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ASME B29.8-2010 (2017) — Leaf Chains, Clevises, and Sheaves
🔗 ASME B29.8-2010 (2017) is an American National Standard covering leaf chains, clevises, and sheaves. It establishes requirements for lacing, pin diameter, link-plate hole diameter, link-plate contour and thickness, chain width, and minimum ultimate tensile strength, and it recommends clevis and sheave design practice. Leaf chain consists of link plates assembled on pins without bushings or rollers; it provides relatively high strength per unit of weight and is widely used where sprockets are not required and high-speed power transmission characteristics are not needed — for example, counterweight, balance, and traction chains in forklift trucks and hoisting equipment. The Standard was initiated by a task subcommittee of the Association of Roller and Silent Chain Manufacturers on September 21, 1951. This edition revises ASME B29.8-2002 (R2008), was approved by ANSI on November 18, 2010, and was reaffirmed in 2017.
💡 The unique value of leaf chain is “high strength per unit of weight”: by eliminating bushings, rollers, and sprocket engagement, the construction is simpler and lighter, making it the classic choice for linear reciprocating and suspended-load applications such as counterweights and balance mechanisms.
1. Scope and General Framework 📌
The Standard is organized in five sections: Leaf Chains (sec. 1), Clevises (sec. 2), Sheaves (sec. 3), Lubrication (sec. 4), and Additional Information (sec. 5). Dimensional data are tabulated primarily in customary inch-pound units, with companion metric (SI) conversions in accordance with the ASME orientation guide for the use of SI units. Certain formulas and relationships are intentionally presented only in customary units to eliminate ambiguity between them and the tabulated values. Nonmandatory Appendix A supplies supplementary information on lubrication and maintenance, connect and disconnect, and general inspection criteria.
Leaf chain design has evolved through several significant revisions: the 1977 edition (ANSI B29.8-1977) eliminated the lighter Type A leaf chain, added even (balanced) lacing to the Type B series, and introduced a 2½ in. pitch chain; the 1993 edition adjusted the maximum pin diameter and minimum hole diameter so that inch and metric values convert to each other without error; the 2002 edition deleted the 8×8 lacing, added a lubrication and maintenance appendix, and adopted preload and manufacturer’s identification requirements to comply with ISO 4347; and the 2010 edition corrected the Wmax values for BL-5xx chains (previously identical to the BL-4xx values) and removed the obsolete Lm term.
⚠️ Leaf chain does not transmit power through sprockets; its ends are connected to the mechanism through clevises and pins. The design must use the Standard’s recommended clevis and sheave arrangements and respect the minimum sheave size, or chain life will be shortened dramatically.
2. Technical Requirements and Specifications 🧾
The Standard governs the following technical elements: lacing, pin diameter, link-plate hole diameter, link-plate contour and thickness, chain width, and minimum ultimate tensile strength (M.U.T.S.). Chain numbers use the BL series (e.g., BL-4xx, BL-5xx). Tables 1 and 2 give general chain dimensions in inches and millimeters, respectively; Table 3 lists minimum ultimate tensile strength; Tables 4 and 5 give dimensions for anchor clevises used with Type B leaf chain in inches and millimeters.
| Lacing Pattern | Construction | Status in Standard |
|---|---|---|
| 4×3, 4×4, 4×5, 4×6 | Plate combinations typified by 4-and-6-layer builds; 4×6 shown in Fig. 1 | Current common patterns |
| Even (balanced) lacing | e.g., 4×4; symmetrical plates, balanced load | Available for Type B since 1977 |
| Uneven (unbalanced) lacing | e.g., 4×3, 4×5; for special sections and sizes | Traditional Type B form |
| 8×8 lacing | Overly wide build, high redundancy | Deleted in the 2002 edition |
| Type A (light series) | Even lacing only; used mainly for replacement | Deleted in the 1977 edition |
| Requirement | Coverage | Reference |
|---|---|---|
| General chain dimensions | Pitch, number of plates, width, pins, and plate holes | Table 1 (in.), Table 2 (mm) |
| Minimum ultimate tensile strength | Tensile strength floor for each BL size | Table 3 |
| Anchor clevises | Dimension series for Type B leaf chain | Table 4 (in.), Table 5 (mm) |
| Preload and marking | Preloading and manufacturer identification | Per ISO 4347 |
🚨 As with detachable link chain, the leaf-chain M.U.T.S. is the failure threshold of a single tensile destructive test — it is not a working load. Selecting a chain on M.U.T.S. is dangerous; working load must be based on the manufacturer’s catalog ratings with an adequate safety margin.
