Washers are essential when coupling parts using bolts and nuts. Here is the purpose of washers.
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Spacing and Alignment
Washers can be utilized as spacers. When we insert a threaded fastener into an object longer than its depth, the fastener protrudes from the rear of the object. For instance, when one tries to insert a 3-inch-deep fastener in a 2-inch-deep object, the 1-inch fastener sticks out the back of the object.
However, inserting a washer into the fastener before screwing it to the object helps prevent this protrusion. Therefore, it does this by creating padding, ensuring the fastener does not go too deep into the object. Also, washers compensate for slight variations in the spacing found between types of fasteners and parts, ensuring proper alignment.
Load Distribution
Washers assist in spreading the load more equally across a broader surface. The risk of material deformation, damage, or failure is decreased by washers because they disperse the force produced by a nut or bolt. For instance, driving a screw into a softer material could result in cracks appearing on its surface. However, with washers, there is minimal damage tendency.
Seal/Liquid Protection
Washers in this category stop water and other liquids from entering and exiting. Seal washes are frequently applied in water pipelines and connectors to make a waterproof seal. Liquid-sealing washers are constructed of a flexible material, and this material choice ensures they press completely against the object’s surface.
Vibration Absorption
Vibration absorption is a feature of some washer types. Washers in this category are mainly not metals. Instead, softer materials like plastic, rubber, or urethane are used to create them. These softer materials are better at absorbing vibrations than harder elements like metal.
Additionally, vibration-dampening washers help protect coupled parts from damage. This is especially true when one of two objects connected by a threaded fastener vibrates violently.
Damage Prevention
The nut or bolt head and the surface it is fastened to are separated by washers, which serve as a protective barrier. This preserves the material’s integrity and maintains the connected surfaces’ visual appeal by preventing marring, scratches, dents, and other damages.
Corrosion Prevention
Washer fasteners, especially those made from corrosion-resistant materials, offer additional protection against corrosion and rust. This is crucial in locations where prolonged exposure to moisture, strong chemicals, or other elements can deteriorate the fastening system.
Manufacturers use types of washers for making and coupling parts. Below are different washers and their uses.
Plain Washers
Plain washers are the most popular kind. They disperse force and safeguard the item that the screw or nut is attached to. It also helps the screw or nut fit properly into a large hole. Plain washers in this category include:
Torque Washer
The principal uses for these washers are in the woodworking industry. When a nut is tightened, the outside prongs of the washers feature square holes that prevent the accompanying bolt from spinning.
Flat washer
Flat washers have a hole in the center and are flat or disc-shaped. They are ideal for small head screws because they spread the weight across a wider surface.
Fender washer
Fender washers are bigger and have a tiny hole in the center. They can spread out the load across a broader region. These washers are primarily used in sheet metal manufacturing, automotive fenders, and plumbing industries.
Finishing or countersunk washer
Countersunk washers in this category often create a flush finish upon securing with a flat-head countersunk screw. This ability to catch countersunk fasteners is due to its sunken top.
Shoulder washer
Shoulder washer fasteners in this category come in various materials, including PTFE, fiberglass, metal, phenolic, and nylon. These shoulder-like shaped washers often serve as insulators for screws and wires.
C-washer
A C-washer resembles a flat washer, but the primary difference is the hole cut from its center to form a C-shape. One primary advantage of this type of washer is that it is possible to adjust, remove or modify it without removing the fastener.
Spring Washers
For machinery that vibrates vigorously while operating, spring washers are ideal. They move with vibrations, thus preventing them from being loose or unfastened because of their axial flexibility, consequently increasing the joint’s flexibility. There are different types of spring washers.
Belleville or Conical washer
These washers, often called conical spring washers, are employed to maintain tension during the assembly’s thermal expansion and contraction. They can support large weights while deflecting only slightly.
Dome spring washer
A dome washer is renowned for having a large load capacity with minimal deflection. They also absorb excessive vibrations and flatten the surface.
In addition, they have ground curves that create a load-bearing surface that is flatter. It can be used everywhere. A crescent spring washer would be useful, although flattening the surface is also necessary.
Wave spring washer
Wave spring washers are curved in two directions and are typically employed as cushions or spacers. They can support a moderate amount of weight and guard against excessive wear on the surface.
Finger spring washer
Made using carbon steel, finger spring steel washers comprise three curved flanges. They help lessen vibration, skidding wear, additional wear, dampening, and noise on rotating parts.
Carbon steel is commonly used to make finger spring washers. They blend the wave washer’s predetermined load spots with the casing washer’s flexibility.
