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Post by Joel_W on Apr 15, 2019 11:30:56 GMT -8
I've never had this issue before, and have absolutely no idea how to deal with it.
Two of the three body sections have imperfections in the plastic. They look like lines that go right through the plastic outside to inside. I use to think that they were caused by impurities in the liquid plastic as it was injected into the molds. I've had them appear from time to time, but lacquer primer has always covered them. That is until today.
I've reached to stage of painting the BT18. So I cleaned all the parts with Iso Alcohol, and air dried them. I primed the body shells with Mr. Hobby 's Mr. Finishing Surface Primer1500 Gray, and thinned it 50/50 with Mr. Color Leveling Thinner #400. I applied the primer with my Grex Genesis air brush with a .3mm setup @ a flow rate of 16 psi. Two light coats, and then two heavier coats. I let this dry for 24 hrs. I then very lightly wet sanded with a piece of Tamiya 3,000 sponge. Those lines were still there but less noticeable, so I figured that they disappear with the color coats.
My next paint session was applying the color coats. I always air brush my color coats with my other Grex AB that has a .5mm setup, at a flow rate of 16 psi. As usual the paint used was Gravity pre-thinned lacquer, and it was a new bottle. Two tack coats, then two heavier color coats, with the last coat being a wet coat.
The lines are all still visible. So now I need to strip all three body assemblies and start over, which I've never had to do before. What's the best method for stripping the lacquer paint? And how do I deal with those lines in the plastic?
Joel
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Post by tatocorvette on Apr 15, 2019 11:54:45 GMT -8
Hello,
Are those like scratches? Do you feel them at the touch? or is it only a color variation? If the lines are scratches and show in the primer, paint will not cover them. It will only augment them because paint will bundle up at the ridges and make them deeper. Gravity paints are not very opaque. They are kind of translucent. That can also be part of the problem if the lines are creating a contrasting base. If you need to strip completely, I usually go for DOT3 brake fluid but it takes forever. Is it viable to just sand down as much as possible and reapply primer?
Thanks, Ismael
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Post by Joel_W on Apr 15, 2019 12:03:08 GMT -8
Hello, Are those like scratches? Do you feel them at the touch? or is it only a color variation? If the lines are scratches and show in the primer, paint will not cover them. It will only augment them because paint will bundle up at the ridges and make them deeper. Gravity paints are not very opaque. They are kind of translucent. That can also be part of the problem if the lines are creating a contrasting base. If you need to strip completely, I usually go for DOT3 brake fluid but it takes forever. Is it viable to just sand down as much as possible and reapply primer? Thanks, Ismael Ismael, None of the lines have any kind of feel to them. Not even the finger nail test could I feel any imperfection. That's why I figured that the lacquer primer would cover all of them. I should have stopped right there and asked for help, rather then applying the color coat. And Gravity paints aren't exactly cheap, plus the cost of shipping from Spain. Joel
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Post by Chris K. Hale on Apr 15, 2019 12:18:56 GMT -8
I strip all kinds of paint with Zep Oven and Grill Cleaner, (Lowes) put the parts in a freezer bag then sprat the Cleaner in the bag , use as much as you feel will work, let sit overnite, the wash the stripped parts with dish soap and water using a firm tooth brush to really clean in small spaces or deeper areas.. I stripped the 64 Corvette engine the other day , that paint was about 40 years old and came off in about 5 hours.. I have no idea what is causing your Line problems though.. Chris
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Ron S
Qualifier
Posts: 78
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Post by Ron S on Apr 15, 2019 13:09:40 GMT -8
Interesting problem. I've had that sort of bleed through from Sharpie ink so I think your original assessment of a contaminant in the plastic is probably correct. I was going to suggest Easy Off oven cleaner as a stripper but I think the product Chris mentioned above might work better as my experiences with Zep products has always been positive.
As far as preventing this from happening again maybe try some kind of sealer. This stuff works well to block color bleed through so might work but I'm sure there are others out there.
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Post by Joel_W on Apr 15, 2019 13:25:08 GMT -8
Thanks guys, I actually removed the paint with a bath of Tamiya X20-A as I never use the stuff any more. 95% of the primer is off and 100% of the paint is gone.
I'm betting that it's contamination of the plastic prior to it being injected into the molds. wouldn't surprise me if it's mold release.
As for sealing, that's what I'm going to do, but not with a Shellac type sealer as I'll only end up sanding through most of it. I'm going to order some Black Mr. Hobby Primer #1500, which should take care of the problem. I'm pretty sure I had this issue with my Ebbro 72E lotus too. But since it's Black, those marks just disappeared.
