Selecting Maintenance-Free Chain

No matter the application, metal-to-metal contact between pins and bushings in roller chain is inevitable. The wear of the pin and/or bushing due to such contact directly causes stretch in the chain.

It is not hard to imagine that it is necessary to lubricate to avoid the wear of those contact areas, just as your vehicle’s engine requires lubrication for a long life. Without it, the engine locks up in just a few hours.

As you are probably well aware, load capacity and wear resistance are the major factors in determining chain life. In most cases, load capacity is well examined in the designing stage because sufficient information is available in catalogues and other publications issued by chain manufacturers.

Designers are able to select the right chains in terms of chain size by referring to the maximum allowable load and tensile strength of the chain. However, how would they know how fast the chain stretches or when it needs to be replaced? The behaviour of chain in operation over time is always a mystery and that is an area major chain manufacturers are trying to improve.

The best scenario for the roller chain, in terms of the wear life, is that fresh oil comes in and out consistently, with no abrasives and other contaminants coming into the bearing area between the pin and bushing. However, except for a few applications, roller chain is used without an oil bath that would provide such an ideal situation, so its wear life highly depends on the initial and post-installation lubrication.

The ideal frequency for chain lubrication depends on the application. However, generally speaking, once a week is recommended. Some people may feel that this is easy enough, but others may not, depending on how easily accessible are the lubricating areas of the chain. It may be a nightmare for the maintenance personnel who have to lubricate chains located 10 feet above their heads, or who have to remove a number of machine parts to reach the chain. Some users cannot afford to stop the machine for such maintenance due to the production level they must achieve in volume competitive industries.

Eliminating such difficulties or downtime due to the maintenance requirement is the concept of maintenance-free chain.

Generally speaking, the maintenance-free chain available on the market can be divided into two groups — the Sintered Bushing Type and the O-Ring/Oil Sealed Type.

It is not the chain manufacturer that determines which one of these is best for your maintenance-free chain requirements. The application determines the best chain for your money.

Unfortunately, sufficient information is often not provided in any books or catalogues to give you a clear picture to determine the best chain for your application. That may be because some chain manufacturers offer either one or the other of the above two types in their product line and may not be able to provide a comparison.

Table 1 shows the basic differences between the Sintered Bushing Type and the O-Ring Type of maintenance-free chains. It provides some ideas to help in determining which one a user should purchase to keep within their maintenance budget.

You may already know about the money-saving advantages of using pre-lubricated, maintenance-free chain. It offers significantly longer life and less downtime, thus a need for fewer replacement chains, reducing the net amount of money needed to gain the same service life needed.

No matter how much you save from buying a less-expensive standard chain, you may have to replace standard chain up to 20 times while one maintenance-free chain is still running. The replacement cost and the labour for the replacement, plus downtime, can easily consume the money saved and, in some instances, cost significantly more.

If you’ve already tried using maintenance-free chain, you may have had an experience where it did not last as long as advertised. In extreme conditions, so-called maintenance-free chain does not last any longer than the least expensive standard chain.

Sintered bushing chain is designed for slow-speed applications where external lubrication is impractical. It has the advantage of built-in lubrication (the sintering process impregnates lubricant into the bushings). O-Ring chain has lubricant retained within the bushings by O-rings.

You need to keep the characteristics of each type in mind when selecting maintenance-free chain. For example, Sintered Bushing Type maintenance-free chain, where you are trying to run #60 size chain at 1,000 ft per minute, will not last long enough to justify the extra money spent because the application exceeds the maximum applicable speed. However, if you install O-Ring type chain, which is capable up to 4,800 ft per minute in #60 size, it will last as long as it should.

Another caveat about using a Sintered Bushing Type is where paper dust exists around the chain, as dust may get into the chain and work as an abrasive to damage the sintered bushing. With O-ring type chain, the O-ring prevents the dust from coming into the chain and keeps the bearing area free of the abrasive material.

You must examine your application to prevent a mistake in the selection of maintenance-free chain. You also need to request full details about the characteristics of each type from the manufacturer or distributor before you make a final selection based on each type’s advantages and disadvantages. As long as you make the right choice, the savings can be significant.

Yasu Nozaki is a product engineer in the marketing division of Daido Corporation of America, Portland, Tenn.