Cap for wet wipes Problem

[maryna]

Hello all! I hope I can get some good advise here, because situation is desperate.

We are making molds and we started to mold plastic products. We mold different products and everything was ok. But now we have a problem with one product - thin cap for wet wipes. http://joxi.ru/MAj9VlJIDpwL2e This is our cap - http://joxi.ru/n2YV75BiaJ41A6

The problem is that the cap does not close tightly on the sides. Here are images: http://joxi.ru/J2baElyTbzlnm6 , http://joxi.ru/bmo9QVdIezw8Ay , http://joxi.ru/krD0eD4TqewDrp
The mold is good quality, we can't see any defects. As for materials, we have already tried a lot of different plastics with different fluidity etc, but the result is the same. :(

Will appriciate for any advise! :confused:

[Jendalf]

Hi,
can You share the pictures directly here (as a Picture) and not as a redirect to some web pages.
j

[maryna]

158 159 160 161

[Jendalf]

Ok,

try to look at the temperatures.

Check surface temperatures of the tool at the beggining and during production period.
Compare waterflow from the biggining of the project and now.

I think it could work
j

[Squirter]

I agree with Jendalf, could be a problem with the surface temperature in the mould. Also check that you have a melt cushion during injection holding phase or that the holding pressure time is not too little. Have you done a holding time study?

[JayDub]

Ok,

try to look at the temperatures.

Check surface temperatures of the tool at the beggining and during production period.
Compare waterflow from the biggining of the project and now.

I think it could work
j

Also check that temperatures are consistent across the tool face (at least in and around the cavity) and between A and B sides. Check that cooling is adequate – water temp “to process’ and “from process” at the chiller are nearly equal.

If that looks good, check that you are not over-packing the part (just enough pack pressure to get a consistently full part). The point here is to avoid excess molded-in stress.

If that looks good, consider opening the gates up a bit to fill easier (lower pressures, less stress).

If all else fails, consider using a resin with a small percentage of glass or mineral filler.

[maryna]

1. We've done the holding time study. We've tried different time - doesn't work.
2. The temperature of water and mould is really different at the beginning and in the end of process. But I supose we can't influence on temp. We have a single channel for the waterflow in our mould, not dot (spot) waterflow. The mould is 8 cells. Water temp "from process" is higher then "to process". Sorry, if my English is not adequate, I am not technical person. :o
3. We've already experimented with pressure too. If open the gates a bit, the product is with a burr. We actually can't set very very accurate settings on this machine we have now.
4. We've already tried to add a bit of mineral filler - the same result.

We are planning to change a bit a mould. To add a bit more material (body) on the sides and also to add a little shagreen on the inner side of cap.

[rickbatey]

You have differential shrinkage in the part. Where is the gate at? How full is the part at transfer position? I think you need to be 90-99% full part with a short, quickly ramping down hold pressure. You cannot run a scientific molding process on a part like this due to the tendency to wrinkle up like a potato chip.
Rick.

[maryna]

162163
the scheme of the cap here https://drive.google.com/open?id=0B4tVx8xpQToYTlpCa09EYnJVLTQ
It is too big to load here
Also the file, how we are planning to change the mould - https://drive.google.com/open?id=0B4tVx8xpQToYcnRLenIwc2R5VDg

Thank you all for advises! We will try more.
Tha gates are close tightly now. We will try to open it a bit with less pressure.

[brentb]

Did they ever function as intended?

If not, consider too shallow ondercuts.

KOM

brent

[maryna]

Nope, it haven't worked as intended yet. The mold was just made recently, is testing now.
We had a sample, made identical product. The sample is good, is closing tightly.

[brentb]

Check undercuts!

KOM

brent

[Josue]

162163
the scheme of the cap here https://drive.google.com/open?id=0B4tVx8xpQToYTlpCa09EYnJVLTQ
It is too big to load here
Also the file, how we are planning to change the mould - https://drive.google.com/open?id=0B4tVx8xpQToYcnRLenIwc2R5VDg

Thank you all for advises! We will try more.
Tha gates are close tightly now. We will try to open it a bit with less pressure.



For me looks like a gate zise issue, stress in the part, I think will be better after you open the runner /gates

Best regards

[JayDub]

Just to clarify, in case of language/communication issues: When Josue and I say “open the gates”, we mean have your toolmaker physically make the gates bigger. On the other hand, what Rick suggested was to back off on hold pressure before gate seal. Either of these will reduce residual stress in the part. A process change is easier than a tooling change, so try Rick’s suggestion first.

[Jendalf]

Just to clarify, in case of language/communication issues: When Josue and I say “open the gates”, we mean have your toolmaker physically make the gates bigger. On the other hand, what Rick suggested was to back off on hold pressure before gate seal. Either of these will reduce residual stress in the part. A process change is easier than a tooling change, so try Rick’s suggestion first.

Carefull about opening gates Jay!

Once before year I´d said at the machine to toolmaker:"We should open the gate more" and his reaction was quite obvious. He went to the gate and open it compleetely so the bright breeze from outside could easily flow...to the building :)
Colleagues from hotplate process was also "happy" :)

j.