Zinc casting

[kadora]

Hello all
I have found on internet this

Compared to aluminum, zinc can be cast to precision tolerances, thinner wall sections, net shapes and much longer tool life.

Guys why do not you use the zinc for casting -say- a crankcase instead of aluminium.
Casting information collector
Thank you
Kadora

 

[enfieldbullet]

has been used on COX engines. Zamak will be superior for casting and is easily sourced from scrapyards.

lower casting temperatures IIRC too.

some people will worry about the zinc fumes but doing it in a ventilated area should make it ok.

 

[stevehuckss396]

All of the aluminum i cast is scrap that cost me nothing. Also aluminum is much lighter. If casting a engine block for an RC plane that could be a huge factor.

 

[Tin Falcon]

Zinc tends to deteriorate over time. You can experiment with it but IMHO aluminum is better for Model engines.
Tin

 

[cfellows]

I've done some Zinc/Aluminum alloy (ZAMAC) casting. I use about 10% aluminum to zinc ratio, making my own alloy from materials on hand. Zinc is harder to find than aluminum, but I stumbled across some ingots on Ebay a number of years ago. I haven't really tried to find any since then. I like working with ZAMAC. It melts at about 900 degrees F and is easy to machine. It's almost as heavy as cast iron, so it makes good flywheels. However, it's not as strong as cast iron so you wouldn't want to spin it at real high RPM's.

ZAMAC ingots are available commercially, but not particularly cheap, certainly not as cheap as scrap aluminum.

http://www.budgetcastingsupply.com/Metals.php

Not sure of Tin's experience, but I've not seen any deterioration of the ZAMAC castings I've done.

Chuck

 

[Tin Falcon]

MY "experience" is based on the deterioration of older products such as parts of toy engines . and the auto advance box on the atlas Shapers.

I have a post war Doll engine the fly wheels were zinc and the fly wheel is gone. replaced by a gyroscope fw not the best fix . And the auto feed box on my atlas was replaced by a shop made one.Made from aluminum. so my experience is based on stuff cast 60 to 70 years ago. It is my understanding this happens over time. the modern alloys probably will hold up better.

Tin

 

[enfieldbullet]

yes, modern alloys aren't susceptible to this.

it is known as 'zinc pest', and happens due to impurities in the alloy.

i would also like to point out that zinc is easily found in batteries common AA or AAA kind. new batteries don't have mercury in them so they're safe to open. the zinc is the casing around the black powder (which is manganese trioxide or dioxide depending on how spent the battery is)

chinese batteries might have mercury. and also manganese oxides are a pain to get rid off, they'll stain everything, but aren't particularly dangerous.

just a thought if you need a small ammount.


commercially available zamak has only 3% aluminum. it can be found in zippers, carburators, butterfly valves, etc in the local scrapyard and shouldn't cost much like this.

 

[kadora]

Thank you guys
Thanks Chuck for link to the budget casting.
Probably i will start my first casting "hokus pokus"
with zinc because of this:
Zinc Alloy ZA-27 is an under appreciated metal for foundry use. This metal is 1.5 to 3 times stronger than cast aluminum, and can have the tensile strength of grey or malleable cast iron! It's casting temperature is in the range of 950-1,100 Deg F as compared to aluminum at 1,450 Deg F.

regards Kadora

 

[Gedeon Spilett]

many years back, for a a small steam tractor I was doing, I did the castings by myself for the wheels, with recycled zamac or the like, very easy to do I thought, I was very proud of my first own castings !
This is the point, now, some 15 years later, the cast parts are completely disintegrated, excess of Zn probably, I was told by an expert, never use and/or mixe unidentified scrap metal he added.
I add pictures to convince you to use the right stuff for your pet castings !
Cheers

 

[metalmad]

Gedeon
That is Heart breaking to see such a lovely model disintergrating like that.
I had thought about zinc, but after seeing that would not consider it at all
Pete

 

[Tin Falcon]

The problem with the the post war doll fly wheels is they were made made in Germany from scrap recovered after the war. Made from stuff the Americans and Brits blew up. lot of impurities apparently mixed in as well .
Tin

 

[Lakc]

From the BCS site:

It is important to keep the material from being overheated when melting.

