conveyor belt Splicing Guide

7/30/2019 conveyor belt Splicing Guide

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A GUIDE TO SPLICING

ORIENTAL RUBBER INDUSTRIES LTD.

SHRAVANI GARDENS 20, VIMAN NAGAR PUNE -411014. (INDIA)

Telephone: (91-20) 26630071Fax: (91-20) 26630840

E-Mail ID: [email protected]


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Introduction

Wherever pract icable, a hot vulcanised spl ice is preferred for making conveyorbelt ing endless as against cold vulcanising and metal fasteners. Some of theadvantages a hot vulcanised s pl ice has over the other two types are:

(a) A hot vulcanised spl ice lasts the longest and even when it fai ls, i t doesnot fai l abrupt ly. Indicat ions of a joint fai lure are apparent well beforethe fai lure i tself , giving suff i c ient t ime and warning either to repair or tore-do the spl ice.

(b) I t maintains a cont inuous smooth surface on the belt face and back,forming a smooth endless band and does n ot let the mater ial seepthrough. I t also t ravels well over the idlers and the pul leys withoutcausing any addit ional wear on the pul leys/ idlers.

(c) I t permits the use of belt cleaners, magnet ic separators, ploughs andscrapers to work smoothly.

(d) I t seals the belt ends, prevent ing any ingress of moisture or dust.

(e) Maintenance and cleaning of vulcanised spl ice joints are negligible.

( f ) When hot mater ials are conveyed, i t performs l ike the other parts of thebelt , unl ike metal fasteners, which abso rb the heat and transmit i t to thebelt pl ies, causing deter iorat ion of the carcass.

The procedure descr ibed in the fol lowing pages for site spl ic ing areapplicable both for Al l-Nylon and Polyester/Nylon reinforced RubberConveyor Belt ing.


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Equipments, materials & tools requiredfor splicing

1. Portable e lect r ical ly operated vulcanising press, capable of provid ing a minimumpressure of 7kg/cm2 across the fu l l width of the platens and sui table for the bel twidth to be jo ined.

2. Two moulding i rons of suf f ic ient length, approximately 25 mm in width, 1.0 to 2.0mm less than the th ickness of the bel t to be spl iced.

3. Two carpenter- jo in ing-clamps to apply pressure on the moulding i rons placed alongthe edges of bel t .

4. A chain b lock or pul l l i f t and tackle for tensioning the bel t .5. Two angle i rons or wooden clamps for lashing the bel t .6. Wooden planks approximately 2 mtr long to bui ld up a plat form sl ight ly wider than

the bel t and about 1 mtr longer than the spl ice. This is to g ive a f i rm working areaunder the bel t to a l low ef f ic ient working whi le making the sp l ice.

7. Heat-resistant leather g loves to handle the vulcaniser.

8. A set of spanners to t ighten the vulcaniser.9. St ra ight edge or ru ler and steel tape about 2 mtr long.10. Right angle steel squ are wi th at least 1.5 mtr long side.11. Rubber cut t ing kni fe.12. Ply cut t ing k ni fe.13. Screw dr iver at lea st 400 mm long.14. Vee kni fe.15. Wire brush.16. P incers.17. Rubber cut t ing sciss ors.18. Hand rol ler .19. Serrated edge wheel .20. Pr icker or sharp pointed awl .21. Sof t hai rbrush.

22. Paint brushes 50 mm wide.23. Emery cloth no.2. Approximately 6 sheets, 300 mm square, are requi red perspl ice.

24. Grease proof paper. Smal l st r ips of greasepr oof paper are placed on the channelsof the spl ice before cur ing to prevent the rubber f rom adher ing to the pressplatens. I f greaseproof paper is not avai lable, Hol land glazed cloth or t racing clothmay be used.


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Splicing Compounds

1. Conveyor belting solution

Conveyor belt ing solut ion is avai lable in 10 l i t re containers. 10 l i t res can coverapproximately 9 sq mtr per coat and 3 coats of this solut ion have to be applied.The solut ion is applied by brush over the fabr ic pl ies/carcass af ter cleaning inorder to replace the fr ict ioning/dipping removed dur ing the str ipping. Shelf l i feof this solut ion is a maximum of 6 months f rom the date of manufacture.

