Here are some pictures of my Austin Seven engine project. block1 is the block with most of the core locating extentions attached. The block is the white bit, the orange bit on top has the cylinder core locators and valve core locators, they are on a plate 2mm thick to add a bit of meat to the casting for machining. The blue bit on the bottom has the core locators and is also 2mm thick. The green part has the exhaust and inlet port core locators and is also on a 2mm plate. block2 shows the water manifold core locators on a 2mm plate. The small yellow "D" shaped part is where there is a core plug and I am using this as where the water core will be supported, one on each end of the block. The water core is also located by the water manifold. head01 and 02 are the top and bottom of the cylinder head. I have an earlier attempt at 3D printing model of this head that I am hoping to cast soon. head core (in red) is the core for the water passages in the head. head and core is a cutaway image of the head with the core. The large cavity under the green part is the valve chest. I will figure out how to produce the core pattern for this part. I am calling these parts "cores", I hope that is right. core mould bottom and core mould top will be 3D printed to make the head core. core mould top is in 3 pieces to make it easier to remove the core. The 3D printed head I have ready for casting is in two pieces. The bottom of the head fits inside the top of the head and forms a cavity so I can make the core first, remove it, and then use the same pattern to make the head mould. I will use green sand casting for this head, but there is zero draft on the sides, so I am not expecting success. I will take a picture of the end result, and then cut the casting in half to have a look inside, and take another picture. I am working my way through the sections of this site to discover what is the best way for me to make the block and head. The crankcase, which I haven't drawn yet, is as complicated as the head, only bigger. I am fairly certain that I can't sand cast them. The alowance for draft is something beyond me. I favour producing a silicone rubber mould from my 3D prints and then taking a wax or low melting point metal casting from the rubber. The wax or metal pattern would then be covered with investment of some description and later cast in aluminium. I did wonder about resin bonded sand as a way of producing a mould instead of the rubber and casting/investment route. Any thoughts? I am not sure how to attach my picture, so here goes! Lee Edit. Whoops! No picture names. I am sure you can figure it, or you shouldn't be playing with fire. Edit 2. The block is 145mm long by 67mm wide by 60mm high.
Lee, look at your full size heads. Try to find parting lines and their draft. As for the water jacket cores, mold your core in to halves, then scratch the vent and glue the pieces back together. With the simple draft cores you can mold and bake on a plate. Some of my later success was baking in a cast core box, but it was a complex core. What is your preferred core material?
ESC. I use sodium silicate with fine sand to make my cores. I think I am over gassing them with co2 though. I put the mould with the core in a small box and feed the gas in until it escapes from another hole that has a candle in front of it. High tech! The candle flickers if it is air, but goes out if it is co2. I then leave it in the box for several hours. The biggest core I have made was about 1/2" dia by 4" long tapering down to 1/8". I had to put thin twisted wire in the core to keep it together. The engine I am using for measuring is 91 years old. It is very hard to find any parting lines. I did wonder if Austin ground off a certain amount of flash.
I use phenolic urethane no-bake resin bound sand and the stuff is very convenient apart from the short shelf life of the resin. The sand moulds can be left for years before use and have superior strength to green sand which eliminates the need for flasks: you can make as many moulds as you have sand and resin for. The sand can't be easily reused without burning off the resin in a kiln but that's a minor issue. Here's some local guys casting Austin Healey blocks in aluminium, pretty sure they are using resin sand: https://healeyfactory.com.au/servic...engine-development-and-manufacturing-process/ Yep, resin bound sand: https://healeyfactory.com.au/services/dmd-australia/dmd-aliminium-engine-block-pattern-making/ These are resin sand moulds for a record player turntable project, the patterns are epoxy soaked MDF then machined to shape.
Thanks for that Mark. I had tried to find out more about resin bound sands but there seemed to be little information available. Now I know more I can start searching again. Lee
Here are a couple threads that may be of interest: http://forums.thehomefoundry.org/in...mal-baking-temperature-and-sugar-content.794/ http://forums.thehomefoundry.org/in...r-core-making-in-cast-iron-molding.702/page-2 I have in the last few months been using propylene carbonate marketed by Clay Planet as Chem-Bond 210 https://shop.clay-planet.com/chembond-catalyst-210.aspx to catalyze my sodium silicate. It is easy to use and very reliable. I do not have to wonder if I got enough/too much CO2 into the detailed depths of my cores. I can strip in about 3 hours at 70 degrees and maybe sooner than that. But that is the time I have been waiting. Denis
How many degrees of draft do you allow for? I have to make new 3D printed patterns, so I may as well try and add draft. How hard does this set?
I have in the last few months been using propylene carbonate marketed by Clay Planet as Chem-Bond 210 https://shop.clay-planet.com/chembond-catalyst-210.aspx I will look that up to see if there is an equivalent over here in the UK. How did you get my comment in your posting? Lee
Just hit the "Reply" button on the lower right. That copies, pastes and highlights the text in a reply frame in which you can type your response. Denis
Wow Mark, that resin bound sand stuff looks like it could be a solution for something I want to make. Are those turntable molds reusable? (I supposed that would be the purpose of it?) Or is the resin/sand mold still destroyed in the process of extracting the finished item?
The molds from the resin bound sand are not reusable. Professional foundries have equipment which recycles the sand but at hobbyist level, it's not practical to reuse the sand either.
I will say I do reuse my silicate-bound sand. I crush it up in the muller and add it to my green sand heap along with a bit of western and southern bentonite. Seems to work just fine that way and I figure the small amount of silicate should not cause problems. None identified so far. Denis
I use three degrees at a minimum, aim for five and up to eight degrees depending on the pattern. Once the sand is in the pattern and tamped down (no ramming needed), you can tap the pattern sides gently to added a small bit of clearance between sand and pattern. The resin sand hardness depends on the resin content, too much and it sets like concrete, while having just the right content gives sand that can be easily filed and carved to add venting, gating and features. The resin eventually chars and disintegrates, releasing the casting from the sand. The process can be used with aluminium, brass/bronze and iron with a suitable mould wash coating.
No, I have not. I would try it if I were in a pinch for sand as I bet it would work fine. But, unless compelled to change, I’ll stick with what is working well. Denis
I seem to think Myfordboy had a session with resin bound sand? (That could be my appalling memory but he mas know UK suppliers)
