Ladle
When you are ladling the alloy, you should have several objectives in mind.
First, you want to ladle the correct amount of alloy. The correct amount of
alloy is that amount that will completely fill the cavity and runner system
and end with a biscuit that is thick enough to remain liquid as the casting
freezes so pressure can be applied to the casting through the gate. Generally,
the biscuit should be 1½-2 times thicker than the main runner leading from
the biscuit. For example, if the runner going away from the biscuit is ½
inches (13mm) thick, then the biscuit should be ¾-1 inches (19-25mm) thick
as a rule of thumb. The cooling at the biscuit, the plunger tip and the biscuit
block is very effective and you want the biscuit to freeze last. If the biscuit
or runner freeze before the alloy in the die cavity does, you will be
ineffective in applying intense metal pressure to the casting as it solidifies.
This will result in defects if this happens.Next, the amount of alloy to be ladled must be consistent. When the shot is
made, the transition point from slow to fast shot, and the point of
intensification depend on the alloy volume. The transition from slow to fast
shot takes place after the sleeve has filled with alloy and before the alloy
reaches the gate. Similarly, intensification is started as soon as the cavity is
completely filled with alloy. The settings for these transition points, slow to
fast shot and intensification, are usually determined by positioning a limit
switch along the plunger travel. When the plunger passes the (slow to) fast
limit switch, it trips the arm and activates the fast shot. Similarly, near the
end of the injection stroke, another limit switch is tripped activating the
intensifier. If too much alloy is ladled, the sleeve will fill quickly and alloy
will also fill the runner and gate before the plunger reaches the (slow to) fast
limit switch. In this case the alloy could start filling the cavity at very low
velocity causing defects and possibly freezing at the gate. If too little alloy is
ladled, the plunger will arrive at the fast shot limit switch before the
chamber is filled with alloy. This could result in lots of turbulence and
mixing air with alloy in the sleeve and porosity defects in the casting. A
biscuit size difference as small as 1/4 inch (6mm) can be very significant
with respect to forming defects; for this reason it is important to ladle a
consistent amount of alloy.
Another objective of ladling is to pour clean alloy. Since the dip well of the
holding furnace is usually not covered during operation, the alloy is exposed
to air. When this happens, the alloy in contact with the air oxidizes, or forms
a chemical bond with the oxygen on the air. In the case of aluminum it forms
aluminum oxide and with zinc it forms zinc oxide. It is undesirable to have
these oxides in the casting. For the most part, these oxides float on top of the
alloy bath and are referred to as “dross”. Avoiding the oxides is usually not a
problem in hot chamber die casting because the gooseneck filling holes are
below the alloy level in the holding furnace. However, in cold chamber die
casting, ladling can be a problem because the alloy is dipped from the top of
the bath in the dip well. In this case the dipping technique is important. You
must make sure the accumulated oxides are not allowed into the ladle. The
recommended procedure is to use the ladle to push the dross back from the
surface and dip out clean alloy.
If ladling is done manually, you must be aware of the proper ladling
technique and use it consistently. You will notice that the dross in the dip
well will build up over time. This occurs slowly, every cycle, as you push
the accumulated dross out of the way to dip out clean alloy, a fresh alloy
LadleWhen you are ladling the alloy, you should have several objectives in mind.First, you want to ladle the correct amount of alloy. The correct amount ofalloy is that amount that will completely fill the cavity and runner systemand end with a biscuit that is thick enough to remain liquid as the castingfreezes so pressure can be applied to the casting through the gate. Generally,the biscuit should be 1½-2 times thicker than the main runner leading fromthe biscuit. For example, if the runner going away from the biscuit is ½inches (13mm) thick, then the biscuit should be ¾-1 inches (19-25mm) thickas a rule of thumb. The cooling at the biscuit, the plunger tip and the biscuitblock is very effective and you want the biscuit to freeze last. If the biscuitor runner freeze before the alloy in the die cavity does, you will beineffective in applying intense metal pressure to the casting as it solidifies.This will result in defects if this happens.Next, the amount of alloy to be ladled must be consistent. When the shot ismade, the transition point from slow to fast shot, and the point ofintensification depend on the alloy volume. The transition from slow to fastshot takes place after the sleeve has filled with alloy and before the alloyreaches the gate. Similarly, intensification is started as soon as the cavity iscompletely filled with alloy. The settings for these transition points, slow tofast shot and intensification, are usually determined by positioning a limitswitch along the plunger travel. When the plunger passes the (slow to) fastlimit switch, it trips the arm and activates the fast shot. Similarly, near theend of the injection stroke, another limit switch is tripped activating theintensifier. If too much alloy is ladled, the sleeve will fill quickly and alloywill also fill the runner and gate before the plunger reaches the (slow to) fastlimit switch. In this case the alloy could start filling the cavity at very lowvelocity causing defects and possibly freezing at the gate. If too little alloy isladled, the plunger will arrive at the fast shot limit switch before thechamber is filled with alloy. This could result in lots of turbulence andmixing air with alloy in the sleeve and porosity defects in the casting. Abiscuit size difference as small as 1/4 inch (6mm) can be very significantwith respect to forming defects; for this reason it is important to ladle aconsistent amount of alloy.Another objective of ladling is to pour clean alloy. Since the dip well of theholding furnace is usually not covered during operation, the alloy is exposedto air. When this happens, the alloy in contact with the air oxidizes, or formsa chemical bond with the oxygen on the air. In the case of aluminum it formsaluminum oxide and with zinc it forms zinc oxide. It is undesirable to havethese oxides in the casting. For the most part, these oxides float on top of thealloy bath and are referred to as “dross”. Avoiding the oxides is usually not aproblem in hot chamber die casting because the gooseneck filling holes arebelow the alloy level in the holding furnace. However, in cold chamber diecasting, ladling can be a problem because the alloy is dipped from the top ofthe bath in the dip well. In this case the dipping technique is important. Youmust make sure the accumulated oxides are not allowed into the ladle. Therecommended procedure is to use the ladle to push the dross back from thesurface and dip out clean alloy.If ladling is done manually, you must be aware of the proper ladlingtechnique and use it consistently. You will notice that the dross in the dipwell will build up over time. This occurs slowly, every cycle, as you pushthe accumulated dross out of the way to dip out clean alloy, a fresh alloy
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