CA1080927A

CA1080927A - Method of jointing textile belting or webbing

Info

Publication number: CA1080927A
Application number: CA273,168A
Authority: CA
Inventors: Christopher Cawthra; Richard K. Brooke
Original assignee: BBA Group Ltd
Current assignee: BBA Group Ltd
Priority date: 1976-03-04
Filing date: 1977-03-03
Publication date: 1980-07-08
Also published as: AU513754B2; FR2343167A1; DE2709553C3; ZA771185B; BE852067A; ES456555A1; AU2278677A; SE425024B; DE2709553B2; DE2709553A1; FR2343167B1; SE7702282L; NZ183457A; GB1560891A

Abstract

ABSTRACT OF THE DISCLOSURE
A method of joining textile belting or webbing is disclosed, which comprises coating two ends of the belting or webbing at ambient temperature with a castable liquid mixture which is heat curable to provide a polyurethane compound. The liquid mixture includes a component which is chemically blocked to eliminate the curing reaction at ambient temperature. The ends are brought into adjacent face-to-face relationship and the mixture thereon is heat cured to join the ends.

Description

The pre~ent invention relates to an improved method of jointing textile belting or webbing such as i~ manufactured by a weaving or other process from yarns of cotton or other fibres, such as hair, flax, rayon, or ~ynthetic fibres such as nylon or polye~ter, or combinations of two or more of these types of fibres.
The invention is particularly useful for joining belting and webbing made of multiple fabric such as that used in con-veyor and transmission belting especially where the belting 0 i9 used in locations having relatively high moisture contents.
Heretofore, several methods have been proposed for jointing textile b~lting and webbing, but in each case the resultant joint, or the method by which it was obtained, has inherent di~advantages. For example, it has been propo~ed to ~- 15 join the textile belting or webbing by using metal fasteners but it wa~ found that the tensile strength of the joint was -; ` far below that of the remainder of the belt or webbing, that is, not usually more than 50~O of the "specified tensile ~trength"
of the belt material. The specified tensile strength of the belt is found by measuring the tensile 3trength of a unit width -~ , (e.g. one inch) of the belt and multiplying it by the width of the belt. Thus, a predetermined "specified tensile strength"
may be obtained by using a belt of particular tensile strength per unit width and particular width, or by using a belt having a greater tensile strength per unit width and a ~maller width~
The normal tensile loading of textile belting or webbing ~; in service i~ usually only l~/o of the specified tensile strength, but ~hock loads can increase thi~ drastically and thereby break ~, , .

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the metal fastener~. A stronger belt joint was provided by stitching the ends together but this tended to make the belt joint too stiff.
An early improvement was proposed in our prior UoKo Patent Specification No. 705,303 which consisted of providing the respective ends of the belting or webbing with a complementary array of V-shaped notches extending across the full width of the belting or webbing, fitting the two ends together leaving a small gap between the edges of the complementary notches, then filling the gap with a suitable polyvinyl compound, such as polyvinyl chloride paste, and curing the compound at 160 C
~; for a few minuteq.
A further improved joint was proposed in our U~Ko Patent Specification No. 901,197 in which the polyvinyl compound was t; 15 replaced by a liquid castable polyurethane compound. Such a joint has a longex life than one of the known polyvinyl com-pounds, but disadvantages are that the polyurethane compound is sensitive to moisture so that the ends of the belting have ~ to be dried before joining.
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Thus, using this system, if the ends of the belt have a ¦~ moisture content of 5% (by weight), the joint will have a ~ tensile strength in the order of only 80% of the specified , ~ i . .
tensile strength. This figure is usually acceptable in ~-~ practice, but when the joint is made with the end~ of the belt '~ 25 having a moisture content o~ between 5% and 6% the tensile strength of the joint begins to drop off very sharply and at 15~o moisture content the strength of the joint may be only 10%
of the specified tensile Atrength. Moisture content is t~ - 3 -~'' ~' . .
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` determined in a standard way when testing, by weighing the belt as received, then heating the belt for three hours in an oven at 110C and re-weighing the belt. The moisture content is taken to be the percentage difference in weight~
Further disadvantages of the method described in UoKo SpeciEication No. 901,197 are that the polyurethane compound has to be mixed immediately prior to use because of its rela-tively short reaction time, and that the optimum physical properties of the compound are obtained by curing at a tempera--ture of loo& over an extended period of three hours.
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In some applications the long cure period required by the method described immediately above, and the nece~sity of having to dry the ends of the webbing or belting to avoid obtaining a : .
foamed polyurethane joint (of much weaker tensile strength) may be inconvenient, particularly in the case of joining a in the presence of moisture textile belt in situ/over one period of time when the total time taken to dry the belt end~ to a maximum of 5% moisture content, to prepare the ends for joining by notching,to prepare and cast the polyurethane compound and to cure the polymer, may be twelve hours. The drying of the belt ends is parti-cularly necessary where the belt is used as a conveyor in an ' underground location such as a coal mine where the ambient r moisture content i8 invariably relatively high and where the~
or one o~ the belt ends may well be lying in water. It should ; 25 be mentioned also that where the jointing i~ taki~g place underground as in a mine, any heat developed for drying the belt ends (and curing the joint) muat be obtained without aparka or ~aked flame~ being emitted. Although heating ' .

