In the third part of Dr. Fletcher's series, the focus shifts to using welding enclosures and trailing shields to prevent contamination during welding, mainly when working with materials sensitive to atmospheric gases.
Welding Enclosures:
Traditional metal enclosures, often used for sensitive welding processes, are effective but costly and cumbersome. Flexible Welding Enclosures made from advanced engineering polymers have been developed to address these issues. These enclosures are cost-effective, easy to store, and provide excellent visibility and access for operators. They are widely used in industries such as aerospace and pharmaceuticals due to their flexibility, smaller footprint, and significant cost savings compared to traditional metal enclosures.
Technical Specifications:
Standard flexible enclosures are constructed with UV-stabilized polymers and equipped with features like leak-tight zips, operator glove ports, and service panels. They also include ports for purging gas and exhaust and connections for monitoring oxygen and dew point levels.
Trailing Shields:
Trailing shields provide secondary protection during welding, ensuring the weld and heat-affected zones remain shielded from the atmosphere until they cool below 400°C. These shields are essential for preventing oxidation, discolouration, and loss of mechanical properties in certain alloys. The shields are typically custom designed to fit specific welding torches and operations, providing a tight seal and optimising inert gas distribution.
Trailing Shield Technology:
The welding torch is attached to the leading edge of the trailing shield, with inert gas directed through ports behind the weld zone. A flexible silicone skirt ensures a seal between the shield and the workpiece. Companies like Huntingdon Fusion Techniques Ltd manufacture trailing shields compatible with manual and mechanised welding processes.
Choosing a Trailing Shield:
Selecting the right trailing shield depends on various factors, including material thickness, sensitivity to oxidation, and welding speed. The Argweld® range offers solutions for diverse applications, including external and internal welds.
Products Mentioned:
Welding Enclosures and Trailing Shields
In the previous parts of this series, we explored the challenges in selecting the optimal gas for weld purging and analysed various purging techniques for tube and pipe welding. In this instalment, we delve into using protective enclosures and trailing shields as practical solutions to prevent contamination during welding.
Welding Enclosures
Traditionally, permanent metal enclosures have been employed when welding materials are sensitive to contamination from atmospheric gases. These enclosures may be evacuated using vacuum pumps or purged with inert gas. However, these solutions tend to be expensive, time-consuming and occupy a large, permanent footprint—making them unsuitable for routine welding applications. For instance, a typical steel GTAW vacuum enclosure with a volume of 1 cubic meter can cost around £11,000, while a simple inert gas version may cost about £5,000. High vacuum electron beam welding plants of similar size can exceed £60,000.
Engineers developed Flexible Enclosures using advanced engineering polymers to address the need for a more economical and flexible solution. These innovative products offer significant advantages over traditional vacuum and glove box alternatives, including reduced cost, minimal floor footprint, and availability in various sizes. Flexible Enclosures are now widely used in aerospace, medical, auto sport, and pharmaceutical industries. They can cost less than 10% of a metal glove box and only 2% of a vacuum system.
Technical Specifications
Standard flexible enclosures have translucent vertical sides and an optically clear top. Ultra-violet stabilized engineering polymers are used throughout their construction, with a material thickness of approximately 0.5 mm (480 microns). These enclosures have leak-tight access zips, operator glove ports, and service panels for welding torches, electrical leads, and cooling water supplies. A purge gas entry port and an exhaust valve for venting displaced gas are also incorporated. In case of accidental damage, a repair kit is provided with each enclosure.
Recent advancements include connections for venting exhaust gas through a Weld Purge Monitor® and Dew Point Meter to ensure that the working environment meets the prescribed oxygen and dew point levels.
Flexibility and Usability
Flexible Enclosures can be customized to meet specific customer requirements, with standard models ranging from 0.3 to 3.0 cubic meters generally available from stock. These lightweight enclosures are easy to move and store, minimizing floor footprint. The upper section of the enclosures is made from optically transparent ultra-violet stabilised polymer, allowing multiple operators to work simultaneously—ideal for training purposes.
Trailing Shields
When welding certain metal alloys, exposure to high temperatures can lead to the formation of oxides, causing undesirable discolouration and loss of mechanical properties. Therefore, all parts of the weld and heat-affected zone must be shielded from the atmosphere until the temperature drops below approximately 400°C.
While the welding torch provides primary shielding, secondary shielding is often achieved through Trailing Shields. These shields protect the solidified weld metal and associated heat-affected zones until the temperature falls below the critical threshold. Trailing shields are typically custom-made to fit specific torches and welding operations.
Trailing Shield Technology
The welding torch is mounted on the leading end of the trailing shield, with inert gas fed through ports behind the fusion zone. A flexible, pre-formed, and replaceable silicone skirt ensures a tight seal between the shield and the workpiece. Companies like Huntingdon Fusion Techniques Ltd design and manufacture trailing shields compatible with mechanised and manual gas tungsten arc welding (GTAW) torches. These shields provide comprehensive inert gas coverage and optimize gas distribution to avoid turbulence.
Shielding may also be necessary on the root side of the fusion zone for complete protection against oxidation. This can be achieved using temporary shields, copper backup bars, or custom-made trailing shields that offer weld root protection.
Choosing a Trailing Shield
Selecting the appropriate trailing shield depends on several factors, including the extent of oxidation control required, material thickness, sensitivity to oxidation, welding process, and welding speed. The Argweld® range of trailing shields covers various applications, from flat surfaces to diameters as small as 25 mm for both external and internal weld configurations.
References
Products Mentioned:
