This article takes an in depth look at metal washers and their use.
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A metal washer is a small flat piece of metal that has a hole in the center and is used as a spacer, a method for absorbing shock, or distributing the load of a fastener. The hole in the middle of a metal washer allows for a bolt or screw to pass through. There are several methods used to produce metal washers, each of which is designed to produce them with a sufficient amount of strength and stress resistance.
The manufacture of metal washers includes many different types of materials, with galvanized carbon steel and stainless steel being the most common. The variations in the metals used to produce metal washers and their many shapes have created a wide assortment of washer types, with plain, spring, and lock being the standard types. Under the three commonly used metal washers are several specialty washers designed to meet the needs of specific applications.
There are endless uses for metal washers with specialty ones being manufactured for unique and unusual applications. Metal washers are designed to distribute the load of a fastener such as a screw, bolt, nut, or another form of connecting fastener that securely fits.
Washers make it easier to loosen or remove a nut from a bolt and easily resecure it. There are many types of washers for home use as well as those that are produced for industrial applications.
The main function of all washers is to distribute the load of a fastener when it is driven in or connected to a material. Fasteners without a washer tend to stress surfaces causing cracks, impressions, and other deformities. Metal washers protect against such damage by distributing and lessening the stress from the fastener by evenly distributing the load. Stress relief is not necessary for all materials except those that are soft such as wood.
Another common use of metal washers is as spacers for fasteners that are longer than the depth of the hole into which they are being driven. When some fasteners are used, a space is left between the head of the fastener and the material’s surface. If a four inch bolt is connected to material that is three inches deep, there will be a one inch gap and the connection will not be secure. Inserting metal washers, as seen below, between the surface and the head of the bolt before it is connected fills the one inch empty space.
Sealing washers are a special type of washer that has a layer of material bonded to the metal, such as neoprene. The strength of the metal washer and the sealing power of the material form a tight seal to prevent leaks and drips. Though sealing washers are very strong and resilient, they are also soft and smooth to prevent damage to the sealed surface. Sealing washers are an ideal tool for the sealing of bolt joints.
The securing of sealing metal washers has to be carefully, and precision completed since over tightening can cause leaks. The washer must be placed against the surface such that it is not convex or concave.
The bonding of the sealing material creates a corrosion resistant surface that cushions the bolt head and seals the joint. In addition to sealing leaks, sealing washers serve as a vibration dampening tool.
A specific type of washer, referred to as a fender washer, is used for repairing connections when a hole has been damaged by rust or corrosion. The washer has a small hole with a very large outer diameter that can cover the hole but allow for a fastener to be attached.
There are few limitations on the types of materials that can be used to produce washers. Though galvanized carbon steel and stainless steel are most commonly used, other metals such as aluminum and copper are also used. The choice of metal for metal washers has a great deal to do with how they will be used.
Specially designed hardened metal washers are used to maintain fastener tension under demanding or difficult conditions. Soft metals, such as aluminum and copper, are ideal for conditions where a washer is used for sealing as well as load distribution.
Washers are made by the stamping process, which is completed on a power press. The washer form is determined by a die attached to the stamping or power press ram.
Metal stamping is a cold metal working process that uses a die to punch a form or shape from a flat piece of metal. Flat sheets of metal, blanks, are fed into the bolster plate where the ram comes down on it with great force to punch out the shape. The mechanism for a stamping machine can be mechanical with a flywheel or hydraulic.
Washer dies are customized forms that are specifically designed for the manufacturing of washers. Since washers are a very small item, multiples are stamped or pressed from a single sheet of metal. Stamping is a fast and smooth process capable of producing large amounts of washers while ensuring the maximum use of the metal sheets.
Several types of dies are used to produce a variety of simple to complex products. The types of dies are simple, compound, progressive, transfer, combination, and multiple. For the manufacture of washers, compound dies are used.
In the compound die process, more than one operation takes place in a single stroke. In the case of washers, the outer edge and central hole are formed in one stroke. The die blanks and perforates the workpiece at a single workstation. The holes and shape of the washer are punched into the blank and moved up while the scrap moves down.
The thickness of the washer is determined by the gauge of the metal, which is a factor in the amount of spacing the washer provides. The gauge method of determining thickness goes back to the middle of the first industrial revolution when there wasn’t any universal method for measuring thickness.
There is a different gauge chart for every form of metal since there isn’t any uniformity between the different gauges. Regardless of which chart is used, the higher the number, the thinner the metal will be.
The thickness of a washer also affects other factors such as rigidity, support, and damping capabilities.
The gauge chart below is for carbon steel.
The choice of metal for a washer affects its strength, corrosion resistance, brittleness, and cost. When choosing a washer, there are several additional factors to consider. To get optimum performance from a washer, it is important that it matches the material with which it will be used. Replacing a washer with a stronger, more durable one may seem ideal but can lead to damage to equipment or safety problems.
