Injection by Plunger
"Injection like a hypodermic syringe"
The "V-LINE" injection is controlled by a closed loop system comparing actual speed to set speed and maximum melt pressure. User selectable limits can be easily input on the process monitor screen. Once the exact amount of material is transferred into the injection chamber, the injection plunger that is retracted via the melt is maintained to a set position. This design eliminates the need for a check valve, a primary source of material degradation and shot volume inconsistency. A linear encoder detects plunger position, and a pressure sensor monitors injection pressure. The exceptional speed of the controller provides real time response during injection. Melt cushion is recorded in 0.001" for accurate process stabilization.
| V-LINE TWO STAGE PLUNGER | RECIPROCATING SCREW |
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| Video: V-LINE TWO STAGE PLUNGER | Video: RECIPROCATING SCREW |
| Metered material is pre-dose. Plunger injection is very reliable due to high response, low mass, and low inertia plunger. High Speed, Low Speed, High Pressure, Low Pressure, Strong Holding, quick response at VP switchover. | There is always speed and pressure loss at injection because of material leaking. While leaking, the metered material is exposed to high shear heat, and that generates degradation and gas. |
| High speed filling is achieved from initial stage of filling because of NO back flow leak. | Material inside plasticizing barrel (Not yet metered!!) is moving along with screw while injection. That leads to degradation of material and adding mass to the screw injection movement. |
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| Material density is stable because screw does NOT retract. | Metered material density is not constant result from uncontrollable balance of "back pressure" and "reciprocating movement". |
| INERTIA: Plunger system is inherently small and low inertia. Good at acceleration and deceleration of speed and pressure. | INERTIA: Reciprocating system is inherently bigger and high inertia. There is a limit in acceleration and deceleration. |
| SPEED MONITORING: Sensor and encoder are attached to plunger, which enables direct measurement and feedback to system. | SPEED MONITORING: Usually data is measured from encoder at AC servomotor. Data is indirect because there are connecting components such as ball screw and belt. |
| PRESSURE MONITORING: Pressure sensor is attached to plunger, which enables to detect real injection pressure and feedback to system. | PRESSURE MONITORING: Usually data is measured from voltage of AC servomotor (Monitoring torque at acceleration and deceleration). Injection pressure is not equal to voltage. |
LINEAR MOTOR TECHNOLOGY
Sodick Plustech develops the injection valve using Linear Motor technology as a drive. By using a linear motor to control the spool of injection valve, the step response becomes 10 times faster than that of conventional servo valve (3msec). As a result, V-LINE Plunger achieves excellent injection control including acceleration and deceleration of the injection speed, vp switch-over position stability, and linearity of molding profile.