Sunday 25 March 2018

What can a jobless mechanical engineering fresher in India do to get hired if he has a good knowledge of AutoCAD, catia and ansys?



well, before i give answer of question, i want to say that Mechanical engineer are awesome. being Mechanical engineer is not a joke. only smart and hard working person can become an engineer. and you have good knowledge of AutoCAD, catia and ansys which is your plus point. but you want job. and before you get job all you have to take care is “Apply to company only if they really require your expertise”. other wise you have some other option such as:
  • go to foreign and use your skill to help those companies which really require your skills.
  • prepare for government exams and you are engineer so you have habit of studying hard so it will be very easy as compare to other graduates to crack exam.
  • open classes for engineering students and start teaching AutoCAD, catia & ansys and also start taking orders from other industries for designing.
  • analyze your situation and situation of market by using your operation research skills which you already studied during your engineering and take decision. you should proud of having knowledge of everything and being scientist of Mechanism.

Monday 19 February 2018

open cycle gas turbine power plant




A simple cycle gas turbine consists of a (1) compressor, (2) combustion chamber and (3) gas turbine.

In the open cycle gas turbine, ambient air enters at the compressor and after the compression of air, fuel is burned in the air itself to raise it to high temperature and then product of combustion are passed on to the turbine for expansion. After delivering the work combustion products are finally rejected to atmosphere. In the open cycle the working medium is continuously replaced by fresh air and fuel. It works on the joule cycle and Brayton cycle.

The air is sucked in by the compressor from the atmosphere through the filter which removes the dust from the air. The rotary blades of the compressor push the air between the stationary blades to raise its pressure to 4-5 atmosphere. Hence the air is available at high pressure at output of the compressor. Then high pressure air passes through combustion chamber, in which heat added to the air at constant pressure by burning the fuel and raises temperature (about 1650) of working medium. This high temperature must be brought down to the level so that the thermal stresses in the turbine blades do not become excessive. This is achieved by allowing the reminder air to enter the combustion chamber at downstream to mix and cool down the combustion gases. The products of combustion comprising of mixture of gases at high pressure and temperature are passes through the gas turbine. These gases in passing over the turbine blades expand and thus result in motion of rotor and finally discharged to the atmosphere at the temperature about 540.

Advantage of open cycle:

         I.            Simplicity: There are only few rotating parts as turbine, compressor and gear train driving the auxilliaries. Hence problem of vibration and lubrication is not so severe. The ignition system is also simple compared to closed cycle.

       II.            Flexibility: since different processes within the cycle take part in separate components, a great variety in the arrangement of the system is possible.

     III.            Low weight and size: The weight in kg. per KW developed is less.

    IV.            Independent system: Open cycle gas turbine power plant, except those having intercooler, does not require cooling water. There fore the plant is independent of cooling medium and becomes self-contained.

      V.            Fuels: Almost any hydrocarbon fuel from high octane gasoline to heavy diesel oils including some solid fuels can be burned in the combustion chamber.

    VI.            Warm-up time: After the turbine has been brought up to speed by the starting motor and the fuel ignited the gas turbine will accelerate from cold start to full load without a warm up time. This is particularly important in stand by emergency plants.


Disadvantage of open cycle:

            I.            Part load performance: The part load efficiency of the open cycle plant decreases rapidly as the considerable percentage of power developed by the turbine, is used to drive the compressor. Also, the system is sensitive to the changes in components efficiency.
          II.            Sensitivity: Since system sensitive to the component efficiency, particularly that of compressor. The efficiency of compressor is affected by change in the atmospheric conditions such as temperature ad humidity of air at the inlet and foreign matter contained in the air.
        III.            High air rate: The simple open cycle gas turbine has a very high air rate as compared to other prime movers. However, the air rate may be lowered by intercooling and reheating.
       IV.            Erosion and corrosion: The working fluid is mixture of air and fuel. Since air contains dirt being deposited on the compressor blades. Due to carbon and other foreign deposits from combustion in the combustion chamber, turbine and regenerator, it is necessary that the dust should be prevented from entering into the compressor in order to minimized erosion and depositions on the blades and passages of the compressor and turbine.
         V.            In the simple open cycle, the turbine exhaust is discharged into atmosphere. Since turbine exhaust contain large amount of heat resulting in loss of heat.


