The load bearing surface on a flange is critical to ensure load is properly transferred from the rotational torque produced by a threaded fastener. Flanges that have been assembled many times can exhibit wear in the area where the nut contacts the back of the flange face. Excessive wear and gouging can create an area where friction can degrade load transfer. Even using a controlled tightening method such as hydraulic torquing can be inaccurate since the friction created by this damaged surface is not taken into account. The nut, typically a forged and hardened material is much harder than the flange material which results in a damage to the flange face during assembly. A hardened washer, typically conforming to ASTM F436 or ASME PCC-1 should always be used ensure this bearing surface is in the best possible condition. Considering all the other aspects of bolted joint assembly that are much more difficult to control, the use of a hardened washer is an economical practice that will result in significant reliability improvements and minimization of variation in load consistency among bolted connections.
Damaged nut bearing surface created by numerous assemblies without the use of hardened washers
Painted coatings in this nut bearing area can cause additional friction and can impede the transfer of load from torque
Flange assembly utilizing hardened washers beneath the nuts to ensure minimal torque and load variation
A washer is a thin plate (typically disk-shaped, but sometimes square) with a hole (typically in the middle) that is normally used to distribute the load of a threaded fastener, such as a bolt or nut. Other uses are as a spacer, spring (Belleville washer, wave washer), wear pad, preload indicating device, locking device, and to reduce vibration (rubber washer).
Washers are usually metal or plastic. High-quality bolted joints require hardened steel washers to prevent the loss of pre-load due to brinelling after the torque is applied. Washers are also important for preventing galvanic corrosion, particularly by insulating steel screws from aluminium surfaces. They may also be used in rotating applications, as a bearing. A thrust washer is used when a rolling element bearing is not needed either from a cost-performance perspective or due to space restraints. Coatings can be used to reduce wear and friction, either by hardening the surface or by providing a solid lubricant (i.e. a self-lubricating surface).
The origin of the word is unknown. The first recorded use of the word was in ; however, the first time its definition was recorded was in .[1]
Rubber or fiber gaskets used in taps (or faucets, valves, and other piping connections) as seal against water leaks are sometimes referred to colloquially as washers; but, while they may look similar, washers and gaskets are usually designed for different functions and made differently.
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Most washers can be categorized into three broad types;
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Name(s) Image Description Plain washer (or "flat washer") A flat annulus or ring, often of metal, used to spread the load of a screwed fastening. Additionally, a plain washer may be used when the hole is a larger diameter than the fixing nut.[
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Fender washer (US), penny washer, mudguard washer, or "repair washer" (UK) A flat washer with a particularly large outer diameter in proportion to its central hole. These are commonly used to spread the load on thin sheet metal, and are named after their use on automobile fenders. They can also be used to make a connection to a hole that has been enlarged by rust or wear. In the UK, the name originally comes from the size of the old British penny. In the UK, most industries refer to all large OD washers as penny washers, even when the OD is as much as twice the size of the old penny.An archaic form of this washer was sold as a "pot mender", usually in small quantities through a retail ironmonger. This included two washers, a nut, and bolt, and a sealing washer of rubber, cork, or fibre sheet. They could be used for sealing small holes, rust spots or removed pipe connections in water tanks or large cooking vessels.
Spherical washer nut and screw Part of a self-aligning nut; it is a washer with one radiused surface, which is designed to be used in conjunction with a mating nut in order to allow for up to several degrees of misalignment between parts.[
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Anchor plate or wall washer A large plate or washer connected to a tie rod or bolt. Anchor plates are used on exterior walls of masonry buildings, for structural reinforcement. Being visible, many anchor plates are made in a style that is decorative.[
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Torque washer Used in woodworking in combination with a carriage bolt; it has a square hole in the centre into which the carriage bolt square fits. Teeth or prongs on the washer bite into the wood, preventing the bolt from spinning freely when a nut is being tightened.[
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Lock washers, locknuts, jam nuts, and thread-locking fluid are ways to prevent vibration from loosening a bolted joint.
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The term washer is often applied to various gasket types such as those used to seal the control valve in taps.
Name Image Description Shoulder washer A plain washer type with integral cylindrical sleeve. Used as a barrier between differing metals and as a seal.[
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This term is also used for electrically insulating grommets.[
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Link to Hebei Bentley Technology
Crush washer A washer made of soft metal such as aluminium or copper. Used to seal fluid or gas connections such as those found in hydraulic systems and in internal combustion engines.[
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Name(s) Image Description Keps nut or K-lock nut A nut with an integral free spinning washer; assembly is easier because the washer is captive. Self-aligning washer A two-part washer: one part has one convex spherical surface, which mates with a concave surface on the other part, to allow tightening to a surface which is not perpendicular to the axis of the screw or nut fastener, in a similar manner to a spherical washer and self-aligning nut Top hat washer A shoulder washer type used in plumbing for tap fitting. Insulating shoulder washer Used to electrically isolate a mounting screw from the surface it secures. Often made of nylon, these are also made of teflon, PEEK or other plastics to withstand higher temperatures. Keyed washer A washer with a key to prevent rotation, and is used to lock two nuts in place, without allowing the torque applied to the top nut to cause the bottom nut to also rotate (such as in a threaded headset on a bicycle). Torque-limiting washer A type of washer used in a variety of torque sensitive applications, designed to limit torque to a predetermined level and not beyond. Dowty washer Has a central rubber ring to provide a strong seal against high pressure liquid or gas.The DIN 125 metric washer standard refers to subtypes A and B. ISO calls these Form A and ISO calls them Form B. They are all the same overall size, but Form B is chamfered on one side.
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Washers can be fabricated from a variety of materials including, but not limited to:[22]
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A number of techniques are used to enhance the corrosion resistant properties of certain washer materials:
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A plain washer and a spring washer are placed on a bolt between the nut (on the threaded end) and the bolt head.The American National Standards Institute (ANSI) provides standards for general use flat washers. Type A is a series of steel washers at broad tolerances, where precision is not critical. Type B is a series of flat washers with tighter tolerances where outside diameters are categorized as "narrow", "regular" or "wide" for specific bolt sizes.[26]
"Type" is not to be confused with "form" (but often is). The British Standard for Metric Series Metal Washers (BS), written in , coined the term "form". The forms go from A to G and dictate the outside diameter and thickness of the flat washers.
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Washers of standard metric sizes equivalent to BS Form A are listed in the table below. Measurements in the table refer to the dimensions of the washers as described by the drawing. Specifications for standard metric flat washers were known as DIN 125 (withdrawn) and replaced with ISO . DIN (Deutsches Institut für Normung - German Institute for Standardization) standards are issued for a variety of components including industrial fasteners as Metric DIN 125 Flat Washers. The DIN standards remain common in Germany, Europe and globally even though the transition to ISO standards is taking place. DIN standards continue to be used for parts which do not have ISO equivalents or for which there is no need for standardization.[27]
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citation needed
]Bowmans Fastener Technical Fast of on page 32 and 33 has SAE recommendation from that lock washers not be used in any critical application. BMW motorcycles experienced a series of broken lock washers and BMW then disallowed their use in U-joints due to the damage of loss of the spacer and nut loosening.
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