1.4.3 Stainless Steel Roller Chain (SS)
Transmission: Corrosive environment. Manufacture of foods, chemicals, and medicines
All parts are made of austenitic 304 stainless steel.
The material composition is:
- Carbon (C): less than 0.08%
- Chromium (Cr): 18.00 to 20.00%
- Nickel (Ni): 8.00 to 10.50%
SS Roller Chains are the most commonly used environmentally resistant chains for the manufacture of foods, chemicals, medicines, or transmission in water. They are also used in indoor conditions where rust is a problem. (See Figure 1.12.)
Figure 1.12 Stainless Steel Chain
Construction and Features
The construction and sizes of SS Roller Chains are the same as ANSI Roller Chains. Each part is formed from 304 stainless steel by cold working processes, such as press processing and machining. The pins are assembled to the outer plates and the bushings to the inner plates. Neither solution annealing nor passivating treatment are done on SS Roller Chains.
SS Roller Chains have the following features:
- Attractive appearance of glossy stainless steel.
- Exceptional corrosion resistance. But in certain highly corrosive conditions, stress-corrosion cracking may occur.
- Exceptional corrosion resistance and strength at high temperatures. These chains can operate in high temperatures, but the manufacturer should be contacted for applications above 400°C.
- These chains may be used in extremely low temperatures, because low temperature brittleness does not occur.
- There is slight magnetism, due to the cold working processes.
- Due to the cold working processes, the surface of the chains may rust in some conditions.
- The tensile strength of SS chain is almost half that of RS Roller Chains.
- The chain parts are not heat-treated (such as quenching and tempering). The tensile strength and hardness of these parts are lower than that of RS Roller Chains.
- Because the surface hardness of the working parts (pins, bushings and rollers) is low, the wear resistance is also less than that of RS Roller Chains. Due to the lower thermal conductivity of stainless steel, the working parts retain more heat, which also lowers the allowable tension of SS Roller Chains. The allowable tension of the chain is determined by the wear resistance.
- Numbers 11 through 240 are available. (Number 15 is not available.) Only sizes smaller than number 80 are usually stocked. Nonhardened materials with low thermal conductivity must be designed with smaller press fits. This fact also makes the allowable tension of these chains lower than RS Roller Chains.
SS Roller Chains run on standard-sized sprockets. In corrosive conditions, stainless steel or engineered plastic (less than 70 m/min.) sprockets should be used. Carbon steel sprockets may corrode and contaminate the chain and the environment.
Selection and Handling
If SS Roller Chain is used in water within the allowable load published by the manufacturer, the water acts as a lubricant, and the chain has additional wear resistance. (See Figure 1.13.)
Check the manufacturer's catalog for the conditions when SS Roller Chain is appropriate.
When determining the allowable tension, do not consider the safety factor and/or the tensile strength of SS Roller Chains shown in manufacturers' catalogs. The tensile strength of SS Roller Chain has no practical meaning.
Surface treatment of the working parts, such as platings or nitriding, may improve the wear resistance of SS Roller Chains, but the coating may peel off and contaminate the environment. Nitriding usually reduces the corrosion resistance of the chains. Contact the manufacturer for additional information.
Figure 1.13 Use of Stainless and Standard Chain in Water
When chains are cycled between the freezer and room temperature, dew forms and freezes on the chains. This may cause noise, difficult articulation, and chain breakage. Silicon grease applied to the gaps of the chain helps to prevent this.
When SS Roller Chains are used at temperatures greater than 400°C, extra clearance in the chain joints is required. The thermal expansion may cause the joints to seize and the chain to break. Advise the manufacturer of the operating temperature(s) in which the chain will be used.
You can extend the working life of SS Roller Chains with proper lubrication. The chains should be lubricated as much as possible when the application allows it.
Other corrosion-resistant stainless steel chains are shown below. For conditions and size availability, check the manufacturer's catalog.
All parts are made of austenitic stainless steel SS316.
The composition of this material is:
- Carbon (C): less than 0.08%
- Chromium (Cr): 16.00 to 18.00%
- Nickel (Ni): 10.00 to 14.00%
- Molybdenum (Mo): 2.00 to 3.00%
NS series chains cost more than SS Roller Chains but have greater resistance to corrosion and heat. When the chains are used in temperatures above 400°C, contact the manufacturer. The allowable tension is the same as SS Roller Chains. These chains are considered almost nonmagnetic.
Pins, bushings, and rollers (double pitch oversized rollers are SS304) are made of precipitation-hardened stainless steel. The plates are made of the same material as SS Roller Chains. Due to the hardened pins and bushings, this series has higher wear resistance. The maximum allowable tension is 1.5 times that of SS Roller Chains. That means you can use a smaller chain and get equivalent performance. The corrosion resistance is less than SS Roller Chains. These chains are somewhat magnetic.
Other Precipitation-Hardened Series
There are other types of stainless steel chains that have case-hardened or all precipitation-hardened stainless steel components, including the link plates. The tensile strength is higher than SS Roller Chains, however, the wear resistance and the maximum allowable tension are the same. Talk with the manufacturer about the availability and applications of these chains.
SS Engineered Plastic Sleeve Series
The engineered plastic sleeve between the pins and bushings make this a lube-free variation of SS Roller Chains. These chains cannot typically work in water or other liquids with some exception, such as Tsubaki LS series, but are good for indoor conditions where rust should be avoided. The allowable tension is the same as SS Roller Chains.
All parts are made of titanium or titanium alloy. These chains have greater corrosion resistance in chloric conditions and no magnetism. The chain's weight is very light (about half of the same-sized steel chain). The allowable tension is the same as SS Roller Chains.
In stainless steel chain design, corrosion resistance is the most important factor. The allowable tension is much lower than RS Roller Chains. For example, the maximum allowable tension for RS80SS is 1.77 kN versus 14.7 kN for RS80. The allowable tension for SS Roller Chain is about one-eighth that of RS Roller Chain. In the AS series, the ratio is 1 to 5.5. Researchers continue to study ways of increasing wear resistance and allowable press fit at assembly.