This is not something I think most homemade foundries are very good at.
Along with precise temperature control, we have had a few stories about impurities, which means no homemade metal crucibles.
I have no idea what kind of impurities might get introduced from the atmosphere in the backyard standard propane/charcoal/waste oil furnace either.
Zamack is a wonderful alloy that I have been meaning to try for a long time, but it seems it has a few extra boxes on the checklist of things to get right.

 

[albertorc19]

Zamak is zinc an alloy commonly used in the automotive industry, it's mostly zinc with Al and Cu as secondary components. The material has good mechanical characteristics but small variations in the casting process can produce a brittle material. Last year I had to make laboratory tests on automotive parts made of Zamak that didn't pass the quality control. The difference of chemical composition between production batches was minimal but enough to cause a lot of trouble. It is true that Zamak can be casted at low temperatures and can have complex forms but the durability of the material can not be compared with cast Aluminum. I think that the best material for cast parts is Silicon Aluminum which is an alloy that can have as much as 30% Si, this alloy is widely used for cast parts in the automotive industry.

 

[n4zou]

99.8% zinc ingots are available from Rotometals. They have babbitt, bismuth, and other alloys too.
http://www.rotometals.com/product-p/zincingots.htm

 

[Wizard69]

I've done some Zinc/Aluminum alloy (ZAMAC) casting. I use about 10% aluminum to zinc ratio, making my own alloy from materials on hand. Zinc is harder to find than aluminum, but I stumbled across some ingots on Ebay a number of years ago. I haven't really tried to find any since then. I like working with ZAMAC. It melts at about 900 degrees F and is easy to machine. It's almost as heavy as cast iron, so it makes good flywheels. However, it's not as strong as cast iron so you wouldn't want to spin it at real high RPM's.

ZAMAC ingots are available commercially, but not particularly cheap, certainly not as cheap as scrap aluminum.

http://www.budgetcastingsupply.com/Metals.php

Not sure of Tin's experience, but I've not seen any deterioration of the ZAMAC castings I've done.

Chuck

I actually have some experience working in the Zinc diecasting industry about 30 years ago. Zinc diecastings are what carburetors where made of all those years ago, also things like valve handles, curtain rod components and a host of other easily fasted items. Zinc is seldom used in demanding structural designs and while I never got into the reasons why ( I worked machinery maintenance) personally I wouldn't trust zinc all that much. For what it is worth zinc discastings are often derisively called "pot metal" due to the big cast iron pots used to melt the metal. Pot metal was often used interchangeably with the word crap and other things not worth printing here.

Is the bad reputation that zinc diecastings have deserved? I really can't say for sure. Often diecastings are designed to be as cheap as possible and since the weight of the parties a factor in pricing, designs are often thin on metal. Thin also means fast cycle times, we had machines that ran 6 second cycle times from mold close to mold close. Memory on the cycle times may be getting old but some dies where runnable at very high speeds.

Beyond that diecast parts maintain most of their strength in the walls of the parts. Back then at least the die designers tried to obtain what is called atomized flow of the zinc in the die. This could lead to porosity in the parts if the machine was not set up right. Interestingly right out of the machine some castings would have the strength of equivalent mailable iron parts. Diecastings at least do age, frankly all castings do be they zinc, aluminum, or iron. Realize too that (well back then) there where three common Zinc diecasting alloys with differing strength and longevity characteristics. These alloys are not the ZA series, ZAMAC allows are for die casting. ZA alloys in some variant can be die cast but that isn't the general usage. These guys have some good info: http://www.eazall.com/.

Now it is 30 some years since I left the industry but that alloys have changed at all. I may be biased but if I was to build something I expected to last I'd avoid the diecast alloys. Honestly Aluminum doesn't require that much more effort to handle and melt, as such I think it is well worth the effort to use aluminum where it works well.

 

[Rex]

So, if you recycle existing ZAMAC casting scrap it should be in the correct alloy and not subject to disintegration?

 

[Lakc]

So, if you recycle existing ZAMAC casting scrap it should be in the correct alloy and not subject to disintegration?

Yes, but at $2 a pound, if your casting something really that important, you should probably not want to recycle. And that would require commercial crucible's, stirrers, etc to ensure you dont contaminate the melt to begin with.

 

[Wizard69]

So, if you recycle existing ZAMAC casting scrap it should be in the correct alloy and not subject to disintegration?

Possibly but back in the day there where 3 common alloys used for Zinc die casting. So how would you know which is which? Today you have even more variety from what I understand.

