Fastener and component enhancement materials By Mark Thurber, CEO, Maelstrom Chemical Technologies LLC Fastening systems have been an engineering necessity dating back to when mankind first attempted construction. Joining two separate elements to work as one is the most fundamental concept of creation.
ince this modest beginning, designers have searched for a means of keeping these elements secure, durable and reliable until removal is required. Though this seems to be the goal most sought after, any weekend mechanic will swear that the opposite seems more often to be the rule, rather than the exception. Fastener enhancement products have traditionally encompassed only the most basic of notions including cotter pins and deformed components for locking, and messy greases and anti-seize for lubricants. In the recent decades, higher tech adhesives, sealants and coatings have come into play, taking strides in the reliability and multitasking of fastener systems. Today, there are a variety of new, highly specialised product choices and wider utilisation opportunities for use on components, far beyond that of fasteners.
Fastener locking devices
Adhesives as locking elements can be most broadly subdivided into two general categories: Pre-applied: Applied to the fastener en-masse by fastener coating services, long before the intended installation. Bottled: Applied to the joint at the time of assembly. Pre-applied products do not impart any direct performance properties that cannot be found in a bottle, however, the advantage is realised in the pre-application ‘delivery system’ itself. Time saved by pre-application of adhesives (and the resulting direct, economic payback) plus the assurance that an adhesive is not inadvertently missing from a joint, are indispensable benefits to mass assembly.
User applied, point of assembly materials
Modern fastener retaining took its biggest leap forward with the development of bottled, liquid thread-locking adhesive. Anaerobic adhesives, as they are sometimes called, are ‘triggered’ (or initiate reaction) by the absence of oxygen contact. A full spectrum of choices of these types of products are available for the user – low strength, high strength, removable, permanent, high temperature, penetrating, high viscosity, low viscosity, thixotropic, fast cure, slow cure, low friction, red, green, yellow, blue and purple; just to begin the list. Regardless of grade, whether permanently retaining a stud in an engine block or installing a serviceable pipe plug in a refrigerator – they are all based on the same chemistry. Recent innovations have come to this field that include a variety of non-anaerobic thread-locking materials offered by STS/ Tectorius®. This includes a variety of user applied materials that mimic the hard to get preapplied products – previously only available through professional service centres in large volume. In addition to easy to use packaging, many are friendly to special substrates, temperature sensitive platings and plastics, where anaerobic adhesives Tec-Bond™ adhesives family should never be used.
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In addition to threaded fasteners, many of these new breed products are finding use in non-traditional types of applications on splines, pulleys and moving assemblies offering a ‘cushioning effect’ to mitigate squeak and rattle for NVH (noise, vibration and harshness) improvement.
Pre-applied thread-locking adhesives
Pre-applied adhesives began being widely accepted in the early 1970s. Prior to this, adhesives were not highly looked upon, and considered less dependable than the more tangible, mechanical methods. 3M® Corporation introduced its highly popular Scotch-Grip® brand, offering several grades of microencapsulated, epoxy-based adhesives. Loctite® Corporation also introduced its line of microencapsulated, acrylic-based adhesives, known as Dri-Loc®. Even though other products are also available on the market, each fall into one of two chemical groups – epoxy or acrylic technology.
Epoxy technology for use on threaded fasteners was initially pursued by 3M. In the most elementary terms, epoxy-based adhesives used for fasteners are quite similar to two-part epoxy kits that can be found in any hardware store. Typical fully cured epoxies are the most durable, chemical resistant, versatile and tough adhesives known. However, delivery of these components to the right place, in correct proportion and preventing the reaction from beginning until the right moment, is an enormous hurdle to overcome. 3M took a unique approach to this delivery and proportion dilemma. A technology, formerly used only in pharmaceuticals and printing, called ‘microencapsulation’ held the key to the problems of component separation. Microencapsulation involves encasing a material within an impermeable microscopic shell; not unlike a miniature egg. Microcapsules are frequently used in consumer products such as ‘scratch and sniff’ swatches, perfume samples, and ‘carbonless’ copy paper. Only close examination with a microscope will reveal clusters of clear spheres dispersed throughout the thread deposit.
The acrylic types of adhesives were a venture in making standard forms of bottled thread lockers fit into the pre-applied mould. Loctite Corporation was on the forefront of this concept with its Dri-Loc product line. Followers in the manufacture of similar types of products are STS/Tectorius® with its very wide collection found in the Tec-Bond™ adhesives family. One largely accepted misconception involving these products is the use of the term ‘anaerobic’ meaning ‘absence of oxygen’. This is often used to describe bottled thread lockers, as the absence of oxygen in the tight confines between the fastener and the mating part will cause the adhesive to cure. This is not the same reaction mechanism taking place in the pre-applied thread lockers. Most of the pre-applied thread lockers based on acrylic functionality, are initiated in a distantly similar fashion to the microencapsulated technology previously discussed. Unlike the epoxy system, the main initiator is encapsulated, rather than the matrix forming resin. Once all components are present in an active state, their reaction will proceed regardless of the presence or absence of oxygen. This type of system offers several positive benefits, with fast development of retaining torque being the most prominent. Some level of removal torque may be detected as early as 10 minutes after installation. Other notable characteristics include the water-based application medium, and an ability to achieve high breakaway torque.