Okwuagbala Uzochukwu Mike holds first degree in Metallurgical and Materials engineering. He has proper practical experience in this area.
In practical institutions, brazing is done by the students in a place called workshop. Also, there are some engineering companies that specialize on brazing for specific results. What is brazing in metallurgical and materials engineering? Of what importance is brazing and why do we brazing?
Brazing is an important working on a jointed portion of a welded metal to produce mechanically acceptable bond between two surfaces. It is very important due to the purpose it was made for. Brazing can be defined as metal-joining process which involves filler metal that is heated to its melting temperature and fluxes to enhance wetting between two or more close-fitting parts by capillary action.
There are certain things which are to be taken into consideration during brazing. The environment and the joint to be brazed must be considered. The base-metal to be brazed together with its surface must be made clean. Why must the brazing -metal and the surface made clean from impurities and oxides? The reason for this is to avoid contaminants which can lead to poor flow of the molten metal during brazing. Also, contaminants like Sulphur, Lead and Bismuth can lead to cracking.
The Science of brazing does not wake up one day and began to exist. In the other words, the Science of brazing has something that caused it. Its application is found in honeycomb structure in aircraft. There, such structure is exposed to elevated temperatures and because abrasive are not suitable for such position, brazing is applied. Again, brazing is applied in engine nacelle and wing panelling for supersonic military aircraft.
Brazing has some techniques adopted before it is achieved. The brazing technique can either be manual or by the use of machine. But in this write-up, brazing technique to be discussed is performed manually using oxyacetylene torch.
Soldering is similar to brazing but the point is that brazing requires higher temperature than soldering. The temperature required for melting filler-metals is higher when compared with the temperature for melting solder during soldering.
In soldering, the technique required to achieve the process is unique. Though both brazing and soldering require clean surfaces, both do not involve same technique practically. Brazing and soldering require the application of number of scientific and engineering skills to produce joints of satisfactory quality and reliability (Brazing by Mel Schwartz).
The Brazing Technique
The brazing techniques are of many types. As there are many ways to kill rats that disturb people living in a home, so are many brazing methods which involve other techniques. Brazing can be conducted by dipping, in a muffle-type furnace, by mean of oxyacetylene torch or by induction heating (Metallurgy of Welding by J. F Lancaster). Based on this topic, brazing technique used is that of torch brazing.
Torch Brazing Technique
The term, technique, is a way of carrying out a particular task especially a scientific procedure. The torch brazing technique is a manual brazing process. In this technique, there nothing like automation. Every brazing process involved is carried out manually. But "neatness" is achieved at the end of the brazing. "Neatness" in the sense that quality work is generated at the end. This involves the use of Oxygen-Coal gas or Oxyacetylene torch.
The techniques that are adopted in torch brazing include selection of the filler-metal and base-metal, assembling of the base-metal and clearance, fluxing and cleaning, and brazing which is followed by final cleaning.
Selection of base and Filler-Metals: Another name for filler metal is brazing metal. The brazing metal used during brazing is dependent on the base-metal to be brazed. When a wrong filler metal is used, the brazed joint obtained will be of low strength. The joint that is usually brazed is the lap-joint. The most common brazing alloy is the brass which may be 50/50 or 60/40 brass.
The filler-metals that can be used during brazing are Iron-wire, Copper, Boron, Phosphorus, Manganese, Nickel, Silver and Aluminium-zinc alloys (Metallurgy of Welding by J.F Lancaster). Copper are used for brazing of Steel and ferrous alloys. When conducting brazing on metal-joints with base-metals of high-temperature, cryogenic and corrosion-resistance, it is advisable to make use of Nickel alloys to achieve high-strength and mechanically standard result.
Cleaning and fluxing: Capillary action will work properly only when the surfaces and the joints are clean (How to Braze Properly by Lucas-Milhaupt). Cleaning and fluxing are conducted before brazing to remove impurities. Examples of impurities are oxides, oil, grease, plain dirt and rust. Fluxing is conduct to remove mainly oxide impurities. Other impurities can be removed mechanically and chemically.
Grease and oil can be removed using degreasing solvent. This solvent is applied on the base-metal as well as on the joint to be brazed. Examples of the flux to be applied are the Handy and Harman’s Handy flux, Borax and Boric acid. The larger the metal to be brazed, the more flux is applied. After the joints have been brazed, the residual fluxes are washed out. Note that fluxing is not done separately in all brazing processes because some filler-metals contain flux in them i.e some filler metals are coated with flux.
Assembling and Clearance: When the base-metals to be blazed are not well assembled, the result to be achieved at the end will be a rough one because the dimensions are not well considered before brazing.
The strength of a defect-free brazed joint in Carbon-Steel increases as the joint clearance is reduced. But note that when the clearance angle is widened too much, the strength of the brazed joint is reduced. Clearance gap of between 0.075 to 0.4mm is suitable for brazing Copper with Spelter, which is 60/40 brass. When brazing with Copper and Steel, the optimum clearance gap is between 0.05 to 0.40mm. If the interest is on Aluminium, it is advisable to make use of clearance between 0.125-0.625mm depending on the process used (Metallurgy of Welding by J.F Lancaster). Due to the fact that metals expand when heated to the brazing temperatures, the clearance must be made in such a way that after the expansion some gaps will also be left.
