the conveyor belt, intersect the traction bearer cables 21 25 and the steel cords 26 in the manner of a fabric weave.
The dimensioning o~ the transverse elements 27 is so selected that they merely assure mutual cohesion and mutual spacing of the traction bearer cables and steel cords during manufacture of the conveyor belt, but have 30 practically no e~ect on the properties of the ~inished conveyor belt.
If ~ertical cuts are made to uncover the aramide traction bearer cables 21 in preparation for a belt joint or splice~ the cutting tool may be guided along 35 the inci~ion-proof steel cords 26 and incisions into ~13~

the delicate aramide cables 21 may be prevented thereby.
So far as horizon-tally made cuts are concerned, the core stratum 22 identi~ied by its colour serves to locate or point-out the position of the delicate aramide cables 21, so that allowance for these may easily be made.
Instead of a special colouration for the core ~tratum 22, a complementary loose insert of incision-proo~ or-resistant material, ~or example in the form of a steel or polyester cord laid in a meandering or tortuous fashion, which serves to protect the aramide cables during horizontal cutting, may also be incor-porated above and below the traction bearer cable stratum in each case. This modification is not illustrated in the drawings.
The longitudinal element~ 26 may also be formed by polyester cords. ~ince these have a greater elon-gation than the aramide traction bearer cables or ropes, they may be processed with a particul~r initial stress during the production o~ the conveyor belt, which may simpl~y manufacture.
As already stated, the transverse elements 27 serve to simplify conveyor belt production, in as much as the traction bearer ropes or cables and the inter-posed elongate or longitudinal elements maybe processedjointly like Q ~abric insert. The transverse elements may, however, be omitted entirely. The proced~e followed in the case of a steel cable conveyor belt is then appropriately applied to the manu~acture of the conveyor belt, with the traction bearers being incorporated in the belt structure by means of a grid establishing their mutual transverse spacing. Precisely the same procedure is followed in respect of the longitudinal elements 26, these being also incorporated in the belt structure by means of a grid for preclse presetting of their positions in the transverse direction.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A conveyor belt of elastomeric material, including separate traction bearers extending generally longitudinally of the belt and comprising ropes or cables of an aromatic polyamide (aramide) and means extending along and embedded within the belt in association with the traction bearers, arranged and adapted to reduce the risk of accidental incision of the traction bearers during incision of the elastomeric material of the belt to expose the traction bearers prepara-tory to splicing of the belting, said means comprising pro-tective elements of a material resistant to cutting extending along the outside of each traction bearer and leaving part of the outside of each traction bearer free for direct bonding of the elastomeric material with the traction bearer.

2. A conveyor belt according to claim 1, wherein each traction bearer is individually sheathed in a protective element in the form of a cancellated structure (as herein described).

3. A conveyor belt according to claim 2, wherein each cancellated structure includes at least one generally longi-tudinal element in the form of a wire, a strand or like elongate element, which is wound generally helically around the traction bearer.

4. A conveyor belt according to claim 3, wherein the traction bearers are assembled from strands or cables, and the generally longitudinal elements wound around the traction bearers are situated in generally helically extending depres-sions formed between the assembled strands of the traction bearers and with a part of their diameter projecting beyond the periphery of the traction bearers.

5. A conveyor belt according to claim 3, wherein the traction bearers are assembled from strands or cables, and the generally longitudinal elements are wound around the traction bearers with a lay of length of twist which is smaller than that of the traction bearers.

6. A conveyor belt according to claim 5, wherein the longitudinal spacing between adjacent turns of each generally longitudinal element corresponds approximately to its cross-sectional width.

7. A conveyor belt according to claim 1, wherein at least one flexible generally longitudinal protective element is arranged beside and generally parallel to the traction bearer.

8. A conveyor belt according to claim 7, wherein the generally longitudinal elements are arranged in pairs between adjacent traction bearers.

9. A conveyor belt according to claim 8, wherein the generally longitudinal elements are embedded in the elasto-meric material of the conveyor belt whilst being largely unaffected by initial stress.

10. A conveyor belt according to claim 9, wherein the generally longitudinal elements have a greater elongation than the traction bearers.

11. A conveyor belt according to claim 7, wherein the traction bearers and said generally parallel longitudinal elements are disposed generally in a common plane and are embedded in a core stratum of elastomeric material embedded in the elastomeric material of the belt, the core stratum having visual characteristics discernable from those of the elastomeric material of the belt.

12. A conveyor belt according to claim 7, wherein the traction bearers and the generally longitudinal elements are held together by separate generally transverse elements which are mutually spaced apart in the longitudinal direction of the belt.

13. A conveyor belt according to claim 1, wherein the protective elements consist of metal.