Author Topic: Casting a flywheel in ZL12 alloy.  (Read 3486 times)

Online A7er

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Casting a flywheel in ZL12 alloy.
« on: September 09, 2022, 09:14:31 PM »
I have been using aluminium from a Renault car wheel for my recent casting attempts. Today I used an aluminium/zinc alloy called ZL12, which is 88% zinc and 12% aluminium. The flywheel cast from the car wheel weighs 169g, from ZL12 it weighs 385g. The first picture shows a slight depression in the rim of the flywheel. The shrinkage is right above the ingate. I am assuming that the metal wasn't hot enough and it "froze". The dip is less than 1mm (it looks deeper because of the rim sticking out), so it would machine out. I had allowed for the removal of 2mm from the outer faces. The second picture shows the small amount of flashing on the casting. It seems I can either get a casting with virtually no flashing, or with a good surface finish, but not both! The flywheel is approx 90mm in dia by 18mm wide.


Offline Jasonb

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Re: Casting a flywheel in ZL12 alloy.
« Reply #1 on: September 10, 2022, 07:05:32 AM »
Certainly a nice surface finish.

The small amount of flash looks to be where sand has come away when removing the pattern rather than poor contact between the two halves

That's a good weight increase using the heavier alloy and only about 50g less than if it were iron

Online A7er

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Re: Casting a flywheel in ZL12 alloy.
« Reply #2 on: September 10, 2022, 08:03:46 AM »
I think you are right Jason. I am still removing my patterns by inverting the flask and tapping it until the pattern falls out. I need to find a better way of extracting the pattern.
Lee

Edit. I am 100% convinced that the flashing is down to the way I have been removing the pattern. I now have something positive to work on!
« Last Edit: September 10, 2022, 08:35:41 AM by A7er »

Offline Jasonb

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Re: Casting a flywheel in ZL12 alloy.
« Reply #3 on: September 10, 2022, 10:15:39 AM »
A common way to do it is to lightly tap the alignment studs which just loosen the pattern  and for the other half that has the mating holes use a couple of tapped ones so you can put a screw in and give then a gentle sideways tap just to loosen the pattern and then lift out by the same screws.  You might just be able to leave small holes in the prints and use self tapping screws

Online A7er

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Re: Casting a flywheel in ZL12 alloy.
« Reply #4 on: September 10, 2022, 01:10:04 PM »
Hi Jason,
I drilled two 6mm holes in the back of the hub of the pattern that has the locating stud holes, the other pattern has the locating pins. I filled the holes with car body filler and will drill two holes for small screws. I can then attach a small buldog clip to the screws, and then with the aid of a vertical puller, which I have yet to make a-la Olfoundryman, extract the pattern. I will use the same procedure on the pattern with a central locating pin. The bulldog clip is 20mm wide and will sit on the pattern without rocking. Well that's the plan anyway!
Lee

Edit. The other alternative is a match plate. I am watching videos to get some ideas.

Online Alyn Foundry

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Re: Casting a flywheel in ZL12 alloy.
« Reply #5 on: September 10, 2022, 03:16:58 PM »
You will definitely get better results from any pattern if they are accurately secured to a plate. My masters were done using 10 mm thickness Aluminium plates with all the runners and feeders built in. They also had “ slip blanks “ the term used for a cone and cup system that ensured mould halves were accurately aligned once the plate was removed.

The shrinkage probably occurred due to insufficient “ head “ of metal. Try increasing the height of the sprue. The sprue will always have the hottest metal after the pour so the casting will try to feed the cooling sprue.

Picture of my Hornsby Akryod flywheel pattern.

 :cheers:  Graham.

Online A7er

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Re: Casting a flywheel in ZL12 alloy.
« Reply #6 on: September 10, 2022, 04:08:05 PM »
Graham.
Did you forget to post the picture or can I find it elsewhere?
Lee

Online Alyn Foundry

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Re: Casting a flywheel in ZL12 alloy.
« Reply #7 on: September 11, 2022, 02:06:24 PM »
Graham.
Did you forget to post the picture or can I find it elsewhere?
Lee

Hi Lee.
My apologies, the photo was stored upon another device.

