Basic Knowledge of Wires and Cables
Overview of the Wire and Cable Manufacturing Process

The manufacturing of wires and cables is completely different from the production methods used for most electromechanical products. Electromechanical products are usually made by assembling parts into components, and then assembling multiple components into a single finished product. Such products are measured in units or pieces. In contrast, wires and cables use length as the basic unit of measurement.

All wires and cables begin with conductor processing. Insulation, shielding, cabling, sheathing, and other layers are added around the conductor layer by layer to form the finished wire or cable product. The more complex the product structure, the more layers are required.

I. Process Characteristics of Wire and Cable Manufacturing

1. Long-Length Continuous Layered Combined Production Method

The long-length continuous layered combined production method has a comprehensive and controlling impact on wire and cable production. This affects the following aspects:

(1) Production Process Flow and Equipment Layout

Various equipment in the production workshop must be arranged reasonably according to the required production process flow, so that semi-finished products at each stage can move forward in sequence. Equipment configuration must balance production capacity according to differences in production efficiency. In some cases, two or more machines may be required to balance the capacity of the production line. Therefore, the selection and combination of equipment and the layout of the production site must be considered comprehensively based on product type and production volume.

(2) Production Organization and Management

Production organization and management must be scientific, reasonable, thorough, accurate, strict, and detailed. Operators must follow process requirements precisely. Any problem in any stage may affect the smooth operation of the production process, product quality, and delivery.

This is especially important for multi-core cables. If the length of a certain pair or basic unit is too short, or if a quality problem occurs, the entire cable may become insufficient in length and be scrapped. Conversely, if a certain unit is too long, it must be cut off, resulting in material waste.

(3) Quality Management

The long-length continuous layered combined production method means that any problem occurring at any stage during production may affect the quality of the entire cable. The deeper the quality defect occurs inside the structure, and the later it is detected, the greater the loss will be.

Unlike assembled products, wires and cables cannot simply be disassembled, reassembled, or repaired by replacing parts. Once a quality problem occurs in any component or process stage, it is usually impossible to fully recover or compensate for the affected cable. Post-production handling is often limited to cutting the cable shorter, downgrading the product, or scrapping the entire length.

Therefore, quality management must run through the entire production process. Quality inspection departments should carry out巡回 inspections throughout production, while operators should perform self-inspections and conduct mutual inspections between upstream and downstream processes. This is an important guarantee for ensuring product quality and improving enterprise efficiency.

2. Wide Range of Process Categories and Large Material Flow

Wire and cable manufacturing involves a wide range of process categories, including the melting and pressure processing of non-ferrous metals, chemical technologies such as plastics, rubber, and coatings, textile technologies such as wrapping and braiding of fiber materials, and metal forming processes such as wrapping of metallic materials, longitudinal wrapping of metal strips, and welding.

The materials used in wire and cable manufacturing are not only diverse in category, type, and specification, but also large in quantity. Therefore, the usage, reserve quantity, material batching cycle, and batch size of various materials must be carefully determined. At the same time, the separation, recycling, reuse, and disposal of defective products and waste materials should be treated as an important part of management. Material quota management and waste reduction should be given high priority.

In wire and cable production, material flow is large, from the incoming and outgoing storage of raw materials and auxiliary materials, to the transfer of semi-finished products between processes, and finally to the storage and shipment of finished products. Therefore, reasonable layout and dynamic management are required.

3. Extensive Use of Specialized Equipment

Wire and cable manufacturing uses specialized production equipment designed for the specific process characteristics of the industry. This equipment is used to meet the structural and performance requirements of cable products and to support long-length, continuous, and high-speed production. As a result, a series of specialized cable manufacturing equipment has been developed, such as extrusion machines, wire drawing machines, stranding machines, and wrapping machines.

The development of cable manufacturing processes and specialized equipment is closely related and mutually reinforcing. New process requirements promote the development of new specialized equipment, while the development of new equipment in turn promotes the application and improvement of advanced manufacturing processes. For example, specialized production lines such as wire drawing, annealing, and extrusion lines, as well as physical foaming production lines, have helped improve cable manufacturing technology, product quality, and production efficiency.

II. Main Manufacturing Processes of Wires and Cables

Wires and cables are mainly produced through three processes: drawing, stranding, and covering. The more complex the model and specification, the higher the degree of process repetition.

