Friday, 13 November 2015

Difference between Speed and Torque...?????

Speed is the measure of how far something travels in a given period of time. It is also known as the rate of change in position.

For a Motor , Speed is measured in revolutions per minute (RPM ).

Torque is force exerted as an object rotates.To turn , a motor shaft requires certain amount of torque.

If some load is added to the shaft , more torque is required to turn it.

Two motors of different sizes may run at the same speed.

A Shaded pole motor ( example ;- window fan ) exerts very little torque.Its common speed is 1200 to 1800 RPM.

Whereas a large Industrial motor (example ;- factory conveyor belt ) may exert a very high torque in order to start a heavy load , and yet it turns at a similar speed.

The same is true for engines. An Eight cylinder car engine can run at 3600 RPM and exert a great amount of torque.

A small generator will run at 3600 RPM , but not exert nearly as much torque as the car.


Wednesday, 11 November 2015

How Laser Printer Works..????

Laser Printer Working :-

A Laser Printer is a bit mysterious , how can a laser beam , a highly focused beam of light write letters and draw pictures on paper.

Many people use laser printers in their day-to-day lives , but most probably never think about the technology that turns those bits of digital data into a legible images and text.

The Primary principle at work in a laser printer is static electricity , the same energy that makes clothes in the dryer stick together,

Static electricity is simply an electrical charge that build up on an insulated object , such as a balloon or your body.

Since oppositely charged atoms are attracted to each other , objects with opposite static electricity fields cling together.

A Laser Printer uses this phenomenon as a sort of temporary glue.The core component of this system is photoreceptor , typically a revolving drum or cylinder.This drum assembly is made out of highly photo conductive material that is discharged by light photons.

Initially, the drum is given a total positive charge by the charge corona wire - a wire with an electrcal current running through it.

As the drum revolves , the printer shines a tiny laser beam across the surface to discharge certain points.

In this way the laser draws the letters and images to be printed as a pattern of electrical charges - an electrical image.

After the pattern is set , the printer coats the drum with positively charged toner - a fine black powder.

Since it has a positive charge , the toner clings to the negative discharged areas of the drum , but not to the positively charged background.

This is something like writing on a soda can with glue and then rolling it over some flour.

The flour only sticks to the glue coated part of the can , so you end up with a message written in powder.

With the powder pattern affixed , the drum rolls over a sheet of paper which is moving along a belt below.

Before the paper rolls under the drum , it is given a negative charge by the transfer corona wire.

This charge is stronger than the negative charge of the electrostatic image , so the paper can pull this toner powder away.

Since it is moving at the same speed as the drum , the paper picks up the image pattern exactly.

To keep the paper from clinging to the drum , it is discharged by the detac corona wire immediately  , after picking up the toner.


Friday, 6 November 2015


A Fourdrinier is a huge papermaking machine which takes input as waste paper Or wood fibres and produces output as a finished paper roll.
Many modern paper making machines are based on the principles of the Fourdrinier Machine.

This Machine was invented in the early 1800's and is accredited to Henry Fourdrinier , a London based Stationer , although it was actually invented by a Frenchmen called Louise - Nicholas Robert.

The Fourdrinier Machine consists of four main sections :-

(1.) Forming section Or Wet end
(2.) Wet Press section
(3.) Dryer section
(4.) Calender section

Although , so many other small things are also present in between these sections like :- Size press , M.G roll , Coaters , Pope reel e.t.c.

(1.) Forming Section :-

Because woodpulp fibres Or waste paper fibres ( in case of recycling ) has a strong tendency to clump, it needs to start off with a very high percentage of water content, allowing the pulp to have an even distribution, the slurry (or furnish) held in the Headbox contains around 99% water.

The furnish travels down the Slice onto the revolving Wire ( woven plastic fabric meshed conveyor belt ) at the Breast Roller point of contact.

As the furnish travels along the wire, so water is removed and the pulp fibres are aligned in a uniform direction.

It is this process that allows perfect distribution of the pulp fibre across the sheet as well as giving the paper strength and stability by aligning the fibres. Suction rollers hold the furnish to the meshed wire and help remove the water content.

By the time the paper or web has reached the Wet Press Section , at that point the consistency has gone from 1% pulp content to 25%.

(2.) Wet Press Section

The Wet Press Section carries the wet web between a series of rollers under high pressure to squeeze more water from the paper, much like a mangle.

The Felts ( woven plastic fabric conveyor belts ) support the web and also aid water removal by absorption. As the web enters the third section the paper web consistency can be as high as 40%.

(3.) Dryer Section

In this section , Steam heated rollers cause further water removal by making direct contact with paper through evaporation as well as further use of felts , bringing the water level down to as low as 30%.

(4.) Calender Section

The final Calendar Section allows the web to pass between Calendar Rollers that smooth out the surface of the paper.
If the paper has a coating then the degree of calendering will change the characteristics of the coating.

For example, gloss artpapers have a higher degree of calendering than a velvet sheet.

The main purpose of Calender section is to make the paper smooth , brighter and glossy.

Now one thing that is not shown in the diagram and is the first thing that strikes anyone who visits a paper mill for the first time is the absolute vastness of Fourdrinier machines.

Each roller in the Dryer Section can have a diameter of several metres, the width of the reel of paper can vary from 5 to 10 metres long and weigh several tonnes.

The Machine from the Top Box to the Dry End could cover the distance of a football field.

The machines are so large that operatives have to use three wheel scooters to move from one end to the other.

What is Size Press in Paper Making Machines..????

Size Press is one of the major part of the Paper Making machine.It generally consists of two rolls of specific diameter.

The main purpose of Size Press is to apply a solution of starch or other material onto the surface of the dry paper coming from the dryers and then it is again dried. 

Some Paper machines contain a unit for the  application of certain liquid media to the Web surface like :- Size Press , Top Coater , Bottom Coater , Pre Top Coater.

The Process of applying Starch solution , a Sizing agent Or a mixture of both by means of Size Press is known as Sizing.

The main reason for paper sizing is to increase the strength and printability of paper products by the chemicals ( mostly starch ) applied acting as binding agent.

Starch is the most agent used , but in recent years a combination of Cationic Starch and synthetic copolymers has been increasingly used to improve the effects of surface sizing.

Cationic starch increases strength of the the paper because it binds to the anionic paper fibres.

In Size Press coating Or a thin film of chemicals is applied on the paper web by means of rolls.