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INDUCTION BARREL HEATING ON PRODUCTION MOLDING MACHINES

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INDUCTION BARREL HEATING ON PRODUCTION MOLDING MACHINES Powered By Docstoc
					        INDUCTION BARREL HEATING ON PRODUCTION MOLDING MACHINES
   -- QUANTIFYING ENERGY SAVINGS & UNDERSTANDING INFLUENCING FACTORS

                              Bruce F. Taylor, Xaloy Corporation, New Castle, PA
                               Yasumitsu Aochi, Xaloy Corporation, Tokyo, Japan


                       Abstract                                                         Methodology and Objectives

This paper quantifies energy savings results achieved with   This paper’s methodology and objectives are to use the
induction barrel heating on multiple injection molding       results of these multiple installations and configurations to
applications. The influence of multiple factors on the       quantify typical nXheatTM energy savings amounts and to
efficiency gains provided by induction barrel heating are    understand how they are affected by machine size, resin
also analyzed. Factors assessed include machine size,        type, material throughput and induction zone configuration.
resin processed, material throughput and the number of
zones heated by induction. The probable phenomenon                                     Present Range of Applications
behind previously reported process consistency
improvements achieved with induction barrel heating is       Present applications of induction barrel heating on injection
also discussed.                                              molding processes span machine tonnages from 85 to 1350,
                                                             with barrel diameters from 90 to 330 mm, processing a
                     Background                              broad range of resins with melt temperatures from 230 to
                                                             370oC, at throughput rates from 5 to 145 kg/hr. The number
                                                             of zones converted to induction heating has ranged from one
Electrical energy savings using induction barrel heating     to six per barrel and the configured output power levels
have recently been documented and reported elsewhere.1,2     have varied from 2 to 8 kilowatts per zone.
Since then this induction technology (nXheatTM, supplied
by Xaloy Inc., patents pending) has been installed and
operated on numerous applications covering a wide range                              Summarized Energy Savings Results
of machine sizes, processing a variety of resins over a
range of throughputs. Entire barrels and portions of         As shown in Figure 2 the reduction in barrel heating energy
barrels have also been configured with this induction        consumption on these applications has ranged from 42 to
heating technology. The induction technology used            76%, with an average of 58%.
(nXheatTM) is shown in Figure 1 and has been described in                    100
detail elesehere1,2.                                                                                                                                   * Calcium carbonate
                                                                              90                                                                      ** ABS + PC/PET/PBT

                                                                              80                                 76.0
                                                                                     70.3                               71.4
                                                                                                   68.4
                                                                              70
                                                                                                          61.2
                                                                                                                                      58.7                             59.4 58.2
                                                              % Reduction




                                                                              60                                               55.3          54.2
                                                                                                                                                           48.6 49.7
                                                                              50
                                                                                            41.6                                                    41.5
                                                                              40

                                                                              30

                                                                              20

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         Figure 1. Typical nXheatTM Installation                              Figure 2. % Reduction in Barrel Heating Energy
       The Melt-Stream Energy Balance                           •                                                  for the same heat input per unit length, smaller diameter
                                                                                                                   band-heaters will have to run hotter and less efficiently
The reduction in energy consumption provided by                 •                                                  with less viscous heating band-heaters must add more
induction barrel heating will vary from one machine to                                                             heat and so must run hotter and less efficiently
another because each machine has a unique energy                •                                                  with high specific heat resins more heat must be added
balance, as illustrated in Figure 3.                                                                               so band-heaters must run hotter and less efficiently
                                    QRAD                        •                                                  with higher resin throughputs more heat must be added
                            QCONV                                                                                  so band-heaters must run hotter and less efficiently
                  QELEC                         QBAND
                                                                These multiple factors explain the variation of results,
                                                                whether they are represented as the energy savings per unit
                                                                of material processed (Figure 4) or as a %-reduction in
         QCOND        QCONTACT        QBARREL      QCOND        barrel heating power or total machine power (Figure 5).
                                                                                                                   1400




                                                                                                                                                         1250
                                                                                                                                                         1238
                                                                                                                                                                                                                           Barrel Heating
         Material
                          QVISC                         Screw                                                      1200                                                                                                    Total Machine




                                                                    Specific Energy Savings (joules/gram)
         Flow




                                                                                                                             1050
                                                                                                                            1032
                                                                                                                                                                                                                           Remainder
                                                                                                                   1000
                                 QPROCESS
        Barrel




                                                                                                                                                                             721
                                                                                                                   800


                           Band-heater                                                                             600




