Vw parts of course Said Id throw this up for the craic, some of you may be interested in the process so I might as well share given the fact that I took pics of the progress and build as I went. First off, this line of work is next near impossible get info on so alot of it I had to design up myself and choose the suitable materials too along the way. Casting is now a dying trade and fully automated around the world in controlled environments. While Im sure nobody will go to the trouble I have here it may rise some interest as to whats involved, the process, materials, procedures, mould making, melting, design, etc. I had to do this to figure out a few things I needed to know for my bigger smelter Ill be using to melt the alloy for the cylinder head Im designing. Using this smaller smelter less heat up times, gas, and raw materials can be used in order to get the feel for molten alloy in general. Plus, its a bit easier than winding up my bigger smelter which can melt approx 9litres of alloy at a time, where as this one can do 1.25 litres. Im going to be using this to make a few parts I have in mind for a while, DTH throttle bodies and a few trick intake manifolds being just some of the stuff. Casting is a pretty simple process, but the finished item all depends on the quality of the mould the metal is poured into. The main mould types ill be using will be of the sand variety, meaning, you make your pattern part you want in timber(Iroko) and you then strike both your sand mould halves off this pattern. The part shape is then formed in the sand and you can pour in your alloy, that way, ending up with the timber pattern shape, just thats its now alloy. Its a bit more complex than that but Ill try my best to explain all as I go. Pattern making is what Im good at as my main ''skill'' is cabinetmaking so making very complex accurate pattern parts is not a problem. Its important to note that this is not the cylinder head thread, this will be covered in another thread on here Ok, so onto the first step of a long road, and that is the smelter itself. A smelter is basically just a round oven where the crucible is placed in order to melt the charge inside it. The smelter must be well insulated as the heat inside is in excess of 700 degrees. The smelter is powered by plan ordinary gas you get for your cooker. Its all pretty basic, now onto the build... For the body of the smelter something round is needed, you could use a large diameter pipe but I used a gas cylinder, the walls are 3mm steel and there tough by nature. I filled it with water to expel any gas still left inside. Next up, off comes the top with my favourite tool A second ring is then cut off the main body to for a locating ring for lid. The ring is then split and welded to lid around the outside. The lid now fits snug back onto main body again. The lid is turned over and I welded some wire lattice in there to hold in the refractory material a bit better. The refractory mix consists of, Perlite Cement Sand Fireclay Perlite is a natural volcanic material, it is a natural insulator. Cement is standard cement. Sand is normal sharp sand. Fireclay is the cement fire bricks are made from, kinda like normal cement but with a better heat resistance tolerance. Mixed up First the base is poured, approx 80mm high. Then, I wrapped up a bit of Formica to form the inner circle. Pouring the walls. Done and tamped. Onto the lid A bit of pipe is placed into where the valve was in order to form a vent hole up through the lining. The pipe is removed when lining is set. Thats the smelter pretty much done now, so next up, onto the crucible. -------------------------------------------------------------------------------------------------------- The crucible is the cup used to place the metal in that is to be melted. This is used from start to finish, that is, the raw unmelted alloy is placed in this and stays in here until it melts, the crucible is then removed from the smelter and the alloy poured from it directly into the mould. So, the material needed for the crucible has to be picked with care, depending on what you are melting, what the part is for, and what properties the finished part has to have all reflect on the crucible material choice. If poor crucible materials are used some material from the crucible walls can leech out into the molten alloy and effect the alloys properties. In this case Ill be using stainless steel >316. Its ok for small parts and doesent really have any bad quality's that will effect the final part. However for the cylinder head, I will be using a pure graphite crucible, graphite poses no threat on the final part qualities, be it strength, structure, or machinable properties. Obviously On such parts as throttle body's, intakes, and the like, the final properties can afford to be altered a tiny bit as there is no work on these parts as such, and machining of parts is minimal, so, stainless is a perfect choice for crucible material. The Crucible manufacture. I got a bit of pipe approx 250mm long with a wall thickness of 5mm, to this I welded a base plate in 6mm. Rods used are also 316 s/s. Next, a 'V' is cut for spout The spout is constructed from two pieces cut to triangle shapes Spout tacked in place Finish weld Next, a ring is needed at the rear in order to tilt vessel in order to pour alloy Pins are welded to the sides to catch crucible with the pouring tongs I gave the whole thing a quick sandblast after to remove any oxides or ****. Sandblasting really works in lifting any dirt or general dirt, a close up of one weld shows surface finish. It may appear an over kill looking at the scale of the plate thickness, welding, ring, spout, sizes etc, but keep in mind this isent a milk jug and has to with stand very tough conditions for may cycles. Thats the crucible done, next up the burner tube. --------------------------------------------------------------------------------------------------------