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apparatus must be used for curing the joint, such apparatus : q .
is invariably heavy and cumbersome because of the fire hazard restrictions placed on itland the need al~o to use the apparatus for drying the belt ends in situ do not make the method dis-'~ 5 closed in U.K. Specification No~ 901,197 attractive for jointing belting in mines where access to the belt ends is ; probably limited.
These potential difficulties were alleviated (assuming the belting wa~ not saturated or nearly saturated in water) by using a method of jointing the webbing described in our !'' U~Ko Patent Specification No. 1,079,136 in which the edges of ' the V-shaped notches were lined with a solid fu~ible poly-urethane, after which the ends of the belting were pushed together ` and heated under pressure to fuse the joint.
~i 15 The application of pre~sure is an es~ential part of the method described in our U.K. Specification No. 1,079,136, but it will be immediately recognised that the same disadvantage~
, ari e in providing and using cumbersome means for compressing the joint in underground locations, as in heating the belt ends and the joint.
:' From the above it may be seen that there are several problems associated with the use of polyurethane in joining ,'~ ; textile beltingtall of which are aggravated when the jointing i9 to take place underground, as in a mine namely, the time taken from beginning to end in joining the~belt ends, the ~; , risk of foaming and the necessity on occasion (and always with some ~ystems) to u~e pressure. ~he time taken to prepare the ~;' belt~ng by,notchin~ will be the same no matter what system is .,. , . . :
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u~ed, but the remaining time may be divided into two part~, that taken to dry the belt ends sufficiently to avoid excessive foaming as previously discussed, and that taken to cure the jointing material. The problem of extended cure time is associated with the necessity to avoid using a curing agent which is excessively reactive, in order to allow sufficient time before the compound sets (working life) after mixing to permit the compound to be applied to the belt ends. It is known that a longer working life usually means a longer cure . .
time to give optimum physical properties 90 that curing ha~
usually taken place in the pa~t over a period of three hours at 100C.
Under some circumstances it may be possible to reduce the cure time of the aforementioned polyurethane belt jointing ~ystem3 by increa~ing the curing temperature above the pre-ferred loo&, but there are limits on this brought about by the maximum temperature sustainable by the material of the belt carcass and the reduction in the physical properties o the joint~ Furthermore, there i~ a signlficant problem in increasing the curing ~emperature of the aforementioned poly-urethane belt jointing systems where the belt ends are moist in that it is known that isocyanates in any polyurethane system have a preferable reaction to moisture/water before reaction with amines, and that, from basic chemical kinetic~, the rate of chemical reaction increa~e~ with increa~ing temperature.
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The chemical reaction of the isocyanates with any water present will cau3e carbon dioxide to be given off to give a porous, in~erior joint and therefore polyurethane belt jointing ~ystems ii , ~ . , :, 6 $~

