Understanding chain drive friction wear and lubrication

06.09.2023

Introduction

Chains are multipurpose design elements used to transfer power. They consist of many links, mostly mechanical ones. They are used in different types of industries to slide, carry, push, pull or move the different materials from one end to another. They can also be used to synchronize the moments of different parts of the machine.

Advantages of chain drive systems

  1. Can operate under wet conditions
  2. High transmission efficiency than friction drive
  3. Can operate under adverse thermal and atmospheric conditions
  4. Not prone to catching fire
  5. Produces less stress on shafts
  6. Occupies less space and more compact than belt drives
  7. One chain can be used to transmit power to more than one shafts

Disadvantages of chain drive systems

  1. There may be velocity fluctuation
  2. Initial cost of production is higher
  3. Chain drives requires accurate and careful mounting
  4. Chain drives require lubrication for optimum performance
  5. Not suitable for parallel shafts
  6. Driving and driven shafts must be perfectly aligned
  7. Generate noise while in operation

Applications of chain drives include:

Chain drives are a great choice for applications where power and durability are important

  1. motorcycles, bicycles, and scooters
  2. stand-up gas-powered scooters
  3. lube oil pumps
  4. conveyor belts
  5. printing presses 
  6. garden tillers
  7. mail sorters 
  8. small boat engine 
  9. large truck engine and many other applications

Types of chain drives

  1. Roller chain.
  2. Silent chain.
  3. Leaf Chain.
  4. Flat-top Chain.
  5. Engineering Steel Chain

Chain drive parts

Plate

The plate serves as the element responsible for withstanding the tension exerted on the chain.

banner

Pin

The pin is exposed to shearing and bending forces that are transferred through the plate.

Bushing

The bushing experiences shearing and bending stresses from both the plate and roller, and it also encounters sudden shock loads when the chain interacts with the sprocket.

Roller

The roller is subjected to impact loads when it makes contact with the sprocket teeth during the chain’s engagement with the sprocket.

banner

Friction in chain drive systems

Inner plates and rollers

The primary source of friction within a chain arises from the interaction between the curved edges of the inner plates and the rollers. In the provided diagram, which offers a cross-sectional view of the chain, these inner plates exhibit a slight bend and come into contact with the rollers. Consequently, these plates execute a rotational movement around the rollers, maintaining a gap that is approximately one-fourth the thickness of a standard sheet of notebook paper. This specific gap measurement is a key factor in quantifying chain wear. With continued use, the friction generated by the rubbing of these surfaces during the bending of chain links leads to elongation of the chain. This elongation occurs due to the gradual increase in the gap present within each link. It’s important to note that this friction is a recurring phenomenon that takes place whenever the chain links undergo bending motions.

Inner plates and the pin

The inner plates function as the rotating surfaces around the stationary pin. Achieving minimal friction in this context is greatly influenced by the precision machining of these inner plates to attain the utmost smoothness. When combined with a meticulously polished pin, the exceptionally smooth surface of the inner plate becomes crucial in minimizing friction. This meticulous approach aims to reduce friction to the lowest conceivable level.

Inner and outer plates

An additional significant cause of friction within the chain arises from the interplay between the inner and outer plates. Though it looks like there is gap between these plates but based on the driving conditions it can occur.

Wear in chain drive systems

Chain stretch

Chain wear is often denoted as ‘chain stretch’ due to the elongation of the chain’s pitch as it experiences wear. Among various types of chain wear, this one holds paramount importance, driven by the gradual erosion of the bushings accompanying the chain pins. This erosion leads to an expansion in the inner diameter of these bushings, concurrently causing the pins to develop indentations.

Chain slop

A distinct form of chain wear is termed as ‘slop,’ which emerges when the rollers of the chain become worn-out. This deterioration contributes to heightened lateral mobility within the chain. Consequently, the precision of gear shifting diminishes, resulting in a less precise and more sluggish transition between gears.

Lubrication of chain drives

Proper chain lubrication involves selecting the appropriate type of lubricant, considering factors such as temperature, load, speed, and environmental conditions. The lubricant’s viscosity, adhesion properties, and ability to withstand the specific operational demands play a significant role in achieving effective lubrication.

