Types of Moulding Sand

In this article we will learn about the types of moulding sand. Sands which are used to make mould is called moulding sand. Almost every manufacturing industries uses moulding sand to make moulds. Casting of materials without use of moulding sand is impossible. Here we are going to discuss about different types of moulding sand.

Types of Moulding Sand

Types of Moulding Sand

The various types of moulding sand are

1. Green sand
2. Dry sand
3. Loam sand
4. Parting sand
5. Facing sand
6. Backing sand
7. System sand
8. Core sand


1. Green Sand

  • Green sand is a mixture of silica sand and clay. It constitutes 18 % to 30 % clay and 6 % to 8 % water.
  • The water and clay present is responsible for furnishing bonds for the green sand.
  • It is slightly wet when squeezed with hand. It has the ability to retain the shape and impression given to it under pressure.
  • It is easily available and has low cost.
  • The mould which is prepared in this sand is called green sand mould.
  • It is commonly used for producing ferrous and non-ferrous castings

2. Dry Sand

  • After making the mould in green sand, when it is dried or baked is called dry sand.
  • It is suitable for making large castings.
  • The moulds which is prepared in dry sand is known as dry sand moulds.
  • If we talk about the physical composition of the dry sand, than it is same as that of the green sand except water.


3. Loam Sand

  • It is a type of moulding sand in which 50 % of clay is present.
  • It is mixture of sand and clay and water is present in such a quantity, to make it a thin plastic paste.
  • In loam moulding patterns are not used. 
  • It is used to produce large casting.

4. Parting Sand

  • Parting sand is used to prevent the sticking of green sand to the pattern and also to allow the sand on the parting surface of the cope and drag to separate without clinging.
  • It serves the same purpose as of parting dust.
  • It is clean clay free silica sand.

5. Facing Sand

  • The face of the mould is formed by facing sand.
  • Facing sand is used directly next to the surface of the pattern and it comes in direct contact with the molten metal, when the molten metal is poured into the mould.
  • It possesses high strength and refractoriness as it comes in contact with the molten metal.
  • It is made of clay and silica sand without addition of any used sand. 

6. Backing Sand

  • Backing sand or flour sand is used to back up facing sand.
  • Old and repeatedly used moulding sand is used for the backing purpose.
  • It is also sometimes called black sand because of the addition of coal dust and burning when it comes in contact with the molten metal.

7. System Sand

  • In mechanical sand preparation and handling units, facing sand is not used. The sand which is used is cleaned and reactivated by adding of water, binder and special additives. And the sand we get through this is called system sand.
  • System sand is used to fill the whole flask in the mechanical foundries where machine moulding is employed.
  • The mould made with this sand has high strength, permeability and refractoriness.

8. Core Sand

  • The sand which is used to make core is called core sand. 
  • It is also called as oil sand.
  • It is a mixture of silica sand and core oil. Core oil is mixture of linseed oil, resin, light mineral oil and other binding materials.
  • For the sake of economy, pitch or flours and water may be used in making of large cores.
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Types of Beams in Strength of Materials

In this article we will discuss about the different types of beams used in the construction. Without beams there will not be any structure which can withstand loads. They are the structural member which helps in bearing loads. If there are no beams, there will be no structure.

What is a Beam?

Beam is defined as the structural member which is used to bear different loads. It resists the vertical loads, shear forces and bending moments.

Types of Beams

The different types of beams are:

Types of Beams

1. Cantilever Beam: A cantilever beam is a beam which is fixed from one end and free at the other end.

Types of Beams: Cantilever Beam

In the figure you can easily see that one end i.e. A is fixed and the other end i.e. B is free. So this beam is called as cantilever beam.


2. Simply Supported Beam: A beam which is supported or resting on the supports at its both the ends, is called simply supported beam.

Types of Beams: Simply Supported Beam


In the figure, both the ends of the beam is supported by supports, one support is at end A and the other support is at end B. this beam is known as simply supported beam.

3. Overhanging Beam: In a beam, if one of its ends is extended beyond the support, it is known as overhanging beam.

Types of Beams: Overhanging Beam


As shown in the above figure, we observe that beam is extending beyond the support B, and hence this beam is called overhanging beam.

