Aluminum Sand Casting a Motorcycle Engine

[GreenTwin]

Many of these molding techniques are available on a hobby level, and this is the material that I use to make mold for engine castings (resin-bound sand).

Bound sand molding is a very versatile process, and a whole lot faster than making ceramic shell molds.

You can ram up a resin-bound mold, and pour it in about an hour (for a typical part that is not too complex).

If the castings does not turn out, you can modify the pattern with 5 minute epoxy, ram another mold, and make another casting in a little more than an hour.

The quality of the castings made with resin-bound sand can be excellent, if you know how to arrange your sprue/runners/gates/risers, and you can get consistently excellent results.
Ceramic mold coat eliminates any cleanup on the surface of the castings, and gives a superb finish.

And resin-bound sand works very well with aluminum, brass/bronze, and most importantly for me, with gray iron.
I have seen a few use Petrobond with iron, but my experience has been that the iron is too hot for Petrobond, and you get mold errosion when you try to pour it.

With resin-bound sand, there is really no need to use the ceramic shell process for engine parts.

Unlike the lost-foam casting method, with resin-bound sand, you can reuse the same pattern multiple times.

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[GreenTwin]

Here is the resin-bound sand method used to make slingshots.

Very versatile material, but not easily reusable.
For small quantities of castings, the reusability of the sand is not a problem.

This guy walks in with a pattern, and not too much later walks out with 8 finished slingshots.
The resin-bound molds can be modified after they harden, with the sprue, runners, risers, gates, etc. cut into the mold after ramming.

I am not aware of a faster casting process using use a raw pattern.
The pattern is not damaged, and can be used over and over again.

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[lee webster]

I sent an email to a metal casting company asking them what made up the resin bound sand they used to cast parts in iron, namely a Ranalah English wheeling machine. I didn't get a reply, so I am still in the dark. I know there are various types of resin bound sand, and I have used an epoxy resin for the binder, but it took a day to go hard. What do you use? (If you've answered this before from either me or someone else, could you point me at the answer please?)

 

[GreenTwin]

I use LinoCure (tm), made by ASK Chemical, which is a 3-part binder system, with a resin, a hardener, and a catalyst.
One does have to wear a commercial-grade chemical-rated respirator, and nitrile gloves when handling this product.
The catalyst is nice since it allows one to vary the set time.
If I am in a hurry, and the mold is not complicated, I have used set times as low as 5 minutes.

There is a set time, and a strip time.
One wants to remove the patterns prior to the end of the strip time, else they will be permanently glued to the mold.

I have seen some use epoxy as a binder, but I am not sure about how to do that.

I also use sodium silicate as a binder, and I have sodium silicate some that uses a hardener, and a catalyst.
Normally sodium silicate is hardened with CO2, but a catalyst gives a more predictable result.
Sodium silicate does not have the harsh chemical properties that the resin binder has, and is a good and readily available product at pottery outlets.
I am told that sodium-silicate bound sand molds work well with iron, but I have not tried that yet.

Bound sand must be very dry, and I use a commercial product called OK85 (from Oklahoma), and I think it is oven-dried.

I use a ceramic mold coat (same as in the slingshot video above), and that really helps with the surface finish.
The product name I think is "Velacoat", which is also made by Ask Chemical.
Velacoat is alcohol-based, and you can spray it on with almost anything including a sandblaster, and then burn it off, and flame it a bit with a light propane flame.

The Velacoat absolutely stops any burn-on of the iron into the sand, and greatly improves surface smoothness.

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[GreenTwin]

These are Velacote-coated molds, and the photos show the gray iron castings right out of the mold, with a light brushing off with a paintbrush.

Saves a huge amount of time with cleaning the surface of iron castings.

I have seen mold coat used with other types of sand, but have not experimented with that, and am not sure exactly which types of sand it will and will not work with. It may not work with Petrobond.