Regular chain lubrication offers several benefits, including:

  1. Friction Reduction: Lubrication minimizes the friction between the chain’s moving parts, preventing excessive heat generation and wear.
  2. Wear Prevention: By forming a protective layer, lubricants act as a barrier against corrosion, oxidation, and abrasive particles, reducing wear and extending the chain’s lifespan.
  3. Smooth Operation: Properly lubricated chains operate smoothly and quietly, contributing to the overall efficiency of the machinery or equipment.
  4. Energy Efficiency: Reduced friction due to lubrication leads to improved energy efficiency, as less energy is wasted in overcoming resistance.
  5. Maintenance Cost Reduction: Regular chain lubrication can reduce the need for costly repairs and replacements, saving maintenance costs in the long run.
  6. Reliability: Lubrication enhances the reliability of chains in demanding environments by preventing unexpected failures.
  7. Safety: Properly maintained chains are less likely to break or malfunction, which contributes to the safety of operators and surrounding equipment.

It’s important to follow manufacturer guidelines or industry standards when performing chain lubrication. Over-lubrication or under-lubrication can lead to adverse effects, including product contamination, performance degradation, or even catastrophic failure. Regular inspection, cleaning, and reapplication of lubricants are essential components of an effective chain lubrication maintenance routine.

Chain drive lubrication methods

  1. Manual lubrication involves applying lubricant to the chain using a brush, oil can, or spray can and is a cost-effective option for chain drive maintenance.
  2. Drip lubrication utilizes a drip oiler to deliver oil between the inner and outer plates of the chain. Regularly checking the oil reservoir and ensuring proper oil flow is crucial. This method is suitable for low bearing pressure drives, with the recommended oil quantity ranging from 5 to 20 drops per minute per chain strand, depending on the speed.
  3. Oil bath lubrication entails running the lower chain strand through an oil bath within the drive enclosure. The oil level should cover the lowest point of the chain during operation.
  4. Oil ring lubrication involves the chain running above the oil level, with a rotating disc submerged in lower oil. This disc spreads oil against the casing walls, allowing it to flow down onto the chain via drip rails.
  5. Force-fed lubrication employs an oil pump and feeding pipe to continuously spray oil onto the inside of the lower chain span. The spray tube should position the oil just before the drive sprocket engages, ensuring the oil is distributed by the chain and dampens the impact of rollers on the sprocket teeth. Force-fed lubrication is ideal for efficient cooling and shock absorption at high speeds.

Measuring chain wear

Chain Wear Gauge: It is a tool that accurately measures leaf chain and roller chain wear and indicates the percentage of elongation so you know when it’s time to replace your leaf chain safely.

Chain test rig: These are rigs or tribometers designed and built to perform wear test on chains

Reducing chain drive friction and wear via coatings

Bobzin and their research team conducted an investigation into the tribological properties of five different (Cr,Al,X)N coatings, where X represents Mo and Cu. They carried out tests using a pin-on-disk (PoD) tribometer and a chain joint tribometer (CJT) on flat specimens and chain pins. The outcomes of their study revealed that the (Cr,Al,MoH)N coating consistently demonstrated the lowest and most stable coefficient of friction (CoF) when combined with a grease + S lubricant, in contrast to the other coatings. On the other hand, the (Cr,Al,Mo,Cu)N coating exhibited a low CoF but displayed less stable performance.

References

  1. The complete guide to chain – Functions of chain parts
  2. What is chain drive: Advantages and disadvantages of chain drive over belt and rope drives
  3. Chain drives and types of chains
  4. Chain friction explained
  5. Bicycle chain wear explained | How to know when to replace a bike chain
  6. Technical concept: Chain drive lubrication
  7. Five roller chain lubrication methods
  8. Properly lubricated chain last longer
  9. Bobzin, C. Kalscheuer, M.P. Möbius, M. Rank, M. Oehler, O. Koch, Triboactive coatings for wear and friction reduction in chain drives, Tribology International, Volume 185, 2023, 108562, ISSN 0301-679X, https://doi.org/10.1016/j.triboint.2023.108562. https://www.sciencedirect.com/science/article/pii/S0301679X23003493

Harshvardhan Singh works as a Senior Service Engineer at a mining firm in India. He is currently working into oil analysis field. Has worked in the filed of tribology and lubrication and loves to write about the same.

Be the first to comment

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.