4. Fixed Beams: A beam which has both of its ends fixed or built in walls is called fixed beam.

Types of Beams: Fixed Beam


In the figure, both the ends of the beams are rigidly fixed in the walls, this type of beams are known as fixed beams.

5. Continuous Beam: It is beam which is provided with more than two supports as shown in figure.

Types of Beams: Continuous Beam


Here we can see in the figure that the beam has more than two supports at A,B and C. This beam is called as continuous beams.

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Difference Between Generator and Motor

In this article we will learn about Difference Between Generator and Motor. The generator and motor are such devices whose function is just opposite of each other. One is used to generate electricity and other uses electricity. In this you will learn about generator and motor and their differences in brief.

Difference Between Generator and Motor

Difference Between Generator and Motor

Generator

  • It is a device which converts mechanical energy into electrical energy.
  • It works on the principle of Faraday’s law of electromagnetic induction. It states that when a conductor is placed in varying magnetic field, an emf is induced in the conductor. The induced emf induces current in the conductor if its circuit is closed.
  • The main parts of generator are yoke, armature, winding, carbon brush, rotor, stator, electromagnet or magnet.
  • It generates electricity from mechanical power.
  • The shaft of the generator is attached to the rotor and is driven by mechanical force.
  • The electric current is produced in the armature winding. The armature can be on the rotor or stator.
  • In Motor, the current is supplied to the armature winding. The armature can be on the rotor or stator.

Motor

  • It is a device which converts electrical energy into mechanical energy.
  • It works on the principle that when a current carrying conductor is place in a magnetic field, it experiences mechanical force.
  • Main parts of Motor are rotor, stator, field magnet, carbon brushes, slip rings, armature.
  • It generates mechanical power with the help of electricity.
  • The motor shaft is driven by the mechanical force produced between the armature and field.
  • It uses Fleming’s left hand rule to determine the direction of force produce between the armature and field.

Difference Between Generator and Motor in Tabular Form

S.no
Generator
Motor
1.
It is a device which converts mechanical energy into electrical energy.
It is a device which converts electrical energy into mechanical energy.
2.
It generates electricity.
It generates mechanical power.
3.
It uses Fleming’s right hand rule to determine the direction of induced current.
It uses Fleming’s left hand rule to determine the direction of force produced.
4.
The shaft of the generator is attached to the rotor and is driven by the mechanical power.
The motor shaft is driven by the mechanical force produced between the armature and field.
5.
In Generator, the current is produced in the armature winding. The armature can be on the rotor or stator.
In motor, the current is supplied to the armature winding. And the armature can be on the rotor or stator.
6.
The maintenance of generator is more as compared to the motor.
The maintenance of generator is less as compared with the generator.
7.
The generators are used in power station, homes, and in many industries to generate electricity.
Motor are used in cars, bikes, home etc. where mechanical energy is required to do any work.

Summary of Comparison Between Generator and Motor

  • Generator is a device which converts mechanical energy into electrical energy where as motor is a device which converts electrical energy into mechanical energy.            
  • Generator is used to generate electricity. On the other hand motor is used to generate mechanical power.
  • In generator the direction of current induced is determine by the use of Fleming’s right hand rule. In motor the direction of force produced is determined by the use of Fleming’s left hand rule.
  • In generators the current is produced in the armature winding where as in the motor the current is utilized in the armature winding to produce mechanical force. The armature can be on rotor or stator.
  • In generator the shaft is driven by the mechanical power. In the motor the shaft is driven by mechanical force produced by the electricity.
  • The maintenance of the generator is more as compared with the motor.

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What is Elasticity, Elastic Limit, Young’s Modulus and Modulus of Rigidity in Strength of Materials?

In this article we will learn about what is elasticity, elastic limit, young's modulus and modulus of rigidity. These terms keeps an important role in the study of subject strength of materials. Understanding about stress and strain is possible when one must have the knowledge of these terms. Let's discuss about them one by one.

What is Elasticity, Elastic limit, Young’s Modulus and Modulus of Rigidity?

What is Elasticity?

When an external force is applied on a body and it undergoes some deformation. If the body returns back to its original shape and size on complete removal of the load, the body is called elastic body. This property by which any material regains its original shape and size when load acting on it is completely removed is called elasticity.

