AEROCONVEYOR BELT SPLICING
Details courtesy of Aeroconveyor
Conveyor belting is to be supplied as per the contractual requirements as specified on the schedule.
Before commencing any field splicing operation the following points shall be carefully checked,
Ensure there is sufficient belting in the system to enable a splice to be made.
Select a suitable point on the conveyor system for making the splice, having regard to:-
Ease of operation, including the handling of a heavy press;
Provision of the necessary cover of the installation if open to the weather, so that the operation can be carried out in dry conditions.
Ability to tension the belt conveniently, i.e. suitable anchorage points available for the clamps and wire lashing used for tensioning with pull lifts or winches.
Check that a satisfactory power supply for the vulcanising press is available where required.
Obtain full details of the type, size and grade of the belt to be spliced so that the correct splicing materials can be obtained and used.
When the splicing operation takes place, make sure before tensioning the belt that any fixed take-up device in the system is at the "fully in" position.
TYPES OF SPLICES
Hot stepped bias splice.
In all cases the belt ends to be joined together shall be stepped down in a series of steps, the number of steps being in each case one less than the number of plies.
The length of the steps to be used in the splices shall be determined from the full thickness strength of the belt and the number of plies. The belt strength in kn/m width is divided by ten times the number of plies, and according to the quotient obtained, the required length if the step (s) can be ascertained from table 1. ( note: 1kN/m is 5.7 lbf/in).
strength in kN/m
divided by 10 times
the number of plies
of the step
|Up to 12||150mm||0.4mm|
|Over 12 to 18||200mm||0.4mm|
|Over 18 to 24||250mm||0.4mm|
|Over 24 to 35||300mm||0.8mm|
|Over 35 to 40||380mm||0.8mm|
EXAMPLE: A belt strength of 500 kn/m and of 5-ply construction would have a value in table 1 of 500 divided by 50 = 10 and hence a length of steps of 150mm. The inside gum layer should be 0.4mm thick.
The bias length for splicing shall be set at one third of the belt width, which is the tangent length of an 18.4 angle. The bias length shall then be defined as x = 1/3W.
The overall splice length will be given by L = X + [S.(n-1)] Where n is defined, as the number of plies and s is the step length.
All splices shall be made by stripping back the plies at the two ends of the belt in the required manner.
The exposed ply surfaces shall then be given two coats of adhesive, each coat being allowed to dry before proceeding with the next operation.
A layer of inside gum (skin gum) in accordance with table 1 shall then be applied on the treated surface of one of the ends, so that a layer of rubber exists between the plies at the splice when the two ends are vulcanised together. The inside gum shall be supplied with a protective backing (generally glazed Holland) which will strip away clean.
The rubber cover on each surface of the belt at both of the stripped ends shall be cut back for a distance of 25mm so as to leave a gap of 50mm at each end of the splice when the belts are assembled together.
When matching the two ends together the protective backing supplied with the inside gum shall be left in place so that the surfaces do not adhere. When the splice is perfectly matched, turn back one half and remove half the backing, then roll down that half of the splice before removing and mating up the other half. See "points of importance". Before vulcanising, these gaps shall be filled in, using cover gum of the requisite thickness.
For rubber covers 2mm and over in thickness, a layer of 40mm wide nylon leno breaker shall be placed under the 50mm wide strip of cover gum, the nylo leno breaker having been suitably treated with a bonding agent and spread with adhesive.
To vulcanise the assembled splice a suitable press must be used having two heated platens, one above and one below the belt, which have to be suitably clamped together to give the pressure of at least 350 kn/m over the area of the splice. The press patterns must be of a rigid design to ensure uniform intensity of clamping pressure over the pattern area. The temperature of the press patterns shall be maintained at 144 c by suitable thermostatic control, for a period of time for vulcanisation or cure as given in table
|FULL THICKNESS OF BELT||CURE TIME||TEMPERATURE|
|UP TO 6mm||25 minutes||144C|
|OVER 6mm TO 12mm||30 minutes||144C|
|OVER 12mm TO 20mm||35 minutes||144C|
|OVER 20mm TO 26mm||45 minutes||144C|
Edge bars shall be used between the platens of the press and at the sides of the assembled joint to ensure a clean appearance by controlling the flow of he inside gum during vulanisation.
POINTS OF IMPORTANCE DURING THE SPLICING OPERATION.