The burner tube is pretty much where it all happens, air is forced in one end, the other end is inserted into the smelter at the base, gas is introduced into a venturi in pipe near the hot end. The air speeds up as it passes through venturi and carries the gas with it, as it emerges inside smelter the air/gas mix ignites and makes the temperatures required to melt the alloy. The pipe enters at the side of smelter and has the effect of swirling the flame around the walls, passing around the crucible completely on all sides, and exits out the top vent hole. With the Formica former now removed you can see the hole where the tube will sit. The burner tube is approx 1200mm long, 50mm in diameter, and has a 3mm wall, its is of mild steel. First, 3mm slots are cut all around to form venturi. These strips left are tapped in to close slots, and once again, they are recut. Tapped in once more you can now see the crude but effective venturi formed This is then welded up, its crude as hell and pretty wide cuts had to be filled in either end but its fine for what it has to do Welder is then turned up to high and a hole blow through to fit a straight fitting to supply gas Fitting tacked in Now the end that sticks into smelter has to reduced down a bit too, few more slots a a bit of tapping and thats it done Fits like so There now has to be some form of way to vary the air from the blower, My blower is the exhaust air from my workshop vac but, it isent vari-speed, so I had to fit a butterfly to burner tube. I wanted this as handy and as basic as possible so I got thinking, I made it just like a throttle body butterfly, one toyota wheel brace with a slot cut in it, and a disc 43mm in diameter. Job done. I fitted a valve spring and a welded washer as to make a bit of resistance and hold it at whatever position I wanted. I also welded a leg to tube to hold free end at correct height, the leg is a bit of scrap from the pile and happened to be just the correct size! Thats the burn tube done. Up next, tempering the refractory lining. -------------------------------------------------------------------------------------------------------- I set the smelter aside for a week to air dry. If it is dried too fast the lining will crack, and thats no good. After a week or so, a small fire was set inside of timber off cuts and paper, this was repeated for a few evenings in order to dry out lining further. The smelter is now ready for the first run. -------------------------------------------------------------------------------------------------------- First run. How the smelter looks after the tempering. Test fit/run Made up the tongs too earlier, forgot to take pictures, its pretty simple A bundle of lit news papers are inserted between crucible and refractory wall, blower is turned on, throttle closed, gas is turned on at low reg setting. As temperatures rise the news papers are burnt, throttle is opened, gas is increased, burner tube sustains ignition by itself and the whole thing comes to life in a fantastic jet engine like roar! For the first melt I used a few alternator brackets, some water pump casings, and some other brackets. This is a bit of a messy way of doing it as it creates a lot of dross, or scum on top of molten alloy that has to be skimmed off before pour. This dross is the impurities and dirt on the old parts. Thankfully I have found a spot in Ireland that sells Ingots off the shelf in 5kg bars, they are LM25 which is the exact alloy I need for the cylinder head as it has all the correct properties I need. It is also Idea for all the other parts. Just warming up, crucible loaded 8 minutes from ignition and all the alloy has now been melted, what you see on the top is the dross, it looks like grey banana skins and is very bad if it makes its way into mould, its pretty easy spoon it off before pour though. My optical thermometer told me that it was approx 700 degrees in there after 8mins. I have to say it was pretty cool, and pouring the molten alloy was a sight to be seen, sadly, I dident get a photo as my hands were full. I poured it into a very crude normal sand mould, just to get it into a shape to be able to be remelted easily. I also wanted to check cooling times, shrink, etc. The blank when cooled Notice the shrink at top once it dried This shrink has to be taken Into account in the design of all parts, moulds, risers, gates, and all other mould aspects. Youll see about all them in the next part when I make up some moulds for parts and other bits. I had trouble getting high grade casing sand but I have some located and ill be picking it up sometime next week along with a crate of ingots and a load of other vital bits incl de-gas tabs. One last shot of the crucible post pour It seems to be well up to the job and can ''take the heat''! The above smelter assembly retails at $2400 and the crucible $100 dollars, total cost so far, 0. Ill continue on this next week, enjoy the first part (Mods, move this if ye want, its an unusual one and Im not too sure where it belongs)
nice. are there any dangerous fumes given off? i always used to get a headache when melting lead as a boy.
That's a cracker that is. I was going to have a stab at this a couple of years ago. Never did get round to it. Inspired again!