Elasticity: The property of a material by which it returns back to its original position (i.e. shape and size) on the removal of external force or load, is called elasticity.

What is Elastic Limit?

A body will return back to its original shape and size when the deformation caused by the external force, is within certain limit. There is a limiting value of force upto and within which the deformation caused completely disappears on the removal of external force. The value of stress corresponding to this limiting force is known as elastic limit of the material.

Elastic Limit: It is defined as the value of stress upto and within which the material return back to their original position (i.e. shape and size) on the removal of external force.

If the value of external force is such that it exceeds the elastic limit, than the body will not completely regain its original position. The body loses its property of elasticity to some extent. And if the external force acting on the body is removed, in that condition the body will not return to its original shape and size and there will be a residual deformation in the material.

What is Young's Modulus?

Young’s Modulus: The ratio of tensile or compressive stress to the corresponding strain within elastic limit is called young’s modulus.
  • Young’s modulus is also known as modulus of elasticity. It is denoted by E.
  • The formula of Young’s modulus is given by

What is Elasticity, Elastic limit, Young’s Modulus and Modulus of Rigidity?
Where

σ = Tensile or compressive stress,
e = Tensile or compressive strain,
E = young’s modulus or modulus of elasticity.

What is Modulus of Rigidity?

Modulus of Rigidity or Shear Modulus: It is defined as the ratio of shear stress  to the corresponding shear strain within elastic limit.
  • It is denoted by C or G or N
  • The formula of modulus of rigidity is given by

What is Modulus of Rigidity?
Where
τ = Shear stress
ɸ = Shear stress
C = Modulus of rigidity

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What is Hooke’s Law? - Strength of Materials

What is Hooke’s law? It is the general question that is asked in the subject strength of materials. This law gives us a relation between stress and strain. It was given by Robert Hooke in 1660. It is defined on elastic materials.

What is Hooke’s Law

What is Hooke’s Law?



Statement: According to the Hooke’s law, when a material is loaded within elastic limit, the stress induced in the material is directly proportional to the strain produced. It means that the ratio of stress with the corresponding strain gives us a constant within elastic limit. The constant is known as Modulus of Elasticity or Modulus of Rigidity or Elastic Modulii.

In the Stress strain curve the proportionality limit indicates the Hooke’s law. The curve shows linearity within elastic limit. The ratio of stress and corresponding strain in the stress strain curve gives us Young’s Modulus

Mathematically
What is Hooke’s Law?

Young’s Modulus or Modulus of Rigidity or Elastic Modulii.

It is defined as the ratio of stress to the strain within elastic limit. It is denoted by the letter ‘E’.
  • It represents the elastic property of a material
  • The unit of Young’s modulus is N/m2 or N/mm2. The unit of young’s modulus is same as that of units of stress.

Where,

σ = Stress
e = Strain
E = Proportionality constant called as Young’s Modulus

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Units of Stress – Strength of Materials

Before finding the units of stress we must know what is stress and what is formula of stress. It is the formula of Stress through which we can easily determines the Units of stress.

Units of Stress – Strength of Materials


Since the stress is defined as the ratio of resisting force or applied load to the cross section area. The formula of stress is given by

Where, 

P = Applied load on the body.
A = Cross section area of the body.

Units of Stress

The units of stress depends upon the unit of load (force) and unit of area.

In MKS unit system, the unit of load is kgf and that of area is square meter (i.e. m2). So the unit of stress becomes kgf/m2. And if the area is expressed in square centimeter than the unit of stress is kgf/cm2.

In the SI system of units, the load is measured in newton and the area measured in m2. So the unit of stress is N/m2. When the area is expressed in cm or mm, than the stress unit becomes N/cm2 or N/mm2.

1 N/m2 = 10-4 N/cm2 = 10-6 N/mm2
1 MN/m2 = 106 N/m2 = 102 N/cm2 = 1 N/mm2
1 N/m2 = 1 Pa

Note: Here
N = Newtons
m = metre
cm = centimetre
mm = millimetre
Pa = Pascal

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Types of Stress – Strength of Materials

In this article will study about the types of stress, normal stress, tensile stress, compressive stress and shear stress. We will discuss about the definition and formula of each stress in detail. 

Types of Stress

Types of Stress – Strength of Materials


A stress acts on a body may be normal stress or shear stress.

