Is it possible to straighten warped diecast shells? I have an extremely bowed prewar American Flyer tender shell and I'm hoping it can fixed because it looks terrible. I have thought about laying it flat in the sun, but I'm not sure if it would work or make it worse. I have also heard from a friend that he straightens bent cab roofs on steam locomotives by heating them up with a torch, but I'd be afraid of damaging the paint or it possibly crumbling.
My other question is why do these warp? I understand that it has to do with zinc contamination but what conditions cause warpage? (not a word )
Trevor
The reason the casting warps is that the piece is actually expanding due to zinc pest. Because it is constrained by more solid connecting pieces, it can't get any longer or wider, so it bows.
So then it becomes a problem, not of only straightening it, but of shrinking it back to its original size. And I'm pretty darn sure that's impossible, unfortunately.
I've used a small torch on maybe half a dozen items and had good results on mostly bent cab roofs and steps. It surprised me that the paint remained intact on a Lionel 726 cab, although I was already planning a complete strip down and fresh paint. I figure if something has a bad bend in it, you don't have much to lose.
Dan
nice, thanks for u sharing it!
Perhaps a couple quick passes with a heat gun will make it pliable enough to press back into shape. Of course, it could craze it worse,
tjl0824 Is it possible to straighten warped diecast shells? I have an extremely bowed prewar American Flyer tender shell and I'm hoping it can fixed because it looks terrible. I have thought about laying it flat in the sun, but I'm not sure if it would work or make it worse. I have also heard from a friend that he straightens bent cab roofs on steam locomotives by heating them up with a torch, but I'd be afraid of damaging the paint or it possibly crumbling. My other question is why do these warp? I understand that it has to do with zinc contamination but what conditions cause warpage? (not a word ) Trevor
There's nothing that can be done to save that shell unfortunately. It is suffering from zinc pest, which is common for Gilbert 3/16" O gauge. It will eventually crumble, and there is nothing that can be done to stop zinc pest.
What tender shell is it? Postwar Gilbert tender shells can be substituted.
green97probe tjl0824 Is it possible to straighten warped diecast shells? I have an extremely bowed prewar American Flyer tender shell and I'm hoping it can fixed because it looks terrible. I have thought about laying it flat in the sun, but I'm not sure if it would work or make it worse. I have also heard from a friend that he straightens bent cab roofs on steam locomotives by heating them up with a torch, but I'd be afraid of damaging the paint or it possibly crumbling. My other question is why do these warp? I understand that it has to do with zinc contamination but what conditions cause warpage? (not a word ) Trevor There's nothing that can be done to save that shell unfortunately. It is suffering from zinc pest, which is common for Gilbert 3/16" O gauge. It will eventually crumble, and there is nothing that can be done to stop zinc pest. What tender shell is it? Postwar Gilbert tender shells can be substituted.
I do understand that once a casting warps like this it's pretty much going to stay that way, until it gets worse.. that's a given.
However as Trevor asks I am wondering if any of our more knowledgeable readers can EXPLAIN in layman's terms exactly what it is that is happening and why? As Trevor suggested was this just a bad metallurgic mix with contaminants in it that would swell and distort after years of heat and humidity? It's obvious to me that there are some pieces that have made it through the years without a problem. I own many of the prewar 3/16" O gauge Flyer pieces that are near perfect. But I have seen others that are warped beyond repair, including one tender base I just replaced that basically crumbled as I was removing it. The tender shell though is intact and looks solid. A few people have told me that if it has made it this far without warping or crumbling that chances are you have a good one.
The other thing I wonder is if a piece has made it this far is there anything that can be done to help ensure that it will stay that way.. for example the UP tender shell for my 571 is in great shape. I was wondering if I coated the inside with some sort of epoxy or say a gastank liner would it help to seal and keep the casting intact over the years to come?
Lover of all things Gilbert, truly a man ahead of his time.
As several folks have posted, a bent shell can often be straightened. However, a shell that is warped due to zinc pest rarely can. Not only does the metal expand and warp, it becomes very brittle. For years, it has been commonly held that the problem is caused by impurities in the alloy. More recently, I have read articles and spoken with folks who believe that zinc pest is (also) caused by moisture. I suspect this is true.
To learn more about zinc pest, I suggest doing an internet search on the term. The problem has been written up from a few different perspectives. Here is the Wikipedia write up:
http://en.wikipedia.org/wiki/Zinc_pest
I doubt the moisture hypothesis.
I have two identical K-Line semi-trailers (flatcar loads). The bodies of the trailers are as good as when I bought them years ago. The roofs, which are separate castings, are buckled and crumbling. I have a Railking Big Boy. A few years ago, the hatches and other small details on top of the boiler, which are glued-on appliques, crumbled. The main body of the boiler casting however showed no distress at all. (MTH replaced the entire out-of-warranty boiler at no cost.) In both of these cases, different zinc castings had exactly the same environmental history; but one failed and the other didn't.
I have also seen this sort of thing in cast-zinc trucks, where, for example, the side-frames will break but the bolster or drawbar will not, or vice-versa.
