Thanks This stuff is actually kinda nice work I have to say, something about it that's relaxing or something, maybe its just me Onwards to the core box, 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)
Yes Indeed, its pretty handy once the core box is made though Onto the sand> 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. Mixed in. 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)
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.
Thanks Boss This is what happens when I get bored.......I guess being outa work isn't totally a waste... 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.
Awesome guide, really goes into detail. Next scene mod, metal seat winders actually I kinda want a set now
Ill have to be careful what I use as mock-ups in the future. Back at this again next week now that the Christmas work pressure and general panic is over with
I bet it does Small update, FINALLY got the exact sand I wanted for casting finer parts. I took an age to find a company that would actually sell this to a normal 5/8th.. I can now finish the thread with this. This sand is oil bonded sand, and not water bonded which is used for rougher castings. The oil in this sand will not boil like the other, therefore pitting on part surface is reduced A LOT. Also got the flux off the same crowd, this helps bring any contaminants to the surface before you rake off the dross(scum) before pouring. These parts your going to see below are the first two parts Ive ever cast. This sand is oil bondd sand and can hold finer detail than the previous sand I did the mock test with. So anyways, onto the casting test... The layout of the pictures below are in the order I did it in, so Ill host them in that order... I fixed the pattern halves onto the parting plate, I had to make a new parting plate as I drove over the other one last week .. . One half fixed... Turned upside down... Other half fixed, must be fixed as accurately as possible to be opposite its other half or you'll end up with a massive parting line in the finished part... All screws and holes filled... I prepped the charge in the crucible, more smashed up water pumps, there great!!... Test fit, and set up burner pipe... Next, I made the cores for the flange using the plaster core box... I need two, as the main pattern is setup for two flanges...I put a nail in the middle to make handling them easier...remember, this sand is just bonded with oil, it doesn't go off or dry, its as Is once the core box is opened, Its amazing stuff when packed... Full, and packed... Out of core box... And one more... Next, I filled the main mould... All filled and packed... Turned over the whole lot and got to work filling the top... Full... Scooped out this area to funnel in molten metal to mould... Lifted off top mould section...and removed parting plate c/w patterns screwed on...this is the bottom half of mould below... Removed the dowels and cut fill gates from dowel holes into rear of flange...this is the top section... Sliced a small flat area off cores as I need a bit of metal thickness in this area for flange bolt counter bores, so that a socket will fit onto bolt head, and clear flange its-self... Placed cores in mould... Made a few vent holds in top mould half before I fitted it, 2mm wire, job done, ... Top fitted, say goodbye!.. Lit smelter... Takes a second to cop on and warm up then off she goes... After 5min... The next bit Ive no pictures of because Ive only two hands, and If I asked anyone to take pictures at 12 o clock at night they'd probably think I was actually demented... What I did was scoop off as much dross as I could, added a spoon of flux, stirred it, little more heat for a min, then raked off the rest of the dross(scum) before I poured it into mould.
Full... Now...the moment of truth, were the patterns correct, did the cores collapse in main mould, did I pack it enough... Gave ten minutes and started digging...it filled perfect...nice... Lifted up, its still very hot, vent hole did its job well... Close-up of fill gate/runner... I cut them apart broke off fill gates and shook out the core sand... A quick run on the beltsander removed most of the flash/gates etc either end, the belt died half way through, I have to take down the flange face approx 1.5mm more yet, but thats minor... Close-up of extra material needed for counterbore created by shaving the core moulds... Few random pictures, they still need a bit of grinding/linnishing, Im extremely happy with the over-all finish direct from mould... You can see the flange is 1.5mm too high yet, there's a bit of material left on there so I can finish them flat... The bits and pieces... Offered up to head, looking good, hose is real snug too, tomorrow, Im going to finish sealing face, and drill holes, that should be it then, sand testing done. I may pack it even harder the next time, and give it more vent holes, see if I can get an even better surface finish, although, I suppose, its not too bad at all, for the first time. Im very happy all in all with the results to say the least, all went smooth, I can now get onto moulding/pattern making my intake parts. You can follow this on my thread about my car on here. There I will be doing more casting and loads more. This thread on a guide to casting Ive done here will hopefully give you a bit of insight as to whats Involved in designing, moulding, and casting parts. Brian
Brilliant thread, and very impressive results. If you ever decide to cast a few replacements for plastic coolent hose flanges to sell, I'd be interested. If you could make the ones which go on the front of the block to the top radiator pipe it would be good too. I'm sure you could do a good trade in small cast aluminium components which regularly fail.
Will do, no bother. I hope to have my project thread up to speed in a day or two, they'll be lots more in it Brian.
Looking forward to the update. Just realised the flange you made is for an 8v, I would need 16v ones. I have a damaged top radiator hose to head flange. If you decide to make some for a 16v, let me know and I can post it to you.
