20 replies to this topic

[The Creative Explorer]

so, I am new to this. First I made a mold, which was surprisingly easy and looks pretty good to me. But then the problems start as I wanted to make resin copy's.

My first attempt went not so good because, after filling the filler hole, when curing the resin pulled back and I don't have a left valvecover, plus a lot of airbubbles.

My second atttempt isn't much better, still missing my valvecover and even though it has some more detail, it still doesn't look good.
Both times, the resin looks like honey (color wise) and stays stickey, even after 8 hours in the mold. I tried to make a 1:1 mixing ratio based on weight and 1:1 mixing ratio on volume, but both with the same result.

I inject my resin via a spout(?) and have 2 shafts in the top of the mold, one to release air or so I thought and one to fill. I will add pictures later.

Please help me to understand resin and how I can make a decent copy.

[Futurabat]

so, I am new to this. First I made a mold, which was surprisingly easy and looks pretty good to me. But then the problems start as I wanted to make resin copy's.

My first attempt went not so good because, after filling the filler hole, when curing the resin pulled back and I don't have a left valvecover, plus a lot of airbubbles.
We need to know what kind of resin you are using. Odds are it didn't really "pull back". The problem is the air in the resin from mixing. To help alleviate this try dusting the inside of the mold with baby powder. Make sure to tap out all the xcess before pouring. This will break the surface tension and help the resin flow as well as get the bubbles to flow easier to the vent hole. Another thing to consider is how the piece is oriented in the mold. Air bubbles are easily trapped under deep undercuts. These can be impossible to get rid if without pressure release galleys and a pressure pot.
My second atttempt isn't much better, still missing my valvecover and even though it has some more detail, it still doesn't look good.
Both times, the resin looks like honey (color wise) and stays stickey, even after 8 hours in the mold. I tried to make a 1:1 mixing ratio based on weight and 1:1 mixing ratio on volume, but both with the same result.This one's easy. You aren't mixing your resin well enough. Most resin companies sell resin with a 90 second pot life. Most novices can't keep up with that and the resin begins to kick before you start pouring. Get some 180 second resin and mix more thoroughly.

I inject my resin via a spout(?) and have 2 shafts in the top of the mold, one to release air or so I thought and one to fill. I will add pictures later.
Pictures will help us see what's happening pour wise.
Please help me to understand resin and how I can make a decent copy.

Hopefully we can. I've already identified a couple of your issues.

[The Creative Explorer]

Thanks,
Since I don't know which type of resin I have, I can't tell you whether it is 90 or 180 second. What I do know is that I have 20 pounds of it, so I am stuck with what I have and need to learn how to deal with this stuff.

I will try another go, but with the addition of baby-powder and use the airing tube as a filler tube and the other way around, bot the airing and filler tube are on the highest point of the engine.

Some pictures:

[Wagoneer81]

How old is your resin? From the pics, it looks like your resin has gone bad. When did you buy it and how long has it been open? Most resins have a finite lifespan after being opened and exposed to oxygen... usually a couple of weeks...

The missing valve cover is caused by a large air bubble gathering in that part of the mold.

[The Creative Explorer]

I opened it yesterday for the very first time, according to the vendor it should be o.k. for a while. Since I have no experience with resin, I don't know whether it is good or bad. Looking at it in the can's, it doesn't seem to be looking bad.

[1930fordpickup]

It looks to me like the air hole and the pour hole are to close together. Shouldn't they be opposite corners ?

[The Creative Explorer]

I was thinking something like that too, so I changed the mold, cut new filler and airing tubes. The mold is now turned 90 degrees and so it fills from one end of the engine, while the other end is the bottom. I hope this might do something.

I also got measuring cups, but the resin still does not cure after an hour. it got a bit better, but not enough I think.

[Lownslow]

its easier to pour your engine while its upside down

[1930fordpickup]

Good idea frank .

[dimaxion]

Fill up these holes . Onward and upward . If not so good otherwise ; clean , paint , cover with burnt oil . The hole is from a wayward Valve Train part on a Trashed Mill . Kept for spare parts .. Every one
casting has these learning curve rejects . Somewhere there is a tutorial for doing this process . It is a free upload online . Any one out there Help please ? Keep it up and keep asking . No such thing as "dumb question " . Thanx ..

[Greg Wann]

Parts should be cast as separate parts. Trying to build an engine and having it come out as a good part is almost impossible. Someone did post an example of an engine that looked pretty amazing awhile back. This Merlin engine is a big piece. The valve covers have a gap underneath them. Once silicone is poured in it will find every nook and crannie it can. The silicone in them may get torn out when the master is removed and you may never get a decent part out that will make the caster happy. When creating parts separately you may have one or two parts that may not come out right so you can try again in the next pour. Parting lines are important. Sometimes it is just best to follow the original parts parting lines. This means that a portion of the part might be in the top of the mold and you will need to pour a small amount in that part of the mold to.

http://smcbofphx.pro...lay&thread=1305

This link might be better.

Attached Files

•  all Judson 1.jpg   270.02K   33 downloads

Edited by Greg Wann, 20 October 2012 - 08:11 AM.