Friday 16 February 2018

Classification of Gas Turbine Power Plant




The gas turbine can be classified as follows:

1)      According to types of combustion process

                                 I.            Constant volume or explosion type gas turbine: This type of Gas turbine works on Atkinson cycle in which combustion of air fuel mixture is takes place at constant volume, hence air and fuel mixture should be isolated from compressor. This is possible by valves in the combustion chamber, resulting in an intermittent combustion which inherently impairs smooth running of machine. This type of turbine has better thermal efficiency than a constant pressure cycle gas turbine. The main disadvantages of this type of gas turbine is that complexity in mechanical system and pressure difference and velocity of hot gases are not constant, so turbine speed fluctuates. The constant volume combustion type gas turbine is not popular in practical use. The constant volume gas turbines are absolute in use.
                               II.            Constant pressure or continuous combustion type gas turbine: This type of gas turbine works on Brayton cycle in which combustion of air fuel mixture is takes place at constant pressure.

2)      According to direction of flow

                                 I.            Axial flow gas turbine
                               II.            Radial flow gas turbine.

3)      According to action of expanding gases

                                 I.            Impulse gas turbine
                               II.            Impulse- Reaction gas turbine

4)      According to path of working substance

                                 I.            Open cycle gas turbine plants: In the open cycle gas turbine, ambient air enters at the compressor and after the compression of air, fuel is burned in the air itself to raise it to a high temperature and then product of combustion is passed on to the turbine for expansion and which after delivering the work are finally ejected to atmosphere. In the open cycle the working medium is continuously replaced by fresh air and fuel.
                               II.            Closed cycle gas turbine plants: In the closed cycle gas turbine power plant, the same air or the working fluid is circulated over and over again. The working medium is not mixed with fuel, but it is heated by the burning of fuel in separate supply of air in the combustion chamber and transferring this heat to the working fluid which passes through tubes fitted in the combustion chamber. The working fluid does not come into direct constant with product of combustion.
                             III.            Semi-closed cycle gas turbine plants: Semi-closed cycle gas turbine plant is combination of open and closed cycle, in which some part of working fluid is recirculated to the plant and another part of working fluid flows into and from the atmospheric air.

5)      According to thermodynamic cycle

                                 I.            Simple cycle
                               II.            Simple cycle with intercooling: in which the air is cooled between stages of compression.
                             III.            Simple cycle with regeneration: in which the air after compression is heated with help of exhaust gases coming from turbine.
                            IV.            Simple cycle with reheating: in which combustion products (gases) after part of expansion in high pressure turbine is reheated in second combustion chamber and then it is expanded in the low pressure turbine.
                              V.            Simple cycle with intercooling, regeneration and reheating.

6)      According to shaft configuration

                                 I.            Single shaft engine: - Examples: Turbojet engine, Turboshaft engine.
                               II.            Multi-shaft engine: - Example: Two shaft engine with power turbine, Turbojet engine, industrial slit shaft engine, Twin-spool engine.

7)      According to applications

                                 I.            Power or industrial gas turbines

                               II.            Aviation or aircraft turbines

Monday 12 February 2018

What is Deburring?

What is Deburring?

What is a burr?
During most machining processes, work pieces become burred, and sharp edges or material compression occurs.This effects the quality of the part and can create a potential sources of error during the assembly process. 

What is burr and how does it occur?

1)   During stamping, fineblanking or forming
2)   During casting, sinter and molding of material
3)   During milling, turning, drilling und grinding
  • Material
  • Tools
  • Cutting speed
  • Stock

Linear Deburring Machines

Most of deburring machines can be equipped with up to four machining stations, each equipped with five brush tools. An ideal transformation ratio between brushes and head ensures constant and optimal deburring results. In the area of flexible single-part production and production of small to medium series, most of deburring machines are optimally suited for cost-effective machining of, for example, punched and precision cut parts, valve plates and precision work pieces. Most of deburring machines can either be supplied as stand-alone solution or – for further increase of productivity – as semi and fully automated setups combined with any other machine (e.g. a double-disk surface grinding machine from the DDG range). Each version follows a modular concept and can be adapted to our customers‘ needs.


Double-Sided Deburring Machines

For  high- precision  series  production  of  work  pieces, machines has been refined. Thanks  to its modular structure, it is already in use as a precision  grinding, lapping, honing and polishing machine. Now Machine manufacturers are also offering a patented solution for double-sided deburring applications in one working step. The changeover to a double-sided precision grinding  machine for deburring applications could not be easier. All that is required is to replace the precision grinding wheels by brush wheels, and to deactivate the central measurement control. this means a precision grinding machine is basically suitable for deburring, and can also be used as a combination machine.

