Different dry and liquid materials will spread at different rates at the same setting, so spreaders must be calibrated with the material that will be used. Use the Salt Institute Calibration Chart for easy record-keeping. The chart is also available (free) as a MS Excel spreadsheet file for the U.S. and Canada, which does all the calculations automatically (Note: if you are not using Microsoft Internet Explorer, you may not be able to view the file online, but can download to disk and open it with a spreadsheet program that can read MS Excel).
Spreader Calibration Procedure
Calibration of spreaders is simply calculating the pounds per mile discharged at various spreader control settings and truck speeds by first counting the number of auger or conveyor shaft revolutions per minute, measuring the material discharged in one revolution, then multiplying the two and finally multiplying the discharge rate by the minutes it takes to travel one mile.
With hopper-type spreaders, specific gate openings must be calibrated. Measure from floor of conveyor to bottom edge of gate.
Each spreader must be calibrated individually; even the same models can vary widely at the same setting.
Equipment needed:
1. Scale for weighing.
2. Canvas or bucket/collection device.
3. Chalk, crayon or other marker.
4. Watch with second hand.
Calibration steps
1. Warm truck's hydraulic oil to normal operating temperature with spreader system running.
2. Put partial load of salt on truck.
3. Mark shaft end of auger or conveyor.
4. Dump salt on auger or conveyor.
5. Rev truck engine to operating RPM (at least 2000 RPM).
6. Count number of shaft revolutions per minute at each spreader control setting, and record.
7. Collect salt for one revolution & weigh, deducting weight of container. (For greater accuracy, collect salt for several revolutions and divide by this number of turns to get the weight for one revolution.) This can be accomplished at idle or very low engine RPM.
8. Multiply shaft RPM (Column A) by discharge per revolution (Column B) to get discharge rate in pounds per minute (Column C), then multiply discharge rate by minutes to travel one mile at various truck speeds to get pounds discharged per mile.*
*For example, at 20 MPH with 30 Shaft RPM and 7 lbs. discharge- 30 x 7 = 210 x 3.00 = 630 lbs. per mile.
Calibrating Automatic Controls
Automatic controls come with factory calibration cards that indicate the proper rate of spread for each setting. However, when there is a need to calibrate, use the following steps:
1. Remove or turn off spinner.
2. Set auger on given number, such as No. 2.
3. Tie sack or heavy canvas under discharge chute.
4. Mark specific distance, such as 100 or 1,000 feet.
5. Drive that distance with spreader operating.
6. Weigh salt collected in sack or canvas.
7. Multiply weight of salt by 5.2 (in case of 1,000 feet) or 52.8 (in case of 100 feet).
This will be the amount of salt discharged per mile, which remains constant regardless of speed, but calibration must be done for each control setting.
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