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7.4.2.3 The die casting machine characteristic effects

There are two type of operation of the die casting machine, one) the die machine is operated directly by hydraulic pump (mostly on the old machines). two) utilizing the non continuous demand for the power, the power is stored in a container and released when need (mostly on the newer machines). The container is normally a large tank contain nitrogen and hydraulic liquid20. The effects of the tank size and gas/liquid ratio on the pressure and flow rate can easily be derived.



The characteristic of the various pumps have been studied extensively in the past [#!poro:Hhandbook!#]. insert the discussion about pump characteristic with the figure from the red folder notes The die casting machine is a pump with some improvements which are patented by different manufactures. The new configurations, such as double pushing cylinders, change somewhat the characteristics of the die casting machines. First let discuss some general characteristic of a pump (issues like empelor, speed are out of the scope of this discussion). A pump is mechanical devise that transfers and electrical power (mostly) into ``hydraulic'' power. A typical characteristic of a pump are described in Figure [*]. = 90 true mm

Figure: General characteristic of a pump

Two similar pumps can be connect in two way series and parallel. The parallel connection increase mostly the flow rate as shown in Figure [*]. The serious connection increase mostly the pressure as shown in Figure [*]. The series connection if ``normalized'' is very close to the original pump. However, the parallel connection when ``normalized'' show a better performance.

To study the effects of the die casting machine performances, the following functions are examined (see Figure [*]):

= 90 true mm

Figure: Various die casting machine performances
The functions ([*]), ([*]) and ([*]) represent a die casting machine with a poor performance, the common performance, and a die casting machine with an excellent performance, respectively.

Combining equation ([*]) with ([*]) yields

rearranging equation ([*]) yields

Solving equations ([*]) for , and taking only the possible physical solution, yields

The reduced pressure, , is plotted as a function of the number for the three die casting machine performances as shown in Figure [*].

= 0.4

Figure: Reduced pressure,, for various machine performances as a function of the Oz number
Figure [*] demonstrates that monotonically decreases with an increase in the number for all the machine performances. All the three results convert to the same line which is a plateau after . For large numbers the reduced pressure, , can be considered to be constant . The gate velocity, in this case, is
    (7.27)

The Ozer number strongly depends on the discharge coefficient, , and . The value of is relatively insensitive to the size of the die casting machine. Thus, this equation is applicable to a well designed runner (large ) and/or a large die casting machine (large ).

The reduced pressure for a very small value of the number equals to one, or , due to the large resistance in the runner (when the resistance in the runner approaches infinity, , then ). Hence, the gate velocity is determined by the approximation of

    (7.28)

The difference between the various machine performances is more considerable in the middle range of the Oz numbers. A better machine performance produces a higher reduced pressure, . The preferred situation is when the Oz number is large and thus indicates that the machine performance is less important than the runner design parameters. This observation is further elucidated in view of Figures [*] and [*].


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Genick Bar-Meir ||| www.potto.org
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