Metal Exam Part 2 Flashcards
True or False: The diacro bender can bend heavier stock than sheet metal benders.
True.
(Hopefully James won’t put this part on the exam but who knows with him…)
Material limits for the BCIT diacro bender:
* round mild steel bar1”
* square mild steel bar 3/4”
* steel tubing (16 gauge) 1-1/4”
* standard iron bar 1” OD
* flat bar (bend on side) 3/8”x 4”
* flat bat (bend on edge) 1/4” x 1”
* mild steel angle iron 3/16” x 1” x 1”
* mild steel channel 3/16” x 1/2” x 1”
What shapes can the diacro bender produce?
- circles
- eyelets
- zero-radius bends (tight corners)
- scrolls
- squares
- springs
When scoring of the material during forming is a problem on the diacro bender, what should you do?
lubricate the forming nose or using a
forming roller instead
What materials can you use with the hossfeld bender?
- Flat and round stock:
~ radius bends
~ square bends - Angle iron:
~ internal bends (after relief cuts
made)
~ external bends (relief cuts needed) - Tubing bends
- Scrolls
What can happen if you attempt to bend brittle materials?
The material may shatter - do not attempt
What are the 4 characteristics Foundry Sand must exhibit?
- Permeability - to allow gasses produced during pouring of molten metal to pass or vent through the mold. Permeability is inversely related to the percentage of clay content.
- Green Compressive Strength - the structural integrity of the sand grains held together by the clay. This determines how the mold will withstand handling and the forces of molten metal entering the mold cavity. Green Compressive Strength is directly related to the percentage of clay content and moisture.
- Dry Strength - upon contact with molten metal the mold dries rapidly. The sand must resist the forces of the metal to prevent erosion, cracking, and other deterioration of the mold cavity.
- Flowability - the ability to conform to the shape of the pattern as the mold is made. This is governed by the size and shape of sand grains and clay content.
Foundry sand is really a mixture of what two components?
Sand and Clay
What are the most common clays used in Foundry sand?
Bentonite and Fire Clay
What type of sand is usually used for aluminium casting? (in combination with clay)
Silica Sand
________ a process which mixes the sand and clay with a heavy roller with a kneading action.
_________ helps maintain high green compressive
strength.
Mulling
What are the Two Broad categories of Foundry Sand?
- Natural Bonded Sand
is used just as it is dug from the ground, making it inexpensive. It doesn’t produce smoke and fumes when metal is poured, is widely available, and may function over a wider range of moisture content (natural sands require 6-8% moisture content).
- Synthetic Sand
is produced through the blending of various types of sands and
clays to offer greater control of permeability, green compressive strength, and moisture content. Most synthetic sands require a 3% moisture content, resulting in less steam generation and greater permeability.
What is ‘Tempering’ foundry sand?
The process of adding an appropriate amount of water, for natural
bonded sands or oil for synthetic sands to allow the clay to hold the grains of sand together.
When tempering Foundry sand what occurs with too little moisture and what occurs with too much moisture?
too little moisture = mould will be weak and fall apart
too much moisture = generation of steam and reduced
permeability
both problems produce faulty castings
True or False: Oil-Tempered Synthetic Sands (Petrobond) require water when tempering.
FALSE
What is used to temper Oil-Tempered Synthetic Sands (Petrobond)?
-Special flour-like binder material (Petrobond)
-non-detergent oil (10 weight)
-a catalyst (P-1 or Methyl Alcohol will work)
Petrobond requires periodic rejuvination through the addition of small amounts of 3 things:
Binder, Oil, Catalyst
What is the procedure for Mulling Foundry sand?
- shovel the old oil base sand into the Muller (or cement mixer)
- add 1lb. of binder to every 100 lb. of sand – mull for 1 min.
- slowly pour in 1lb. of 40-weight oil – mull 10 min.
- add 1 ounce of P1 catalyst – mull for 5 min.
What is the procedure for making a sand mold for casting?