@ Alex, nope, nothing noticeable, having said that Its all done outside so that has to be a good thing. I know what your saying about lead, sometimes depending on timber quality I have to add to the weights in sash windows and lead does seem to be a bit rotten when melting, but alloy seems to be pretty ok, still, I wouldent try it in the Kitchen now or anything @ Rob, I actually looked up Fred Dibna there on wiki, looks like He was a joiner too as a lad, maybe that has an effect of warping people minds who are also involved/interested in this sort of stuff too, the time does eventually come when you combine the two out of boredom Lets see how it goes anyway sure, I wont buy glasses and a tweed cap just yet mind you @ everyone else, thanks folks, this is all new to me too, but hopefully (and I think) I have enough homework done to pull it off eventually! Ill update regularly, actually, this thread will be a great help with regard the cylinder head as I can kinda explain the basics here so hopefully it will make the head thread a bit more understandable and less cluttered with details. The head thread methods will also make more sense once I have all the parts casting chat covered here. Ill be puttin another bit later regarding mould design and different sands required for different type parts. I was wondering at first would I post this stuff up, but looking at the replies its seems some are interested Brian.
Looking 'forward' I was pondering earlier how a quality cast is achieved, no bubbles, no contaminants etc. What level of lab conditions and prep are needed to get a quality cast?
Well there is steps you need to take, the sand, mould cavity, and molten alloy has to be closely monitored. All dross has to be completely removed from surface before pour, temperatures and dwell times also have to be monitored. All gases have to be removed before pour also, this is done by inserting degassing tablets into the molten alloy towards the end of the melt. These aid to remove all gas from the alloy before it goes into mould. Theres loads more too which Ill add during the thread Brian
Next up a run down on the basic casting methods and the various moulds needed to make particular parts. Simple parts such as brackets and other solid items are pretty easy cast, meaning they only require one pattern in order to make that particular shape. Slightly more complex parts which have a hole through them such as the flange on the end of a cylinder head require a ''core'' to be installed inside the main mould in order to create the void through the flange. This core is also made of sand and requires a pattern to make that too. All parts in or on an engine that fall into the sand casting category use these two types of casting methods. Depending on part complexity the mould may require multiple patterns to be made up in order to strike the associated sand moulds off them in order to build up the final mould for the part required. Take two basic parts below as an example> One is an alternator bracket. The other a coolant flange. First up, the bracket, this is a basic part and requires only one pattern, and just the two mould halves, the top half and the bottom half. The top half of the sand mould is called the cope, and the bottom half is called the drag. The sand is held inside frames called flasks. There is a flask for each mould half. Casting sand isn't like the sand your used of, once packed into say a block the size of a concrete block it holds its shape because of the binders added to it. Its very fine also and takes sharp details pretty easy. Therefore no support is needed to hold it in shape, a simple frame(flask) is used in order to aid positioning of both mould halves, even though the moulds are open top and bottom the sand will not fall out of its frame, its brilliant stuff. Anyway, onto the bracket As you can see its fairly basic, Now, lets imagine you wanted to make that, you would need an exact replica pattern in order to ''make'' that shape inside the moulds. Sadly, if you wanted to make a copy of the above part, you cannot use that part as a pattern because you have to factor in shrinkage, as the alloy cools it shrinks back a bit, so, this has to be factored in when making the timber pattern. If you were to use the alloy bracket as the pattern once your new part had cooled it would actually be slightly smaller that the original...not good. LM25 is the alloy Ill be using throughout and the approx rate of shrinkage for this material is 1-1.3% from pattern dimensions. Or approx 3mm shrink on a 300mm long part, enough to throw things a bit. So lets say I had that part made in timber with the shrink rule factored in and it was ready to use as a pattern, heres how you would go about striking the sand moulds off it in order to create the ''space'' to pour the alloy into. First off, you can see the line all the way across the centre of the part, this is called the parting line and it is where the top and bottom mould halves come together. Parting lines exist on alloy items that are cast this way, and also exist on ALL plastic items too as the moulding process is similar, you will see them on may items if you have a closer look. Parting line In an ideal world parting lines would not exist, but they do, on very cheap parts parting lines will be more prominent because of lack of accuracy, tolerances, and general sloppiness when it comes to positioning both mould halves exactly in-line and opposite each other. If they are off a bit, the mould halves become offset and this can be seen on the finished part. Have a look at some cheap kids toys, you'll find them in a second. Another extremely important feature you have to keep in mind when designing parts is the ability to be able to remove the timber pattern from the moulds once the sand has been packed around it. If the part had angles that widened as they originated from the parting line more mould design would be needed leading to a more complex setup and a 'multiple sand parts mould build' so that the pattern would be able to be withdrawn from the sand without causing damage to mould. On a two part mould design its pretty easy to get around, you just have to make sure that the angles never widen as they originate from parting line. This insures easy pattern removal from the sand mould before pouring. Below you can see this slight angle present on the bracket, this angle is know as the draft angle, and for sand casting its usually anywhere between 2-6degrees.