                                                                                                                                                                                                                                     509




                                                                                                                                                                                                                                                        496
                                                                                                                                                                       489




                                                                                                                                                                                                                                    476

                                                                                                                                                                                                                                                  455
                                                                                                                                                                                                         362
                 Figure 3. Barrel Heat Balance                                                                     400




                                                                                                                                                                                                       294
                                                                                                                                            251




                                                                                                                                                                                           246
                                                                                                                                                                                   232
                                                                                                                                           224




                                                                                                                                                                                                                         220
                                                                                                                                                                                          207




                                                                                                                                                                                                                       171
When a band-heater generates heat (QELEC) the                                                                      200




                                                                                                                                                                                                               68


                                                                                                                                                                                                                               49




                                                                                                                                                                                                                                                              42
temperature gradient between it and the barrel drives heat
                                                                                                                                                  27
                                                                                                                                     18



                                                                                                                     0
(QCONTACT) inward across the contact interface between
                                                                                                                                                                -12




                                                                                                                                                                                                                                            -33
                                                                                                                                                                                                 -39
                                                                                                                                          * Calcium
them. Simultaneously, friction between the barrel, resin                                                                                   carbonate
                                                                                                                   -200
and screw generates heat through viscous heating (QVISC).




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These two sources provide the energy needed to melt the
                                                                                                                                       50




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resin. Process response is then dampened by absorption
                                                                                                                                                              S
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of energy by the band-heaters (QBAND) and barrel
                                                                                                                          PP




(QBARREL) as their temperatures rise. Finally, thermal
efficiency is reduced by heat losses to ambient from the                                                    Figure 4. Specific Energy Savings (joules/gram resin)
external surfaces of the band-heaters and barrel due to
convection (QCONV) and radiation (QRAD) -- and from axial                                                          100                                                                                                                                  40




                                                                                                                                                                                                                                                               % Energy Savings -- Total M/C & Remainder
                                                                                                                                                                                                                    Barrel Heating
heat conduction (QCOND) to upstream and downstream                                                                  90                                                                                                                                  35
                                                                              % Energy Savings -- Barrel Heating




                                                                                                                                                                                                                    Total Machine
machine elements (i.e. water-cooled feed housing).
                                                                                                                    80                                                                                              Remainder
                                                                                                                                                                       71.4
                                                                                                                                                                                                                                                        30
                                                                                                                             70.3                       68.4
Induction heating speeds process response by virtually                                                              70
                                                                                                                                                                                                                                                        25
                                                                                                                                                                                                                           59.4
eliminating the thermal inertia of the heating element                                                              60                                                                     55.3
                                                                                                                                                                                                                                           56.4

(QBAND → 0), while raising the thermal efficiency by                                                                                       41.6
                                                                                                                                                         16.4                                          48.6 49.7
                                                                                                                                                                                                                                                        20
                                                                                                                    50
essentially eliminating external surface heat losses (QCONV                                                                  13.2                                                                                              12.8                     15
and QRAD → 0).                                                                                                      40                                                     12.0
                                                                                                                                                                                                     10.6                                  10.5
                                                                                                                                                                                                                 7.5                                    10
                                                                                                                    30                            8.9                                    5.6
         Analysis of Energy Savings Rates                                                                           20
                                                                                                                                                                      3.83
                                                                                                                                                                                                  2.15           1.73
                                                                                                                                                                                                                                                        5
                                                                                                                                           1.05                                                                                            0.92
                                                                                                                                 0.24
                                                                                                                    10                                                                                                                                  0
When induction barrel heating replaces band-heaters the                                                                              * Calcium          -0.17                                  -1.13                -0.99
                                                                                                                                        carbonate
resulting energy savings depends on what the ambient                                                                 0                                                                                                                                  -5
losses were with band-heaters beforehand, which
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depended primarily upon on the surface temperatures of
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the heaters and barrel, which in turn were influenced by
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all aspects of the heat balance described above.
Understanding how these factors affect the energy savings                                                                                  Figure 5. % Energy Savings
can be aided by considering some practical examples;
Figure 5 shows that the energy savings achieved with                        Energy savings results presented in this fashion in Figure 7
induction barrel heating averages about 10% of the total                    document that induction barrel heating saves on average
machine power on hydraulic machines. (All of the                            more than 1 joule for every joule needed to melt the resin.
machines cited in Figures 4 and 5 were hydraulic. A                         From the perspective of reducing the “energy footprint” of
larger %-reduction in total machine power would be                          the plastic melting process this is a significant improvement.
expected on electric machines.) Figure 5 also suggests
induction generally reduces the extruding power slightly                                                             3.5                           3.31                                   * Calcium carbonate
(as indicated by the “remainder” in the charts).                                                                                                                                         ** ABS + PC/PET/PBT