- place the drag on the molding board with the alignment pins down
- place the mold in the centre of the drag (small side up)
-
lightly dust the pattern with parting compound
4.riddle facing sand onto the pattern, covering 2” above the pattern - fill the drag with unriddled backing sand
- use the peening end of the bench rammer to ram sand around the pattern (one pass all over with wedge, one pass with flat end)
- add additional unriddled sand to allow the drag to be fully packed
- use the butt (flat) end of the bench rammer to complete packing
- strike off the excess sand with the strike-off bar
- place the bottom board on top of the drag & turn it over
- remove the molding board
- use the slick & oval or trowel to smooth & level the sand if necessary
- press the sprue & riser pins into the sand about 1” away from the pattern
- dust the pattern with parting compound (use sparingly)
- riddle, ram & strike-off the sand in the cope as you did before
- carefully lift the cope from the drag & place it on the edge
- remove the sprue & riser pins
- cut a gate from the mould to the sprue & the riser gate should be ≈ 1/2” X 1/2”
- place a screw into the pattern & tap the screw lightly
- carefully lift the pattern straight up from the mould
- use your finger or the slick & oval to smooth the resulting
surfaces in the gates - remove any loose particles using moulder’s bellows
- carefully reinstall the cope on the drag
- use your fingers to smooth the resulting holes into a funnel
shape
-ready to cast
5 steps to water-tempering foundry sand:
- Spread the sand a few inches deep on the floor. If new sand or clay is to be added,
distribute it evenly over the old sand and then mix by shoveling. - Sprinkle tempering water over the entire surface of the sand. Mix the sand and
water by shoveling. Err on the side of caution - don’t add too much water. Molding
sand is strongest when it appears to be slightly dry. Too much water gives the
impression of suitable tempering but results in low strength when the mold is used. - Test water content by grasping a handful of sand (palm facing down) and squeezing
firmly. Turn your hand over, relax the grip, and allow the sample to roll forward so
the sharp edges roll to the top side. Flowability is indicated by sharp edges, a clean
contour, and smooth surface. If the sand tends to crumble or is rough, it’s too dry -
add water sparingly and try again. - Grasp the sample by the ends and bend it. Good green compressive strength is
shown by a sharp break and toughness (resistance to breaking). - Riddle the sand to remove impurities and to aerate it to improve flowability around
the pattern.
What are the 5 basic steps to sand casting? (simplified)
- Prepare the Mould
a) Make the Pattern
b) Make the mould cavity
2) Prepare material for casting
3) Pour metal into mould: metal of proper temperature is introduced rapidly so the sprue is kept full.
4) Metal is allowed to solidify.
5) Mould is broken up to remove the casting, and sand is reclaimed for reuse
Name AT LEAST 5 things needed to cast aluminum
*pattern
*flask
*bottom & molding boards
*sand
*shovel
*rammer
*sprue & riser pins
*parting sand
*riddle
*draw spike
*striking bar
*crucible
*aluminum
*furnace
*skimmer
*degasser rod &tablets
*lifting & pouring tongs
*slick/spoon
What sand is easiest to work with when aluminum casting?
Synthetic sand
True or False: when aluminum casting the metal is poured at over 1300ºF (740ºC).
True
What is the minimum you should fill a crucible when melting?
Do not melt less than half a crucible full as this is hard on it
What is the maximum you should fill a crucible when melting and why?
Fill the crucible loosely to the top lip only. The metal must be able to rattle if shaken.
Pieces which are jammed in can expand when heated and break the crucible.
What safety precautions should you take before pouring melted aluminum?
Put on safety gear: leather shoes, leggings or pants, jacket, mitts, and helmet
with screened face shield. Turn ventilation fan on.
What is the procedure for heating and pouring aluminum?
- Weigh out aluminum to suit the crucible. Do not melt less than half a crucible full as this is hard on it.
- Fill the crucible loosely to the top lip only.
- Centre the base block and put a piece of cardboard on it to prevent its sticking to the
crucible. If the furnace is hot, first dampen the cardboard so it doesn’t burst into flame. - Place the charged crucible centered on the base block.
- Close the lid and confirm that it seats properly all around its circumference. Remove any obstruction which prevents proper seating. Open the lid and leave it to the side.
- Arrange the pouring area for safety and efficiency. Consider access to the flasks, ingot molds, etc. Be sure there are no tripping hazards present. Confirm that the lifting tongs, pouring shank, degassing plunger, skimmer, and garbage container are present and conveniently located.
- Put on safety gear
- With lid left to the side, light the furnace – follow posted directions.
- After a minute of warm up, close lid. Fine tune the flame.
- Using tongs, put the remaining metal around the lid of the furnace, but not covering the hole in any way. This will drive any moisture off the ingots.
- At first sign of melting, add about 2 tablespoons of Coveral flux (pink powder). Wrap in aluminum foil and throw in.
- As a molten heel develops, slowly and carefully add the rest of the preheated metal with preheated tongs. No moisture! No splashing.
- When the metal is all melted, add the rest of the flux (2 Tbs.).
- Monitor the metal for a shut off temperature of 1300º-1350ºF (705º-732ºC).
- Shut off furnace (including gas valve), open lid, briefly heat the skimmer and plunger over the furnace (not metal) to preheat and dry.
- Monitor temperature. As soon as the temperature peaks, degas with 1/3 to 1/2 tablet.
Hold down with plunger until bubbles stop, then move up and down without breaking
surface of metal (to stir the metal). - Carefully remove the crucible and place in pouring shank. Be sure the crucible is secure in the lifting tongs and move slowly.
- Skim with preheated skimmer. Place waste in metal garbage can.
19.Check temperature. Pour at about 1320º-1375ºF (715º-745ºC). - Pig any remaining aluminum - do not leave in the crucible unless you intend to place it back into the furnace to immediately melt more metal for casting. If the aluminum is allowed to solidify in the crucible it will likely expand and crack the crucible when it is next heated.
Explain what a misrun is and how it is caused.
A casting which was not successful because the mold was not filled entirely with metal.
- metal poured too slowly or too cold.
- Sprue too short or small, gating too small.
- Natural sand contained too much water, resulting in fast cooling of metal
