Machine validation

[processtech]

Hello,
Doing some validations at the minute,the one im going to ask about is injection speed linearity,im wondering am i following the correct procedure on this,i turn off hold pressure and time,i then set the machine to near max injection speed,and adjust changeover to give a short shot,about 80% full,i then start off with a low injection speed(3mm/s), and record the fill time,then double this speed and record fill time again,and continue this way up until i reach maximum injection speed,getting mixed results,some good,some bad. Any advice, opinions, experiences with same welcome.

[rickbatey]

Your looking for ~98% full parts, by weight, without any pack and hold pressure. Then shoot parts at the slowest speed the screw will move and record peak psi, for each step. Make your samples or steps smaller so you will get more points and consistent data to set your shear rate from. I tend to use 5-10 mm/s changes but that can depend on screw size. Then I can make a decision to run more in a range at 1-2 mm/s steps. You want to build a solid graph where you see the shear thinning working for you.
Do you have someone's capability sheets for this or you trying to do it on a home made spread sheet?
Rick.

[brentb]

Hello,
Doing some validations at the minute,the one im going to ask about is injection speed linearity,im wondering am i following the correct procedure on this,i turn off hold pressure and time,i then set the machine to near max injection speed,and adjust changeover to give a short shot,about 80% full,i then start off with a low injection speed(3mm/s), and record the fill time,then double this speed and record fill time again,and continue this way up until i reach maximum injection speed,getting mixed results,some good,some bad. Any advice, opinions, experiences with same welcome.

From what I know, Injection Speed Linearity shows how actual ram speed compares to speed set on the press. This is especially important for older presses that use thumb wheels type devices to set controls rather than PC devices. Even with computer control you want to judge response too.
Many presses use a percentage (%) setting on controller rather than say a mm/sec or inch/sec setting or volumetric/time setting.
Say you set up your test as much of what Rick says above above and have a 2 second fill time at say 100%, velocity, you should get a 4 second FT at 50%. This can be applied to the other systems of measurement too. If you set a 2 inch shot size and set 2 inch/sec speed, your FT should be 2 sec and so on. Or 2 ccm/sec etc.
In the old days we would do this with a stop watch to judge FT since controllers didn't display these things and pressures were shown on analog manometers (gauges)

Don't confuse this test with In- Mold Rheology Test also called Relative viscosity Curve, I think among other things. Or valve response test which does just that on hydraulic machines and compares controller settings with actual pressure confirmed on a known good pressure gauge .
Suhas has excellent info on the Viscosity Curve in his book, on his site and in various presentations.

Keep on Molding
brent6

[processtech]

Your looking for ~98% full parts, by weight, without any pack and hold pressure. Then shoot parts at the slowest speed the screw will move and record peak psi, for each step. Make your samples or steps smaller so you will get more points and consistent data to set your shear rate from. I tend to use 5-10 mm/s changes but that can depend on screw size. Then I can make a decision to run more in a range at 1-2 mm/s steps. You want to build a solid graph where you see the shear thinning working for you.
Do you have someone's capability sheets for this or you trying to do it on a home made spread sheet?
Rick.
Thanks for your reply, Would i neeed to record peak psi though,would that not only be required when completing a viscosity study.

[brentb]

http://www.ptonline.com/columns/the-basics-of-machine-evaluation-part-ii

[processtech]

The first one pressure response is saying <0.2sec/100bar. Can you clarify why it says divide pressure difference by 1000 for melt pressure, i wonder going between melt and hydraulic should the intensification ratio not come in to play?

115

Or i wonder looking at this, should it be ignore dividing by the 100 or 1000, and say for example a peak of 1200 bar, with hold pressure of 800bar, in this case expect a time of 0.8seconds or less?

The other study is load sensitivity, comparing the change in pressure between a mould and air shot, again this says divide by 100 or 1000, so can you explain these, help me understand the,, getting out of spec results according to some i have completed