Disc Brushes 

Countless different specifications can be configured. In most cases an individual polyamide fiber is coated with abrasives. Grain size and abrasive material play a decisive role in this.
Typical Deburring Brushes

Most used materials:
  • Silicon carbide
  • Aluminum oxide
  • Ceramics
  • CBN
  • Diamond

Sunday 4 February 2018

What is the difference between brazing and welding?


WELDING :

Welding is a process in which both the participating metals are metaled and re solidified to complete as one metal. Proper melting of mating parts is a basic criteria to result a sound weld.


BRAZING :

>In case of Brazing both the participating metals are not melted but a third metal of lower melting point is used to be filled in between the two. The solidification of this third metal results the joining. 

>The filler metal is drawn into the gap between the closely fitted surfaces of the joint by capillary action.

>The design of the joint should incorporate a minimum gap into which the braze filler metal will be drawn.


Thursday 1 February 2018

Lapping Machines

Lapmaster Wolters Single Sided Lapping Machines 



Fundamental Lapping Theory

 The basic theory of lapping starts with the components being placed within the confines of conditioning rings directly onto the surface of a rotating lap plate that is coated with a precision film layer of slurry. The components should never come into direct contact with the lap plate surface. Through powered lap plate rotation, the loose and rolling abrasive particles within the slurry layer transfer cutting energy with their sharp cutting edges by penetrating the contact surface of the components removing microscopic chips of material. Concurrently the abrasive is acting on the lap plate via the contact surface of both the components and conditioning rings causing wear that when controlled by adjustable radial ring position will effect spherical curvature changes to maintain a flat lap plate condition.

Lapping successfully: Factors to consider
  • Type of material being processed
  • Speed of plate
  • Pressure on work-piece
  • Plate material
  • Size and type of abrasive
  • Vehicle used
  • Flatness of plate
  • Feed system
  • Method of charging and conditioning the plate
  • Plate temperature

Peter Wolters AC microLine® Double Sided Lapping Machines  

 


The high productivity double sided lapping machines of the Peter Wolters AC microLine® range display state-of-the-art design and concept. The modular system of main components together with the precision of the latest control-, drive and measuring technologies superb process reliability and make the system simple to operate. Easily removable machine linings and fully covered process areas give the best accessibility and industrial safety. For automatic loading and unloading, the upper wheel can be swung out.
Durability, reliability, low cost of ownership, variety in applications and automation solutions – these are the outstanding features which characterize every AC microLine® machine. For further increase of productivity, all machines can be equipped with automation setups. Choose between semi and fully automated versions. These automation choices guarantee optimal unit cost combined with high throughput and, therefore, the most economic solution.
The Lapmaster DSL series of double sided lapping machines are driven by three, variable speed motors for maximum process control flexibility. All three rotating machine components, the sun gear, top plate, and bottom plate, are independently controlled. Process down pressure requirements are pneumatically regulated and continuously monitored by a load cell.

Wednesday 31 January 2018

Fine Grinding vs Lapping

What is Fine Grinding?

  • Fine Grinding is a batch-mode abrasive machining process that combines the speed and aggressiveness of super abrasive wheels with accuracy of lapping kinematics to produce flat and parallel work piece surfaces.
  • The cutting tool consists of an upper and lower wheel composed of diamond or cubic boron nitride (CBN) with different bond types (vitrified bond, resin bond or metal bond) and act as the support plates for the work pieces.
  • The machine tool has evolved from the vertical double-wheel lapping machine design with a planetary work drive system, also known as “lapping kinematics”.
  • In place of lapping wheels, grinding wheels are fitted and cooled through labyrinth in the working wheels and a coolant fed through holes in the upper wheel.
  • Since Fine Grinding requires higher forces and uses higher cutting speeds, motors, gears and the rigidity of the machines are much stronger than lapping machines.
  • Work pieces are guided between the upper and lower working wheel in an epicyclical path as defined by inner and outer pin ring, upper and lower working wheel, speeds and directions, while material removal takes place simultaneously on both sides.

FIne Grinding Technology

Definition of the Tooling Methods

  • Lapping flat parts – single or double-side) is the abrasive machining process for removing material using a loose abrasive in a liquid mixture (known as a slurry) at low speeds.
  • Loose abrasive is moving over the surface under pressure , will knead, abrade, chip or scrape away the surface of the workpiece . By exceeding the bending strength the material breaks out.
  • Fine Grinding (flat parts – single or double-side) is the abrasive machining process for removing material using a bonded Superabrasive wheel at low speed with a liquid to keep the part cool. The fixed grain of a geometrically indefinable cutting shape acts like a plow and material is removed by micro-grooving /-cutting . The chip formation occurs by exceeding the shearing strength.

