There is still a lot of misunderstanding about how to build welded tubes, even though high frequency pipe mill machine supplier makes up the vast majority of tubes manufactured worldwide. A thorough understanding of the method, though, might boost production rates and quality. The procedure is beneficial since it is somewhat lenient.
Theory of operation
A “virtual transformer” made up of the working coil (primary winding) and the tube itself takes the place of the massive spinning transformer required for lower frequencies electrical resistance spot welding (ERW) (secondary winding). A ferromagnetic core, analogous to the core material in a conventional transformer, is house within the tube.
As the coil transfers energy, a magnetic field forms around it. With a section of this field passing through the gap in the lid. Because of this, an electric field is generate on the outer surface of both tubes. Which causes a voltage difference across the ends of the strip. At the frequencies used by induction welders, the interaction of the electromagnetic and electric fields might result in current flows that were not anticipated. Due to the “skin effect,” which limits the flow of current to within a few tenths of an inch of both surfaces. The voltage across strip boundaries often induces electric current to flow in a radial direction.
The current create on the inner surface of the outer tube flows counter clockwise around the whole circumference of the inner tube.
However, with the help of high frequency ss tube mill machine supplier and at high frequencies, inductor rather than resistive regulates current flow, and this is because of the close proximity of the friction between two edges of the strip from the coils to the tip of the vee. This phenomenon is also known as the “proximity effect.”
This exemplifies the fact that when a voltage is applied across the edges of the strip, current might largely go down two paths. The trick to making the most of a frequency welder is to minimise the inefficient current. That flows around the inner tube’s surface and instead direct it along the faying edges. Where it does useful work by burning them. To do this, the input resistance of the vee must be lower in relation to the I.D. surface.
The point of the obstruction
The first tool you have is an impeder, which raises the impedance of the tube. An impeder is, in the simplest terms, a bar make of ferromagnetic that is place within the tube at the weld. Because of this, the surrounding capacitance of a circuit has been raise by the use of such materials. At higher frequencies, the inductor is more important than the tube’s inner low resistance to determining the direction of current flow (or, more particularly, inductive reactance). The term “impedance” refers to the sum of the quantities “reactance” and “resistance.” This is the “normal” method through which impeders function.
Layouts for weld rollers
An induction heater only heats the edges of the strip. The squeeze rollers provide pressure to the material, causing it to flow and ultimately weld. This section of the tube mill presents one of the greatest challenges to the mill designer. The weld pressures unit (or weld box) must be able to withstand being driven through with unwelded tubing while providing an extraordinarily high degree of precision. Rolls and supports need to be as small as possible. Because induction welder geometry requires it and because this is the only part of the mill subject to high temperatures and thermal stress.
Size of a Vee
Because the strip is heat before it reaches the coil, vee length is affect by coil placement and, to a lesser extent, coil length.
The width and size of the welder’s roll box normally determines where the coils go. While the welder’s skill at material matching determines how long each coil may be.
At play here are two factors:
To begin with, induction welding is quite productive since it requires the ignition of just a little amount of metal. If you lengthen the vee, heat has more time to dissipate and spread out. But it also takes more effort to do it.
Second, the amount of current that flows between the vee and the inner layer of the tube varies depending on the impedances of both circuits. Due to its higher impedance, a longer vee scatters more of the current’s kinetic energy within the tube. As impeders lose effectiveness due to a lack of space. This is especially important when welding tubes with a small inside diameter.
Faying edges are physically closer together when their capacitance is reduced. This reduces the impedance of the vee as the parasitic current flows along the outer surface of the inner tube. As a limitation, you may use the smallest vee angle. Increasing the weld temperature, any mechanical instability. Such as “breathing,” will cause a greater variance in vee length when the angle is lower.
Arcing may occur if the voltage across the vee is strong enough to ionise the air in the space between the edges. However, there is still a mechanical limit of around 2–3 degrees for carbon steel tubes and about 8–10 degrees for steel and non-ferrous metals. Since a frequency band reduces voltage, it is helpful, but it is ultimately ineffective.
Measurement of the diameter of the coil
When the diameter and the length of a coil are the same. The coil conducts electricity most effectively. Due to the larger coil use in induction tube welding, more energy is lost to heat dispersion before the strip edges are even warm. This is why article recommend keeping your hair short. If the coil is too short, the impedance rises and the welder can’t be match to it.
The welding machine will have a maximum amount of power it can send to the coil all at once. If the welder hits an over-maximum cap before achieving maximum voltage. The coil resistance is too low, and either the turns need to be raise or the time has to be shorten. In the event that a voltage limit is achieve before the impedance is, the voltage limit is attain.
Either the coil has to be make longer or some of the twists remove.
However, due to stainless steel’s poor thermal conductivity. The strip’s edges will often overheat and a film of molten steel will form on its surface. One possible solution is to use a narrower wavelength. The same outcome can be achieve. However, by moving the impeder closer to the mill entrance end or eliminating it altogether. Additional power is require. Growth has occurred, although it’s not as fast as
Therefore, the need for the impeder is reduce when ferritic stainless steels are used instead of austenitic stainless steels or other non-ferrous alloys use with carbon steel.