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Block 16 Drum Plants 13

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Block 16 Drum Plants 13

  1. 1. Senior/Graduate HMA Course HMA ProductionConstruction Drum Plants 1
  2. 2. What you will learn….• How gradation is controlled in a drum-mixer• How asphalt is controlled in a drum-mixer• Different styles of drum-mixers• Using RAP with a drum plantConstruction Drum Plants 2
  3. 3. Drum-Mix ProductionHot Mix Asphalt production characterized by: • Gradation Control at Cold Feed • Measure aggregate flow with belt scale • Meter asphalt binder to aggregate flow • Produce HMA continuouslyConstruction Drum Plants 3
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  5. 5. Cold Feed Proportioning Composite gradation is controlled at cold feed by proportioning material from individual bins. Gradation and quality of the individual materials is controlled at the quarry.Construction Drum Plants 5
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  7. 7. Cold Feed ProportioningVariation in material flow from individual bins: • Based on variable speed motor on belt • Adjustable manual gates help control minimum and maximum flowConstruction Drum Plants 7
  8. 8. Cold Feed Proportioning• Accomplished by calibrating the feeders• Material output is charted against belt speed in calibration charts• Different charts are created for different gate settings on the same feederConstruction Drum Plants 8
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  10. 10. Cold Feed Gradation Control Many styles of feeder controls found in field. All can perform satisfactory proportioning.Construction Drum Plants 10
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  12. 12. Asphalt Binder ProportioningAsphalt binder must proportion to aggregate flow.First step in asphalt binder proportioning ismeasuring aggregate flow.Belt scale is used.Construction Drum Plants 12
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  14. 14. How a Belt Scale Works• Weigh bridge measures weight of aggregate.• Speed sensor measures speed of belt.• “Integrator / Totalizer” calculates aggregate flow in ton (tonnes) per hour• “Integrator / Totalizer” reports flow rate to plant control systemConstruction Drum Plants 14
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  17. 17. Asphalt Binder ProportioningAsphalt binder must proportion to aggregate flow.Second step is regulating asphalt binder flow.Asphalt binder pumping / metering unit is used.Construction Drum Plants 17
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  20. 20. How the Asphalt Binder Proportioning System Works• Controls system reads wet aggregate flow from belt scale.• Controls accepts moisture content entered by operator to establish dry flow rate of aggregate• Control system accepts target asphalt content entered by operator.• Control system drives pumping/metering unit flow control device.• Control system adjusts asphalt binder flow control system based on signal received back from meter Construction Drum Plants 20
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  22. 22. Plant Automation Many types of systems and levels of complexity found in the field.Construction Drum Plants 22
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  24. 24. Drum-Mix Plant CalibrationConstruction Drum Plants 24
  25. 25. Step 1 - Calibrating Belt ScalesConstruction Drum Plants 25
  26. 26. Step 1 - Calibrate Belt Scale• Verify belt scale reads zero per manufacturers guidelines• Set the cold feed gates at an opening that will allow a good material feed• Start main conveyor belt• Run the variable speed belt feeder for the coarse aggregate bin - about 50% of desired production rate• Record the belt feeder speed and weight indicated on the belt scale.Construction Drum Plants 26
  27. 27. Step 1 - Calibrate Belt Scale (cont.)• Stop belt and remove a six foot section of material from the conveyor• Weigh the material removed• Repeat process to get an average of two weights• Adjust instrument so that it reads correctlyConstruction Drum Plants 27
