FEATURE


FASTENINGS & ADHESIVES On July 20 1969,


Apollo 11 was the first manned mission to land on the moon.


Flash forward to 2021, and billionaires have started a new space


race of their own. This is just one example of how engineering


has advanced beyond recognition. Peter Swanson, managing


director of adhesives specialist Intertronics, reflects on some key changes in the adhesives industry


A


lmost everything made by industry, from rockets to smartphones, has component pieces that must be fixed together.


Adhesives are often used for bonding as opposed to mechanical fixing to reduce costs, improve performance or durability, gain greater design freedom, or achieve certain aesthetics. Over the years, trends towards digitalisation, miniaturisation, electrification, and more, have placed changing needs on a key technology required to bring everything together – adhesives.


the holy grail of dispensing


When dispensing materials like adhesives, coatings and lubricants, manufacturers aim for a process that is both repeatable and accurate to within the specified tolerances. All engineers dislike variability in production, including in the application of materials. This has become a more pressing requirement as technology has advanced and the need for accuracy and repeatability has grown. In the early 1970s, fluid dispensers based on


a time/pressure principle started taking over from wholly manual techniques like brushing, dabbing, or hand syringes. These work by applying a pulse of air to a syringe barrel, which forces liquid out through a needle or nozzle. They deliver quality, efficiency, and health and safety benefits, and therefore remain in many factories around the world to this day. However, while time/pressure dispensers work reasonably reliably, they do not offer the accuracy that more sophisticated assembly demands. The effects on a time/pressure dispenser


that limit accuracy, such as variations in output caused by changes in material viscosity, can be


AN EVER-CHANGING INDUSTRY


The preeflow eco-PEN can achieve a volumetric dispensing process with an accuracy of ±1%


3-axis benchtop robots, right up to multi-axis robots with vision-based control and feedback. While the use of industrial robots in large-


scale facilities is widely reported, the desktop robot industry typically remains out of the limelight. However, since the mid-1990s, when sales first took off, tens of thousands of these smaller machines have taken on assembly tasks and brought automation to even quite small manufacturing facilities all over the world. Robots can work in tandem with dispensing


somewhat mitigated with a dispensing valve. These valves are usually pneumatically controlled and mean the operator can turn material on and off like a tap with improved control. There are many types of dispensing valve on the market, including needle valves, spool valves and diaphragm valves. However, they are still based on time/pressure principles, and the variable results may still not be acceptable for more critical applications. Because the precise control of a pressurised


flow of material will always be susceptible to changes in the material rheology, industrial dispensing technologies have been developed based around a positive displacement concept. This means an amount of material is physically established in the pump or valve and then ejected or displaced to generate a reproducible volume. Examples include dispensing valves designed with an auger screw in a metal tube, and peristaltic pumps. The Holy Grail of volumetric dispensing is now


possible and available for manufacturers to trial in their processes. Such technology is based on the progressive cavity pump principle, typically consisting of a single helix metal rotor and a double helix hole in an elastomeric stator. The rotor seals against the stator, forming a series of spaces or pockets, which translate along as the rotor rotates, keeping their form and volume. The pumped material is moved inside the pockets. Because the pockets taper and overlap, the output is continuous, even, and non-pulsing. One example of this technology is the preeflow eco-PEN, which can achieve a volumetric dispensing process with an accuracy of ±1%, more than 99% of the time.


aUtomation rises


As the trend towards miniaturisation, particularly in electronics, has continued, there has been more demand for precise, repeatable technology. Naturally, robots are suited to this, helping to offer accuracy and repeatability in the placement of material to match the capabilities of more advanced dispensing equipment. Once dispensing equipment has been specified, it can be mechanised: options include rotary tables, simple


44 DESIGN SOLUTIONS JULY/AUGUST 2021


devices and other technology to deliver the required precision for critical applications. For example, Intertronics offers a vision system for Fisnar ADVANCE Series Dispensing Robots which provides an auto-alignment function to guarantee fluid is being dispensed at the exact required location. They are now very affordable, with easily understood benefits and an easy to justify return on investment.


UV cUring sweeps the market


Ultraviolet-cured adhesives first became available in the early 1960s, but developed rapidly with advances in chemical and equipment technology during the 1980s. These materials are made up of monomers, oligomers, thickeners, adhesion promoters, and other additives, and include a relatively small proportion of photoinitiators (PIs). When the right light hits the PIs, they split and form highly excited free radicals, which initiate and accelerate the curing/crosslinking process. Supplying this appropriate light energy is key to a fast and complete curing reaction. Historically, they were cured with UV light,


reacting with light in the near-visible, long- wave UV-A range (315-400 nm). However, many plastics have UV blocking ingredients to prevent ambient UV light from affecting their properties, so adhesives have been developed to use a synergistic combination of UV and visible light. Synergistic use of UV and visible light gives better cure speed and depth, and allows use in applications that were previously difficult or impossible. UV adhesives based on acrylic chemistry


are popular with design engineers as they can distribute load and stress well, offer improved impact resistance, reduce the finishing requirements, and can offer aesthetic enhancements. From a process perspective, they are single part, which means no metering or mixing is required and less waste is produced. They cure very quickly and on demand – only when exposed to light of the correct wavelength – reducing work in progress. Specifying them will therefore earn design engineers the gratitude of their production engineering colleagues. They are particularly popular in the


electronics and medical device industries because their properties and process advantages are a good fit for the manufacturing requirements dictated by current industry


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