Saturday, June 2, 2018

Fire Fighting Training Module in Bangla

Govt. Job Questions with Answers

Monday, August 7, 2017

Steel : Stainless steel Vs. Carbon Steel

Steel is one of the most usable materials in factories and infrastructure development in the world. About production of steel is 1.3 billion tons a year. The application of this material is not only in factories and infrastructure but now-a-days in almost everywhere in our modern daily life. The Bridge construction, machine manufacturing, building constructions, vehicle manufacturing, process industries, aviation industries and many other places steel is required.

The properties of steel are likely dealt with strength, ductility, hardness, aesthetics etc. These properties classified the sub-categories of steel. Engineers and technician selects the proper steel type for their respective projects counting the quality and cost.

Steels are likely categorized into four groups (According to American Iron and Steel Institute) on their chemical composition as-
1. Carbon steel
2. Alloy steels
3.  Stainless Steel
4. Tool Steels  

Steel Numbering Systems
There are two major numbering systems used by the steel industry, the first developed by the American Iron & Steel Institute (AISI), and the second by the Society of Automotive Engineers (SAE). Both of these systems are based on four digit code numbers when identifying the base carbon and alloy steels. There are selections of alloys that have five digit codes instead.
If the first digit is a one (1) in this designation it indicates a carbon steel. All carbon steels are in this group (1xxx) in both the SAE & AISI system. They are also subdivided into four categories due to particular underlying properties among them. See below:
  • Plain Carbon Steel is encompassed within the 10xx series (containing 1.00% Mn maximum)
  • Re-Sulfurized Carbon steel is encompassed within the 11xx series
  • Re -Sulfurized and Re-Phosphorized Carbon Steel is encompassed within the 12xx series
  • Non-Re-Sulfurized High-Manganese (up-to 1.65%) carbon steel is encompassed within the 15xx series.
The first digit on all other alloy steels (under the SAE-AISI system), are then classified as follows:
2 = Nickel steels.
3 = Nickel-chromium steels.
4 = Molybdenum steels.
5 = Chromium steels.
6 = Chromium-vanadium steels.
7 = Tungsten-chromium steels.
8 = Nickel-chromium-molybdenum steels
9 = Silicon-manganese steels and various other SAE grades
The second digit of the series (sometimes but not always) indicates the concentration of the major element in percentiles (1 equals 1%).
The last two digits of the series indicate the carbon concentration to 0.01%.
For example: SAE 5130 is a chromium alloy steel containing about 1% of chromium and approximately 0.30% of carbon.

The widely used steels are Stainless steel and Carbon Steel in our industries.
Stainless steel:
It is defined as a steel alloy with a minimum of 11.5 wt% chromium content. Stainless steel does not stain, corrode or rust as easily as ordinary steel (it “stains less”), but it is not stain-proof. It is also called corrosion resistant steel when the alloy type and grade are not detailed, particularly in the aviation industry. There are different grades and surface finishes of stainless steel to suit the environment to which the material will be subjected in its lifetime. Common uses of stainless steel are cutlery and watch straps.
Stainless steel differs from carbon steel by amount of chromium present. Carbon steel rusts when exposed to air and moisture. This iron oxide film is active and accelerates corrosion by forming more iron oxide. Stainless steels have sufficient amount of chromium present so that a passive film of chromium oxide forms which prevents further corrosion.

Carbon Steel

Carbon Steel can be segregated into three main categories: Low carbon steel (sometimes known as mild steel); Medium carbon steel; and High carbon steel.

Low Carbon Steel (Mild Steel):  Typically contain 0.04% to 0.30% carbon content. This is one of the largest groups of Carbon Steel. It covers a great diversity of shapes; from Flat Sheet to Structural Beam. Depending on the desired properties needed, other elements are added or increased. For example: Drawing Quality (DQ) – The carbon level is kept low and Aluminum is added, and for Structural Steel the carbon level is higher and the manganese content is increased.

Medium Carbon Steel: Typically has a carbon range of 0.31% to 0.60%, and a manganese content ranging from .060% to 1.65%. This product is stronger than low carbon steel, and it is more difficult to form, weld and cut. Medium carbon steels are quite often hardened and tempered using heat treatment.

High Carbon Steel: Commonly known as “carbon tool steel” it typically has a carbon range between 0.61% and 1.50%. High carbon steel is very difficult to cut, bend and weld. Once heat treated it becomes extremely hard and brittle.
Sources : American Iron and Steel Institute 

Wednesday, January 11, 2017

Petroleum Products Abbreviated words

Abbreviated Word
High Speed Diesel
Super Kerosene Oil
High Octane Bleaching Component
Motor Spirit
Light Diesel Oil
High Sulfur Furnace Oil
Jute Bleaching Oil
Mineral Turpentine
Liquefied Petroleum Gas
Jet Aviation -1
Single Boiling Point Solvent

Saturday, April 30, 2016

Mechanical Engineering job questions Answer (Part: 1)

What is Boiler mountings and accessories> Write down three names of mountings and accessories. (Asuganj Power Station limited )
Mountings: These are the fittings which are mounted on the boiler for its proper and safe functioning. Boiler mountings are:-
1) Water level Indicator 2) Pressure Gauge 3) Blow-off-cock 4) Fusible plug 5) safety valve

Accessories: These are the devices which are used as integral parts of a boiler and help in running efficiently. Boiler accessories are:-
1) Feed pump 2) Economizer 3) Super heater

         What is parallel flow heat exchanger and counter current flow heat exchanger? (Asuganj Power station limited, Bangladesh Bank-2012 )
Parallel flow Heat Exchanger: Parallel flow heat exchangers, the fluid flow in the same direction. The temperature difference is maximum at inlet and rate of flow of heat and the rate of decrease of temperature are maximum here.
Counter-Current flow heat exchanger: In counter current flow heat exchanger the fluids flow in the opposite directions. The heat transfer takes place between the fluids at the moment when each is in its coldest state or when each is in its hottest state. The average temperature between two fluids is greater than in parallel flow heat exchanger.

         What is ton of refrigeration? (Asuganj Power Station Limited)
Ton of Refrigeration:  A ton of refrigeration is defined as the amount of refrigeration effect produced by the uniform melting of one ton (1000 Kg) of ice from and at 00C in 24 hours.

         Write down the Bernoulli’s Equation. (Asuganj Power station Company Limited)
Bernoulli’s Equation stats that for a perfect in-compressible liquid flowing in a continuous steam the total energy of particle remains the same while the particle moves from one point to another.
Mathematically, +  + Z1  =+  + Z2    

         What is the difference between shaper and Planer?
The fundamental difference between a shaper and planer is that in a Planer, the tool remains stationary and the work reciprocates whereas in a shaper, the work remains stationary and the tool reciprocates.

         What is absolute pressure? (DHAKA WASA )
Absolute Pressure = Atmospheric Pressure + Gauge Pressure