Fillet weld

Selective closure technology for glass flanges

Aim of development

Glass tubes are used in a wide range of glass apparatus engineering and laboratory applications, especially in the chemical and pharmaceutical industries and in the semiconductor sector. Mostly borosilicate glass (B33) is used here, but it can only be used up to temperature ranges of approx. 400 °C. For higher temperatures up to 1,100 °C, only quartz glass can be used. Irrespective of the type of glass, glass tubes in plant engineering are usually attached to each other or to other apparatus by flange connections and sealed off from their surroundings by connection systems with gaskets for reactor applications. In this way, different types of glass apparatus with different functions can be connected to each other. Often, material-locking tube-ring, tube-plate or tube-round disc connections are found at the ends to enable adaptation of different laboratory vessels to each other. The production of such flanged ends for tubes or closures is an enormous challenge in terms of manufacturing technology. The component must be heated up to the transformation range of the glass in the area of the joint in order to avoid fracture due to introduced thermal stresses. Only then can the actual joining process be carried out. This production step is very demanding for the apparatus glassblower and requires an enormous amount of time and energy. If flange ends or caps (-caps) are very massive, they can only be produced with great effort or not at all using conventional burner technology due to the thickness of the material and the high processing temperature of approx. 2,000 °C (quartz glass). Flanged ends with tube extensions are then produced cold by grinding and polishing and then completed by a tube-to-tube joint to form a tube-to-flange joint. This is also associated with a high resource commitment of time, personnel and material as well as additional processing and disposal costs for grinding suspensions. Conversely, especially when processing borosilicate glass (B33), too much melt volume is often available in the joining process due to the significantly lower softening temperatures. This then leads to severe deformation of the glass tube and glass flange or glass sheet, especially in the case of thinner glass thicknesses < 3 mm. In the present project, these limitations of conventional processes were to be eliminated by using laser technology. This can improve the quality and durability of products while reducing material, time, energy and cost requirements. Laser processing can enable the joining of thicker materials as well as the production of more filigree component structures and drive the digitization of automated glass manufacturing.

Advantages and solutions

The aim of the project was to develop a process strategy for the direct joining of component combinations in the form of tube-ring or tube-round glass joints using laser technology. The aim was to produce a high-quality welded joint (T-joint) by heat conduction welding for borosilicate glass (B33) and by deep penetration welding for quartz glass. The joint should be characterized by a uniform, rounded inner and outer seam formation (fillet weld). This avoids notch effects, reduces the heat-affected zone and thus the material changes compared to the conventional process using torches, and significantly increases product quality and durability. This was achieved by investigations into the geometry of the individual components, the development of system technology (allocation of the parts in fixtures, the heat guidance and the irradiation strategy of the laser), and was demonstrated by the material characterization of the joints. The technical target parameters were specified together with interested companies and the investigations were carried out on glass samples and production-typical sample glasses/molds. CO2 laser sources (? = 10.6 µm) with laser powers of up to 3.5 kW and flexible focusing conditions, various preheating techniques such as adapted electric heaters, induction current source or gas burners, as well as handling systems and measurement technology were used to carry out the experiments. As a result of the investigations, it was possible to demonstrate that the quality of the fillet weld for laboratory measuring vessels (B33) can be significantly improved by laser joining compared to burner-based production. In terms of process time, further optimization potential from the experimental setup to an industrial plant is necessary for industrial introduction, which could be realized, for example, by multi-station operation, higher laser powers or preheating. Laser welding of quartz glass can be implemented for wall thicknesses up to 2 mm as heat conduction welding (e. g. filigree structural components) and up to 15 mm with the hybrid deep welding process.

Target market

For flange connections and tube closures, various companies worldwide, in Germany as well as in Thuringia cooperate directly on overlapping technology and business fields of glass apparatus engineering and laboratory requirements for applications in the chemical and pharmaceutical industry as well as in the semiconductor industry. After the end of the project, the knowledge gained can be applied and marketed for the manufacture of products made of borosilicate glass and quartz glass in glass apparatus engineering, and the technology can be further developed with interested companies in the glass industry. The use of optical technologies can contribute to further energy savings, a minimized use of burner gases and thus to CO2 reduction in glass production and thus in the glass industry as well as to an increase in the quality of glass products. Furthermore, the great flexibility provided by the use of lasers compared to conventional technologies enables new product designs, which are directly reflected in the component costs. Following the project, the process technology developed at ifw Jena can be used for single-item and small-series production, and manufacturing and automation solutions can be established in the industry for mass production in cooperation with equipment manufacturers. However, the costs and benefits must be considered in relation to the application, economically and ecologically, depending on the type of glass, the geometry of the joints, the technological process parameters and the manufacturing solutions.