If I gave you a piece of wire and asked you to break it, you would probably move it back and forth rapidly between your fingers. You would feel it getting hot, and soon the wire would break. You have just experienced a fatigue failure. Fatigue is probably the most common cause of failure of any steel product, whether chain or any other mechanism that uses steel.
Individually all parts of a chain are important, but none as important as the chain pin. This is the heart and soul of chain, and will in most cases determine the life of the chain. Engineers like to say the pin “articulates around a sprocket,” which in my language means, the pin moves back and forth between two rigid parts – something like the wire held rigidly in your fingers. That creates a condition of fatigue that can lead to failure, or breakage.
So then, our problem is to find a way to reduce or minimize the possibility of a fatigue failure. Fatigue occurs by slow growth of a crack which usually begins at a weak point on the surface, or at a point where the loads are higher than elsewhere. (Engineers call this a “stress concentration” – they like to confuse us with big words.)
Welded steel chains usually have the designation, “WR” or “WH” preceding the chain size. The “WR” designation means the pins only are heat-treated. The “WH” designation means all the parts, sidebars, bushing and pins are heat-treated.
Pre-lubing a chain before installation can add many months and years of life to the chain. There are many ways this can be done, but probably the easiest way is to immerse the chain into a barrel of ordinary motor oil of the proper viscosity for the prevailing conditions. Let the chain sit for some time to allow the oil to seep into chain joints and the barrel cavity.
Then, install the chain, run it for a period of time to set the joints, and you should have a chain that will out-perform anything you tried before. Through regular, periodic lubrication in the months ahead, you will have a chain that will last and reduce your maintenance and downtime costs.
Improperly designed sprockets can raise havoc with even the best chains. The chain sprocket interface is probably the greatest contributor to excessive chain wear, so if you want to improve chain life, give extra care to sprocket selection. Some rules of thumb to consider:
Smaller sprockets are harder on chains than larger sprockets. If you have room in your drive or envelope consider using a larger sprocket with more teeth. Increasing a sprocket by even two teeth will help improve chain life.
Try to use sprockets with an uneven number of teeth. Chain tends to strip off the bottom of the sprocket better, especially with a 180⁰ wrap installation.
We generally recommend the diameter of the sprocket to be about 4 times the chain pitch.
Be particular about the chain return. The chain should have enough slack to provide a catenary of from 5-10% of the center distances between the sprockets.
The selling of chains in the Industry has added much confusion to a very simple problem. New “Buzz Words” are added that increase the confusion. New phrases are used, unsubstantiated claims are made, warranties are written based upon what the customer is willing to pay, and most serious of all, minor design changes are made to keep the customer captive to one manufacturer
There are claims made for “armour case,” “selective induction hardening,” “alloy equivalents,” “induction hardening,” “case hardening,” and the list goes on, and on, and on. The user doesn’t really know what to think about these claims, and what is fact or what is fiction. Yet, some explanation and understanding of good chain design, maintenance practices and how to use the product correctly could reduce the confusion, increase the life of the chain, and eliminate the “unscheduled down time,” caused by a chain failure.