Joel
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Post by Joel_W on Apr 15, 2019 13:50:55 GMT -8
Major Update, I decided to help the X20-A along and started to work all three body parts with a piece of #600 emery cloth, and those lines were gone as I must have ruffed up the surface enough. I checked the inside and they were still there. So, I went over the surfaces with a piece of .3,000 sponge, and now the surfaces are all smooth with no molding shine, and so far no lines that I can see!!
Tomorrow I'll go over all the sections again, and if I don't see any sign of those lines, I'll re-prime with Mr. Hobby 1500 again, and go from there.
Just knew that the modeling Gods would find away of testing me, as the BT18 has been a true joy to build so far.
Joel
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Ron S
Qualifier
Posts: 78
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Post by Ron S on Apr 15, 2019 14:32:33 GMT -8
Sounds like you got it figured. I assumed you had already fine surface sanded before paint. Surface contamination makes sense now. Good luck with your project.
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Post by tatocorvette on Apr 15, 2019 17:20:25 GMT -8
It was a sign! [Eerie voice] "Don't cover all that beauty with a body....."
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Post by robhart on Apr 15, 2019 17:27:31 GMT -8
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Post by Joel_W on Apr 16, 2019 4:38:12 GMT -8
Thanks guys for the info and the support. I just checked the body sections and since the super shininess is gone from the sanding and polishing, so are those pesky lines. I'll finish up the polishing, the shoot another coat of Mr. Hobby 1500 Gray primer on. And then go from there.
A few friends from another forum that I've been on for more then 8 years feels that it's not contamination, but the result of slightly different densities of liquid Plastic as batches are mixed together for a continuous pour. Sounds more plausible then my contamination theory. But one thing it does prove, is that you can certainly teach a very old Dog a new trick or two.
Joel
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Ron S
Qualifier
Posts: 78
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Post by Ron S on Apr 18, 2019 13:37:29 GMT -8
Rosanne Roseannadana not withstanding, any updates on this issue? Just curious if the discussed solution resolved the problem?
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Post by Joel_W on Apr 18, 2019 13:55:35 GMT -8
Rosanne Roseannadana not withstanding, any updates on this issue? Just curious if the discussed solution resolved the problem? Ron, I've sanded, polished, primed, painted, and have gotten half way through decaling all three body sections, and not one of those lines has re-appeared. So I figured that it was two different pours, and I was just the unlucky one. Then for some reason the other day I googled reviews on the BT18 kit, and one review was from an Eastern European site with translation. They had posted pictures of all the sprues, so I took a closer look at the sprue with the body panels, and there were all those lines once again! So it can't be a pour issue, but maybe it is a contamination issue with one or more sets of molds? Joel
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Ron S
Qualifier
Posts: 78
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Post by Ron S on Apr 20, 2019 8:09:41 GMT -8
Rosanne Roseannadana not withstanding, any updates on this issue? Just curious if the discussed solution resolved the problem? Ron, I've sanded, polished, primed, painted, and have gotten half way through decaling all three body sections, and not one of those lines has re-appeared. So I figured that it was two different pours, and I was just the unlucky one. Then for some reason the other day I googled reviews on the BT18 kit, and one review was from an Eastern European site with translation. They had posted pictures of all the sprues, so I took a closer look at the sprue with the body panels, and there were all those lines once again! So it can't be a pour issue, but maybe it is a contamination issue with one or more sets of molds? Joel Hmmmmm...so the plot thickens. Interesting problem for sure. Mold contamination sure sounds valid at this point.
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Post by Joel_W on Apr 20, 2019 8:55:02 GMT -8
Ron, As for those swirls and resulting issues, I gave in and did a few Google searches. I finally came up with some knowledgeable answers. 1st, the problem is very common. The less adherence to molding Quality Controls, the more issues you're going to have. In our case of plastic injected models, the sprue trees are knocked out as quickly and cheaply as possible. Hence, one of the major factoring issues. Here's what one of the swirls actually looks like. You can clearly see that the density of the plastic is different before and after the swirl. The greater the difference in density, the harder it is for our paints to cover it up, so we end up with a uniform and consistent painted surface. Sanding/polishing ruffs up the surface and creates a uniform surface to paint on. What I found in my searches is that this and related problems are caused by several issues. 1-The temp of the liquification process of the Plastic pellets is to high, causing excess gases to be trapped within the liquid. In the above picture you can see the bubbles of the trapped gases. 2- To high of an injection pressure, ei. fills up the molds at a faster rate. 3-Contaminants of both the liquid Plastic and or the molds. These are main issues mentioned in several of the articles I read. It's pretty obvious that reducing costs are a major consideration to profitability, and the results are swirls, short molded parts, & cracked parts (especially clear parts). Joel
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