Lubed Chains Live Long Lives
Ken Bannister | July 12, 2018
If the proper lubricant is applied in the proper places, chain wear can be greatly minimized and maximum performance sustained.
The industrial world relies heavily on sprockets and chains to connect driveshafts to driven shafts and transport goods and materials from point A to point B in endless loops, among many other functions. Chains are widely used because they inexpensively and efficiently transmit and transfer dynamic and static loads. There are four primary categories:
• drive chains—a pedal bicycle chain
• control chains—an automotive silent “hyvo”-style (inverted tooth) timing or transmission chain
• transport chains—an overhead power and car-assembly-line conveyor chain.
• lifting chains—a sluice-gate lift or chain-hoist loop chain.
The majority of chains are manufactured from formed-metal sections, known as links, which are drilled at both ends to take a bushed or non-bushed pin used to join it to the next link to allow the multi-link chain to articulate around a drive, idle, or driven sprocket with close to 270 deg. of motion. Larger conveyor chains use rolling-element bearings in which the locate/swivel pin acts as the shaft.
Because industrial chains perform complicated movements in a variety of working conditions and environments, they create a unique set of lubrication demands due to:
• oscillation movement of the friction components that create a permanent state of demanding sliding and rolling friction
• line contact of pins, bushings, and rollers that create high surface pressure
• intermeshing of chain links and sprocket teeth that result in high shock loads.
Most chains fail as a result of ineffective lubrication. Arguably, the highest failure rate results from pin and bushing wear caused by dry running a chain. This condition can prevail even when lubrication is attempted but the delivery fails to place the lubricant in the bearing-surface area. It also results when a non-chain-friendly lubricant is used. Wear causes the chain to elongate which, in turn, alters the pin-to-pin link pitch. When this occurs, the chain no longer mates smoothly with the corresponding sprocket teeth, resulting in the chain dragging and snatching and sometimes “skipping” a tooth, thus changing the driver-driven timing and causing the machine to fail dramatically.
Improper mating also wears/damages sprocket teeth. Replacing worn sprockets can often be much more expensive than maintaining or even regularly replacing a chain.
When a chain demonstrates such behavior, the tendency is to believe it has “stretched,” but this is not the case. Chain stretch is cause by fatigue brought on by overloading the chain with tension which causes the chain to literally be pulled apart.
To meet the demanding service conditions in which chains are used, combat premature wear, and stop the chain from rusting, specialized lubricants are needed with the following features:
• Corrosion protection: Ferrite metals rust quickly when moisture collects on unprotected surfaces. This manifests itself as a reddish-brown staining on the surface and throughout the oil when no anti-corrosion additive is present.
• Wetting or creeping property: This allows the oil to penetrate, displace water, and carry the lube to the intended and most vulnerable part of the chain where maximum wear occurs.
• Adhesiveness: Tackifier agents are often added to ensure the lubricant is not easily slung off the chain by centrifugal action of the rotating sprockets and the chain moving at speed.
• Temperature stability: Whether a chain is used in a refrigeration plant to carry product through a fast-freeze process or in a bakery to move dough through a high-temperature oven, the oil must be able to function in a wide temperature range. This requires the correct base oil with a high viscosity index (VI) rating.
• Low-coking tendency: Coking leaves a residue on the chain. Should it fall off, it can damage the conveyed product.
Applying the Lube
Chain lubricants can be applied in several ways, depending on the work application.
Manually pouring, brushing, or spraying the oil directly onto the chain whenever it appears to be dry can be risky business if chain failure is an unacceptable consequence. If manual lubrication is an acceptable practice, always ensure the chain is lubricated on the inside face as it moves into the sprocket to ensure the sprocket receives adequate lubrication at the mating faces.
Gravity-drip oilers are an inexpensive way to apply lubricant to chains, either by dripping directly onto the chain or onto a brush that touches the chain surfaces. These types of systems, although inexpensive, require setup and regulation time to prevent over-lubricating the chain. When chains are used in contained spaces, such as in an engine or an enclosed-guard system, an oil-bath lubrication design, with the lower portion of the chain running directly through a flooded sump in the enclosure, is preferred. The chain should only be submerged to its running pitch line for a short section of the chain to avoid overheating and oil churning.
An alternative in a closed area is an automated oil-mist or continual oil-spray system that applies lubricant to the chain in droplet form. This will not only lubricate and continually clean the chain, but also allow it to run cooler and energy-efficiently.
Large, slow-moving conveyor chains with forged links and chain pitch as high as 7 in. are predominantly lubricated by fully automated dynamic chain lubricators. Those devices volley or shoot a lubricant charge directly into the pin-link gaps and into the open race rolling-element bearings that convey the chain through the plant. Many of these lubricators are switched on when the drive amperage reaches a determined level. Link counters then count how many links it takes to go one or two chain-length revolutions before switching the lubricator off until the cycle starts again.
The key point to remember is that a quality lubricant applied correctly will significantly increase a chain’s efficiency and life cycle. Failure to properly maintain your site’s chains will lead to the cost and frustration of unplanned replacements and all the downtime that goes with them. EP
Contributing editor Ken Bannister is co-author, with Heinz Bloch, of the book Practical Lubrication for Industrial Facilities, 3rd Edition (The Fairmont Press, Lilburn, GA). As managing partner and principal consultant for Engtech Industries Inc., Innerkip, Ontario, he specializes in the implementation of lubrication-effectiveness reviews to ISO 55001 standards, asset-management systems, and training. Contact him at firstname.lastname@example.org, or telephone 519-469-9173.