Roller Chain Failure: Causes and Prevention Strategies
No one wants a roller chain to fail, and stopping operation while replacing a roller chain is disruptive and costly to the roller chain. Unfortunately, this is something we have to deal with occasionally.
There are many reasons for a chain to break. When the drive load exceeds the chain rating, the chain is at risk of breaking. This problem is relatively easy to avoid at the design stage. Roller chains can also break due to prolonged use and occasional accidents. Chain fatigue is hard to spot. Accidents (by their nature) are difficult to predict.
Let's explore some safety precautions you can take to keep your roller chain from failing on the job.
Prevention is better than cure
The first line of defense against roller chain failure is a well-designed drive. Run the numbers and confirm that the chain can calculate the capacity of the prime mover. Doing this should prevent the chain from breaking completely.
First, check the service factor of the drive. The service factor is created by including the type of driving equipment, prime mover, duty cycle, and load severity of the drive. Giving any combination of these factors a numerical value at the design stage, allows the service life to be balanced by the strength of the selected components.
Requiring the chain to move an excessive load can lead to failure. Specifications to consider include average tensile strength, minimum ultimate tensile strength, and maximum working load.
A tensile strength test measures the load required to break a chain. The average tensile strength is the average weight of the load breaking the chain during repeated tests. The minimum ultimate tensile strength is the minimum load at which a new chain breaks. Roller chain failure does not have to meet the ultimate or minimum ultimate tensile strength. Repeated overloads at or near the stretch limit will be enough to cause the chain to fail.
Asking your chain to do more work than it can handle can lead to roller chain failure. Planning ahead can prevent these outright disruptions from happening. However, preventing fatigue can be a little tricky. The process of fatiguing the chain takes longer, making it harder to find the cause.
Is your chain installed correctly?
Improper installation can increase fatigue rates. Safety precautions are always the first step in any installation or maintenance process. We recommend that you check each part for wear and replace it if necessary.
For chain installation, it is also important to make sure the shaft and sprocket are aligned. Check for multiple points on each axis and make sure they are equidistant. Since the chain drive comes together during assembly, remember to consider using connected or offset links. These are easy to overlook in the drive design process, but if used, they become the weakest part of the chain. Be sure to take them into account when determining the maximum load for your application.
Is your chain well lubricated?
Lubrication is essential to keep the chain in good condition. Unlubricated connections within the drive can increase friction and quickly lead to fatigue. The lubrication method must be changed as the speed increases. Higher speeds require more lubrication at the pin-socket connection.
Use high-quality, non-detergent, petroleum-based oils. Heavy oils and greases are too hard to properly lubricate all chain surfaces and maintain an oil film between pins, bushings, and rollers.
Lubrication methods can vary widely, but there are some better options. Pump or flow lubrication will most thoroughly oil all critical surfaces. Oil bath or slinger lubrication is also an effective method.
Grease lubrication is possible but not recommended. If required for your application, limit chain speed to less than 13 ft/sec. For proper operation, soak the chain in hot liquid grease until no air bubbles rise. Repeat this operation periodically.
Is it time for maintenance?
Regular maintenance is an effective way to prevent premature chain fatigue. Ideally, you would check the drive after the first 100 hours of operation. Check the elongation of the chain, the functionality of the lubrication method chosen, and any other signs that the chain is not properly aligned - such as wear on the inside of the side plates.
After the initial inspection, most drives require a maintenance inspection every 500 hours. Check for excessive chain sag. Chain sag must not exceed 4% of sprocket center-to-center distance.
Care must be taken with the chain connection as it is the weakest part of the chain and the sprockets must also be checked for wear. As a general rule, your sprockets should be replaced every third chain change.
Accidents cannot be controlled but can be mitigated with some safety precautions. First, use the proper chain cover. Ideally, leak-proof housing will provide additional protection for the chain and help maintain a high level of lubrication when needed. Guards also prevent things from falling between the chain and sprockets, which could lead to catastrophic failure.
Overload safety devices (OSDs) also prevent costly and dangerous failures. The OSD contains a torque limiter to prevent overloading the equipment. They disengage when the set maximum load is reached. Essentially, this allows the driver to slide until the obstacle is removed.
Regular maintenance and proper installation go a long way in preventing accidents. Your roller chain will only work better when it's well lubricated, within the chain's design capabilities, and not wearing out. A chain in good condition is less likely to fail suddenly or cause an accident.
The above describes how to effectively prevent the failure of the roller chain. If you want to know more or want to replace your failed roller chain, please contact us.
As a power transmission chains manufacturer, ZMIE provides high-quality roller chains to meet the needs of different industries. With over 15 years of experience in the conveyor and transmission industry, our technical team can issue kinds of drawing formats as per the customer's sample. Our automated assembly system and progressive die stamping on standard roller chain plates increase productivity. This means that we can achieve the most cost-effective price, the most stable quality, and can deliver in the shortest time.