                                                                                                                     3.0




                                                                             Energy Savings Ratio (joules/joules)
Indications from multiple installations suggest an extruder
savings is likely due to more heating being done earlier in
                                                                                                                     2.5             2.38
the rear zone with induction -- thereby reducing shear and
viscous heating by presenting a hotter more thoroughly                                                                     2.11
mixed melt-stream to the transition section of the screw.                                                            2.0
Improvements in part weight and dimensional consistency                                                                                                   1.67
documented elsewhere2, and observations that deep and                                                                                       1.54
                                                                                                                     1.5                                                                                     1.38
shallow thermocouples read more closely in the rear zone                                                                                                                       1.25                   1.28
with induction, all further support this hypothesis, which                                                                                                                            1.14
                                                                                                                                                                                             1.04
is pictorially represented in Figure 6. To date this likely                                                          1.0
                                                                                                                                                                 0.75
phenomenon has not been aggressively exploited to try to                                                                                                                                            0.63
minimize shear and viscous heating. In the near future it                                                                                                               0.53
                                                                                                                     0.5      0.33
will be interesting to see how it can be used to
significantly impact injection molding performance.
                                                                                                                     0.0
   Shorter Effective Mixing Length           Melting the Resin with




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    for Less Homogeneous Melt                    Band-heaters




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                                      Band-heated Barrel



                                                                                                                        S
                                                                                                                      B
                                                                                                                     A
        300               295          290               285          280
                                                                                                                    Figure 7. Joules Saved per Joule of Melt Energy
                  Screw

        300               295          290               285          280   Inspection of Figures 2, 3, 4, 5 and 7 shows a trend toward
                                                                            higher %-savings on smaller machines. This probably
                             Material Flow                                  reflects a higher viscous heating contribution and a higher
                                                                            fixed energy component on larger machines.
                                     Induction-heated Barrel
  580
         300                295                             290 285 280
                                                                            This dynamic improves the return-on-investment on smaller
                  Screw                                                     machines, while on large machines the higher material
  580
  580    300                295                             290 285 280     throughput and resulting energy consumption rate provides
                                                                            an even faster payback.

               Longer Effective Mixing Length        Melting the Resin
                                                                                                                    Analysis of Energy Savings Distribution
                for more Homogeneous Melt             with nXheatTM

                                                                            nXheatTM injection molding applications have shown a
    Figure 6. Comparative Barrel Heating Isotherms
                                                                            tendency for the energy savings and process impact to be
                                                                            weighted towards the rear of the barrel, where the cold resin
The energy savings documented in Figures 2 through 5
                                                                            first enters and needs to be quickly heated.
can also be represented as a ratio of the heat needed to
melt the material (QMELT), where;
                                                                            To objectively investigate this phenomenon the power
                                                                            distribution with band-heaters and induction along the
QMELT (joules/sec) = m x cp x (TM – TF)
                                                                            length of the barrel was compared for two different sized
                                                                            machines (85 and 1000 ton), both processing the same
m = mass throughput of material (gram/sec)
                                                                            material (ABS). In Figure 8 normalized results are plotted
cp = resin specific heat (joules/gram-oC)
                                                                            versus the relative position of the zone’s centerline along the
TM = resin melt temperature (oC)
                                                                            barrel’s heated length, with the band-heater power outputs
TF = resin feed temperature (oC)
                                                                            in the rear zone being the maximum values to which the
                                                                            other zonal power values are normalized.
                                                                         100
        Band-heaters, 3 zone barrel                                                                                     As expected, the maximum %-reduction in energy
                                                                         90
        Band-heaters, 4 zone barrel                                                                                     consumption is towards the middle of the barrel (point A in
        Induction (nXheat), 3 zone barrel
                                                                                                                        Figure 9), where heat losses to ambient explained the power




                                                                                       Relative Power (Maximum = 100)
        Induction (nXheat), 4 zone barrel                                80
                                                                                                                        consumption in that region with band-heaters. With the
                                                                         70                                             barrel insulated by nXheatTM these losses, and therefore the
                                                                         60
                                                                                                                        need for heat addition, were virtually eliminated in the
                                                     896
                                                             4653
                                                                                                                        middle region of the barrel. However, as band-heaters’
                                                    watts
                                                             watts       50                                             relative power output is at a minimum toward the middle of
                                                                                                                        the barrel (see point B in Figure 8), the %-power savings is
                                                                         40
                                                                                                                        lowest near the middle of the barrel (point C in Figure 9)
                                                                         30                                             and highest in the rear of the barrel, where maximum power
            Material Flow                            374                                                                is needed to quickly heat the cold incoming resin.
                                                    watts    1885
                                                             watts       20


