Power and Free Conveyors

How do Overhead 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, you can attach the loads that the conveyor will carry via load bars and trolleys. This second track is known as the “free track” of the conveyor. Our engineers will specify small mechanical devices called  “pusher dogs” 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 move along with the pusher dog at the same speed as the power chain.

During operation, 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.

Start and stop any load at virtually any location along the line

As a result, Power and free conveyor 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. Additionally, 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:

Power-Free conveyors are generally considered to be part of the family of overhead conveyor systems. The most basic overhead conveyor system is the hand push trolley system (with a trolley on an I-beam or enclosed track). When a motor and chain is added to the system, these conveyors can move continuously or stop/start (indexing mode) with the parts moving along with the chain. Finally, Power and Free conveyor systems are the most useful of the overhead conveyor family as the loads can engage and disengage with the moving chain. Although we think of them as being in the overhead conveyor group, power and free conveyors can also be used when mounted to the factory floor. In this case, they are known as inverted power and free conveyors. They are also known as Power Free conveyors or Power & Free conveyor.

Types of Power and Free Conveyor Systems

• I-Beam Power and Free
• Enclosed Track P&F
• Inverted I-beam Power Free
• Inverted enclosed track
• Over-Under
• Tandem

Power-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. Click this link to see a video of 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.

Power and Free Conveyors at a Ford Motor Company Assembly Plant

What are the Advantages of Power and Free Conveyor Systems?

Because P&F 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.

How much do Power and Free Conveyor Systems Cost?

Each application has its own unique considerations such as the part weight, conveyor length and complexity of the system. In general, Power and Free conveyors cost more than hand push or monorail (indexing) style overhead conveyors because they have two tracks and the trolleys are more complex. However when compared to other overhead style conveyors that offer the same functionality, Power and Free conveyors are typically the most affordable. Compared with Friction drive systems, Power and Free conveyors have far fewer motors and controls. When compared with Electrified Monorail Systems (EMS), Power and Free Conveyors will typically have 20-30% lower total installed cost.

Considerations for safety

Installation factors make it difficult to provide “per linear foot” estimates, as the support structure for Power and Free conveyors can be either floor supported (on columns mounted to the floor) or supported from above. When the conveyor path crosses over production areas, it is typical to provide falling parts protection for staff that work below. This protection can be a simple as safety nets, but more typically is wire mesh ‘basket’ structures as shown in some of the photographs on this page. Depending on the customer preference, this guarding may be strong enough for maintenance staff to walk up inside the structure or it can be simpler and lighter. OSHA regulations typically require some type of protection for the entire pathway underneath loaded areas of the conveyor at a minimum.

If you are at the early stages of evaluating project feasibility, we can advise you in more depth on the benefits of these types of conveyors, and at the same time provide some budgetary guidance on the cost/benefit of different types of conveyor systems.

P&F Conveyor Systems: Use in harsh or special environments

Power and Free Conveyors are routinely used in harsh environments, including paint ovens, above dip tanks and throughout paint pre-treatment facilities. Where necessary, special shrouding and carrier design can be used to prevent any drips from the chain from landing on the product.  For food safe conveyor systems, Ultimation and Webb’s overhead conveyor systems may be used in food-safe environments with appropriate component and lubrication selection. This includes conveyors utilizing H1 category food safe lubricants.

Why Choose Ultimation Industries?

 We’ve served some of the largest manufacturers in the world, designing and building automation and conveyor equipment in facilities of all sizes. As a woman-owned enterprise with more than 30 years of experience, we’re unique among our competitors. We can address your needs with complete turn-key service from start to finish.

 For more information about any of our systems or to begin working with us, contact one of our representatives today. Our knowledgeable and experienced professionals can help you get started on a solution that meets your facility’s requirements.

Need help learning about other conveyor types, which types to use and how to specify them? This step by step guide will help.