Air Pockets ?

[Jig Man]

I'm using Bear's tube molds, Bear's injectors and Calhoun medium plastisol.  I have several dozen tubes to make and am finding about 1 out of 12 have air pockets on the sides.  I thought it was just a thin spot but it is indeed an air pocket.  I have no idea how they get there.

 

Anyone have a guess or know the answer?

[Apdriver]

Several things can cause them. I'll start with air being pulled into your injector. Make sure your o rings are in good shape. After you pull hot plastic into your injector, if I think I may have a bit of air, I'll turn the nozzle skyward and ever so slightly depress the plunger. Any air will tend to rise to the top and you can purge it this way.

[Jig Man]

I had not thought of that.  That makes sense.  My O rings are old.  I asked for replacements but was sent the wrong size with my order.

[Jig Man]

Thanks.  I thought they might be some special heat resistant stuff and hard to find.  I'll check at Lowe's or an auto supply store.

[Apdriver]

After you replace your o rings and start shooting just watch for this. When you put your injector into your cup to draw hot plastic and start pulling on the plunger, sometimes it will get hard to pull. It's like the plastic is hardening and stopping up the nozzle. I've found most times it's because I've let my nozzle down onto the bottom of my cup and that's what's plugging it up. This is when you will draw air around your o rings especially the top one as they go bad. Usually when I find myself doing this, just canting the injector at a 45 usually solves it.