All measurements and marking-out lines shall be made to the centre line of the belt and not to the edges so as to ensure that the splice is straight even if the edges are not parallel at the splice. Measure from a base line (away from the splice area) to avoid cumulative errors on measurement.
Make sure the belt to be spliced is thoroughly dry. Good splices are impossible in damp belts and the belt ends must be dried out using hot air blowers or heat lamps before commencing splicing but after stepping back.
Great care shall be taken not to cut deeper than intended or cut into or destroy any fabric that is to remain a part of the splice.
Make sure that the splice is properly aligned and that the fabric steps do not overlap at any point. Do not leave any gaps between the steps.
Never apply adhesive to any fabric surfaces unless they have been thoroughly cleaned. Dirty surfaces will not vulcanise or adhere properly. Care must be taken so as not to damage the fabric in any way.
Always allow adhesive and solvent to dry thoroughly before proceeding.
Use a vulcaniser which has platens at least 100mm wider than the belt which is being spliced.
If the splice length is such that one application and heat of the vulcanising press is necessary, at least 50mm overlap shall be allowed on each heat and the press platens shall extend at least 50mm beyond the splice on the first and last heats.
Adhesive, iside gum, cover gum and solvents shall be of the correct type for the belt being vulcanised in order to ensure a satisfactory splice.
Conveyor belts are made using various textile material combinations including 100 per cent synthetic fibres and various polymers such as natural rubber, sbr, polychloroprene, niterile rubber, and butyl rubber.
Petrol is frequently used for swabbing and cleaning, but great care shall be taken to see the petrol used is of the non-leaded type.
In calculating the amount of adhesive required to make the splice, it can be taken that one litre will cover approximately 1,3 square metres.
PVC conveyor belts will also used in certain applications
When ordering stocks of materials the makeup of the belt shall be correctly be known so that the proper material for splicing can be provided while this specification covers the splicing of "rubber type" belting, it is realised that pvc belting may have to be spliced. When splicing PVC belting, a cooling period is required after hot pressing, before the press can be removed, because of the thermoplastic nature of the PVC belting.
Reference shall be made to the belting manufacturer for materials and information on splicing, but the types of splicing referred to above are suitable for PVC belting provided that the correct materials and precautions are used.
TOOLS FOR SPLICING.
Suitable tools for splicing shall compromise of:
Square, straightedge and steel tape for measuring and setting off the splice.
Hand-knife for cutting the belt, and a specially ground knife for cutting through one ply at a time, when cutting the individual steps
A 50mm hand roller for rolling down.
A stitcher roller or edge wheel for ensuring that the inside gum is tight along the edges of the steps.
Pincers for ply and cover stripping.
Scissors for cutting gums.
A "v" knife shall be used for removing the outer ply overlaps so they can be trimmed to butt snugly up against one another.
A blunt screwdriver shall be used for ply lifting to enable the start to be made with the pincers; but it is important to see that it is, in fact, a blunt one and has no sharp corners.
An awl shall be used for releasing any trapped air.
A suitable electric supply for the vulcanising presses being used shall be the responsibility of the sub-contractor. All equipment shall conform to the accepted electrical standards and be in good working order.
When the belt has been positioned in the conveyor trough it shall be tensioned by the use of clamps before the splice is made, in order to reduce the stretch in the belt after the splice has been completed and the clamps have been removed.
A suitable clamp shall be fixed to each belt end and the tension applied through the clamps by means of pull-lifts or suitable tensioning devices. Stretch shall then be taken out of the belt by drawing the two clamps together, the prepared ends of the belt being slack between the two clamps.
Alternatively one of the clamps shall be fastened to the structure, tension then being applied between a point of the structure and the other clamp. With this method, however, it is necessary to use more tension than with the method where the two clamps are drawn together.
Similarly, slope belts, which are spliced at the top of the slope, require more tension during splicing than those spliced at the bottom.
When a belt system is fitted with a moving gravity weigh take-up, apply the tension and lift the weight until it has reached the position where it is expected to float when the belt is running empty. This operation shall be performed by clamping to the structure the end of the belt nearest to the gravity weight and by pulling the other end so that the pull is transmitted right round the system and into the gravity take-up position. All pulleys shall be free to rotate during tensioning operation. Care shall be taken not to rotate the pulleys against the conveyor holdbacks during tensioning.
The bottom platen of the vulcanising press shall be placed in position at the start of the operation and the splice assembled on top of it. The top platen shall be placed over it and the splice vulcanised when the latter has been completed.