Design of Screw and Nut MCQ Quiz - Objective Question with Answer for Design of Screw and Nut - Download Free PDF

Explanation:

Effect of Adding a Locking Feature to a Threaded Fastener

• In mechanical assemblies, maintaining the integrity and stability of fasteners is crucial to ensure the safety and reliability of the structure.
• One common challenge is the loosening of fasteners due to vibrations, which can compromise the assembly.
• To address this issue, various locking features can be added to threaded fasteners. One such feature is the nylon insert, also known as a nylon locknut.
• A nylon insert is a polymer ring placed within the threads of a nut.
• When the nut is tightened onto a bolt or screw, the threads cut into the nylon, creating frictional resistance.
• This resistance prevents the nut from backing off, even under conditions of vibration and dynamic loads.

Primary Effect:

The primary effect of adding a locking feature, such as a nylon insert, to a threaded fastener is:

Option 1: Prevents the fastener from loosening due to vibration.

This is the correct answer. The nylon insert creates a frictional force that resists rotation, effectively preventing the fastener from loosening when subjected to vibrations and dynamic forces. This characteristic is particularly valuable in applications where vibration is a significant concern, such as in automotive, aerospace, and machinery components.

Advantages:

• Enhanced reliability of mechanical assemblies by preventing loosening of fasteners.
• Cost-effective solution for improving the stability of threaded connections.
• Easy to implement without the need for additional tools or complex procedures.

Disadvantages:

• May not be suitable for high-temperature applications where the nylon can degrade or melt.
• Potential for wear and degradation of the nylon insert over time, especially in high-vibration environments.

Applications:

• Automotive industry: Used in various components to ensure fasteners remain secure under the vibrations of a moving vehicle.
• Aerospace industry: Critical in maintaining the integrity of assemblies in aircraft subjected to dynamic forces and vibrations.
• Machinery and equipment: Commonly used in industrial machinery where vibrations are prevalent.

Explanation:

Designation of bolts:

∴ M 24 × 2 means the nominal diameter of bolt is 24 mm and pitch is 2 mm

Explanation:

Designation of screw thread

The size of the screw thread is designated by the letter ‘M’ followed by the diameter and pitch, the two being separated by the sign ×.

Tr 40 × 14

• Multi start trapezoidal threads are designated by the letter 'Tr'
• Followed by nominal diameter and the pitch separated by sign x.

Here nominal diameter = 40 mm and pitch = 14 mm

The nominal diameter in the case of the screw is the major diameter of the screw. 

Additional Information

Here are the types of thread mainly used.

Explanation:

• Nuts used along with bolts in an assembly which may loosen due to vibration.
• Different types of nut-locking devices are used depending on the severity of the condition in which the fastener is used.
• The following are the most commonly used types:

Swan nut (Wiles nut)

• A slot is cut halfway across the nut.
• A screw is fitted with a clearance hole on the top part and matching thread on the lower part of the nut.

Penn, ring or grooved nut:

• It has an upper portion hexagonal and a lower part cylindrical.
• It is largely used where the bolt passes through connected pieces.
• The bottom portion is cylindrical and is recessed to receive the tip of the locking set screw.
• The bolt hole requires counterboring to receive the cylindrical portion of the nut.
• In order to prevent bruising of the latter bu the case hardened tip of the set screw, it is recessed.

Slotted/Castle nut:

• It consists of a hexagonal portion with a cylindrical upper part which is slotten inline 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 the jobs subjected to sudden shocks and considerable vibrations.

Explanation:

Basically, when a helical groove is cut or generated over a cylindrical or conical section, threads are formed. 

Fasteners: A mechanical fastener is a device that is used to mechanically join (or fasten) two or more objects together.

Some Fasteners are:

• Screws
• Bolts
• Pins
• Rivets
• Nails
• Concrete Anchors

Threaded Fasteners: The fasteners in which threads are designed on either outer or on the inner surface.

Some threaded Fasteners are:

• Bolts: They are basically threaded fasteners normally used with nuts. Which are almost right cylindrical from inside.
• Screws: They engage either with a preformed or self-made internal thread. The hole is generally tapered so as to fit the tapered head.
• Stud: A metal rod or shaft with threads on both sides is called a stud. One end is generally fixed and in another end, we use the nut.

Note:

The nails come under fastener but not under threaded Fasteners.

