Chapter 5.Soldering And Brazing

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Soldering And Brazing :

Soldering And Brazing

Introduction To Soldering :

HS LOH PSDC Introduction To Soldering QUICK and USEFUL method of joining metals. Used to make joints in LIGHT articles made from copper, brass, steel, etc. The Joints CANNOT withstand heat because of LOW MELTING TEMPERATURE SOLDER. The Joints NOT VERY STRONG. Use Riveting/Brazing/Welding if need strong joint.

Slide 3:

HS LOH PSDC LOW TEMPERATURE thermal joining process – 100-500  C Parent metal is NOT melted. Joint faces “tinned” by a film of solder. Solder are made to fuse (melt) filling the space between the joint faces of parent metal. Tinman’s solder used for most mechanical assembly joint. melts at 183  C composed of two parts of tin and one part of lead. Small joints - using a soldering iron larger soldering area – use sweating soldering

Soldering Iron:

HS LOH PSDC Soldering Iron

“Sweat” Soldering in action:

HS LOH PSDC “Sweat” Soldering in action

Slide 6:

HS LOH PSDC Sweat Soldering is used when large areas require joining The heat given off by a bit would be insufficient. Steps of Sweat Soldering the areas to be joined are first cleaned and ‘tinned’ Heat is then carefully applied upon the joint. When the solder melts, the weight will force out the surplus solder and bring the two parts into close contact the source of heat being removed at this point.

Use Of The Soldering Iron :

HS LOH PSDC Use Of The Soldering Iron Soldering irons are made of copper because it is a good conductor. Large bits are preferred because they can contain a large quantity of heat. For a successful soldering, the work must be clean, free from dirt, grease and clear of any oxide film. A bit must be ‘tinned’ or coated with solder before use.

Slide 8:

HS LOH PSDC This is done by heating the bit filed to remove the oxide film dripped in flux inserted in some liquid solder.

Tinning Soldering Iron Bits:

HS LOH PSDC Tinning Soldering Iron Bits

Method Of Soldering :

HS LOH PSDC Method Of Soldering Soldering steps heating the joint applying the flux adding the solder The bit is made of copper because: 1. This metal is a good heat conductor. 2. It easily alloys with tin.

Soft Solders :

HS LOH PSDC Soft Solders Soft solders are lead-tin alloys and some also contain a small amount of antimony.

Fluxes :

HS LOH PSDC Fluxes For solder to be successful the metal surfaces to be soldered must be absolutely clean. This is done by hand with a file, sandpaper or emery cloth. Large areas are usually pickled in an acid bath.

Slide 13:

HS LOH PSDC Functions of Fluxes maintaining the cleanliness. protect the cleaned surfaces from fumes and from chemical action due to the atmosphere. There are two common kinds of fluxes: 1.Passive Fluxes - Merely protect the surfaces 2. Active Fluxes - Protect the surfaces and also help to clean it.

Passive fluxes :

HS LOH PSDC Passive fluxes - Demand a very clean surface as they have little or no cleaning action, but prevent oxidation. - Have a resin or tallow base. - No corrosion action when used. - Always used for electrical work.

Active fluxes (‘killed spirit’) :

HS LOH PSDC Active fluxes (‘killed spirit’) - Have an acid base which helps to clean the job. - Have corrosive action. - Seldom allowed for the soldering of radio, television components and aircraft parts. - Consist of hydrochloric acid.

Slide 16:

HS LOH PSDC Resin, tallow, Vaseline, pure turpentine, etc., fall into the first group of fluxes. Zinc chloride (killed spirits), ammonium chloride and zinc ammonium chloride are fluxes which fall into the second group. The second group is the most useful and hence most widely used.

Table below shows the fluxes which are used for various metals. :

HS LOH PSDC Table below shows the fluxes which are used for various metals. Metal Flux Steel Ammonium chloride Lead Tallow Zinc and galvanized work Dilute hydrochloric-acid Brass Zinc chloride or resin Tin plate Zinc chloride

Soldering products:

HS LOH PSDC Soldering products Printed Circuit Board Copper Fitting

Brazing :

HS LOH PSDC Brazing Used when really strong soldered joints are needed. Brazing or Hard Soldering is a process of joining metals in which the molten filler is drawn by capillary attraction into the space between closely adjacent surface of the parts being joined.

Brazing In Action:

HS LOH PSDC Brazing In Action

Slide 21:

HS LOH PSDC It is a general term used to cover brazing and silver soldering. These processes demand higher temperatures and require flame or other heating. The solder is now called spelter (copper-zinc alloy: brass). The flux used is usually borax (sodium borate) The spelter has a lower melting point than the metals being joined.

Slide 22:

HS LOH PSDC Brazing solder contains approximately equal parts of zinc and copper and it melts at about 870°C. The metals to be joined have to be heated to a cherry-red colour in the neighbourhood of the joint. Joints in steel and brass are often brazed. When silver is added to the brazing solder the melting point of the solder is lowered.

Brazing Joint:

HS LOH PSDC Brazing Joint

Slide 24:

HS LOH PSDC Such solders are called silver solders and they can be obtained with a melting point as low as 630°C. The heat source used when brazing is a blow pump of blowpipe. Sometimes in production brazing a furnace is used. The braze must be cooled in still air.

Slide 25:

HS LOH PSDC Quick cooling reduces the strength of the parent metals but it does not effect the braze itself. Borax and water is used as a brazing flux.


HS LOH PSDC QUESTION List out two weakness of the soldering joint. Answer : Cannot withstand high temperature. Not very strong. When “sweat” soldering needs to be carried out instead of using soldering iron? Answer : When the solders have to cover large area of joint. What have to be done before soldering ? Answer : Ensure that the joining surfaces are clean, free of dirt, grease and any oxide films.


HS LOH PSDC QUESTION (Cont.) Why the soldering bits need to be made of copper ? Answer : It is a good heat conductor It easily alloys with tin What is the difference between active fluxes and passive fluxes ? Answer : The active fluxes help to clean the joint surface but not the passive fluxes. What is the strong point of brazing compared to soldering ? Answer : Can produce stronger joint.

Slide 28:

HS LOH PSDC The end.

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