Kinematics of the Fine Grinding Process

Fine Grinding generally follows the same kinematic principle as lapping. The workpieces are held in carriers which are driven to describe a planetary motion covering the full surface of the Fine Grinding wheel. The drive mechanism consists of an inner and outer pin ring. The outer ring is generally fixed while the inner ring rotates in either the opposing or the same direction as the lower working wheel to create a series of epicyclic rotations.

Fine Grinding vs Lapping


Fine Grinding

  • Performed with super abrasive (diamond or cubic boron nitride - CBN) wheels
  • Stock removal caused by micro grooving / -cutting
  • Fine-ground surface has cross-hatched marks
  • Coolant is recycled
  • Fine-ground parts are coated only with a thin layer of coolant and therefore only minimal workpiece cleaning is necessary
  • Wheel speeds are typically 2 – 15 m/s
  •  3 – 20 times faster than lapping (removal rate)

Lapping 

  • Lapping is a working process, during which workpiece and tool slide over one another on a loosely applied medium (lapping compound) and are subject to continually changing direction of rotation.
  • Stock removal caused by rolling and sliding action of abrasive grains
  • Lapped surface is dull and crater-like
  • Material and lapping compound are not recycled
  • Lapped parts are contaminated with lapping compound and require cleaning
  • Lapping speeds are generally limited to < 1 m/s

Why use Fine Grinding?

General

  • Accuracy results, previously only achieved by lapping
  • The pellet structure allows a layout of the grinding medium, corresponding to the kinematics conditions
  • Long and constant process cycles without dressing processes
  • The space between the pellets allows a high flow rate of the coolant
  • Very good chip flow without temperature problems
  • High process quality, consistent repeatability of achieved values
  • Also large surface work pieces can be machined
  • Batch processing
  • Work pieces are loosely held in carriers and therefore machined stress free (without distortion - especially for machining of thin or delicate parts)
  • Work pieces of different shapes could be machined (i.e. round, rectangular or irregular; full surface or with cut-outs)
  • Easily to be automated

 Fast

  • High removal rate using super abrasive diamond and CBN (3 – 20 times faster than lapping)
  • Possible saving of pre-machining steps
  • Long intervals between resharpening
  • High flexibility
  • Automated solutions

Clean

  • Recycling of coolant
  • Tremendous less waste than with lapping
  • Minimal work piece cleaning necessary
  • Reduced downtime
  • Cleaning of work pieces without problems by rinsing; in comparison to lapping ultrasonic or chemical cleaning is not necessary

Economic 

  • High removal rate (reduces capital costs and personnel expenditure)
  • Low wheel wear _ long life time of the grinding wheels (reduces the tool costs)
  • Low waste disposal costs (reduces the current running costs)
  • Low work piece cleaning costs (reduces the current running costs)
  • Possible saving of additional machining steps
  • Easy wheel maintenance _low tool manufacturing costs by using a “Standard-Pellet-Form”

Tuesday 30 January 2018

hot and cold spark plugs explained



Introduction:

In order to ignite air fuel mixture we need heat.In case of diesel engines (compression ignition engines) this head is achieved by the compression of gases.But in case of spark ignition engines we need to have an external source to ignite air fuel mixture because compression is not enough to ignite the mixture.

spark plug is a device for delivering electric current from an ignition system to the combustion chamber of a spark-ignition engine to ignite the compressed fuel/air mixture by an electric spark, while containing combustion pressure within the engine.


There are two types of spark plug :

  • Hot Spark Plug
  • Cold Spark Plug

“Cold” spark plugs normally have a short heat flow path. This results in a very quick rate of heat transfer. Additionally, the short insulator nose found on cold spark plugs has a small surface area, which does not allow for a massive amount of heat absorption.



On the other hand, “hot” spark plugs feature a longer insulator nose as well as a longer heat transfer path. This results in a much slower rate of heat transfer to the surrounding cylinder head.

The heat range of the spark plug must be carefully selected in order to create an optimal thermal performance. If the heat range is not correct, you can expect serious trouble. Typically, the appropriate firing end temperature is  900-1,450 degrees. Below 900 degrees, carbon fouling is possible. Above it, overheating becomes an issue.