This is the quick explanation of casting metal and details the making of a a mould using an original part as a template. If your are interested in a more detailed explanation of casting go to my casting webpage.
Rather than making a template, I tried using the original plastic mirror base as a template. Aluminum shrinks about 3% or so depending on how hot it is when you pour it. Since this part is just for holding a mirror, the shrinkage is not important and can be ignored.
Some green sand was placed in the empty flask . The base was placed in the cope side of a flask and more green sand was screened on top using a riddle (buzz words).
The plastic part ready to become a template was test fitted to see the best placement
Screening out the lumps using a riddle
The green sand (actually black in color) is pressed into the flask by fingertips, more sand was placed on top and rammed into place using the sharp end of the ram. More sand was placed on top using the flat end of the ram and then some sand sprinkled on top and rubbed into place using a piece of plywood. The last part is to make sure that the sand is perfectly level and flat so that when the flask is turned over and rammed from the other side, the sand can't have any room to move and fall out.
Making sure the sand is flat by rubbing with plywood
When the flask was turned over, only a small portion of the base was visible. Now the job of coping out the template started. Excess sand was carefully spooned out following the parting line of the plastic. It takes a steady hand and lots of patience to finish the coping out.
Carefully removing sand along the bases plastic parting line - coping out
After coping out the part, parting dust is sprinkled over everything. Then the empty drag side of the flask is placed on top. Green sand is riddled on, pressed in with fingertips, more sand added and rammed solid. After the drag side is completely rammed and leveled. The two sides of the flask are separated and the base was carefully removed.
Flask is separated, template carefully removed
Notice that the each of the flask's green sand is not flat and follows the curve of the template. Next air vents were added using a piece of coat hanger wire to make vent holes and a sprue was added for pouring the molten aluminum in.
Pouring the aluminum into the mould
The aluminum pours at about 1200 deg F and uses a steel crucible. You can see that the temperature is much lower than iron as the crucible and aluminum are not glowing at all. Iron glows bright red!
Here's the piece still sitting in half the mould
Once the piece is removed from the sand and cleaned. The excess aluminum caused by the sprue and the tiny vent holes, that have filled with aluminum during the pour, are cut off. To see how the part came out, view the close up picture at the start of the Casting Aluminum Side Mirror Bases webpage.
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