Identify typical temperatures for workshop operations, Temperature for Soldering, brazing, braze welding, welding, Hardening, Tempering and forging.

4.3SCIENCE

PREPARED BY: ALTAF HUSSAINSAJJAD ALI

PROCESS USED TO CONNECT TWO MATERIALS

• The connecting process is broadly known as welding. The welding can be performed only on metals and polymer materials.

THREE PROCESSES USED TO CONNECT TWO MATERIALS

• Soldering• Brazing• Welding

SOLDERING

• Soldering is the process of joining two agents (Materials) using another jointing agent

• lead based jointing agent is used to join two agents.

• This process is take place in the temperature of about (?)

3000C to 4270C• The soldering agents have to be selected taking

care not to damage the items to be joined

BRAZING

• This is the process that is taking place at temperatures above (?)

4270C• Then there is a requirement of the bonding agent having

its melting point above this temperature• In this process the widely used bonding agent is an alloy

of copper in most cases brass alloys rather than bronze• This process is useful to connect different kind of metals

such as tool steel to mild steel, copper to steel etc

WELDING

• Process of connecting two pieces of materials. • Two pieces are heated to their melting points and

allow to run together.• The required temperature is obtained in three forms

namely induction heating, flame and arc.• Induction heating is used to weld non-metallic

materials as their melting points are comparatively low.

• Metallic materials as their melting points are very high flames and arcs are used as sources of heat.

• Common type of flame used in welding is oxy-acetylene flame.

• The flame is having temperatures such as high as 32000C.

• In arc heating process the temperature is high as 35000C to 40000C and at this temperature the metals get white-hot and it gives a very bright light

WELDING

HEAT TREATMENT

• After performing certain operations upon the metal it develop certain qualities that will make the piece of metal not very suitable for the operations that it intended to be used for. Such bad qualities are relieved from the work piece by alloying it to undergo certain processes which use heat as the main treatment agent. These processes are called heat treatments.

FOUR MAJOR HEAT TREATMENTS

• Annealing• Hardening• Tempering• Normalizing

ANNEALING

• This is the process used to softening the metal. This process improves the machinability of the metal piece.

• It releases the internal stresses in the metal.• In this process three stages are present• Heating the metal piece to the required temperature• Holding the metal piece at that temperature for period long

enough to relieve from the stresses.• Cooling slowly to the room temperature• The temperature used in this process is depend upon the

composition of the metal. It ranges from 7600C for Tool Steel to 9250C for mild Steel

HARDENING

• This process is employed to hard the steel piece.• Heating the piece to a temperature prescribed by

the heat treatment graph depending to the carbon percentage of the steel plate.

• then suddenly cooling it down to a low temperature well below the critical temperature.

• critical temperature is at about 7000C.• Steel piece is cooled down to a temperature

about 3000C.

TEMPERING

• The process by which some hardness is removed but keeping the toughness is the tempering.

• If the steel piece is hardened then it will improve the ductility of the material and it will become unsuitable to be used as a cutting tool which is the most frequently used application of steel in industry.

NORMALIZING

• The term is often used for ferrous alloys that have been heated above the upper critical temperature and then cooled in open air

• Forging is a manufacturing process involving the shaping of metal using localized compressive forces. Forging is often classified according to the temperature at which it is performed: '"cold," "warm," or "hot" forging.

FORGING

OBSERVING THE COLOUR OF THE HEATED PIECE

Colour Temperature Purpose

Black Red 4260C to 5380C Tempering high speed steel

Very Dark Red 5930C - Do -

Dark red 7600C Hardening and annealing tool steel

Cherry red 815 0C - Do -

Orange red 981 0C Hardening alloy tool steel

Yellow white 1259 0C Hardening high-speed steel