Re: [Phono-L] Pot metal swelling geographically speaking (new topic)
While the term 'potmetal' was used for many low melting point alloys the modern name for the potmetal we are familiar with is 'die cast zinc.' Zinc is actually a wonderful metal to cast with a melting point of 419.53 °C or 787.15 °F. This is low enough so that a mold can easily be made of many materials. Today the purity of zinc is very high, around 99.999% before it is mixed with other metals to make alloys. Aluminum is common but any alloy commonly raises the melting point so pure zinc is preferred for most applications. Some metals cannot be added to the zinc in even tiny amounts without creating a dimensionally unstable alloy. The potmetal problems we see on phonographs is mostly due to 'inter granular crystal growth' and is not temperature related. The old timers called this 'dezincification' which is a misnomer since the zinc really does not go anywhere unless a piece falls off. If even a tiny amount of certain elements like tin, lead, cadmium, sulfur, or other contaminate is introduced into the liquid casting metal the result with time will be slow deformation of the casting as atomic bonds dissociate along crystal lines while other crystals actually grow. Thus, some portions of the solid casting may contract while others expand. A very pure potmetal will be dimensionally stable for very long periods of time. The contaminated batches may have been inadvertent. Old pipe organ pipes made of zinc could have been used for scrap in the melting pot without the people thinking about the lead/tin solder seams. Just that small amount of contamination is enough to ruin a full batch of zinc. Some batches were very pure and that is why you can find a perfect potmetal reproducer body with some regularity. Another problem is the cooling rate when the casting was removed. A rapid cooling of a die cast zinc will leave stress in the metal. A slow cooling allows for the metal to naturally anneal at lower stress. Die cast zinc today that needs to be accurate to a high degree is removed from the mold and allowed to go through a series of cooler furnaces before reaching room temperature. There are environmental elements that can add to a bad batch of zinc. If the casting was exposed to salt air (a.k.a. sodium chloride) or acidic air such as the sulfur dioxide coal plants produce, then any porosity may become a source of oxidation and the casting will suffer. Zinc oxide will form along the microscopic lines between zinc crystals and they too will cause expansion but much less than a bad batch would cause. But HEY, these things were not supposed to last more than a couple of centuries anyway! ! ! May all your finds be rare ones, Al ___ Phono-L mailing list http://phono-l.org
Re: [Phono-L] Pot metal swelling geographically speaking (new topic)
you are so right al what we collect today were consumable goods and not supposed to last forever zono In a message dated 8/20/2013 2:13:12 A.M. Eastern Daylight Time, clockworkh...@aol.com writes: While the term 'potmetal' was used for many low melting point alloys the modern name for the potmetal we are familiar with is 'die cast zinc.' Zinc is actually a wonderful metal to cast with a melting point of 419.53 °C or 787.15 °F. This is low enough so that a mold can easily be made of many materials. Today the purity of zinc is very high, around 99.999% before it is mixed with other metals to make alloys. Aluminum is common but any alloy commonly raises the melting point so pure zinc is preferred for most applications. Some metals cannot be added to the zinc in even tiny amounts without creating a dimensionally unstable alloy. The potmetal problems we see on phonographs is mostly due to 'inter granular crystal growth' and is not temperature related. The old timers called this 'dezincification' which is a misnomer since the zinc really does not go anywhere unless a piece falls off. If even a tiny amount of certain elements like tin, lead, cadmium, sulfur, or other contaminate is introduced into the liquid casting metal the result with time will be slow deformation of the casting as atomic bonds dissociate along crystal lines while other crystals actually grow. Thus, some portions of the solid casting may contract while others expand. A very pure potmetal will be dimensionally stable for very long periods of time. The contaminated batches may have been inadvertent. Old pipe organ pipes made of zinc could have been used for scrap in the melting pot without the people thinking about the lead/tin solder seams. Just that small amount of contamination is enough to ruin a full batch of zinc. Some batches were very pure and that is why you can find a perfect potmetal reproducer body with some regularity. Another problem is the cooling rate when the casting was removed. A rapid cooling of