Power transmission by roller chain and sprockets for machines and conveyors

01

Select the chain and sprockets from design power

U.S. Tsubaki's chain drive selection procedure starts from the machine type, power, shaft speeds and diameters and centre distance, then multiplies the power by a service factor to get design power. Its Table I gives 1.0 for smooth loads such as belt conveyors with small load fluctuation, 1.3 for some impact such as general machine tools and dryers, and 1.5 for large impact such as presses, all with an electric motor; internal combustion engines take 1.0–1.7 depending on load and hydraulic drive. [1]

The large sprocket's teeth equal the small sprocket's teeth times the speed ratio; Tsubaki prefers more than 15 teeth on the small sprocket and suggests no more than 120 on the large one. Where one strand is not enough or space is short, a multi-strand chain is used, with multiple-strand factors of 1.7 for double strand and 2.5 for triple strand. Chain speed is S = P·N·n/12 ft/min and chain tension T = 33,000·HP/S lb. Its selection table assumes ambient temperatures of 15–140 °F, horizontal shafts and proper lubrication. [1]

Editorial calculation: a 5 hp drive with some impact needs 5 × 1.3 = 6.5 hp design power. With 3/4 in pitch chain on a 17-tooth sprocket at 300 rpm, S = 0.75 × 17 × 300 ÷ 12 ≈ 319 ft/min and T = 33,000 × 5 ÷ 319 ≈ 517 lb. These pitch, tooth and speed values are assumptions for illustration. [1]

Give the supplier the motor or gear unit power and speed, the driven speed (or ratio), the machine and its shock level, shaft diameters and keyways, centre distance and any space limit, number of strands allowed, ambient conditions such as wood dust, lubrication method, and the guard required.

02

Plan wear checks and guard the drive

Tsubaki's chain wear indicator literature marks 0.7% elongation as the point to start planning chain replacement and 1.5% as the limit at which sprocket wear starts and the chain should be replaced as soon as possible; it advises replacing chains before 1.5–2% elongation to avoid significant sprocket wear, and measuring at more than one point along the chain because wear is uneven. Its ANSI kit covers sizes 35 to 80 and its British Standard kit sizes 06B to 16B. [2]

OSHA's 29 CFR 1910.219 requires all sprocket wheels and chains to be enclosed unless more than 7 ft above the floor or platform, with protection against falling where the drive extends over other work areas; where frequent oiling is needed, openings with hinged or sliding self-closing covers are required. Overhead roller-chain drive guards must be at least 6 in wider than the drive on each side. [3]

Editorial note: a hinged guard gives access to the tensioner and lubrication points; ask the supplier how the guard is interlocked or secured and where the oiling openings are. [3]

03

Compare drive arrangements

04

Drive shaft, coupling, bearing housing, chain and sprockets, guard and motor drive

05

Design power, service factor, tooth ratio and strand count for a roller chain drive

Start from design power, not motor nameplate power: Tsubaki multiplies by 1.0, 1.3 or 1.5 with an electric motor depending on the impact in the driven machine. [1]

06

Send the power, speed and guarding data together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Power: [kW; motor or reducer]
Speeds: [driver and driven rpm]
Load: [machine; shock level]
Geometry: [shaft diameters; centre distance; space]
Chain: [number; strands; lubrication]
Guarding: [enclosure; oiling openings]

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