What are the ERW pipe making machines?

What are the ERW pipe making machines?

The ERW pipe forming unit initially adopted the chain drawing method. Later the United States created roll molding. The structure of the primary roll forming device is a cross arrangement of flat rolls and vertical rolls, and is mainly used to produce small diameter ERW welded pipes. After continuous improvement, the forming arrangement was changed to the form of flat, vertical roller + vertical roller group, the pipe diameter was developed from small diameter to medium diameter, and high-frequency welding was adopted. It is generally called a small and medium-sized roller forming welded pipe unit. Later, it was further developed into the row and roll type. Roller forming main production process layout and equipment composition Roller forming machine is the main component of the welded steel pipe production line. It is the core of production and the key equipment on the production line, responsible for bending flat steel strips into round tube blanks.

According to the process requirements, the row roller forming unit generally includes pinch rollers, preforming device, rough forming device, bending roller, outer row roller, upper deformation roller, lower driving roller, inner row roller, precision forming frame, guide rail, etc. It is described below.

1. Roller forming positioning method: Most units adopt the center positioning method. The advantages of this centering method are:
1) When changing the specifications and sizes, the upper and lower rollers of the rough forming device are adjusted together, and the adjustment amount is relatively small; the four rollers of the fine forming device are adjusted up, down, left, and right, and the adjustment amount is relatively small; the vertical rollers are positioned accurately.
2) High frequency transmission lines can be highly fixed.
3) The amount of ultrasonic up and down adjustment of the medium frequency annealing sensor can be reduced by half.

2. Pinch roller
It is generally a two-roller type (no hole type), driven by a DC motor, and can be adjusted up and down. The purpose is to ensure that the linear speeds of rough forming and fine forming are consistent during the strip forming process, so that the strip does not produce bending deformation in the frame and begins to deform after leaving the frame. The pinch roller is very important for centering the strip. The vertical roller should be adjusted and operated in conjunction with the downhill forming method.

3. Preforming device
The strip steel is bent and deformed from the center (belonging to the center bending method), and its bending angle is fixed and does not change with the pipe diameter. This section is the primary stage of roller forming, and its structure varies depending on the unit.

4. Rough forming device (frame)
It is generally a two-roller type driven by a DC motor. The upper and lower rollers are divided into three sections, and the middle driving end slides freely. This kind of rack has 1 or 2 seats, but the upper and lower rollers have holes (concave and convex types) and a larger diameter.

5. Bending roller
The purpose is to bend the strip edges to the desired size, preventing the production of a "pear-shaped" finished tube. A pair of bending rollers can be adjusted up, down, left and right at the same time, or individually. When changing product specifications, if one-time rough forming is used, most of the pass shapes need to be replaced; if two-time rough forming is used, fewer bending rollers need to be replaced, and only a few models need to be replaced. Generally speaking, although using one rough forming rack requires more replacement of bending rollers, it is more economical than installing one more rough forming rack.

6. Outer row rollers
The outer rollers are symmetrically arranged on both sides of the center line between the bending roller and the finishing frame. Bend the strip steel into an open tube blank of 300°~330° so that it can easily enter the hole pattern of the precision forming frame. The bending angle is related to the number of precision-formed frames and the number of inner row rollers, lower support rollers, and deformation drive rollers. Its layout structure is designed into different structural forms according to the diameter of the formed steel pipe. When the diameter of the formed ERW pipe is 1120mm, one pass can consist of two rollers, three rollers, four rollers or five rollers. When the diameter of the formed ERW pipe is 610mm, the hole pattern basically consists of two rollers.

7.Inner row rollers
Evenly arranged on the inner surface of the longitudinal tube blank. On the pass section, the number of rollers is determined according to the inner diameter of the welded pipe.

8. Deformation and driving roller
The upper roller is a deformed roller without drive, and the lower drive roller is driven by a DC motor. The lower driving roller is correspondingly arranged below the deformation roller, which increases the driving capacity of the strip and makes the deformation more uniform and reasonable.

9. Precision molding device
Set behind the row rollers, two precision forming machines are used when the row rollers bend and deform the strip into a 330° open tube blank. When the row of rollers bends and deforms the strip into a 300° open tube blank, three precision forming machines are required. The precision forming passes are all closed passes, and the upper roller is equipped with a guide plate. The hole design adopts vertical oval type, the general machine base is four-roller type, and the upper and lower rollers are driven by DC motors. There are also two types of stands: one is the archway type of an ordinary rolling mill; the other is the arch type of an ordinary rolling mill; the other is an arch specially designed for rollers. The latter has good rigidity and is easy to change rollers and adjust. In order to ensure reliable deformation, the number of precision forming racks when producing general round tubes is 4; if round tubes and square and rectangular tubes are produced at the same time, 5 racks are required.

10. Seam guidance
The purpose is to control the weld opening angle between 3° and 6° to ensure good welding. The welding seam guide itself has insulation and adjustment mechanisms to ensure the welding angle requirements.

