We continue our look at the diverse industries that use fasteners. In April, we touched on general fastener information and the equipment used to heat treat fasteners. We discussed the aerospace and medical industries, and this article picks up where we left off.
Fastener applications are as diverse as the industries they service. In this article, we take a look at automotive, construction, mining, marine, petrochemical, nuclear and specialized applications. It is estimated that some 350 manufacturing plants produce more than 200 billion fasteners per year in the U.S. alone.[1]
Fastener Usage in the Automotive Industry
The automotive industry alone is estimated to use between 25-35 billion fasteners. This manufacturing segment continues to see sales of greater than 14.5-15.5 million vehicles in North America. The automotive market share (as of 2012) is divided as follows: GM 17.9% (up 3.7%), Ford 15.5% (up 4.7%), Chrysler 11.4% (up 21%), Toyota 14.4%, Honda 9.8% and Hyundai/KIA at 8.7%.
Steel and stainless steels, including duplex and austenitic grades (Table 1 and 2-4 online), as well as plastic fasteners dominate the automotive landscape. These four tables summarizing the types of materials used in the various automotive applications appear exclusively in the online edition of this article. Many fasteners are plated or coated for increased corrosion protection.
Fastener Usage in the Construction Industry
Fasteners are the critical link in the load path of a building structure. They provide structural integrity and are a major point of energy dissipation under seismic and wind loads. Construction fasteners are generally classified as those fasteners that are used to secure building materials and can be classified as commodity fasteners or task-specific fasteners. Typical applications include:
- Roofing (flat, sloped)
- Decks (steel, wood, composite)
- Bridges (ladder deck, multi-girder, suspension)
- Buildings (residential, commercial, skyscraper)
Typical examples include cement-board screws, drywall screws, needlepoint screws, outdoor screws, pole-gripper screws, self-drilling screws and woodworking screws. Steel (Table 5) and stainless steel fasteners are commonly used in the construction industry.
Fastener Usage in the Mining Industry
A key requirement for fasteners in the mining and excavation industry is their resistance to vibration and corrosion. Vibrating conveyors, crushing and pulverizing equipment, mining machinery, railroad cars and material-handling devices are examples of applications where vibration is a significant issue that requires the fastener to be designed so that it won’t “back off” while in service (Fig. 3). Furthermore, corrosion and/or cracking is often involved in mining fasteners being related to hydrogen-induced cracking (aka hydrogen embrittlement), often in the form of stress corrosion cracking (SCC) or sulfide stress cracking (SSC).
The types of fasteners used in the mining industry are quite diverse and include bolts (e.g., anchor, eye, structural, swing), rods (e.g., elevator, rock, tie, sag), washers, nuts and plates. Materials include carbon and alloy steels, construction steels and stainless steels.
Fastener Usage in the Marine Industry
The marine industry is literally held together by fasteners designed to survive the extremely harsh and corrosive environments to which they are exposed. Bolts, screws, washers, locking washers, wing nuts, split rings and slating nails are just some of the many marine construction fasteners used on docks and ramps, ships, tanks, winches and for underwater construction projects.
Because fasteners are generally much smaller than the components that they support, the fasteners generally must be more corrosion-resistant. As such, heat-treatment processes need to be carefully chosen and controlled in order to not have a negative impact on corrosion resistance or other important physical or mechanical properties.
In addition, since the fastener material is often dissimilar to the components being joined, galvanic-induced corrosion is a principal concern. Should the fastener be anodic to the remainder of the structure, the relative-size effect could cause severe corrosion and degradation of the fastener in a short period of time. Failure of a nut or bolt can have catastrophic results.
There are many copper alloys suitable for marine service, including coppers, copper-nickels, bronzes (aluminum and silicon bronze), brasses and copper-beryllium. For seawater systems, copper-nickel and aluminum bronze are often preferred, although other copper alloys are used in marine service and have their specific advantages. Copper alloys differ from other metals in that they have an inherent high resistance to biofouling, particularly macrofouling, which can eliminate the need for antifouling coatings or water treatment.
Many other materials can be used provided they demonstrate superior corrosion resistance. One such example is Inconel 686, a high-performance nickel-based alloy that exhibits high tensile strength and fracture toughness as well as resistance to corrosion, especially crevice corrosion, superior to that of other nickel-based alloys (such as K500 Monel).
Different combinations of properties can be produced in each of these materials by varying the heat treatment, which influences strength, hardness, ductility, conductivity, impact resistance and inelasticity.
Fastener Usage in the Petrochemical Industry
Petrochemical products are those derived from petroleum, being obtained from crude oil and natural gas. They are mainly used in the production of petrochemical derivatives (e.g., ethylene, methanol, butadiene, propylene, formaldehyde, polyvinyl chloride, acetic acid and epoxy resins among many others).
