Cleanroom equipment must also be manufactured under cleanroom conditions
Whenever high-quality joints are required, GTAW (Gas Tungsten Arc Welding) or TIG (Tungsten Inert Gas) welding, as it is commonly called, offers a perfect solution.
A wide range of products must be manufactured under white room or cleanroom conditions. These products may be susceptible to microbes, as is the case with pharmaceutical ingredients, to contaminations, as seen in the field of micro-electronics, or to foreign objects, which have to be kept out of optical devices and precision mechanics.
In many cases, the components for equipment intended to be operated inside cleanrooms, must also be produced, and assembled in a controlled atmosphere. Tube network, for example, is frequently used to supply clean room installations with ultra-pure gases and liquids, which are used for inertisation, etching, rinsing, diluting and injection purposes.
In order to minimise the effort on site, as many as possible of the connections for the tube network installation of a cleanroom supply, are prefabricated. In the factory, standard pieces such as micro-fittings, tees, elbows and valves are welded together with matching tube segments. In this instance, the use of orbital TIG welding can provide significant advantages. Complete weld cycles are carried out automatically and lead to consistently high-quality results.
White or cleanrooms are specifically designed for the requirements of a particular sector of activity. Composition, temperature, and humidity of the controlled atmosphere are regulated by precise specifications, but the most important limits concern the size and number of airborne particles. Depending on the highest permitted particle concentration, the standards ISO 14644-1 and FED STD 209E divide cleanrooms into different classes: Iso Klasse 1 and FED class 1 stand for the lowest particle concentration, whereas Iso Klasse 9 and FED class 100,000 are equivalent to unfiltered room air.
The human body as a source of contamination
To keep the contamination inside a cleanroom as low as possible, any generation or emission of particles must be avoided. Sending out an average stream of 100,000 particles per minute with a size of less than 50 µm, the human body is considered one of the most important particle sources in a clean environment, especially where fast movement is involved. Thus, workers or visitors in a cleanroom must wear specialised protective clothing: the head and hair are covered by a cap, the face including eyes, nose and mouth is completely enclosed by a protective mask with goggles, the hands are gloved, galoshes fit over standard footwear and the rest of the body is wrapped in an appropriate lab coat or protective suit.
Manufacturing processes can also be the origin of significant particle emissions. Each electric arc which is struck during a TIG welding procedure is accompanied by clouds of vaporising metal and streams of welding and backing gas. Additionally, the released heat provokes turbulences between inert gas and the surrounding air and entrains undesired pollutants. Last, tube end preparation could also create contamination.
Closed orbital welding heads keep the cleanroom clean
However, such adverse side-effects of an open arc can be avoided by using closed orbital welding heads, which were initially invented as fast and efficient tools for the numerous butt weld connections of airplane hydraulics. Ease of use, productivity and outstanding weld quality were the targets for their development, all of which were met in full. Subsequently, the advantages of an arc burning inside a closed chamber were exploited for cleanroom purposes. Hot surfaces, turbulences, radiation, uncontrollable particle emission – the entire gamut of problems provoked by an open electric discharge could be eliminated. Today, closed orbital TIG welding heads have become indispensable tools whenever tubes and accessories have to be welded together under cleanroom conditions.
How to weld High-Purity and Ultra-High-Purity Tubing
In order to provide the best possible benefits for a wide range of applications, welding equipment must be designed and developed specifically for the various requirements of operational cleanrooms.
A smart welding station should be able to supply and control the entire range of closed orbital welding heads, for micro-fittings and important tube diameters. Due to its very low weight, it can be moved by the operator without any hoisting equipment, which is important in maintaining the sterile state of the cleanroom. The operating elements should be independent from the power source, so that the power source itself can be located outside the area of the work bench. If a liquid cooling circuit becomes necessary for larger tube diameters or improved productivity, the cooling device should also be independent from the power source.
Meeting the requirements of the Industry 4.0 concept already today
To meet the upcoming challenges of Industry 4.0, the recent findings regarding digitalisation, connectivity, communication, and traceability should also be taken into account. This applies both to the data exchange between the different components of the equipment and the internal network of the factory. In this context, the OPC-UA protocol delivers the perfect interface to the Industry 4.0 process.
The operator who works in a cleanroom environment has to face a lot of restrictions. Fast movements are forbidden, his visual field is obstructed by a mask and his tactile sense reduced by gloved hands. A professional welder can check the condition of his equipment at a glance, before starting a weld cycle. In the same way, working in the constrictive conditions of a cleanroom should be made as easy as possible for the operator. A barcode scanner, which may be used plugged or unplugged, can read the QR-code on his work suit to verify identification. Similarly, the operator can identify welding head, welding gas and workpiece, via his tablet. The matching welding programme is also proposed on his tablet and necessary inputs can be completed, even whilst wearing protective gloves.
You can see the European Hygienic Engineering and Design Group (EHEDG) Guidelines here or more information on EHEDG Guidelines portal, the EHEDG Connects video session presenting Polysoude and the American Welding Society website.
Clearly structured work sequence for welding
Preparing of the weld is divided into two parts: the fixing of the workpiece in the clamping unit, whether it be a Polysoude clamping device, or one manufactured by another company, then the final positioning of the welding head including motor, gear, supply hose etc.
The real-time progress of the weld cycle can be watched on the tablet, where the momentary welding parameter values are displayed as well. All data is transmitted to the factory network at the same time.
Finally, after a visual inspection of the completed weld the operator can confirm the successful production of the joint.
To summarise, the constraints of working in the high purity sector have led to a constant striving for technological advances. Polysoude has been able to develop "clean" equipment, essential for use, where the presence of particles can corrupt the quality of manufactured products, nullify the use of materials, or expose human life to danger.
Polysoude specialises in the design and manufacturing of high-quality orbital welding equipment, welding heads, power supplies and automated solutions for TIG / GTAW welding and TIGer weld overlay / cladding with bi-cathode technology. Contact email@example.com. For service inquiries, contact firstname.lastname@example.org. Polysoude would be pleased to hear from you and your future projects. Contact us to learn more. You can download all our brochures and data sheets from the Download Section.
DR.- Ing. Jürgen Krüger