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what do you make moulds out of????
what I'm asking about is the materials used to build the casting moulds for little model engine crankcases. ones cast in alooominumm. what sort of head do you need in the aluminium to get a reliable mould filling? what aluminium alloys do you use for casting? which alloys do you avoid like the plague? how much venting do you guys find necessary? how long do your moulds last? TUMESFFFFFF |
what do you make moulds out of????
In article ,
Stealth Pilot wrote: what aluminium alloys do you use for casting? which alloys do you avoid like the plague? More from reading than from doing thus far, but obviously if starting with scrap, start with _nice_ _cast_ aluminum scrap - a good source of which is old computer hard drive casings. I'll be interested in the responses to your questions from those doing more. -- Cats, coffee, chocolate...vices to live by |
what do you make moulds out of????
On Oct 20, 12:25 pm, Ecnerwal
wrote: In article , Stealth Pilot wrote: what aluminium alloys do you use for casting? which alloys do you avoid like the plague? More from reading than from doing thus far, but obviously if starting with scrap, start with _nice_ _cast_ aluminum scrap - a good source of which is old computer hard drive casings. I'll be interested in the responses to your questions from those doing more. -- Cats, coffee, chocolate...vices to live by Here is a qualitative description of what I know about this topic: Metal molds, aka die-casting dies, are made from MOLD STEELS. A variety of steels is available for different temperature ranges, life expectancy, and of course, costs. The molten aluminium is injected into the mold under PRESSURE to ensure strength and absence of voids and leaks. Aluminium can be sand cast; cylinder heads, older model transmission cases and differential housings spring to mind. Surface finish and dimensional accuracy are quite a bit coarser than die castings or INVESTMENT CASTINGS. Investment casting is an alternative for the model maker. A wax pattern is produced (for mass production these may be molded in a die!) and "invested" in a ceramic slurry. The wax is removed by melting it out, and the ceramic shell heated and the molten metal poured in (very abbreviated description). The pressure required to fully fill the mold depends on a number of variables such as alloy, mold complexity, size of the mold cavity, etc. For simple dies I would think that 12" of head would suffice. Simple steel molds have been made by modellers using common hot rolled or cold rolled steel. For a dozen or so castings this metal is just fine. A simple plunger injector can be arranged to force the metal into the mold. If you wish to carry out this process in your home workshop try to read some reference works on this topic dated from the 1930's or so. Early die casting used simple equipment and was used for producing automotive radiator grilles. As for the alloy to use....I would start with modern transmission cases or cylinder blocks. I know for a fact that the TOYOTA small 4 cylinder block is a die casting. Wolfgang |
what do you make moulds out of????
|
what do you make moulds out of????
Stealth Pilot wrote:
what I'm asking about is the materials used to build the casting moulds for little model engine crankcases. ones cast in alooominumm. what sort of head do you need in the aluminium to get a reliable mould filling? what aluminium alloys do you use for casting? which alloys do you avoid like the plague? how much venting do you guys find necessary? how long do your moulds last? Nobody uses reusable molds for hobby projects. I'm not sure the auto makers use them, either. Either iron or aluminum engine blocks are usually sand-cast. There are several variations on the system. The old traditional system is wood patterns and molding sand, with a clay-petroleum based binder. Another system is lost-foam casting, where the sand is rammed arounds a pattern made out of styrofoam, like the blue stuff used for home insulation. I watched Rick Chownyk do some lost foam pours at this year's CNC Workshop in Galesburg, IL. Very interesting. We have a guy in St. Louis who has set up a very elaborate casting shop, and I've watched and helped him ram up some wood patterns and then pour them. There is also the lost-wax method, usually used on small projects. Investment casting is a time-consuming process, but gives amazing detail. A wax pattern is made, sometimes in a mold also, then coated ("invested") with a refractory slurry that is painted on in layers and allowed to dry. The pattern/investment is then packed in sand to support it, and the wax is melted out in a furnace. The metal is usually poured while the mold is still hot. A 6" head is plenty for mold filling with aluminum, often 2 -3" will suffice. More head is needed with the lost foam, as the foam is burning out with huge greasy flames as the aluminum is being poured in. Too much head forces the mold flask apart, and the aluminum starts leaking out. Venting is often done with coat hanger wire or small welding rods. Molds last one time if you do anything with the sand processes. Alloys are rarely controlled, as most backyard casters don't have a metallurgical analysis lab on site. You use nice castings of known purpose, like hard drive cases or pistons. Jon |
what do you make moulds out of????
"Jon Elson" wrote in message ... Stealth Pilot wrote: what I'm asking about is the materials used to build the casting moulds for little model engine crankcases. ones cast in alooominumm. what sort of head do you need in the aluminium to get a reliable mould filling? what aluminium alloys do you use for casting? which alloys do you avoid like the plague? how much venting do you guys find necessary? how long do your moulds last? Nobody uses reusable molds for hobby projects. I'm not sure the auto makers use them, either. Just to clear up a point, high-pressure diecasting, squeeze casting, and permanent-mold casting are all used in making car engine blocks today, along with traditional baked sand, thin-wall refractory-lined sand, and lost-foam sand. The old B-O-P V8 from the early '60s was made in a steel, permanent mold. Ferraris are made in plaster molds that are similar to investment molds. -- Ed Huntress |
what do you make moulds out of????
what I'm asking about is the materials used to build the casting moulds for little model engine crankcases. ones cast in alooominumm. what sort of head do you need in the aluminium to get a reliable mould filling? what aluminium alloys do you use for casting? which alloys do you avoid like the plague? how much venting do you guys find necessary? how long do your moulds last? Sand casting is probably your first choice, both for cost and something the home shop can accomplish. Oil bonded sand, often called petrobond, is the easiest to work with. Water bonded sand, sometimes called green sand, needs a little more work to keep it in condition and needs more venting. It usually isn't necessary to vent petrobond molds for aluminum. Sand casting is a one shot mold that you simply remold for your next casting. The pattern lasts a long time. 356 alloy aluminum is a good starting point or you can remelt aluminum bell housings, etc., to get a feel for how the process works. Stay away from extrusions and beverage containers unless you are prepared to experiment with additives. A couple inches of sprue should give you enough "head", however, to get complete castings gates and runners will likely be necessary. Take a look at this video on YouTube: http://www.youtube.com/watch?v=NKXj5Ng3X58 and also by looking at "more from this user" you will find a short video about investment casting. If you follow the link to my projects page, there are a couple examples of lost foam and also a project using gates and runners. Rod |
what do you make moulds out of????
|
what do you make moulds out of????
On Oct 21, 7:52 am, Gerry wrote:
An interesting link to whet your appetitehttp://images.google.com/imgres?imgurl=http://www.dmdaustralia.com.au... Here's a better link I hope http://www.dmdaustralia.com.au/block.html |
what do you make moulds out of????
On Sat, 20 Oct 2007 21:38:27 -0500, "chips-'n-swarf"
wrote: what I'm asking about is the materials used to build the casting moulds for little model engine crankcases. ones cast in alooominumm. what sort of head do you need in the aluminium to get a reliable mould filling? what aluminium alloys do you use for casting? which alloys do you avoid like the plague? how much venting do you guys find necessary? how long do your moulds last? Sand casting is probably your first choice, both for cost and something the home shop can accomplish. Oil bonded sand, often called petrobond, is the easiest to work with. Water bonded sand, sometimes called green sand, needs a little more work to keep it in condition and needs more venting. It usually isn't necessary to vent petrobond molds for aluminum. Sand casting is a one shot mold that you simply remold for your next casting. The pattern lasts a long time. 356 alloy aluminum is a good starting point or you can remelt aluminum bell housings, etc., to get a feel for how the process works. Stay away from extrusions and beverage containers unless you are prepared to experiment with additives. A couple inches of sprue should give you enough "head", however, to get complete castings gates and runners will likely be necessary. Take a look at this video on YouTube: http://www.youtube.com/watch?v=NKXj5Ng3X58 and also by looking at "more from this user" you will find a short video about investment casting. If you follow the link to my projects page, there are a couple examples of lost foam and also a project using gates and runners. Rod I've not made a melt for some years now but I am well versed in greensand casting. I made my own casting sand using washed sand and about 5% bentonite rubbed to coat each sand particle and 5% moisture. If anything my sand is just a shade coarse but it vents extremely well. I have two nemisis projects.both are tiny compression ignition model aircraft engines. one is to remake a 0.1cc Nano that actually runs beyond a prime this time. the other is to make a mills 0.75cc replica. it is the steel mould for gravity casting the crankcase that I was asking about. I think the key to good micro size screwthreading is to use an alloy harder than 1214 free machining steel. it is wonderful for general turning but useless for threading because it tears. I havent given up trying on this quite yet though. TUMESFFFF |
what do you make moulds out of????
On Sun, 21 Oct 2007 06:03:59 -0700, Gerry wrote:
On Oct 21, 7:52 am, Gerry wrote: An interesting link to whet your appetitehttp://images.google.com/imgres?imgurl=http://www.dmdaustralia.com.au... Here's a better link I hope http://www.dmdaustralia.com.au/block.html now THAT was impressive. Tumesffff |
what do you make moulds out of????
Jon Elson wrote:
I'm not sure the auto makers use them, either. Â*Either iron or aluminum engine blocks are usually sand-cast. I'm sure that at least valve heads (out of aluminium) are cast in steel moulds. Just the ports and water ways are sand cores. Sand casting is too expensive for high volume productions. Nick -- The lowcost-DRO: http://www.yadro.de |
what do you make moulds out of????
"Nick Mueller" wrote in message ... Jon Elson wrote: I'm not sure the auto makers use them, either. Either iron or aluminum engine blocks are usually sand-cast. I'm sure that at least valve heads (out of aluminium) are cast in steel moulds. Just the ports and water ways are sand cores. Sand casting is too expensive for high volume productions. Nick -- The lowcost-DRO: http://www.yadro.de It depends on the accuracy, size and reusability desired. Plaster, rtv, sand are common materials. For big metal objects there are other choices in foundry practice. There are plenty of good books out there on the processes. Regards, Edward Hennessey |
what do you make moulds out of????
Stealth Pilot wrote:
it is the steel mould for gravity casting the crankcase that I was asking about. Did you ever try petrobond? A friend made his very first casting (with lots of mistakes; riser, feeder) and the result was just incredible. Walls with 1mm thickness came out perfect. Nick -- The lowcost-DRO: http://www.yadro.de |
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