Simply put: Use hydraulic cylinder core pulling when lifters, sliders (sliding mechanisms) cannot be used, space is insufficient, stroke is too long, force is too great, or precise sequence control is required.
Applicable Scenarios: Long core pulling stroke: Ordinary sliders rely on mold opening force, resulting in limited stroke. Hydraulic cylinders can pull cores tens to hundreds of millimeters long. High force, large undercuts: Deep cavities, thick plastic parts, high clamping forces make lifters prone to breakage and sliders prone to collapse. Hydraulic cylinders provide greater thrust and stability. Confined space/special angles: Angled guide pillar sliders cannot be installed; undercuts are on the inside, angled, or undercut direction is inconsistent with mold opening direction. Requires strict control of mold opening/core pulling sequence: Core pulling must be performed before mold opening, or vice versa. Ordinary sliders cannot achieve this sequence control. Hydraulic cylinders are preferred for four-sided/multi-directional core pulling, large molds, automotive parts, and deep-cavity parts for home appliances. Slider is too heavy, angled guide post cannot be pushed, and hydraulic cylinder is stable.
Not suitable for: short stroke, simple inverted molding, prioritize ordinary sliders/lifters for lower cost.

 

1. Hydraulic Circuit: Core pulling and resetting directions have independent hydraulic circuits, and reverse connection is strictly prohibited; generally, oil inlet in rodless cavity = core pulling, oil inlet in rod cavity = resetting. (If possible) Add a hydraulic lock (hydraulic control check valve): Prevent hydraulic cylinder from being pushed back by glue pressure during high-pressure injection molding, resulting in poor product dimensions and runaway. (If possible) Add a throttle valve/speed control valve: Control core pulling and resetting speed to avoid impact, mold collision, and damage to inserts. Hydraulic circuit layout: Oil pipes should run along side/bottom of mold, avoiding parting surface, should not interfere with mold opening and ejection; use high-pressure quick connectors to withstand hydraulic pressure of injection molding machine. Hydraulic Cylinder Selection: Thrust force > clamping force + frictional resistance; generally, a safety factor of 1.5 to 2 times should be reserved.
2. Limit Positioning (Critical): Hydraulic cylinders themselves have poor precision and are prone to drift. High-precision molds cannot rely on hydraulic cylinders for positioning. Core Pulling Limit Position: Use hard limit blocks/wear-resistant blocks. Hydraulic cylinder only pushes, relying on a mechanical structure to lock core pulling endpoint, preventing over-pulling and product damage. Reset Limit Position: Slide/stationary slide resets using a shovel base + wear-resistant block for mechanical positioning. Hydraulic cylinder only assists in pushing back. During injection, force is applied by shovel base, not hydraulic cylinder. Limit Switches/Inductive Switches: Magnetic inductive switches are installed for both core pulling and reset positions. Signal is sent to injection molding machine; injection/mold opening is not allowed if position is not reached.

 

3. Safety Design: Interlock Logic: If slide is not reset to correct position → mold closing and injection are not allowed; if slide is not core pulled to correct position → mold opening and ejection are not allowed. Anti-retraction structure: In addition to hydraulic lock, after resetting, a shovel base must press down on slider, and injection pressure is borne by shovel base; hydraulic cylinder does not bear pressure. Anti-collision: Buffers are added to both ends of hydraulic cylinder, anti-collision rubber/buffer blocks are added to both ends of slider stroke. Oil pipe protection: To prevent it from being pinched or worn by template, oil pipe grooves are made on mold. Mold opening sequence (crucial, directly determining whether there will be mold collision).
Timing of hydraulic cylinder core pulling must be strictly controlled. There are two common methods: ① Core pulling first, then mold opening (90% of household appliances, deep cavities, and internal undercuts use this method). Sequence: 1. Injection molding machine signal → hydraulic cylinder core pulling back; 2. Core pulling in place, sensor switch confirmation; 3. Injection molding machine receives signal → starts mold opening; 4. Ejection and removal of part after mold opening. Purpose: To prevent product from being pulled apart or slider from scratching product during mold opening. ② Mold opening first, then core pulling (for a few cases with long undercuts on the outside): 1. Open mold a short distance first; 2. Use hydraulic cylinder to pull core; 3. Fully open mold + eject; Applicable to: Undercuts on the outside, pulling directly will scratch product, so it is necessary to create distance before pulling. ③ Mold closing sequence (reset): 1. Before mold closing → hydraulic cylinder resets and pushes slider back; 2. Reset signal confirmation; 3. Injection molding machine is allowed to close mold only; Absolutely prohibited: closing mold before slider returns to its original position → directly damaging mold.

Long stroke, high force, requires sequence → use hydraulic cylinder; Hydraulic circuit: two-way hydraulic circuit + hydraulic lock + speed regulation; Limit: hydraulic cylinder only pushes, mechanical positioning, switch confirmation; Safety: do not open mold/inject plastic if not in position, lock slider with base; Sequence: mostly pull core first, then open mold, reset, then close mold.