For years the pharmaceutical industry has relied heavily upon the American. Welding Society’s AWS D weld dis- coloration chart1 to gage the acceptability. 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.
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If another configuration is to be welded, the entire experiment must be repeated.
Purging for Improved Weld Profile | Arc Machines, Inc.
Since the pressures are quite low, on the order of 0. One way to establish the inlet pressure is to repeat the empirical testing with the inlet pressure as the controlled variable. This variable orifice is especially important because as the joint is welded shut, asw 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.
The required weld pressure is input to the device, and it correctly offsets the pressure for the tubing configuration as tested.
Experimentation is required to establish the ideal pressure for a given tube size, wall thickness and material. This level of measurement and accuracy permits the EXEL SG-1 xws repeatedly maintain the exact internal pressure required for a perfect weld. Most 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, 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. Orbital Welding Internal Pressure Control.
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. Purging for suitable weld color is relatively simple.
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. 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. Many methods 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.
Welding Journal, July Dennis Cobb has spent more than 25 years both designing and managing the design of semiconductor capital equipment. SEMI Ass F78 includes a chart with minimum and maximum purge pressures and awx rates for various tube sizes and wall thicknesses.
The input gas is controlled both for pressure and flow, using a variable orifice iris controlled by a microprocessor in a closed loop system. Figure 1 – AWS D However, gauging the internal pressure was that the weld ID profile is acceptably flat is a more difficult task. 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.
Since the internal pressure at the weld-site is dependent upon the purge gas delivery pressure, the distance from the entry measurement 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.
However, given the dangers associated with the use of hydrogen, it is hard to recommend it unless a critical need exists. This experimentation requires several sws pressures, with a weld coupon created for each test condition, until acceptable results are obtained; a time consuming and costly activity. 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.
The unit then utilizes this offset for all welds performed with this same configuration.
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. The combination of flow awa and prepurge time determines how much oxygen is still present, and thus, the amount of weld color caused by oxidation.
Purging for Improved Weld Profile
He is a registered professional California Electrical Engineer. In addition, most standard gas pressure regulators are not nearly accurate enough to deliver awws exacting performance required. 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, awe from weld to weld.
In order for all color to be eliminated, oxygen levels must depending on the material fall below approximately 20 ppm. The prepurge time is an empirically derived value dependent on many factors including tube size, gas flow rate, exit orifice size, number, sizes and locations of dead-legs or other components that d18.2 trap atmosphere, and thus take more time to purge.
However, this value will only be correct for the specific assembly tested. 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.