Best thread on the internet
Wouldent say that now cnbrown, but hell, Im enjoying it!!
Onto the core pattern,
Much the same process again, blank of correct size, centres marked, centres driven home, corners knocked off with planer.
Next, the main points are marked out on the now round blank.
Not forgetting the extra material either end for the ''hanger spigots''.
Taking shape, care is needed at curve area to provide sufficient strength and wall thickness on the finished part.
Nearly done, diameters are checked and the ends narrowed down with the parting tool to make cutting off waste easier.
When held up against main pattern you can now see how the core will look inside the mould.
If you look at the plastic flange two dimples can be seen inside, these are clearance for the bolt heads holding flange to head, I have to make two hollows yet in core pattern to ensure there is sufficient material here after the pour for when I counter-bore the bolt holes. I could make the same two dimples in the main pattern doing away for the need to counter-bore, but Ill be boring the flange holes in a jig anyway so its only a matter of using a stepped counter-bore bit. That way, the flange holes are bored, and the clearance around them is also done at the same time using the stepped bit. You'll see that later anyway, its very simple.
Some of you may be wondering where the groove for the ''o'' ring is, I chose to omit it for a reason, on some heads pitting can occur at the flange area making sealing a problem when using an ''o'' ring, this way, I can face the flanges flat and use a gasket or sealer, or I can machine the groove with a simple mill jig. That way I have options. If you wanted to mould the groove you could very easily by inserting a removable core on that end, but doing it this way I wont need to.
Next up, transferring the core mould to a core box. The core box is basically a box with the shape of the core I just turned inside it. You then pack sand into this box tightly, the box is separated and you then have the core shape replicated, but in sand and ready to place inside mould.
(more to follow)
The core box is very simple, its exactly that, a box to transfer timber core pattern, to a plaster of Paris negative core shape. Once this is done the sand can be rammed inside it from the end, the plaster mould opened, and the sand core removed.
A rough box is made, the only real size that matters is the length, pins are used to hold it together, these should not be long, just enough to hold sides together, that way making taking the casing off plaster easy.
Next, pins are driven into the core pattern, making sure they are central, the heads are cut off after, bringing them to approx 10mm long.
It hangs central on the mould half, slots are cut to position it.
At this point I decided that I wouldn't bother making the indents in the core pattern for the bolt relief's, Instead it'll be way easier to just skim off a bit in that area with a small trowel before it gets placed in the mould.
You'll see that later anyway.
A plaster mix is made up, this is moulders plaster I had for repair to crown mouldings, but Im sure any plaster or repair compound will do.
The core box and timber core pattern are given a wipe of release agent, I have used light grease for concrete moulds in the past so its not that important what you use, Im sure car/household wax would do too.
The bottom mould is filled almost to the top.
The core pattern is placed in and tapped down onto sprigs.
Any excess is taken off with the mini trowel.
The plan is once the bottom layer is hard enough to coat with mould release, its given a coat, that is, all the exposed plaster surface and again the core pattern.
The top mould box is then filled up level with plaster and allowed to dry FULLY.
Once dry the sides are removed and the mould split, the mould faces are coated with sealer and it is then ready to use in order to create the sand core.
Because Ive never done this before I haven't a clue how long its going to take to set, but I do know that too much heat indoors will dry plaster too quick and it may crack. Not good!
So, ill leave that aside for the time being and go on to talk about the sand, mixing it, mulling it, and doing a practice mould mock-up to check workability, I need to see just how good it is and how fine a detail it can hold, and, whats its like to work with in general!
(more to follow)
There are a few different types of sand used for sand casting, the main ones Ill be using in this thread and the head thread are>
Green casting sand.
Oil bonded sand.
And Co2 curable sand.
+The green sand is made up of fine sand, bentonite, and water, its an ok sand and holds detail well.
The good thing about this sand mix is its pretty easy make, safe, fairly clean to handle and its also cheap to make.
The bad thing about it is it dries out, this can be a problem if there is a delay for some reason and the mould is left for a while, it can dry out inside and start to loose its detail as it starts to crumble.
+Oil bonded sand is made up of sand, bentone, oil and a catalyst, this is a very good sand mix for fine detail.
The good thing about this mix is it doesn't require frequent re-wetting like the green sand does, as in it doesn't dry out.
It also doesn't steam like green sand does, and therefore requires less venting to release gases around the hot new part.
Bad thing is, if you could call it a bad thing is that its a bit dirtier for handling due to the oil and is also more expensive.
+Co2 curable sand is a mix of sand and sodium silicate, this is a very useful mix as once Co2 gas contacts the sand mix it sets hard. It can be used for complex cores, and the main moulds themselves, it also has the added advantage of NO moisture content as no wetting or binding agent is needed since it is totally chemical. I will be using this alot on in the head thread.
Onto the Green type casting sand, Im going to see how I get on making the flange moulds from this, Im still waiting on my Co2 and oil bond sands so I might as well give it a shot first.
Below Im going to mix up the sand recipe, and mull it ready for use.
