What is plasticity

What is plasticity :

Answer 

• Plasticity us defined as the ability of the material to retain the deformation produced under the load on a permanent basis.

What is elasticity

What is elasticity :

Answer 

• Elasticity is defined as the ability of the material to regain the original shape and size after the deformation, when the external forces are removed.

All the materials are elastic but the degree of elasticity is varies.

What is strength

What is strength :

Answer 

Strength is defined as the ability of the material to resist, without rupture, external forces causing various types of stresses. 

Strength is measured by different quantities.

Types of Bearing

Bearing is a mechanical element that permits relative motion between two parts, such as the shaft and the housing, with minimum friction. 
The function of the bearing are the following :

• The bearing ensures free rotation of the shaft or axle with minimum friction.
• The bearing supports the shaft or axle and holds it in the correct position.
• The bearing takes up the forces that act on the shaft or the axle and transmit them to the flame.

Bearing are classified in different ways :

Depending upon the direction of the force that acts on them :

1. Radial bearing
2. Thrust bearing

Radial bearing supports the load, which is perpendicular to the axis of the shaft.

Thrust bearing supports the load, which acts along the axis of the shaft.

Depending upon the types of friction :

• Sliding contact bearing

Types of sliding contact bearing :

• Hydrodynamic bearing 
• Hydrostatic bearing 

• Rolling contact bearing 

Types of rolling contact bearing :

• Deep groove ball bearing
• Cylindrical roller bearing
• Angular contact bearing
• Self-aligning bearing
• Taper roller bearing
• Thrust ball bearing

Sliding contact bearing is any bearing that works by sliding action, with or without lubricant. This group encompasses essentially all types other than rolling-element bearings.

Sliding contact bearing is also called plain bearing, journal bearing or sleeve bearing.
Lubrication is critical to the operation of plain bearings, so their application and function are also often referred to according to the type of lubrication prin­ciple used. Thus, terms such as hydro­dynamic, fluid-film, hydrostatic, boundary-lubricated, and self-lubricated are designa­tions for particular types of plain bearings.

Application of Sliding Contact Bearing :

• Crankshaft bearing in petrol and diesel engine
• Centrifugal pumps
• Large size electric motor
• Steam and gas turbine
• Rope conveyors

Rolling contact bearing is a bearing which carries a load by placing rolling elements (such as balls or rollers) between two bearing rings called races. The relative motion of the races causes the rolling elements to roll with very little rolling resistance and with little sliding.  

The principal types of roller bearings are cylindrical, needle, tapered, and spherical. In general, they have higher load capacities than ball bearings of the same size and are widely used in heavy-duty, moder­ate-speed applications. However, except for cylindrical bearings, they have lower speed capabilities than ball bearings. See the following figure for roller bearings. 

 

 
Application of Rolling contact bearing :

• Machine tool spindles
• Automobile front and real axles
• Gear boxes
• Small size electric motors
• Rope sheaves
• Crane hooks
• Hoisting drums

Advantages and disadvantages of power screw

A power screw is a drive for converting rotary motion into a linear motion for power transmission in a machine. A power screw is also sometimes referred to as a translation screw. Instead of holding the parts together, it uses helical screw motion to transmit the power. Now in this article, you can check out the pros and cons of the power screw to understand more about it. 

Advantages of power screw:

• Large load-carrying capacity.
• Simple to design.
• Compact construction.
• Easy to manufacture.
• By applying small effort as 400 N, a load of 15 KN can be raised.
• Gives smooth and noiseless service without any maintenance.
• Self-locking property.
• Precise and accurate linear motion.

Disadvantages of power screw:

• Very poor efficiency is as low as 40%.
• It can be used for intermittent motion.
• High friction in threads causes rapid wear.

What is power screw

A power screw is a mechanical device used to convert rotary motion into linear motion and transmit power.

The power screw has three main parts such as screw, nut, and a part to hold either the screw or the nut. 

The power screw operates in two different ways depending on the holding arrangement. 

• In its bearing, the screw rotates, while the nut has axial motion.

The lathe's lead screw is an example of this category.

• The nut is kept stationary and screw moves in the axial direction 

Screw Jack and Machine Vice are examples of this category.

Applications of power screw : 

The main application of the power screw is the following below.

