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Capacity Calculation of Air Compressor

09/16/2017 5:41 AM

Hello,

How can calculate capacity of High Pressure air compressor (m3/hr) for a PET blow molding (CSD) machine for the below mention information:

- Blow molding machine speed: 36000 BPH

- High pressure air required : Max- 37 Bar & Min- 35 Bar

- PET bottle size: 500 ml

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#1

Re: Capacity calculation of Air Compressor

09/16/2017 5:48 AM
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#7
In reply to #1

Re: Capacity calculation of Air Compressor

09/18/2017 11:26 AM

Here's my one cheap shot:

Lyn knows one hell of a lot about blowing hot air, and the links are not bad either.

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#8
In reply to #7

Re: Capacity calculation of Air Compressor

09/18/2017 11:34 AM

From what I have seen buddy, your not so bad at it, yourself. (at times)

But, then we all have our moments, don't we?

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#10
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Re: Capacity calculation of Air Compressor

09/18/2017 12:02 PM

Yes, hot air is pretty common in West Texas. At least we don't have any cheese factories here, those are over in Roswell, NM, and maybe a smaller one in Lovington.

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#2

Re: Capacity calculation of Air Compressor

09/16/2017 7:04 AM

At least 300 liters per minute or 18m3 per hour.

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#3

Re: Capacity Calculation of Air Compressor

09/17/2017 2:38 PM

18000 Bottles/hr x 37 Bar x .5 liter/bottle = 300 bottles/min x .5 liter/bottle x37 bar = 3700 + 1850 =5350 liters/min

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#4
In reply to #3

Re: Capacity Calculation of Air Compressor

09/18/2017 4:26 AM

???

Where did 18,000 bottles/hr come from? 36,000 BPH was the quote.

...and this last part really has me puzzled:

"..300 bottles/min x .5 liter/bottle x37 bar = 3700 + 1850 =5350 liters/min..."

Where does "..+ 1850..." come from?

.

Shouldn't it be ...

600 bottles/min × 0.5 liters/bottle x 37 bar x 0.987 atm/bar = 10,995.7 liters (@stp)/min

.

.

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#6
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Re: Capacity Calculation of Air Compressor

09/18/2017 8:10 AM

Should have been 36000 not 18000. Left my computer at home and was replying on iPad, misremembered original number. Sorry.

1850 is half of 3700, was mentally multiplying 150 x 37. Computer is easier to work with.

Compressor capacity is referenced to 1 atmosphere.

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#11
In reply to #4

Re: Capacity Calculation of Air Compressor

09/19/2017 3:56 AM

As per your calculation its ok. But practically we are using 22 M3/min High pressure air compressor for 500 ml PET bottle blowing purpose @ 36000 BPH.

But dont know what is its calculation.

Would anyone clarify it.

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#13
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Re: Capacity Calculation of Air Compressor

09/19/2017 4:50 AM

tinac calculates in #4 about 11m3/min. There will be some losses and dead volume so in practice consumption will be higher. 2x sounds a lot, but maybe it's the best that can be achieved with your system. There might be things you can do to improve it, but we can't see the kit from here.

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#14
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Re: Capacity Calculation of Air Compressor

09/19/2017 4:53 AM

1000 liters per m3

So you are using 22,000 liters/min. That's about twice the air needed to fill 36000 BPH of 500ml each at around 37 bar.

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#15
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Re: Capacity Calculation of Air Compressor

09/19/2017 10:01 AM

Hard to calculate linearly unless we have some more of the variables covered such as the amount of air blown out (to the room) as each PET bottle comes off the mold.

You know as well as I do, you are not recovering the air in the bottle once inflated, and probably do not have a tight grip on the air behind the bottle (at the inflating nozzle).

Take the volume of the bottle in cubic feet (convert from 500 mL) multiply by the Bar pressure, then factor in your losses such as 50%, so that you now have

36000 b/h X 0.5L X 35 bar (example) X 150% = 945000 L/h = 15750 L/m = 15.75 m3/min, so it appears your air losses are higher than I thought.

(22000 L/m)/(600 b/m X 0.5 L X 35 bar) = 2.095, so you are "wasting" more than half the air applied.

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#5

Re: Capacity Calculation of Air Compressor

09/18/2017 7:20 AM

Easy. Pick up the phone and talk to a few air compressor suppliers. They are in the phone book and have websites listing those numbers. Ask for "air compressor sales".

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#9

Re: Capacity Calculation of Air Compressor

09/18/2017 11:34 AM

You need to know the regulated pressure at the PET bottle. You are most likely not putting 555 psi in the bottle in the blown cavity. Run the capacity of the bottle x regulated blow air pressure x # bottles per minute x blown pressure in Bars to get the SCFM for the compressor.

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#12
In reply to #9

Re: Capacity Calculation of Air Compressor

09/19/2017 3:59 AM

At the blow molding machine maintaining air pressure 35 to 36 bar, due to some line loss is there.

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#16
In reply to #12

Re: Capacity Calculation of Air Compressor

09/19/2017 10:59 AM

Not the delivered pressure to the machine. You need to know the regulated pressure applied at the mold. Most machines have a regulator to set blowing pressure in the mold. You need the downstream pressure developed in the blown bottle at the end of the blowing cycle. I'm accustomed to ABS blow molding where the pressure in the mold is only about 6 to 8 Bar in the molded product at the end of the cycle.

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#17
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Re: Capacity Calculation of Air Compressor

09/19/2017 11:57 AM

Oh, that would lower the calculation nicely into range.

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#18
In reply to #16

Re: Capacity Calculation of Air Compressor

09/20/2017 4:01 AM

But that would give theoretical consumption only ~ 2.5m3/min, an even bigger discrepancy.

If air is compressed to 37bar (maybe because something else on the plant needs that pressure) and regulated down to 8bar at the machine, it wouldn't be ideal from an energy viewpoint, but air consumption would relate to the 8bar.

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#19
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Re: Capacity Calculation of Air Compressor

09/20/2017 11:21 AM

True, the volume would be theoretical, but ratings on compressors are usually in SCFM, standard cubic feet per minute, which means the cubic feet volume is for air at 1 Bar. Once you have the theoretical consumption, then you add additional capacity to account for leakages and inefficiencies. It's also normal to see ratings on a compressor show different SCFM values for different outlet pressures., such as 10 SCFM @ 75psi, 8 SCFM @ 100 PSI and 6 SCFM @ 125 PSI.

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#20
In reply to #19

Re: Capacity Calculation of Air Compressor

09/20/2017 1:09 PM

Yes, we've all been talking about flow at standard conditions. If it's 37bar theoretical flow (ignoring losses) = bottle volume x bottles/min x 37, if it's 8bar it's x 8.

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