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involving a relatively high cure - ~ are generally avoided whenever moisture i9 involved. A comparatively high tempera-ture curing system for (inter alia) polyurethanes has been proposed in U.S. Patent Specification No. 3,755,261, but for the reasons given above, such a sy~tem is not a natural choice for joining wet belt ends.
It ls the main object of the present invention to provide a method of jointing textile belting or webbing which removes the need to reduce the moisture content of the belt ends to 5%
or less before they are joined and in which pressure is not an essential feature of the curing operation, and in the search for a jointing system which provided these objects, the system proposed in UOS. Patent Specification No. 3,755,261 was tried on wet belt ends and surprisingly a good quality joint was achieved.
Therefore, according to the present invention there is provided a method of jointing textile belting or webbing in ~itu with a polyurethane compound, which method consiAts of the steps of:
20 ~ complementarily shaping the two ends of the belting or webbing to be joined and fitting the compl~mentary ends together so as to leave a gap between the ends, before or after the ends are fitted together, applying a sufficient amount of a liquid castable mixture at substantially ambient temperature to fill said gap when the ends are fitted together~ the liquid castable mixture being heat curable to provide the polyurethane compound and comprising a polyisocyanate ; ~r a polyurethane prepolymer compri~ing a reaction product of .. ,,~ ;

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a polyisocyanate, and a polyactive hydrogen containing com-~- pound in which active hydrogen groups are chemically blocked ~,; at ambient temperature, ~: and heat curing the mixture in the gap at a temperature above ambient and at or above a temperature at which said polyactive hydrogen containing compound becomes unblocked, to join the complementarily shaped ends.
Further according to the present invention, there is provided textile bel~ing or webbing having a joint or joints produced by the method described in the immediately preceding paragraph.
?~ By the term "chemically blocked" we mean that the reactive ~; group or groups of the polyactive hydrogen containing compound are temporarily reacted with another chemical (blocking agent) to make them inert~ In this form the polyactive hydrogen con-~ tai~ing compound can be mixed with the polyisocyanate or t polyurethane prepolymer with no reaction occurring until the . , .
blocking agent i3 released by heating. The principal chemicals can then react to give the polyurethane compound with the 20 , released blocklng agent playing no part in the reaction.
Since there is no reaction in the liquid castable mixture at ambient temperature, the reactivity of the active hydrogen `~ containing compound used to cure the polyisocyanate or poly-! , , ' ~
urethane prepolymer can be very high (when not blocked) 80 that the reaction to cure the liquid castable mixture goes very quickly once the mixture is heated to overcome the chemical blocking. It is not fully understood why the method of the ; . .;
;~- pre~ent invention is able to give a good quality joint between ~J
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- moiqt belt ends, but it is believed that the reason may be that when the reactivity of the hydrogen containing compound i9 high, the curing reaction becomes so rapid that the curing mass becomes highly viscous in the early stages of cure 90 that any water vapour or carbon dioxide gas formed at the cure temperature cannot escape to ~orm bubbles or void~ in the joint. However, the advantage of the highly reactive hydrogen containing compound is double in that not only is drying of moi~t belt ends not required, but also the cure time is reduced.
Thus, for example, the time to cure the polyurethane joint formed by the method of the present invention may be a3 short 1.
. as fifteen minutes at 150& ~
; The use of the polyurethane compound in accordance with . the method of the present invention, which when applied to the belting or webbing at substantially ambient temperature, is'a substantially unreactive mixture of the components necessary 1 . to make the compound, provides the con~iderable advantage that ;.
the mixture may-be made up at a lower temperature than the ; .
~ ~ cure temperature and stored for long period~ at the lower , ;
temperature without curing, prior to use. Thi~ is particularly . -:
convenient with the method of the present invention, where the joint is made up in ~itu, for example on belting or webbing :~
on machiner.y at a relatively inaccessible location. Further-: ~ .
more, becau~e there is no significant reaction in the mixture . to forrn the polyurethane compound at ambient temperature, the .: adhesive should be of a con~istent viscosity which does not ;: change throughout the as~embly of the joint until curing is ~ initiated.

