AWS D () SS Discoloration – Free download as PDF File .pdf), Text File .txt) or read online for free. AWS D – Download as PDF File .pdf), Text File .txt) or view presentation slides online. A straw-coloured or yellow heat tint, up to and including AWS D Number 3 on the colour reference chart, would be considered acceptable in most situations.

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However, in recent years, this focus on smooth, clean, particle-free internal weld requirement has migrated from the semiconductor industry to the biopharmaceutical industry, and on to the food equipment industry. Figure 1 – AWS D Experimentation is required to establish the ideal pressure for a given tube size, wall thickness and material.

Purging for suitable weld color is relatively simple. The prepurge time is an empirically derived value dependent on many factors d8.2 tube size, gas flow rate, exit orifice size, number, sizes and locations of dead-legs or other components that can trap atmosphere, and thus take more time to purge. However, gauging the internal pressure such that the weld ID profile is acceptably flat is a more difficult task.

This experimentation requires several trial pressures, with a weld coupon created for each test condition, until acceptable results are obtained; a time consuming and costly activity. Purging for Improved Weld Profile. Once that is determined, the next problem is to correlate the required pressure at the weld with the measured pressure at the delivery inlet.

Orbital Welding Internal Pressure Control. However, given the dangers associated with the use of hydrogen, it is hard to recommend zws unless a critical need exists.

The input gas is controlled both for pressure and flow, using a variable orifice aqs controlled by a microprocessor in a closed loop system.

Purging for Improved Weld Profile

The internal pressure at the weld location, typically arrived at empirically, is influenced by the gas flow rate and the size of the exit orifice.


This variable orifice is especially important because as the joint is welded shut, the effective purge gas exit area is reduced, so as the joint is sealed the SG-1 is making real-time adjustments to accurately maintain the required pressure.

Qws users are satisfied with the results obtained with pure argon as a purging medium; although a few organizations like to add a small percentage of hydrogen to produce a reducing environment. In addition, most standard gas pressure regulators are not nearly accurate enough to deliver the sws performance required.

Welding Journal, July Since the internal pressure at the weld-site is dependent upon the purge gas delivery pressure, the distance from the entry awz point and the weld, and the gas venting rate, a closed loop pressure controller is required, such that a specific, low value pressure can be maintained.

The required weld pressure is input to the device, and it correctly offsets aas pressure for the tubing configuration as tested. The initial purpose of internal tube purging with inert gas usually argon was the prevention of surface oxidation on the internal diameter of the tubing surrounding the weld Heat Affected Zone.

Many xws have been devised to deliver the purge gas to the weld site, but few methods exist to control the internal gas pressure, thus the internal weld profile.

In the interest of exercising control over the weld profile, the ID purge is introduced with a certain level of pressure, and in order to maintain consistency and repeatability that pressure must be consistent throughout the weld, and from aaws to weld. One way to establish the inlet pressure is to repeat the empirical testing with the inlet pressure as the controlled variable.

He is a registered professional California Electrical Engineer. The only remaining hurdle is to obtain the corresponding inlet pressure for the known weld pressure, and fortunately, the EXEL SG-1 also provides the capability of measuring the inlet and weld pressures simultaneously.


Dennis Cobb has spent more than 25 years both designing and managing the design of semiconductor capital equipment. In order for all color to be eliminated, oxygen levels must depending on the material fall below approximately 20 ppm. If another configuration is to be welded, the entire experiment must be repeated. It is conventional wisdom that the semiconductor industry was, and remains, the primary driver for the continuous improvement of orbital autogenous weld profiles and internal cleanliness for process gas delivery tubing.

Purging for Improved Weld Profile | Arc Machines, Inc.

However, this value will only be correct for the specific assembly tested. In addition, measuring the pressure some distance from the weld location due to pressured drop will not provide an accurate method of determining the pressure at the weld zone. SEMI Standard F78 includes a chart with minimum and maximum purge pressures and awd rates for various tube sizes and wall thicknesses.

This level of measurement and accuracy permits the EXEL SG-1 to repeatedly maintain the exact internal pressure required for a perfect weld. The unit then awz this offset for all welds performed with this same configuration. Since the pressures are quite low, on the order of 0. Since the pressures are given as a range, they serve as a useful starting point for the empirical determination of the best pressure for the ideal weld profile.

The combination of flow rate and prepurge time determines how much oxygen is still present, and thus, the amount of x18.2 color caused by oxidation.

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