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Sand casting
Outline
Requirements to sand
Types of sand
Advantages of sand casting
Disadvantages of sand casting
Steps for Sand Casting
Sand casting is a good option, if you already have a part. And you
can draw a parting line on the part so that the both halves can be
pulled from the sand without distorting the sand.
Requirements to sand
• Ability to retain mold shape during packing and pouring.
• High temperature stability.
• Permeability for the gases liberated from the mold and solidifying metal.
• Collapsibility - ability of the sand to be shake out.
Types of sand
• Green sand.
• petro – bound sand
• Sodium silicate bonded sand.
Advantages of sand casting
• Low cost of mold materials and equipment.
• Large casting dimensions may be obtained.
• Wide variety of metals and alloys (ferrous and non-ferrous) may be cast (including high melting point metals).
Disadvantages of sand casting
• Rough surface.
• Poor dimensional accuracy.
• High machining tolerances.
• Coarse Grain structure.
• Limited wall thickness: not higher than 0.1”-0.2” (2.5-5 mm).
Steps for Sand Casting :-
Place your part/s on the molding board. Sprinkle
them with parting dust. Simple Backing Soda works
well as parting dust and it's cheap.
1
Place a frame, called the "drag" around the
part/s, then start adding your sand, being
sure to tamp it in well around the parts,
especially when there are fine details.
2
Once the "drag" is full, level the sand with
the top of the frame using the other board
or "bottom board" that will also be
used to cover the drag. Then hold onto
both boards and turn the flask over so the
"bottom board" really is on the bottom.
3
4
Remove the molding board.
5
Use a knife or blade to excavate the sand
around the part/s just until you can safely
lift the part from the sand without disturbing
the remaining sand.
6
Add a "sprue" or the hole through which
your molten metal will be poured. I am
using a pipe to mold the sprue. First
pushing one end into the sand to remove a
core and form a hole that is a little deeper
that the bottom of the part/s. Then add
parting dust.
7
Place the pipe back in place to from the
sprue. Paper towel rollers work well if you
don't have a piece of pipe. Then set on the
top frame or the "cope". Latch the frame in
place if you have latches.
8
Add more sand and again gently tamp it in around
the part as well as the pipe to from the sprue.
There are special tools for this, almost anything
including your fingers works well. A blunt 5 pound
bock of steel make a good ram for packing frames.
Larger frame will need to be more tightly packed.
9
Flatten off the sand level the the top edge of the
frame or "cope" and also form a funnel cup around
the pipe that is forming the sprue. This will give
you a bit larger target when you pour the molten
metal. Be sure to leave some sand between the
funnel opening and the wood frame.
10
Gently remove the pipe that was forming
the sprue. Then place the "molding board"
on top.
11
Unlatch the frames and carefully lift off the
top frame or "cope" and set it on its
side. You should be able to rest it on its
top, but less movement is better.
12
Using a couple of knife blades, delicately
lift the part/s from the bottom frame or
"drag". Be careful to lift the part/s straight
up so as not the disturb the sand.
13
Using a knife or blade carve out the "gating" system
that will allow the metal to flow into the part and the
air to flow out. The "gates" connect the sprue to the
part a little above the bottom of the sprue. The
vents are very small channels that run from the
smallest section of the part to the edge for cope.
14
Time to melt some aluminum.
15
Pour the flask with molten aluminum. Don't
pour too slowly or the aluminum will harden
too quickly in the gate, coking the part off.
16
After 5 minutes the flask can be opened for
inspection.
17
Final Parts next to original after the being
brushed off.
Any questions ??