Power and Free Conveyor

Power and Free conveyors at a Ford Motor Assembly Plant

Power and Free Conveyors

Power and free conveyors are the workhorse of the overhead conveyor product family. Ultimation’s systems are exceptionally flexible and easy to maintain. We integrate Jervis Webb Power and Free Conveyor components in our overhead conveyors. They are ideally suited to demanding industrial environments that require a high degree of versatility and production accuracy. Ultimation’s range of Webb power and Free Conveyors can handle loads from as light as 5 pounds per unit to 20,000 pounds. Unlike basic continuously moving overhead monorail conveyor systems, these systems provide the unique ability to stop individual loads without stopping the entire production line. Webb Power and Free Conveyors offer a wide range of features designed to maximize your production capacity including:

  • Variable chain speeds
  • High-speed indexing
  • On-line storage
  • Adaptability to changes in elevation

How do Power and Free Conveyors Work?

Power and Free conveyors have two tracks, with one track located above the other. On one track which is known as the “power” track, a rivetless conveyor chain is attached. This conveyor runs continuously when the overhead conveyor is in operation. On the second track, the loads that the conveyor will carry are attached to the conveyor system via load bars and trolleys. This second track is known as the “free track” of the conveyor. Small mechanical devices called  “pusher dogs” are located at regular increments along the moving chain. The purpose of the pusher dog is to push the free trolleys along the conveyor track. Provided the track in front is free from either other trolleys or mechanical stop locations, the free trolleys are pushed along by the pusher dog at the same speed as the power chain. When a trolley comes up against another carrier in front, the free trolley system automatically disengages the trolley. This allows the power chain to continue running. In this way, the free trolleys can stop and start at various points within the conveyor system. The loads on the conveyor can also accumulate (i.e. bunch together) when necessary, or alternatively, they can be separated to travel one by one by means of a pneumatically operated stop which stops the free trolleys.

Power and free trolleys can therefore allow each of the individual conveyor loads to stop and to start. They are able to accumulate together, and then to be separated again in a controlled manner. The system can include horizontal turns, vertical turns (changes in elevation) and switches to send some trolleys in one direction and others in a different direction. Many power and free conveyors also feature two or more chains pulling the free trolleys around the conveyor system. In the production areas, the chain may move slowly on a “production speed chain”, and then the free trolley can then transition to a high speed. This high speed chain can quickly move the conveyor loads to the required delivery areas. The graphic below shows how the pusher dogs interact with the free trolleys:

How do Power and Free Conveyors Work

Power and Free Conveyors in Action

Webb’s exclusive Wide Wing™ design trolleys, and lug channel track provide smoother conveyor to conveyor transfers, increased load stability, and the strongest track section available on the market.  Load capacities range up to 20,000 lbs. individual unit loads.

Webb’s exclusive Wide Wing™ design trolleys, and lug channel track provide smoother conveyor to conveyor transfers, increased load stability, and the strongest track section available on the market. Load capacities range up to 20,000 lbs. individual unit loads.

Power and free conveyor Power and Free Conveyors at a Ford Motor Company Assembly Plant

Advantages of Power and Free Conveyor Systems

Because Power and Free Conveyors combine many of the advantages of other conveyor types and conveyor systems with relatively few disadvantages, they have long been the first choice for the automotive industry and other industries where high volume, durability and high reliability are very important. Compared with other overhead conveyor technologies, power and free systems generally have far fewer motors and far fewer moving parts that can go wrong. Electrical systems for power and free conveyors are typically much simpler than for friction conveyors or for electrified monorail systems. Simple pneumatic devices (air cylinders) can be located along the line at any location where carriers need to be stopped and then released when ready to move again. These pneumatic stops can be relocated fairly easily as required if the customer’s needs change. The Webb “Dog-Magic” system which allows trolleys to accumulate and the disengage provides a mechanical intelligence un-matched by many other conveyor types.