You can see the size difference between the sand used for casting and normal building sand, normal sand on the right. Casting sand is as fine as salt.
To get the correct amount I filled one flask twice, this gives me the correct amount of sand needed to fill both upper and lower flasks. I ended up with 12kg in total.
To this 12kg approx 1.75kg of powdered bentonite is added.
Now, this is when the fun starts and the water gets added, approx 2-3litres.
The next few steps are called mulling, mulling is basically working the living daylights out of the mix with your hands, I only have one book on casting wrote in approx 1945 concentrating on train and ship building and even with pig Iron great emphasis is shown towards this step. The more mulling the better it gets. What your doing is coating each sand particle with clay particles(bentonite) making them sticky, and in turn stick to each other, and hold their shape in the mould(Hopefully!)
Machine mullers are recommended for correct distribution of clay particles, but I have enough things for making so Ill mix it by hand as much as I can for a while.
You can see it taking shape as it fluffs up after even a short while doing it by hand, it can already hold thin shapes and is pretty strong!
I let it rest for a while before giving it another mix. Its everything I thought it would be even at this early stage.
(more to follow)
I don't know if it applies here but something I always do when making a multi-part plaster molds is to use a soda cap to put a small cylinder shape into the drying plaster. Soda caps are nice because you push them in maybe 1/3 the way and with a slight angle to the walls, you won't run into any overhangs. Anyway, when you pore the second layer it's helps to lock them all in line properly.
as for your sand,,, I did ALOT of glass casting (my undergrad is in glass blowing and design) and we used a olivine sand mixed with betinite. I don't know if it would apply to your project as well or not, but just some more info.
Modified by BrothersinArms at 3:22 PM 12-1-2009
Ya Good point, Im gonna drill mine, or maybe just fit the core box on it/them the other way clamping them together. Its not too bad given you can see both ends, but on a big mould, with only the fill open then the caps are an ace idea
Ive used threaded rod too in the past on a different setup, with drinking straws pushed over the section in the upper mould.
Whatevers handy really
Nice screen name by the way
On the sand, Ive a whole pipe of cool stuff on route, you cant get damn all in Ireland, has to be shipped in
Modified by chippievw at 12:24 PM 12-1-2009
I know you've seen my core making video, in that, I didn't have any such thing for registering the two halves but, because I could also see both ends, just like you can, it really wasn't much of an issue, I just lined the two halves up visually and clamped them together. Pins or bottle caps or whatever would have made it absolutely foolproof and I think maybe I'll add that feature on my next core box.
Modified by ABA Scirocco at 4:40 PM 12-1-2009
I had to travel about 60 km (one way) to get my silicate, with that supplier, I was restricted to one type of silicate and not the most ideal one for this application, the manufacturer of the stuff has a location another 25 km further down the road with a much broader selection of products, I'll probably go there when I need a refill.
BTW, any estimate on how much sand you'll need to mold the cylinder head, my manifold project required about 60 kg of green sand and the core was 1.4 kg.
Amazing thread, maybe best ive read! Keep it up!
Definitely an outstanding thread. There was a pretty good episode on "How it's made" (iirc) where they showed the whole process of casting engine blocks start to finish.
All very cool stuff to you for this thread.
Back to the core box again for a minute, the plaster is now dry enough to remove casing so Im going to whip it off to allow it to dry further.
Top casing removed, it came off real easy due to the short pins, and probably due to using plenty of release agent.
With the bottom casing removed the two halves split very easy, I removed pattern from also.
When this are dry fully I'm going to clean off release agent and coat the mould area with lacquer to make removing the sand core easier.
You can now see the core former together, it'll will soon be ready to make some sand cores.
Ill be doing a mould mock up in a while on a random shape to check everything in the line of what the sand is like to work, the tools, and just to get a general feel for it regards cutting the gate and creating the fill sprue shape etc.
I wont be pouring this mould, its only a test run.
Then after that I'll be moving onto the flange, mounting the patterns to plate, making the sand moulds, core, and pouring.
Modified by chippievw at 11:14 AM 12-2-2009
I don't think you'll need the lacquer, I didn't coat my plaster core box with anything at all, I just very throughly cleaned off the release agent from molding process and I found that the core sand with the silicate binder pulled away from the plaster without any trouble at all.
Modified by ABA Scirocco at 2:34 PM 12-2-2009
Really? Im not going to use Co2 cure in this, just normal green sand with a chaplet pin down the centre, I may need all the release powers I can get, It should be ok though, its pretty small...
If not, ill wait for my proper sands to arrive, but I dont see why green sand shouldn't be able to pull it off on this core
For a relative small simple core like this, I think normal green sand should work okay, dust the core box with a little talc or other suitable parting compound and I think you'll get a good release
For the more complex and delicate cores you'd need for a cylinder head, I'm quite sure green sand will not be adequate. What type of core binding agents do you plan to use for those?
