Electrical stick-out and contact-tip-to-work distance should not the identical factor, however they each play a job in welding a top quality joint. rusak/iStock/Getty Photos Plus
I’ve a basic query. We use many welding process specs (WPSs) which were written by a number of folks through the years. Some use the time period ESO, or electrical stick-out, and others use CTTWD, which is contact-tip-to-work distance. I’ve requested the welders and a few high quality of us, and everybody tells me they imply the identical factor. Why the totally different phrases?
They’re totally different phrases as a result of, by definition, they signify various things. This can be a frequent mix-up all through the welding trade.
These two phrases describe measurements for the gasoline steel arc welding (GMAW), flux core arc welding (FCAW), and submerged arc welding (SAW) processes.
CTTWD is a simple measurement between the contact tip and the floor of the supposed weld joint. Remember the fact that if you’re welding in a deep groove weld, that you must measure to the underside of the groove weld the place the weld steel is deposited.
For many GMAW and FCAW functions, this measurement falls between 5/8 and 1 in. If you’re utilizing a big FCAW wire comparable to 3/32 in. dia., that distance can method 1.5 to 1.75 in. If you’re welding with the SAW course of, the final rule of thumb is eight instances the wire diameter, however usually by no means lower than ¾ to 1 in.
ESO, then again, measures the gap from the highest of the welding arc to the contact tip. For apparent causes, that is extraordinarily tough to measure. You may ask, then, why use it in any respect? That is the place you may optimize your welding parameters or leverage welding circuit principle.
The overall distance, or CTTWD, minus the ESO leaves the remaining distance as your arc size, which is your voltage. This data may come in useful, even when it doesn’t appear apparent at first.
If you find yourself welding with GMAW or FCAW, you often use a constant-voltage (CV) energy provide. For these machines, you set your voltage and desired wire feed velocity (WFS). WFS is mounted and fixed, and the machine does no matter it could actually to keep up your set voltage. Your CTTWD determines the machine’s output amperage. The longer the CTTWD, the decrease the amperage required to soften the filler steel. Conversely, the shorter the CTTWD, the upper the mandatory amperage to soften the filler steel. This is because of Ohm’s legislation and resistive heating within the wire.
A approach to consider that is to fake the ESO portion of the wire is a fuse in {an electrical} circuit. We all know that present flowing via a conductor, comparable to a wire, cable, filler steel, or a fuse produces warmth on account of resistance to move. When the ESO is elevated, it’s like utilizing a smaller fuse in a circuit, so it takes much less amperage to burn that fuse (i.e., your filler steel). When you shorten your ESO, you lose the preheating impact, and it takes extra amperage to soften the filler steel. Equally, it’s like putting in a bigger fuse that requires extra amperage to soften it.
Welders who’ve found this phenomenon probably have tried shortening their ESO to extend amperage and penetration, or they use an extended ESO to cut back amperage and stop blowing a gap via their workpiece, comparable to when they’re welding on a weld joint with some small gaps.
For the SAW course of, it’s commonplace to keep up a gentle amperage to provide a constant depth of penetration or weld steel deposition charge. For this software, the machine management mode is ready to fixed amperage (CA), additionally known as fixed present (CC). This implies the operator units a desired amperage and voltage, and the machine varies the WFS to keep up them. On this situation, if the CTTWD is just not constant, variations in deposition charges happens. An extended CTTWD will increase WFS to keep up voltage and amperage, thereby rising deposition charges. Conversely, a shorter CTTWD reduces WFS and reduces deposition charges. Subsequently, in these functions which can be extremely automated, sustaining constant CTTWD stabilizes deposition charges.
This idea is just not new. Many years earlier than the most recent applied sciences arrived to optimize deposition charges, strain vessel fabricators would benefit from it. Many strain vessels are fabricated from carbon metal however require a stainless-steel overlay inside to guard the carbon metal from a corrosive surroundings. The SAW operators would swap the cables on the entrance of the facility provide to alter from DC+ to DC-. We all know DC-, or straight polarity, produces the best deposition charge and the bottom depth of penetration, which is what you need for an overlay software. They’d then use an prolonged CTTWD of three or 4 in. to additional improve the deposition charge based mostly on the CA welding mode. This could permit them to weld maybe two layers of deposit to realize the suitable weld chemistry required for the applying at a excessive deposition charge, saving loads of money and time.
