Zinc stearate for parts sticking

[Joel JS]

Has anyone used zinc stearate as sprayable agent to help parts release from the tool? If so, how long does it last?... (part is PP)

Thx - Joel

[iautry1973]

I have used it before. Works pretty good. I don't remember how many shots it lasted, but I do remember it lasting longer than normal release sprays.

[brentb]

You can mix with resin at a very small%


KOM

brent

[rickbatey]

You can get better release agents for PP than zinc stearate. Too much zinc can cause melt slippage when trying to plasticize. What's the reason for the mold release? Would you be better served coating the tool or a lifter?
Rick.

[Joel JS]

You can get better release agents for PP than zinc stearate. Too much zinc can cause melt slippage when trying to plasticize. What's the reason for the mold release? Would you be better served coating the tool or a lifter?
Rick.

New tool arriving..... many ej pins were bent when high pack psi applied at tool shop...... part still has sink..... I was asked about using zinc stearate, but have not used in in last 5 years, and wanted to see what others thought. Thx for the feedback!

Joel

[MTUHusky]

New tool arriving..... many ej pins were bent when high pack psi applied at tool shop...... part still has sink..... I was asked about using zinc stearate, but have not used in in last 5 years, and wanted to see what others thought. Thx for the feedback!

Joel

Are you having any parting line issues like flash? PP is usually pretty forgiving so you may be able to get away with raising your melt temp high enough to get your pressures down. If your injection pressure can come down then your pack pressure can come down which may help with sticking, as well as allowing you to pack out your sinks.

As to the original question, I do use some zinc releases but I have to go check what exactly they are. In my experience, you will get more life out of your mold release by spraying it and letting it dry completely. I don't know about your shop but the foreman at my shop like to spray the mold release and then immediately shoot it.

[JayDub]

many ej pins were bent when high pack psi applied at tool shop...... part still has sink.....

Joel

If you are over-packing the part and still have sink, mold release is going to be a Band-Aid solution at best. try to identify root cause and address that. Off the top of my head:

Part design: Sink on a thick section? Opposite a rib? [Live with it or re-design around it].
Process: Inject speed high enough? Transfer position minimum of 95% full part?
Tool: Draft, undercuts, finish?

[rickbatey]

Joel, if you have sink and are packing the part that hard; I think you have a gate freezing off to soon or the runner and sprue are under size causing you to not fully pack out the part. Try a blowing or foaming agent to foam the sinks out, providing if the part cosmetics aren't like a class A surface.
Rick.

[Joel JS]

Lots of good advice here guys.... thx for the feedback...... I will process the tool today or tomorrow. (Part is a dishwasher tray, and customer wants it to look nice.)

Thx! - Joel

[Wittmann_Molder]

We use it for a nylon job that was a poor design from the beginning. We got a bag of powder and mix it in at like a gram / 100lbs or something close. The part is small and we mixed up 100lbs in December (still using it). It wasn't a spray but if fixed our sticking issues immediately.

[Joel JS]

We use it for a nylon job that was a poor design from the beginning. We got a bag of powder and mix it in at like a gram / 100lbs or something close. The part is small and we mixed up 100lbs in December (still using it). It wasn't a spray but if fixed our sticking issues immediately.

Ok, good to know...... I will keep that in mind... Thx! Joel

[Joel JS]

You can get better release agents for PP than zinc stearate. Too much zinc can cause melt slippage when trying to plasticize. What's the reason for the mold release? Would you be better served coating the tool or a lifter?
Rick.

Hey Rick, what do you recommend for the better release agent? (spray, or mix in material)

thx! -Joel

[rickbatey]

Joel,
Akzo used to sell their Mold Wiz which is dehydrated chicken fat. It worked great and you could use a good color auger feeder to meter into the mix. The nano mold coating sold has worked great for lifters on a POM job I ran and lasted a long time. Zinc stearate works best in ps and abs resins. How often do you think you'll have to spray the mold to get good parts? What's the end use and no painting, coating or bonding after molding? I've used Slide releases as well as Stoner and I'll have to search for a dry teflon spray I found once. One can lasted for over a year! You sprayed the mold and let the spray dry before molding parts. BTW if you have sinks after serious packing, maybe you need a CFA or blowing agent to foam out the sinks? Used CFA on seat belt bezels that still had to show class A surface after molding. Only used .5-1% by weight. UCC as well as others make CFA's now days.
Rick.

[Joel JS]

Joel,
Akzo used to sell their Mold Wiz which is dehydrated chicken fat. It worked great and you could use a good color auger feeder to meter into the mix. The nano mold coating sold has worked great for lifters on a POM job I ran and lasted a long time. Zinc stearate works best in ps and abs resins. How often do you think you'll have to spray the mold to get good parts? What's the end use and no painting, coating or bonding after molding? I've used Slide releases as well as Stoner and I'll have to search for a dry teflon spray I found once. One can lasted for over a year! You sprayed the mold and let the spray dry before molding parts. BTW if you have sinks after serious packing, maybe you need a CFA or blowing agent to foam out the sinks? Used CFA on seat belt bezels that still had to show class A surface after molding. Only used .5-1% by weight. UCC as well as others make CFA's now days.
Rick.

Thank Rick,

I have a job that has been badly designed......it is a dishwasher tray, has lots of tiny posts that are textured, with little to no draft, and the posts themselves are not round, but square..... Of course the customer needs 50 parts yesterday, and when I ran on Monday, I bent 50 epins that push out these wonderful posts.... now it is going in again today to get 50 pcs, and I am armed with mold release, and spray zinc stearate, ........(but no dehydrated chicken fat unfortunately :-)

I don't think the part is thick enough to warrant a blowing agent. The part is not painted. I have not been able to pack as yet for above reasons. The part only has one gate (needs two), as the customer does not want a knitline in the center of the part, and, of course, most of the bent pins were right around this gate. And last good point is that the material is a homopolymer PP with a 2 melt flow!? Wish me luck!

(what is a cfa?)

(If I can get parts out the next plan is to add more epins close to the bottom of the posts to help pull them out.)

Thx again for the feedback!,
Joel

[rickbatey]

Joel,
CFA is a chemical foaming agent. So it makes small bubbles in the part that expand but usually these parts look better than blowing agent parts. Just do an internet search for suppliers.
Rick

[Joel JS]

Thanks Rick,

On second thought a foaming agent may work to alleviate the sink, and I will likely try on our next sampling, unless the extra e-pins works really good.

Thx again! - Joel