energy management | Perspective
Energy theory and reality The average power (kW) used in most machines (not only injection moulding machines) is related to the production rate (kg/h) and can be expressed by: Machine power (kW) = A x Production rate + B
(where A and B are variables to be determined from experimental data) The SEC is then related to the production rate by: Machine SEC (kWh/kg) = B x (Production rate)-1 The theory shows that as the production rate
+ A
FIG URE 1: MACHINE POWER (KW) VERSUS PRODUCTION RATE Source: T
angram T echnology
increases the SEC will automatically decrease. Energy use of injection moulding machines is closely related to production rate and any measurement or assessment of machines must take this into account. This is something that the Euromap 60 standard does not do. Applying the theory to reality, Tangram Technology
has collected data from machines at production sites around the world. It is relatively easy to use this data to correct for production rate, to assess the relative energy effi ciency and to energy rate machines. This is shown in Figure 1. The data displays a high scatter because the machines are operating at differing levels of production effi ciency, i.e. poor or good individual machine utilisa- tion. This is one of the penalties of measuring real machines in real factories. Under production conditions, both hydraulic and
FIGU RE 2: ENERGY RATING BANDS Source: T
angram T echnology
method for calculating the Specifi c Energy Consump- tion (SEC) for machines and includes a rigorous test procedure that covers three types of cycle. These are: Cycle 1 - Thin-walled parts. Cycle 2 - Technical parts. Cycle 3 - Commodity parts/Thick walled parts. This method is based on using standard measure- ment equipment, standard materials and a standard cycle. This provides a value for the SEC under standard conditions and this is reported in the form: Specifi c machine related energy consumption (EUROMAP 60), Cycle ll, 0.95 kWh/kg, 20 kW, 30s, cos φ = 0.95.
This standard provides standard test conditions and
reporting but provides no method of assessing the relative energy effi ciency of a machine. This has prevented Euromap 60 from achieving the recognition that it deserves and stopped it becoming a major market transformation tool.
20 INJECTION WORLD | September 2012
all-electric machines follow the theory, with all-electric machines needing less power than hydraulic machines. The material processed does not signifi cantly affect the results; Tangram’s data includes the material pro- cessed but analysis shows no consistent trend as the effect of the material used is lost in the variations due to machine utilisation and setting.
Determining the rating Using this data, it is now possible to energy rate injection moulding machines irrespective of the production rate dependency. A provisional rating scale is shown in Figure 2. This rating scale is based on production measurements and includes hydraulic, all-electric and hybrid machines. The rating of a machine is determined by the sector of the graph that the data lies in – so the line above the machine data point determines the rating level. On this basis, the majority of the hydraulic machines tested fall in the rating bands C – G while the majority of all-electric machines are in the rating bands A – C. This is what would generally be expected. This rating is based on production machines but an
industry adopted rating scheme would be based on laboratory machines operating to Euromap 60. When manufacturer’s laboratory data (to Euromap 60) is used, then all-electric machines again fall mainly in the A – B
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