Power Selection Example A heavily loaded coal conveyor operates continuous duty, 24 hours per day. The application requires a right angle reducer due to space constraints. The gear drive will be driven by a 600 HP electric motor at 1750 rpm. A low-speed shaft speed of 70 rpm and a maximum sump temperature of 200°F has been requested. Ambient temperature at the conveyor does not exceed 68°F. The conveyor is installed underground in an open air environment with unrestricted air flow. The high-speed and low-speed shafts of the selected gear drive will be connected to the driving and driven equipment by flexible couplings. Select a base-mounted right angle gear drive for this application as follows: 1. The mechanical service factor is 1.50 for a heavily loaded conveyor operating over 10 hours per day, from page 4, Table 2 (Conveyors, Heavy Duty). 2. The equivalent power in HP = 1.50 x 600 = 900 HP. 3. The ideal ratio is 1750 ÷ 70 = 25.00. The closest nominal ratio is 25.0:1 from the Right Angle Triple Reduction Power Ratings Table on page 148. 4. Using the Right Angle Triple Reduction Power Ratings Table on page 148 and in the section associated 25.0:1, trace right through the columns to the first power rating that equals or exceeds the equivalent of 900 HP calculated in Step 2. The selection is a size 173VR3 (shown at the top of the column) that has a power rating of 908 HP. Actual mechanical service factor is 908 ÷ 600 = 1.51 Exact ratio is 25.65:1, found on page 214 (exact ratio table). 5. Check thermal rating. The application-adjusted thermal rating must equal or exceed the actual power transmitted (600 HP). Basic thermal rating for the 173VR3, nominal ratio 25:1, high-speed shaft of 1750 rpm, no auxiliary cooling, equals 262 HP, per page 168. Thermal factors from page 6 for no auxiliary cooling are as follows. B1 = Ambient Temperature Factor from Thermal Table 1 = 1.00 B2 = Altitude Factor from Thermal Table 2 = 1.00 B3 = Ambient Air Velocity Factor from Thermal Table 3 = 1.00 B4 = Duty Cycle Factor from Thermal Table 4 = 1.00 Application-adjusted thermal rating with no auxiliary cooling = 262 x 1.00 x 1.00 x 1.00 x 1.00 = 262 HP Application-adjusted thermal rating does not equal or exceed the 600 HP transmitted, so auxiliary cooling is required. Basic thermal rating for the 173VR3, nominal ratio 25:1, high-speed shaft 1750 rpm, shaft fan cooling, equals 975 HP, per page 168. Thermal factors for shaft fan cooling are as follows: B1 = Ambient Temperature Factor from Thermal Table 1 = 1.00 B2 = Altitude Factor from Thermal Table 2 = 1.00 B4 = Duty Cycle Factor from Thermal Table 4 = 1.00 Note: Thermal factor B5 is not necessary because this is not an alignment- free package. Application-adjusted thermal rating with shaft fan cooling = 975 x 1.00 x 1.00 x 1.00 = 975 HP Application-adjusted thermal rating does equal or exceed the 600 HP transmitted so shaft fan cooling is required. Right angle VRC3 unit utilize a split axial fan so the direction of rotation of the high-speed shaft must be provided at the time of order. 6. It is not necessary to check overhung load or thrust capacity of the gear drive for this example. Gear drive shaft extensions are connected by flexible couplings, which do not impose significant overhung load. No thrust load is present. 7. Determine the complete Falk V-Class Unit nomenclature per page 14. You must specify the shaft orientation and accessory mounting position for your installation. For example, the final nomenclature for this unit could be M173VRC3A25.65-0421B. Catalog 171-110 9 Thermal Factors & Procedures Torque Selection Example V-Class A dredge utility winch requires 500,000 lb.-in. of torque at its output shaft, which operates at 16 rpm. The winch is in service eight hours per day and is driven by a coupling-connected 150 HP, 1750 rpm electric motor. The ambient temperature never exceeds 68ºF. The approximate air velocity is 10 feet per second, and the dredge operates in Lake Superior (sea level). The winch never operates more than 30 minutes in a given hour. The space available is best suited to a base-mounted right angle gear drive, and a maximum sump temperature of 200°F has been requested. Select a gear drive for this application. 1. The Service Factor is 1.25 for a dredge utility winch operating 10 hours per day, from page 4, Table 2 under Dredges. 2. The equivalent torque is 1.25 x 500,000 = 625,000 lb.-in. 3. The ideal ratio is 1750 ÷ 16 = 109.4:1. The nearest standard nominal ratio is 112:1 from the Right Angle Triple Reduction Table on page 149. 4. Using the Triple Reduction Table on page 149, in the 1750 rpm high-speed shaft section and at the 112:1 ratio and 16 rpm, trace right to 767 (x 1000, the first torque exceeding the equivalent torque of 625,000 lb.-in.) and read the drive size 167 at the top of the column. 5. The basic thermal capacity with no auxiliary cooling for an 167VR3, 112:1, at 1750 rpm from the table on page 169 is 145 HP. The ambient temperature factor (B1) from Table 1, page 8, is 1.00. The altitude factor (B2) from Table 2, page 8 is 1.00. The ambient air velocity factor (B3) is 1.4 from Table 3, page 8. The Duty Cycle is 50% (30 min/hour), so the duty cycle factor (B4) is 1.15 from Table 4, page 8. 6. The application-adjusted thermal capacity is 144 x 1.00 x 1.00 x 1.40 x 1.15 = 233 HP, which exceeds the power rating of the motor (150 HP). Therefore, no additional cooling is required. 7. It is not necessary to check overhung load or thrust capacity of the gear drive for this example. Gear drive shaft extensions are connected by flexible couplings, which do not impose significant overhung load. No thrust load is present.
