Senko mold Bubbles/Denting

[Hammer]

I have been shooting Do-It senko mold and struggling with air bubbles and/or denting.

I have tried 350-360 degrees, faster, slower, more and less pressure but cannot find the sweet spot. I have thought about opening up the entry point but once the material is gone it cannot be put back so haven't done it yet.

Any thoughts or suggestions before I start hogging out the mold??

[ctom]

How are you getting the plastic into the injector? I stick the nozzle about 1/2" into the plastic in the cup and pull it up while pulling the plunger out. I have to "follow" the plastic as the level drops, but when I discovered the wonderful world of bubbles, this method of loading the injector cured it.

Denting is either a temperature thing or the baits are running out of plastic as they cool. Your temps seem to be in line but you could try injecting slightly cooler and see if that helps.  When you finish injecting but still have the nozzle in the gate, push out a little bit more plastic for the baits to pull on while they cool. Sometimes if the injector gets pulled off the mold too quick there is no extra plastic for the baits to suck in as they cool and contract.

[olsarge]

You did not specify which senko mold.  I had the same problem (referring specifically to denting) with the essential version of this mold.  I tried everything.  For the best results I found I had to pre warm the mold and shoot the plastic at a cooler temp (310 degrees).  Inject slow and hold pressure for 10 or so seconds then top off.  Like I said my results improved greatly but I still wasn't happy.  I wound up taking a rat tailed filed to both sides of each gate to open them up.  I took it easy (10 strokes on each side then reinject until I was happy).  I will admit I was not very comfortable doing this because I knew I could totally destroy the mold.  Happy to report that it shoots fine now and I am happy with it.

[Hammer]

It is the Yamamoto 5" (not ES) mold.

I do keep the nozzle in pretty deep while loading the injector.  I am usually filing a couple molds at a time so once full I pull off and shoot extra on top to keep it full as it cools and draws in and move onto the next mold

You bring up a good point that makes we wonder if when I pull off if it is cooling to fast on top and not allowing enough time to draw more in.

I will try heating the mold first and see if that works. If not, I will  try and shoot one at a time and keep the plunger on with slight pressure to make sure it has a supply of hot plastic available while cooling. If neither work it may be time to open up the gates

[Fishermanbt]

I would absolutely love it if mold makers would CNC a copy of their molds (same size and layout) in a clear media and then post videos of them being injected. Something on the lines of the old MF plastic molds. It would be amazing to see them fill and possibly help use take the guesswork out of troubleshooting.

With what Ctom said you might also try this. After injecting and holding pressure, carefully keep pushing hot plastic out of the injector as you pull the injector out of the mold. On some of my molds I get problems if I just inject then pull the injector out and top off the mold. I suspect it causes a bit of a vacuum which leads to voids in the cavity.

I would also recommend that you try each suggestion separately keeping the plastic temperature as the constant. This way you can dial in on what worked best and make a note of such for future creations.

[Agronomist_at_ia]

To reduce bubbles, I have taken the tip off my injector and poured the plastisol into the injector. Put the tip on.....pushed the plunger until plastisol started to come out of the tip. Helps keep bubbles from the plastisol when sucking it up with plunger.

[Hammer]

I don't think the bubbles are coming from sucking in bubbles but rather the cooling.

I shot twice at 350-360 again but only 1 mold at a time and held pressure for about 10 seconds then pulled off and topped up and out of 8 senkos I only had 1 with a slight dent and no bubbles in any. I ran out of time but plan on shooting more this weekend using the same technique  to make sure I wasn't just lucky.

[Apdriver]

I never shoot that hot. On the initial heat, I go to 350 to make sure the plastic turns over, let it cool to 320 and add my flake as a precaution for the flake giving up its color and curling. Also, I’ve had problems with dents shooting too hot. On the reheats try to stay below 320 for those reasons plus alleviates some yellowing.  It just works best like this for me.

[Hammer]

Interesting.
I have not tried cooler temps and is something VERY easy to try. I will be shooting more this afternoon and cooler temps will be the first thing I try!