                               B                                         10                                                  Hybrid Barrel Heating Configurations
                                                                         0                                              The end result is that about 50% of the total energy savings
 100   90      80    70      60    50   40     30       20   10      0
                                                                                                                        can be achieved with induction installed in just the first 25%
                          % of Heated Length                                                                            of the barrel’s length (as indicated by point D in Figure 9).
                                                                                                                        This finding suggests that the hybrid approach shown in
 Figure 8. Normalized Barrel Heating Power vs Position                                                                  Figure 10 (with nXheatTM in the rear zone and band-heaters
                                                                                                                        thereafter) is a compelling investment option on smaller
Notably, the data from these two very different                                                                         machines with two to four temperature control zones.
applications conforms nicely to the same normalized
power consumption curves (red for band-heaters, blue for
induction), suggesting an inherent distribution that will
vary little from one machine to another. Additional
installation experience and tests on Xaloy’s lab machines
have confirmed that power consumption curves exhibit
the same shape on the majority of injection molding
applications. The results charted in Figure 8 are then
manipulated and re-plotted in Figure 9 to portray the
typical energy savings distribution along a barrel.
                      A                                                  100

                                    % Power                              90
                                   Reduction
                                                                         80
                                                                               Normalized Power Savings




                      Cumulative %
                                                                         70
                      Power Savings

                                                                         60

                                                    D                    50
                                                                                                                             Figure 10. Typical nXheat-HybridTM Installation
                                                                         40
               Material Flow
                                                                                                                                    Forecasting Energy Savings
                                                                         30
       % Power                                                                                                          Figures 4 (joules saved/gram of resin), 5 (%-reduction in
       Savings                                                           20
                               C
                                                                                                                        barrel heating energy use or total machine energy use) and 7
                                                                         10                                             (joules saved per joule of energy needed to melt the resin)
                                                                                                                        suggest different ways to forecast the energy savings that
                                                                         0                                              will be achieved on an induction barrel heating installation.
100    90     80     70     60     50   40     30       20   10      0
                      % of Heated Length                                                                                Given all the process variables discussed previously the
                                                                                                                        most accurate method is to simply measure the existing
             Figure 9. Energy Savings Distribution                                                                      power consumption with band-heaters and then apply an
                                                                                                                        expected %-reduction of 40-75% (58% average is
recommended). This approach can be used by measuring                                                                                                               The third recommended approach is to multiply the
the band-heater power consumption with a power meter                                                                                                               machines’ forecasted resin throughput by an appropriate
or by estimating it, as explained in the following example:                                                                                                        specific energy savings, such as an average value of 500
                                                                                                                                                                   joules/gram (as Figure 4 might suggest). This approach
                          Actual with Band-heaters                                                                        Forecasted with nXheatTM                 makes it easy to visualize the range of savings across all
                                                                                                                                                                   machine sizes and applications. In Figure 11 the financial
                                                             Control Interval (sec)




                                                                                                                        Power Consumption
           Rated Band-heater




                                                                                                       % Power Output
               Wattages


                                                                                       Time ON (sec)
                                                                                                                                            Expected Power         savings produced by a range of specific energy savings is
                                                                                                                                               Savings
                                                                                                                                                                   plotted versus throughput (assuming operating metrics of
                             Rated Wattage


                                             Total Zone kW


 Zone
           Band-heaters




                                                                                                                               (kW)
            Number of




                                                                                                                                                                   8,000 hours operation per year, $0.20/kW-hour electricity
                                                                                                                                                                   rate, 10% peak-demand adder, and 35% incremental air-
                                                                                                                                            %    kW       %
                                                                                                                                                                   conditioning savings for 4 months of the year).
1 (feed)       4           3000              12                                        15              75               9.00                55   5.0      48
                                                                                                                                                                                                             70
   2           4           2500              10                                           5            25               2.50                75   1.9      18                                                                                              2 kg part + runner         1.25 kJ/gm
   3           4           2500              10              20                           4            20               2.00                80   1.6      16                                                 65                                              90 sec cycle              savings
                                                                                                                                                                                                                                                       120 mm screw, 1500 ton
               3           3000                                                                                                                           18                                                 60
   4                                         12                                           7            35               4.20                45   1.9                                                                                          1 kg part + runner
               1           2000                                                                                                                            0                                                                                                                           1 kJ/gm




