Analysis of Common Causes of Buildup on Internal Burrs in Welded Steel Pipes

Internal burr removal is a critical process in high-frequency welded steel pipe production. Improper adjustments or operation can lead to buildup during this process, compromising the quality of the internal burr removal. This article examines the types of buildup that can occur on the blade or shank of high-frequency welded steel pipe internal burrs, analyzes the causes of buildup, and identifies preventative measures by observing and identifying buildup during production line operation. Internal burr removal has always been a challenging issue in high-frequency welded steel pipe production. Buildup (also known as weld buildup) on the blade during production not only seriously impacts internal burr removal quality but also frequently causes production line downtime, reducing the yield rate of welded steel pipes. Furthermore, excessive amounts of internal burrs in welded steel pipes can significantly complicate subsequent processing and significantly reduce production efficiency. Therefore, it is necessary to analyze the buildup problem that occurs during internal burr removal, identify the root cause, and develop appropriate countermeasures.

There are many methods for removing burrs from high-frequency welded steel pipes, including roller pressing, grinding, and tool scraping. Tool scraping is widely used in production due to its high precision, flexible adjustment, and reliable quality. This article details the causes and solutions for common buildup problems in high-frequency welded steel pipe production.

1. Buildup: This refers to the lumps formed by the convergence of molten metal droplets during high-frequency welding. Common buildup types are small and large.

2. Small buildup: Small buildup is very common in high-frequency welding and appears to be an accumulation of small particles. Sparks fly during high-frequency welding, producing particles as small as sesame seeds. If not removed promptly, these small particles will continue to aggregate and form lumps, becoming lodged above the inner burr bar. Once these particles grow to a certain size, they can prevent the bar from lifting properly or block the inner hole of the inner burr ring, preventing proper scraping. Small buildup is generally resolved by adjusting the cooling air pressure and air outlet position on the inner burr bar. The image below shows a small particle buildup that often forms on the internal burr bar.

3. Large particle buildup: Large particle buildup is composed of larger particles with strong bonds between them. Compared to small particle buildup, large particle buildup forms more quickly and is more likely to result in poor internal burr removal, even causing welding failure and machine downtime. Large particle buildup can be divided into shank buildup and internal burr bar buildup based on where it forms.

4. Shank buildup: This primarily forms on the shank or protective sleeve below the weld V-angle and is caused by excessive welding power. The higher the welding power, the more fluid the molten metal at the plate edge. During high-frequency welding, a large amount of molten metal extruded from the steel pipe drips onto the shank or protective sleeve, forming a large particle buildup. This seriously affects the proper lifting of the shank, resulting in poor internal burr removal.

5. Internal burr bar buildup: This primarily occurs on the internal burr bar or upper roller, which is also caused by excessive welding power. The higher the welding power used in steel pipe welding, the softer the internal burrs produced. During the scraping process, the internal burrs continuously adhere to the internal bayonet and quickly accumulate on the bayonet or upper roller, forming a buildup. This seriously degrades the quality of the internal burr scraping.

First, causes of buildup:

1. Excessive high-frequency welding power

During production, high-frequency welding operators often judge the welding power level based on the color and shape of the external burrs. The shape and color of the external burrs are related to the shape of the strip edge during welding. Different strip edge shapes result in significant differences in the shape and color of the external burrs. Inexperienced operators often misjudge this, leading to excessive welding power and buildup.

A. Misalignment. During high-frequency extrusion welding, the strip edges are misaligned.

B. Excessive curvature on one side of the plate edge: During rough or fine forming, this may be due to deformation of the roll stand after long-term use, poor roll bearing operation, or other factors, resulting in greater rolling force on one side of the plate edge than on the other, resulting in different curvatures on both sides. C. Chamfered or rounded corners on one side of the plate edge: Before high-frequency extrusion welding, the plate edge undergoes a series of processes, including overhead crane hoisting, uncoiling, shearing and butt welding, looping, and forming. These processes may cause a chamfer or rounded corner on one side of the plate edge.

All three of these conditions can cause uneven burr sizes on both sides of the steel pipe during welding, leading to operator misjudgment of the welding condition and excessive welding power.

2. Unsatisfactory butt joint configuration

The following shows three different butt joint configurations during welding. The ideal butt joint configuration is an I-shape between the two plate edges, resulting in excellent weld quality. If the plate edge is V-shaped, the bottom V-shaped area will converge first during welding. A large amount of current will flow through the inner surface, causing the metal in the inner weld area to overheat and melt. Furthermore, to achieve full penetration (i.e., to melt the outer weld area as well), the welding power must be increased, resulting in excessively high welding temperatures, a large number of weld beads, and a buildup of large particles. In this welding condition, the outer burrs are smaller, while the inner burrs are larger, requiring a large amount of scraping. If the plate edge is in an inverted V shape, the outer burrs are generally larger, while the inner burrs are smaller. Therefore, an inverted V-shaped plate edge should be avoided as much as possible during welding.

