3.5 Swim Shad Help Please

[BassDetective]

I don't see any light.  I don't have a distinct pattern for clamping.  It is random.

[andrewlamberson]

I couldn't stand it...so I went downstairs and injected a couple rounds on my swim shad mold. I used only one clamp. CCM medium plastic. No color. No glitter.

Round 1: I injected at 350 until "full"...held pressure (light) for 8 secs. I did not pour any plastic into the sprue.....and I watched that sucker (literally !) suck the plastic right out of the sprue...and I ended up with air in the top bait...just like the pics!

Round 2: I injected at 350 until full...held pressure for 8 sec...and used the injector to keep the sprue full...and the baits turned out perfect.

I guess I'm used to refilling/keeping the sprue full...because when I did any other mold...I found myself automatically making sure the sprue is full until it sets.

Probably because I started this hobby with hand pour 2 sided mold Senko baits...which suck like a vacuum cleaner... I just automatically watch the sprue!

Most of my Swim Shads I hand poured the belly and then injected...so there was no hot plastic pulling from the sprue on those.

So...if you are injecting the entire bait at once....as was stated in a previous post...that's a lot of plastic in the belly ....and it's bound to contract and draw from the sprue...especially if the plastic is really hot.

[pjmcla]

I downloded and looked at the second picture.
I am asking these questions more as a "defining the problem" than anything.
 
The air bubbles in the body of the middle and bottom baits look to be more or less in the center of the baits -  Is this correct?
Also, no air bubble in the sprue area or "bait to sprue joining area" of the bottom bait -  Is this correct?
Also, There is an "isolated" air bubble in the sprue of the middle bait that is "flowing" into the joint between the bait and sprue, but does not "reach" the air bubble in the head of the bait  - Is this correct?
Is the bubble associated with the middle bait more or less in the center of the sprue or along an outside edge?
The top bait is perfect; or is there a long thin tapered bubble in it?
( can't tell if it is light reflection or a bubble )

[BassDetective]

The air bubbles in the body of the middle and bottom baits look to be more or less in the center of the baits -  Is this correct?

Correct

Also, no air bubble in the sprue area or "bait to sprue joining area" of the bottom bait -  Is this correct?

Correct

Also, There is an "isolated" air bubble in the sprue of the middle bait that is "flowing" into the joint between the bait and sprue, but does not "reach" the air bubble in the head of the bait  - Is this correct?

Correct

Is the bubble associated with the middle bait more or less in the center of the sprue or along an outside edge?

Middle

The top bait is perfect; or is there a long thin tapered bubble in it? ( can't tell if it is light reflection or a bubble )

Only a reflection the bait is good

****

Thanks Andrew - At least I know I am not crazy    

[ghostbaits]

I used only one clamp.

Is this the reason the plastic "sucked" into the sprue? I have been using mine for about 2 hours now, 2 clamps. The sprue does dimple in but never does it get to where I think I need to add plastic.

If you use 2 clamps, do your molds still "suck" the plastic in Andy?

Curious. I am thinking like Paul is now. Air has to be entering the mold from another source other than the sprue or injector.

Jim

[pjmcla]

While you are "hugging" - do you feel any plastic being injected into the mold?  While "hugging" - Do you apply just enough pressure to "float" the body of the injector from the body - nozzle joint just a tad or do you keep all three ( injector body, nozzle, mold ) locked together?
If there is constant postive pressure to inject liquid plastic into the mold I can't see where the air is coming from unless it is being injected with the plastic or the air is not being vacated from the mold as injecting takes place and is accumulating in the head / head-sprue area.  Are the air vent cuts complete or being restricted in any way? ( I do not own this mold so I am grasping here ). 

[pjmcla]

Andrew - are you saying the mold pulled the sprue from full to empty after eight seconds of hugging "with a little injector pressure" but the mold did not want any plastic during the hugging cycle? ( case 1 ).

[pjmcla]

I read a thread on another forum where A gentleman was having a heck of a time with a mold.  As I remember the air vents were insufficient to vent the air as he injected and this created bubbles. But; if I remember correctly, they were down toward the bottom of the bait.
They solved it by "opening up" the air vents and slowing down the injecting speed some if I remember correctly.  I sort of find it hard to believe that air being "trapped" would make it into the sprue; but that would be it's last avenue of liquid escape I guess. But; right in the middle of the bait / sprue bugs me; unless it can be that this is the last area to solidify and the final trapping spot.
Some one who knows more than I do is going to have to solve this one.
I am sorry I quized and questioned without coming up with an answer. I hope I at least provided some value by "information gathering" for the person that solves this riddle.   

[BassDetective]

Thank you very much too all.  I really appreciate the ideas.  I am going to try a a few more things and be a little more precise and keep track.  I will post back in the morning.  I will check the air vents.  I haven't really inspected the molds for detail but I will tomorrow.

  While you are "hugging" - do you feel any plastic being injected into the mold?

I do not - feel real firm like its all full and will not accept anymore

  While "hugging" - Do you apply just enough pressure to "float" the body of the injector from the body - nozzle joint just a tad or do you keep all three ( injector body, nozzle, mold ) locked together?

Lately I have been pressing really hard to force the plastic - I don't see plastic squirting out the sides so I assume I have a good seal

 

[pjmcla]

Don't press hard. If you loose seal, hot plastic squirting with force is not a good thing.
I apologize;  I just can't leave this alone.  Hard to break old habits.
If it is not taking plastic while you are holding, ( and the sprue in the picture tends to support this ), then the air is getting "trapped" during the injection process.  You have stated before that this mold is the only mold that it happens with while injecting molds both before and after it.  This is a good indicator that the air isn't coming from the injector.
Try slowing down your injection speed. This will give the air more time / less exhaust pressure.  Also; Look at the "drop port" between the sprue and the bait body.  There is a "half moon" cut right the juncture of the head of the bait and the "drop / runner" from the sprue.  Look at both sides of the mold.  Compare them to the last cavity and to other molds. Are they smaller or not uniform on one side of the mold versus the other.  Maybe a vortex is being created that is "trapping" air.  I am at my wits end; again; with these thoughts.  
Jason will probably take one look and say - Hey this is an easy one  - It's  "onyonlyx".