The growing demand of petrochemicals from major end-use industries, including transportation, construction and packaging, drives the petrochemical market. The demand for industrial fasteners is expected to grow at a rate of 5.4% through 2018[1] and is expected to fall just shy of $100 billion by 2018. In addition, the petrochemical industry is incredibly diverse, encompassing regional markets in North America, Latin America, Europe, China, Asia Pacific, Africa and the Middle East.
This diversity is also evident in the products and materials from which fasteners are constructed. Examples include threaded rod, studs (full-thread, double-end), studbolts, hex bolts and nuts, gaskets (spiral-wound, full-face, rings), setscrews, sockets, standard fasteners and specialty products such as tie bars, socket screws and machined parts.
The range of chemically resistant materials includes petrochemical grades of stainless steel, duplex and super-duplex steels, nickel and cupronickel alloys, carbon and alloy steels, titanium and other nonferrous materials, and superalloys. Coatings are common and include zinc, cadmium, nickel, galvanized (hot dip, sherardizing), phosphate and PTFE (polytetrafluoroethylene) coatings.
Fastener Usage in the Nuclear Industry
A typical nuclear power plant contains some 40,000 fasteners, including bolts, washers, nuts, studs, cap screws, pins, rivets and machine screws.[1] These fasteners are subjected to very specific design rules. Problems can develop, however, either immediately or over time.
The most common cause of fastener failure in the nuclear industry is reportedly due to SCC of certain stainless steel alloys.[1] Other contributory factors include improper material selection, poor installation practices (e.g., improper torque), bolts that were not properly sized and failures induced by a variety of heat-treatment issues (e.g., overheating, decarburization and quench cracks).
Fasteners for the nuclear industry are made from a wide variety of materials (Fig. 4). These include carbon and alloy steels, stainless, Nitronic® and Monel® alloys, Inconel® and titanium as well as brass, bronze and copper. This diversity means that required properties and heat treatments are always specified, often in ASME and SAE standards (e.g., ASTM SA193/SA194/SA276/SA307 and SAE J429/J995). A variety of coatings can be applied after heat treatment. These include zinc, cadmium, phosphate, ceramic, chromium and black oxide to name a few.
Fastener Usage in Specialized Applications
Critical applications require the use of materials whose performance envelope encompasses both normal-duty and extreme-duty demands. It is the latter that differentiates specialty fasteners and components from standard ones.
What are specialty fasteners?
Specialty fasteners are those whose applications demand performance over cost. Mechanical, physical and metallurgical properties are more stringent than those involving standard fasteners. Examples of equipment and industries that rely on specialty fasteners include power generation (e.g., gas turbines, offshore performance platforms), pulp and paper mills and electronic devices.
In aerospace (aircraft, rotorcraft, space) applications, specialty fasteners are used are on exteriors, interiors, avionics and flight systems (e.g., landing gear). Product examples include captive screws, rivets, gas springs, clamshell flexible couplings, quick-release pins, tension latches and telescopic slides. In automotive (motor sports, cars, off-road, heavy truck), fasteners and clamping device are commonplace throughout, including the engine, body and subsystems.
Alloy Fastener Materials
There are some unique material selection challenges in the design of very high-strength/high-performance fasteners. These type of fasteners are often exposed to high stress concentration in the thread roots (caused by the tensile stresses produced from extremely high clamping loads), on top of which are superimposed any fatigue loads. To meet these challenges, the designer often selects alloys classified as “exotic” primarily due to their chemistry and ability to perform at elevated temperatures (Table 6).
References
- Industrial Fasteners Institute Annual Report, 2012
- Industrial Fastener Market (Externally Threaded, Aerospace Grade and Standard) for Automotive OEM, Machinery OEM, MRO and Construction Applications – Global Industry Analysis, Size, Share, Growth, Trends and Forecast, 2012-2018, Transparency Market Research
- Herring, Daniel H., Atmosphere Heat Treatment, Volume I, BNP Media Group, 2014
- Wikipedia (www.wikipedia.com)
- Herring, Daniel H., “Overview of Fastener Heat Treatment: Present & Future Direction,” Fastener World International (FW143), November/December 2013
- Herring, Daniel H., “Heat Treatment of Fasteners for the Nuclear Industry,” Fastener Technology International, August 2013
- Herring, Daniel H., “Heat Treatment of Fasteners for the Petrochemical Industry,” Fastener Technology International, October 2013
- Herring, Daniel H., “Heat Treatment of Fasteners for the Medical Device Industry,” Fastener Technology International, December 2013
- Herring, Daniel H., “Heat Treatment of Fasteners for the Marine Industry,” Fastener Technology International, February 2014
- Herring, Daniel H., “Heat Treatment of Fasteners for the Mining Industry,” Fastener Technology International, April 2014
- Herring, Daniel H., “Heat Treatment of Fasteners for the Automotive Industry,” Fastener Technology International,April 2015
- Herring, Daniel H., “Heat Treatment of Specialty Alloy Fasteners,” Fastener World International (FW148), September/October 2014
- Herring, Daniel H., “Heat Treatment Aerospace Fasteners,” Fastener Technology International, October 2014