Explanation:

Basically, when a helical groove is cut or generated over a cylindrical or conical section, threads are formed. 

Fasteners: A mechanical fastener is a device that is used to mechanically join (or fasten) two or more objects together.

Some Fasteners are:

• Screws
• Bolts
• Pins
• Rivets
• Nails
• Concrete Anchors

Threaded Fasteners: The fasteners in which threads are designed on either outer or on the inner surface.

Some threaded Fasteners are:

• Bolts: They are basically threaded fasteners normally used with nuts. Which are almost right cylindrical from inside.
• Screws: They engage either with a preformed or self-made internal thread. The hole is generally tapered so as to fit the tapered head.
• Stud: A metal rod or shaft with threads on both sides is called a stud. One end is generally fixed and in another end, we use the nut.

Note:

The nails come under fastener but not under threaded Fasteners.

Explanation:

Designation of bolts:

∴ M 24 × 2 means the nominal diameter of bolt is 24 mm and pitch is 2 mm

Explanation:

Locking devices

Locking devices are used to prevent loosening of fastening.

Some of the locking devices are discussed below:

1. Penn, ring or grooved nut:

• It has upper portion hexagonal and a lower part cylindrical.
• It is largely used where the bolt passes through connected pieces.
• The bottom portion is cylindrical and is recessed to receive the tip of the locking set screw.
• The bolt hole requires counterboring to receive the cylindrical portion of the nut.
• In order to prevent bruising of the latter bu the case hardened tip of the set screw, it is recessed.

2. Jam nut or lock nut:

• The thin lock nut is first tightened down with ordinary force, and then the upper nut (thicker nut) down upon it.
• The upper nut is then held tightly while the lower nut is slackened back against it.

3. Slotted/Castle nut:

• It consists of a hexagonal portion with a cylindrical upper part which is slotten inline with the centre 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 the jobs subjected to sudden shocks and considerable vibrations.

4. Sawn nut

• It has a slot sawn about 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 loosening of the nut.

6. Spring lock washer

• As the nut tightens the washer against the piece below, one edge of the washer is caused to dig itself into that piece.
• It results in increasing the resistance so that the nut will not loosen so easily.

Explanation:-

There is a particular method of the designation of threads:

Square threads:

Single start: 

• Square thread is designated by the letter Sq followed by nominal diameter and the pitch expressed in mm and separated by sign ×.
• For eg. Sq 40 × 3

Multiple starts:

• Multiple square threads are designated by the letter Sq followed by nominal diameter and the lead expressed in mm and separated by sign × and in brackets letter P followed by the pitch expressed in mm.
•  
• For eg. Sq 40 × 14 (P7)
• \(No. of\;starts=\frac{Lead}{Pitch}\)

Hand:

• Sometimes, the hand of the thread is given i.e Left hand (LH) and right hand (RH). It is written at the end.
• For Eg. Sq 30 × 16 (P8) RH

Trapezoidal thread:

In the trapezoidal thread, Sq is replaced by Tr.

For eg. Tr 30 × 16 (P8) RH

Explanation:

Effect of Adding a Locking Feature to a Threaded Fastener

• In mechanical assemblies, maintaining the integrity and stability of fasteners is crucial to ensure the safety and reliability of the structure.
• One common challenge is the loosening of fasteners due to vibrations, which can compromise the assembly.
• To address this issue, various locking features can be added to threaded fasteners. One such feature is the nylon insert, also known as a nylon locknut.
• A nylon insert is a polymer ring placed within the threads of a nut.
• When the nut is tightened onto a bolt or screw, the threads cut into the nylon, creating frictional resistance.
• This resistance prevents the nut from backing off, even under conditions of vibration and dynamic loads.

Primary Effect:

The primary effect of adding a locking feature, such as a nylon insert, to a threaded fastener is:

Option 1: Prevents the fastener from loosening due to vibration.

This is the correct answer. The nylon insert creates a frictional force that resists rotation, effectively preventing the fastener from loosening when subjected to vibrations and dynamic forces. This characteristic is particularly valuable in applications where vibration is a significant concern, such as in automotive, aerospace, and machinery components.

Advantages:

• Enhanced reliability of mechanical assemblies by preventing loosening of fasteners.
• Cost-effective solution for improving the stability of threaded connections.
• Easy to implement without the need for additional tools or complex procedures.

