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Post by steveturner on Sept 1, 2016 6:56:18 GMT -8
Guys I was reading with interest on another forum N scale issues with loco frames crumbling into powder. Wonder if this scenario has or is happening to HO scale locos or metal framed cars ?. Like most of you I have a vast assortment of locos purchased over 30 years that are used or sit in display case. Sounds like a terrible issue.Some folks un packaging N scale locos for first time in years to find out out when they touch them the frames break into pieces. What causes this issue with the metal ?. I have some old MDC Shays and MDC metal framed cars and they seem fine. My locos are from many suppliers. Anyways this is a scary situation and I feel bad for modelers with this problem.Steve
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Post by Christian on Sept 1, 2016 7:16:49 GMT -8
Zinc Pest. Well known problem with diecast metal. Caused by too much lead in the zinc alloy. Not fixable. Common in 20th century toys. Part of the reason for those high prices for *rare* collectables. It is appearing again in foreign made toys with zinc alloy castings. Shows up ten to forty years after the part is cast.
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Post by steveturner on Sept 1, 2016 7:37:16 GMT -8
Any products familiar to HO scale with or had this problem.I have Keystone log cars and MDC log cars still in boxes not made up yet. I don't know what the alloy make up of the metal in these would be. Interesting subject. So if toys have it how about other products, scary Steve
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Post by edwardsutorik on Sept 1, 2016 8:24:42 GMT -8
It all depends on always using a good non-contaminated alloy.
There was also some talk about the dies getting contaminated by using bad alloy. Thus one mistake can ruin a die "forever". I've never heard anything backing up that theory, though.
Consider what Kadee couplers are made of...............
Ed
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Post by scl1234 on Sept 1, 2016 8:39:30 GMT -8
What are some of the brands suffering from this issue? NOT ALL LOCO FRAMES have the "zinc pest" issue!!! (Sorry for the yelling, had to make a point)
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Post by roadkill on Sept 1, 2016 9:09:06 GMT -8
Bachmann diesls from the early Seventies were notorious for zinc rot, especially their U36B. Saw many at train shows with frames so badly swelled that the shells broke.
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Post by Christian on Sept 1, 2016 10:26:37 GMT -8
Any products familiar to HO scale with or had this problem.I have Keystone log cars and MDC log cars still in boxes not made up yet. I don't know what the alloy make up of the metal in these would be. Interesting subject. So if toys have it how about other products, scary Steve "Zamak" was a common zinc alloy used by train mfrs in the fifties into the sixties. Lionel, American Flyer, Athearn, MDC, Varney, Penn Line, Mantua and so on have all had zinc pest. Bachman has been mentioned. Lots of n scale imports that I can't remember OEM names. Keystone used a different alloy - at least the Keystone stuff I have is a soft metal. Zinc alloys are very hard. You can't chip them with an X-Acto knife. My sixties MDC stuff seems OK for now. It's not all production. Just occasional short runs of pieces. Depended on what was in a given ingot when it went into a casting machine. It was fairly rare and most anything that has the pest is likely to have already disintegrated. As I mentioned above, zinc pest pretty much went away. |
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Post by jonklein611 on Sept 1, 2016 11:02:24 GMT -8
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Post by talltim on Sept 1, 2016 11:15:12 GMT -8
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Post by canrailfan on Sept 1, 2016 11:30:19 GMT -8
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Post by dti406 on Sept 1, 2016 11:32:55 GMT -8
The frames on the Con-Cor GP38, GP40 etal that were copiers of the old Atlas/Roco engines all seemed to have the Zinc Pest, and only in a couple of years. At least you got a good motor out of one of those.
Rick Jesionowski
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Deleted
Deleted Member
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Post by Deleted on Sept 1, 2016 11:59:47 GMT -8
"Zamac" is supposed to be a mainly zinc and aluminum alloy. The problem is not with use of Zamac itself but with impure versions of the alloy containing too much lead.
In the case of model train manufacturers, just about all of them occasionally made the mistake of accidentally mixing lead with zinc in the factory at one time or another, resulting in some zinc pest issues. There are others not named above who also did experience issues.
Lead was used at one time in the past to help metal "flow" more effectively into the molds. This is why some pre-WWII Lionel trains will crumble into dust (mainly the wheels). Best thing is to keep paint on the old metal toys. That slows down the reaction.
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Post by edwardsutorik on Sept 1, 2016 13:22:57 GMT -8
I've noted the problem with Ulrich freight cars and the cylinders on my Rivarossi 0-4-0T Duckside. The former were probably cast in the late fifties/early sixties. The latter mid-sixties.
