According to the overall functional structure, the plastic mold can be divided into a guiding system, supporting system, forming part system, pouring system, cooling system, ejecting system, and exhaust system.
The plastic flow channel in the mold from the nozzle of the injection machine to the cavity. It consists of a main channel, a branch channel, a gate and a material hole.
Main channel: The main channel refers to the section from the part where the nozzle of the injection machine is in contact with the mold to the runner.
Runner: The section between the main runner and the gate, it is the transition section where the molten plastic flows from the main runner into the cavity, and it is also the transition section in the gating system through the change of cross-sectional area and the plastic turning, so that the plastic can be smoothly converted.
The layout of the runners has two forms: balanced feed and unbalanced feed. Balanced feeding is to ensure that each feeding port is fed in a balanced manner at the same time. Unbalanced feeding is that each feeding port cannot be fed in a balanced manner at the same time. Generally, mold flow analysis is required for evaluation.
Gate: Also known as feed port or inner runner. It is the narrow part between the runner and the plastic part, also known as the shortest part of the gating system. It can accelerate the flow rate of the molten plastic conveyed by the runner, form an ideal flow state, fill the cavity in sequence, and quickly, and also play the role of sealing the cavity to prevent the backflow of the molten material, and it is convenient to use after molding. The gate is separated from the plastic part.
Sprue sleeve: Since the sprue needs to contact and collide with the high-temperature plastic and the nozzle, the sprue part of the mold is usually designed as a detachable and replaceable bushing, referred to as a sprue sleeve or a sprue sleeve.
Its main functions are:
(1) When the mold is installed, it is convenient to enter the positioning hole, and it is well-positioned on the injection molding machine to match the nozzle hole of the injection molding machine, and can withstand the back pressure of the plastic, so as not to be pushed out of the mold
(2) As the main channel of the pouring system, the plastic in the barrel is transferred into the mold to ensure that the material flow can reach the cavity forcefully and smoothly. There should be no plastic overflow during the injection process, and at the same time, the main channel condensate can be easily removed.
Structural forms include the integral type and split type
Integral type: that is, the shoulder is integrated with the part that constitutes the main channel
Split type: that is, the shoulder and the part that constitutes the main channel are produced separately
There are various forms of gates: inner gate, common side gate (edge gate), outer gate, etc.
Choice of gate location:
(1) The gate selects the closest distance to the barrier.
(2) The size and location of the gate should be selected to avoid jetting and creeping.
(3) The gate should be opened at the thickest part of the section of the plastic part.
(4) The selection of the gate position should make the plastic flow the shortest and the material flow change the least.
(5) The selection of gate position should be conducive to the discharge of gas in the cavity.
(6) The selection of gate location should reduce or avoid weld lines of plastic parts to increase weld fastness.
(7) The selection of the gate position should prevent the material flow from squeezing and deforming the cavity, core and insert.