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[lee webster]

Many thanks for the reply. It has given me the information I need to start looking for UK based alternatives. The main problem for us is that there doesn't seem to be many companies who will sell small quantities to hobbiests. I contacted a company a year or so ago about buying materials from them, they made bespoke beds with cast iron ornamentation. No luck. I lost count of the number of emails I sent.
I haven't found anyone in the UK who sells a sodium silicate catalyst. I got the impression (not proved) that it might be illegal here.

 

[Jasonb]

Lee Artisan Foundry do the Sodium Silicate, CO2 to set it off

https://www.artisanfoundry.co.uk/product_info.php?products_id=89

 

[GreenTwin]

I have not used a lot of sodium silicate cores and molds, but I did use a few before I found resin binder.

I made a lot of mistakes in the beginning with sodium silicate, and I have seen others do the same, so I will note those here.

I have seen recommendations of 3-5% sodium silicate, and many make the mistake of using higher percentages.
The higher percentages create a rock hard core that cannot be easily broken down after casting the metal.

Adding water to the core after casting helps break it down.
If done correctly, a core with water added should break down easily after casting.

Over-gassing is another mistake I made.
I assumed more is better, but if you gas a sodium silicate core or mold for more than 5 seconds, you will ruin it.
Never put a core or mold into a plastic bag full of CO2, as this will also ruin the core or mold.

The first sodium silicate molds I made were gassed for about 30 seconds (using about 3% SS), and I put them on the shelf and the next day they crumbled by themselves.

I decided to add more SS, and eventually getting up to the 7% range, and again making the mistake of over-gassing, and those molds also would crumble on the shelf after a few days.

I saw a video online that warned about overgassing SS, and so I tried a 5 second gas with I think 5% SS, and low and behold some of those cores have been solid sitting on the shelf for years, and they break down easily after casting when I add water.

I typically use a 1/4" wood dowl rod in the center of round cores, and vent that hole up and out the top of the mold.

You can also bake or lightly flame SS cores or molds to help rid them of any residual moisture that would cause gassing.

Sometimes a SS mold has to be gassed from both sides.

Using a catalyst with SS eliminates the need for the CO2, since SS with a catalyst is self-hardening.

I have seen some add a slight amount of sugar to SS cores to help them break up, but I don't think this is really necessary for most cores.
Adding sugar to anything outside around here will summon massive armies of ants that cannot easily be dispatched.

Some also add a slight amount of seal coal to improve surface finish, but I think a sprayed-on alcohol-based ceramic mold coat is what I would try to improve surface finish.
I am not positive you can use alcohol-based mold coat with SS, but I think it works.

And supposedly adding 10% propylene carbonate to a SS mix will cause it to act as a catalyst and self-harden without CO2.
I am not sure what propylene carbonate is, and have not used it.

I do have a catalyst for SS cores/molds, but it is not labeled as to what it is.
It may be propylene carbonate.

Hope this helps.

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[lee webster]

Thanks JasonB, I have made lots of mistakes with the correct mix of ss to sand, and then too much Co2. I would prefer a catalyst such as GreenTwin mentions. The sand cores I made with epoxy resin were very nice, and very strong, but the cores needed a full day to harden.
Thanks to you too GreenTwin for the extra info.

 

[lee webster]

A search of the web shows that propylene carbonate is sold as a nail polish remover here in the UK. I don't know, yet, if it used elsewhere, but I will keep looking. I have to get some shopping tomorrow, so I will buy a jar of nail polish remover to try with my sodium silicate and some fine dry sand. Any ideas of quantities for propylene carbonate to sodium silicate?

 

[gadabout]

A search of the web shows that propylene carbonate is sold as a nail polish remover here in the UK. I don't know, yet, if it used elsewhere, but I will keep looking. I have to get some shopping tomorrow, so I will buy a jar of nail polish remover to try with my sodium silicate and some fine dry sand. Any ideas of quantities for propylene carbonate to sodium silicate?