Ed
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Post by bdhicks on Sept 1, 2016 14:03:17 GMT -8
The run of Chinese QJs that Bachmann imported several years back had a problem with this, or at least all of the ones I've come across in my half-hearted attempts to do one of the IAIS steamers.
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Post by talltim on Sept 1, 2016 14:06:10 GMT -8
I've heard a story of the lead seal from a barrel/box of zamac power being tossed into the melting pot, with obvious consequences
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Post by edwardsutorik on Sept 1, 2016 16:13:14 GMT -8
I've heard a story of the lead seal from a barrel/box of zamac power being tossed into the melting pot, with obvious consequences A person could wonder WHY one would use a lead seal. ESPECIALLY when it's known as a contaminant to the substance you're trying to protect. It sounds kinda like a story someone might make up to divert attention from what really happened. I'd sure like to hear more about the lead-seal-zamac-powder-tossing event. Ed |
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Post by Judge Doom on Sept 1, 2016 17:00:57 GMT -8
There was some talk in the past of people having some early P2K E-unit frames break due to this, in the thinner area where the weight screws go in the frame near the front truck. Haven't noticed any issues on mine though. Over on the Tyco forum, someone posted this photo of a Bachmann FT made for AHM whose chassis expanded so much it cracked the shell:  |
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Post by fourteen on Sept 1, 2016 22:47:07 GMT -8
Ouch on that ft unit. that gotto suck.
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Post by lvrr325 on Sept 2, 2016 5:18:00 GMT -8
AHM is who had that FT first, it just happened to be made by Kader in Hong Kong, like the Lionel HO GP30 who's shell is still being sold by Bachmann today. Somewhere I have one that the frame pushed the back of the shell outward.
Anyhow, the only entire run of product that I'm aware of to suffer this was Varney's colorful Docksiders released around 1961. All I've ever found of them are shells. But I've seen it in all sorts of vintage stuff, every brand seems to have had a bad batch of metal here and there. Even Athearn, primarily in the Pacific they offered in the early 1960s.
Outside of Bachmann's Chinese 2-8-2 I'm not aware of any current, modern release of American train that's been known for that issue.
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Post by edwardsutorik on Sept 2, 2016 7:54:43 GMT -8
...I'm not aware of any current, modern release of American train that's been known for that issue. Here's hoping! But keep in mind that my Rivarossi Duckside didn't get its rot until it was about 30 years old. There was also quite a delay in it showing up in my pile of old Ulrich kits. So its not showing up in "current, modern" is not as reassuring as you might think. These days, zinc pest is most likely going to be caused by a morally challenged person in the zinc alloy supply chain, rather than sheer ignorance. Ed |
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Post by Donnell Wells on Sept 2, 2016 8:12:07 GMT -8
I have about four or five Walthers Trainline Amtrak Dash 8s, and one of them, AMTK #506, the frame broke apart in several places when I tried to straighten. The metal seemed brittle, which I can only assume that it suffered from this "Zinc pest" that some of you have mentioned. I like the engine, and will be transferring the shell, trucks, and motor to a new frame scratchbuilt from brass stock. It kind of sucks that this happened, but at least I get to develop a new skill from the experience!
Donnell
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Post by edwardsutorik on Sept 2, 2016 9:09:41 GMT -8
Donnell,
Zinc alloys don't seem to be interested in bending. As opposed to things like brass, steel, and most aluminum. Yes, it's happened to me.
So, to me, your description doesn't sound like zinc pest.
Zinc pest will usually show itself be self-generated dimensional distortions. Usually an increase.
It also goes from pretty smooth pretty shiny metal to crumbly moon dust. That's what greeted me when I last saw my Duckside--the cylinders looked just awful.
Ed
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Post by craigz on Sept 2, 2016 11:32:58 GMT -8
Back in my college days when I was studying metallurgy, one of my professors who happened to be a tinplate train collector and restorer told me his theory was that poison Zamac aka zinc pest isn't an electrolytic problem or a temperature problem. It is, as others have said, an atomic problem, a metallurgical problem with impurities as others note - typically lead, antimony and bismuth. Zamac/zinc alloy, like almost all metal, has a 'grain' structure. When liquid metal solidifies, the metal doesn't start freezing uniformly - it begins at nucleation points in many places more or less at the same time. A cubic atomic structure of atoms grows out of each of those nucleation points forming a grain. As the grains continue to grow they bump into each other, forming grain boundaries. When the contaminated Zamac alloy is poured and solidifies, the contaminant atoms are trapped inside the grains...but the contaminants don't like being inside the grains. Through a process known as diffusion the impurity atoms move thru the grain structure heading for the boundaries. As the impurities gather at the boundaries they push the grains apart...which is what you see with the 'poisoned Zamac' that we see in old models that are swelling and crumbling. The time it takes for the failure to appear is consistent with diffusion theory as well; what's pretty scary is that these failures are happening in a matter of 3-5 years; the old Lionel era stuff took decades to appear. I've seen it very recently on some 2009 run Atlas RS-3s that had frames that banana'd so badly that the pilots and couplers were up at a 45 degree angle. And they crumbled immediately when any pressure was applied to them. At least it didn't damage the plastic shell.