[Casey]

Parts should be cast as separate parts.

I agree. Casting an engine as one (mostly) complete part does not work well, leaving you with some voids in areas...not good. You want to aim for zero voids, period. The valve covers have a flat bottom, so they can be made in a much simpler, easier one-part mold, and you'll get more consistent results. You will need to use two-part molds for some parts. There's just no way around that sometimes, so you have to practice. Break the engine down to the engine block, cylinder heads, valve covers, exhaust manifold, and so on.

If rapid production isn't a concern, use a slower curing mold rubber and resin. It will give you more time to mix the A and B parts, and allow a bit more time for any air bubbles to escape. Think of how each part sits in the mold, and how and where an air bubble could become caught as it rises, and try to eliminate every possible place that could happen.

Looking at all the air bubble in the cured translucent resin, I'm going to assume those were not present when you mixed and before you poured the mixed resin into the mold? Again, no bubbles is what you want to aim for.

It's possible the resin and mold rubber are not reacting well with each other, but how does the cured resin look in the mixing cup? The resin which didn't make it into the mold will not have any contact with the mold rubber, so you can compare it to the resin inside the mold as a first troubleshooting step.

[Casey]

Thanks,
Since I don't know which type of resin I have, I can't tell you whether it is 90 or 180 second. I am stuck with what I have and need to learn how to deal with this stuff.

Mix a small amount of parts A & B, and leave it in the container. Time how long it takes to cure, and you will know what your working time is.

Also, what type of container are you mixing the A & B parts inside?

I will try another go, but with the addition of baby-powder and use the airing tube as a filler tube and the other way around, bot the airing and filler tube are on the highest point of the engine.

You want to fill at the lowest point if you're using a fill port and a vent(s). Even then, you have to consider how the air is escaping from the mold as it's being displaced by the liquid resin. You may need multiple vents at the high points so that you don't get trapped air bubbles.

[Greg Wann]

It might just be that the silicone and resin do not like one another.

[Art Anderson]

Your resin appears to have pretty serious moisture contamination--that is what causes those bubbles throughout your casting. That's indicative of a container that did not seal properly, or old resin.

Urethane resins are hygroscopic, meaning that in liquid form, they can and will absorb water vapor out of the surrounding air. I'm afraid your batch of resin may be rather liquid toast.

Speaking as one who's had that very thing happen a couple of times in my 12 years of resin casting, that's what I am seeing.

Art

[Futurabat]

Your resin appears to have pretty serious moisture contamination--that is what causes those bubbles throughout your casting. That's indicative of a container that did not seal properly, or old resin.

Urethane resins are hygroscopic, meaning that in liquid form, they can and will absorb water vapor out of the surrounding air. I'm afraid your batch of resin may be rather liquid toast.

Speaking as one who's had that very thing happen a couple of times in my 12 years of resin casting, that's what I am seeing.

Art

Exactly what I was thinking. For normal mixing that's WAY too many bubbles. Pressure potting won't even help that. I would suggest sending an e-mail with those parts pics to the manufacturer and ask for a replacement on the resin. Of course the maker will tell you it SHOULD be okay, but that doesn't make it so. I wonder how long it sat on the dealer's shelf?

[Ben]

That appears to be a fiberglass resin which is most likely why it remains sticky. It also appears to be very contaminated. Those tiny air bubbles should not be there and will constantly produce voids on your finished piece. I wish I could help you with what you have but I honestly think you'll be wasting your time trying to produce parts with it.

[wisdonm]

Lownslow has got it right. Plug those valve cover vents, cut a pour vent in the oil pan and pour your engine upside down.

Othe things I do. Use a brush to paint all finely detailed mold surfaces with resin, before pouring the rest of the resin. I use a resin that cures in a hour. This gives bubbles a long time to work away from the outer surfaces and into the vents. I have also used a hand held back messager to vibrate the mold for a few minutes to shake out the trapped air bubbles.

[Mr mopar]

That resin looks like the wrong stuff to use , por-a-cast from bear metal co works good I use it all the time with a 2 1/2 min pot live gives you lots of time to work with and very little air bubbles .

[Art Anderson]

That appears to be a fiberglass resin which is most likely why it remains sticky. It also appears to be very contaminated. Those tiny air bubbles should not be there and will constantly produce voids on your finished piece. I wish I could help you with what you have but I honestly think you'll be wasting your time trying to produce parts with it.

Ben,

I had forgotten about fiberglas (polyester) resins! That's likely why the resin refuses to cure out "click hard" on the surface in contact with the rubber mold. Silicone RTV rubber will "leach out" the hardener from the resin in contact with the mold, leaving a thin layer of sticky, uncured resin right there. Years ago, like 30-35 years ago, I tried making model parts from polyester resin, and nothing I did would solve this problem.

Polyurethane resin, say such as Alumilite, doesn't have this problem.

In addition, a large, fairly complicated thing like the Merlin engine is far better cast as separate parts, just as they come in the plastic kit from where it came. That way, there are no vents that need be added to the molds, and no unsightly marring of visible, exposed surfaces either.

Art