How to Choose the raw material for fasteners

2018-09-06

What are fasteners?

A fastener (US English) or fastening (UK English) is a hardware device that mechanically joins or affixes two or more objects together. In general, fasteners are used to create non-permanent joints; that is, joints that can be removed or dismantled without damaging the joining components. Welding is an example of creating permanent joints.

We mainly use a fastener for a non-permanent joint. What do we mean by a non-permanent joint? A joint that can be removed or dismantled without the destruction or damage of the joining components can be termed as a non-permanent joint. A welding joint or riveted joint can be termed as a permanent joint, which if required to be removed tends to damage or destruct both the joining components as well as the joint itself.

This is how a fastener terminology looks like.

The basis of a fastener is basically a screw thread. – The male part is basically the screw with an external thread and the female part is a hole with an internal thread. The female part can also be a nut. Here are some ways by which a fastened joint can be created.

Based on the application area of the fastener, the head portion of the fastener is available in various shapes and sizes as shown below.

How to Choose the raw material for fasteners?

Fasteners are made with a wide variety of of materials. These include everything from common steel to titanium, plastic and other exotic materials. Some of these materials are again separated into different grades. This is done to describe specific alloy mixtures, hardening as well as processes involved.

Apart from this some nuts and bolts are available with a variety of coatings or platings. This is done to increase the resistance against corrosion or alter the appearance of the fastener.

Fastener material can be important when choosing a fastener due to keeping in view the strength, brittleness, corrosion resistance, galvanic corrosion properties. Cost of course an important factor which determines which materials to choose from. Let us now see them in details.

Steel

Steel is the most commonly used material in fastener production, constituting nearly 90 percent of all fasteners manufactured annually. This metal’s popularity stems from its high degree of formability coupled with tensile strength and durability. Compared to other metal stock, steel is also relatively inexpensive to fabricate. It is frequently processed with zinc or chrome plating, but can also be formed without any surface treatments.

Carbon steel is the most common type of steel used in fastener production. Grades 2, 5, and 8 are typically the standard for carbon-steel based screws and bolts, with alloyed carbon steel being a higher-end variation on these metals. Their mechanical strength ranges from approximately 50 ksi (kilo-pound per square inch) up to 300 ksi in a finished product. Material properties for these grades include:

• Grade 2: This is a low carbon category that features the least expensive, but also least durable, types of steel. Grade 2 material is highly workable, and forms the bulk of steel grade fasteners.

• Grade 5: Grade 5 steels are produced from unalloyed medium carbon groups, such as type 1038, and are usually work-hardened to improve their strength. This is the most common grade used in automotive applications.

• Grade 8: These steels are typically medium carbon alloys, such as types 4037 and 4340. They are work-hardened to a high degree, making them stronger and better-suited for mechanically straining applications, like vehicle suspension systems.

Alloy Steel

Alloy steel bolts are made from a high strength steel alloy . They are further heat treated to make them even stronger . These are mostly not plated, resulting in a dull black finish. These types of bolts are very strong. Nut they are very brittle at the same time.

Stainless Steel Fasteners

Stainless steel is an alloy that combines the properties of low carbon grades with certain percentages of chromium and nickel. Its chromium component lends stainless steel a high degree of corrosion resistance that does not decrease from deformation or long-term use. However, the low carbon content prevents it from being effectively hardened, making the metal stronger than most grade 2 steels, but weaker than many hardened grade 5 and 8 varieties. The final strength of most stainless steel grades ranges from around 70 to 220 ksi, depending on the ratio of metals in the alloy. Stainless steel fasteners are also less magnetic than their standard steel counterparts. The two main categories of stainless steel fastener materials are:

• Martensitic Stainless Steel: The martensitic group includes strong, durable stainless steels that can be further strengthened through heat treatments. They are more magnetic than other types of steel, but have lower corrosion resistance.

• Austenitic Stainless Steel: The vast majority of stainless steel fasteners are produced with metals from the austenitic family. Their high levels of chromium and nickel provide tough corrosion resistance and the ability to withstand considerable physical strain without fracturing, albeit at a higher cost than the martensitic varieties.

Silicon Bronze

Silicon bronze often referred to simply as bronze. This is an alloy made mostly from a mix of copper and tin. They also contain small amount of silicon. These are mainly in marine environments. It is often preferred over stainless in wooden boat construction.

Brass

Brass is an alloy which is primarily made from a mix of copper and zinc. This alloy happens to be highly corrosion resistant .It is also electrically conductive. But this is usually not used in fasteners because of its relative softness.

Aluminum

Aluminum happens to be a light, soft, as well as a corrosion resistant metal. Much like stainless steel, aluminum is known to be very corrosion resistant. Fasteners are made from a variety of aluminum alloys. These may be with elements such as manganese, silicon, iron, magnesium, zinc, copper, etc. Rivets are often made from aluminum alloys.

Chrome

Nuts and bolts and other fasteners are often chrome plated and polished. This is mainly for appearance. Chrome plating provides corrosion resistance. But this is very costly and thus not very popular.

Nylon Fasteners

Nylon is a lightweight synthetic plastic material used for specific fastener applications. It is corrosion resistant, has high electrical and thermal insulating properties, and can be easily dyed to meet aesthetic requirements, such as those necessary for fastener replacement. However, nylon is subject to severe deterioration under elevated temperatures and may become weakened in low temperature conditions. In addition, its comparatively low tensile strength makes it less effective for applications with demanding physical stress requirements.

Source: China Fasteners Manufacturer – Yaang Pipe Industry Co., Limited (www.ugsteelmill.com)

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

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References:

https://www.yaang.com
https://en.wikipedia.org/wiki/Fastener

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How to Choose the raw material for fasteners