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Air Bubbles And Swelling In Castings
12 replies to this topic
Posted 05 November 2012 - 10:40 PM
I used some old featherlite yesterday in a new mold. The castings bubbled up and expanded out of the mold. The castings were full of air bubbles and the insides looked like swiss cheese. Also the casted baits were about 30% bigger due to swelling.
The humidity was bad last night and the featherlite was about a year old. Any experience with this situation. What causes this to happen?
Posted 06 November 2012 - 12:52 AM
ive had this happen to me on some older baits... with older resin, you need to make sure each part is thoroughly stirred or shaken before mixed together. this was my main problem.
i would shake each part of the resin vigorously, then let the bubbles from shaking it go away, mix the two together, and see if it still does it. if it does, get rid of the humidity, and try again. if it still does, junk the old stuff.
Posted 06 November 2012 - 10:08 AM
I'm out of the old stuff now. Getting some new featherlite and smooth cast 300. I plan to use them both to cover all bases, ballast and bouyancy. Has anyone else tried this combination?
Posted 06 November 2012 - 08:29 PM
I havent used the that resin before, however, I do know the resins I use have a shelf life of 6 months. Moisture is a real bastard to resins, they cause bubbling and I would guess what you described. To try and extend the life of them I keep them in constant temp area and blast some argon in each time I use them. As they get older though they definately get harder to use.
Posted 07 November 2012 - 10:01 AM
Be sure to get an dry gas blanket to shoot into the resin container too. This will replace humid air. Also, only crack open your larger container to re-fill smaller containers. This will also minimize exposure and improve the shelf life.
Posted 08 November 2012 - 09:35 AM
That sounds like what my situation was. Age and humidity= failure.
I just recieved a couple of trial size containers of resin. The featherlite is in quart cans. Do you think I should pour some of that in a smaller jar or something? I guess it depends on how long it takes me to use it.
I poured a bait in the house last night (no humidity in there) and the bait came out very consistent with no bubbles and no swelling. Also the two resins joined together seamlessly. Bait floats upright and straight. So far so good.
I am using tape to hold the mold together before i pour the resin. Anyone have a better idea?
Posted 08 November 2012 - 10:45 AM
I have actually been using solo cups to make my split 1-piece mold. The mold forms to that of the solo cup. So when pouring my resins, I put the mold back into a solo cup. Since it is conical, it not only prevents the mold from buldging out too one side (because it would be fighting the round shape of the cup), but it also is much quicker than trying to use clamps. The mold comes out of the cup fairly easy. Worse comes to worst, you break the cup trying to get the mold out... and then just use another solo.
Ooo, also its a much cleaner process. The resin that bubbles out stays in the cup and just accumulates on top.
Posted 08 November 2012 - 03:34 PM
A-Mac, i'm totally lost on that process. I'd have to see a pic.
Are you pouring silicone into a solo cup and embeddding half the lure in it, letting it cure, then pouring the remaining silicone over the remaining part of the lure? Does the lure go in the cup head first?
If all that can work, it sounds a hell of a lot easier than making a clay bed and building a box around it all.
Posted 08 November 2012 - 04:22 PM
Oh yeah, much easier.
I'll try to take a pic and post later tonight. I pour and cover the entire lure all at once (I normally brush a coat on the lure itself first to try to avoid air bubbles in the mold). I then slice one side of the mold to take the lure out. RTV is tough stuff, and the less you cut, the better the cast.
You have to experiment with the lure and you can really only do 1 piece at a time (I ran into issues trying to do multiple pieces). A normal crankbait body lure, I would position with the nose of the crank pointing down at the center of the cup with the "tail" pointing up. I would use the "tail" as the pour area and just trim the excess resin off when cured. However, when doing swimbait or multi-section lures, you need to make sure that the position of the piece prevent air bubbles from being trapped and allows them to vent to the surface.
I almost always do 2-3 molds of a new design before I really figure out a way I like. But the nice thing with RTV, if you don't like your mold just chop it up into small cubes and mix it in with the next batch of rtv. It will still as long as the previous mold wasn't drenched in mold release.
Posted 08 November 2012 - 09:38 PM
Hey capt Mike,
The 300 and the FeatherLite are compatible. F-Lite is just S-on 300 series with fillers.
Humidity is the number one thing for bad castings. Age of product will do the same. Those resins must be used up pretty quick.
Posted 09 November 2012 - 12:46 AM
You definitely need to use any opened urethane relatively quick or it goes bad. If its fresh you can pour in high humidity and and still get away with it. As mentioned you can just use the 300 or any other unfilled resn and mix in your own mb's and meter your own ratio of mb's and have more control and versatility than using featherlite. Like that bass carving...: )
Posted 19 November 2012 - 02:18 PM
My bad guys on getting pics on here. I've been very busy lately. I plan to make a new mold over thanksgiving and will take pics of the solo cup mold making process as I go.
Posted 19 November 2012 - 04:35 PM
I found using the clear plastic display boxes from Hobby Lobby great for making molds. They come in a varriety of sizes, and they are cheap (~$1.00-$2.50). Plus they come with covers, to keep dust out. You can drill holes in the bottom to push out the mold if needed, but most of mine just stay in the container. I only remove the top half of a mold after a pour.
I do have issues with bubbles in some of my molds, especially in thin or small areas; but I think this is from poor venting, or positioning. Something I am still trying to master.