2. Insulation compound

Insulat ion compound is avai lable in 150 mm width and 0.35 mm/0.6 mmthickness inter leaved with alkathene and packed in 1,5 kg containers. Thecompound is applied over and above the Conveyor Belt ing Solut ion in order toskim coat the pl ies, thus improving the level of adhesion. I t has a shelf l i fe of 6months f rom the date of manufacture.

3. Cover Compound

This compound is required to replace cover rubber and is used to bui ld up theface and back cover channels in spl ices and also for replacing damagedport ions of the cover. Cover compound is avai lable in 150 mm width and 1,6mm thickness inter leaved with alkathene and packed in 1.5 kg containers. Anythickness of cover rubber can be bui l t up by using the requisite number oflayers of this compound.


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General Information on Splicing

Oriental recommends stepped biased type spl ic ing for mult i-ply al l synthet icconveyor belt ing. The belt ends to be joined together are prepared in a ser iesof steps, the number of steps being one less than the number of pl ies. Thelength of these steps are dependent upon the strength of the individual pl iesand are indicated below for al l standard construct ions in table 1:

Dimensions of Splice The table below should be used in conjunct ion with Figure on Page 13

TABLE 1

Total Splice Step Lengths Insulat ion CompoundBelt Rat ing Length (mm) (mm) (mm)

315/3 0.5W + 325 150 0.7400/3 0.5W + 375 175 0.7500/3 0.5W + 425 200 0.7630/3 0.5W + 525 250 0.7630/4 0.5W + 625 200 0.7800/4 0.5W + 775 250 0.7

1000/4 0.5W + 925 300 1.051250/4 0.5W + 1165 380 1.051250/5 0.5W + 1225 300 1.05

1400/5 0.5W + 1545 380 1.051600/5 0.5W + 1825 450 1.401800/6 0.5W + 2275 450 1.40

W = Width of the belt in mm

The above spl ice lengths are based on the use of 26 1/2 degree bias angle.Alternat ively, i f the bias angle is made to correspond with a rhomboidal shapepress platen angle, the bias length should be suitably modif ied.

While al l standard construct ions are covered in the above table, should you f indany construct ion not l isted here, please refer to us. For belts running on idlers,the spl ice should be assembled in such a way that the cover compound buil t onthe back cover channel leads the one on the face cover. In the case of beltsrunning on sl ider plates, this has to be reversed.


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Preparation of the Belt for Splicing

1. Once the belt has been posit ioned on the conveyor structure, i t must betensioned using clamps in order to reduce the stretch in the belt af ter thesplice has been completed and the clamps have been removed. Addit ionalcare should be taken to provide extra tension on the clamps if the spl ic ing isdone on top of the slope.

2. I f the system is f i t ted with a gravity take-up, i t wi l l be necessary to applytension and l i f t the weight to the posit ion where i t is expected to f loat whenthe belt is running empty. When the belt system is f i t ted with a f ixed screw

take-up device, the pul ley must be moved to the of f posit ion so that the beltis at i ts shortest endless length when spl iced.

3. Often i t is convenient to posit ion the bottom platen of the vulcanising pressin place and assemble the spl ice on top of i t . Once the assembly is ready,the top platen may then be placed over the spl i ce and the spl ice vulcani sed.

4. Af ter cut t ing the belt end square, mark the t rue centre l ine of the belt to beused as a datum l ine for al l other measurements. Belt edges should neverbe used for reference.

5. At r ight angles to the belt centre l ine, mark a base l ine to denote the l imitof the spl ice length. To al low for subsequent t r imming of the outer end ofthe spl ice, i t is suggested that the base l ine should be drawn 50 mm furtherthan the total spl ice length indicated in Table 1 and as measured from thebelt end. This base x l ine should be marked on the face cover for theleading end and on the back cove r for the t rai l ing end.

