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INSTALLATION  

STEEL CORD CONVEYOR BELT SPLICING - STEP BY STEP

It is important that the splice technology is not compromised when carried out in practice. This requires an air-conditioned, dust-free assembly hall with a modern vulcanization device, fresh and suitable (unvulcanized) splicing material, and experienced engineers and splicers who carry out the work in accordance with the instructions from the conveyor belt manufacturer.

Some hints regarding the equipment can be found here
.

1 Splice components The components of a steel cord conveyor belt splice:

1) Cover sheets.

2) (optional) Transverse reinforcement embedded in unvulcanized core rubber. It is applied like a second core rubber sheet.

3) Core rubber sheets.

4) Steel cords with original core rubber.

5) Intermediate rubber strips.

2 Work area setup

Setup of the working table.

For positioning of the bottom platen(s) of the curing press both belt ends are folded back.

The bottom part of the vulcanizer is used as a working table.

3 Tensioning The belt ends have to be tensioned as much as possible to avoid sag.
Both lengths will be laid one on top of the other over the whole splice length.

If it is necessary to shorten the belt(s), a wedge-shaped strip of approx. 20 mm width is cut out of the upper cover so that the steel cords become visible. The steel cords will be cut with a high-speed abrasive cutting tool with fabric reinforced disc.
Do not forget to take safety precautions!

4 Center line The belt centre is marked on both belt ends and also at a minimum of three other points that are approx. 1500 mm (5 feet) apart. These centre points are then joined into a centreline using a chalked string.
Approximately half a metre behind the splice area a crossline is drawn at right angles to the centreline as a reference line.
One marked belt end is placed on top of the other marked belt end. The centrelines on each end must be precisely aligned.
5 First cut The cover is cut transversally down to the cables.
The knife is held at a 45° angle.

The rubber edges are removed as far as the first steel cord.The belt centre is marked on both belt ends and also at a minimum of three other points that are approx. 1500 mm (5 feet) apart. These centre points are then joined into a centreline using a chalked string.
Approx. half a metre behind the splice area a crossline is drawn at right angles to the centreline as a reference line.
One marked belt end is placed on top of the other marked belt end. The centrelines on each end must be precisely aligned.

6 Cover stripping By means of a tensioning tool the cover is removed, supported by a knife that cuts between the cover over the steel cords.
Do not tear the cover off!

The procedure is repeated for the bottom sides of the belt ends.

7 Stripping The rubber between the steel cords is removed.
The cords should be carefully buffed with a rotary brush.
They remain completely covered by rubber after this procedure.

This procedure can be done very conveniently with a "CordStripper" (see video on the left).

"Piano wires" or similar methods should not be used.

8 Cable grinding The top and bottom sides and the ends of the separated steel cords will be brushed with a grooved wire brush.
Buffing dust be swept off by means of a hand brush.
Do not use cleaning solvent!
The steel cords will be coated with a special rubber solution, and dry completely.
9 Steel cords folded back

An unvulcanized cover rubber sheet is placed at the bottom of the splice on top of a separation cloth (e.g. Vulkatrix - see video).
The cloth should be approx. 300 mm (12 inches) longer in the longitudinal directions.

See also storage requirements for splicing material.

10 Aligned cords
The alignment is checked again.
11 Positioning of steel cords The steel cords have to be positioned as determined by the belt manufacturer or by the standard (f.i. DIN 22129).
12 Cable end position By the way: No cable has contact to any other cable.
13 Laying of core strips

 

All gaps between the cables are carefully filled with intermediate core rubber up to the height of the cables.
The entire splice area will be sparingly coated with rubber solution and dry completely.
Rubber edges are applied on both beld sides, coated with solution and dry well. The edges are tapped thoroughly with a mallet. Protruding rubber is cut off.
The straightness of the splice is again checked.

 

 

14 Press assembly Traverses
Heating platen
Metal sheet
Separation cloth (f.i. Vulcatrix)
Steel cord conveyor belt
Separation cloth (f.i. Vulcatrix)
Metal sheet
Heating platen
Traverses
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Edge bars, approx. 1 mm thinner than the belt, are placed against both belt edges (see video left side) and clamped outside the splice area.
The bars are 1-2 mm (1/16 inch) thinner than the belt.
Vulcanizer

Upper platens are placed and aligned (see video bottom right side).
End locking bolts are tightened slightly.
Oil pumps will be connected to upper traverses.
End bolts are tightened thoroughly.
Electrical cables are connected to the heating platens.
A pressure of approx. 10 bar (150 psi) is applied with oil pumps.

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The vulcanization is initiated by plugging the heating platens in.
Pressure will be increased as temperature rises. Temperatures at all heating platens are controlled.
Temperature is regulated by self-controlled heating platens or by switching energy on and off.
After several minutes allow temperature to rise to 142°C (290°F). The curing time counts when temperature reaches 142°C (290°F).
Disconnetion at 145°C (295°F). Plugging-in again when temperature drops to 142°C.
After curing time has elapsed, platens will be allowed to cool down to 80°C (150°F).
A typical temperature/pressure curve is shown here.

Important: Please use the appropriate figures of your belt supplier! Here only examples are given.

  Vulcanizer A vulcanizer setup in a climatized working shed.

The curing time is depending on belt thickness and rubber grade. As a rule of thumb, a curing time of 3 minutes per 1 mm belt thickness is required.

Some further instructions are given at the last column of multiply textile conveyor belts.

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Dismantling of Press:
Traverses and end bolts will be loosened and removed.
Upper heating platens will be removed.
Edge clamps will be loosened and removed.
Spliced belt will be lifted and lower heating platens are removed.
Working platform will be removed.
Rubber overflow at both edges will be trimmed off.
Belt surface, ramps and edges are being inspected visually.
Belt is put into service.
Moving belt
Just as a very basic guideline for the splice design, there are some rules of thumb in the market:
Step length of oppositing cables: min. 100 x cable diameter,

Rubber width between cables: min. 2 mm or min. 0,3 x cable diameter,
Steel cord butt end gap: approx. 50 mm,
No splice should contact two pulleys at the same time.
An investigation following a tragic accident in a South American copper mine showed that excellent results are achieved when the splicing is carried out on-site appropriately. External factors caused a tunnel there to collapse in which a Phoenocord St 6800 conveyor belt, was being used. The collapse was so powerful that the running conveyor belt, which has a breaking strength of 10,000 kN, tore abruptly - not directly in the splice, but several meters away from it. The nearest splice was cut from the belt and sent to ITA/University Hanover for assessment. The findings were reassuring: The splice demonstrated the same dynamic efficiency as the test splices made in the project phase. The splice did not suffer – despite the splicing conditions on site, despite aging, and despite the extreme tensile forces caused by the collapse of the tunnel. Meantime the remaining splices have been successfully in use for 17 years.

Note: There are so-called preformed splice mats on the market. Although they can have certain cost advantages for a big number of simple splices to be made continuously, their risks should also be considered:
Transportation and handling of the preformed mats is difficult - they are still in an unvulcanized plastic state. Deformations can hardly be avoided, and at least the sides of the mats are exposed to contamination. The shelf-life of the mats will be shorter, and a component cannot be replaced if only that one is not good anymore. Blisters and inclusions occur frequently. Thus more opening of blisters is necessary. Irregularities cannot be compensated as is the case for a skilled splicer when shiving intermediate rubber between the cords.
Splicers in spool
And don't forget to have a break -

at the right time at the right place...!

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