• To raise the load. Example - Screw-jack
• To obtain accurate motion in machining operations. Example - The lead screw of a lathe
• To clamp a workpiece. Example - Vice
•  To load a specimen. Example - Universal testing machine

What is factor of safety

In machine design, while designing the component, it is necessary to provide sufficient reserve strength in case of an accident so this is achieved by taking a suitable factor of safety.

fs = Failure stress / Allowable stress

fs = Failure load / Working load

The magnitude of the factor of safety depends upon the following factors:

• Effect of failure 
• Types of load
• A degree of accuracy in force analysis
• Material of component
• Reliability of component
• Cost of component
• Testing of the machine element
• Service conditions
• Quality of manufacture

Points mention below the following condition where a higher factor of safety is chosen :

• Magnitude and nature of external forces acting on the machine component cannot be precisely estimated.
• The material of the machine component has a non-homogeneous structure.
• The component of the machine is subject to the force of impact in service.
• There is a possibility of residual stresses in a machine component.
• The machine part is subjected to a high temperature during operation.
• In applications such as aircraft components, higher reliability is required.
• There is a possibility if abnormal variation in external load on some occasions.
• The machine part's manufacturing quality is poor.
• There is stress concentration in a machine component.

A higher factor of safety increases the component's reliability.

Factors to be considered during machine design

In machine design, there are so many factors to consider when designing the machine because the small amount of machine error leads to a high amount of loss so it is better to take care of some factor when designing the machine.

The list of these factors is given below :

• Cost
• High output and efficiency
• Strength
• Stiffness or rigidity
• Wear resistance
• Lubrication
• Operational safety
• Ease of assembly
• Ease and simplicity of disassembly
• Ease and simplicity of servicing and control
• Lightweight and minimum dimensions
• Reliability
• Durability
• Economy of performance
• Accessibility
• Processability
• Compliance with state standards
• The economy of repairs and maintenance
• Use of standard parts
• Use of easily available materials
• The appearance of the machine
• Number of machines to be built

What is Machine Design? Introduction | Process | Purpose

Introduction :

Machine design is the use of scientific principles, technical information and imagination in the description of the machine or any mechanical system to perform a specific function with maximum economy and efficiency.

While any design takes part below features are take care :

• A designer uses the principle of basics and engineering science.
• The designer has technical information on the basic elements of a machine.
• The designer uses his skill and imagination to produce a configuration.
• The final outcome of the design process consists of the description of the machine.
• A design is created to satisfy the need of the customer.

The basic procedure of machine design :

• Market survey
• Define the specifications of the product
• Study alternative mechanics for product
• Prepare the general layout of the configuration
• Design individual components
• Prepare assembly 

The Purpose of Machine Design :

The knowledge of machine design helps the designers as follows:

• To select proper materials and best-suited shapes
• To calculate the dimensions based on the loads on machines and strength of the material
• Specify the manufacturing process for the manufacture of the designed component of the machine or the whole machine.

Machine Design is the application of mathematics, kinematics, statics, dynamics, mechanics of materials, engineering materials, mechanical technology of metals and engineering drawing. It also involves the application of other subjects like thermodynamics, electrical theory, hydraulics, engines, turbines, pumps etc. Machine drawing is the integral part of the machine design since all the components or the machines that have been designed should be drawn to manufacture them as per the specifications. Without machine drawing the subject of the machine design is incomplete.

What is Fits

Definition of Fits:

Fits is when two parts have assembled the difference between their sizes before assembly are called fit.

There are mainly classify three groups:

• Clearance Fit - Always provides a positive clearance
• Interference Fit - Always provides a positive interference over a whole range of tolerance.
• Transition Fit - Which may provide either a clearance or interference 

What is Tolerance

Definition of Tolerance: 

The components are manufactured that all lie in between maximum and minimum limits.

The basic dimensions are called the normal or basic size while the difference between the two limits is called permissible tolerance.

Tolerance is defined as the permissible variation in the dimension of the components.

Tolerance has two systems of specifications :

• Unilateral
• Bilateral

In unilateral one tolerance is zero while others take care of all permissible variation in the basic size.

In bilateral tolerance, the two tolerance are often equal.

In machine design, there are two basic systems for giving

tolerance to the shaft or hole :

• Hole basis system
• Shaft basis system

According to the Bureau of Indian Standards, tolerance is specified by an alphabet, capital or small followed by number Example: G8 or h6

There are eighteen grades of tolerances: IT1, IT2 up to IT18

The letters of symbol IT stand for INTERNATIONAL TOLERANCE GRADE

Basic Procedure of Design

The basic procedure of machine design:

• Market survey
• Define the specifications of the product
• Study alternative mechanics for product
• Prepare the general layout of the configuration
• Design individual components
• Prepare assembly

The basic procedure of machine elements:

• Specify the function of an element
• Determine forces acting on an element
• Select suitable material for an element
• Determine the failure mode of an element
• Determine geometric dimensions of an element
• Modify dimensions for assembly
• Prepare a working drawing element