Normal Stress: Normal stress is a stress that acts perpendicular to the area.
The formula for the normal stress is given by


The normal stress is again subdivided into two parts.

Tensile Stress: The stress which induced in a body when it is subjected to two equal and opposite pulls as shown in the figure given below is called tensile stress.
Types of Stress – Normal Stress
  • Due to the tensile stress there is an increase in the length of the body and decrease in the cross section area of the body.
  • Tensile stress is a type of normal stress, so it acts at 90 degree to the area.
  • The strain which is induced due to tensile stress is called tensile strain. It is equals to the ratio of increase in the length to the original length.

Compressive Stress: The stress which induced in a body when it is subjected to two equal and opposite pushes as shown in the figure given below is called compressive stress.
Types of Stress – Normal Stress

  • Due to the compressive stress, there is a decrease in the length and increase in the cross section area of the body.
  • Compressive stress is also a type of normal stress and so it also acts at 90 degree to the area.
  • The strain which is induced due to compressive stress is called compressive strain. It is equals to the ratio of decrease in the length to the original length.

Shear Stress: Shear stress induced in a body when it is subjected to two equal and opposite forces that acts tangential to the area.

Types of Stress – Shear Stress

  • The strain produced due to the shear stress is called shear strain.
  • The shear stress is denoted by the symbol τ (tau). It is a Greek letter.
  • It is defined as ratio of shear resistance to the shear area.
  • The formula for the shear stress is given below.



  • Shear stress is responsible for the change in the shape of the body. It does on affect the volume of the body.
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What is Stress - Strength of Materials?

In this article you will learn about what is stress in strength of materials.

What is Stress?

Stress is defined as the resistance force acing per unit cross section area of the body. It is also defined as the ratio of applied load to the cross section area of the body.
What is stress - strength of materials?

Let’s understand this while taking an example. Considered a body which is subjected to an external load. Due to this applied load, internal forces induce within the body. This internal force is called as resisting force and the direction of resisting force is opposite to the direction of applied load. The resisting force induced resists the deformation in the body. When this resisting force is taken on unit basis, we get a quantity called stress. Within certain limit the resisting force induced in the body is proportional to the deformation produced. This certain limit is called elastic limit. Within this elastic limit the resistance force is equals to the applied load.

So finally the stress is defined as the ratio of applied load to the cross section area. It is denoted by the symbol σ (sigma).
Mathematically,

Since resisting force is equals to the applied load i.e. P = R. So

Where,                 R = Resisting force induced in the body.
                           P = Load applied on the body.
                           A = Cross Section area of the body.
                               

Units of stress

Since the unit of load is N and the unit of cross section area is m2 or cm2 or mm2. So the SI unit of stress is N/m2 or N/cm2 or N/mm2. Generally in the numerical problems we use N/m2 or N/mm2.
Relation between units of stress:
1 MN/m2      = 106 N/m2
                   = 102 N/cm2
                   = 1 N/mm2

Types of Stress

The various types of stress in strength of materials are:

1. Normal Stress: the stress that acts perpendicular to the cross section area is called normal stress.

Normal stress is further sub divided into two types
(i). Tensile stress
(ii). Compressive stress

(i). Tensile Stress: When a body is subjected to two equal and opposite pulls, than the stress induced in the body is called tensile stress. Tensile stress results in the increase in length and decrease in the cross section of the area of the body.

Types of Stress - Tensile Stress


(ii). Compressive Stress: When a body is subjected to two equal and opposite pushes, than the stress induced in the body is called compressive stress. Compressive stress results in the increase in the cross section area and decrease in length of the body.

Types of Stress - Compressive Stress


2. Shear Stress: When a body is subjected to two equal and opposite forces acting tangential to the resisting section, than the stress induced in the body is called shear stress. The shear stress tries to shear off the resisting section. The shear stress acts tangential to the area. It is denoted by symbol ‘τ’ (tau).

Types of Stress - Shear Stress


For better understanding of what is stress let’s see this numerical problem
Supposed we have given a bar of cross section area 20 mm2 and it subjected to a tensile load of 60 N. than calculate the stress induced in the body.

