The metal pumping system is shown in fig. 1, which consist essentially of pressure and power cylinders plunger, gooseneck and nozzle is typical of hot chamber injection (shot ) systems. The gooseneck containing the pressure cylinder and plunger is submerged in the molten casting metal and is thus at the temperature of the metal bath. This arrangement allows the metal to be injected into the die cavities in minimum time and with minimum decrease in temperature.
With the plunger in the up position as shown in fig. 1, molten metal flows from the pot into the pressure cylinder through the intake ports. With the die closed and locked, the power cylinder is energized to move the plunger downward. This seals off the intake ports. With further downward movement of the plunger, of the plunger the molten metal is forced through the gooseneck channel and the nozzle into the die cavity. After a present time to allow the metal to solidify in the die cavity, the power cylinder is activated in the reverse direction, thus pulling the plunger up. This uncovers intake ports, and metal flows from the port into the pressure cylinder the machine are ready for the next cycle. The power cylinder can be actuated either by air or oil.
Castings weighing from a fraction of an ounce to about 50lb can be produced in hot chamber machines of metal cast with one stroke can be varied by using different sizes of gooseneck assemblies. The weight of castings that can be made depends on the alloy being cast, the projected area of the shot, and the locking pressure.
Depending on degree of mechanization, process variables and the part being cast, hot chamber machines are generally at rates of 50 to 500 shots per hour. Special machines greatly exceed this rates, ranging from 2000 to 5000 shots per hour upto 18000 shots per hour for a zipper- casting machines.
The gooseneck is made of gray, alloy or ductile iron, or of cast steel. The choice of material is dictated by operating pressure, casting metal, and cast. Common practice is to insert a replaceable liner in the bore of the pressure cylinder (Fig. 1). The material for the liner should have good wear resistance and resistance to softening at operating temperature. The goosenecks usually have a nozzle seat (Fig. 1), which can be replaced when the
spherical sealing surface becomes damage. A good seal must be maintained at the junction of the components (pressure cylinder, gooseneck channel, nozzle seat, and nozzle) through which the molten metal flows to the die.
Liners and nozzle seats usually are made from H13 or a high speed tool steel, nitrided alloy steel, or stainless steel. Nozzles must be able to resist the washing action of the molten metal and the scaling action of externally applied heat, and must be strong enough at operating temperature to resist the pressure of molten metal. Alloy cast iron, H13 tool steel, and stainless steel are among the materials used for nozzles.
Life of the pressure cylinder may be extended by honing the inside wall of the cylinder (often as much as 0.030 in. oversize in inside diameter ). A proportionally larger plunger is then used regardless of whether rings are included. A plunger-to-cylinder clearance of 0.002 to 0.003 in. per inch of bore diameter is considered optimum.
B.3.1.2
HOT CHAMBER MACHINES AND PARTS
Regardless of types of machines used, it is essential that die halves, cores and other movable sections be securely locked in place during the casting cycle. Generally, the lamping force is governed by (a) the projected area of the casting (measured at the die parting line) and (b) the pressure used to inject metal into the die. Most mechanisms actuated by hydraulic cylinders (sometimes air pressure) to achieve locking. Others use direct acting hydraulic pressure. Safety interlock systems are used to prevent the die during casting cycles. Die casting machines.
Hot chamber machine:
- A type of die casting machine in which the pumping chamber submerged in molten metal to inject metal into the die. Plunger or air pressure is applied in the chamber of the machine. Which are known respectively plunger die casting machines and air operated die casting machines.Gooseneck machine: -
The hot chamber machine is also called as gooseneck machines as the pressure vessel or metal injection pump has the metal channel in the shape ofgooseneck.
Holding furnace:
- Furnace used for holding molten metal preparatory to pouring castings. This provides molten alloy at the desired temperature.Locking force or clamping force :
- The capacity of die casting machine to resist metal injection force which tend to separate the die halves.Platens:
- A member in die casting machine that supports die halves.Movable: -
This holds and supports the moving die half. The movement of this platen is used in the actuation of the ejector system in the die.Stationary platen: -
This holds and supports the cover die half which generally contains the cavity.Tie rod: -
A bar used in a casting machine to hold dies against pressure; also serves as a way along which the movable die platen slides.Toggle: -
Linkage in a casting machine employed to multiply pressure mechanically in locking the dies. Also, linkage used for core locking and withdrawing in a die.Injection cylinder: A hydraulic cylinder which is used for actuating the injection plunger. Injecting force: The force exerted by the injection plunger on the molten alloy in the shot sleeve.
Injection stroke:
- It is the total travel of the injection plunger.Induction furnace:
- Furnace heated by resistance of metal to flow of flux lines induced by alternative electric current.Injection: -
The act or process of forcing molten metal into a die.Plunger machines:
- Die casting machines having a plunger in continuous contact with molten metal (Hot chamber machines).Reverberatory furnace: -
A furnace having a vaulted ceiling that throws back the flame and heat toward the hearth of the upper surface of the charge to be melted.Shot: -
That portion of the casting cycle in which molten metal is forced into the die.Plunger: -
That part of the die casting machine which forces the metal alloy into the die. Distance between tie bars: The distance between tie bars that is available for clamping the die halves. The center distance between tie bars minus the size of one diameter of the tie bar gives this distance. (Fig .1)Maximum clamp stroke:
- It is the maximum amount of stroke the moving platen of the machine can travel from the open position to the close position. (Fig.1)Minimum die thickness or minimum closed daylight: When the machine is in the fully closed position the minimum distance that is available between the fixed and moving platen for fixing the die. The moving platen will not travel further to meet the fixed platen. (Fig. 1).
Maximum die thickness or maximum closed daylight: It is the maximum distance between the fixed platen and moving platen in the closed position, which can accommodate a die of this thickness.