Canadian Plastics

The tale of the tape: All-electric vs. hydraulic

According to manufacturers, electric injection molding machines are more efficient. But how much more efficient? The following table compares operating costs for molding a 430 gram part made of polyst...

September 1, 1999   Canadian Plastics



According to manufacturers, electric injection molding machines are more efficient. But how much more efficient? The following table compares operating costs for molding a 430 gram part made of polystyrene on an Ube Machinery Inc. 720 ton electric versus a 720 ton hydraulic machine. The comparison makes assumptions about electricity costs and operating conditions. The calculation can be customized for a molder’s operation by substituting specific values for machine and operating conditions. Savings vary according to the size (tonnage) of the machine. Ube estimates the average pay-off time for an all-electric machine to be about three to five years.

COST SAVINGS COMPARISON*

720 ton electric 720 ton hydraulic
Electricity Consumption 13.4 57.6
(kwh)
Savings/month $1,166.88
Calculation (Hyd-Elec.)kw x 20 hr. x 22 days x elec. cost/kw
________________________________________________________________________________
Cycle Time (sec) 30.1 32.8
Reduction rate 8.2%
Savings/month $1,195.24
Calculation Machine Only Charge ($/hr) x reduction % x 20 hr. x 22 days
________________________________________________________________________________
Cooling Water (gal/min) 2.65 47.55
Savings/month $118.54
Calculation (Hyd-Elec.) x 60 x 20 hr. x 22 days x water $/gal
________________________________________________________________________________
Hydraulic Oil (gal) 0 330
Savings/month $96.97
Calculation (Oil quantity x oil $ + $1,000 oil change) / 24
________________________________________________________________________________
Scrap Rate (%) 0.5 1.5
Savings/month $145.20
Calculation Machine Only Charge $/hr. x (Hyd. Scrap – Elec. Scrap ) x 20 hr. x 22 days
________________________________________________________________________________
Production Start Up (shots) 10 30
Saving month $484.00
Calculation Machine Only Charge $/hr./60 (1 min/shot) x 20 shots x 2 times x 22 days
Monthly Savings $3,206.53
Yearly Savings $38,478.32

ASSUMED OPERATING CONDITIONS

Machine Only Charge ($/hr.) $33
Work hours/day 20
Work days/month 22
Price per shot $0.27
Water cost (G) $0.0001
Electricity cost (kwh) $0.06
Hydraulic Oil (G) $4.00

*Figures based on Michigan rates in U.S. dollars provided by Ube Machinery Inc.

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