1.6.2 Leaf Chains
Lifting, counterbalance, forklifts, machine tools
Leaf Chains are used for fork lift masts, as balancers between head and counterweight in machine tools, or for low-speed pulling (tension linkage). This type of chain is also called "Balance Chain," and is regulated by ANSI B29.8M, JIS B 1804, and ISO 4347. (See Figure 1.23.)
Figure 1.23 Leaf Chain and a Leaf Chain Application
Construction and Features
These steel chains have a very simple construction: link plates and pins. The chain number indicates the pitch and the lacing of the links. (See Figure 1.24.) The chains also have the features shown below.
- High tensile strength per section area. This allows the design of smaller equipment.
- There are A- and B-type chains in this series. Both AL6 Series and BL6 Series have the same chain pitch as RS60 (19.05 mm), but they differ, as shown in Table 1.10.
- These chains cannot be driven with sprockets.
Sheaves, not sprockets, are used to change the direction of these chains (Figure 1.25).
Figure 1.24 Leaf Chain Lacing Patterns
|AL6 Series||BL6 Series|
|Plate Lacing||2×2, 4×4|
Even lacing is standard
Odd lacing is standard
Selection and Handling
- In roller chains, all the link plates have higher fatigue resistance due to the compressive stress of press fits. In Leaf Chains, only two outer plates are press fit. Therefore, the tensile strength of Leaf Chains is high, but the maximum allowable tension is low. Use safety guards at all times, and be particularly alert to assure that the safety factor is in the manufacturer's catalog. Use extra safety factors where consequences of chain failure are severe.
- The more plates used in the lacing, the higher the tensile strength. But this does not improve the maximum allowable tension directly; the number of plates used may be limited.
- The pins articulate directly on the plates, and the bearing pressure is very high. The chains need regular lubrication. The use of SAE 30 or 40 machine oil is suggested for most applications.
- When the chain speed is greater than 30 m/min., or if the chain is cycled more than 1,000 times in a day, it will wear very quickly, even with lubrication. In either of these cases, use RS Roller Chains.
- AL-type should be used only under conditions in which:
- There are no shock loads.
- Wear is not a big problem.
- Number of cycles is less than 100 a day.
- If you select a chain using a low safety factor, the stress in parts becomes higher. In this situation, if the chain is used in corrosive conditions, it may fatigue and break very quickly. If you're operating under these conditions, perform maintenance frequently.
- The shape of the clevis depends on the type of end link of the chain (outer link or inner link). Manufacturers produce clevis pins or clevis connectors, but typically, the user supplies the clevis (Figures 1.26 and 1.27). The strands should be furnished to length by the manufacturer. An incorrectly made clevis may reduce the working life of the chain. Contact the manufacturer or refer to the ANSI standard.
- The sheaves are usually supplied by the user.
Figure 1.25 Leaf Chain Sheave
Figure 1.26 Leaf Chain
Figure 1.27 Leaf Chain