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The liquid castable mixture may comprise a mixture of one or more polyisocyanates with one or more polyactive hydrogen containing compounds and the or each polyisocyanate may be of a simple structure such as 2,4 tolylene , diisocyanate m-phenylene diisocyanate, 1,5 naphthalene diisocyanate or tri-phenyl methan triisocyanate. Alternatively, the polyisocyanate may be in the form of a compound of higher molecular weight containing free isocyanate groups such as the reaction product of a polytetramethylene glycol reacted with 2,4 ¦ tolylene diisocyanate in a molecular ratio of 1:2 or the reaction product of polyethylene adipate reacted with 2,4 tolylene diisocyanate in a molecular 10 ratio of 1.5:2.0 (such higher molecular weight compounds being generally known in the art, and herein referred to as, polyurethane prepolymers).
~- The term "active hydrogen" refers to hydrogen atoms which display activity according to the Zerewitinoff test as described by Kohler in the Journal of the American Chemical Society 49, 31~31 (1927). These hydrogen atoms react with isocyanate groupings allowing polymer chain formation or crosslinkingpoints. Chemieal blocking of the active hydrogen atoms prevents this reaction until the reactivity of the active hydrogen atoms is returned by removal of the chemical blocking by heating. The preferred example of a polyactive hydrogen eontaining compound which is chemically blocked to de-activate active hydrogen at relatively low temperatures, is a methylene dianiline complex with sodium chloride, which has a high order of reactivity when unblocked to ensure a fast eure.
The step of eomplementarily shaping the two ends of the belting or webbing may be earried into effeet by providing interengaging formations on the ends, sueh formations providing ~, ~, ~i1 -10-.

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t~ 0 ~:' a contact area for the jointing compound on each end of the ~ belting at least twice as great and preferably several times s~; greater than the minimum cross-sectional area of the belting :~t:~ at the ends to be joined. Preferably the formations comprise a c4mplementary array of V-shaped notches that extends across the full width o each of the two ends of the belting, the notches being arranged 90 that when the two ends are brought together they are disposed in inte~engaging relation, and the present invention will be described hereinafter with particular reference to such V-~haped notches.
The length of each notch (in the longitudinal direction of the belting or webbing) should be con~iderably greater than the width to achieve optimum results. The length and width of the notches may be ~aried, but the ratio of notch length to notch width should conveniently be within the range 2:1 to 30:1 inclusive, and preferably 2:1 to 20:1. It will be under-stood that the term "V-shaped notches" as used herein is intended to include modification~ to the notches as by rounding or squaring the peaks, provided that the joint faces or edges between the notches are of ~ubstantial length in relation to their width and extend in the general direction of the length of the belting or webbingO Improved jointing may be obtained by slight roughening of the V-shaped notches wlth a suitable instrument, before the complementary notched ends are fitted together. ` `~ `
s~ ~ The castable liquid mi~ture may be applied to the comple-mentary notched ends of the belting before the ends are fitted together, and then cuxed, but preferably the two uncoated ends ~ ;' ' ' , - , .

