What are the ERW steel pipe making machines?

Electric Resistance Welding (ERW) steel pipes are produced using specialized machinery designed to handle various stages of pipe formation, from the initial shaping of the steel strip to the final welding and finishing. Below is a detailed explanation of the key components and processes involved in the production of ERW steel pipes.

1. Roller Forming Positioning Method

Most ERW pipe production units utilize the center positioning method for roller forming. This method offers several advantages:

Efficient Adjustment: When changing pipe specifications and sizes, the upper and lower rollers of the rough forming device can be adjusted simultaneously, with minimal adjustments needed. The fine forming device’s four rollers—adjusted in the up, down, left, and right directions—also require minimal modification. This precise positioning ensures accurate alignment of vertical rollers.

High-Frequency Stability: The high-frequency transmission lines can be securely fixed, ensuring consistent performance during the forming process.

Optimized Annealing: The ultrasonic adjustment range for the medium-frequency annealing sensor is reduced by half, enhancing the efficiency of the annealing process.

2. Pinch Roller

Typically, the pinch roller is a two-roller type, driven by a DC motor, and is adjustable in the vertical direction. Its primary purpose is to maintain consistent linear speeds between rough forming and fine forming stages during the strip forming process. This ensures that the strip does not bend or deform prematurely, allowing it to begin deforming only after leaving the forming frame. The pinch roller is crucial for strip centering and should be operated in conjunction with the vertical roller in the downhill forming method.

3. Preforming Device

The preforming device bends the strip steel from the center, following the center bending method. The bending angle is fixed and does not vary with the pipe diameter. This section marks the initial stage of roller forming, and its structure can differ depending on the specific production unit.

4. Rough Forming Device (Frame)

The rough forming device usually features a two-roller design driven by a DC motor. The rollers are divided into three sections, with the middle driving end sliding freely. The frame may have one or two seats, with the upper and lower rollers featuring holes (concave and convex) and having a larger diameter.

5. Bending Roller

The bending roller is designed to bend the strip edges to the desired size, preventing the formation of a "pear-shaped" finished tube. These rollers can be adjusted simultaneously or individually in the vertical and horizontal directions. When changing product specifications, fewer pass shapes need to be replaced if two-stage rough forming is used. Although one-stage rough forming requires more roller replacements, it is more cost-effective than installing an additional rough forming rack.

6. Outer Row Rollers

These rollers are symmetrically positioned on both sides of the center line between the bending roller and the finishing frame. They bend the strip steel into an open tube blank with an angle between 300° and 330°, allowing it to enter the precision forming frame’s hole pattern more easily. The bending angle depends on the number of precision-formed frames and the arrangement of inner row rollers, lower support rollers, and deformation drive rollers. The layout structure varies according to the diameter of the formed steel pipe. For example, a 1120mm diameter ERW pipe may require two to five rollers per pass, while a 610mm diameter pipe typically uses two rollers.

7. Inner Row Rollers

These rollers are evenly distributed along the inner surface of the longitudinal tube blank. The number of rollers in each pass section is determined by the inner diameter of the welded pipe.

8. Deformation and Driving Roller

The upper roller in this setup is a non-driven deformation roller, while the lower driving roller is powered by a DC motor. Positioned beneath the deformation roller, the lower driving roller enhances the strip’s driving capacity, leading to more uniform and efficient deformation.

9. Precision Molding Device

Located behind the row rollers, the precision molding device includes two precision forming machines when the strip is bent into a 330° open tube blank, and three machines when the angle is 300°. The precision forming passes are fully enclosed, with the upper roller equipped with a guide plate. The hole design is a vertical oval, and the base is typically a four-roller type driven by DC motors. There are two types of stands: the ordinary rolling mill archway type and a specially designed arch for rollers, with the latter offering better rigidity and ease of roller adjustment. To ensure reliable deformation, four precision forming racks are used for general round tube production, with five racks needed when producing both round and square or rectangular tubes.

10. Seam Guidance

The seam guide controls the weld opening angle, maintaining it between 3° and 6° to ensure a strong weld. The guide includes insulation and adjustment mechanisms to meet the required welding angle specifications.

11. Squeeze Roller

The squeeze roller, typically featuring four or five rollers (with the five-roller type being the most common), is essential for applying the necessary pressure to the tube edges before welding, ensuring a tight seam and a strong final weld.