### Working Principle and Applications of Multi-Roll Cold Rolling Pipe Mill

A **cold rolling pipe mill** is a piece of equipment used for cold rolling of hollow tubes using a ring-shaped die. This machine is particularly effective for initial rolling and for producing seamless tubes with common accuracy, including non-ferrous metals. The most notable feature of cold rolling pipe mills is their high material utilization rate, along with superior precision and surface finish compared to cold-drawn tubes.

Cold rolling pipe mills are generally divided into two types: LG-type and LD-type. The **LG-type** is a two-roll mill, while the **LD-type** is a multi-roll mill (with at least three or more rolls). The main components of an LG-type cold rolling mill include the bed, rotary feeding mechanism, frame, main motor, mandrel, transmission system, and electrical systems.

### Key Components of the Cold Rolling Pipe Mill:
– **Rotary Feeding Mechanism:**
Early cold rolling mills used single rotation and single feeding mechanisms. With technological advancements, newer designs include single rotation with double feeding, double rotation with single feeding, and other combinations. The feeding methods can be mechanical, photoelectric, or servo-driven.

– **Frame:**
The frame is the most critical part of the machine, containing the rolls, gears, and racks. The working principle revolves around the rolls and mandrel forming a regulated cavity, where the elastic deformation of the metal enables the rolling of the steel tube.

### Working Principle:
The cold rolling pipe mill uses an electric motor to pull the steel rod, applying force through the support roll and working roll onto both sides of the steel rod. By adjusting the gap between the rolls, the machine can produce ribbed steel rods of various diameters.

1. **Support Roll:**
This roll is closest to the machine base. It supports the steel rod and distributes the weight of the steel rod and working roll evenly, creating ribbing on the lower surface of the steel rod.

2. **Working Roll:**
Positioned above the support roll, the working roll presses against the steel rod, forming ribbing on the upper surface of the rod.

### Structure and Applications of Multi-Roll Cold Rolling Pipe Mill:
Multi-roll cold rolling mills are equipped with 3 to 5 rolls arranged circumferentially with uniform cross-sectional round holes. These rolls move reciprocally with the machine head while following a track that causes them to open and close. This allows the multi-roll mill to cooperate with a fixed cylindrical mandrel in the center of the die to periodically roll the hollow tube in segments.

The elastic flattening of multi-roll cold rolling mills is proportional to the diameter of the mill at the same unit pressure. To reduce elastic deformation, smaller roll diameters are used. For economic production of thin-walled materials, the smallest possible roll diameter is employed.

### Specifications and Applications of Different Cold Rolling Pipe Mills:
– **LD20 Two-Roll Cold Rolling Mill:**
Produces tubes with outer diameters of φ10–25mm and wall thicknesses of 1.0–5mm.

– **LD30 Two-Roll Cold Rolling Mill:**
Produces tubes with outer diameters of φ15–60mm and wall thicknesses of 1.0–10mm.

– **LD45 Two-Roll Cold Rolling Mill:**
Produces tubes with outer diameters of φ25–83mm and wall thicknesses of 1.5–14mm.

– **LD50 Two-Roll Cold Rolling Mill:**
Produces tubes with outer diameters of φ30–108mm and wall thicknesses of 2–20mm.

– **LD60 Two-Roll Cold Rolling Mill:**
Produces tubes with outer diameters of φ30–90mm and wall thicknesses of 2.0–20mm.

– **LD80 Two-Roll Cold Rolling Mill:**
Produces tubes with outer diameters of φ45–123mm and wall thicknesses of 2.0–20mm.

– **LD90 Two-Roll Cold Rolling Mill:**
Produces tubes with outer diameters of φ60–127mm and wall thicknesses of 3.0–25mm.

– **3LD Three-Roll Cold Rolling Mill:**
Produces tubes with outer diameters of φ4–45mm and wall thicknesses of 0.7–5mm.

– **LG120 Three-Roll Cold Rolling Mill:**
Produces tubes with outer diameters of φ50–140mm and wall thicknesses of 1.5–25mm.

– **LG150 Five-Roll Cold Rolling Mill:**
Produces tubes with outer diameters of φ114–235mm and wall thicknesses of 3.0–35mm.

– **LG280 Three-Roll Cold Rolling Mill:**
Produces tubes with outer diameters of φ194–325mm and wall thicknesses of 6.0–60mm.

### Conclusion:
Multi-roll cold rolling pipe mills are highly effective for producing seamless pipes with high precision, reduced surface roughness, and optimized material utilization. They are widely used in manufacturing seamless tubes for various industries, including energy, aerospace, and construction, where high-strength, high-precision tubing is essential.