ASME B29.12M-1997 (2018) — Steel Bushed Rollerless Chains, Attachments, and Sprocket Teeth

⚙️ ASME B29.12M-1997 (reaffirmed 2018), Steel Bushed Rollerless Chains, Attachments, and Sprocket Teeth, is the American National Standard defining dimensions and interchangeability requirements for steel bushed rollerless chains (commonly called engineering steel chains). Chains of this type were introduced early in the 20th century and found considerable success on material conveyors and elevators, with manufacturers developing many sizes and types in subsequent years. In November 1960, a working group of producers formed to accomplish standardization within what was then the American Sprocket Chain Manufacturers Association (now the American Chain Association); the first edition of this Standard was adopted and published on October 18, 1968, after approval by the USA Standards Institute. The current 1997 revision adds chain numbers S-856, S-857, S-859, and S-864 plus attachments K-24, K-3, K-35, K-44, and K-443, adds the minimum bolt-hole diameter required for a given attachment bolt diameter, and revises the Minimum Ultimate Tensile Strength definition. It was approved by ANSI on March 25, 1997, and reaffirmed in 2018.

1. Scope and Construction 📌

A steel bushed rollerless chain consists of a series of block links having steel bushings — the bushings contact the sprocket teeth — alternating with links composed of sidebars and pins that articulate in the steel bushings of the block links. Pins and bushings are fixed against rotation in the sidebar pitch holes by mechanical locks such as flats, interference fits, or both; pins may be assembled from either side or alternated at the manufacturer’s option (Figs. 1 and 2).

The core objective of the Standard is to ensure interchangeability and interconnectability of block links, connecting links, and attachments produced by different manufacturers. It therefore publishes controlling dimensions — the maximum and minimum limiting dimensions required to guarantee interchangeability — rather than actual manufacturing sizes. Dimensions are given primarily in the decimal-inch system; metric equivalents are provided for reference only. Chains made to this Standard and its sprocket tooth form may also operate over sprockets designed to ASME B29.11M-1994 or combination-chain sprockets, provided strength and the additional sidebar clearance required for sizes S111 and S150 are considered.

2. S-Series Chain Numbers and Dimensions 🔧

The Standard covers chain numbers with an S prefix, including S-102B, S-110, S-111, S-131, S-150, S-188, S-856, S-857, S-859, and S-864. The 1997 revision introduced the four large-pitch numbers S-856 through S-864. Key parameters of common chain numbers (from Table 1 of the Standard) are summarized below:

Note: values above are selected rows from Table 1 of the Standard; complete data (sidebar thickness, inside width W, overall chain height F, number of pitches per nominal 120 in. strand, maximum/minimum strand lengths, etc.) is given in the Standard, together with metric equivalents such as 690 kN for the S-864 M.U.T.S.

3. Performance Parameters and Key Definitions 🔩

3.1 Minimum Ultimate Tensile Strength (M.U.T.S.)

M.U.T.S. is the minimum force at which an unused, undamaged chain could fail when subjected to a single tensile loading test. The Standard warns explicitly: M.U.T.S. is NOT a “working load” — it greatly exceeds the maximum force that may be safely applied to the chain, and the tensile test is destructive. Even if the chain does not visibly fail at the Minimum Ultimate Tensile Force, it has been damaged and is unfit for service.

3.2 Measuring Load and Strand Length Tolerance

The measuring load (in pounds or newtons, Table 1) is the load under which a dry or lightly lubricated chain should be measured for length. New chains under measuring load may exceed the theoretical length by up to 0.38 in. per 120 in. (9.7 mm per 3048 mm) but must not fall below it; maximum and minimum strand lengths for each chain are listed in Table 1. The 1997 revision also added the minimum bolt-hole diameter required for a given attachment bolt diameter, ensuring attachment interchangeability and connection strength.

4. Attachments and Sprocket Tooth Form 🔧

The Standard standardizes common attachment types, including A-class attachments A-1, A-2, A-22 and K-class attachments K-1, K-2, K-3, K-35, K-44, K-443 (Tables 4 through 11), covering mounting interfaces for scrapers, cross-bars, buckets, and other load-carrying elements. The sprocket section specifies the method for determining sprocket tooth form, maximum eccentricity and face runout tolerances (Table 12), and sprocket tooth-form factors (Table 13), ensuring reliable meshing between the chain and sprockets. Sprocket pitch diameter should be calculated from chain pitch and tooth count, with allowance for wear elongation.

5. Engineering Practice Essentials 🛠️

• 🔍 Selection workflow: determine conveying rate, chain speed, and working tension → choose an S-series chain (pitch and width) → verify M.U.T.S. against a proper safety factor → select attachment type and confirm bolt-hole diameter → match sprockets to the Standard.
• 🔧 Assembly direction: pins may be assembled from either side or alternated; follow the manufacturer’s instructions to lock pins and bushings reliably (press fit or mechanical locks) to prevent rotation or withdrawal in service.
• 📊 Lubrication and maintenance: these chains typically run heavy and slow; lubricate articulating joints regularly. Compensate wear elongation with the tensioner and inspect sprocket teeth for hooked profiles.
• 📋 Interchangeability management: only block links, connecting links, and attachments manufactured to the controlling dimensions of B29.12M are guaranteed interchangeable; mixing non-standard parts breaks meshing and strength.

6. Frequently Asked Questions ❓