Load Sensitivity Test

[Rojan]

Hi guys,

I have a question to those of you who conduct Load Sensitivity Tests. I have the procedure from here: http://webcache.googleusercontent.com/search?q=cache:YdIQMwq4lDMJ:www.brownpackaging.com/documents/Testing%2520Injection%2520Molding%2520Machines%252 0%2520www.scientificmolding.com.pdf+&cd=3&hl=pl&ct=clnk&gl=pl

What experiences do you have with this method? Is it reliable?

Thanks for your thoughts.

Robert

[Rojan]

And there is this formula for calculation of the load sensitivity:
((FT1 – FT2) ÷ FT1) ÷ ((PK1 – PK2) ÷ 1000) × 100 = % error/1000 psi

How does the formula looks like if I work with hydraulics bars. Is the following one correct?
((FT1 – FT2) ÷ FT1) ÷ ((PK1 – PK2) ÷ 69) × 100 = % error/69 bar

Thanks for your thoughts.
Robert

[Suhas]

Hi Rojan,

John and the Rod Groleau (from RJG) were the people who came up with these studies. They are considered one of the pioneers.

In regards to your question, load sensitivity is 'How sensitive (or how fast does the machine react) is the machine to changes in loads (material viscosity)' So, it is how sensitive is it to a change in 1000 psi with the formula you have. But you can do it how sensitive is it for every 100 bar to keep it simple. The units are not important, the number are. Now, as you go to 100 bar you may get larger 'per/100' numbers. You will need to come up with your own 'what is good what is bad'.

Machines are not my area of expertise and so I would like to give only one cent out of the two :)

Regards,
Suhas

[brentb]

Never did one on an electric press, only on OLD hydraulic presses!

KOM
brent

[Rojan]

Thank you guys for your answers.

I understand electric presses do not deviate a lot under verious loads?

Brent, do the tests show more sensitivity as the machine gets more wear? I suppose it should but have you observed such relationship?

THX

[brentb]

Microprocessor controls,really help in sensitivity,versus the "good ol, days of relays,mechanical timers and thumb-wheel potentiometers for velocity and timer settings.
On hydraulic machines, the modern ones with microprocessor controls,servos and /or digital hydraulics approach electric press for accuracy/sensitivity,if well maintained and oil that is CLEAN!

kom

brent

[chrisprocess]

Load Sensitivity Instructions:
1. With machine running on cycle, record the fill time and peak pressure to fill the cavity.
2. Stop the press, on cycle, insert a purge plate in the locating hole on platen.
3. Zero the nozzle against the purge plate.
4. Set the machine to semi-automatic and start the cycle.
5. Record the fill time and peak pressure.

Then do the calculation you mentioned above is correct ((FT1 – FT2) ÷ FT1) ÷ ((PK1 – PK2) ÷ 1000) × 100 = % error/1000 psi
Generally less than 5% kpsi is a good rule of thumb :)

It would be a good test do use when purchasing a used machine or if you wanted to understand machine sensitivity to changes in viscosity by molding different materials, temperatures etc.