Buying Used Cold Chamber Die Casting Machines
The process for these machines start with melting the metal in a separate furnace. Then a precise amount of molten metal is transported to the cold-chamber machine, where it is fed into an unheated shot chamber (or injection cylinder). This shot is then driven into the die by a hydraulic or mechanical piston.
Cold-chamber machines are used when the casting alloy cannot be used in hot-chamber machines; these include aluminum, zinc alloys with a large composition of aluminum, magnesium and copper. The biggest disadvantage of this system is the slower cycle time due to the need to transfer the molten metal from the furnace to the cold-chamber machine.
Purchasing of cold chamber die casting equipment goes along with modern high-volume die casting production lines. As these lines are upgraded, and newer technology becomes available, earlier equipment becomes available for re-sale as used or second-hand.
The purpose of this site is to provide an overview of such used cold chamber die casting equipment, so that die casting plant owners may encourage economy and so raise profits in order to improve their return on investment.
Cold chamber process:
- When the pressure chamber is filled with a molten metal, the plunger starts traveling forward and builds up a pressure forcing the metal to flow through the sprue to the die cavity.
- After the metal has solidified, the plunger returns to its initial position allowing a new portion of the molten metal to fill the pressure chamber.
- The die then opens, and the ejector pins removes the casting from the die.
- The casting cycle now may be repeated.
Design aspects of die casting
- Since the metallic mold of a die casting expands when it is filled with a molten metal and then both the casting and the mold shrinks during cooling, the shrinkage allowances taken in the die mold design are smaller than those in the Sand casting.
- Parts of 0.05 lb (20 g) to 75 lb (34 kg) may be cast.
- The section thickness of permanent mold casting may vary in the range 0.02” - 0.5” (0.5-12 mm).
- The dimensional tolerances are 0.01-0.03” (0.25-0.75 mm) depending on the casting section thickness.
- Allowances of 0.004-0.01” (0.1-0.25 mm) are taken for the dimensions crossing the parting line of the mold.
- The draft angle is commonly about 1%.
- Lower (as compared to other casting methods) radii of the part corners may be achieved by die casting process.
- Changes of the section thickness should be as gradual as possible.
- The parting line should not cross critical dimensions.
- Water-cooled dies may be used for obtaining faster Solidification at a desired direction.
- The dies are fabricated from tool and die steels. The die life is determined the ability of the material to withstand wear caused by the molten alloys and fatigue caused by multiple heating and expansion.
- The cores are made of refractory ceramic materials. Sand based cores are not applicable due to their insufficient strength under pressure applied in die casting.
(Sources: Wikipedia, substech.com)