Crescent spring washer
The crescent spring washer, also called curved spring washer, has a somewhat curved appearance that gives them a lighter pressure while maintaining flexibility. They have an extensive deflection range and can withstand extremely light loads.
These washers have linear load-deflection characteristics and offer uniform spring rates throughout the deflection range.
Lock Washers
Lock washers are designed to help prevent the screws and nuts from rotating toward their loosening position. Consequently, this preserves them even during intense vibrations produced by the machine or equipment’s operation. In other words, they hold the fasteners that tend to loosen due to friction in place. The different types of lock washers include:
Split lock washer
The split lock washer, commonly called a helical washer, is used to secure fasteners. They are non-continuous rings bent inward and outward in opposing directions. When this fastener is used to secure the bent, both ends of the bent flatten out and dig into the mating surface.
External tooth lock washer
External tooth lock washers employ a teeth-structural action to keep the nut or screw head from coming undone. They function better with screws that have a larger head. The numerous teeth on their outer diameter bite into the surface to produce exceptional compression resistance, consequently ensuring they provide the highest level of torsional resistance.
Internal tooth lock washer
On the inside diameter of the internal tooth locker are many teeth that prevent the bolt or nut head from loosening. They serve to dampen noise and shock while locking shallow-head fasteners into position.
Specialized Washers
Specialized washers do not fall expressly into any of the above categories. Here is their information.
Keps nut
Also referred to as K-lock nuts, these washers with built-in washers facilitate spinning. The assembly functions more efficiently, thanks to the nuts.
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Top hat washers
These washers are perfect to utilize while repairing or installing a tap because they are typically used in plumbing applications.
Keyed washers
Typically used between bolts to prevent them from spinning, these washers are placed keyed washers typically find application in the automotive industry. These washers have an internal tab that prevents the automobile shaft from rotating. They also find use in chassis parts and cylinder heads.
Insulating shoulder washer
Insulating shoulder washers are often made from nylon, peek, plastic, and other insulating materials. The best use for these washers is in the electrical sector, where they help isolate mounting screws from electrical current.
Gaskets
Gaskets, also known as O-rings, and made of rubber, come in different shapes and sizes depending on the purpose. It is a mechanical seal that fills the space between two or more surfaces in contact to prevent leaks and spills. In the automotive sector, their primary use is to slam shut oil and gas connectors and stop leaks.
Aside from rubber, gaskets can be made from light metals, such as aluminum, and other metals. These washers maintain a tight seal regardless of pressure and temperature, preventing gases and liquids from escaping.
Every mechanic has used them, but most don’t know how many different types of washers there are, what materials they are made of, and how to properly use them. Over the years, we have received numerous questions concerning washers, so a tech article sharing information on these hardware devices is long overdue.
We recently covered the art of making high-performance fasteners with Automotive Racing Products, Inc. (ARP), thoroughly covering the nuts and bolts of the subject. It is now time to pay respect to the fastener component that is often taken for granted, the humble washer.
In the following paragraphs, we will cover what washers are, the different types of washers, what they do, how they are made, where and when to use them – and yes, we will even discuss if washers are directional or not.
The Basics
Generally speaking, a washer is simply a disk-shaped, wafer-like plate with a hole in the center. While the design may sound primitive, washers actually provide a complicated task. They are commonly used to distribute the load of a threaded fastener, like a bolt or cap screw.
They can also be used as spacers — or in some cases — can be a wear pad, locking device, or even used to reduce vibration — like a rubber washer. The basic washer design features an outer diameter that is twice as large as the washer’s inner diameter.
Usually made of metal, washers can also be made of plastic or rubber — depending on the application. In machinery, high-quality bolted joints require hardened steel washers to prevent indenting the joint’s surfaces. This is called Brinelling. These small indentations can eventually lead to a loss of preload on the fastener, chattering, or excess vibration. As the condition continues, these movements can accelerate into other wear that is often defined as spalling or galling.
Washers also help prevent galvanic corrosion, a condition that exists when certain metals come in contact with each other. One metal acts as an anode, and the other as a cathode. To slow down or prevent this process from the beginning, a washer is used between the bolt or nut and the metal being joined.
The Basic Purpose
In addition to evenly distributing the pressure over the part being secured and reducing the chances of damaging the part, washers also provide a smooth surface for the nut or bolt. This makes the fastened joint less likely to loosen compared to an uneven fastening surface.
There are special washers designed to provide a seal, an electrical grounding point, align the fastener, hold the fastener captive, insulate, or provide axial pressure to the joint. We will discuss these special washers briefly in the text below.
