1.4.1 Nickel-Plated Roller Chain (NP)
Transmission, conveyor: Mild corrosive environment
Nickel-Plated Roller Chains combine strength close to ANSI Roller Chain with the corrosion resistance that comes from the nickel plating. These chains are used in applications where you want light corrosion resistance. For example, NP chain might be used in an application that has limited contact with water. (See Figure 1.11.)
Construction and Features
Plated Roller Chains have corrosion resistance and the attractive appearance of nickel plating for a low cost. The strength and wear resistance are almost the same as standard chains. These chains are a good buy if they are selected correctly. Numbers 25 through 120 are standard.
Generally, small pitch chains are plated before assembling, and large pitch chains are plated after assembling. Either way, the interior surfaces of the components may not receive complete coverage.
Standard sprockets are used. When the application requires no rust, use stainless steel or engineered plastic sprockets. With engineered plastic sprockets, the strength and speed (less than 70 m/min.) are limited.
Selection and Handling
- Plated Roller Chains, however well plated, will experience flaking of the plating from the interior surfaces and the roller surface that rotates on the roller guide and impacts the sprocket. If this flaking presents a problem (for example, danger of flakes getting mixed into foods), use stainless steel chains.
- Nickel has a higher electrical potential than the base metal. If the nickel plating flakes off, corrosion will progress faster at that point. Zinc plating has a lower electrical potential than the base metal, therefore, the corrosion will progress more slowly. But frequent exposure to acid during the zinc-plating process increases the likelihood of hydrogen embrittlement in the hardened plates. Therefore, zinc plating is not available for some chains.
- Nickel plating may also create hydrogen embrittlement. In an application where a broken chain may create serious damage, WP® series chain may be a better choice. Of course, safety guards must be installed.
- Link plates are shot peened for greater fatigue strength. The plating process reduces the effects of shot peening, therefore, the fatigue strength of plated chain is 10 percent less than that of standard chains.
- Plated Roller Chains are prelubricated with mineral oil after assembly. If the prelubrication is unwanted, advise the manufacturer when ordering.
Figure 1.11 Nickel-Plated Chain