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Q&A on adhesives equipment

Earlier in this series on engineering adhesives we looked at dispensing equipment. With the help of Henkel, we return to this topic and address some more questions concerning the equipment used in the successful application of adhesives.

When it comes to light curing adhesives - what equipment is available for this technology? Ultra Violet curing systems are state of the art units specially designed for the fast and reliable curing of UV-adhesives. Obviously, the lamp is the core element of a light curing system, and selecting the correct one for the job is a combination of technical requirements and economic considerations. As a result, manufacturers generally offer a comprehensive line of light curing equipment, which typically includes low intensity flood systems, high intensity wands, chambers, conveyors and unshielded light sources and light metering equipment for process monitoring.   

Recent developments have seen the increased used of LED technology for curing UV cure adhesives.  Compared with traditional mercury style lamps, LEDs provide an instant on/off facility that means no warm up period is necessary (so faster production start up), focussed wavelength at the required level to suit the adhesives, no Infrared radiation to cause heating of the components and longer life. 

What do we need to know about robots when we're discussing dispensing? Robotic technology is ideally suited to the application of adhesive and sealants because it can apply material to exact positions time and time again - and at high speed.  The units vary from very big units that occupy a large space, right down to compact bench top models.  In the end, the choice depends on the size of the component part and the complexity of the required bead path. That said, even the capabilities of a relatively small bench top unit are quite sophisticated - being available in several different configurations which deliver three or four axes of movement. The synchronised control over these axes provides for 3D linear and arc interpolations needed for complicated dispensing processes. Just as important, such units provide an accuracy of 0.01mm when it comes to positioning the adhesive.  

How can the correct application of an adhesive be verified? The simplest check is, of course, a visual inspection. To be realistic, though, in a production line situation such an operation is both time consuming and labour intensive. A better solution is to incorporate an automatic controller unit interfaced with some kind of flow monitoring system. Prior to a production run, the critical references to the dispensing cycle are created using a known 'good' bead. During the run, a signal from the transducer within the dispensing valve is automatically compared with these pre-set parameters. If there is a discrepancy, such as air bubbles, pressure changes, needle touch down, or the loss or clogging of nozzles, an alarm alerts the operator to a potential problem. One major benefit is that this technology can be used with a variety of adhesive types, including RTV silicones, cyanoacrylates, anaerobics and acrylics.

Can 'clogging' of dispensing equipment be avoided, for example during a tea break or over the weekend? Indeed it can, but the method will vary according to the specific adhesive technology. Anaerobic adhesives only cure when they are in contact with metal in the absence of air. That means unless metal has contaminated the nozzle or pipe in some way, the adhesive will remain in liquid form. On the other hand, RTV silicones cure by atmospheric moisture, so in order to prevent nozzles being clogged such moisture must be prevented from reaching the adhesive. 

This can be achieved during down times by immersing the nozzle in paraffin oil on automatic machines or capping the nozzle on manual handguns. Similarly, cyanoacrylates (instant adhesives) cure when they come into contact with airborne moisture. However, if adhesive does solidify at the dispensing end of the equipment, then the quick and inexpensive remedy is to change the nozzle.  

By their very nature, two component adhesives will only begin to cure when mixing takes place.  Nevertheless, any product left in the nozzle will eventually cure if it remains static for an extended period. Automatic machines generally incorporate 'purge' cycles that will dispense two-part products from the nozzle at regular intervals to prevent curing taking place.  

Overall, in those circumstances where small quantities of product are involved, it is usually more efficient simply to dispose of the nozzle. As already stated, they are not costly and are quick to replace.  

Briefly, then, what are the benefits of dispensing units? They are highly cost effective, clean and accurate when it comes to applying adhesives and sealants. However, it is essential that the right units are used. There is a variety of equipment on the market, with each unit designed to meet differing needs. In the end, a few minutes of discussion with a reputable maker will ensure the most efficient solution.
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