PDA

View Full Version : Sink Mark near gate



Maheshkumar Hiremath
6th July 2012, 04:27 AM
Hi ,

I came across the problem of Sink mark near the gate ( Dia 1.1 * 1.2) in one of the connector housing.The raw material used for the same is Schulamid 6 mu 14 FR (PA 66).It is a 2 cavity mold.Temp setting on barrel 265 , 250 , 245, 240. Mold temp 60*C. Screw dia 25.0 mm. Part wt 5.375grams and Runner wt 3.437grams.Done various trials like changing injection time from 0.8 Sec to 1.50 Sec. MTC temp 40* to 60*C. Holding pressure 30% to 50%.Gate freeze off time is 3.0 Sec. But sink mark not eliminated in the part.

Suhas
6th July 2012, 08:14 PM
What is the base material of Schulamid? What is the wall thickness in the gate area? and what is the overall average part thickness? Let us know.
Suhas

ruhlj
6th July 2012, 08:43 PM
Also, what kind of gate, is it a hot tip or a cold runner subgate?

rickbatey
7th July 2012, 03:33 AM
The sink mark is more than likely from too large of base diameter of the gate to the nominal wall stock. Run your hold pressure even higher and see if it improves. Also run the mold temps even higher to see what happens. What is the part temp at ejection? What is the actual steel temp? How much cooling time are you running?
You may also see this defect due to difficulty in pulling the gate from the cavity,ejector stress or a vaccum void in the sprue. All of the corrections will require a different method to correct.
Rick.

Maheshkumar Hiremath
9th July 2012, 04:23 AM
Thanks for your quick reply...
IT is Nylon 66. Wall thickness in gate area 1.02 mm. Overall average part thickness 2.50mm.
And also noticed these sink marks in short fill itself when the parts are filled 40% and these sink mark remains in the part even when the parts are filled 100 %.

Maheshkumar Hiremath
9th July 2012, 04:25 AM
It is Coldrunner Submarine gate..

Maheshkumar Hiremath
9th July 2012, 04:30 AM
Ejection Temp - 50 * C.
Steel temp 58 *C.
MTC temp 60*C.
Colling time 10 Sec ( Tried up to 15 Sec - but no chnage in the sink mark)
Degating is smooth
No stress mark on the part noticed at ejection pins and other areas also.
No voids in the Spurue.

tfrounfe
9th July 2012, 03:56 PM
What is the gate diameter of your subgate? Have you checked to see when your gate freezes?

Maheshkumar Hiremath
10th July 2012, 03:56 AM
gate ( Dia 1.1 * 1.2) and gate freeze of time is 3.0 sec.

Suhas
10th July 2012, 03:04 PM
Hi Mahesh,
I think gating into the thin section (1.4mm) and having the rest of the part at 2.5mm may be the issue here. Your gate size is close to your part thickness - not only is the gate freezing off but also the part in that area. You may have to modify the part design by adding some small flow promoters or mold design by adding a gate. It may not be a good idea to open the gate size since it is close to the part thickness since if you open it up you may see some damage.
Regards,
Suhas

Steve_D
12th July 2012, 02:45 PM
I would have to agree with Suhas. Why would the tool be designed with the gate at the thinnest section of the part? By doing this you are not only increasing the pressure required to fill but also risking freeze off within the thin section( which you are experiencing ) Going up on the mold and melt temperatures may help but moving the gate to the correct position is the correct solution.

Maheshkumar Hiremath
19th July 2012, 05:44 AM
Thanks to all for giving your thoughts.

We have tried with increased gate size , Filling time varying and step injection . But all trials have sink mark in the part.

Rgds,
Maheshkumar

Suhas
19th July 2012, 06:27 AM
Hi Mahesh,
This could be a part design and/or a gate location issue that probably cannot be fixed by processing.
Sorry!
Suhas

Robert Bates
19th July 2012, 05:30 PM
Very informative. Thanks

Maheshkumar Hiremath
9th August 2012, 04:51 AM
Thank you alice,

Still we have not fixed the problem....looking the option of changing gate location / product modification.
Will keep in touch with you,

Warm regards