Joining processes systems

Michael Baldea is Assistant Professor in the Department of Chemical Engineering at The University of Texas at Austin. Prior to joining The University of Texas, he held industrial research positions with Praxair Technology Center in Tonawanda, NY and GE Global Research in Niskayuna, NY. He has received several research and service awards, including the Model Based Innovation Prize from Process Systems Enterprise and the Best Referee Award from the Journal of Process Control, and has co-authored over 60 papers and presentations. 

There are but a few typical basic polymer resin suppliers. However, there are many companies that formulate filled plastic systems from these basic resins. These smaller companies are quite often the ultimate suppliers to the manufacturer of the end-product. Both the basic resin manufacturer and the formulator have considerable influence on the joining characteristics of the final material. Because of this, they should be considered to be the primary source of information regarding joining processes and expected end results. 

How does the order of ranking so obtained (a) relate to the actual lifetime that will be seen in bonded components and structures subjected to changing environmental conditions, and (b) relate to the cost effectiveness of the adhesive system chosen, i.e. has a very conservative overkill been made in the choice of the adhesive system needed to attain a given durability, to the extent that adhesive bonding is now not an economically viable option for the joining process ... 

An advantage of manual operation is the availability of a sequential process from adhesive mixture to pressurization. This whole process can be carried out continuously by one person. On the other hand, a parallel process is dangerous because the pot life of the adhesive applied to many queuing parts can be attained if the production line stops before the joining process. Since automation needs a parallel process, a waiting system for the adhesive application, which is activated when the following processes consume too much time, has to be installed. 

To minimize possible sources of error and improve the application procedure that directly enhances the bond properties, several tools can be used to stabilize the joining process. The utilization of static mixing tubes, which are available for almost every two-part adhesive system... 

Automation For the production of high-quality textiles in high-wage countries, a semiautomated joining process is a prerequisite. This requires a constant surveillance of the textile s position using sensors and also a feedback loop regarding the quality of the seam. First steps have already been done toward this kind of system. 

The application of adhesives can also be assisted by various other means. For instance, it is possible to use spaces with a predefined depth to dose exactly the amount of glue required. An adhesive with a low viscosity will penetrate these spaces under capillary action. This technique is called capillary space adhesive technique and is very often used in the microtechnique for example to join microvalve systems by adhesive bonding [341]. The fabrication of a micropump and the optimisation of microstructures for the adhesive bonding process are described in the literature [339,340]. 

There is hardly a metal that cannot, or has not, been joined by some welding process. From a practical standpoint, however, the range of alloy systems that may be welded is more restricted. The term weldability specifies the capacity of a metal, or combination of metals, to be welded under fabrication conditions into a suitable stmcture that provides satisfactory service. It is not a precisely defined concept, but encompasses a range of conditions, eg, base- and filler-metal combinations, type of process, procedures, surface conditions, and joint geometries of the base metals (12). A number of tests have been developed to measure weldabiHty. These tests generally are intended to determine the susceptibiHty of welds to cracking. 

Programs to develop MCFC technology are also under way in Europe. Ansaldo SpA (Italy) is setting up faciUties to produce 1-m cells in an automated process, and their goal is to test 100-kW stacks in 1994. The 100-kW stack is also to be tested by IBERDROLA in Spain as part of a complete power plant system. Two Dutch companies. Stork and Royal Schelde, have joined with the Dutch government to form Brandstofcel Nederland (BCN), which plans to test a 50-kW MCFC and two 250-kW MCFC stacks in 1994. 

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