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| Hi all, I’ve been putting the finishing touches on my new prototype called the Molly Diver. I didn’t like the way the 2k urethane finish was performing with my new molding material, so I decided to epoxy the baits. I epoxied up a small batch as I’ve done many times before and put them on the rack, when I turned out the basement lights out they were spinning away looking great without a flaw. When I came down the next morning a fine line of small bubbles appeared along where the parting line in my mold is. You can see this in the attached pic. I’m molding the baits out of a hand mixed hand poured 2 part foaming polyurethane. Similar to the stuff some duck decoys are made out of. The material has a density halfway between balsa and cedar and it forms a hard outer skin layer on the outside of the bait. The mold is designed to vent and flash around the parting line so no voids will occur when molding the bait. I think this may be part of the puzzle. After the bait comes out of the mold I sand the parting line smooth.
Here’s my theory to what’s causing the bubble line: When the epoxy starts to cure it will begin to shrink, the bait being of light density will begin to compress, the skin area around the parting line is thinner from the sanding and air is being squeezed out along the parting line. The blemish was not consistent, and the pics are of the worst bait. I think the variance between baits is due to how tight I clamp the molds, I know some I left a little looser to help vent better. I have a hunch those are the ones with more bubbles. The integrity of the bait and finish is fine, it is very tough and is through wire construction; I just want most of the bubbles to be gone.
Has anybody experienced this before? Anybody solve this before?
TIA
Attachments
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 Bubleline1.JPG (46KB - 182 downloads)
MollyDiver1.jpg (83KB - 191 downloads)
MollyDiver2.jpg (82KB - 173 downloads)
MollyDiver3.jpg (85KB - 176 downloads)
MollyDiver4.jpg (72KB - 184 downloads)
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Location: Ohio | Are you sure it's not the epoxy heating when it starts it's curing and in turn is making your 2 part compond expand and let air come out on mold line where you've sanded. Maybe use a poylmer based primer to seal the paint and clear coat |
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| Temperature could very well be playing a factor in this. When you epoxy coat a light density wood bait do bubbles tend to occur where you have drilled holes or in grain sections of the wood that are less dense? After I mold the baits I cure them in the oven at a low heat for a while. The baits are fully cured after that, but expansion from heat can occur. So I think it could be both. Both the heat and the shrinking of the curing epoxy is putting gas pressure on my parting line area.
Edited by MRichardson 10/16/2012 11:02 AM
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Location: Ohio | It does if it is not completly seal with a primer or a sealing agent before paint and putting the epoxy on them |
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Posts: 1202
Location: Money, PA | If its only occuring along the seem on top; it could only lead me to believe that its either air or gas escaping from the inside of the bait. Especially if the rest of the lure is coming out bubble free.
You may have to sand and seal the seem better.
Nice lookin bait by the way.
Edited by ShutUpNFish 10/16/2012 1:03 PM
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Posts: 941
Location: Freedom, WI | I would say air coming out of the bait. As bait rotates maybe air deep inside is working its way out. Is the air temp steady? On wood baits the temp after coating needs to be steady or falling to keep air from coming out of the wood. Something to think about. Like shutupnfish said seal the seem maybe, possibly super glue. |
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| Thanks guys, I was doing some searching and found out that epoxy shrinks on average 3.5%. The exothermic reaction generates heat but I can’t find any data to what degree. So I’m sure the combination of heat and pressure is forcing gas out the seam line. I guess I need to add another step to my process. I like the super glue idea, are there any issues with paint adhesion?
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Posts: 1207
Location: Pigeon Forge TN. | Hey Mike, I don't have the scientific approach as to why the bubbles form but I have had my wooden baits do it a lot. Yes you can paint over super glue as that and what I call liquid plastic is what I use to seal the porous pockets of air. All little pores have air in them and it is "trapped" when you coat over them The heat exchange from the epoxy could well be the reason they "pop" up. I catch it if I look close at the bait and see the pores. I put acetone and scrap plastic lure pieces in a container and the acetone will liquify the plastic in a couple three days. I than fill a small syringe with it and put the needle in the pores and inject a small bit and let it dry. I have fixed tons of leakers that way too. I have used it with plastic and some wooden lures with great success. Brush on a little clear lacquer in place of the other and it will help also.
Just watch to make sure you have the problem area sealed.
Edited by Stan Durst 1 10/16/2012 8:07 PM
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Posts: 1202
Location: Money, PA | Or you could simply let them cure completely before painting them. I'd bet letting them air dry for a few days would do the trick.  |
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| Stan, thank you, that’s some great information. You have seen and done it all man. That why when I send you blanks I know I’m going to get a high quality durable paint job. We never had any problems like this with the injection molded ABS baits, but these new RIM molded ones have this unique challenge. I received a message the other day from a guy you custom painted a MDR Chopper for; he said the patter was “Chrome River Dace”? Sounds juicy, do you have any pics? I might need some of those.
ShutUpNFish, I’m fairly confident they are fully cured, this particular lot sat around for a couple of weeks before I was able to paint them. I did learn that lesson the hard way though ;) lol If in a hurry an oven cure gets the job done.
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Posts: 1207
Location: Pigeon Forge TN. | Hey Mike,
Yeah I did, he is going to Webster with it.
I am going to do a chrome walleye for him in another bait too.
Send me two of those new problem baits and I will paint them for you
Don't have a picture handy but it is a good catcher. |
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