1.3.2 Sealed Roller Chain
Lube-free type: High-speed transmission, in dusty conditions
Sealed Roller Chain may be useful for general industrial applications that run at high speeds or in dusty conditions. (See Figure 1.9.)
Figure 1.9 Sealed Roller Chain
Construction and Features
Sealed Roller Chains have O-ring seals between the pin link and the roller link plates. These seals keep the lubricant in and contaminants out. The inner width of the chain is the same as ANSI specifications. The total width of the chain is larger than the ANSI measurement because the bushings usually extend beyond the roller link plates to protect the O-rings.
Sealed Roller Chains are available in sizes 40 through 100. The average tensile strength is slightly lower than ANSI Roller Chain.
Standard sprockets are used for single strand chain.
Selection and Handling
- O-ring seals are usually made of acrylonitrile-butadiene rubber, which is highly resistant to oil, heat, and abrasion. Fluorine rubber O-ring seals are available for high heat operations (greater than 120°C).
- The link plates holding the O-rings are under compression. This means greater force is required to articulate the chain, and the transmitted power is decreased. At places where the chain tension is low (such as the return side) the strand will retain the bend. The manufacturing tolerances of the O-rings are generally large, therefore, it is difficult to make the bending resistance of O-ring chain smaller and stable.
- When the oil film between the O-ring and the link plate is gone, the O-ring will wear and deteriorate. Rubber has a "creeping" property, and it tries to make the contacting surface flat. Therefore, it becomes more difficult to get the lubricant into the working parts.
- During long-term operation, the O-rings may start to fall off the chain. Then, the elongation at that spot will progress very rapidly. If this occurs, it is time to replace the chain, even if the total chain has not reached the elongation limit (1.5 percent).
- The cost of Sealed Roller Chain is higher than ANSI Standard Roller Chain. The higher cost is because of the additional and special parts (O-ring seals, longer pins and bushings). Unfortunately, less expensive standard components cannot be used for Sealed Roller Chain.
Chain manufacturers are constantly striving to improve the quality and wear life of chains in general, including Sealed Roller Chain.
In the area of seal research, a variety of shapes of seals has been tested. The goal is to reduce the bending resistance and yet keep the lubricant in the working parts. Currently, O-rings are the most practical alternative.