- Ice components can last without melting up to 45 min in ambient temperatures as high as 20C
- Use water to learn the insights of moulding techniques employed in real life metal castings
- Ice set has a total weight of 150g
The assembly of FROZOR is made of ice and plastic fixtures. The goal is to end with a rotor similar to an airplane propeller that rotates smoothly over ice bearings. There are three ice parts that you need to make: i) Shaft , ii) Hub and iii) Bearings . The bearings support the shaft at the front and at the back (two sets) and are made by the repetition of two identical ice components placed one on top of the other. The fixtures complete the assembly by providing a supporting structure for the ice set or ROTOR. Blades are used to aid the rotation of the shaft either by hand or if the iced parts have been made very precisely, by simply blowing air on to them.
Begin by 3D Printing and assembling the bearing mould . As shown on the drawing, this mould is made of two identical halves (01-FROZOR), an insert (02-FROZOR), an O-Ring (K1-OR100) and fasteners and nuts (K1-F12, K1-NT). The O-Ring fits the mould groove to prevent (or minimize) water leakage. Once the two halves are fastened together and the cavity filled with water, place the insert on top of the mould to create the bearing conical-bore. This insert is provided with two self-threading holes to be used with jack screws for de-moulding The mould is to be placed in the freezer to convert the water into ice. Do not limit your bearing production to only 4 components, produce as many spares as you can (note that making two moulds can help speed up the process).
To create the hub, you will need to combine the mould (06-FROZOR) and the disc (07-FROZOR). The disc is set to embed within the ice and its function is to connect hub and shaft and also to provide an assembly port (dovetail) for the rotor blades (10-FROZOR). Printing more than one disc will help you make different hubs for spares. In order to de-mould the Hub, jacking screws are also employed .
Finally, the most challenging bit to create is the shaft. Its mould requires of two different halves (03-FROZOR and 04-FROZOR), three O-Rings, fasteners, and end-covers (05-FROZOR). The shaft is set to form in the freezer at a horizontal position. This is done to relief through the central port, the expanding volume of water when converted to ice (if completely sealed, the expansion would break the mould!). Also, filling with water is recommended to happen through the top to avoid air bubbles (top cover open, thumb covering the central port). To demould, follow this sequence:
– Remove both end-covers, place vertically and wet with water the exposed end. Let it rest for a few minutes.
– Take out all fasteners and set the three self-threading jack screws on the respective half (03-FROZOR)
– Carefully screw in cross-sequence each jack-screw until the first half pops out . Then use a non-metal peaky object to push out the shaft from the remaining half.
Once both shaft and Hub are ready, push the shaft on to the disc cavity to connect both ice components. Once done, place the subassembly back into the freezer to help the junction solidify.
Notice that although ice formation is never exact, you can even surfaces by scratching lightly or by rubbing with your warm hands some portions of the ice. After every demoulding, place the ice components back into the freezer. It is expected that some water leakage will occur through the O-Rings as the plastic grooves in which these fit in have a “layered” surface finish. As long as the moulds are placed in the freezer immediately after filling with water, the component will come out right.
A lot of mechanical parts are produced by the casting of molten metal on to moulds (usually made out of sand) that shape the metal to practically any form. The process however is by no means easy, in fact it can be considered as a complete science. Foundries constantly seek for advanced methods to achieve good, wholesome castings. Foundries accumulate endless knowledge of tricks, techniques and even industrial secrets on how to cast components correctly.
A very basic trick is the provision of “draft angles” so that once solidified, the part can be demoulded easily. On FROZOR you can notice on every mould that this is the case. An ice cube, usually employs a draft angle of 20 ° to easily come out of its tray. The correct draft angle depends on a lot of different factors (including material type) and it is never the same. For the Shaft in FROZOR a 7 ° draft angle is used and 27 ° for the Hub.
The second basic trick is the use of INSERTS. Molten metal will flow by gravity and will level according to it. Inserts like 02-FROZOR can then be used to push the liquid around to take some of the desired shape. Its use is rather difficult, as the inserts need to be fixed to the main mould through ways in which: i) can be easily removed and ii) will hold strongly without exposing any fasteners or fixtures that are undesired on the cast part. Also, inserts can be employed as “embedded” components but their correct alignment within to the casting needs to be guaranteed by precise methods.
Finally, consideration needs to be given to the likelihood of trapped bubbles of air. As the liquid metal fills the different mould cavities, air needs to exit the mould without being trapped and forming undesired bubbles. Once the metal solidifies, its volume will contract, so computing the level of contraction is key so as not to end with undersized parts.
So casting is not as easy as it sounds, huh? Next time you meet anyone working in a foundry, make sure to let them know you appreciate how challenging their jobs can be.
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