3. Clevis and Sheave Design 🔩
The Standard defines several clevis types (Fig. 4) and general clevis proportions (Fig. 5). Anchor clevises connect the end of the leaf chain to a fixed or moving member and are used with clevis pins. Sheaves (Fig. 6) support the chain when it changes direction or carries a suspended load; the Standard gives general sheave proportions and requires compliance with a minimum sheave size. A sheave that is too small forces the link plates to bend at excessively small radii, causing early fatigue of the plates and eccentric pin loading.
💡 A classic pairing: forklift mast lifting chains use BL-series leaf chain with anchor clevises and a top sheave — one chain end is anchored to the carriage while the other is routed over the sheave to the counterweight or cylinder for vertical lifting.
4. Lubrication and Maintenance 💧
Lubrication and maintenance are decisive for leaf-chain life. Section 4 and Nonmandatory Appendix A set out the following essentials:
- Lubrication: keep adequate lubricant between pins and plate holes to limit articulation wear, except for self-lubricating (“sealed” or maintenance-free) designs.
- Connect and disconnect: connecting links must be seated and locked properly; the manufacturer is responsible for ensuring that its chains are correctly connected.
- Inspection criteria: check plates for cracks and pins for visible wear and elongation; replace the chain as a set when needed.
- Preloading: preload new chain as required to remove initial stretch and stabilize length.
5. Engineering Practice Essentials 🛠️
- 🔍 Selection workflow: establish load and travel → select BL-series chain number and lacing from strength margin → match anchor clevises and sheaves → verify minimum sheave size → plan the lubrication schedule.
- 🔧 Twin chains and counterweights: forklifts commonly use left/right twin chains; both chains must be preloaded to equal length to avoid skew and eccentric loading of the mast.
- 📏 Alignment and guiding: keep the clevis, sheave groove, and chain plane in one vertical plane to prevent chain twist and edge wear.
- 📋 Traceability: require preload certificates and identification per ISO 4347, and confirm the BL-series number and strength grade on purchase.
- 🔄 Replacement strategy: because leaf-chain failure is safety-critical, replace both chains as a pair when cracks or significant elongation appear — never mix new and worn chains.
6. Frequently Asked Questions ❓
❓ Q: Why does leaf chain not use sprockets?
A: Leaf chain has no bushings or rollers; the plates hinge directly on the pins and are not suited to sprocket-tooth engagement. Its typical duty is linear reciprocation or suspended traction, with clevises and sheaves providing end connection and guidance.
A: Leaf chain has no bushings or rollers; the plates hinge directly on the pins and are not suited to sprocket-tooth engagement. Its typical duty is linear reciprocation or suspended traction, with clevises and sheaves providing end connection and guidance.
❓ Q: What is the difference between Type A and Type B leaf chain?
A: Type A was the lighter series with even (balanced) lacing only; it was deleted in 1977 and survives mainly as replacement stock. Type B is the heavier series, offered with either even or uneven lacing, and gained a 2½ in. pitch size — it is the mainstream of current design.
A: Type A was the lighter series with even (balanced) lacing only; it was deleted in 1977 and survives mainly as replacement stock. Type B is the heavier series, offered with either even or uneven lacing, and gained a 2½ in. pitch size — it is the mainstream of current design.
❓ Q: How does B29.8 relate to ISO 4347?
A: Since the 2002 edition, B29.8 has adopted the preload and manufacturer-identification requirements of ISO 4347, harmonizing North American leaf-chain practice with the international specification.
A: Since the 2002 edition, B29.8 has adopted the preload and manufacturer-identification requirements of ISO 4347, harmonizing North American leaf-chain practice with the international specification.
🔍 Q: Why must the minimum sheave size be respected?
A: With an undersized sheave, link plates bend at excessive curvature, accelerating fatigue cracking and eccentric pin wear; respecting the minimum diameter keeps the plates bending within their elastic range.
A: With an undersized sheave, link plates bend at excessive curvature, accelerating fatigue cracking and eccentric pin wear; respecting the minimum diameter keeps the plates bending within their elastic range.