                                                                                                                                                                        Energy Cost Savings ($1000 / Year)
                                                                                                                                                                                                             55                                  60 sec cycle
Total Barrel                                                                                                                                                                                                                                   90 mm, 1000 ton                         savings
                                             44                                                        40               17.7                58   10.3     100
                                                                                                                                                                                                             50
                                                                                                                                                                                                                               500 gm part + runner
                                                                                                                                                                                                             45                    40 sec cycle
       Table 1. Sample Power Data and Computations                                                                                                                                                                             70 mm screw, 500 ton
                                                                                                                                                                                                                                                                                      750 J/gm
                                                                                                                                                                                                                                                                                       savings
                                                                                                                                                                                                             40
                                                                                                                                                                                                                       250 gm part + runner
Step 1: Note the band-heater’s rated wattages (orange                                                                                                                                                        35            30 sec cycle
                                                                                                                                                                                                                       50 mm screw, 400 ton
cells in Table 1) from the machine electrical drawings.                                                                                                                                                      30
                                                                                                                                                                                                                                                                                      500 J/gm
Step 2: Note the temperature Control Interval and each                                                                                                                                                       25                                                                        savings

zone’s Time ON (blue cells), by timing with a watch the                                                                                                                                                      20
interval and duration of outputs (most machine operator                                                                                                                                                      15                                                                       250 J/gm
displays indicate with lights when heaters are ON).                                                                                                                                                          10
                                                                                                                                                                                                                                                                                       savings

Step 3: Compute the % Power Output for each zone                                                                                                                                                              5
(green -- divide the Time ON by the Control Interval).
                                                                                                                                                                                                              0
Step 4: Compute the Power Consumption for each zone                                                                                                                                                               10      20     30      40       50      60       70   80      90       100
(purple -- multiply % Power Outputs by Rated wattages).                                                                                                                                                                                 Material Throughput (kg/hr)
Step 5: Assume appropriate % Power Savings (yellow),
per zone or overall (refer to Figures 2 and 9).                                                                                                                                                                         Figure 10. Financial Savings Scenario
Step 6: Compute expected kW Power Savings (pink cells
– multiply Power Consumption by % Power Savings)                                                                                                                                                                                        Conclusions
Once the kW Savings is estimated the financial return can
                                                                                                                                                                   •                                         Average energy savings from induction barrel heating
be computed, as in the following example:
                                                                                                                                                                                                             are 58% of barrel heating energy, 10% of total machine
                                                                                                                                                                                                             energy (hydraulic machines), 500 joules/gram of resin,
Operating Rate                                                                        hours/year                                                         7,000
                                                                                                                                                                                                             and 1.4 joules/joule of energy needed to melt the resin.
Electricity Rate                                                                      $/kW-hour                                                           0.18
Basic Electrical Savings                                                              $/year                                                            12,997
                                                                                      %                                                                    10
                                                                                                                                                                   •                                         About 50% of the energy saved by equipping the entire
Peak-Demand Savings
                                                                                      $/year                                                             1,300
                                                                                                                                                                                                             barrel with induction heating can be achieved by
                                                                                      % added savings                                                      35
                                                                                                                                                                                                             equipping only the rear 25% of the barrel.
Air-conditioning                                                                      months/year                                                              4
                                                                                      $/year                                                             1,516     •                                         There are multiple straight-forward methods available
Total Electrical Savings                                                              $/year                                                            15,813                                               to forecast induction barrel heating energy savings.
Total Investment                                                                      $/year                                                            16,000
Payback Period                                                                        months                                                               12                                                                            References
               Table 2. Sample Return-On-Investment                                                                                                                1.                                        B. Taylor, T. Womer, R. Kadykowski, Efficiency Gains
                                                                                                                                                                                                             and Improvements using Different Barrel Heating
A second straight-forward way to forecast the energy                                                                                                                                                         Technologies for the Injection Molding Process, SPE
savings is to measure the total machine power with a                                                                                                                                                         Antec 2007
power meter and then assume a 10% reduction (in future                                                                                                             2.                                        G. Tremblay, D. Sowle, B. Taylor, Investigation of
Xaloy intends to derive more precise savings guidelines                                                                                                                                                      Injection Molding Performance using Induction Barrel
for different types of machines and applications).                                                                                                                                                           Heating, Molding 2008 Conference

				
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