The machine intensification ratio, or the material/hydraulic pressure ratio is the direct relationship between the injection pressure and the hydraulic pressure. This is the ratio of the resin pressure in front of the screw, compared to the oil pressure in the piston of the injection molding machine.
The injection pressure and hydraulic pressure differ significantly in an injection molding machine. The injection pressure is the pressure applied directly to the plastic by the ram, which causes the material to flow. The injection pressure can be measured directly by locating a transducer in the nozzle. The hydraulic pressure is the pressure in the main supply line from the pump, which moves the ram; it is typically measured by means of a gauge in the hydraulic line.
Refer to the machine manual to find the machine intensification ratio. A typical ratio is 10, and the typical range of the ratio is between 7 and 15.
To calculate the machine intensification ratio, divide the piston area (Ah) by the screw area (Am), as shown in the following diagram.
- Ah is the piston area in the hydraulic oil
- Am is the screw area in the melt
- Ph is the pressure in the hydraulic oil
- Pm is the pressure in the melt
- Pm = Ph (Ah / Am)
The following graph is an example of a machine intensification ratio graph in a machine manual. In this example, several screws are used on one machine: 25mm, 30mm, and 35 mm. The ratio depends on the screw area; therefore, to calculate the ratio, choose a round value, for example 100 bar, on the pressure axis (1), project to the curve of the screw used on the machine (2), and then project to the injection pressure axis (3), divide the injection pressure (3) by the hydraulic pressure (1) to find the machine intensification ratio.