 :cheers:  Graham.

Online A7er

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Re: Casting a flywheel in ZL12 alloy.
« Reply #8 on: September 11, 2022, 05:03:49 PM »
Thanks Graham.
I looked up the price of aluminium plate at 8mm to 10mm thick. The price was far too high for me to contemplate, so I made mine out of what I had available, 8mm plywood. The first casting I did would have been a lot better if I had reversed the order of taking the flasks off the matchplate. I took the one off that was uppermost at the time, it was the flask with the locating dowels in. This left the other flask with nothing to guide it as the matchplate was removed. The casting was still good and at least proved that I had the alignment right. The second casting I turned the flasks over and removed the one with the alignment holes in first. This gave me a much better casting. Now I know it works I will seal the ply with a coat of paint. I think the bare plywood might be sapping a bit of moisture out of the sand in contact with it causing a small area of flashing.
I am looking forward to the next few tries.

Offline bent

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Re: Casting a flywheel in ZL12 alloy.
« Reply #9 on: September 12, 2022, 06:34:40 PM »
A7er,

I've looked at zinc alloy casting, but thought it would be too difficult due to the high vapor pressure of the molten metal?  Are you just using green sand molds for the flywheels?

 :popcorn:

Online A7er

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Re: Casting a flywheel in ZL12 alloy.
« Reply #10 on: September 12, 2022, 07:08:32 PM »
Bent.
I am unaware of high vapour pressure with the zl12. I have used it for several different castings in the past, including a small oval nameplate where I wanted good definition of the lettering. I use a home made electric foundry of about 1800 watts on 240-ish volts. I melt the metal at 500c, a bit higher than I would like but if I only use a temp of 450c it takes forever to melt the metal. I use very fine green sand for all my casting, so far. I would like to try fine sand mixed with epoxy resin, I just haven't got round to it yet. The picture is of the nameplate. The lettering is about 6 to 8mm in height (I forget which) and about 1 to 2mm extruded from the surface.


Offline bent

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Re: Casting a flywheel in ZL12 alloy.
« Reply #11 on: September 13, 2022, 05:00:35 PM »
Thanks A7er!  I know nothing about zinc casting other than what I've read, so it's good to hear from somebody doing it in the real world.  Will be paying more attention to these posts now that I'm in the 3d printing business.

Online A7er

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Re: Casting a flywheel in ZL12 alloy.
« Reply #12 on: September 13, 2022, 11:50:57 PM »
Bent.
The youtuber "Myfordboy" casts many parts in zl12, especially flywheels. I can't point you to the relevant vids, sorry.
I think the lower casting temp, 450 to 500c is kinder to my little foundry. My next casting will be a conrod in zl12 using a matchplate mould. I am getting to like matchplates! The conrod patterns have a 5 degree draft whereas the previous patterns only had 3 degrees. I hope this makes it easier to seperate pattern and sand mould.
Lee

Online Alyn Foundry

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Re: Casting a flywheel in ZL12 alloy.
« Reply #13 on: September 14, 2022, 11:59:38 AM »
I have been using Zinc alloy for many years now. Mainly for small parts. It is quite dense and really works well as a substitute for Bronze or Brass bearings. I use Steel dies which are heated up during the melting process. The metal shrinkage aids the removal from the die, once cooled. Here’s a short video of casting a Gardner main bearing.

<a href="https://www.youtube.com/watch?v=tXp8hEamWtY" target="_blank">http://www.youtube.com/watch?v=tXp8hEamWtY</a>

Hopefully the attached pictures are self explanatory?

 :cheers:  Graham.

Online A7er

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Re: Casting a flywheel in ZL12 alloy.
« Reply #14 on: September 14, 2022, 03:15:50 PM »
Nicely done Graham.
I had hoped to be casting today or tomorrow, but other things have got in the way. I am now gaining a bit more experience with casting using a match plate and am slowly working towards casting the cylinder head in zl12. The head is 56mm dia with inlet and exhaust tracts, plus sparkplug and a water jacket. I am now looking forward to it.
Did you have to upload your video to youtube before inserting it here? I had thought about posting a video of the conrod casting as well as a few images.
Lee

 

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