In all hydraulic injection units, hydraulic power is converted, multiplied, into plastic pressure. The law of physics involved is F = P x A. That is force (F) is equal to pressure (P) times area (A). The large hydraulic piston acts on the screw, or essentially the non-return valve. The hydraulic piston has a large surface area, for example 100 cm2. The non-return valve during injection forward acts like a smaller area piston, for example 10 cm2. This causes the hydraulic pressure to be converted to melt or plastic pressure in the barrel of the injection unit.
In this specific case hydraulic pressure is “intensified” or multiplied by a factor of 10. That is 800 psi of hydraulic pressure provides ~8,000 psi of melt pressure inside the nozzle of our machine. Often this is called the machine's intensification ratio and explains how hydraulic pressure can provide tens of thousands of psi plastic pressure inside the nozzle. Today you can buy machines with intensification ratios ranging from 6:1 to 43:1.
All machines are NOT 10:1. It is plastic pressure that pushes plastic into the sprue, runner, gate and mold cavity, NOT hydraulic pressure. If your plant has different machines, most likely they have different intensification ratios. That is 800 psi pack and hold pressure on one machine with an intensification of 10:1 may be packing out the part with 8,000 psi plastic pressure, but on another machine with a different intensification ratio of 12.75:1; 800 psi hydraulic pressure may be 10,200 psi plastic packing pressure in the nozzle. You will not make the same part, sorry!
Recording and determining intensificatoin ratios for all of the machines in your operation can be a tedious and time-consuming process. The Universal Setup Sheet developed by John Bozzelli can make this process dramatically easier.
Figure 1 & 2, provide illustrations:
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