Sheath Mold – Technical Overview and Application Guide  

The sheath mold described here is a precision mold solution specifically designed for producing PP and PE sheath parts with high consistency, repeatable quality, and long production life. This sheath mold is engineered to meet strict dimensional and performance requirements in cable, wire, and protective covering applications. Below is a comprehensive technical description and application guide for this product.

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1. Product Name and Classification  

Product Name: Sheath mold  

This mold is used to manufacture plastic sheaths, often applied as protective layers on cables, wires, tubes, or other elongated components. Depending on the specific customer design and application needs, this sheath mold can be adapted into different structural categories within the mold family:

- Plug mold  
- Wire mold  
- Twisted tooth mold  
- Material saving mold  
- Hot runner system mold  

In practical use, the sheath mold can be integrated with features from one or more of these categories to improve efficiency, save material, or stabilize product performance. For example, a sheath mold for wire protection may be configured as a wire mold, while one focused on material efficiency could include design elements characteristic of a material saving mold. A high-output configuration may use a hot runner system mold concept to reduce waste and improve cycle times.

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2. Material and Structural Characteristics  

2.1 Mold Material: SKD11  

The core and cavity components of the sheath mold are manufactured from SKD11, a high-carbon, high-chromium tool steel widely used for its:

- Excellent wear resistance  
- Good dimensional stability under repeated thermal cycling  
- High hardness after proper heat treatment  
- Resistance to deformation over a long service period  

Using SKD11 ensures that the mold can withstand high injection pressures and abrasive conditions when processing PP and PE materials. This choice of material significantly prolongs the mold lifespan, which in this case is rated at 300,000 times (approximately 300,000 molding cycles) under normal operating conditions and proper maintenance.

2.2 Mold Frame and Chamber  

- Mold frame: nothing  
- Chamber: nothing  

This means the sheath mold is designed as a relatively compact, specialized tool without an additional standardized mold frame or separate pressure chamber integrated into the description. It can be installed into suitable injection molding machines using compatible mounting dimensions and fixing methods. The absence of a specified mold frame provides flexibility for integration into different machine setups or for combination with a custom frame according to end-user requirements.

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3. Surface Treatment Options  

The surface of the cavity and certain external mold surfaces can be finished with several surface treatment options:

- Screen printing  
- Coating  
- Painting, etc.  

These treatments may serve different purposes:

1. Screen printing:  
  Used mainly for labeling, marking reference lines, indicating parting directions, gate locations, or cavity identifications on the mold exterior. It improves operational clarity for mold technicians during setup, maintenance, and production.

2. Coating:  
  Functional coatings can be applied to improve lubricity, corrosion resistance, or demolding behavior. Examples may include PVD or other thin-film coatings on SKD11 surfaces. Such coatings help:
  - Reduce friction between the plastic part and cavity surface  
  - Enhance wear resistance, thereby extending mold service life  
  - Improve surface gloss and consistency on the molded sheath  

3. Painting:  
  Typically applied to non-functional external mold surfaces for:
  - Corrosion protection  
  - Visual identification and safety marking  
  - Aesthetic consistency on the production floor  

The exact combination of surface treatments can be tailored to the user’s production environment, especially considering humidity, cleaning chemicals, and maintenance frequency.

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4. Mold Structure and Dimensions  

4.1 Mold Size and Configuration  

- Mold size: 200 mm × 150 mm × 15 mm  
- Number of mold cavities: four  

The sheath mold is designed as a compact tool, with a relatively small thickness of 15 mm, making it suitable for confined spaces or smaller injection molding machines. The four-cavity layout increases productivity by allowing four sheath parts to be produced during each injection cycle.  

A four-cavity configuration provides several advantages:  

- Enhanced output per cycle compared to a single-cavity mold  
- More efficient use of machine time and energy  
- Better balance between tooling cost and per-part cost  

The overall size of 200 mm × 150 mm is convenient for mid-range molding machines and allows for ease of handling, mounting, and maintenance without being overly heavy or bulky.

4.2 Draft Angle  

- Draft angle: (to be defined by part design)  

While the draft angle is not numerically specified here, it remains a critical parameter of the sheath mold design. A suitable draft is essential to:

- Enable smooth ejection of the molded PP or PE sheath  
- Minimize the risk of part scratching, deformation, or sticking  
- Ensure consistent part dimensions without damage  

For PP and PE materials, typical draft angles are often between 0.5° to 2°, but the final value depends on sheath geometry, length, surface texture, and tolerance requirements. The actual draft angle should be determined and verified in the 3D design phase, considering shrinkage and release behavior.

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5. Plastic Material Compatibility  

- Plastic material: PP / PE  

This sheath mold is optimized for:

1. PP (Polypropylene)  
  - Low density, good chemical resistance  
  - High fatigue resistance and flexibility  
  - Commonly used for cable sheathing, protective tubes, and lightweight covers  

2. PE (Polyethylene)  
  - Excellent impact resistance and toughness  
  - Good electrical insulating properties  
  - Frequently used for wire and cable jackets, tubing sheaths, and protection sleeves  

The mold design, including runner dimensions, gate configuration, and cooling layout, is tailored to the flow and shrinkage characteristics of PP and PE. Gate placement and cavity shape aim to minimize warpage, sink marks, and internal stress, ensuring stable performance of the final sheath part.