The most common metals used to produce washers are zinc plated steel and various grades of stainless steel. Though these two metals are normally used for their strength and corrosion resistance, softer metals such as copper and aluminum are used to meet the special needs of specific applications.
The wide assortment of washer configurations also includes a varied selection of metals. One of the required characteristics of metals for washers is that they are resilient, strong, and durable. In some cases, washers need to be pliable enough to form a seal and maintain a tight connection.
The selection of the proper metal is a crucial and essential part of the washer production process since the wrong metal can cause an application or operation to fail. Metals for washers are chosen in conjunction with the type of environment and conditions where they will be used.
Stainless steel is a natural choice for the manufacture of washers due to its many positive properties. As a steel alloy with chromium, stainless steel does not rust or corrode. The various elements in stainless steel react with oxygen and moisture to produce a film that serves as a barrier against corrosion and other harmful substances. Stainless steel washers are used in the petrochemical industry, aerospace, and the auto industry.
Galvanized steel is coated with zinc as a means of protection against corrosion. Hardened steel made by stamping is used to produce the initial washer shape before being coated with zinc. Galvanized steel washers have a rough, uneven surface and come in different colors. They are the ideal choice for marine applications since the zinc coating protects against the effects of salt water.
Like stainless steel, aluminum has many characteristics and properties that make it an ideal metal for manufacturing washers. When aluminum is exposed to the air, it forms a layer of aluminum oxide that protects against corrosion. It has excellent thermal and electrical conducting properties that are far superior to other metals. Aluminum washers are widely used in applications that require heat dissipation.
Inconel is an alloy that is made from nickel, chromium, and molybdenum alloys. It has superior strength at high temperatures with exceptional corrosion resistance. Inconel’s range of temperatures runs from cryogenic to 2200o F or 982o C. The alloy content of Inconel washers allows them to withstand severe and harsh conditions. The combination of nickel and chromium provides resistance to oxidizing chemicals, while the nickel and molybdenum are resistant to non oxidizing environments. Typical grades of Inconel used to produce washers are 600, 601, 625, 686, 718, and 725.
Inconel’s resistance to corrosion, temperature stability, toughness, and strength make it the first choice for washers used for chemical processing, aerospace applications, the marine industry, and oil and gas production.
The main feature of copper that makes it a good choice for making washers is its ductility, which makes it soft and easily malleable. The ductility of copper makes it possible to form and shape it to meet the requirements of any application. Copper is an excellent conductor of heat and electricity and can be used for heat dissipation applications. It is a very cost effective material for the production of washers since its ductility reduces production time.
Brass is an alloy of copper and zinc and has many of each metal's positive properties. The low melting point of brass makes it very malleable and easy to shape. A typical use for brass is for applications such as plumbing and electrical work due to its low friction properties.
There is an endless number of washers that are made for innumerable applications. Washers are an essential part of any product, component, or device that requires a secure connection between two surfaces. Though there is a long list of commonly used washers, there are even more washers that have been designed for special applications made of an assortment of metals and materials.
Under the three basic types of washers, which are spring, lock, and plain, are specialized washers designed to meet the specific needs of unique applications. As simple as the construction of washers may be, they have been an essential part of building and design for many years.
A spring washer has ends that are slightly raised to produce spring tension that has been created in the metal. They are placed above or below a nut or bolt. When the nut or bolt are tightened, the raised and lowered ends level to prevent nuts or bolts from loosening.
The name lock washer is a description of its purpose, which is to lock nuts and bolts in place. Lock washers are available in many forms, with split and teeth types being the most common. When the split or teeth are locked in place, the nut or bolt is prevented from loosening.
Plain washers are the typical flat washer with a hole in the center and a metal ring. Though flat washers are very common and have been used for many years, they, as with other washers, have variations to conform to the needs of an application.
Though the three common forms of washers listed above are the most widely used types of washers, specialty washers have the same function as traditionally shaped washers, with the exception that they do not have the circular oval form. They have an irregular shape on the outside or inside.
Square washers have a square exterior around what would be its circumference if it were circular. They can be flat or beveled on one or both sides. They are used with square headed bolts to prevent pull through and offer a larger surface area than traditional round washers.
A multiple hole washer is designed with continuous holes to avoid installing several washers that would have a small distance between them. They can more evenly spread the load over their connecting bar to create a uniform clamping force and exceptionally secure and tight connection.
All washer manufacturers follow the standards for manufacturing as published by the International Organization for Standardization (ISO), which has created a set of quality standards in reference to all products that are produced for public and industrial use. Producers identify the adherence of their products to ISO standards 9001, 14001, and 18001, which relate to the quality of their products and prevention of harm to the environment.
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