6. Mark the bias length along the belt edge from one edge of the base l ine.Join this marked point to the other end of the base l ine to provide for thesplice l ine. Mark a l ine paral lel to this 25 mm inward and str ip of f the coverrubber in this 25 mm width. Now re-mark the spl ice l ine on the outer ply andremove another 25 mm wide str ip of cover rubber outward the spl ice l ine.This wil l ensure that the spl ice l ine is st i l l v isible when the two str ips ofcover rubber have been removed. The second strip is removed to ensurethe use of the single ply cut t ing knife.

7. Now cut through the f irst ply along the spl ice l ine using the single ply cut t ingknife. Adequate care should be taken not to cut deeper than required anddestroy the fabr ic, which is to remain as part of the spl i ce.

8. Remove the f irst ply and cover rubber outwards of the spl ice l ine, preferablyin thin str ips.


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9. Mark bias + step length along the belt edge from the base l ine and draw the

step l ine. Now cut the second ply again, taking care not to cut deeper thanintended.

10. Mark the other steps from the base l ine in the same way.

11. Cut through the last ply and cover rubber at the end of the spl ice to makethe last step 12 mm longer than the normal step length.

12. Remove cover ru bber for a str ip of 38 mm width on the reverse si de of thebelt .

13. Repeat the str ipp ing down ope rat ion for the reverse side on the other end,commencing from marking the bias length along the belt edge from the baseline.

14. In preparat ion of the steps for spl ice, measurements are always taken fromthe base l ine across the belt . The edge of each step must be measuredfrom this base l ine and not f rom the edge of the previou s step.

15. Using coarse emery cloth and wire brush, clean the surface of the ply stepswithout damaging the fabr ic. Care should, however, be taken that therubber impregnat ion within the pl ies does not come off . Also buff the coverrubber adjacent to the spl ice to ensure sat isfactory bonding. Dir ty surfaceswil l not adhere together adequately

16. After ensur ing tha t the step en ds are clean and dry, pai nt steps at both endsof the belt with three coats of Conveyor Belt ing Solut ion. Between twocoats enough t ime should elapse to al low the f irst coat to dry beforeproceeding with the next coat.

17. Lay a layer o f Insulat ion compoun d over the exposed steps on the face side,leaving a channel. Roll this down in posit ion with the rol ler avoiding any

crease, over lap and trapped air . Finish by edge wheeling the insulat ioncompound.

18. Lay out the belt end prepared with insulat ion and f i t the other end to i t .While matching the two ends i t is advisable to leave the protect ive alkathenein place, so that the surfaces do not adhere. Make sure that the spl ice isproper ly al igned and that the fabr ic steps do not over lap at any point . I t isequally important not to leave gaps between th e fabr ic steps.

19. When the sp l ice is perfect ly matched, turn back one half and remove thealkathene and then rol l down that half of the spl ice before removing andmating the other half .


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20. Dig in and tr im of f the over l apping end of the last p ly on the face and back

to make a close f i t t ing joint .

21. Apply solut ion to the edges of the rubber al ong the channel i n covers. Inserta str ip of 0.35 mm insulat ion compound in the requisite width along thechannel. Apply a coat of solut ion and f i l l with Cover compound of requisiteguage.

22. Roll thoroughly and pr ick the whole spl ice area. The joints are f inal ly edgewheeled and tr immed with the t r imming knife, i f necessary giving a closebutt joint . Roll down the whole spl ice area with hand rol ler .

23. Remove the working surfaces from the conveyor and posit ion the vulcanisingpress.


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Precautions to be taken while splicing

1. Great care should be taken in the use of the ply cut t ing knife in order not tocut deeper than intended.

2. The buff ing operat ion should be done careful ly, so that the fabr ic ply andthe rubber impregnat ion between the pl ies are not damaged, since i t wouldreduce the strength of the spl ice considerably.

