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DESIGN ENGINEERING

ASSURED RELIABILITY

FASTENERS & ADHESIVES

ADHESIVES ASSURE HYDRAULIC SYSTEMS’ RELIABILITY FOR 25 YEARS

gigantic Berg Propulsion propeller with a A typical use for Loctite threadlocking is on a spacer
diameter of more than nine metres dwarfs the that protects the propeller’s control units. The spacer is
men standing next to it and at every stage of its fitted in place with four screws and locked with Loctite
Amanufacture, Loctite engineering adhesives from 243. Other applications for this product include securing
Henkel have an important part to play. Loctite end cap fixings and dowel pins to prevent self-loosening
threadlockers and thread sealants secure assemblies in and in general pipe assembly. Loctite 243 is a medium
the hydraulic systems in the propeller hub. The systems strength threadlocking adhesive that is suitable for joining
have to be pressure resistant and threaded assemblies all materials including passive substrates such as stainless
immune from vibration loads. Indeed, a minimum of 25 steel, aluminium and plated surfaces. As a single
years of reliable service is the expected norm. component it is clean and easy to apply that cures at room
“Our customers require ship propulsion systems with temperature to a hard, solid thermoset plastic.
the highest availability at all times,” explained Anders “We started using Loctite in 1964,” Christofferson
Christofferson, managing director of Berg Propulsion continued. “Erik Berg, son of the company’s founder,
Technology. “Loctite increases the reliability of our brought a Loctite product back from the UK as a
products. The products allow quick and easy assembly replacement for the locking washer and it worked.”
and we also rely heavily on Henkel’s technical support.” Loctite has underpinned the reliability of Berg Propulsion
The thread of the hydraulic pipes responsible for products ever since.
controlling the individual blades are retained by Loctite Henkel’s continuous development of core products
638. They have to withstand more than 70 bar of oil such as threadlocking adhesives have seen the
pressure which equals twice the force the blades will have introduction of many upgrades and new developments
to bear at sea. The adhesive sealing has to create an since 1964. For example, today’s choice includes Health
hermetic seal after an hour because the hydraulic pipes and Safety formulations that carry hazard-free labelling.
are then embedded into the shaft. The technical performance of the products also been
Loctite 638 is a high strength retaining compound that also extended. Threadlockers can now tolerate higher form, as well as a wide range of different liquid viscosities
provides the best resistance to dynamic, axial and radial operating temperatures and are tolerant to oil, making and strengths to suit the application. Another important
loads. Applied as a liquid it forms 100% contact between them less sensitive to improperly cleaned parts. And development is the introduction of new packaging to
mating metal surfaces and provides many advantages over importantly, these qualities have been achieved without minimise the risk of users unwittingly using inferior,
conventional assembly methods. It floods into the inner compromising any of the products’ other key properties counterfeit products that could compromise
spaces between components, curing to form a strong, such as chemical resistance and shelf life. Threadlockers application success.
precision assembly. are also now available as semi-solid adhesives, in stick MORE INFORMATION: www.henkel-adhesives.co.uk

OVER-SPECIFICATION OF THREADED FASTENERS

ltimately, one can never know completely how components, given the changing loads and environments This generally occurs in applications where there are
a fastener will function in-situ until you try it they are often called upon to compensate for in their daily issues of weight and space but where cost is secondary
which is why accelerated aging trials and service. The simple act of holding together two separate because of the safety critical nature of the situation.
Uextended excess load tests are frequently components requires a balancing of forces – this is a However sometimes given a minimum lifetime expectancy
performed to ascertain a realistic safety margin. complex matter often addressed by application of a “safety there can be a tendency to “play it safe” and add a safety
Guidelines from hard-won experience can normally be margin” judged to be sufficient to deal with the unknowns margin on top of a safety margin, leading to gross over
accessed, but sometimes an unusual situation needs to be involved. specification, for example going up one or two sizes with
evaluated or perhaps a replacement of the exact same However, some industries deal with much more life consequent weight and space implications. Calling for an
type is simply not available. and performance critical situations than others and so the exotic and expensive alloy where a lower-cost high-grade
Under those circumstances it is easy and tempting to concept of designing for a product lifetime has evolved – treated steel would be more appropriate. Over specifying
over-specify.Fasteners can almost be regarded as active in one way to ensure that the specification is adequate, one fastener may not be a problem but over specifying
but on the other to time-limit the expectation, and so thousands can make a big difference overall.
ensure that proper maintenance is mandated. Design for a specific lifetime is often a highly skilled art
Aerospace, automotive and rail industries all follow of combining knowledge from different areas, for example
this design for a specific lifetime philosophy – an approach specific performance of the fastener, effect of varying
rarely used elsewhere – and sometimes this leads to over material, options for head types and the stress they
specification in products which do not need it. This over involve, stresses inbuilt into the fastener from its
specification is often a comfort issue, as a sort of safety manufacturing process or treatment - a solution which can
margin which often makes the custom spec prohibitively be achieved in concert with a fastener specialist such as
expensive if not actually impractical. Over specification is Challenge Europe.
a significant potential problem in the fastener industry. MORE INFORMATION: www.challenge-europe.co.uk

34 INDUSTRIAL TECHNOLOGY • May/June 2020