Casting pullies - what metal - aluminum or ZA27 (zinc/Aluminum alloy)

I need to make a number of pulleys of specific sizes that I can't easily find for reasonable prices but I have a forge and materials to cast them then turn the on a lathe. I'm looking at using a 2-5HP motor for various applications.

ZA27 is something like 72.5% zinc, 27% Al and .5% copper and it is very close in properties as cast iron. It's very hard and seems fairly resistant to surface corrosion. I don't have a ton of zinc, but I can probably find a source for it.

On the other hand I have access to 100-1000's of lbs of extruded aluminum (high quality heat sinks) and maybe some very heavy duty window frames & possible some pistons, cylinder heads and other automotive parts. I can keep all these types seperated so the alloys don't get mixed. I also have lots of access to 6061 T6 and some 7075 T6 though that is more stock but there is lots of scrap and lots of shavings (CNC) & cuttings of these - buckets, which I can melt down.

Now the ZA27 is almost 3x as dense so if I'm working with 12" diameter pulley's I woudl think that might help add inirtia to the equation for making a multi speed band saw & table saw & router (edger).

I'd cast the rough shape with the metal of choice and finish with it on the lathe and balance it using a balanced shaft and magnetic points to suspend/levitate the pulley to completely balance it - IDK if this is necessry or too much, but I'd like to get the experience and this seems a good project to learn on where I can't screw up too bad.

So can someone suggest a good metal? I guess I could also go to copper/Aluminum or some other as I have 100's of lbs of 99+% copper.

Zinc is a poor choice and unless you wanted as cheap product as possible and had a die casting machine. It suffers from zinc disease where it turns to powder over time, it creeps under load among its other properties.

For your purposes I would use aluminum. Specific alloy here is unimportant. Pure copper is generally a machinist's nightmare because it is soft and gummy. Sell that for scrap.

Tom

Have you considered how you will heat treat your castings? Machining as cast aluminum can be a nightmare depending on the alloy. 6061 or 6063 (extrusions) are not generally used for sand casting. Forget using aluminum chips unless you have a way to compress them into briquets as the loss from oxidation will be huge. Just some food for thought.

Sounds very "Gingery like"....suggest you try one of the Homeshop foundry forums.

its been my experience making castings and machining them the total cost of money and labor is extremely high.
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like a bought pulley if $20. to $50. or spending over 10 hours and over $20. in fuel, and good quality metal cost money to make a pulley the pulley you make even if you pay yourself minimum wage is going to easily be over $200. plus it might be many days or even weeks to til you are finally done.
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its like making nuts and bolts. 99.999% of times it cheaper and easier to buy them than to make them.

I agree with the home shop forums.

I was going to discourse on the differences between casting and extrusion aluminums which would appropriate for production but I recalled my days in the school foundry where if it was aluminum it went into the pot. I also thought that if the alloys are segregated they could be sold for scrap and buy the correct materials. The quality alloy for cast parts was Tenzaloy alloy 713.

Sounds like this is an educational trip in which case have at it.

Tom

If you do want use chips or other small scrap (cans) it will melt better/easier if you already have a liquid pool of metal to drop them into. Melt a big chunk first then add the smalls.

Use the pistons and heads and other castings, it may be a little more stable since it is/was made for casting.

The zinc alloy issue is very interesting. The common early alloys were known as Zamak, and there were a number of formulations.

Zamak - Wikipedia

They were much lower in aluminum than the ZA27.

The failure of the Zamak alloys with time and moisture are related to trace lead contamination. Current specifications for Zamak show maximum lead levels of 0.002% to 0.005%. ZA27 allows a maximum of 0.006%. One name for the problem is "Zinc Pest".

Zinc pest - Wikipedia

I have a machine with a number of Zamak parts. A couple of bevel gears and a pulley could be crushed with your fingers, while others are perfectly solid. It was very material batch dependent, as the manufacturers were unaware of the problem early on.

Well I have some ZA27 I made and it is a truly amazing alloy which is about 65% the weight of Cast Iron and has very similar properties (but no where near as brittle) and after 5+ years exposed to harsh conditions, it still looks like when it was poured - a nice shiny silver finish - maybe a SLIGHT oxide dulling. It is a little difficult to drill (with a hand drill) but a drill press does a great job. I've cast a lot of things with it and it does a very nice job, especially if it is going to be machined later.

As far as aluminum, I have access to extruded heat sinks which are a very high % of Al and it makes some of the best castings I've done.

All my zinc is above 99.9% pure (electro refined over a long time) so all my materials are very pure.

I was wrong about the content of ZA27 - it is:
70.45& Zn
27% Al
2-2.5% Cu
.075% Fe
.02% Mn

I've made it with only Zn, Al and Cu. It can be made by heating Zinc to melting then slowly adding Al and Cu and it will dissolve all of it at 800-1000F, well below all the other melting points. Once formed the MP of ZA27 is 710-900F and handled higher temps up to 1500 easily if you want to cast with a very hot metal.