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of the belting or webbing should be brought together ~o that there i~ a small gap remaining between the complementary notches. ~his gap may be filled with the liquid castable mix-ture which is then heat cured to give the polyurethane compound.
j 5 In a preferred embodiment of the invention, the liquid castable mixture comprises a methylene dianiline sodium chloride aomplex di~persed in an equal weight of dioctyl phthalate, together with a polyurethane prepolymer formed by reacting polytetramethylene ether glycol with a molar excess of tolylene diisocyanate to give a reactive isocyanate content of 5.3% to i 5.7% by weight, which when applied to the ends of the belting may be cured by heating for approximately fifteen minute3 at about 150C to give an elastomeric polyurethane compound of j ~ durometer hardness in the order of Shore IAI 90~ .
In order to ensure a good surface fini~h of the joint the ~tep of applying the liquid castable mixture may include applying a thin layer of the mixture, as by painting, on to ~he top and bottom ~urfaces of the area of the belting to be joined before heating takes place. A layer of open mesh fabric ~0 or scrim cloth may also be placed over the top and bottom sur-faces of the area being joined to provide additional reinforcement The reinforcement may be retained on the belting by casting the mixture over it and heat curing. The scrim cloth i9 pre-ferably made from a synthetic yarn such as nylon.
Thq fitting together of the complementarily shaped ends preferably comprises placing th~ notched ends of the belting - or webbing in a suitable ~upport 80 that the notched ends and any liquid ca~table mixture between them i8 supported by a - 12 - ~
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~ flat sheet. The sheet may be painted with the liquid castable ! ~ mixture pxior to placing the end~ upon it to ensure an even, continuous surface on the finished joint. If the liquid castable mixture i5 applied to a gap between the notched ends, the gap should preferably be approximately 1/8". With the ~; liquid castable mixture located between the interengaged notched ends the whole joint is then covered by a fur-ther flat sheet which may also be coated aq above. A suitable release agent must be used on the two flat sheets, such as, for example, a ! lo silicon release agent for metal ~heets. If required the scrim cloth may be added by locating it7between the surface of the belting and the respective flat sheet.
The joint is then cured by the application of heat at a comparatively high temperature to release the active hydrogen ~' 15 containing compound from its chemical blocking agent, for example by placing the whole in an oven, or, if not convenient, by placing the joint between the heated platens of a press or ~imilar machine and, if desired, applying a slight pressure to the joint.
Prior to its application to the joint, various additives may be included in the liquid castable mixture in varying pro-portion~. Such additives may comprise fillers, pigmentsj flame retardan~s, plasticisers and/or qtabili~ers, and may be added singly or in suitable combination. An example of when flame ~5 retardants may be used is to en~ure that the polyurethane com-pound formed by the method of the preaent invention i~ suitable ` ~or u~e, for example, to join a conveyor belt in a coal mine.

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Claims

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

1. A method of jointing textile belting or webbing in situ with a polyurethane compound, which method consists of the steps of: complementarily shaping the two ends of the belting or webbing to be joined and fitting the complementary ends together so as to leave a gap between the ends; before or after the ends are fitted together, applying a sufficient amount of a liquid castable mixture at substantially ambient temperature to fill said gap when the ends are fitted together, the liquid castable mixture being heat curable to provide the polyurethane compound and comprising a polyisocyanate or a polyurethane prepolymer comprising a reaction product of a polyisocyanate, and a polyactive hydrogen containing compound in which active hydrogen groups are chemically blocked at ambient temperature; and heat curing the mixture in the gap at a temperature above ambient and at or above a temperature at which said polyactive hydrogen containing compound becomes unblocked, to join the comple-mentarily shaped ends.

2. A method as claimed in claim 1 in which the liquid castable mixture is applied to the complementarily shaped ends before they are fitted together.

3. A method as claimed in claim 1 in which the complementarily shaping step comprises forming in each of the two ends an array of V-shaped notches that extends across the full width of the belt at said end, the two arrays being complementary.

4. A method as claimed in claim 3 in which the length to width ratio of each notch lies in the range of 2:1 to 30:1 inclusive.

5. A method as claimed in claim 3 in which the complementarily shaping step comprises roughening the shaped ends before they are fitted together.

6. A method as claimed in claim 1, 2 or 3 in which the polyisocyanate is selected from the group of 2,4 tolylene diisocyanate, m-phenylene diiso-cyanate 1,5 naphthalene diisocyanate, or triphenyl methane triisocyanate.

7. A method as claimed in claim 1, 2 or 3 in which the polyactive hy-drogen containing compound comprises a complex of methylene dianiline and sodium chloride.

8. A method as claimed in claim 1, 2 or 3 in which the curing step com-prises heating the liquid castable mixture at a temperature of about 150°C for fifteen minutes.

9. A method as claimed in claim 1, 2 or 3 in which the liquid castable mixture includes at least one material selected from the class consisting of fillers, pigments, flame retardants, plasticisers and stabilisers.

10. A method as claimed in claim 1, 2 or 3 in which the applying step includes applying a layer of the liquid castable mixture to the surface of the textile belting or webbing adjacent the ends.

11. A method as claimed in claim 1, 2 or 3 in which the applying step includes applying a layer of the liquid castable mixture to the surface of the textile belting or webbing adjacent the ends, and in which a reinforcing open-mesh fabric or scrim cloth is placed over said surface and retained thereon by heat curing said liquid castable mixture.