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3-Roll Bending Process Working Principle And Equipment Features

3-roll bending process (also known as a three-roller plate rolling) is one of the most classic and widely used circular forming in the field of metal sheet forming. It is widely used in pressure vessels, air ducts, storage tanks, steel structures, shipbuilding, bridges, and machinery manufacturing industries.

Below is a systematic and in-depth analysis of its working principle, structural composition, forming mechanism, technical characteristics, advantages, comparison of different structural forms, and application scenarios.

1. Basic Working Principle of 3-Roll Bending Process

The core principle of three-roll plate rolling is: By changing the relative positions of the three rollers, the sheet metal undergoes continuous plastic bending deformation under stress, ultimately forming the desired arc or cylindrical shape.

1) Basic Structural Components

A standard three-roll plate rolling machine typically consists of:

Upper roller (main roller)
Lower roller (support roller)
Side rollers (adjusting rollers)
Main drive system
Hydraulic system
Electrical control system
Tilting mechanism (for unloading)

2) 3-Roll Bending Forming Process

Step 1: Plate Feeding and Positioning

The sheet metal is inserted between the upper and lower rollers.

Step 2: Side Roller Lifting and Lowering

The side rollers rise or fall, changing the three-point support position.

Step 3: Generating Bending Moment

As the sheet metal passes through the three rollers:

The upper roller applies pressure.
The lower roller provides support.
The side rollers control the bending radius.
The sheet metal undergoes continuous plastic deformation.

Step 4: Repeated Feeding

Through repeated rolling, the bending gradually reaches the set radius.

Step 5: Complete the forming process

Form a cylindrical or arc-shaped work piece.

2. Mechanical Principles of Three-Roll Plate Rolling

The essence of 3-roll plate bending is: Continuous three-point bending forming

Mechanical characteristics:

The upper roll is the driving roll (in most structures)

The plate is subjected to bending moment

The outer side of the plate is under tension

The inner side is under compression

The neutral layer remains essentially unchanged

When the stress exceeds the material’s yield strength, plastic deformation occurs.

Principle of Bending Radius Control

The bending radius depends on:

Roller spacing
Side roll position
Plate thickness
Material strength
Upper roll pressure

The closer the side roll is to the upper roll:

→ Smaller bending radius

→ Greater forming curvature

3. Structural Types of Three-Roll Plate Rolling Machines

– Symmetrical Three-Roll Plate Rolling Machine

– Asymmetrical Three-Roll Plate Rolling Machine

– Mechanical Level Down Plate Rolling Machine

– Upper Roller Universal Plate Rolling Machine

Custom configurations are available based on plate thickness, processing precision, and automation requirements.

1) Symmetrical 3-Roll Plate Bending Machine

Features: Two lower rollers are fixed; the upper roller lifts vertically.
Advantages: Simple structure; low cost; suitable for medium and heavy plates.
Disadvantages: Requires pre-bending assistance; slightly lower precision.

2) Asymmetrical Three-Roll Plate Rolling Machine

Features: Lower roller is adjustable; one side roller is movable.
Advantages: Can be pre-bent directly; easier operation; higher precision.
Suitable for: Small and medium-sized processing plants.

3) Level Down Three-Roll Plate Rolling Machine

Features: Two side rollers move horizontally; the upper roller is fixed.

Advantages: High precision; high degree of automation; suitable for large plates.

4) Upper Roller Universal Three Plate Rolling Machine

Features: This machine is hydraulic 3-roll bending machine, used to complete the processes of pre-bending, rounding, and straightening at the end of various containers without the need to turn around after one feeding.
Advantages: With hydraulic system, it is suitable to roll thick metal sheet. Upper roller universal type machine can add the cone rolling device to roll the conical shapes.
Suitable to produce heavy duty plate rolling machine model and its price is lower than 4 roller rolling machine.