3. Improper Cooling Air Adjustment

The cooling air on the internal bayonet bar plays a crucial role in the internal bayonet scraping process. It not only removes slag to prevent slag from accumulating on the bar and burning the protective sleeve, but also cools the internal burrs to prevent sticking during scraping. However, in actual production, buildup is often caused by insufficient cooling air pressure on the internal burr bar and improperly positioned air outlets. If the cooling air pressure is too low, the slag will not be blown away with sufficient force, resulting in small particles of buildup that accumulate on the bar or blade. If the air outlet is improperly positioned, it can prevent the slag from being blown away from certain areas of the internal burr bar or bar, leading to buildup.

4. Improper Cooling Water Adjustment

In addition to cooling the magnetic rod, the cooling water on the internal burr bar also removes weld buildup and slag that accumulates on the front of the protective sleeve during welding, preventing it from accumulating and forming hard lumps on the bar. In actual production, leaks or blockages in the water supply line can cause low water pressure at the outlet, making it impossible to flush the buildup on the front of the resistor.

5. Improper Adjustment of the Internal Burr

In actual production, improper cutting angles of the internal burr bar, improper positioning of the burr bar, or gaps in the internal burr bar can lead to poor internal burr removal and easily cause buildup.

6. Poor operation of the upper and lower rollers

In actual production, operators often overlook the operation of the upper and lower rollers on the internal burr removal cutter bar. Inadequate inspection or improper adjustment can cause the rollers to malfunction. If these rollers malfunction, welding slag formed during welding can accumulate on the rollers and remain trapped, forming weld nubs. This can affect the proper raising and lowering of the cutter bar or cause the cutter bar to shift position. Poor operation of the upper rollers can lead to excessive buildup on the rollers, preventing the cutter bar from lifting properly or causing the cutter bar to shift, resulting in poor or complete removal of burrs from the welded pipe. Poor operation of the lower rollers can cause the lower rollers to be elevated by the buildup or cause the cutter bar to shift, causing burrs to be scraped off-center, deep-scratched, or even prevent proper cutting of the butt weld joint during high-frequency welding.

7. Weld seam torsion

Small-diameter steel pipes are prone to weld seam torsion. Severe weld seam torsion can cause internal burrs to be scraped off-center and even cause weld nubs to form.

Second, observe and identify buildup.

During production line operation, it's impossible to inspect the internal burr or blade position of the welded steel pipe by opening a "skylight" to check for buildup. However, the internal burr removed after flying sawing can be used to assess the scraping performance of the internal burr and, therefore, determine whether buildup is present. Frequent buildup on the internal burr indicates improper high-frequency extrusion welding parameter settings. If the production line continues to operate despite this condition, blade sticking is likely to occur, leading to a large buildup. If the buildup is small and can pass smoothly through the circular hole of the internal burr, it will be clearly visible on the internal burr produced after flying sawing. However, if the buildup is large and cannot pass through the circular hole, it will accumulate on the internal burr and nearby areas, severely impairing scraping and even causing the production line to shut down. Therefore, if buildup appears on the internal burr after flying sawing, check the high-frequency welding power and the cooling air pressure on the internal burr blade for abnormalities.

Third, Methods for Preventing Buildup

1. Methods for Preventing Small Particle Buildup:

Small particle buildup is primarily caused by the failure to properly remove particles from sparks after cooling during welding. Therefore, to prevent small particle buildup, before starting the machine, carefully check the air and water lines of the internal hair cutter, check the air and water pressure gauges for normal operation, and check the pipes and pipe heads for blockages. Also, check the upper and lower rollers of the internal hair cutter for proper operation.

2. Methods for Preventing Large Particle Buildup:

The direct cause of large particle buildup is excessively high welding temperature. This can be caused by improper process parameters, but in most cases, it's due to improper weld edge butt jointing, resulting in increased welding power to ensure the entire weld reaches the welding temperature. Therefore, adjustments should be made to ensure an I-shaped weld joint between the two edges to reduce the likelihood of large particle buildup.

Many factors contribute to the formation of internal burrs and buildup during welding, including welding parameters, cooling air, cooling water, plate edge quality, upper and lower rollers, tool bar straightness, and tool quality. Only by fully understanding each influencing factor and paying close attention to its manifestations can we adjust equipment and process parameters in a timely manner, thereby reducing weld buildup and ensuring the quality of internal burr removal and efficient operation of the production line.