How to ensure the quality of high frequency welded pipe in the process of production? We should take the effects of roll adjustment into consideration, except that, we also need to consider the geometric dimensions of steel strip.
When the width of the steel strip is less than the allowable deviation, the squeezing force of the welded steel pipe will be reduced, which will cause the welding of the steel pipe loose, and cracks or open-end pipe will appear. When the width of the strip is greater than the allowable deviation,the squeezing force will be increased when the steel pipe is welded, which will cause tip, welding or burr welding defects appearing on the weld of the steel pipe. Therefore, the fluctuation of the strip width not only affects the accuracy of the steel pipe's outer diameter, but also seriously affects the surface quality of the steel pipe.
About the steel pipe that requires the same section wall thickness difference does not exceed the specified value (that is to say the uniformity of the steel pipe wall thickness is high), the fluctuation of strip thickness will transfer the allowable value that exceeds the thickness difference of one steel strip to the wall thickness difference of finished steel pipe, which will waste a large number of steel pipe for the thickness of the pipe exceeds the allowable deviation. Thickness fluctuations not only affect the thickness accuracy of the finished steel pipe, at the same time, the difference of steel strip's thickness will cause the extrusion pressure and welding temperature are instability while the steel pipe in the welding, which will result in welded steel pipe weld quality instability.
In addition, the existence of interlayer, impurities, trachoma and other material defects in the interior of steel is also an important factor to affect the quality of steel pipe .
Therefore, before welding the steel strip , we should check the surface quality and geometric size of each steel strip. For the steel strip that the quality does not meet the standard requirements, we shouldn't carry out production to avoid unnecessary losses.
The emergence and maturity of high-frequency welding technology, directly promoted the development of Longitudinal Welded Pipe industry, it is the key processes of Longitudinal Welded Pipe(ERW steel pipe) production. High-frequency welding originated in the fifties of last century, it is a new welding process that uses the skin effect and adjacent effects produced by high-frequency current to make the steel plate and other metal materials docked.Good or bad quality of high-frequency welding directly has an impact on the overall strength, quality grades and production speed of welded pipe products. As a manufacturer of welded pipe, you must understand the basic principles of high-frequency welding, understand the structure and working principle of high-frequency welding equipment, and understand the high-frequency welding quality control points.
Relatively the 50Hz AC current frequency speaking, high frequency is generally refers to 50KHz ~ 400KHz high frequency current. When high-frequency current flow through the metal conductor, it will produce two strange effects: skin effect and proximity effect. And high-frequency welding just uses these two effects to weld the steel pipe. So, what are the those two effects?
Skin effect refers to a certain frequency of AC current flow through the same conductor, the current density is not evenly distributed in all sections of the conductor. It will mainly focus on the surface of the conductor, that is, the density of the current in the conductor surface is big, the density of the conductor inside is small. So we vividly called it "skin effect". Skin effect is usually measured by the penetration depth of the current, the smaller the penetration depth, the more obvious the skin effect. And the penetration depth is proportional to the square root of the resistivity of the conductor, and is inversely proportional to the square root of the frequency and permeability. In layman's terms, the higher the frequency, the more concentrated current will be on the surface of the steel plate; the lower the frequency, the more dispersed current will be on the surface. It must be noted that, although the steel is a conductor, its permeability will drop with the temperature rise, that is, when the steel plate temperature increases, the permeability will decline, skin effect will be reduced.
The proximity effect refers to the fact that when the high frequency current flows counter currently in two adjacent conductors, the current will flow collectively toward the edges of the two conductors. Even if there is a shorter side in two conductors, the current does not flow along the shorter route. We call this effect "proximity effect". Proximity effect is essentially affected by inductive reactance, inductance plays a leading role in the high frequency current. The proximity effect increases as the frequency increases and the spacing of adjacent conductors approaches. If adding a core around the conductor, the high frequency current will be more concentrated on the surface of the workpiece.
These two effects are the basis for achieving high frequency welding of metals. High-frequency welding just used the skin effect so that the energy of high-frequency current concentrated in the workpiece surface, and used the proximity effect to control the location of high-frequency current flow and range. The speed of the current is very fast. It will heating and melting adjacent to the edge of the steel plate in a very short period of time, and achieve docking through the extrusion.
Some buyers haven't a very clear concept about what is ERW pipe and what is ERW tube manufacturing process, they also don’t know its application. Today, Prime steel pipe will give you a detailed introduction about that.
What is ERW pipe?
ERW pipe (also called ERW steel pipe) is the abbreviation Electric Resistance Welded Pipes. Electric resistance welding refers to a group of welding process (including spot and seam welding) that produce coalescence of faying surfaces where heat to form the weld is generated by the electrical resistance of material combined with the time and the force used to hold the materials together during welding. ERW steel pipes and tube are available in various qualities, wall thicknesses, and diameters of the finished pipes.
What is ERW tube manufacturing process?
ERW steel pipe is manufactured by rolling metal and then welding it longitudinally across its length. ERW steel pipes are welded longitudinally, manufactured from Strip / Coil and can be manufactured up to 24”OD. ERW pipe cold formed from a ribbon of steel pulled through a series of rollers and formed into a tube which is fused through a electric charge.
Typical ERW tube manufacturing process of Prime Steel Pipe generally involves the following stages in a step by step procedure.
The application of ERW steel pipe
ERW steel pipes are used in various engineering purposes, fencing, scaffolding, line pipes etc. It is available in lengths from single random to 120 feet depending on mill capability. What's more, ERW steel pipes are usually used for Agricultural purposes, Drinking Water for housings, in collieries for extraction of Water, Thermal Powers, Transports, Hand pumps for deep boring wells, as a strong protection for cables by Telecom Department, Structural Purposes etc. ERW steel pipe is available with square ends or beveled for welding, threaded and coupled and victaulic grooved. Surface finish of it is available in black or bare, or with protective coatings.
Prime Steel Pipe have a very large production capacity of ERW steel pipes, so that we can manufacture ERW pipes and tubes of different size and shape based on the customers requirements.