Disadvantages:

• May not be suitable for high-temperature applications where the nylon can degrade or melt.
• Potential for wear and degradation of the nylon insert over time, especially in high-vibration environments.

Applications:

• Automotive industry: Used in various components to ensure fasteners remain secure under the vibrations of a moving vehicle.
• Aerospace industry: Critical in maintaining the integrity of assemblies in aircraft subjected to dynamic forces and vibrations.
• Machinery and equipment: Commonly used in industrial machinery where vibrations are prevalent.

Explanation:

Standard conventional proportions may be considered while drawing a hexagonal nut:

• ·    Width of the nut across the flat surface (known as size across flat) = (1.5 × D) + 3 mm
• ·    The diameter of the nut = D in mm
• ·    The thickness of the nut = (0.8 × D) to D
• ·    The radius of front chamfer = 1.5 × D
• ·    The angle of chamfer = 30°
• ·     Depth of cut = 0.61 × P​

Explanation:

Nut

A nut is a type of fastener with a threaded hole.

Wing Nut

• The wing nut is used to tightening two mating parts by hand and is used for light-duty purposes.
• When the mating parts are frequently used to adjust (such as tightening of hacksaw blade), this nut is used.

Some other types of nuts are:

1. Penn, ring or grooved nut:

• It has upper portion hexagonal and a lower part cylindrical.
• It is largely used where the bolt passes through connected pieces.
• The bottom portion is cylindrical and is recessed to receive the tip of the locking set screw.
• The bolt hole requires counterboring to receive the cylindrical portion of the nut.
• In order to prevent bruising of the latter bu the case hardened tip of the set screw, it is recessed.

2. Jam nut or lock nut:

• The thin lock nut is first tightened down with ordinary force, and then the upper nut (thicker nut) down upon it.
• The upper nut is then held tightly while the lower nut is slackened back against it.

3. Slotted/Castle nut:

• It consists of a hexagonal portion with a cylindrical upper part which is slotten inline with the centre 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 the jobs subjected to sudden shocks and considerable vibrations.

4. Sawn nut

• It has a slot sawn about 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 loosening of the nut.

6. Spring lock washer

• As the nut tightens the washer against the piece below, one edge of the washer is caused to dig itself into that piece.
• It results in increasing the resistance so that the nut will not loosen so easily.

Explanation:

Basically, when a helical groove is cut or generated over a cylindrical or conical section, threads are formed. 

Fasteners: A mechanical fastener is a device that is used to mechanically join (or fasten) two or more objects together.

Some Fasteners are:

• Screws
• Bolts
• Pins
• Rivets
• Nails
• Concrete Anchors

Threaded Fasteners: The fasteners in which threads are designed on either outer or on the inner surface.

Some threaded Fasteners are:

• Bolts: They are basically threaded fasteners normally used with nuts. Which are almost right cylindrical from inside.
• Screws: They engage either with a preformed or self-made internal thread. The hole is generally tapered so as to fit the tapered head.
• Stud: A metal rod or shaft with threads on both sides is called a stud. One end is generally fixed and in another end, we use the nut.

Note:

The nails come under fastener but not under threaded Fasteners.

Explanation:

Designation of bolts:

∴ M 24 × 2 means the nominal diameter of bolt is 24 mm and pitch is 2 mm

Explanation:

Locking devices

Locking devices are used to prevent loosening of fastening.

Some of the locking devices are discussed below:

1. Penn, ring or grooved nut:

• It has upper portion hexagonal and a lower part cylindrical.
• It is largely used where the bolt passes through connected pieces.
• The bottom portion is cylindrical and is recessed to receive the tip of the locking set screw.
• The bolt hole requires counterboring to receive the cylindrical portion of the nut.
• In order to prevent bruising of the latter bu the case hardened tip of the set screw, it is recessed.

2. Jam nut or lock nut:

• The thin lock nut is first tightened down with ordinary force, and then the upper nut (thicker nut) down upon it.
• The upper nut is then held tightly while the lower nut is slackened back against it.

3. Slotted/Castle nut:

• It consists of a hexagonal portion with a cylindrical upper part which is slotten inline with the centre 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 the jobs subjected to sudden shocks and considerable vibrations.

4. Sawn nut

• It has a slot sawn about 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 loosening of the nut.

6. Spring lock washer

• As the nut tightens the washer against the piece below, one edge of the washer is caused to dig itself into that piece.
• It results in increasing the resistance so that the nut will not loosen so easily.