It's not repairable. It's not preventable once the contaminated metal has been poured. Anything you do to the existing chassis will effectively be rearranging the deck chairs on the Titanic...how long it takes your particular ship to sink is the great unknown but it will eventually sink. Your chassis will disintegrate into chunks and dust or at least deform into uselessness. If you can get a replacement chassis that's the only real long term alternative...and hope it's not contaminated as well.
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Post by steveturner on Sept 2, 2016 17:34:40 GMT -8
This is scary business.I thought it was old stuff but 2009, wow. I am now looking at my display cabinets with locos wondering!!!!!!!!!!!. Units from 1987 a mix of Athearn, Atlas, Bowser, Intermouintain, Rivarossi and a few MDC Shays. I thought the shays might have it but good so far.Keystone metal log cars and MDC metal kits still good.Guess its going tobe a crap shoot down the road. Feel so bad for guys that have had this virus! Sure would be a heart stopper. Steve
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Post by theengineshed on Sept 2, 2016 18:55:39 GMT -8
Tungsten chassis are now being used on some model locomotives in lieu of zinc alloys. DJ Models come to mind, tungsten is denser than zinc without the potential pest problems. Quality control being what it is in China, more manufacturers should follow suit...
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Post by edwardsutorik on Sept 2, 2016 20:21:51 GMT -8
Tungsten chassis? Wow, so neat. And SO heavy!
Ed
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Post by craigz on Sept 3, 2016 4:59:20 GMT -8
Tungsten chassis? Wow, so neat. And SO heavy! Ed Just don't decide you want to drill into it... |
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routerock
Junior Member
Rock Island in 1977
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Post by routerock on Sept 3, 2016 8:03:49 GMT -8
I had two Proto Rock Island GP38-2 that had that happen to them. It sucks.
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Post by neilcaldwellrr on Jun 10, 2022 10:14:29 GMT -8
On the subject of metal fatigue developing in die-cast zinc or Zamac components. e.g loco frames, etc.
This phenomena is not due, as commonly stated, to a bad mix of the metals used in the alloy. Contamination in the mix might cause a bad casting, but not fatigue.
The cause of the fatigue which sometimes develops in die-castings is due to incorrect settings or parameters during the molding process. i.e. the temperature of the melt, the mold temperature and the injection pressure. When the mold/melt temperatures are correct the melt will flow easily into the mold at a relatively low pressure, and a stable casting will result. When the temperatures are too low the melt flows badly and a much higher injection pressure has to be used to force the sluggish melt into the mold. This causes stresses in the casting and these stresses will eventually work their way to release and thereby to deform or destroy the casting.
The same can be true of injection molded thermoplastic parts. But since thermoplastic is a more malleable material, the finished part will warp and maybe develop cracks, but only very seldom will a thermoplastic item disintegrate or crumble.
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Post by Baikal on Jun 10, 2022 10:32:06 GMT -8
On the subject of metal fatigue developing in die-cast zinc or Zamac components. e.g loco frames, etc. This phenomena is not due, as commonly stated, to a bad mix of the metals used in the alloy. Contamination in the mix might cause a bad casting, but not fatigue. The cause of the fatigue which sometimes develops in die-castings is due to incorrect settings or parameters during the molding process. i.e. the temperature of the melt, the mold temperature and the injection pressure. When the mold/melt temperatures are correct the melt will flow easily into the mold at a relatively low pressure, and a stable casting will result. When the temperatures are too low the melt flows badly and a much higher injection pressure has to be used to force the sluggish melt into the mold. This causes stresses in the casting and these stresses will eventually work their way to release and thereby to deform or destroy the casting. The same can be true of injection molded thermoplastic parts. But since thermoplastic is a more malleable material, the finished part will warp and maybe develop cracks, but only very seldom will a thermoplastic item disintegrate or crumble.
Where's more info on this theory of zinc pest? Interesting.
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