Viscosity Study on parts that stick to the A-Side

[Suhas]

Can you or how do you do a viscosity study if a short part sticks to the A-side of the mold?

[Jason]

Yes you can do a Viscosity curve if short shots stick in the Mold. All you have to do is use pack/hold pressure and time on the machine's second stage to ensure the parts are full. Your data is only pertinent to first stage. The tough part is knowing your part is full at transfer at max. injections speed. You may have to stick a couple to figure this out. Once you have short parts, injecting at max. velocity, add pack/hold pressure and time to fill them completely. You may have to increase your pack/hold pressure and or time as you use slower injection velocities due to the "fill only" shot volume getting smaller due to less inertia. No problem. If you notice your parts getting short or sinky as you slow down, increase pack/hold psi. Take you data as normal. Fill time and Psi @ xfer. Second stage pressure and or time doesn't effect the rheoogy curve one bit.

[NATHAN]

step1 : Set the charge position (stroke volume) accurately for the specified shot weight. H= Shot weight / Melt densityx3.14x(radius of screw)^2
Additonally provide cushion value 5~ 8mm or follow the material spec recommendation on the polymer type.
STEP 2: Perform the viscosity test from high speed to low speed in which the I stage pressure should be 80% of the machine available.
when start with fast speed better the fill time (95~98%) of the part weight should be 0.10sec.
If the fill time higher than 0.10sec then better try some high injection speed.
STEP 3: Once perform the test from high to low there is little chance of part sticking on the mold.
When reduce the injection speed there is a chance to stick. Below this speed it is no point to try.

OR
Some product design the ribs/undercut on the core-side will pull the part so there is possibility to stick due to zero on second stage.
Some times it is due to mold design / fabrication error (polishing) or in-sufficient draft.
It is quite better to correct the mold if machining error
Proceed the viscosity test if purely on product design.