Tracking belts on elevators conveyors

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Flexible flat belts are used on bucket elevators and belt conveyors to carry loose, bulk product. The belt is stretched tight from head drum to tail drum and the friction generated on the turning head drum is used to drive the belt and carry the product. The belt must run true on the end pulleys (drums) and stay within the sides of the equipment structure. If the belt runs off the drums, buckets will be destroyed and belt edges frayed. In the worst cases the belt runs off the pulleys resulting in a breakdown repair. Proper and long-lived tracking of belts is critical for trouble-free operation.

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Tracking belts on elevators conveyors

  1. 1. Process, Plant and Equipment UP-TIME F o r p l a n t o p e r a t o r s a n d m a i n t a i n e r s From www.feedforward.com.au – Teaching engineering to plant operators and maintainers so they can solve problems and improve reliability. Tracking belts on elevators and the structure. There are three common methods to join the ends of bucket belts - overlap, butt and strap and turn-up conveyors. clamp. Figure No. 1 shows the joining methods. ABSTRACT Tracking belts on bucket elevators and short belt conveyors. Flexible flat belts are used on bucket elevators and belt conveyors to carry loose, bulk product. The belt is stretched tight from head drum to tail drum and the friction generated on the turning head drum is used to drive the belt and carry the product. The belt must run true on the end pulleys (drums) and stay within the sides of the equipment structure. If the belt runs off the drums, buckets will be destroyed and belt edges frayed. In the worst cases the belt runs off the pulleys resulting in a breakdown repair. Proper and long- lived tracking of belts is critical for trouble-free operation. Keywords: belt alignment, Head and Tail Pulley Designs Figure No 1. Joining Bucket Elevator Belts. The head and tail drums on belt bucket elevators and short Insure joins are square to the running direction of the belt so conveyors are usually solid steel cylinders. A shaft is that the belt runs as straight and true as possible. mounted thorough them at the center and extending outward long enough to mount bearings on both sides. Often the Drum Crowning shell is steel pressure pipe and the ends are cut from flat Belt tracking is greatly improved when one of the drums is plate and welded in place. The shaft can be welded into the crowned. The drive pulley is the one usually crowned end plates, but for easy repair, it is best mounted in taper though the bottom drum can also be used. Only one of the locks that are welded to the end plates and the shaft clamped drums is crowned and not both. Crowning allows the natural into them. The shell length is usually 25 – 40 mm (1” – 1- elasticity of the belt to act like a spring and pull the belt back 1/2”) longer than the belt width down the rise of the crown if it starts to wander to one side. The height of the crown is 1% to 2% of the belt width. Where additional friction is required the head pulley can be lagged in rubber or grooved with a 45o herring bone pattern. Tracking Belts in Place Once the belt is installed and pulled tight, the distance On belt bucket elevators carrying powdered or dusty product between drum shafts is measured on both sides and the shell on the bottom pulley can be replaced with round positioned the same distance apart. The belt is run unloaded bars spaced around the end plates so that the gaps between and if it wanders the tail pulley is adjusted and made tighter them allow the product to fall out and the pulley self-cleans. on the side the belt moves toward. The basic rule is that the Drum Adjustment and Alignment belt moves toward the slack side and away from the tight To insure the belt runs central the two pulleys must be side (this is also why crowning one pulley works). Another aligned center to center. This is done with a string line way to look at it is that the belt goes from the high-energy stretched from the mid-point on both drums. The distance side (tight) to the low-energy side (loose). from a straight edge datum on the support structure is Once the unloaded belt is running true product is then measured and the position of the shaft bearings adjusted until introduced onto it. If the belt wanders under load the tail the string lines up with the straight datum edge. pulley is further adjusted as was done when set-up unloaded. The head and tail pulley axes must also initially be aligned Only tension the belt enough to insure it does not slip under parallel to each other and in the same plane. Once the drum full load. Over-tensioning the belt rips the internal fibers centers are inline the centerline distance on both sides from and the belt stretches and creeps continuously. shaft to shaft is measured from a datum line on the support structure. Bring the drums as close together as possible so All snub rollers, carrying rollers and return rollers must be that the belt can be later stretched. The drums are now square to the centerline of the belt and parallel to each other. aligned both horizontally and axially. The belt is then fitted Check this by measuring diagonals, which should be equal. on the pulleys. Some times the belt can take on a ‘banana’ shape or Belt Joining ‘crescent’ camber along its length. Usually this is a sign of Belts for short conveyors are usually purchased with the uneven internal fibre lengths. In this case the belt wanders ends joined and are slipped into place over the pulleys. A from side to side during a rotation and little can be done to splice at 45o to the belt running direction and not square is control it except to get it running as near to center as preferred. This allows the edge to lead into the scrapper and possible. Depending on the severity of the ‘banana’ it may lessens the chance of the join catching and ripped. even require that one of the drums be offset from the center- to-center alignment so that the belt stays on the pulleys. If The belt for belt bucket elevators can be supplied either with the camber exceeds 1% of the belt length replace it. buckets already mounted or without. Once the buckets are mounted it must be fed into the structure from the top and It can also be useful to install ‘digging’ buckets every tenth the ends of the belt joined later through a hatch in the wall of bucket. These buckets are slightly oversize in length and FEED FORWARD PUBLICATIONS, PO Box 578, BENTLEY, West Australia, 6102 Web: www.feedforward.com.au E-mail: info@feedforward.com.au Because the authors, publisher and resellers do not know the context in which the information presented in the flyer is to be used they accept no responsibility for the consequences of using the information contained or implied in any articles.
  2. 2. depth to the rest of the buckets and act as a scrapper to clear away any product build-up on the sides of the structure. Make them of metal or a harder material than the regular buckets. Mike Sondalini – Equipment Longevity Engineer FEED FORWARD PUBLICATIONS, PO Box 578, BENTLEY, West Australia, 6102 Web: www.feedforward.com.au E-mail: info@feedforward.com.au Because the authors, publisher and resellers do not know the context in which the information presented in the flyer is to be used they accept no responsibility for the consequences of using the information contained or implied in any articles.

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