Electrical System for Plastics Injection Moulding Machine

Some of the basic things to know, any one who is using Plastics Injection Moulding Machine either small or big. These are more practical and easy to understand. I hope reading this page would save you some money.

AC Motor Speed Calculation and its Relevance

Motor Speed (rpm) = 120F / P

where F = Frequency of the Power Supply, i.e. 50Hz, in India

P = Number of Poles in the Motor Winding.

Most commonly used configuration for AC Motors is 4 poles so we get 1500RPM. Due to slip practically we get 1440 RPM.

Most Japanese Injection Moulding Machines are fitted with 6 pole motors which produces 960RPM. There is an advantage with this, it will produce less noise than the motor running at 1440 RPM. But due to reduction in RPM Higher Flow Hydraulic Pump is to be used. While changing the pump other than the original pump, consider this fact.

Single Phase Power Calculation

HP = V * I * Eff * PF / 746 or kW = V * I * Eff * PF

Where HP = Horse Power, kW = Kilowatts

V = Voltage in Volts, I = Current in Amps, Eff = Efficiency

Three Phase Power Calculation

V_P = Phase Voltage across a winding.

V_L = Line Voltage is Voltage Measured between Line and Line. Between R and Y, Y and B and R and B

for STAR Configuration of Motor,

each winding get voltage of 400 / "3 = 230V and current measured in each line is Line Current.

I_L = Line Current = I_P, Phase Current

for DELTA Configuration :

each winding gets a voltage of 400V

I_L = Line Current = "3 * I_P, Phase Current

There are two ways of operating the AC Motors, either in STAR or in DELTA configuration.

3Ph. AC Motor Power Calculation, P in kW for STAR Connection

P = V_L * I_L * PF * "3, Where V_L is Line Voltage, I_L is Line Current and PF is Power Factor

in STAR connection, V_L becomes 1/"3 of V_L in DELTA connection and I_L also becomes 1/"3 of I_L in DELTA Connection

then P = 1/3 * V_L * I_L * PF * "3. It becomes 1/3 of the power of DELTA connection.

Injection Moulding Machines from US and JAPAN operates with 220V 3PH supply, where as in India the supply voltage is 3ph, 415V. Then how to use those machines with 415V supply?.

If a 220V, 3ph Motor is Connected to 415V, 3Ph supply, in STAR connection, then Power produced by the Motor is.

if the Motor is in DELTA then Power P = 1/3 * V_L * I_L * PF * "3, Since we are connecting it in STAR then P = 1/3 of Power in DELTA so it will become

P = 1/3 * V_L * I_L * PF * "3 where V_L = 400V, = 220 * "3, also if Voltage is increased by

"3 times then current also increases by "3 times, So I_{L (400V)} = "3 * I_L220V , Then Formula becomes

P = 1/3 * (220 * "3) * (I_L220 * "3 )* PF * "3

after simplification,

P = 220 * I_L * PF * "3 which is same as 220V, 3ph in DELTA connection.

So , it is safe and also produces same amount of Power. Since Motor is Connected STAR connection, STAR to DELTA Converter is not required. You can use DOL starter with Single Contactor and OLR (Over Load Relay). But Contactor shall be of higher rating.

Who do not have this awareness are using a Step Down Transformer, for whole machine. Transformer's efficiency is less than 90% means wasting 10% of Power.

Graphical representation of the same is given below.

400V STAR = 220V DELTA

Remaining Elements which are operating at 220V can be safely converted to 220V single Phase by connecting one line to Neutral. Heaters, Contactor Coils, Relays can be connected like this.

Theory of Power Factor :

For a Shop floor person or to the Management there is no necessity to go deep into this theory.

I have given the theory in plain words which is very simple and straight forward. No electrical Knowledge is necessary.

Explanation of Terms :

Power Factor ( P F) = Cos 타
= Real Power / Apparent Power. ( Technical Terms )

= Used Power / Costed Power

Used Power is which you have got some thing useful done on the machine.

Costed Power is what you have paid as Electricity Bills.

Wasted Power is something which could not be used.

If Your PF is less say 0.9 then you are paying 10% more. In addition to this Electricity board also loosing as Transmission Losses due to excess current of wasted power at your end. So it is not only the Board but also you loosing the money on low power factor setup. Investing for this is justified no matter how small it is, still PF correction pays.

Power Factor Correction

Simplest way to correct the Power Factor is to connect suitable capacitor across the terminal of Inductive loads like AC Motor. Three phase Capacitor to be connected across the Terminal of Motor. It is good for the constant load applications. But for, Injection Moulding Machines load is not constant, so Power Factor keeps varying continuously. When load on the Motor is less Power Factor also becomes less than 0.5.

Most sophisticated method is to use PF control Systems connected in the Main Incoming Line.

Do not just think it is only a statuary requirement to maintain Power Factor.

Saving Power on Injection Moulding Machine

There are several methods one can use to save power on Injection Moulding Machine.

They are given the order of Most savings on top and least savings at the bottom.

• ALL Electric Machine

• Hydraulic Machine with Servo Motor as driving Hydraulic Pump

• Fixed Displacement Pump with Power Saver installed on the Motor

• Variable Displacement Pump.

• Fixed Displacement Pump with load sensing

• Fixed Displacement Pump

Cost of the Machine also follows the same order as above. Advantages and disadvantages of various options are discussed in brief.

ALL Electric Machine.

It gives maximum savings and performance and cost is prohibitive for small industry. Also there is no provision for Core Pulling arrangement on the machine which shall be done by external power packs which in turn reduces the savings. If machine is going to run with Core pulling always then considering Servo Motor options is better. System works closed loop. Good for Clean room applications like medical disposables

Servo Motor for Main Pump

It is most suitable option now available for smaller machines upto 400 Tons. Best option compared to other options. But opting for good branded machine is better than to save some money on low end brands. System works closed loop. Low cooling requirement

Fixed Displacement Pump with Power Saver

This is well proven for savings are concerned, but there is slightly downgrading of performance of the machine due to poor response time of the AC Drive. Can be used for existing machines also. Easy to install and maintain, and better support available. Low cooling requirement

Variable Displacement Pump

This is not a new concept. Its performance is better than the Fixed Pump with Power Saver. Cost is higher than the Power Saver Option. Difficult to maintain. Repairing options are less. Oil to be maintained in good condition. Low cooling requirement

Fixed Displacement with Load Sensing

It is available in almost in all Hydraulic Machines except some local brands. Low cost easy to maintain.

Fixed displacement Pump

Hope no Injection Moulding machine is manufactured in this way. It is used on some Blow Moulding Machines.

There are other methods for saving energy which are not related to pump or motor but by mechanical design of the machine, application specific design, using electrical motor for Refilling etc. Using of AC drive will always saves some energy because it incorporates Power Factor Control. Even if the motor is run at full speed some savings are possible. Replacing Motor with Small Capacity will not help unless there is a reduction in flow rate of the pump.