We’ve also seen a couple of ways to improperly use washers as part of a fastened joint. There have been many instances where shade-tree mechanics have used bolts or nuts that are too small in diameter for the part they are joining. In these instances, the washer has an inner diameter that fits the bolt, yet, doesn’t allow the bolt head or nut to slide through the bore of the component that is being joined. This is begging for trouble and should never be attempted anywhere on a race car.
More commonly, mechanics will use a bolt that is too long, but lacking enough threads, which does not allow the joint to be tightened. Stacking a handful of washers on the shank as a spacer until the nut can be tightened should also be avoided. Choose the right bolt length. Using washers improperly can lead to damage or injury.
Types Of Washers
Generally speaking, there are several types of washers manufactured in the world today. Some are specifically made for use on wood joints while some are for plumbing purposes. When it comes to automotive needs, ARP’s R&D specialist, Jay Coombes, tells us there are only five types used in automotive maintenance. There is the plain washer (or flat washer), fender washer, split washer (or lock washer), star washer, and insert washer.
Interestingly, you will not find a split washer in ARP’s massive fastener offerings. “They’re primarily useful with small diameter fasteners in low load conditions,” Coombes explained. ARP tends to focus on high-performance racing fasteners that work under higher load conditions. There are variants of these types of washers that serve specific purposes, like the plain washer with serrations on the underside.
Plain Washers
A flat washer is the preferred intermediary between the head of a bolt (or nut) and the object being attached. Its primary purpose is to spread the load of a tightened fastener to prevent damage to the joining surface. “This is especially important with aluminum components,” Coombes says.
The American National Standards Institute (ANSI) has provided a set of standards for general use, plain washers calling for two types. Type A is defined as a washer with broad tolerances where precision is not critical. Type B is a flat washer with tighter tolerances where the outside diameters are categorized as narrow, regular, or wide for their respective bolt sizes (inner diameter).
As we mentioned before, washers are more complicated than a simple explanation from one organization. In fact, there are several. The Society of Automotive Engineers (SAE) categorizes plain washers in material thickness, with smaller inside and outside diameters compared to how the United States Standards (USS) organization has defined flat washers.
The USS standards are the standards of inch-based washers. This organization characterizes a washer’s inside and outside diameter to accommodate coarse or larger bolt threads. USS washers are often used in automotive applications. With three organizations specifying three different standards for plain washers, clearly, washers are more complicated than its simple appearance would lead anyone to believe.
According to ARP’s Coombes, “The size and quality of the washer itself merits close consideration. It should have sufficient thickness and size to properly distribute the load.” Coombes adds, “It’s also very important that the washer is parallel ground and perfectly flat for those crucial applications with higher torque loads. Anything else can cause unequal preloading.”
Fender Washer
These are washers that have an extra-large outside diameter in proportion to its central hole. It is also designed to distribute the clamping force, but due to the larger size, the load is broadcast over a larger area. For many years, these washers were used to attach fenders to vehicles, hence the name. Fender washers may have a larger outer diameter, but are typically made from thin-gauge material.
Split Washer
Split washers, also called spring or lock washers, have axial flexibility. These are used to prevent loosening due to vibration. The concept behind split washers is simple: It acts like a spring to put pressure on the object being attached and the head of the bolt or a nut.
ARP does not manufacture these washers because most fasteners that play key roles in the engine, drivetrain, chassis, and suspension are tightened to a specific torque spec, applying the proper clamping force. There is little to no chance of the fastener loosening without using a tool.
Most engineers agree that a spring washer — when torqued to higher specifications — will stretch to some degree. When that happens, the split washer will lose its tension and can even disrupt accurate preloading the fastened joint.
Star Washers
Star washers serve almost the same purpose as a split washer. They are intended to prevent a fastener from loosening. These are washers with serrations that extend radially (inward or outward) to bite into the surface of the component. By design, they are supposed to “dig in” to the bolt head/nut and the substrate to prevent the fastener from loosening. Star washers are typically used with smaller bolts and screws associated with electrical components.
Preventing rotation, and thereby affecting preload accuracy, has prompted ARP to manufacture special washers that are serrated on the underside. The idea is for them to grip the item being attached and provide a stable platform.
Another special washer manufactured by ARP is the insert-type washer. They are designed to protect the top of holes to prevent galling or the top of the hole collapsing. Common uses include cylinder heads, chassis components, and other high-wear areas that require a washer.
Final Thoughts
It’s important to note that lubrication plays a key role in accurate preloading. In addition to putting a lubricant on the threads of a fastener, it’s recommended to put a small amount on the underside of the bolt head (or nut) or the top of the washer. Never lubricate the underside of the washer (unless installation instructions say otherwise) as you don’t want it to rotate.
Paying attention to proper washer usage and lubrication is something that merits the consideration of all race teams.
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