Solution:
Given:  P = 60 N; A = 20.
Than from the definition of stress, the stress is given by

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Stress Strain Curve – Relationship, Diagram and Explanation

In this article we will Study About the stress strain curve relationship, diagram and explanation. stress strain curve is the graphical representation of the stress against strain for a ductile material. A tensile test is conducted in order to get the stress strain diagram.

What is Stress Strain Curve?

Stress strain curve is the plot of stress and strain of a material or metal on the graph. In this the stress is plotted on y axis and its corresponding strain on the x axis. After plotting the stress and its corresponding strain on the graph, we get a curve, and this curve is called stress strain curve or stress strain diagram.
The stress strain curve for different material is different. It may vary due to the temperature and loading condition of the material.

How to Draw Stress Strain Curve or Diagram

  • A tensile test is done on the material for the drawing the stress strain curve. A specimen of specific dimension is taken generally a circular rod. A tensile test is than conducted on this rod by the use of tensile testing machine.
  • In this test, the specimen is fixed at one ends and tensile load is applied on the other end. The value of load and the extension in the rod is noted down. As we have noted down the load and extension, the stress and the corresponding strain can be easily calculated.
  • The formula that is used for the calculation of stress and strain are

Stress and Strain Formula

Where,

·         σ = stress
·         P = Load
·         e = strain
·         dL = extension produced in the rod
·         L = original length
·         A = cross section area
  • We plot a graph between the stress and strain and a curve is obtained. This curve so obtained is called the stress strain curve or stress strain diagram.
  • The stress strain curve for the same material is different for different temperature and loading condition of the material.
  • In the graph the slope represents the young's modulus of the material.

Explanation of Stress Strain Curve

Stress Strain Curve – Relationship, Diagram and Explanation

Stress strain curve has different regions and points. These regions and points are:
(i).  Proportional limit
(ii).  Elastic limit
(iii). Yield point
(iv). Ultimate stress point
(v).  Fracture or breaking point.

(i). Proportional Limit: It is the region in the strain curve which obeys hookes law i.e. within elastic limit the stress is directly proportion to the strain produced in the material. In this limit the ratio of stress with strain gives us proportionality constant known as young’s modulus. The point OA in the graph is called the proportional limit.

(ii). Elastic Limit: It is the point in the graph upto which the material returns to its original position when the load acting on it is completely removed. Beyond this limit the material cannot return to its original position and a plastic deformation starts to appear in it. The point A is the Elastic limit in the graph.

(iii). Yield Point or Yield Stress Point: Yield point in a stress strain diagram is defined as the point at which the material starts to deform plastically. After the yield point is passed there is permanent deformation develops in the material and which is not reversible. There are two yield points and it is upper yield point and lower yield point. The stress corresponding to the yield point is called yield point stress. The point B is the upper yield stress point and C is the lower yield stress point.

(iv) Ultimate Stress Point: It is the point corresponding to the maximum stress that a material can handle before failure. It is the maximum strength point of the material that can handle the maximum load. Beyond this point the failure takes place. Point D in the graph is the ultimate stress point.

(v). Fracture or Breaking Point: It is the point in the stress strain curve at which the failure of the material takes place. The fracture or breaking of material takes place at this point. The point e is the breaking point in the graph.


What is First Moment of Area?

In this article we will discuss about definition of first moment of area or moment of area, application and example. We will also derive the formula for it.

First Moment of Area

Considered a thick lamina or a body having area A. let x is the distance of C.G. of the area from the axis OY and y is the distance of C.G. of the area from the axis OX.
First Moment of Area

Here

x = Distance of C.G. of area A from axis OY
y = Distance of C.G. of area A from axis OX

Then,

First Moment of Area Formula


This equation (1) is known as the first moment of area about the axis OY
Similarly

First Moment of Area Formula

This Equation (2) is called the first moment of area about the axis OX.

Conclusion:

First moment of area/moment of area:

The first moment of area of a lamina about an axis is defined as the product of area of the lamina and the perpendicular distance of the C.G. of the area form the axis.

Application

It is used to determine the center of gravity of area.

Numerical Example

If we have a lamina having area 10 cm2 and the distance of its C.G from the axis are shown in the figure given below.
First Moment of Area Example
Then

The first moment of area about axis OY = 10 x 5 = 50
The first moment of area about axis OX = 10 x 7 = 70

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