Monday, February 25, 2013

Welding Electrodes in Pakistan

DIAMOND WELD RODS (Pvt) LTD and
SHANGHAI INDUSTRIES (Pvt) LTD
ISO 9001:2008 Certified Company
Manufacturer of Welding Electrodes in Pakistan, both companies are well renowned in Pakistan and producing a variety of good quality electrodes and competing with all other manufacturers and importers especially China brand. Brand of these companies are very famous in Pakistan with affordable prices. Company main suppliers in Pakistan are:- 
  Aslam & Sons, Kashmir Road, Rawalpindi (051-5568274)
Bilal Traders, Lahore
Muhammad Sajid, Vehari
Muhammad Hanif, Chowk Shaheedan, Multan
Punjab Hardware, Peshawar

Comapny was established in early 80s with a firm conviction and determination of enhancing and advancing the welding line by giving it a new dimension and by introducing high standard welding electrodes and accessories. Famous brands are:-

Pak Bridge
Diamond Brand







Sunday, February 24, 2013

POWER SUPPLIES

To supply the electrical energy necessary for arc welding processes, a number of different power supplies can be used. The most common classification is constant current power supplies and constant voltage power supplies. In arc welding, the voltage is directly related to the length of the arc, and the current is related to the amount of heat input. Constant current power supplies are most often used for manual welding processes such as gas tungsten arc welding and shielded metal arc welding, because they maintain a relatively constant current even as the voltage varies. This is important because in manual welding, it can be difficult to hold the electrode perfectly steady, and as a result, the arc length and thus voltage tend to fluctuate. Constant voltage power supplies hold the voltage constant and vary the current, and as a result, are most often used for automated welding processes such as gas metal arc welding, flux cored arc welding, and submerged arc welding. In these processes, arc length is kept constant, since any fluctuation in the distance between the wire and the base material is quickly rectified by a large change in current. For example, if the wire and the base material get too close, the current will rapidly increase, which in turn causes the heat to increase and the tip of the wire to melt, returning it to its original separation distance.[1]

The direction of current used in arc welding also plays an important role in welding. Consumable electrode processes such as shielded metal arc welding and gas metal arc welding generally use direct current, but the electrode can be charged either positively or negatively. In welding, the positively charged anode will have a greater heat concentration and, as a result, changing the polarity of the electrode has an impact on weld properties. If the electrode is positively charged, it will melt more quickly, increasing weld penetration and welding speed. Alternatively, a negatively charged electrode results in more shallow welds.[2] Non-consumable electrode processes, such as gas tungsten arc welding, can use either type of direct current (DC), as well as alternating current (AC). With direct current however, because the electrode only creates the arc and does not provide filler material, a positively charged electrode causes shallow welds, while a negatively charged electrode makes deeper welds.[3] Alternating current rapidly moves between these two, resulting in medium-penetration welds. One disadvantage of AC, the fact that the arc must be re-ignited after every zero crossing, has been addressed with the invention of special power units that produce a square wave pattern instead of the normal sine wave, eliminating low-voltage time after the zero crossings and minimizing the effects of the problem.[4]

Duty cycle is a welding equipment specification which defines the number of minutes, within a 10 minute period, during which a given arc welder can safely be used. For example, an 80 A welder with a 60% duty cycle must be "rested" for at least 4 minutes after 6 minutes of continuous welding.[5] Failure to observe duty cycle limitations could damage the welder. Commercial- or professional-grade welders typically have a 100% duty cycle.