Wednesday, November 30, 2022

How to choose fasteners for mechanical work?

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Used as a base or to hold items together, nuts and bolts are essential, especially on mechanical-type projects.

Before choosing any clamping type you should ask yourself the following:

  • What materials do you need to join? Bolts are typically the fastener of choice for metal, although some are made for other applications.
  • What is the thickness of the material to be joined? For a secure connection, the fastener must be the correct length.
  • What are the weight and strength requirements? From securing structural steel to working on crafts and hobbies, there’s a fastener for every job.
  • Will it be used indoors or outdoors? There are specific fasteners and finishes for both applications.

What is a mechanical fastener?

A mechanical fastener is a device used to mechanically join (or fasten) two or more objects. There are many different types of mechanical fastenersBut in general, bras can be divided into two main categories; non-permanent and permanent.

The non-permanent bras they allow parts to be assembled and disassembled repeatedly, and can be divided into two groups:

  • General fasteners: keys, pins, retaining rings, etc. They are often associated with axes.
  • Threaded Fasteners: bolts, screws, studs, set screws, etc. They are the most widely used type of non-permanent fastener as they can be easily removed and reused.

On the other hand, rivets are considered permanent fasteners, as removing them will destroy them.

rivets

threaded fasteners

Threaded fasteners are the main devices used for assemble components and they are generally grouped into three main categories as shown in the figure:

  1. Bolts: A bolt has a head on one end and threads on the other end and is paired with a nut.
  2. Screws: Screws are used to join two mating pieces together and similar to bolts, they have a head on one end and threads on the other. However, screws generally have longer threads than bolts, and can also be made with slotted heads. Screws are sometimes divided into two subcategories: cap screws and machine screws. Machine screws are generally smaller than cap screws and are used for driving into thin materials.
  3. Asparagus: A stud is a rod that is threaded at both ends and joins two mating parts. A nut can be used on one end.
Threaded Fasteners

Threaded Fasteners

Differences between bolts, screws and studs

Bolts are generally used to join two or more components without threading. When used in conjunction with a nut, the bolt will remain securely in the unthreaded component; thus, keeping it together and fulfilling its intended purpose.

The screws are used with threaded components. This does not necessarily mean that the component(s) used with the screws must be threaded, as the installation of the screw may create the thread.

A asparagus is an externally threaded fastener that can be inserted into the holes of pre-assembled components, used to connect with a preformed internal thread, or to create your own thread. Studs are normally tightened by turning the nut and stud together until the assembly is snug.

fixing screws

Setscrews are a special type of screws which are generally headless and are used to prevent rotation or movement between parts (such as a shaft and a collar). The main difference between one set screw and another type of screws is that a set screw is driven through one member so as to apply a compressive force on the other member while a screw or bolt holds the two members together.

In most cases, set screws do not have heads, so they can be fully screwed into the threaded holes using a socket or slot in the screw shank.

fixing screws

fixing screws

nuts

A nut is the counterpart of a screw. The bolts and nuts they are used together to hold two or more parts that have unthreaded holes. While the most commonly used types of nuts are regular hex nuts, there are different types of nuts where each one is more suitable for a different type of applications.

types of nuts

types of nuts

washers

Washers are commonly used under the heads of the bolts and screws and are also used under the nuts. The most common type of washer is the flat washer, it is used to increase head bearing areas and protect the material finish during assembly. The use of washers also prevents the sharp corner of the hole into which the bolt or screw is inserted from damaging the leading edge of the bolt, which can lead to bolt failure in service.

The other common type of washers are lock washers, which are used to prevent loosening of bolts and nuts by providing continuous friction due to their spring action. Some of the types common of safety washers are shown in the figure.

Pressure Washers

Pressure Washers

rivets

The rivets they are considered permanent fasteners, as opposed to removable (or non-permanent) fasteners, such as bolts and screws. Rivets are generally used to hold metal plates or sheets together.

The rivets They are used in a wide variety of applications, from aircraft structures to civil steel structures, automobiles, ships and boats, to clothing, etc.

There are many different types of rivets where each type is more suitable for certain types of applications. The two types of rivets most common and distinctive are solid rivets and pop rivets.

  • solid rivets are one of the rivets oldest and most reliable They simply consist of a cylindrical stem with a single head. When the stem is inserted into the hole, the other end of the rivet is deformed with a hammer or rivet gun. This type of rivets is used in civil steel structures, such as bridges, and generally requires heating to facilitate the deformation of the other end. A similar type of rivets it is used in aircraft structures, but does not require heating.
  • pop rivets (also called blind rivets) are the type of rivets most used for general purpose applications. The installation of pop rivets it is very easy and fast, and one of the main advantages of this type of rivet is that the installation does not require access to both sides of the assembly. Pop Rivets are tubular and supplied with a mandrel through the center. After inserting the rivet In a hole drilled through the parts to be joined, a specially designed tool is used to insert the mandrel into the rivet. This expands the blind end of the rivet and then the mandrel breaks off, as shown in the figure. However, such rivets are not very reliable and are not capable of withstanding large loads.
Pop riveting process

Pop riveting process

So far a brief introduction to the fixing elements, we will continue to delve into it in a future technical article!

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