  28. 28. Example• Conveyor is run at 225 feet per minute• Run the belt feeder until the digital readout reads 90 tons per hour• Weight of material on a six ft section of belt = 76 lbs and 78 lbs for an average of 77 lbsConstruction Drum Plants 28
  29. 29. Example - cont.• Determine the aggregate weight in lbs per minute. WR Q= rwhere Q = weight of aggregate, lbs/min W= wt of agg measured, lbs R = speed of belt r = length of belt from which material was removedConstruction Drum Plants 29
  30. 30. Example - cont• Therefore the aggregate weight in lbs/min is: q = WR/r = 77 x 225 = 2887.5 lbs/min 6• To convert to tons per hour (q x 60)/2000 2887.5 x 60 = 86.63 tph < 90 tph 2000Construction Drum Plants 30
  31. 31. Example - cont• Adjust instrument per manufacturer’s guidelines so that next test it reads 86.63• Repeat test, adjust, until two consecutive readings are within acceptable tolerance (Unlike batch plant no department spec on this scale tolerance - because mix purchased from silo weigh tickets)Construction Drum Plants 31
  32. 32. Step 1 - Alternate Calibrating Belt Scale• Verify belt scale reads zero per manufacturers guidelines• Set the cold feed gates at an opening that will allow a good material feed• Start main conveyor belt• Run the variable speed belt feeder for the coarse aggregate bin - about 50% of desired production rate• Starting with empty belt run material in tared truck and stop material flow to end with empty beltConstruction Drum Plants 32
  33. 33. Step 1 - Alternate Calibrating Belt Scale• Record the total weight indicated on the belt scale.• Compare weight total on belt scale with actual weight on truck.• Following manufacturers guidelines, adjust belt scale instrument based on weight difference.• Repeat test, adjusting instrument, until two consecutive tests are within tolerance.Construction Drum Plants 33
  34. 34. Example• Start belt scale and verify reads zero• Tare empty truck at 22,375#• Record belt scale totalizer at 437897.65• Start feeder at approximately 50% flow• Fill truck and stop and empty belt• Record belt scale totalizer at 437906.87• Calculate tonnage on scale at 9.22 tons (437906.87 - 437897.65 = 9.22 tons)Construction Drum Plants 34
  35. 35. Example - cont.• Weigh truck at 41,401#• Calculate weight in truck at 9.51 ton (41,401- 22,375 = 19,026 ÷ 2,000 = 9.51 ton)• Recall “span” value of instrument at 897654• Adjust span value by 1.0314 (9.51 ÷ 9.22 = 1.0314)• New span value = 925,840 (897654 x 1.0314 = 925,840)• Re-test, re-adjust, until two tests passConstruction Drum Plants 35
  36. 36. Asphalt Binder Distribution in Drum-Mix PlantsConstruction Drum Plants 36
  37. 37. Asphalt Binder DistributionUnderstanding asphalt binder distribution…..• Calculating Flow Requirements• Calibrating Asphalt Binder MeterConstruction Drum Plants 37
  38. 38. Asphalt Binder Distribution Calculating AC FlowNeed to know the number of gallons/minute of asphaltbinder that is to be delivered R = P x T x 2000 x 1 100 W 60Where R = asphalt binder to be delivered, gpm P= optimum asphalt binder T= production rate, tons per hour W= unit weight of asphalt binder (typically about 8.4 lb/gal)Construction Drum Plants 38
  39. 39. Example – Asphalt Binder Flow RequiredThis example, Asphalt Binder target is 6.0% of 200 tons per hour R = P x T x 2000 x 1 100 W 60 Where R = asphalt binder to be delivered, gpm P= 6 T= 200 W = 8.4Construction Drum Plants 39
  40. 40. Example – Asphalt Binder Flow RequiredThis example, Asphalt binder target is 6.0% of 200 tons per hour R = 6 x 200 x 2000 x 1 100 8.4 60 Where R = asphalt binder to be delivered, gpm P= 6 T= 200 W = 8.4Construction Drum Plants 40
  41. 41. Example – Asphalt Binder Flow RequiredThis example, Asphalt Binder target is 6.0% of 200 tons per hour R = .06 x 200 x 238.095 x .0167 R = 47.71 gpmConstruction Drum Plants 41
  42. 42. QUESTIONS ?Construction Drum Plants 42

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