3. Bl isters are somet imes formed while cur ing the spl ice. I t could occur due tolack of suf f ic ient t ime for the conveyor belt ing solut ion to dry or due toforeign matter/moisture. Bl isters should be cut open and the area careful lyexamined to determine the cause of bl isters. Any evidence that has causedthe bl isters must be removed. The area should be cleaned with Naphthaand when dry, two coats of conveyor belt ing solut ion should be applied,al lowing each coat to dry thoroughly. I f only the cover is bl istered, this partof the cover must be removed and replaced with cover compound by bui ldingup the required thickness. I f the bl ister is in the carcass, this area must becut open longitudinal ly and dr ied thoroughly. Af ter roughening up thesurface with emery cloth, two coats of conveyor belt ing solut ion should beapplied, al lowing each coat to dry thoroughly. The opening must then beclosed and the belt cured at recommended tempera ture and pressure.

4. The edges of the belt along the spl ice somet imes become porous. This

happens when the moulding irons are not f i t ted t ight ly or i f the pressure isinsuff ic ient dur ing cur ing. In such cases the area of porosity must beremoved careful ly and replaced with new compound. In case the channel isfound to be porous, the channel rubber must be removed and treated forrepairs.


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Vulcanising the Splice

1. I t may sometimes be necessary to cure the ful l spl ice length in more thanone charge in wide or mult i-ply belts. In such cases care should be taken tosee to i t that the channels are vulcanised always in one single cure. Alsoensure that the f irst and the last ch arge at the ends of the spl ice are at l east75 mm inside the platens of the vulcaniser and that an adequate over lap of75 mm exists between two consecut ive charges.

2. Place moulding irons 0.5 mm to 1.0 mm less in thickness than that of thebelt along the edges of the belt and press them up against the belt justsuf f ic ient ly to make contact with the belt by means of a joiner s clamp andt ighten these clamps.

3. Posit ion the top sect ion of the press and careful ly t ighten the press,ensur ing even pressure. I t is preferable to t ighten al l the nuts in pairsacross the press.

4. The vulcaniser should be set according to the makers instruct ions and thetype of machine so as to give a minimum cur ing pressure between the pressplatens on the belt surface of 7 kg/cm2.

5. The fol lowing table provides the detai ls of the recommended vulcanisingtemperature and vulcanising t ime for the var ious belt thicknesses.

TABLE II

Total Belt Vulcanising Vulcanising TemperatureThickness Temperature Time at Press opening(mm) Degree C (minutes) Degree C

0 - 6 144 25 936 - 12 144 30 93

12 - 20 144 35 9320 - 25 144 45 93

Note : When spl ic ing belts with heat resista nt quali ty of rubber covers, thepress should be opened at a temperature of 65 deg ree cent igrade.

6. Af ter cur ing one charge, open the press at the temperaturerecommended for press opening and posit ion the next charge for cur ing,providing for 25 mm over lap on the previous one. Repeat for furthercharges.

7. Once the whole spl ic ing area has been cured, remove this, examine forany defects and tr im the edges for excess spew.

8. Re-instal l the idlers and release the belt af ter one hour.


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Conclusion

While vulcanised joints are longer last ing than metalfasteners, even a vulcanised joint cannot producea tensi le strength at the joint equivalent to the beltstrength i tself . While i t can produce a tensi lestrength close to the belt strength, the normal pract iceadopted for calculat ion of the tensi le strength at the

jo int is approximately 1 ply less i .e. , for a bel t ing offul l thickness tensi le strength of 630 KN/metreincorporat ing 4 pl ies, the joint strength is calculatedas 472.5 KN/metre, even though the actual strength

may be more than this. However, this drop in thetensi le strength at the joint would not af fect the beltperformance, i f belt select ion takes into account aminimum factor of safety of 1: 5 at the spl iced

jo int , under maximum tensi le loading (start ing/stoppingtension) for operat ing safety of mult i-ply text i lereinforced belt ing. Also, please note that theeff ic iency of a vulcanised joint depends a lot onthe capabil i ty of the equipments used, the workmanship

and the quali ty of the compounds used, apart f romthe quali ty of the belt i tself .


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conveyor belt Splicing Guide