Here are some good links describing the properties of ZA27 - many compare it to cast iron.


ZA-27 Alloy Properties | Zinc Aluminum Die Casting | Dynacast

Zinc aluminium - Wikipedia

Zinc-Aluminum Alloys – ZA27

and NO, this isn't a "gingerly" project. Some people have a reason of needing to do various things. I thought some woudl have experience with the alloy and I'm not sure if a heavier pulley is better or if it doesn't matter.

As for pricing, I can make these for free (minus time) but I have a feeling I'll have a few others who will be making the same ones I do, so instead of 10 people buying 4-8 pulley's, some very large, we can make them with the free material we already have.

Rob F. said:

If you do want use chips or other small scrap (cans) it will melt better/easier if you already have a liquid pool of metal to drop them into. Melt a big chunk first then add the smalls.

Use the pistons and heads and other castings, it may be a little more stable since it is/was made for casting.

Click to expand...

Yes, always start out with a good amount of melted metal when melting chips or things like cans - for those who do it.

There's a few tricks to keep oxidation to almost zero, adding charcoal on the top layer, or sawdust, it brns slowly and the carbon doesn't sem to absorb into the Al and it keeps any air from oxidizing the top surface and creating dross. This worksfor lots of metals, reducing them from the oxide to the base metal!

Hi Tuprox can you tell us the application? You have tantalized us with this project of needing non-standard pulleys for some serious application but not so serious that the time/cost calculation says buy them, which would be the case for 99% of normal paying jobs. I'm sure I'm not the only one who is fascinated.

ps. As a public service I should relate the following engineering story involving pulleys: I once had to help complete a skid with gas motor, transmission and bull wheel for a rope tow for a mountain bike dual slalom course. This was in a rural setting where being in an engineering mindset was not necessarily a natural state of thought. A second round of pulleys and belts had to be ordered, which I installed, as the first configuration ran approximately 6.282 times too fast. An error had been made in the calculation(not by me) which led to the memorable engineering observation, "Don't get high, you might forget to divide by pi".

tuprox said:

Yes, always start out with a good amount of melted metal when melting chips or things like cans - for those who do it.

There's a few tricks to keep oxidation to almost zero, adding charcoal on the top layer, or sawdust, it brns slowly and the carbon doesn't sem to absorb into the Al and it keeps any air from oxidizing the top surface and creating dross. This worksfor lots of metals, reducing them from the oxide to the base metal!

Click to expand...

Years ago, and perhaps they still do, foundries melting and casting magnesium and mag alloys would throw sulfur in the crucible. The sulfur would burn to create sulfur dioxide that is heavier than air. Time to pour, the heavy blanket of SO2 would follow the stream to mold protecting it.

Tom

As a kid,I knew a guy made alloy step pulleys for a small drill press he made .....the alloy he used came for Harley and Indian motorbikes........he preferred the alloy head bikes,british bikes had a lot less alloy in them.

well don't use that extrusion aluminum has the consistency of bubble gum
when machining, old transmission cases cast wheels or old heads, old pistons
ect, you want a casting alloy.

cast iron isn't bad either if weight isn't a issue and if you can melt it in your furnace
casts great though.

This is definitely the wrong forum to be asking the OP's question. Very few people here cast metal of any kind on a regular basis if ever. If you go to AlloyAvenue or Thehomefoundry.org you can pose your questions to a lot people actively involved in casting aluminum alloys and nearly any other alloy you can think of. So, if you want useful information.... Some of those folks are quite knowledgeable and have years of experience. Their knowledge might save you a whole lot of time and frustration. Or you can have ?fun? reinventing the pulley.

Denis

I'm writing quickly b/c I have to go. This isn't an exactly new design, it's somewhat like a CVT transmission but not nealy infinate now I'm looking at making something wit 4-5 sullies on each side and they are going to be either keyed or some other method of keeping them aligned.There will be something that will allow the user to change on which pulley the chain is on. My

So each spindles will have 4-5 pulleys on it and then a mechanism to make these easily electable.

You are talking simple step pullies?.............you can easily cast ally if you get the right scrap......you must find some sandcast scrap......extrusion is useless,as is cans,gravity die cast ally may be ok.........but basically ,you need sandcast scrap......and it needs to be clean too,or your metal will be full of dross..........note that oxide doesnt float on the melt,so some other method must be used to clean the melt......its easiest to use clean scrap.

Do not use a steel crucible
Molten aluminium dissolves steel like mercury does to gold
Buy a original one

Peter

Stainless crucibles for Al are currently under discussion at Thehomefoundry. One of the members today reported retiring a shop-made stainless crucible after 260 melts. Others are reporting good results using schedule 40 pipe. Most active melters there are using stainless or carbon steel crucibles. See my post above in this thread.

Denis

till you overheat it a bit and the bottem drops out
Also some of the iron from the crusible goes into the aluminium
Peter