Hitachi

Engineering Class Chains Drive Chain Selection Introduction Engineering Class Drive Chains are one of the most efficient and cost effective ways to transmit mechanical power between shafts. They handle large working loads in the slow to moderate speed range, have very small energy losses, and are generally inexpensive compared with other methods of transmitting power between rotating shafts. Successful selection involves following several simple steps involving algebraic calculation and the use of Horsepower, Service Factor tables and/or working load calculation. For any given set of drive conditions, a number of possible chain and sprocket combinations are possible. The designer therefore, should be aware of several selection principles which, when applied correctly, help to balance overall drive performance and cost. The purpose of this section is to help designers make selections that meet the requirements of the drive, and are cost efficient. General Drive Chain Selection Principles a) The recommended number of teeth for the small sprocket is 12. The minimum which should be used is 9. Smoother operation is achieved with more teeth. b) Speed ratios should be 7:1 or less (optimum) and never more than 10:1. c) The minimum wrap of the small sprocket is 120 degrees. General Drive Chain Operating Principles a) Lubrication: A separating wedge of high quality oil formed between the operating joints protects chains from rapid wear out due to metal to metal contact and if supplied in sufficient volume also provides effective cooling and impact load damping. Effective lubrication is the single most effective way to improve chain performance and prolong life. The chain should be protected against moisture and kept free of contamination. High quality non-detergent petroleum based oil is recommended. Heavy grease is generally too stiff to penetrate chain joints effectively. The following indicates the recommended viscosity for a given temperature: SAE20: 20ºF - 40ºF SAE30: 40ºF - 100ºF SAE40: 100ºF - 120ºF SAE50: 120ºF - 140ºF b) Alignment: Accurate alignment of shafts and sprockets helps provide uniform distribution of loads across the entire width of the chain and contributes to optimum drive performance. c) Direction of Travel: For offset bar chains used in power transmission service (i.e. drives), the narrow end should face the smaller sprocket on the tight side. Note that this is not always the best running direction for offset side bar chains used on conveyors. d) Sprockets: Hardened tooth sprockets are recommended. Required Information for Drive Chain Selection a) Type of input power (electric motor, internal combustion engine with mechanical or hydraulic drive), and type of equipment to be driven. b) Amount of horsepower required to provide sufficient power to the driven shaft. Full load speed of the fastest running shaft (rpm). 8 c) Desired speed of the slow running shaft (i.e. the speed ratio). NOTE: If speeds are variable determine the horsepower to be transmitted at each speed. d) Diameters of the driver and driven shafts. e) Center distance of the shafts. NOTE: If this distance is adjustable determine the amount of adjustment. f) Note the position of the drive and any space limitations that might exist. These space limitations usually limit the diameter of the large sprocket and may require the speed reduction (or speed increase) be accomplished in more than one (1) drive ratio. g) Conditions of the drive. It is advisable to consult with Hitachi engineering personnel when unusual conditions such as widely fluctuating loads, temperatures, or severely abrasive or corrosive environments exist. Abbreviations Used in Equations Number of teeth on the large sprocket. N: Number of teeth on the small sprocket. n: Speed in revolutions per minute (rpm) of large sprocket. R: Speed in revolutions per minute (rpm) of small sprocket. r: Linear Chain Speed in feet per minute (fpm). S: Shaft center distance in chain pitches. C: HP: Horsepower of the drive motor or engine. SF: Service Factor DHP: Design Horsepower Speed Factor P: Calculated chain tension. T: Chain Selection by Calculating Chain Tension The method for selecting Engineering Class Drive Chains in this catalog will involve: a) Calculating the "design horsepower" (DHP) based on the motor or engine capacity and the drive conditions. b) Determining the "calculated chain tension" from the design horsepower and chain speed. c) Comparing the calculated chain tension (T) to the "rated working load" of the selected chain and in some situations to a value equal to 15% of the selected chains average ultimate strength. Most Engineering Class Drive Chains operate at relatively slow speeds. The rated working load values found in the dimensional tables in this catalog are based on maintaining a maximum bearing pressure between the pin and bushing of 3,500 pounds per square inch (psi). This means that if the calculated chain tension in the drive is equal to or less than the selected chain's rated working load we will be operating at or below the optimum pin/bushing bearing pressure of 3,500 psi and we can expect successful chain performance. We note however that often chains can be operated successfully in excess of the "rated working load" limit. The applications that lend themselves to successful performance in this situation are slow speed (less than 50 ft/min), well lubricated chain drives. In this case we may operate the chain at a calculated chain tension (T) up to 15% of its average tensile strength. When selecting chains by this criterion confirm the selection with Hitachi engineering personnel.

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