Multi-Cavity Design of Injection Molds for Non-Slip Plastic Hangers

Non-slip plastic hangers are widely used daily-injection products with a huge market demand. Featuring surface non-slip textures and undercut hook structures, these small-sized, uniform-wall-thickness parts are highly suitable for high-volume automated production using multi-cavity molds. The core of multi-cavity mold design lies in balanced filling, uniform cooling, and smooth demolding across all cavities, while ensuring clear non-slip texture molding, no flash or warpage, and balancing manufacturability, service life, and production efficiency. This article elaborates on the standardized design of each structural module.

1. Cavity Number and Layout Design

As small thin-walled parts, non-slip plastic hangers are commonly produced in 8-cavity, 16-cavity, and 24-cavity molds, all using industry-proven reliable parameters. A standard household non-slip hanger weighs 20g–30g. The final cavity number is determined by the injection molding machine’s clamping force, shot volume, and platen size, with a 1.2× safety margin for shot volume and clamping force calculated by single-cavity projected area and cavity pressure.

Multi-cavity molds adopt a symmetric rectangular array layout. The optimal mass-production solution is 4×4 16-cavity layout, which effectively ensures balanced filling. Cavity spacing is strictly controlled at 15mm–20mm to reserve sufficient space for cooling lines and parting-surface venting. Hangars are arranged along the long side of the mold plate, with all hooks facing inward, simplifying the machining and assembly of core-pulling mechanisms and improving overall mold stability.

2. Parting Surface and Molding Structure Design

The main parting surface is set at the maximum cross-section of the part to meet basic demanding requirements. For the undercut hook structure, the industry universally adopts slider core-pulling with a standard stroke of 15mm–20mm. The overall draft angle is 1.5°–2°, while the non-slip texture area is increased to 2°–3° to effectively prevent demolding scratches and jamming.

The parting surface fitting clearance is ≤0.03mm, and the overall mold positioning accuracy is ±0.02mm, completely eliminating flash during production. Molds with 8 cavities or fewer use one-piece cavity and core for easy machining and high rigidity, made of P20 mold steel with a heat-treated hardness of 48HRC–52HRC.

Molds with 16 cavities or more adopt insert structures, separating the main cavity, hook sliders, and non-slip texture inserts for independent machining, facilitating later maintenance and replacement and reducing costs. Sliders and key texture components use S136 stainless mold steel with hardness 50HRC–54HRC, offering excellent wear and rust resistance. All corners use R0.5–R1 rounded transitions to reduce stress concentration and avoid sticking or cracking.

3. Gating System Design

Balanced filling is critical for multi-cavity molds. For 16-cavity and higher production molds, a hot-runner + cold-runner composite system is widely used, with a 4mm diameter needle-valve hot nozzle as the main sprue, greatly reducing material waste and improving efficiency. The sub-runner uses a balanced layout with a standard section of 6mm×4mm.

Simple 8-cavity molds use conventional cold runners with circular cross-sections of 6mm–8mm diameter. All runner corners are rounded, and cold-slug wells are set at the ends to trap cold slugs and contaminants. Submarine gates are adopted for automated mass production, enabling automatic degating without secondary trimming.

The gate diameter is 1.2mm–1.5mm, located on the side of the hanger body or the root of the hook, away from the non-slip texture surface to avoid visible gate marks. Each cavity uses 2–3 gates to ensure uniform filling. Runner length, section size, and gate specifications are identical across all cavities, with a filling time difference within 0.1s, ensuring consistent weight, dimensions, and quality.

4. Cooling and Venting System Design

The cooling system uses corresponding layouts on the moving and fixed halves. The moving core is equipped with 10mm diameter straight cooling lines, spaced 20mm–25mm apart and 10mm–15mm from the cavity surface. Cooling lines are densified at critical areas such as hooks and non-slip textures to improve uniformity.

The fixed cavity uses circular cooling lines matching the moving half, with a temperature difference controlled within ±2℃. Production cooling water temperature is set at 40℃–60℃ with a flow rate ≥2m/s; lower mold temperature is applied at non-slip areas to ensure clear and full texture molding.

Venting grooves are placed at the parting surface, ends of non-slip textures, hook roots, and weld-line locations to resolve trapped gas, burning, and short shots. Standard vent dimensions: depth 0.02mm–0.03mm, width 5mm–10mm, spaced 10mm–15mm apart, all open to the atmosphere for complete gas evacuation and improved part quality.

5. Ejection System Design

The mold uses a multi-point balanced ejection structure. Each cavity is equipped with 4–6 ejector pins of 2mm–3mm diameter, evenly distributed at the shoulder, bottom, and both sides of the hook to ensure uniform force and no deformation. Ejector pin ends are set 0.05mm–0.1mm below the cavity surface to avoid visible marks or protrusions.

The fitting clearance of slider guide pins and bushes is 0.01mm–0.02mm, ensuring smooth, jamming-free motion over long-term operation and extending mold life.

6. Molding Material and Injection Molding Parameters

Non-slip plastic hangers are mainly produced from PP and PE, with a small amount of elastomer added to enhance anti-slip performance. The molding shrinkage rate ranges from 1.5%–2.5%, and molds are universally compensated at 2.0% shrinkage, complying with industry standards.

Stable mass-production parameters:

Injection pressure: 80MPa–90MPa

Holding pressure: 40MPa–50MPa

Mold temperature: 40℃–60℃

Cycle cooling time per part: 8s–12s

These settings balance molding quality and production efficiency.

7. Overall Design Summary

The multi-cavity mold for non-slip plastic hangers adopts mature, reliable industrial parameters in cavity layout, parting structure, gating, cooling, venting, ejection, and material selection. Symmetric layout ensures balanced filling; sliders solve hook undercut demolding; rational cooling and venting control warpage, short shots, and blurred textures. With proper steel grades and process parameters, the mold meets high-volume continuous production, ensures dimensional accuracy and anti-slip performance, and features convenient maintenance and stable operation, fully satisfying the practical requirements of the daily-use plastic injection industry.