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6. Injection System Design  

6.1 Gate Type  

- Gate type: Unilateral injection of glue  

“Unilateral injection of glue” indicates that the molten plastic is introduced into the cavity from one side. In practical terms, this usually means a side gate or an offset gate location designed to:

- Achieve directional flow filling the sheath cavity from one end to the other  
- Reduce weld lines or flow marks in critical functional areas  
- Facilitate uniform packing pressure along the sheath length  

For a four-cavity sheath mold, the gating system is laid out to provide even filling across all cavities while maintaining consistent shear rates and avoiding excessive pressure drops. Proper balancing of unilateral gates ensures each cavity receives an equal amount of material under stable conditions.

6.2 Channel Type  

- Channel type: Cold and hot aisle  

The mold combines elements of cold runner and hot runner concepts. A “cold and hot aisle” configuration may refer to:

- A hot runner manifold feeding near-gate areas to keep the main channels molten  
- Short cold runners or sub-runners extending from the hot drops into each cavity  
- Reduced sprue and runner waste compared to a purely cold runner system  

Advantages of this combined approach:

- Less material waste than full cold runner systems  
- Faster cycle times due to more stable melt temperature and shorter flow paths  
- Improved consistency in cavity packing, reducing dimensional variance among the four sheath parts  

The design of hot and cold sections must ensure reliable sealing, easy maintenance, and controlled temperature gradients, especially important when processing PP and PE, which are sensitive to over-heating and oxidation.

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7. Mold Life and Reliability  

- Mold lifespan: 300,000 times  

The sheath mold is engineered for 300,000 production cycles under standard operating conditions. Factors contributing to this lifespan include:

- SKD11 steel with proper heat treatment and finishing  
- Wear-resistant cavity surfaces and guiding elements  
- Controlled injection parameters suited to PP and PE  
- Regular maintenance, including cleaning, lubrication, and inspection  

This lifespan strikes a balance between initial mold investment and output volume. It is suitable for medium- to high-volume production of sheath components in automotive, electronics, industrial equipment, or general wiring markets.

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8. Delivery and Project Timing  

- Delivery time: 45 days  

From design finalization to tooling completion, the typical delivery period is approximately 45 days. This timeframe generally covers:

1. Detailed design and engineering of the sheath mold  
2. Machining of SKD11 core and cavity components  
3. Heat treatment, grinding, and precision finishing  
4. Assembly of mold components, runner systems, and ejection mechanisms  
5. Trial runs, adjustments, and validation of dimensions and function  

The 45-day delivery schedule assumes the sheath design, including dimensions, tolerances, and required functions, is clearly defined and approved early in the project. Modifications or complex design changes may influence the final delivery timing.

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9. Design Data and Visualization  

- Original and 3D images: available  

Original design files and 3D images of the sheath mold are used for:

- Visualizing the layout of the four cavities, gate positions, and runner paths  
- Evaluating the fit with the injection molding machine and related equipment  
- Conducting mold-flow analysis to optimize gate size, channel balance, and filling behavior  
- Pre-assembly review and communication with engineering teams  

3D models allow for quick verification of draft angles, wall thickness, and interference clearances. They are also essential for simulating PP and PE flow patterns, shrinkage, and cooling performance.

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10. Application Scenarios  

The sheath mold can be applied in multiple fields where PP or PE protective coverings are required, such as:

- Electrical cables and wiring harnesses  
- Communication and signal cables  
- Protective sleeves for sensors and connectors  
- Tubing covers in industrial or household equipment  
- Lightweight protective sheaths for mechanical parts  

Thanks to the four-cavity configuration, unilateral injection system, and combined cold and hot aisle design, the mold maintains a balance of efficiency, quality, and cost per part. It is suitable for medium to high throughput production lines requiring stable, repeatable sheath dimensions.

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11. Summary of Key Specifications  

- Product Name: Sheath mold  
- Mold type: Can be configured as plug mold, wire mold, twisted tooth mold, material saving mold, or hot runner system mold depending on project needs  
- Material: SKD11  
- Surface Treatment: Screen printing, coating, painting, etc.  
- Mold frame: nothing  
- Mold lifespan: 300,000 times  
- Chamber: nothing  
- Plastic material: PP / PE  
- Gate type: Unilateral injection of glue  
- Channel type: Cold and hot aisle  
- Draft angle: To be determined based on final part design  
- Mold size: 200 mm × 150 mm × 15 mm  
- Number of mold cavities: four  
- Original and 3D images: available for design review and verification  
- Delivery time: 45 days  

This sheath mold offers a robust, efficient, and adaptable solution for manufacturing PP and PE protective sheaths, combining durable SKD11 construction, optimized gating, and multi-cavity productivity to meet demanding industrial requirements.