In the injection mold, in the ejection system, the key to the finished product is the position of the ejector pin. To obtain a plastic product without scratches and in good condition, the ejector pin plays a significant role.
The thimble layout needs to follow these principles:
(1) The ejector pin arrangement should make the ejection force as balanced as possible. The demoulding force required for the complex structure is large, and the number of thimbles should be increased accordingly.
(2) The thimble should be set with ineffective parts, such as bone position, column position, steps, metal inserts, local thick glue and other structurally complex parts. The thimbles on both sides of the bone position and the column position should be arranged symmetrically as much as possible. The distance between the thimble and the bone position and the column position is generally D=1.5mm. In addition, it should be ensured that the center line of the thimble on both sides of the column position passes through the center of the column position.
(3) Avoid setting thimbles across steps or on inclined surfaces. The top surface of the thimbles should be as smooth as possible, and the thimbles should be arranged in the structural parts where the rubber parts are well stressed.
(4) The flat thimble should be used in the deep bone position (depth ≥ 20mm) or when it is difficult to arrange the round thimble. When a flat thimble needs to be used, the flat thimble should be in the form of an insert to facilitate processing.
(5) Avoid sharp steel and thin steel, especially the top surface of the thimble should not touch the front die surface.
(6) The distance between the thimble and the waterway should be considered in the arrangement of the thimble, so as to avoid affecting the processing of the waterway and water leakage.
(7) Considering the exhaust function of the thimble, in order to exhaust the ejection, the thimble should be arranged in the part where it is easy to form a vacuum. For example, at the larger plane of the cavity, although the packing force of the plastic part is small, it is easy to form a vacuum, which leads to an increase in the demoulding force.