BASIC INTRODUCTION TO CONVEYORS

SECTION FOUR
CHAIN CONVEYOR

There is a wide variety of chain conveyor classified into four separate types:

A. Sliding chain conveyors.
B. Rolling chain conveyors.
C. Pusher Bar chain conveyors.
D. Vertical chain conveyors.

Sliding chain conveyor: This is the type of conveyor consisting generally of two parallel strands of chain. For light unit loads and for short distances, the chain can be a double pitch roller chain with the standard small rollers running in a track lined with high density low co efficient friction plastic material. For heavier loads, it is best to consider a heavy duty cast pintle chain which will also run in a channel track lined with a high density, low coefficient of friction plastic material of which there are many available today. The sliding chain conveyors carry the loads on the chains and the bottom of the chains are in low frictional contact with the track.

Rolling chain conveyors: This is the type of conveyor, which utilizes generally, two parallel strands of double pitch roller chains (sometimes three strands), with the rollers running on key stock material of width to fit between the side plates of the roller chain. Again, this design is used for fairly light loads and for short conveyors. For heavier loads, we can use the double pitch chain with oversize rollers where the rollers are greater in diameter than the width of the chain side plates thus the rollers do project below the side plate of the chain. This rolling friction design utilizes a lower horsepower requirement and thus can be used for longer runs of chain driven conveyor. The loads are carried on attachments, which raise the load above the chain rollers.

A slat or apron conveyor using steel or wood slats or even a ball bearing conveyor rollers between the two parallel strands of roller chain actually fits the category description for roller slat conveyor previously described. In the use of steel or wood slats, heavy loads can be carried under such conditions where perhaps a PVC or a rubber belt could not possibly be utilized.

Also another type of sliding chain conveyor, which utilizes single strand of link chain riding in a plastic lined track in the center of the conveyor. Outboard of this center track on both sides to the outer frame rails are gravity rollers or wheels spaced on suitable centers compatible with the container being handled. The link chain, which is powered, projects slightly above the side rollers and is the driving force which carries the containers while the side rollers or wheels merely balance the load. Some advantages of this conveyor are:
1. Excellent for wash down conditions.
2. A single drive can be used to convey on the level, up an incline, down a decline, around a curve, etc.

Some disadvantages are that it can only be used satisfactorily for fairly light loads and inclines and declines cannot be too steep, probably not more than 15 degrees.

Pusher Bar Conveyors are similar in design to the horizontal slat conveyor in that we have two outboard strands of roller chain adjacent to the side frames. We can use an attachment on the chain to which we can fasten an angle, a flat bar or a round rod. This angle, flat bar or rod is the pusher bar. Under the chain track and between the side frames we have a slider bed. The units to be conveyed will slide on the slider bedplate and will be pushed by the pusher bars. The spacing of the pusher bars must be such as to permit the conveyed items to fit in between. Some advantages of this type of conveyor are:
1. Can convey heavy items up much steeper inclines than conventional Hilltopper belt.
2. Can handle wire bound crates or bales of hay.
3. Can handle heavy burlap or cotton bags of flour, rice or green coffee items which might be difficult to incline or decline at angles in excess of 25 degrees on Hilltopper belt.

Some disadvantages are:
1. The height of the pusher bars above the slider bed must be such that the containers will not fall forward or backward. This limits the variation of box sizes.
2. The timing of containers is critical so two containers cannot try to get between the two pusher bars simultaneously.
3. This type of conveyor can definitely not be used with sheet polyethylene bags, as the frictional heat generated would create holes in these bags.

Vertical chain conveyors can be designed for use to handle individual cartons as well as full pallet loads. The design can be similar to a dumb waiter style where the unit is a reciprocating lift handling one unit at a time or can be a continuous lift with flights attached to side roller chains. Each flight can handle one unit, therefore the flight spacing vertically depends upon the maximum height of the unit being handled.

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