Then you have the issue of heating the metal up and not changing its alloy mix. In the Zinc diecasting world we controlled temperatures pretty tightly throughout the process to avoid damaging the alloy by over heating. The only way to do this in a home foundry is to monitor melt temperatures closely and cut the heat when you get to set point. Or you could build a more advanced furnace with a temperature controller, pilot and safety mechanisms. Zincs problem is that it is subject to failure if the alloys aren't kept in the right proportions and maybe more importantly the pour has to be free of contamination.

A point of interest: Even 30 years ago the people I worked for where obsessed with the quality of the alloy they used. It went so far as to outlaw all candy bars with foil wrappers in the break room vending machine. They wanted nothing to change or harm the alloy they where using.

By the way I'm not trying to scare people off zinc alloys, I'm just trying to make people aware of the problems. Zinc alloys can be very useful for manufacturing products and die casting can do high quality in high volume. Just think about the old cars with their carburetors that where mass produced from zinc die castings. Many other parts seen around the home are often zinc diecastings such as valve handles and the like. The problem for the home foundry is making sure the alloy is right to begin with and that you can control the melt properly. If you want to use a zinc alloy in your home projects I highly recommend buying ingots from a vendor that certifies the alloy. Further make sure that alloy is one recommended for sand casting. Watch your melt temperatures closely and you should be good. Getting the crucible really hot like some do to melt aluminum isn't really a good idea.

A few more things:

Zinc alloys are never used for things associated with swimming pools. I forgot what the alloys react to in the water, probably the chlorine, but Zinc alloys break down fast in that environment. In fact you wouldn't even want to have a zinc alloy parts stored near a storage area for swimming pool chemicals.

Diecast zinc alloys can have porosity and inclusion issues. This can lead to broken taps and other machining problems. I have no experience with the gravity casting alloys but it pays to be clever with your design to avoid as many drilled and tapped holes as possible.

It is interesting that zinc die castings and the zinc they are made form have been called "pot metal" for years. That comes from the large cast iron pots the metal is melted in to feed the casting machine. The interesting thing here is that those castiron pots last for a very long time in industry. However if you drop a steel bolt into the pot you best fish it out right away. The steel reacts with the zinc to create an effect that eats through the cast iron rather quickly. I'm not sure of the chemistry here and I never got a chance to actually ask somebody that knew, but always found it fascinating that a bolt that is largely iron could have such an effect. In one case, a pot I looked at after being drained had castiron eroded away precisely matching the threads of a bolt.

 

[Cogsy]

The interesting thing here is that those castiron pots last for a very long time in industry. However if you drop a steel bolt into the pot you best fish it out right away. The steel reacts with the zinc to create an effect that eats through the cast iron rather quickly.

Funnily enough, when I was involved in hot dip galvanising, we were told exactly the same thing, but told not to put copper into the pot/bath. Supposedly a 2 cent coin would erode right through the bottom. We had lots of steel and iron end up at the bottom of the bath, and would only be scooped out about once every 6-8 weeks when a whole shift would be devoted to removing the dross from the bottom of the bath, and all the loose bits of steel and iron would be recovered. I never saw the bath empty as it was 2.5 metres (8ft) deep, 2 metres (6ft) wide and over 13 metres (42ft) long, so I don't know what, if any, erosion occurred.

 

[Wizard69]

Funnily enough, when I was involved in hot dip galvanising, we were told exactly the same thing, but told not to put copper into the pot/bath. Supposedly a 2 cent coin would erode right through the bottom. We had lots of steel and iron end up at the bottom of the bath, and would only be scooped out about once every 6-8 weeks when a whole shift would be devoted to removing the dross from the bottom of the bath, and all the loose bits of steel and iron would be recovered. I never saw the bath empty as it was 2.5 metres (8ft) deep, 2 metres (6ft) wide and over 13 metres (42ft) long, so I don't know what, if any, erosion occurred.

That is one big bath of molten metal! Back then we had a large central furnace to pre melt zinc to distribute to the machine pots. That wasn't even close to the size described above but it was of steel construction and lined with refractory. No bare cast iron anywhere.

Working in that foundry I was very young and hadn't seen much manufacturing, what impressed me was the use of a pump to transfer the molten zinc to the transfer ladle. Pumping anything that is 800 some odd degrees hot just amazed me.