Waterway core removal 3

[BrianGar]

Looking at old posts Im hoping Greg may shed some light on this!
How do they 'normally' flush waterways of sand cores?

Are the sand cores sodium silicate bound and flushed with water?
I have ten test cores setup of various sodium silicate percentage, and they do take a bit more than just water to dissolve, as in they like to be hacked a bit to get things moving.

Or, are the cores resin bound, such resins could be polyester, or more likely epoxy bound, and flushed with a solvent? Is_there a solvent for epoxy?

What are the common resin binders? Actual resin names/makeup if possible, and not trade names.

Thanks in advance folks,

Brian,

 

[HRHtex]

Methylene chloride will dissolve or soften pretty much anything. It is available from fibreglass materials supply shops.
Also handy to have for cleaning injectors, throttle bodies, carbies etc.

 

[patprimmer]

Just stand upwind and don't breath in.

Regards
Pat
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[BrianGar]

HRHtex, thanks for that, Ill have to ''sample'' it!

Pat, of course, that goes without saying, I might close my eyes too,

BG.

 

[BrianGar]

Just googling there Pat, its got a moderately sweet aroma, I may stand downwind yet..

BG

 

[patprimmer]

It's also a chlorinated hydrocarbon.

Regards
Pat
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[MikeHalloran]

Methylene chloride will give you a terrible headache, which is a sign that you've already been overexposed. It's actually _much_ worse than that; the stuff is toxic in nearly every possible way, so is best used in a hurricane.

Detergent may help you with removal of more ordinary cores.

Core removal is not a new problem. I saw a gigantic fluidic oscillator (think firehose size) installed as part of a machining line in 1967. The line was in tryouts at the builder's facility; I have no idea how the oscillator worked out long term.



Mike Halloran
Pembroke Pines, FL, USA

 

[btrueblood]

If you are using water glass binder (sodium silicate), flush cores with mildly acidic hot water. It does diddly squat for the SiO2 that is created when the waterglass is cured with CO2, but it helps dissolve the sodium carbonate and/or sodium oxides that are also bound up with the silica.

I'd avoid resin cured cores if your water passages are long, narrow, and will be difficult to clean out. Unless you like getting cancer from sniffing methylene chloride.

All core/mold sand removal I've seen starts with a shake-out process. Imagine the biggest dang rock tumbler you've ever seen, lined with heavy gauge screens to let the sand and chunks of core material fall out. After the loose stuff is shaken out, shot blasting, and manual removal with tools ranging from needle scalers to 5-lb sledges, dental picks to prybars, and wire brushes to the kind of automated grit-flinging devices Mike describes get used.

Good mold design includes thought on how (or whether) the core will be removed.

 

[GregLocock]

I am ashamed to say that it is so long since I have been in a casting plant I can't remember how they do it. Mind you the engine plants I am familiar with were probably using best practice from WW2, so probably weren't much help. 'My' crankshaft lathe was commisioned in 1946.

Cheers

Greg Locock


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[anyoldname]

When my employers had their own foundry I'm sure the filled core packs were heated to help remove the sand, its a while ago now but from what I remember the heat dried out the sand then they were vibrated, air-blasted and washed to get the sand out.

 

[swall]

I hate to state the obvious, but cores are formulated to degrade/decompose upon being heated by the molten metal. They need to hold together just long enough to last through solidification. If the cores don't thermally degrade, then you get other problems like hot tears in the casting. So, the degraded cores should be readily removable by the mechanical or hydro means described above. Proper casting design will also ensure that you don't have blind passageways that can't be flushed out.

 

[BrianGar]

Lads, thanks very much for the great replies, all advice taken on board as always. Looking at some of the dates makes me feel really young I have to say!! That can be a good, or bad thing I guess depending at what way you look at it! Bad for me In that I was born in 82, and missed all the basic processes 'back then' before newer more advanced methods came along. I find starting at the basics and working forwards is the best way, you get an idea why and how they advance then through the yrs.

Brian,

 

[berkshire]

Brian,
one resin binder for cores that was popular in the 1970's was urea-formaldehyde (Think Aerolite.), mixed water thin with a slow hardener added, mixed into the sand, then baked to dry, the theory was that the resin would burn out when the casting was poured. Allowing the sand to run out. Phosphoric acid was used to remove the remaining residue if needed.
B.E.

 

[patprimmer]

Most polymers start to degrade at about 400 Deg C I think.

Regards
Pat
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[btrueblood]

The problem is that on long, thin cores, the resin may never get a chance to fully burn out, as no air ever gets in far enough for the resin to truly combust. Instead, it chars, and you get a lovely mix of carbonaceous "coke" and sand, welded together with cast metal...for iron plus carbon, you get really, really hard iron carbides in that mix too, and it chews up your tools quite nicely.

There are ways to form the cores as shells, with hollow interiors, allowing better venting and burnout/shakeout, but this makes a weaker core, and one that is more likely to float in the molten metal and get out of alignment.

I'd be talking to a foundryman about all this stuff, as they know better what methods might work for your specific part design, metals, etc. Then again, a foundryman might not talk to you, as a lot of what they know they consider trade secrets. You could try posting some questions in the metal and mettalurgy forum, you'll likely get more expert help there. I'm certainly not an expert, just have done a fair number of cast metal designs.