Author Topic: The poor man's sand binder  (Read 4853 times)

Offline ironman

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The poor man's sand binder
« on: July 12, 2013, 02:55:54 AM »
Hi everyone

Here is an alternative to baking, gassing and using two part resins when making sand cores.

I use portland cement 9% and water 4% by weight and leave it to cure for 3 days. There are fast setting cements like Ciment fondu but are more expensive than portland cement.

To gain full strength cement needs 30 days to cure but full strength it not always welcome so the 9% cement and 3 days to cure are optional.

If you use over 4% water drying the core is essential. I would not go over 4% water until you have some experience with this method. Have a look at the video.   

     

« Last Edit: July 12, 2013, 09:27:13 AM by dsquire »

Offline vtsteam

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Re: The poor man's sand binder
« Reply #1 on: July 12, 2013, 10:15:16 AM »
Thank you very much for that, Ironman.  :bow:  Just what I needed. And great results with your casting finish!  :clap:

My earlier mistake was trying to extrude it from the core box before cure.

One nice thing about the cement core I see is that you need no vent through the core.

Baked molasses water and flour core binders produce gasses. The cement core doesn't seem to. It's tough pushing a vent wire through a long small diameter core without hitting the sides of the core box. Eliminating a through-vent will make these cores much easier to make.

I also like your method of springing open a slit core, rather than using clamps to keep a wider slit closed. Simple.

One question -- for your facing sand on the exterior, what mix are you using now.? Wonderful surface finish!
I love it when a Plan B comes together!
Steve
www.sredmond.com

Offline ironman

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Re: The poor man's sand binder
« Reply #2 on: July 12, 2013, 08:21:50 PM »
Nothing has changed, have a look at my video "How to make cast iron molding sand". I use that mix to cover the pattern only. Over the years the sand becomes darker until it is a black colour.

Two weeks ago I threw out all my iron sand (750kg) I went to a quarry and purchased a trailer load of new sand, so that is the reason why my sand looks different. A friend who does casting picked up the old sand from my home and used it to fill the holes in his gravel driveway. He made a comment saying it was a waste using the old sand for that purpose.

Offline vtsteam

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Re: The poor man's sand binder
« Reply #3 on: July 12, 2013, 08:27:56 PM »
So you use the same fineness of sand for the facing sand -- it just has the seacoal in it, while your main sand has none now.

What grade of sand do you use for your regular sand  -- or is it graded at all? I guess coming from a quarry it is natural mixed sand.
I love it when a Plan B comes together!
Steve
www.sredmond.com

Offline ironman

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Re: The poor man's sand binder
« Reply #4 on: July 14, 2013, 10:06:23 PM »
I just ask them for their finest sand and I use that sand for both. There is no point having two sands, one finer than the other when it works for  both. I have priced foundry sand in 50kg bags but why buy it when sand from the quarry is 40 times cheaper.

Offline vtsteam

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Re: The poor man's sand binder
« Reply #5 on: July 14, 2013, 10:43:15 PM »
 :thumbup: Thank you!

Sand pits around here seem to be all mixed sedimentary stuff and coarse grains.

Maybe I'll start looking further afield.
I love it when a Plan B comes together!
Steve
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Offline ironman

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Re: The poor man's sand binder
« Reply #6 on: July 16, 2013, 08:24:32 PM »
vtsteam Here are two photos of sand grains. Quarry sand is the sand I use and the pro sand is a sample of graded sand a friend gave me.  Also have a look at this video it shows portland cement being used the same way I use graphite on my cores.

     


« Last Edit: July 16, 2013, 10:17:12 PM by dsquire »

Offline vtsteam

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Re: The poor man's sand binder
« Reply #7 on: July 16, 2013, 09:23:46 PM »
Great photos, and a really wonderful movie. Thank you Ironman!

I think what you have as quarry sand would be called "sharp sand" here. Both samples look to be nearly entirely quartz (silica) sand.  I'm going to have to hunt for a source for that. I'll post pix of what is commonly found here for sand.

That movie was really fascinating. Tough though. No shoes pouring and on shakeout. But amazing work. With dirt. Pulling those handle patterns, wood fired aluminum melter (I was just mentioning wanting to build such a thing in another thread).

Now that dirt was very fine -- detail was amazing -- the lettering, etc. Nice work with the spoon!

That movie was something....

Thank you again!
I love it when a Plan B comes together!
Steve
www.sredmond.com

Offline vtsteam

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Re: The poor man's sand binder
« Reply #8 on: August 31, 2013, 11:39:00 AM »
Back to original topic I thought I'd try making some cores using a different cement -- Rockite -- readily available in small quantities here at hardware stores. Saves having to buy a 94 lb bag of Portland.

The last time I tried this I used some of a used bag of Portland I had in storage of uncertain date. Probably not fresh enough.

The Rockite is nice because it comes in a small box with a plastic bag sealed with a rubber band inside, and I can keep it indoors, out of the damp barn.

Anyway, used ironman's 9% cement 4% water mix with sand. The first core came out nice and firm and clean -- not sandy/crumbly like my last effort. However it did break into 3 pieces in getting it out of the PVC pipe core box. It Probably weak layers from uneven ramming -- I could see the sand was more open grained at the breaks. This is a pretty long core, so maybe that's also the problem.

It might have held together if I'd embedded a length of wire as reinforcement. I have another one to unmold -- I'll wait another day to see if that helps.




Otherwise I think it's good. Haven't tried to
I love it when a Plan B comes together!
Steve
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Offline ironman

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Re: The poor man's sand binder
« Reply #9 on: September 01, 2013, 06:22:47 AM »
The smallest core I make is 19mm (3/4") dia. The core would always come out in one piece but would have 100% failure rate when poured in iron. I fixed the breakage problem by using a wire to strengthen the core.

That rockite looks like could be very useful because it sets faster than Portland cement. Does it set in one hour like label says?

Offline vtsteam

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Re: The poor man's sand binder
« Reply #10 on: September 01, 2013, 09:58:45 AM »
Ironman, I didn't check for how quickly it cured -- waited two days to check the first core. Some of the leftover loose stuff did seem to harden up quickly. But evaporation at the edges of the pile prevented cure there.

I covered the ends of the core boxes with a plate of glass as you do, to prevent evaporation of the ends before cure.

I will check a sample for quick cure next.

The label says it "contains Portland and gypsum cements".

I haven't yet tried the core in a casting.
I love it when a Plan B comes together!
Steve
www.sredmond.com

Offline awemawson

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Re: The poor man's sand binder
« Reply #11 on: September 01, 2013, 10:20:25 AM »
Rapid setting cement is widely available here in the UK from builders merchants. Frequently used on repairs and alterations to underground salt glazed drains, as use can recommence within an hour so the loo can then be used !

I've used it to repair bitumen lined brick built water tanks when I had my launderettes, as it's impossible to dry the tank wall in a sensible time to make a proper bitumen repair. Also useful for grouting in rag bolts to hold machinery though nowadays epoxy resins are more usually used.
Andrew Mawson
East Sussex