TPT May 2023

ARTICLE

Thermatool Corp

Shandong Province Sifang Technical Development Group HF weld power calibration

weld mill setup variation by providing calibrated power supply metrics established during power supply manufacturing.

In this section, the importance of calorimetric power calibration is explained. Calibration of power supplies is very important as it ensures output accuracy. In other words, how well the power supply output settings and displayed output values (feedback) compare to its actual voltage and current. Customers often ask how power supplies are calibrated. Thermatool performs calorimetric calibration, which is the proven rating for tube and pipe high frequency welders. Calorimetric calibration proves to be the most accurate method for proving the output power at the coil into the load (tube or pipe), not the lead set. The calibrated and known power supply output is the foundation of precise HF weld heat input control. The key parameters: • Input KVA • Output voltage measured at the induction coil • Water flow through the calorimetric steel load (calibrated GPM or LPM). • Water pressure through the calorimetric steel load (calibrated psi or bar). • A temperature rise of the water at known flow and pressure. • kW’s Induced into the load is derived and the HF welder power is calibrated. • Over a one hour period we have the calibrated kWhr energy rating. Thermatool weld rate calculators also use calibrated kWs (power) induced into the load. Thermatool kW ratings can be combined with specific product (tube or pipe mill) mass flow rates to determine kW۰hr/ton consumed by the HF welding process. Below you can find the mass flow rate calculation on a tube mill: m = ρ * V * A Where m is the mass flow rate, ρ is the material density, V is the mill speed, and A is the cross-sectional area. The tube cross-sectional area can be calculated as: A = –– * (D 2 – (D – 2 t) 2 ) Where D is the tube OD and t is the wall thickness. Understanding the power consumption of the HF welding process becomes simple when using a properly rated and calibrated power supply and a measured material mass flow rate. Energy consumption can be expressed in kW۰hr/ton. By using the simple equation below, the electric utility cost per ton of tube and pipe produced can be calculated. –––––– x –––––– = ––– π 4

Process efficiency in HF welding There can be confusion in HF welding applications when talking about efficiency. The confusion is caused by a focus on SiC MOSFET switching efficiency and advertised power supply efficiency ratings backed up by things like cooling water consumption. This can be misleading, especially when the more important factor is process efficiency. Power supply efficiency and process efficiency are two completely different terms that should not be used interchangeably. Earlier in this article, the efficiency and ratings of the power supply were discussed. Now it is necessary to establish the term ‘process efficiency’. The HF welding process is dependent on a list of key process parameters such as power, frequency, weld area setup (vee length and vee angle), impeder (ferrite volume and placement), the product being welded (OD, wall thickness, material) and so on. To have the highest process efficiency, these parameters have to be optimised. Although the material, wall thickness, and OD of the product cannot be changed, power, frequency and other setup variables can be controlled. While power is the method of inducing amperes (the heat) into a workpiece, frequency (the heated width) is a means to control the distribution of the heat. The highest efficiency can be achieved with the lowest welding power consumption. By optimising the welding frequency, the width of the heat-affected zone (HAZ) can be kept to a minimum, which means that less material is heated and therefore less energy is consumed. It is easy to remember that the frequency is inversely proportional to the electrical reference depth, meaning that the higher the frequency, the shallower the electrical reference depth. The narrowest HAZ produces the best weld quality. The goal is to reduce the width of the HAZ as much as possible while allowing sufficient heat penetration to ensure a good weld.

Figure 2: Effect of frequency on electrical reference depth at the strip edges

kW ⋅ hr ton

$ kW ⋅ hr

$ ton

Sensitivity to frequency variations in process parameters also impacts process efficiency. It is also important to note a consistent and stable frequency delivers the highest efficiency across different tube and pipe size ranges.

This straightforward yet valuable calculation demystifies talk of power factor, load matching, impeder effectiveness, and

71

www.read-tpt.com

MAY 2023