Top 3 Criteria For Choosing The Right Fastener Material

The materials or alloys of the fasteners are equally important to their size specifications. In spite of the fact that many erroneously believe that you need an engineering diploma to figure the ideal material for the bolts and screws, in reality this dilemma is actually much simpler. Following are the 3 criteria to account for when shopping for industrial fasteners.

1. Proof stress

Proof stress refers to the overall strength of the alloys and it is measured in pounds per square inch or psi. In the fastener manufacturing industry, pure steel and low carbon steels are the materials with the lowest acceptable proof stress, namely they have a strength of around 60,000 psi. Even though steel fasteners are available in numerous grades, only 4 of them are in high demand in various industries, namely:

• Grade 2 – a standard hardware grade steel, useful in light industrial application as well as DIY home projects
• Grade 5 – the fasteners undergo various treatments for enhanced strength and are a common sight in the automotive applications
• Grade 8 – stronger than grade 5 steel fasteners, grade 8 bolts are utilized in demanding applications, such as a vehicle’s suspensions
• Alloy steel – the fasteners gain their extra strength due to a heat treatment; although they are the strongest fasteners, they are also very brittle

At the opposite end, there are the super alloys with strengths that exceed 250,000 psi. Metals and alloys that surpass 180,000 psi are rarely utilized in industries nowadays; in fact, the super alloys are designed for extreme applications such as building rockets and space probes, for instance.

2. Corrosion resistance

Corrosion is the process of wearing down the metal due to the material’s interactions with the chemicals in the surrounding environment. The most common form of corrosion is oxidation, in which the metal reacts to the oxygen and produces rust.

To augment the metal fasteners’ resistance to corrosion, manufacturers apply a protective coating that can vary according to the particularities of the application. The most common types of plating include:

• Chrome – the coating is not only employed for its high anti-corrosion properties, but also due to its appearance; the main disadvantage of chrome coating is the price.

• Zinc – fasteners that are electro-plated with zinc are best used in outdoor applications; the metal doesn’t perform well in marine environments.
• Hot dip galvanizing – while the metal utilized is still zinc, the hot dip galvanized fasteners are considerably more resilient; because they include the thickest possible coating of zinc usually, it makes them useful in costal environments.

It is necessary to mention that the only materials that are not prone to the damaging effects of corrosion are non-ferrous or plastic alloys.

3. Setting temperatures

Last, but not least important, you should also account for the average temperatures at which the screw or bolt will provide fastening. Obviously, plastics and non-ferrous alloys have no place in settings with temperatures that exceed 450° F, like a vehicle’s engine for instance. While stainless steel and steel alloys will do the trick for temperatures between 450° F and 1,200° F, they tend to lose their ductility and become brittle in severely cold environments of over -100° F; for settings that see low temperatures you’re better off with aluminum, titanium, copper, brass or Teflon alloys.