Negrican Sandalcı 030070084 7th Week

Hard Facing

(OLD)

Hardfacing is defined as the process of obtaining desired properties or dimensions by applying, using oxyfuel or arc welding an integral layer of metal of one composition. The hardfacing operation makes the surface highly resistant to abrasion.
There are various techniques of hardfacing. Some apply a hard surface coating by fusion welding. In other techniques, no material is added but the surface metal is changed by heat treatment of by contact with other materials.
(Jeffus L.F, Welding: Principles and Applications, 5th Edition p.708)

( NEW /BETTER )

Hardfacing is the application of a hard, wear-resistance coating by welding,  thermal spraying or similar process. Hardfacing is used to improve wear resistance of new components and to repair and rebuild worn parts. Hardfacing material is applied either in powder form, as solid welding rods, or as tube rods.

A wide variety of proprictary alloy powders are employed inhardfacing and thermal spraying to provide protection from wear or loss of material by galling, abrasion, crosion or corrosion. Powders are particulary suited to this application because of the possibility of tailoring the composition of the hardfacing alloy to obtain specific improvements. Many of these alloys cannot be produced by convention methods because the alloy compositions present fabrication difficulties.

(Joseph M Capus, Metal Powders: A Global Survey of Production, Applications And Markets 2001-2010, p.4 )

 

Stud Welding

 

(OLD)

Stud Welding is a semiautomatic or automatic arc welding process. An arc is drawn between a metal stud and the surface to which it is to be joined. When the end of the stud and the underlying spot on the surface of the work hace been properly heated, they are brough togetter under pressure.

(Welding: principles and applications, L. F. Jeffus, p.708)

(NEW / BETTER)

Stud welding can be described as the joining of a metal stud to another metal workpiece by means of are, resistance friction or other appropriate welding process.

The stud weld symbol is always shown placed below the reference line, with the arrow of the welding symbol pointing to the surface to which the stud is to be welded. An arrow side significance is applied to the symbol. However it is not used with an other side or both sides significance.

( A. E. Bennett,Louis J. Siy, Blueprint Reading for Welders, p.235 )

 

Electroslag Welding

 

(OLD)

 Electroslag welding (ESW) uses the same-basic equipment as some of the arc-welding processes, and it utilizes an arc to initiate the welding operation. However, it is not an AW process because an arc is not used during welding. Electroslag welding (ESW) is a fusion-welding process in which coalescence is achieved by hot, electrically conductive molten slag acting on the base parts and filler metal. As shown in Figure 31.24, the gen­eral configuration of ESW is similar to electrogas welding. It is performed in a vertical orientation (shown here for butt welding), using water-cooled molding shoes to contain the molten slag and weld metal. At the start of the process, granulated conductive flux is put into the cavity. The consumable electrode tip is positioned near the bottom of the cavity, and an arc is generated for a short while to start melting the flux. Once a pool of ' slag has been created, the arc is extinguished and the current passes from the electrode to the base metal through the conductive slag, so that its electrical resistance generates heat to maintain the welding process. Since the density of the slag is less than that of the molten metal, it remains on top to protect the weld pool. Solidification occurs from the bottom, while additional molten metal is supplied from above by the electrode and the edges of the base parts. The process gradually continues until it reaches the top of the joint.

 (Mikell P. Groover,Fundamentals of Modern Manufacturing,4th Edition,pg.728)

( NEW / BETTER )

Electroslag welding (ESW ) process is not a true arc welding process. The energy for  melting the base metal and filler is provided by a molten bath of slag that is resistance heating by the welding  current. An arc is employed only to melt the flux initially, after being struck at the bottom of the joint. Welds are produced in the vertical up direction, with the joint edges being melted and fused by molten weld filler metal contained in the joint by water cooled dams or shoes, as shown in Figure.  The molten flux or slag provides excellent protection to the weld.

Deposition rates are typcially 7- 13 kg. per hour per electrode, and multiple electrodes can be employed. In the guide tube mode of this process, a consumable, thick walled tube is employed to provide additional filler and guide the continuous wire to the bottom of the joint. Here, deposition rate can easily reach 15- 25 kg. per hour per electrode tube.

Neither electro gas nor electroslag welding is widely practised in the US,  although borth are practised elsewhere, especially in the former Soviet States.

( Robert W. Messler, Principles of Welding: Processes, Physics, Chemistry, and Metallurgy, p.70 )

 

Oxyacetylene Welding

 

(OLD)

Oxyfuel welding is the process that uses the heat from a gas flame to melt base materials and cause them to join together. The gas flame is created by the combustion of oxygen and a fuel gas which is usually acetylene. Oxygen and acetylene burn in a neutral flame at a temperature between 5600 F and 6300 F, the hottest of any gas flame and capable of melting most metals. Other oxygen-fuel gas combinations are hot enough to use for soldering and brazing, but not hot enough for welding. Oxyfuel welding with acetylene is called oxyacetylene welding, but it is often simply referred to as gas welding.

(Creative Publishing International, Welding Basics: An Introduction to Practical & Ornamental Welding, p.26)

 

( NEW / BETTER )

Oxygen gas welding, commonly known as oxyfuel or oxyacetylene welding may also be perfomed with such fuels as natural gas, propane and propylene.  It involves melting the base plate and filler metal with a welding torch flame. The fuel gas and oxygen are mixed in the proper proportions in a mixing chamber. Molten meta from the groove faces intermixes with the filler metal and upon cooling  forms a continuous deposit.

 

Oxyfuel welding is most typically used to fabricate thin materials, such as sheet metal and thin wall pipe or tubing. Oxyfuel processes are also used for repair work and metal cutting. One advantage of oxyfuel welding is taht the equipment and operating costs are less than with other methods.

 

 

( David A. Madsen, Engineering drawing and design, p.694 )

 (ASM International. Handbook Committee, Cast Irons, p.3 )

                                                                

 

Furnace Brazing 

 

(OLD)

The popularity of furnace brazing derives from comparatively low cost of equipment, the adaptability of the furnace, and the minimal jigging required. With many brazing assemblies, the weight of the parts alone is sufficient to hold them together. With other configurations, one or two rectangular blocks of metal are all fixturing needed.
Furnace brazing is used extensively where parts to be brazed can be assembled with the brazing filler metal preplaced near or in the joint.
Furnace brazing is used extensively when:
the parts to be brazed can be preassembled or jigged to hold them in correct position;
the brazing filler metal can be placed in contact with the joint;
multiple brazed joints are to be formed simultaneously on a completed assembly;
many similar assemblies are to be joined;
complex parts must be heated uniformly prevented the distortion that would result from local heating of the joint area
(Schwartz M.M.,Brazing, for the engineering technologist, 2003, p.59)

 

(NEW / BETTER)

Almost all furnace brazing of stainless steel is done in protective atmosphere. One exception is the application described, in which air was the furnace atmosphere. In this case a liquid flux was used and the time at brazing temperature was short which helped to prevent excessive oxidation.

 

The low cost exothermic atmospheres that are widely used in furnace brazing of low-carbon steel are not suitable for stainless steel.

 

 (ASM International. Handbook Committee, Stainless Steels, p.408 )