Nail polish remover here in OZ is Acetone
Mark

 

[GreenTwin]

I generally see single digit percentages of mixing catalyst.

Digging around on the net, one source mentions a 2-3 hour strip time for proplene carbonate.


This is from the "Ask Chemical" website:

SODIUM SILICATE BINDERS (ACCOSET™)
ACCOSET no-bake binders are water-based solutions of sodium silicate that can be hardened on sand by curing with an organic ester catalyst. The ACCOSET no-bake sodium silicate binders are all-purpose binders used to produce a variety of molds and exterior cores which require high strengths for handling purposes.
Benefits:
Several types available depending on strength and shakeout needs. Low smoke and odor. A wide range of catalysts to determine work time/strip time.


This is the sodium silicate that is common on this side of the pond.

https://shop.clay-planet.com/sodium-silicate-solution---pint-1.aspx
This is what I think is the catalyst that can be used with sodium silcate:

https://shop.clay-planet.com/chembond-catalyst-210.aspx
It appears that "Chembond 4905" is a brand name for a sodium silicate product, and Chembond Catalyst 210 is used to harden it.

The mixing instructions are visible on the Chembond 210 catalyst bottle shown below, ie: 10 parts resin to 1 part catalyst, with the "resin" being the sodium silicate.

 

[GreenTwin]

Here are some instructions for a sodium silicate binder and associated catalyst sytem.

These instructions mention that a mold coat can be used with sodium silicate molds, and I highly recommend a mold coat if you can find it, since it greatly improves surface finish, and pretty much eliminates sand sticking to the castings.

Sodium silicate molds seem to stick to the pattern somewhat easily, and so the patterns have to be well waxed in order for them to release from the mold.

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[GreenTwin]

Note that the instructions above mention mixing the catalyst with the sand first, and then mixing in the sodium silicate.

Edit:
Also note as the instructions mention, that when you strip (remove) the pattern from a bound sand mold, the mold has not reached full strength yet, and so the mold has to be kept on a flat surface for 20-30 minutes until it is fully hardened.

I moved my molds too quickly the first time I tried bound sand, and they warped slightly.

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[lee webster]

Thanks GreenTwin. I will design and 3D print a split core box that holds about 100g of sand and start the experiment. I can't get too involved at the moment because I have family staying with me. I tried striking my moulds made with epoxy resin too soon and they crumbled. Left too long to harden makes them difficult to strike.
Mark. Propylene carbonate is supposed to be a safer alternative to acetone. I have a small tin of acetone I use as a cleaning agent, I could try that too. Thanks for the info.

 

[100model]

I have seen a few use Petrobond with iron, but my experience has been that the iron is too hot for Petrobond, and you get mold errosion when you try to pour it.

I have never had mold erosion with petrobond but pouring iron into a petrobond mold I have problems with lots of graphite forming on the surface of the iron which will not dissolve in iron and leaves a strange irregular surface on the iron. The graphite forms when the oil burns in the mold. When I knock out the mold I can see the graphite and if I rub the surface a shiny black stain forms on my fingers.

 

[GreenTwin]

I got a nice iron casting with a good surface finish using Petrobond with iron, but the mold eroded in several places and left some large sand inclusions where the sand caved in from the extreme heat.

I have seen others use Petrobond with iron successfully, but I would not use Petrobond for anything other than aluminum.

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[100model]

In this video of mine I got a really reflective surface on cast iron and it shows how a good a surface finish you can get with petrobond. I have used green sand, bound sand, SS sand and none of them compares with petrobond.

 

[lee webster]

A very interesting video. If I build a bigger furnace to melt iron I will use your design.
I can buy the brand of oil bound sand here in the UK made by Petrobond, and also a couple of variants made by other companies. Is yours "Petrobond", or a look-a-like?

 

[GreenTwin]

The zircon coating seems to be hard to source.

I have seen others substitute satanite for zircon, and the satanite seems to hold up to iron temperatures.

Satanite is not expensive, and seems to be readily available.

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