Tube Forming and Sizing Mill

ERW Carbon Steel Tube Mill

Tube Mill Machine Compose

Cold Roll Forming Machine

Steel Coil Slitting Line

Carbon Steel Coil Slitting Line

Steel Coil Cut To Length Line

Auxiliary Equipment And Spare Parts

Round to Square Forming and Sizing Section

In ERW tube production, the round-to-square forming process is a key technique for manufacturing square and rectangular pipes. It involves reshaping a fully welded round tube into a square or rectangular section through a series of precision sizing and forming rolls under cold forming conditions.

Product Details

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Product Details

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Product Description

1. Technical Overview: Round-to-Square Forming Process

Process Flow:

Raw material → Forming → HF Welding → Burr Removal → Cooling → Round-to-Square → Sizing → Flying Saw → Finished Pipe

Key Features and Technical Notes:

Stepwise Deformation: The tube undergoes three stages: pre-forming, transitional forming, and final shaping, progressively transforming the round section into a square.
Cold Bending Principle: The shaping relies on plastic deformation across multiple roll passes to gradually modify the profile.
Precision Control: Equipped with CNC adjustments and inline measuring systems to ensure dimensional accuracy and edge/angle precision.
Flexible Tooling: Only the final forming and sizing rolls need to be replaced for different specifications, allowing fast product changeovers.

Technical Advantages:

High dimensional accuracy and straight edges with clean corners
Centralized weld seam, ensuring better structural performance
Reduced energy consumption and tooling wear compared to direct square forming
Widely used in construction, mechanical frames, furniture tubing, and automotive profiles

2. BASIC DESIGN DATA

Design of the proposed line is based on following specification:

Raw Material Specification

Raw Material Feeding	CR bright tube with oiled, Galvanized steel, HR coil
Material Tensile Strength	Max 517MPa (75,000 psi max)
Material Yield Strength	Max 460MPa （67,000 psi max）
Coil OD	1200mm to 2000mm
Coil ID	508mm&610mm (customer order)
Coil Weight	Max 7000 kg
Strip Width	Min 240mm, Max520mm
Strip Thickness	Min2.0mm Max6.35mm

Production Range

Type of production	▪Round Tubes ▪Square and Rectangular Hollow Sections
Round Tube OD	Min 76mm, Max 165mm
Round Tube Thickness	Min 2.0mm, Max 6.35mm
Square Hollow Section	Min 60x60mm, Max 130x130mm
Rectangular Hollow Section	Min 80x40mm, Max 100X160mm
Square and rectangle Tube Thickness	Min2.0mm, Max 5.0mm
Tube Cut Length	Min 6 meter, Max 12 meter

Line Specification

Forming Section

Shaft material:	40Cr, HF tempering quenching
Material of bevel gear:	20CrMnTi
Driven stand	7 sets
Idle stand	8 sets
Gear box	7 sets

Sizing Section

Shaft material:	40Cr,HF tempering quenching
Material of bevel gear:	20CrMnTi
Driven stand	5 sets
Idle stand	5 sets
Gear box	5 sets

The Flow of the Production Line

Forming section（Flattening unit +Main driving unit +Forming unit +Guide unit +squeeze roller）+ De-burr frame →→Cooling unit →→ Sizing unit and straightener

Forming and Final Sizing Section of ERW Pipe Mill

2. Frequently Asked Questions (FAQ)

Q1: Why choose the round-to-square process instead of direct square forming?
A: The round-to-square method ensures better weld seam alignment, stronger structural integrity, and greater tooling flexibility, especially for mid-to-thick wall and high-strength materials.

Q2: How is the corner quality controlled? What are the common issues?
A: Corners are formed through gradual pressing in multiple roll passes. Issues like cracking, over-rounded corners, or misalignment can be resolved by optimizing roll design and adjusting pressure settings.

Q3: How to prevent weld seam misalignment during forming?
A: Keep the weld seam centered after welding and ensure symmetrical roll forces during forming. Optional weld seam tracking systems can further stabilize seam position.

Q4: Do we need to replace the entire roll set when changing specifications?
A: No. Only the round-to-square and sizing sections need to be changed, significantly reducing downtime and tooling costs.

Q5: What causes edge waviness or "bamboo-like" defects?
A: These are typically due to excessive deformation per pass or improper roll design. Adjusting the deformation rate and optimizing pressure balance in the sizing unit can solve this.

Q6: Is round-to-square suitable for small-size thin-wall tubes?
A: Generally not. Thin-wall small tubes are prone to instability or cracking during transformation. Direct square forming is more appropriate for such sizes.

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Forming & Sizing Section FAQs

Why choose the round-to-square process instead of direct square forming?

The round-to-square method ensures better weld seam alignment, stronger structural integrity, and greater tooling flexibility, especially for mid-to-thick wall and high-strength materials.

How is the corner quality controlled? What are the common issues?

Corners are formed through gradual pressing in multiple roll passes. Issues like cracking, over-rounded corners, or misalignment can be resolved by optimizing roll design and adjusting pressure settings.

How to prevent weld seam misalignment during forming?

Keep the weld seam centered after welding and ensure symmetrical roll forces during forming. Optional weld seam tracking systems can further stabilize seam position.

Do we need to replace the entire roll set when changing specifications?

No. Only the round-to-square and sizing sections need to be changed, significantly reducing downtime and tooling costs.

What causes edge waviness or "bamboo-like" defects?

These are typically due to excessive deformation per pass or improper roll design. Adjusting the deformation rate and optimizing pressure balance in the sizing unit can solve this.

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