# Injection pressure?

This topic contains 5 replies, has 2 voices, and was last updated by Matias 1 year ago.

Hi everyoneI am manufacturing the plastic injection machine, as a project to motivate students of a university to experiment with the recycling of plastics.

And I was trying to calculate the injection pressure of the machine, but I don’t know how

does anyone have any formula to calculate?I know that maybe it’s something very variable but I just need something approximate or an example of the calculation please

I found on this page it says that the injection pressure is 45 bar:

https://community.preciousplastic.com/academy/build/injection

but can someone tell me how that calculated please? if someone can help me I would be very grateful

Well, if you are building a machine to the specifications on that page, it states that it has a leverage of 3. So if you are 70 Kg (about 700 N) and hang of the end of the bar, you will apply 2100 N of force on the piston. If you divide that by the area of the piston in sq. meters, you will get the pressure in Pascals.

If you take more accurate measurements of the machine you are building, you will get more precise estimates for your machine.

If you need more pressure, the rack and gear designs are an alternative.

Hello thank you very much for your answer

i made the calculations taking the example and the specifications of the original design and got as a result 36833.7 pa, which is equivalent to 0.368337 bar…

but this value is well below 45 bar, which is shown in the machine specifications, maybe I did the calculation wrong or maybe there are other variables to consider to obtain a value similar to the one shown on the page?

It should just be the area of the piston face pushing on the plastic. In your case

I get 5.3e-4 sq meters and about 39.6 bar. I think to get to 45 bar, the PP guys eat more chocolate.

If you need more pressure using the current levered design, @andyn made a clever change in his version where he could change the piston diameter without changing the tube. Of course, you trade injection volume for pressure but for small molds with narrow passages it may be an option.

Now I managed to do the correct calculation and yes, maybe the man should have eaten more chocolate and weighed about 80 kg to hit a pressure of 45 bars jajaj

Very grateful for your help, have a nice day

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