Excessive Roller Chain Wear? Why It Occurs
There’s a reason we replace roller chains regularly. The movement of chain around a sprocket naturally causes wear, but excessive roller chain wear and fatigue cause problems. A well-maintained chain drive will keep your machine running strong over time, making it important to minimize the impact of wear.
As the chain wraps around the sprocket, the pins and bushings wear through constant friction. Inevitably this movement causes elongation of the chain as the pin and bushing materials wear away. Once roller chain elongation reaches 3% when used with a sprocket under 67 teeth, or 1.5% when used with a sprocket with 67 teeth or more, the chain needs to be replaced.
The first lines of defense against any roller chain problem are proper installation and regular maintenance. Assuming the correct installation of your drive – lubrication, material finish, and sprocket placement can be factors in excessive roller chain wear.
Let’s troubleshoot with the most likely culprits first.
Prevention is key
Before troubleshooting, we recommend you review proper installation practices. When installing your chain drive, make sure all the drive components are in good condition – from the bearings to the sprockets.
Alignment is crucial in preventing unnecessary wear and tear. The angular alignment of the shafts should be parallel to each other, and the axial alignment of the sprockets should be on the same plane. You can use a straightedge or laser to check both these alignments at multiple points.
Finally, your chain drive needs to be correctly tensioned and have an appropriate lubrication system in place before operation. Chain sag should be 2-4% of center distance, which is the distance between the center of the two shafts. Inspect the entire span of the chain once installed for the proper function of all components. There should be no unusual noises or visible problems with the chain.
Exceeding max working load?
Once you’ve confirmed the correct installation of the roller chain, what’s next? A common problem causing excessive roller chain wear is load size. Comprehensive testing by the manufacturer establishes the max working load for every chain. This rating is developed through multiple types of tests examining when chains break and at what load breaks occur.
When designing a chain drive, make sure the parts used – including the chain – can handle the horsepower of your prime mover. Remember, these numbers came from manufacturer tests in a controlled environment. If your machine runs somewhere hot, humid, at high altitudes, or is abnormal in any other way, your working load will be affected. It’s worth confirming your calculations, consulting an engineer that specializes in power transmission or using a higher rated chain if your conditions are a bit extreme.
What materials are used in your chain?
The material and finish of the pin and bushing surfaces will influence how quickly they wear down. Factory-preloaded chain will reduce initial stretch, and consistent precision heat treatment creates a harder, more robust roller chain. Manufacturing methods and processes will have significant effects on how well the chain will perform. Higher quality chains last longer.
Most roller chain manufacturers have features included in certain lines, typically premium roller chain, that will deter premature wear. Oil ports in bushings provide improved lubrication to the areas that need it. Solid bushings will be able to better handle the requirements of operation compared to a bushing with a seam, resisting deformation at a much higher level. The same can be said for the rollers as well. Quad-staked pins will increase the durability and resistance to heavy shocks.
There is also a heavy series version for most chains that feature thicker side plates and longer pins, which increase the max working load by about 10%. Even small changes to chain components like this are often the most economical way to increase chain life. Matching specific features of roller chain to your application can result in more prolonged and efficient operation.
Never hesitate to reach out to an industry professional for help in determining what may work best in an application.
Is your lubrication system up to the job?
Lubrication is always critical for moving parts. Every drive requires lubrication, and the best option is a pump or stream lubrication. Depending on your chain drive and the horsepower of your prime mover, a less robust system may work for you.
Regardless, we recommend high-quality, non-detergent, petroleum-based oil. A few critical internal surfaces of the roller chain require a coating of oil. Heavy oils and greases cannot get between the tight tolerances between the roller and roller-link and between the roller-link and pin-link plate.
It’s also important to note that your drive will require minimum lubrication requirements based on small-sprocket rotation speed and tooth count. The viscosity of oil needed changes depending on the system, but not everyone realizes the method of lubrication may change as well.
Your method of lubrication will limit the allowable feet per minute rating of your chain. For example, if you’re using manual lubrication with #80 or 1-inch pitch chain, your maximum feet per minute is 90. If you’re using an oil-bath method, it increases to 1100 ft/min. Pump lubrication (as seen below) is the only way to achieve a roller chain’s maximum rated speed.
Occasionally a chain drive will require more than two sprockets. You can make a drive with an 8:1 ratio work with careful design and excellent maintenance, but a smaller ratio will save you a lot of headaches. Double reduction drives have improved operating characteristics and are often more economical and efficient in the long run.
When it comes to tooth count, there are a few things to consider. Ideally, the total number of teeth between the large and small sprockets should be at least 50. On any sprocket with fewer than 25 teeth, you should have an odd number of teeth. The same goes for your small sprocket regardless of tooth count. This will ensure uniform wear of your roller chain.
If you’re using a small sprocket with a small tooth-count, there are some minimums to consider. A slow-speed drive with manual or drip lubrication will need at least 11 teeth. A medium-speed drive with bath or slinger disc lubrication will need at least 17 teeth. A high-speed drive with pump lubrication will need at least 25 teeth.
What’s your chain length?
Chain length must always be a whole number of pitches. Very rarely will the standard length of chain purchased fit your machine. When you’re adjusting the roller chain length to fit your drive, make sure the adjustments are made properly. We recommend using a chain length with an even number of pitches to avoid using an offset link.
If an offset link is unavoidable, use a two-pitch offset section instead of a one-pitch offset length. Remember, any offset you use will become the weakest link in your chain, and the max working load of your chain will decrease.
As a general rule of thumb, you want your roller chain length to be between 70 and 160 pitches. This is a guideline, not an absolute. Chain lengths of up to 200 pitches are viable without excessive catenary tension or the risk of jumping sprocket teeth.
Proper care during installation, along with standard safety precautions and maintenance, will help you avoid catastrophic failure and maximize the effectiveness of your system.