[andrewlamberson]

I kept slight pressure on the top of my injector for 8 secs. then I assume it will provide plastic as needed.

One of the principles we teach in on of our plastics workshops is "differential shrinkage"...which is a principle that plastic does not shrink evenly...in shrinks more in the "direction of flow"...which would be down the sprue. Therefore it would expected that a long, sprue (for a 3 cavity bait) would have more shrinkage than a 1 cavity sprue. Thus...you would need to add more plastic during this shrinkage.

In plastic molding (the big machines!) there are some important variables that cause issues (the below is over generalized but I think the principles still apply to our small molds, with hand injectors):

1. Temperature: The hotter the plastic ...the more shrinkage. Colder plastic causes uneven or incomplete fills. "Dialing in" the correct molding temperature is critical. Of course there is also the cold mold...vs. hot mold issue.

2. Pressure and cycle time: For a part to fill correctly you must have a consistent pressure...for a specific period of time.

3. Shrinkage: Plastic does not shrink uniformly. There is more shrinkage in the direction of flow. Material of course has a significant effect.

Material: Now here is a BIG variable. I'm sure there is considerable differences in molding characteristics between the different plastics. Additives can make a HUGE difference. For example (that we use in the class) we molded 2 rulers from the same material. One is just the plastic ...the other has chopped glass fiber.  The ruler without the glass fiber is more than a 1/4 shorter (!) than the one with chopped glass fiber! And yes...it was shorter in the direction of flow. So to minimize shrinkage you can either change the direction of flow...or incorporate additives.

There are all sorts of materials (and chemicals) we add to our plastics to make them flow better, faster, slower. Higher temp...lower temp

So....when we add glitter...it probably affects flow. When you clean out your injector with worm oil or WD40 it may have a significant effect!!! Contaminants in our pyrex cups....Humidity obviously plays a HUGH role....I had significant issues with microbubbles this summer (hot and humid) and now the same plastic (same box even) has zero issues.

I had our mold flow/mold design expert look at the pictures and he quickly said it was shrinkage in the direction of flow causing air to be introduced at the end of the shrinkage.....thus keep the sprue full!

Now...here is another thought (because my fingers are getting tired typing and I need another cup of coffee!)...It clearly looks like air is being introduced at the end of the injection and is being pushed down the sprue. This mean the injector is nearly empty...near the end of it's cycle and the tolerances within the injector have changed significant during the injection...I wonder....could there be a nick in the o-ring...or the head of plunger is loose...or bent and thus allowing a tiny bit of air into the plastic???

After all of that....I think it's onyonlyx !

[ghostbaits]

LOL!! onyonlyx!!

Thanks for the lesson professor! Very interesting!!!

Also, what about the end of the injector not being on completely? I have noticed that they will come unscrewed after time to some degree. If additional air can escape via the rear of the injector, then plastic is not "heading in" but just sitting in place as there is nothing to force it further. Just a random thought...

I don't know what is happening but I know it is frustrating for BassDetective!!!!

Jim

[Jason]

I'll post a video and explanation in just a bit.  Jason

[Justin9j]

The is support is very impressive on this site. 

[Jason]

This has been a really good thread, sorry it has had to come at Steve's expense.

Before I go into detail, I am 99.9% positive the air is coming from the injector.  Let me explain why:

Here is the pic of your bait from your earlier post:



The entire mold is solid with plastic, except an air bubble in the middle bait.

What does this tell us?

1) It isn't a problem with sucking plastic from the spru / runner (see example in video below).  If it was it would be hollow like a straw leading to the bait(s).

2) It isn't a problem with sucking air from the venting.  If this was the case the bubble or dent would be close to the vents, not the head of the bait.

3) The venting is working properly.  It it wasn't there would be significant back pressure and the ends of the bait (closest to the vents) wouldn't form properly.  The tails look good.

4) You're not running out of plastic - all the baits are well formed / complete.

5) The cavities and mold overall all proportioned, clamped and sealing correctly.  If this wasn't the case there would be a big dent in the bait near the thickest part of the bait, or near the breach in integrity.

Here is a video that illustrates how to troubleshoot common air problems and how you can address them:

http://youtu.be/Ezj97apmgNc


So what's causing the problem???  There are some small air bubbles in the bait, but there was at least one big bubble that made it's way into the mold as well.  Interesting is that it is not in the bait furthest from the spru.  This would indicate that the bubble was around 1/2" from the tip of your nozzle (in your injector).  I'm not sure how it got there, but I would try the following to get it out.

1) Make sure there are no bubbles in your plastic

2) Once you injector is full, hold it tip up over your cup, allow any air in the injector to rise to the top (this is key given where the bubble is in the mold - give them a chance to rise to the top), and purge.  You should see plastic, air, plastic.  At this point you should be ready to go.

If you are still having the same problem, I would try a thin walled injector to see if you get the same results.

I know you said you didn't have this problem with other single cavity molds, I would shoot several of them back to back in clear plastic as well, just to verify that you aren't having the same problem and just haven't recognized it, or to rule out a new problem with an o-ring on your injector that is new.

If this problem stays isolated to this one mold, and none of the above helps, let me know and we'll do whatever we need to do to take care of it.

Jason