Bob Nelson
cwburfle As several folks have posted, a bent shell can often be straightened. However, a shell that is warped due to zinc pest rarely can. Not only does the metal expand and warp, it becomes very brittle. For years, it has been commonly held that the problem is caused by impurities in the alloy. More recently, I have read articles and spoken with folks who believe that zinc pest is (also) caused by moisture. I suspect this is true. To learn more about zinc pest, I suggest doing an internet search on the term. The problem has been written up from a few different perspectives. Here is the Wikipedia write up: http://en.wikipedia.org/wiki/Zinc_pest
Thanks for the link on Zinc pest, being new to collecting prewar Gilbert AF I wasn't aware that it was an actual named problem. I had heard Zinc pest a few times on the forum but thought it to be a nick name. I've been collecting post war American Flyer S gauge for many many years and have never had a run in with Zinc Pest in any of the post war castings. Although recently when scouting out the parts to replace a tender floor in a 571 I found that the replacement was made to replace the tender floor in the S gauge 336, that they were problematic. I do remember from years ago though that a toy train store owner I used to buy from commented to me about AF prewar not being as valuable due to the castings and wheels falling apart. I guess at that time there weren't many reproduced parts. At that time I had no interest in it.
I had heard Zinc pest a few times on the forum but thought it to be a nick name. I've been collecting post war American Flyer S gauge for many many years and have never had a run in with Zinc Pest in any of the post war castings.
Problems with zinc pest are very common with items made before WWII. Probably the most notable example in the Lionel world is the 700E. According to what I have read, the later engines don't seem to exhibit the problem, with the exception of a few parts that were cast earlier, such as the boiler front.
I have seen Lionel engines from as late as the late 70's with zinc pest. Folks have written about Zinc pest in other product made in the last 30-40 years.
As far as Bob's personal experience discounting the effect of moisture goes: There are plenty of people who smoke and do not get lung cancer. That doesn't mean there isn't a link.
Below are two copy/pastes from sites I am reading up on. I will continue to read and research this as it's fascinating to me.
At this early point in my reading, it seems that the introduction of lead impurities in the early casting process (where controls to detect these things and measure purity were not yet in place), would allow certain external conditions to start the seed of unstable crystallization withing the metal casting. The growth and movement of this crystal structure being formed (seeded) is what causes the swelling or growth of the part involved and then the subsequent crumbling or breaking apart. Perhaps the castings that have made it through unscathed, by chance had a purer mixture, without the lead contaminents that are present in the castings that are swollen and brittle. I would also venture to guess at this time.. shipping early castings in cold weather or transporting them from hot to cold probably not a good idea. Storage in less than a climate controlled environment not a good idea.. Don't keep them in the attic. Of course for those of us in the Northeast (I'm in Pennsylvania) that would pose a problem since most of the train shows where we find these precious items are held in cold weather. Although humidity probably plays a role in accelerating the process of deterioration I would assume that it probably doesn't contribute to it's start.
I'll continue to research this and edit where appropriate.
1- Zinc pest, (from German Zinkpest), is a destructive, intercrystalline corrosion process of zinc alloys containing lead impurities.[1] It was first discovered to be a problem in 1923.[1]
2- Polymorphism refers to the ability of a solid to exist in more than one crystalline form or structure. According to Gibbs' rules of phase equilibria, these unique crystalline phases will be dependent on intensive variables such as pressure and temperature. Polymorphism can potentially be found in many crystalline materials including polymers, minerals, and metals, and is related to allotropy, which refers to elemental solids. The complete morphology of a material is described by polymorphism and other variables such as crystal habit, amorphous fraction or crystallographic defects. Polymorphs have different stabilities and may spontaneously convert from a metastable form (or thermodynamically unstable form) to the stable form at a particular temperature. They also exhibit different melting points, solubilities, and X-ray diffraction patterns.
Another example is elemental tin (Sn), which is malleable near ambient temperatures but is brittle when cooled. This change in mechanical properties due to existence of its two major allotropes, α- and β-tin. The two allotropes that are encountered at normal pressure and temperature, α-tin and β-tin, are more commonly known as gray tin and white tin respectively. Two more allotropes, γ and σ, exist at temperatures above 161 °C and pressures above several GPa.[16] White tin is metallic, and is the stable crystalline form at or above room temperature. Below 13.2 °C, tin exists in the gray form, which has a diamond cubic crystal structure, similar to diamond, silicon or germanium. Gray tin has no metallic properties at all, is a dull-gray powdery material, and has few uses, other than a few specialized semiconductor applications.[17] Although the α-β transformation temperature of tin is nominally 13.2 °C, impurities (e.g. Al, Zn, etc.) lower the transition temperature well below 0 °C, and upon addition of Sb or Bi the transformation may not occur at all.[18]
you may also enjoy reading up on the product ZAMAC itself.Here are a couple of sites I have bookmarked to get started:
http://www.zincbig.com/content/getZincElem.asp
http://www.eazall.com/diecastalloys.aspx
http://www.diecasting.org/default.php
Thanks for the links. I did previously read up a little bit on ZAMAC (acronym for an alloy consisting of Zinc Aluminum Magnesium and Copper). It's all good stuff!
While zinc pest seems to be prevalent in tender shells, tender bases, boiler shells and wheels, it seems it can also attack the occasional motor chassis.
I have a prewar Royal Blue Set that is truly in what looks like well cared for excellent original condition. I had a problem with it "knocking" as it ran and occasionally locking up. I thought that perhaps it had the wrong side rods, since there were two different ones. I changed them out with a better set. It still knocked. Upon visual inspection it looked like the wheels were quartered properly, but this really was the only other thing I could easily think of that was wrong with it since it knocked when I ran the motor assembly alone with just the side rods on. Well after handing it over to someone with a quartering jig we found out that the problem was that the motor casting had "grown" slightly. It grew in size only enough to cause the knocking of the side rods. It is not deformed in any way or swollen. Only longer when compared to another. The problem was solved by elongating the holes at both ends of the side rods. For now it's running well. Fortunately I have spares.
Bottom line is that it amazes me how and where this zinc pest can strike, as well as the variations of damage. Visually this motor chassis looks fine.
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