11. Squeeze roller
The extrusion roller is generally a four-roller or five-roller type, with the five-roller type being the most common.

The above are some ERW production tools. Next, let us understand its defects and the causes of them.

ERW tube offset defect

The offset defect of ERW pipe is also called lap welding, which refers to the misalignment of the two edges of the tube blank during welding. Even after the internal and external burrs are removed, traces of offset are still visible on the internal and external surfaces of the steel pipe.

The main hazard of offset is to reduce the effective wall thickness of the steel pipe. The API SPEC 5L standard states that the deflection plus residual burr of electric welded steel pipe shall not exceed 1.5 mm (0.060 inches). In addition, offset will also affect ultrasonic and X-ray inspection of steel pipes. During the use of steel pipes, offset will also become the starting point of chemical corrosion of steel pipes.

Causes of offset defects in ERW steel pipes

1. Deviation caused by poor molding quality
ERW steel pipes need to go through a series of rolls (rough forming roller string, fine forming) to gradually roll the coil into a cylindrical shape, and the forming quality has a great influence on the welding quality. If the center of the strip is offset during forming, the edge of the tube blank will be uneven and offset. Usually, this offset is one-way and easier to judge. Secondly, if the parameters of the forming roller are set improperly, before entering the extrusion roller, the height of both edges of the strip will change in a wavy manner. After entering the extrusion roller, there will be a small local deviation, resulting in deformation of the strip. The direction of the offset is uncertain.

2. The influence of extrusion force
ERW steel pipes are welded by heating the edges of steel strips and extruded by extrusion rollers. Extrusion force is one of the main parameters of the welding process and has a great impact on the quality of ERW steel pipes. The extrusion force is small, the number of eutectics formed is small, and the strength of the weld is low. At the same time, non-metallic inclusions and oxide residues formed in the weld also affect the strength of the weld. If the extrusion force is too great, all the metal reaching the welding temperature will be squeezed out, thereby reducing the strength of the weld. In addition, excessive extrusion force can easily cause offset, and it is difficult to adjust this offset without reducing the extrusion force. Generally speaking, the extrusion force is expressed and calculated by the difference in circumference of the tube blank before and after the extrusion roller - the extrusion amount, which is usually half of the steel pipe wall thickness.

3. Influence of rollers and tooling
(1) Influence of rollers. The rolls that affect the deflection of ERW steel pipes are mainly finishing rolls and extrusion rolls. The finishing roller wear is too large, and the guide parts of the finishing roller have different wear on both sides. Damage to the edge of the extrusion roller, especially the upper extrusion roller, and the difference in wear between the two extrusion rollers will cause offset, generally with a certain period.
(2) The influence of rolling bearings. The bearing of the extrusion roller is damaged, causing the extrusion roller to not rotate or rotate unevenly, resulting in uneven extrusion force and deviation. In addition, extensive wear of the bearings or excessive bearing clearance will also cause the squeeze roller to rotate unevenly and cause deviation.
(3) Influence of the installation quality of rolling tooling. The finishing roller and the side extrusion roller are not installed levelly. The gap between the upper extrusion roller shaft and the bearing and the gap between the shaft and the roller seat are too large, which will cause offset.

Judgment and confirmation of offset
The judgment and confirmation of offset mainly rely on visual observation. When there is significant offset, it can be discovered by squeezing the roller. But for small offsets, it is necessary to observe the internal and external burrs and the shape of the weld after removing the internal and external burrs. It can be judged from the following aspects.
(1) Observe the outer burr. The melt extruded by welding is not in the middle of the outer burr.
(2) The outer weld bead is not straight after burr removal, and the width and shape of the outer weld bead change after scraping.
(3) Observe the inner burrs. If there are intermittent cracks or cracks in the inner burrs, there may be an offset defect.

Adjustment and elimination of offsets
When an offset occurs, determine the cause of the offset based on the offset phenomenon, and take the following measures to make adjustments:
(1) After the strip enters the forming machine, ensure that the center of the strip does not deviate from the rolling center. When waves and bulges appear on the edge of the tube blank, the diameter reduction amount of the fine forming and the diameter reduction of the small row of rollers should be reasonably adjusted to reduce and eliminate the edge waves and bulges.
(2) Select reasonable process parameters, especially appropriate welding extrusion force.
(3) Grind the excessively worn or differently worn rollers on both sides of the precision-formed guide rollers, and repair the squeeze rollers with damaged edges.
(4) Check and replace bearings with large wear or large bearing clearance, and do a good job of lubricating the bearings.
(5) Ensure that the rollers are installed horizontally when changing lanes, and eliminate excessive gaps between the extrusion shaft and the bearings, and between the shaft and the roller seat.

ERW pipe is a welded steel pipe using resistance welding process. Resistance welding is a method of combining workpieces, applying pressure through electrodes, and using resistance heat generated when electric current passes through the joints and adjacent areas of contact. Resistance welding is a method in which electric current flows through the contact surface between the workpiece and the adjacent area, heating it to a molten or plastic state, and forming a metal bond.