locknut: Types and How does it work?

What is Locknut?

A locknut, also known as a lock nut, locking nut, self-locking nut, prevailing torque nut, stiff nut, or elastic stop nut, is a nut that will resist loosening under vibrations and torque. There are many types of lock nut but they can be broadly divided into those which use friction to prevent loosening and those that have some form of positive locking device. 

Friction lock nuts

Locknuts that use friction to resist loosening usually require a greater torque to both tighten and loosen, especially during the initial free rotation before they start to clamp down on the part. This means that they cannot be spun rapidly along a long length of thread, greatly increasing manual assembly time.

Examples include:

  • A nylon lock nut, or nyloc nut, has a polymer collar, inserted into a recess at the top of the nut, which is slightly smaller than the outer thread diameter. This collar deforms elastically when the nut is tightened, causing friction. Because they rely on a polymer collar to provide friction, they are not reliable at elevated temperatures.
  • Distorted thread locknuts have a section of thread that is shaped so that it must elastically deform to mate with the threaded shaft. This causes a surface normal force and therefore the increased friction required for locking. Because their construction is all metal, they continue to work at elevated temperatures. Distorted thread locknuts may be categorized according to where the distorted thread is located or the shape of the distortion. For example, enter lock nuts have a distortion in the center, allowing them to be started from either end, while top lock nuts have a distorted thread at one end.
  • A jam nut, or half nut, is a thinner nut, designed to be tightened, or ‘jammed’ against the primary nut. The jam nut should be tightened first and the main nut then fitted over the top.

What are Locking Devices?

Locking devices are a device that is used in conjunction with fasteners to positively lock the fastener. This means that the fastening element cannot loosen due to vibrations. The security of an entire system often depends on locking devices.

They are common in systems that require coupling to multiple components.

Operating conditions such as initial installation errors, temperature fluctuations, vibrations, and others can cause problems. These are critical components. Ordinary thread fastenings, generally, remain tight under static loads, but many of these fastenings become loose under the action of variable loads or when the machine is subjected to vibrations.

The loosening of fastening is very dangerous and must be prevented. In order to prevent this, a large number of locking devices are available,

Positive locking nuts

Lock nuts that use a positive locking device can be freely rotated to both tighten and loosen, they only lock when a positive action is performed to lock them in their current position, such as inserting a pin. This can enable both more rapid assembly and more secure fastening. Examples include:

  • A castellated nut, or castle nut, is a positive locking nut with a cylindrical extension at one end containing notches. These bear against a pin inserted through the threaded shaft, preventing the nut from rotating. A castellated nut may be secured with a cotter pin, an R-clip, or safety wire.
  • A slotted nut is similar to a castellated nut but the notches are cut into the flat face of the nut.

The following is a list of positive locking nuts: 

  1. Jam nut or lock nut
  2. Castle nut
  3. Sawn nut
  4. Penn, ring, or grooved nut
  5. Locking with pin
  6. Locking with plate
  7. Spring lock washer

Locknut or Jam Nut

A locknut, also known as a lock nut, locking nut, self-locking nut, prevailing torque nut, stiff nut, or elastic stop nut, is a nut that will resist loosening under vibration and torque.

In the past, companies simply used two nuts in applications where vibration was a concern. After inserting a nut on the end of the screw, a second nut was placed on the screw. The use of two nuts, while preventing vibration-induced loosening, is not cost-effective for manufacturing companies performing high volume manufacturing operations. Finally, any case using a bolt would require two nuts instead of one, doubling the cost of nuts for manufacturing companies.

Locknuts were invented in the 1930s and offer a simpler, more cost-effective solution to protecting against loosening due to vibration. With just one lock nut, manufacturing companies can connect multiple objects without worrying about vibrations loosening the nut. Locknuts are generally not “free-spinning,” which means they require more than just manual turning to remove. Even with strong vibrations, they remain stable and secure on the bolt-on which they are used.

Locknut

Locknuts have a unique design that prevents them from loosening when subjected to vibration. Conventional nuts simply consist of a blind thread hole so that constant vibration can loosen them from the screw on which they are placed. However, lock nuts protect against loosening by having a design that increases the vibration resistance of the nut.

There are several types of locknuts, the most common of which include metal locknuts and nylon-lined locknuts. Metal nuts have a crowned top that can be crimped to secure the nut in place. In comparison, nylon lock nuts have a layer of nylon material that covers the internal threads. When a nylon lock nut is placed on a bolt, the nylon fibers expand to grip the bolt.

Castle Nut or Castellated nut

A castellated nut, also known as a castle nut, is a nut with slots or notches cut into one end. The name comes from the nut’s resemblance to the crenelated parapet of a medieval castle.

Castellated nuts are a positive locking device that’s used to ensure that the nut remains affixed and resists vibration.

It consists of a hexagonal portion with a cylindrical upper part which is slotted in line with the center of each face. The split pin passes through two slots in the nut and a hole in the bolt so that a positive lock is obtained unless the pin shears. It is extensively used on jobs subjected to sudden shocks and considerable vibration such as in the automobile industry.

These components are used in combination with a screw that has a pre-drilled radial hole. The nut is attached and a pin is passed through the notches and the hole in the screw, preventing the nut from turning.

Additionally, a castellated nut is a locking device that’s resistant to movement and vibration but that can be readily removed. This makes it a popular choice for securing the position of a bearing onto a spindle. Castellated nuts are commonly used within the automotive, aircraft, and locomotive industries.

Sawn locknut

The sawn nut has a slot sawn halfway through. After the nut is screwed down, the small screw is tightened which produces more friction between the nut and the bolt. This prevents the loosening of the nut.

Ring Nut, Penn nut or Grooved Nut

It has an upper portion hexagonal and a lower part cylindrical. It is largely used where bolts pass through connected pieces reasonably near their edges such as in marine type connecting rod ends.

The bottom portion is cylindrical and is recessed to receive the tip of the locking set screw. The bolt hole requires counter-boring to receive the cylindrical portion of the nut. In order to prevent bruising of the latter by the case-hardened tip of the set screw, it is recessed.

Locking with Pin

The nuts may be locked by means of a taper pin or cotter pin passing through the middle of the nut. But a split pin is often driven through the bolt above the nut.

Locking with plate

These come in the form of thin metal plates. With the help of a set-screw, its rotation is retained round a nut after the nut has been tightened. The plate consists of a hole which may be usually a twelve-sided one for enabling easy adjustments. The set screw used for securing the locking plate is kept intact with a spring washer. Double-sided locking plates are also available and are used for locking two nuts simultaneously.

Spring Locknut Washer

As the nut tightens the washer against the piece below, one edge of the washer is caused to dig itself into that piece, thus increasing the resistance so that the nut will not loosen so easily. There are many kinds of spring lock washers manufactured, some of which are fairly effective.

A regular nut may also be locknut by applying thread locker or by drilling and pinning.

FAQ

1. What is Locknut?

A locknut, also known as a lock nut, locking nut, self-locking nut, prevailing torque nut, stiff nut, or elastic stop nut, is a nut that will resist loosening under vibrations and torque. There are many types of lock nut but they can be broadly divided into those which use friction to prevent loosening and those that have some form of positive locking device. 

2. What is locking Devices?

Locking devices are a device that is used in conjunction with fasteners to positively lock the fastener. This means that the fastening element cannot loosen due to vibrations. The security of an entire system often depends on locking devices.

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