218 GD-6 Selection Process Application Description A company would like to use a grid coupling to connect a standard AC electric motor to a rotary lobe compressor. The electric motor is rated for 60 horsepower running at 1,760 RPM. The shaft size on the electric motor (driver) is 2-1/8 inches with a standard 1/2” square key. The shaft size on the compressor (driven) is 48 millimeters with a standard 14mm key. Both the motor and compressor shaft are 3 inches long and the gap (BSE) between the shaft ends is 1/8 inch. The following steps provide an excellent selection process that will work for most standard grid coupling selections. For assistance in this selection process, feel free to contact Lovejoy Application Engineering or Technical Support. Step 1: Using the information provided by the customer, determine the application torque: Application Torque (in-lbs) = ( horse power x 63025 ) RPM for this example: Application Torque (in-lbs) = ( 60 x 63025 ) = 2,149 in-lbs 1,760 Step 2: Select the application service factor from the chart on pages GD-7 and GD-8 to determine which value best corresponds to an electric motor driven rotary lobe style compressor. In the charts find the application category ‘Compressors’, ‘Rotary lobe and vane’, and under the column for ‘Electric Motors’, is the service factor number 1.25. If the service factor did not appear on the service factor charts for the defined application, a generic value could be selected from the chart located on the right side of this page. Step 3: Calculate the Selection Torque for the application: Selection Torque = Application Torque x Service Factor Selection Torque = 2,149 in-lbs x 1.25 = 2,687 in-lbs Step 4: Reference the Grid Coupling Performance and Dimensional data on pages GD-10 and GD-11. Use the Selection Torque to make an initial selection based on the nominal torque allowed for the coupling size. The first coupling size that can accommodate 2,687 in-lbs or torque is the size 1050 grid coupling with a nominal torque rating of 3,850 in-lbs. Step 5: Note, that the electric motor’s 2-1/8 inch shaft diameter exceeds the maximum allowable bore size for a size 1050 coupling which is 1-7/8 inches. Using the same chart, scan the column for maximum bore sizes and find the first coupling size larger than the 1050 that will accommodate the 2-1/8 inch bore size. The size 1060 coupling will accommodate the 2-1/8 inch bore. The horizontal cover can be selected since the application speed of 1,760 RPM does not exceed the coupling’s maximum speed of 4,350 RPM. Step 6: Prior to finalizing the 1060 selection, it is always a good idea to review all of the coupling details to ensure the correct coupling has been selected. The following are the comparisons usually made. 1060 Coupling Application Acceptable? Torque: 6,050 in-lbs 2,687 in-lbs yes Bore Size: 2-1/8” max 2-1/8” yes BSE 0.13” 1/8” yes Speed 4,350 RPM 1,760 RPM yes Mount length 5.13” OAL 6-1/8” yes Check the Grid Series Misalignment Chart to ensure the application meets the misalignment requirements. If the items above are acceptable and the application misalignment falls within the allowable range of the 1060 grid coupling, the 1060 grid coupling appears to be the correct coupling for this application. Step 7: Using the UPC Selection tables on Pages GD-16 thru GD-19, find the required hubs for the corresponding coupling size and the required Cover and Grid Assembly. 1060 Hub Bore 2-1/8” see page GD-16, use 05491 1060 Hub Bore 48mm see page GD-17, use 05815 1060 Horizontal Cover and Grid assembly with inch hardware see page GD-18, use 05353 Prefix all grid coupling part numbers with 697904 Selection Example JW JIS CJ SF MC G HP GD D T SP UJ VSD R SLD ED JW JIS CJ SF MC G HP GD D T SP UJ VSD R SLD ED Typical Applications for Electric Motor or Turbine Driven Equipment Typical Service Factor Constant Torque such as Centrifugal Pumps, Blowers, and Compressors. 1.0 Continuous Duty with some torque variations including Printing Presses, Extruders, Forced Draft Fans. 1.5 Light shock loads from Briquetting Machine, Rubber Calendar, or Crane and Hoist. 2.0 Moderate shock loading as expected from a Car Dumper, Reciprocating Feeder, or Vibrating Screen. 2.5 Heavy Shock load with some negative torques from Crushers, Manipulators, and Braking Drum. 3.0 For applications like Reciprocating Compressors with frequent torque reversals which do not necessarily cause reverse rotations, contact Lovejoy Technical Support. General Service Factors www.jbj.co.uk/gridcouplings.html
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