Oil bond along with co2 cure sand. I have to do a lot of testing yet but co2 will be my main choice. I have some talc here ill try that first, ive read though that it has to be water proof dust, like parting dust, I really dont know till I try stuff
This bit is just a fast ''get to know the procedure'' rundown for me, Im waiting for the core mould to dry out fully so I may as well. I want to see how the sand holds it shape and if I need to add more bentonite. I also want to get familiar with the tools, ramming the mould, and how easy the sand is to work when cutting the gate, removing sprue former, etc...
Its also a test as to how the sand comes up on camera and if the various shapes can be seen in it.
Everything is laid out on a clean board.
The cope and drag, the plate and the various tools. Even after studying casting for ages I still sometimes forget as to which is which with reference to the cope and drag, I remember them this way, drag starts with a ''D'' ''Down'' starts with a ''D'' also so I think of the drag as ''down'' or bottom so that kinda makes sense for me!! Im still going to call them the top and bottom flask for a while so no need to worry yet, actually, I may just write it on them so the camera picks it up to avoid confusion.
The tools used, I have seen these called different names so Im going to use the ones I know, from left to right:
The moulding trowel, The sprue former, The pattern screw(used to remove half a pattern from the sand), The mini heart trowel, The Gate trowel, and The vent wire.
The bottom flask(drag) is placed on a clean board and the moulding sand container behind it(which should be kept closed to prevent it drying out)
Its filled up a bit, paying attention to filling around the sides first.
The sand is rammed with a stick, but not too hard or this could effect the sands permeability, if its too tight the gas/steam may have trouble passing through it and the mould could rupture before the metal hardens.
More sand is added and packed.
Any excess sand is drawn off with a stick pulled along the top edges of the flask.
The parting plate is then fitted.
Of course in this mock up, I wont really be using the lower flask as I wont be pouring any metal, but its no harm to fill it to practice..
The upper flask is fitted(cope).
I placed in a random part with a bit of detail, the part has a good draft angle on the sides so it will release from mould no bother, its actually a seat winder from a Mk2.
Sand is sprinkled on first then the flask is filled around sides filling in to centre around the part.
At this point the sprue or ''fill'' former is also placed, its just a bit of tapered timber.
The sand is rammed and more is added.
Rammed again and the finishing top layer is added and packed.
Once flat or pretty flat a scoop or funnel shape is dug around riser with the trowel, this helps with the pouring and guides metal in.
Its actually hard to see it here which means Ill have to take the flange moulding pics a bit different or at a different angle to fully show things off fully, but thats what this test is for.
Once thats done the top flask(drag) is lifted off, you can now see the underside of the pattern, and the tip of the sprue former. The flask is on its edge here so you can now see how much of a hold the sand has inside it.
One thing I noticed is, some sand came out between the flask and parting plate as I rammed it, you can see it all around the edge, Im going to have to clamp the flasks together on the proper run.
Once the pattern is removed, You can see the sand detail, the shape got a bit lost when photographed so again Ill have to change the angles I take them at in the real run, but you get the idea. The detail was held very crisply so Im pretty happy with the sand.
The sprue former is now removed in a twisting action from the top, it comes out pretty easy. I cut a rough gate from the sprue to the part just to see how easy the sand is to work, it cuts real good and sand Is harder than you think!
Thats the test done, Im happy with the sand, it seems to be ok, Ill have to try photographing it a bit different for the flange run but I think I should be able to capture it a bit better. Its pretty hard see the detail in them photos.
Up next, Fixing the flange patterns to the parting plate.
Quote, originally posted by turbinepowered » So the cope's the top one, right?
So maybe... "Cope" and "Cap," the cope's the cap flask?
Correct. Cope (or a variation of it) is the word for head in several European languages, German, Dutch etc. I thinks that's probably where the word comes from. Your head's on top of your body, the cope's on top of the mold.
Here's a picture of one of my molds with a few of the parts and features labeled.
The box the mold is made is is referred to as the flask, they're usually in two pieces, top and bottom, cope and drag respectively, some more complex mold require a flask with more than two piece, the additional pieces are called cheeks.
The sprue is a hole that runs all the way through the cope, you pour the metal into the sprue, from the sprue, the molten metal goes through the runner and fills the mold and the riser.
The riser is a reservoir of metal which, if you've designed it properly is the last thing to solidify, metal shrinks quite a lot when it solidifies, the riser helps control/eliminate shrinkage defects.
The core fills selected sections of the mold cavity thus allowing hollow castings to be made.
Modified by ABA Scirocco at 6:51 PM 12-3-2009
Updates coming in the next few days, Im re organising the cars around the workshop, and making the place generally more casting friendly so that its in turn safer as well. Im also making room to fab up the bigger smelter as it going to be quite big. We also had 3 weeks of very cold weather which pretty much froze everything inside and out.
Ive to finish up the crankshaft post too but thats minor enough compared to the organisation needed for this thread in order to keep both the process and the pictures as clean as possible, and hopefully easy to follow. Thanks to all watching for your patience. Im looking forward to the next number of steps myself too.