Brazing and final cleaning: It is the last step in the brazing technique. It comes after selection, cleaning/fluxing, and assembling. A small area of the base-metal is heated with oxyacetylene torch. The joint portion of the metal is heated to some extent before bringing the filler-metal into play. Where applicable, a globule of filler-metal is deposited on the portion to be brazed (brazing joint) together with the flux. The filler-metal is heated by oxyacetylene flame until its melting temperature is reached, filler-metal begins to flow and capillary action starts. During this stage, care is taken so that the brazing-metal flows in the hottest part of the joint and in the right direction. The flow velocity is predicted to rise with temperature. The final brazing process takes place at the temperature of about 540 to 1620 o C (Brazing by Mel Schwartz).
After the proper brazing process, the brazed portion is carefully cleaned. Cleaning involves wiping out of the flux residues, and pickling to remove any oxide formed during brazing. The cleaning step taken makes the brazed joint appear neat and presentable. The flux residue can easily be removed by quenching the brazed portion in hot water. Quenching is rapid cooling of heat treated metal. Quenching for removal of residual flux can take place at temperature of about 50 degree Celsius of water. The brazed joint can further be cleaned by brushing with wire brush. ‘Stubborn’ fluxes can further be removed by chemical e.g with the use of 25% Hydrochloric acid. Once cleaning is achieved, other finishing processes like electroplating can proceed.
The Soldering Technique
Soldering is like a “brother” to brazing. But the point is that soldering requires less temperature than brazing. Again, in soldering, solder takes the place of filler metal. In soldering, at temperature of about 128 degree Celsius, solders melt (Soldering Technique by W. E Olmon et. al).
There are techniques applied during soldering operation, and the “key players” are the soldering iron or soldering machine and the Solder. The technique includes cleaning and aligning of wires or components to be soldered, choosing of soldering equipment, and heating and soldering.
Cleaning and aligning: It is possible to encounter impurities on the wire or circuit board to be soldered. Contaminants can cause a lot of damages in a circuit board if not properly clean or removed before soldering. The impurities if oxides can be removed by means of fluxing.
Aligning or arranging is very important in soldering. If it is soldering of two wires, the wires are first positioned with the possible device so that the soldering process can easily be carried out. Also, if proper arrangement is not well done on the circuit before soldering, error will be incurred at the end of the soldering process.
Choosing of soldering instrument: As there are specific school uniform for students in primary and secondary schools, so are specific instruments for a particular soldering method. There are solders used on pipes and are not the same with that used for soldering wires and circuit board. Soldering technique in this write-up is based on the use of pencil soldering iron. The equipments that are used along with the soldering iron are replaceable tape, solder, power source, positioning device, and the wash cloth. Soldering wash cloth is used for removal of solidified solder from the tape of the soldering Iron.
Heating and Soldering: After cleaning, aligning, and choosing of the soldering equipment for conducting of soldering operation, the next is heating and “final soldering”. The wire joints or circuit boards to be soldered are first heated. This is done to have good joint at the end of soldering.
When wire is heated and ready for soldering, solder is placed in contact with the tape of the soldering Iron and the portion to be soldered. Note that the soldering Iron must first be connected to power source and heated to appropriate temperature. In soldering, the solder melts at the temperature of about 128 degree Celsius. An author, J. F Lancaster, wrote that soldering is carried out using alloys having a melting temperature of about 450 degree Celsius or less.
When solidified solders stick on the tape of the soldering Iron, it is removed using wash cloth for keeping the tape neat and shining. When soldering is due, the heat source is removed and a uniform and complete bond formed between the solder layer and the wire or part of the material soldered.
This topic discussed brazing and soldering techniques. The techniques applied in both of them are not same. Brazing and soldering is an important part of Metallurgical and Pipeline Engineering.
In brazing, the technique applied is selection of base-metals, cleaning and fluxing, assembling of the base-metals and clearance gap, and brazing and final cleaning. These steps were well explained in such a way that any who has no knowledge of brazing and soldering before can understand.
Also, justice is done in the explanation of soldering technique. The processes that are involved in the technique include cleaning and aligning, selection, and heating and soldering. Note that these steps could be split into other headings by different authors but all speak the same language at the end.
- Brazing by Mel Schwartz
- Metallurgy of Welding by J.F Lancaster
- Principles of Brazing by David M. Jacobson, Giles Hampton
- Brazing and Soldering: Preceding of the Third International Brazing and Soldering Conference, edited by John, J. Stephens
- Soldering Technique by W. E Olmon et. Al
- How to Braze Properly by Lucas-Milhaupt
This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.
© 2014 Okwuagbala Uzochukwu Mike P