Crucial Facts for Purchasing New or Replacement Conveyor Chain

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2 Crucial Facts for Purchasing New or Replacement Conveyor Chain OVERHEAD CONVEYOR SYSTEMS Powered overhead conveyor systems are a space-efficient solution for many types of operations such as material handling, WIP, finishing, distribution, warehousing, and fulfillment centers in many industries including automotive, electronics, consumer goods, and appliances. Monorail or Power & Free Two types of overhead conveyors, Powered Monorail Conveyors and Power & Free Conveyors, are commonly used. Powered Monorail Conveyors are continuously powered systems that directly move the load from one point to the next on a single continuous track. They have no flexibility for multiple paths. Power & Free Conveyors are more versatile for many applications, having multiple lines. This design allows work to be done in an interface area that is not moving, and then releases that product to a powered line for the next operation. The Power & Free design can divert work to a temporary holding place or a long term storage area and also call back work in process for the next operation. Both types of conveyors require the use of an enclosed track that houses chain. Conveyor chain is the heart of the system and can yield improved efficiencies, more throughput, and lower labor costs. The dependability of chain directly correlates to the success or downfall of a production operation. Monorail Whether buying chain for a new overhead conveyor or purchasing replacement chain for an existing one, it s important to be aware of key factors that can have an impact on overall system performance. First, let s explain the specifics of chain design in order to explore the differences among various chain options. Power & Free

3 CONVEYOR CHAIN BASICS Overhead conveyor chain consists of a series of linked vertical and lateral wheels either riveted together, connected by nuts and bolts, or connected by means of alloy pins and hardened steel rollers. The following diagram identifies a typical conveyor chain and the glossary below further explains each component. Vertical Wheel Link The Vertical Wheel Link consists of two machined wheels connected by an axle and load pin. The vertical link carries the load and rolls on the bottom of the track. A vertical link can hold a load pendant and carrier to move loads of up to 75 pounds. Lateral Wheel Link The Lateral Wheel Link is a forged steel link with a heavy-duty machined wheel. It rolls against the sides of the track when going around horizontal curves, bearing all the side forces in relation to chain pull. Axle Vertical Wheel Link Lateral Wheel Link Load Pin

4 TYPES OF CHAIN CONNECTIONS Cotter Pin Chain A cotter pin chain consists of vertical and lateral links connected with an alloy pin along with a cotter pin through a hole in the alloy pin. The connection is very stable. The alloy pin does not turn during use because of a d-slot in the link which matches the underside of the alloy pin s head. Cotter pin connection, while being very stable, allows for easy chain adjustment when there is a need for removal of links. This is crucial for taking up chain slack and for preventive maintenance to remove individual links at the onset of chain wear. Cotter Pin Riveted Chain A riveted chain connects vertical and lateral wheels permanently. This type of chain is inherently harder to adjust and more labor intensive to remove links of chain with chain wear. Removal of riveted chain sections requires careful drilling or grinding out the rivets and replacing the new section with nut and bolt fasteners. There s risk of damage to the adjacent chain links during the drilling or grinding process. Where the connection now becomes nut and bolt, there is a risk that the nut may loosen over time and the chain may separate. Riveted Nut and Bolt Chain Vertical and lateral links can be joined together with nuts and bolts. The ability to detach links when necessary is an advantage over riveted chain. However, installation of nut and bolt chain is more labor intensive than installing other types of chain. There can be costly and continuous maintenance with this chain because nuts and bolts have a tendency to loosen over time, causing loss of components that can jam the entire system. The end result can be expensive in lost productivity costs while an entire production line is shut down to troubleshoot. Nut and Bolt

5 CHAIN BEARINGS & CHAIN FUNCTIONALITY Chain Bearings Full Complement or Caged Bearings Bearings are used in lateral and vertical wheel links to distribute the load efficiently. Free falling, full complement wheel bearings do not distribute the load evenly around the bearing race, can cause unequal wear on the wheels, and contribute to drag. Additionally, systems with full complement bearings are noisier because the bearings fall against each other. A caged bearing design distributes bearings evenly around the wheel for the lateral and vertical links to run smoother and more efficiently. Caged bearings are prevented from scuffing against each other, resulting in less drag for better performance and creating an inherently quieter running system. Chain Pitch Chain pitch is the distance between carrier hanging points and is usually 6 or 8 in most systems. Chain pitch is an important consideration: closer chain pitch is more desirable for negotiating smaller radius curves and for providing 35% more loading capacity per foot of conveyor than longer 8 pitch. Tighter curves can yield a more space efficient system and increased load capacity can translate to greater efficiency and higher throughput. Caged Bearings Full Complement Chain Pitch 6 or 8

6 CHAIN BEARINGS & CHAIN FUNCTIONALITY Chain Stretch Chain stretch is the result of normal chain wear over time when the metal is worn away at the link. This results in chain elongation. The industry standard for replacing chain is when chain stretch reaches one-quarter inch per foot. Chain elongation that is not monitored can create a multitude of operation malfunctions. Slack from elongation that is not removed can cause chain pulsation which is the acceleration and coasting of the chain instead of smooth uniform movement. A more serious problem caused from chain slack is when the slack backs up into the drive unit. This will cause failure at the drive unit with possible damage to the conveyor chain itself. This can and will result in an accelerated rate of system wear and failing. Chain Pull Chain pull is the combination of forces resisting the movement of chain through the system. These forces consist of the frictional resistance of the chain wheels to the track and the chain wheel bearings brought about by the weight of the chain, carriers, and loads being moved; the weight being lifted through vertical inclines; and the speed at which the chain is traveling. Chain pull will dictate the length of the system, the number of drive units, and whether multiple conveyors are required for efficiencies. A properly designed system with carefully planned chain pull limits increases the life of the track and chain before its maximum elongation. Chain Stretch Wear Point Chain Pull Frictional Resistance Wheel Bearings Chain Speed Carriers Wheels to Track Load

7 CHOOSING THE RIGHT CHAIN When selecting new or replacement conveyor chain it is important to consider productivity and throughput goals, daily run time, and acceptable down time for maintenance. Is increasing throughput the top goal? Then the system would benefit from a 6 chain pitch that could increase productivity by 35% rather than an 8 chain pitch. Is system longevity a key requirement? Caged bearing chain with reduced drag can extend overall system life and performance by as much as 40% to 60%. Is the operation limited by floor space? Carriers spaced closer together on 6 centers can negotiate tighter curves and reduce overall system size. Are maintenance hours limited? Do shift requirements or lack of personnel translate to a small window of opportunity for conveyor maintenance? Then chains such as riveted or nut and bolt configurations might not be appropriate. Is occasional line failure an unacceptable risk? Consider buying quality chain with high performance value to reduce line failure. Line shutdown can cost hundreds of thousands of dollars in lost production. Cheaper after market replacement chains that fail after a short time can be a poor value in the long run. Published life cycle tests* comparing replacement chains with identical chain pull and loading have determined that certain chain designs outperform others by as much as 19% to 40%. This translates to replacing the entire system s chain with much greater frequency, either every 3 or 4 years for certain chains versus a 5 year period for the high performance chain. An economy chain that is perceived as an initial value might prove to be very expensive over time. Choose your conveyor chain wisely for increased life expectancy, lower maintenance costs, and greater productivity. The best value in chain is the one with the highest life expectancy and proven performance. Cotter Pin Caged Bearing 6 Chain Pitch *Life cycle test published by Richards-Wilcox, Inc., Copyright, December 2007.

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