4. Features & Advantages: 3-Roll Bending Equipment

The following is a detailed breakdown of its advantages:

1) Strong Structural Stability

The three rolls form a three-point support structure, resulting in balanced stress, strong load-bearing capacity, and suitability for heavy-duty processing. Especially suitable for: Pressure vessels, storage tank bodies, and large steel structures.

2) Wide Forming Range

Can process: Cylinders, Cones (with conical devices), Curved plates, and multi-segment curves. Material types include: Carbon steel, Stainless steel, Aluminum plates, High-strength plates, and Alloy steel.

3) High-Efficiency Continuous Forming

Compared to bending machines: Bending machines perform multi-segment bending, while three-roll roller forming involves continuous bending.

Therefore: Smoother surface, better roundness, and more precise weld joints.

4) Strong Pre-Bending Capability

Supports partial structural pre-bending: Plate head pre-bending, plate tail pre-bending, reducing straight edge residue.

Improvements:

Material utilization rate
Welding quality
Finished product aesthetics

5) Large potential for automation upgrades

Modern three-roll plate bending machines can be equipped with:

CNC control system
Automatic diameter measurement system
Automatic feeding system
Angle compensation system
Automatic centering system

Achievements:

One-click rolling
Parameter memory
Mass production

6) Energy saving and drive advantages

Main drive methods:

Mechanical transmission
Hydraulic transmission
Full servo drive

Among them:

Hydraulic is suitable for heavy loads
Servo is suitable for high precision

5. Comparison between three-roll rolling machine and four-roll plate rolling machine

Comparison table of 3-roll bending and 4-roll:

Comparison Items	3-roll	4-roll
Structural Complexity	Simple	Complex
Cost	Lower	Higher level
Operational Difficulty	Slightly higher	Simpler level
Pre-bending Capacity	Partially supported	More powerful
Automation	Upgradeable	More suitable for automation

The advantages of three-roller compressors are: economical and practical, structurally stable, and easy to maintain.

Technical Principles and Structural Advantages:

1) Continuous Three-Point Bending Forming

The equipment consists of a three-point support system composed of an upper roller, a lower roller, and side rollers. By adjusting the position of the side rollers, the stress state of the sheet metal is changed, allowing the sheet metal to gradually reach the set bending radius during rolling, achieving uniform and stable plastic deformation.

Outer layer of the sheet metal is under tension
Inner layer is under compression
Neutral layer is stable
The forming process is continuous and smooth

2) High-Strength Frame Structure

Integral welded frame
High-rigidity side plate structure
Large-diameter alloy steel rollers
Heavy-duty bearing system

Ensuring stable operation and precise control even when rolling thick plates and large diameters.

3) Pre-bending Function Design

Supports pre-bending at the head and tail of the sheet metal, effectively reducing straight edge residue, improving material utilization and welding quality, especially suitable for manufacturing high-requirement container shells.

6. Key Technical Indicators

Main technical parameters include:

Maximum coil thickness
Maximum coil width
Upper roller diameter
Lower roller diameter
Minimum coil diameter
Main motor power
Rolling speed
Pre-bending thickness

Key Technical Parameters (Sample Template)

(The following are template parameters; actual project parameters can be adjusted according to requirements.)

Item	Technical Parameters
Maximum coil thickness	2500 mm
Maximum coil width	≤ 245 MPa
Material yield strength	φ320 mm
Upper roll diameter	φ280 mm
Lower roll diameter	≥ φ350 mm
Minimum coil diameter	15 kW
Main motor power	4–6 m/min
Rolling speed	≥ 16 mm
Pre-bending thickness	2500 mm

We can perform verification calculations based on the strength grade of the customer’s board material.

7. Summary of the Core Advantages of 3-Roll Bending Machines

In short:

Three-roll bending machines are classic equipment for “continuous plastic bending forming,” possessing comprehensive advantages such as structural stability, high load-bearing capacity, economical cost, and a wide processing range.