1. Drawing

In metal pressure processing, metal drawing refers to a technical process in which metal is forced through a die or roller under external force. The cross-sectional area of the metal is reduced, and the required cross-sectional shape and dimensions are obtained.

The drawing process can be divided into:

• Single wire drawing
• Stranding and drawing

1. Stranding

To improve the flexibility and overall integrity of wires and cables, two or more single wires are twisted together in a specified direction. This process is called stranding.

The stranding process includes:

• Conductor stranding
• Cabling
• Braiding
• Steel wire armoring
• Wrapping

1. Covering

According to different performance requirements, specialized equipment is used to cover the conductor with different materials. The covering process can be divided into:

A. Extrusion coating: rubber, plastic, lead, aluminum, and other materials.

B. Longitudinal wrapping: rubber and corrugated aluminum tape.

C. Tape wrapping: paper tape, mica tape, alkali-free glass fiber tape, non-woven fabric, plastic tape, and fibrous materials such as cotton yarn and silk.

D. Impregnation coating: insulating varnish, asphalt, and similar materials.

III. Basic Manufacturing Process Flow of Plastic Insulated Wires and Cables

1. Drawing of Copper and Aluminum Single Wires

Copper and aluminum rods commonly used in wire and cable production are processed at room temperature through one or more drawing dies using a wire drawing machine. This reduces the cross-section, increases the length, and improves the strength of the wire.

Wire drawing is the first process in most wire and cable companies. The main process parameter in wire drawing is die matching technology.

2. Annealing of Single Wires

Copper and aluminum single wires are heated to a certain temperature to improve their toughness and reduce their strength through recrystallization. This ensures that the conductor meets the requirements of wire and cable applications.

The key point of the annealing process is to prevent oxidation of the copper wire.

3. Conductor Stranding

To improve the flexibility of wires and cables and make installation easier, the conductor core is made by twisting multiple single wires together.

Based on the stranding structure, conductor stranding can be divided into regular stranding and irregular stranding. Irregular stranding includes bundle stranding, concentric composite stranding, and special stranding.

To reduce the occupied area of the conductor and minimize the geometric size of the cable, compacted conductors are often used during stranding. This changes the ordinary circular shape into semi-circular, sector-shaped, tile-shaped, or compacted circular shapes. This type of conductor is mainly used in power cables.

4. Insulation Extrusion

Plastic insulated wires and cables mainly use extruded solid insulation layers. The main technical requirements for plastic insulation extrusion are as follows:

4.1 Eccentricity

The deviation value of the extruded insulation thickness is an important indicator of extrusion process quality. For most product structures, dimensional requirements and allowable deviations are clearly specified in relevant standards.

4.2 Smoothness

The surface of the extruded insulation layer must be smooth. Surface roughness, scorching, impurities, and other defects are not allowed.

4.3 Compactness

The cross-section of the extruded insulation layer must be dense and solid. No visible pinholes are allowed, and the presence of air bubbles must be avoided.

5. Cabling

For multi-core cables, the insulated cores are usually twisted together into a circular shape to ensure proper formation and reduce the overall cable diameter. The cabling mechanism is similar to conductor stranding. Because the lay length is relatively large, non-retracting methods are usually adopted.

The main technical requirements for cabling are:

• Prevent irregular insulated cores from turning over and causing cable twisting.
• Prevent damage or scratching of the insulation layer.

During cabling, two additional processes are usually carried out at the same time:

• Filling: used to ensure that the cabled core remains round and stable.
• Binding: used to prevent the cable core from becoming loose.

1. Inner Sheath

To protect the insulated cores from being damaged by armoring, an appropriate inner protective layer is required. The inner sheath can be divided into:

• Extruded inner sheath, also known as a separator or isolation sheath
• Wrapped inner sheath, also known as a bedding layer

The wrapped bedding layer may replace the binding tape and is carried out simultaneously with the cabling process.

7. Armoring

Cables laid underground may be subjected to certain compressive forces during operation. In such cases, an internal steel tape armor structure may be selected.

For cables installed in environments where both compressive force and tensile force are present, such as underwater installations, vertical shafts, or soil with large elevation differences, a steel wire armor structure should be selected.

8. Outer Sheath

The outer sheath is the structural part that protects the insulation layer of the wire or cable from environmental damage. Its main functions are to improve mechanical strength, resist chemical corrosion, provide moisture resistance, prevent water ingress, and reduce the risk of cable combustion.

Depending on the specific requirements of the cable, a plastic outer sheath is directly extruded using an extrusion machine.