a die cast zinc will leave stress in the metal. A slow cooling allows for the metal to naturally anneal at lower stress. Die cast zinc today that needs to be accurate to a high degree is removed from the mold and allowed to go through a series of cooler furnaces before reaching room temperature. There are environmental elements that can add to a bad batch of zinc. If the casting was exposed to salt air (a.k.a. sodium chloride) or acidic air such as the sulfur dioxide coal plants produce, then any porosity may become a source of oxidation and the casting will suffer. Zinc oxide will form along the microscopic lines between zinc crystals and they too will cause expansion but much less than a bad batch would cause. But HEY, these things were not supposed to last more than a couple of centuries anyway! ! ! May all your finds be rare ones, Al ___ Phono-L mailing list http://phono-l.org ___ Phono-L mailing list http://phono-l.org
[Phono-L] Pot metal swelling geographically speaking (new topic)
From: Steven Medved Normally the Diamond B does not expand that much unless it was stored where temperatures varied over the years like an unheated attic where it got very cold in the winter and very hot in the summer. Pot metal reproducer on Vancouver Island in the Victoria area remain pristine due to the relative small variance in temperature. Hi Steven, I thought I should delicately chime in here on the issue of pot metal swelling. I live in Victoria, have collected phonographs for 40 years and have seen many examples of reproducers and parts which have swollen due to dezincification or inter granular crystal growth (thanks to Al Sefl for that phrase). In fact, one of my first projects in the 70's was to machine a new lower mounting plate for an S reproducer which had suffered breakage due to swelling. While I can't speak to how local pot metal deterioration may compare to other areas, I can say that the effect is not uncommon here. I don't think that pristine would be an accurate description of how a lot of pot metal ages on Vancouver Island. Interestingly, though, it would be fun to put a Vancouver Island pot metal reproducer or some other object on eBay to see if there might be a halo effect that would apply to pot metal objects which have spent their lives here : ) Thanks very much for your informative posts, Steven. I always enjoy your illuminating comments, particularly on serial numbers as they relate to design changes. All the best, Don Mayer ___ Phono-L mailing list http://phono-l.org
Re: [Phono-L] Pot metal swelling geographically speaking (new topic)
I am thinking this oak Amberola 75 was not kept in a great place. The finish is pretty nice actually, but the reproducer is spotty and the limit loop and pin are rusted. It needs the motor gone over, and the springs need regreasing if not outright replacement. I bought this for eventual resale so I hope I don't have to put TOO much into it, but it has the potential to be a nice machine. I am thinking it may have been kept in an attic or basement. I don't know where it came from, I'll have to ask the seller. John Robles From: Don Mayer donma...@shaw.ca To: phono-l@oldcrank.org Sent: Monday, August 19, 2013 1:00 PM Subject: [Phono-L] Pot metal swelling geographically speaking (new topic) From: Steven Medved Normally the Diamond B does not expand that much unless it was stored where temperatures varied over the years like an unheated attic where it got very cold in the winter and very hot in the summer. Pot metal reproducer on Vancouver Island in the Victoria area remain pristine due to the relative small variance in temperature. Hi Steven, I thought I should delicately chime in here on the issue of pot metal swelling. I live in Victoria, have collected phonographs for 40 years and have seen many examples of reproducers and parts which have swollen due to dezincification or inter granular crystal growth (thanks to Al Sefl for that phrase). In fact, one of my first projects in the 70's was to machine a new lower mounting plate for an S reproducer which had suffered breakage due to swelling. While I can't speak to how local pot metal deterioration may compare to other areas, I can say that the effect is not uncommon here. I don't think that pristine would be an accurate description of how a lot of pot metal ages on Vancouver Island. Interestingly, though, it would be fun to put a Vancouver Island pot metal reproducer or some other object on eBay to see if there might be a halo effect that would apply to pot metal objects which have spent their lives here : ) Thanks very much for your informative posts, Steven. I always enjoy your illuminating comments, particularly on serial numbers as they relate to design changes. All the best, Don Mayer ___ Phono-L mailing list http://phono-l.org ___ Phono-L mailing list http://phono-l.org
