Characteristics and Molding Differences between Traditional (straight) Screws and V-shaped Screws
Injection molding is an important process in the production of
electrical connectors, where the plastic housings of the connectors are
typically made during the injection molding stage. This involves
injecting melted plastic into metal molds, which then rapidly cool and
solidify. The screw is a critical component of the injection molding
machine, used for conveying, compacting, melting, mixing, and applying
pressure to the plastic. Below, based on GREENCONN's years of experience
in connector production, engineers have summarized the characteristics
and molding differences between two different types of injection molding
machine screws (traditional straight screws and V-shaped screws).
Straight Screw Method: In the
case of the straight screw method, the difference between the downward
force of resin extrusion screw and the controlled back pressure
determines the density of the metered resin. The density of the resin
changes depending on the magnitude of the back pressure.
Figure 1: Characteristics of Traditional (Straight) Screws
Electric Hydraulic Hybrid V-shaped Method: The V-shaped method contains a back-flow prevention mechanism, which has more advantages over the straight screw method's non-return ring.
Figure 2: Characteristics of V-shaped Screws
The following compares the molding differences between V-shaped screws and straight screws in three aspects:
1.Stability of Actual Filling Amount in the Filling Process
Straight Screw Method: The
straight screw has a non-return ring, which cannot control the resin
cutoff amount at the beginning of the molding process, leading to
unstable filling amounts in the position command control, necessitating
supplementary filling through the holding pressure process.
V-shaped Screw Method: Because
the V-shaped screw does not have a non-return ring, a certain filling
amount can be ensured at the beginning of the molding process, reducing
the occurrence of insufficient plastic molding due to premature
solidification of the gate during the holding pressure stage.
Figure 3: Comparison of two filling methods
2. Stability of Resin Melting State
Straight Screw Method: The material supply position can move, causing changes in resin temperature.
V-shaped Screw Method: With the
screw rotating in a fixed state, the resin supplied from the plastic
inlet can undergo a certain heating process, ensuring a stable melting
state.
Figure 4: Comparison of the melting state of resin in two methods
3. Setting of Back Pressure
V-shaped Screw: The metering
method using a plunger does not require a plastic inlet, allowing a
certain back pressure unaffected by this change to be provided to the
resin being metered, resulting in very stable and effective resin
density measurement.
Figure 5: Comparison of back pressure settings in two methods
Characteristics of V-shaped Injection Molding Machine:
●Melting at a certain temperature, metering at a certain density: By rotating the screw at a certain position, the meltable resin will push the plunger up to the metering point. The position for metering will be memorized on the controller, ensuring a fixed resin density during metering.
●Filling at a certain time, with a certain amount: With an encoder resolution of 0.5µm accuracy and closed-loop speed control, the filling time from the metering position to the V-P position remains fixed even if there are changes in resin viscosity or temperature. With the plunger, there is no back-flow, enabling quantified filling.
●Maintaining a certain time and pressure during holding: Pressure sensing with a pressure sensor of precision MAX pressure/4000 in 0.0-second units can achieve closure during holding. Furthermore, because of the plunger and hydraulic control, effective holding can be performed under good pressure.
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