أنواع لحام القوس الكهربيِ بطريقه مختصره

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أنواع لحام القوس الكهربيِ بطريقه مختصره

مُساهمة من طرف ENG_3ALIM في الأحد مارس 16, 2008 11:35 pm

Arc Welding Types


Shielded-Metal Arc Welding



/Shielded-Metal Arc Welding (SMAW) is one of the oldest, simplest, and most versatile arc welding processes. The arc is generated by touching the tip of a coated electrode to the work piece and withdrawing it quickly to an appropriate distance to maintain the arc. The heat generated melts a portion of the electrode tip, its coating, and the base metal in the immediate area. The weld forms out of the alloy of these materials as they solidify in the weld area. Slag formed to protect the weld against forming oxides, nitrides, and inclusions must be removed after each pass to ensure a good weld.

The SMAW process has the advantage of being relatively simple, only requiring a power supply, power cables, and electrode holder. It is commonly used in construction, shipbuilding, and pipeline work, especially in remote locations.



Gas Metal-Arc Welding



Gas Metal-Arc Welding (GMAW), also called Metal Inert Gas (MIG) welding, shields the weld zone with an external gas such as argon, helium, carbon dioxide, or gas mixtures. Deoxidizers present in the electrode can completely prevent oxidation in the weld puddle, making multiple weld layers possible at the joint.

GMAW is a relatively simple, versatile, and economical welding apparatus to use. This is due to the factor of 2 welding productivity over SMAW processes. In addition, the temperatures involved in GMAW are relatively low and are therefore suitable for thin sheet and sections less than ¼ inch.

GMAW may be easily automated, and lends itself readily to robotic methods. It has virtually replaced SMAW in present-day welding operations in manufacturing plants.




Electroslag Welding



Electroslag Welding (ESW)deposits the weld metal into the weld cavity between the two plates to be joined. This space is enclosed by water cooled copper dams or shoes to prevent molten slag from running off. The weld metal is produced from a filler wire that forms an initial arc with the workpiece until a sufficient pool of liquid metal is formed to use the electrical resistance of the molten slag.

This process requires special equipment used primarily for horizontal welds of very large plates up to 36 inches or more by welding them in one pass as in large machinery and nuclear reactor vessels.

There are also variations of ESW where shielding is provided by an appropriate gas and a continuous arc is used to provide weld metal. These are termed Electro gas Welding or EGW machines.

Fluxed-Core Arc-Welding



[/url]Fluxed-Core Arc-Welding (FCAW) uses a tubular electrode filled with flux that is much less brittle than the coatings on SMAW electrodes while preserving most of its potential alloying benefits.

The emissive fluxes used shield the weld arc from surrounding air, or shielding gases are used and nonemissive fluxes are employed. The higher weld-metal deposition rate of FCAW over GMAW (Gas Metal Arc Welding) has led to its popularity in joining relatively heavy sections of 1" or thicker.

Another major advantage of FCAW is the ease with which specific weld-metal alloy chemistries can be developed. The process is also easily automated, especially with the new robotic systems.
Plasma Arc Cutting



Plasma arc cutting can increase the speed and efficiency of both sheet and plate metal cutting operations. Manufacturers of transportation and agricultural equipment, heavy machinery, aircraft components, air handling equipment, and many other products have discovered its benefits.

Plasma cutters are used in place of traditional sawing, drilling, machining, punching, and cutting. The high-temperature plasma arc cuts through a wide variety of metals at high speeds. Although plasma arc cutting can cut most metals at thicknesses of up to 4 to 6 inches, it provides the greatest economical advantages, speed, and quality on carbon steels under 1 inch thick, and on aluminum and stainless steels under 3 inches thick.

Plasma arc cutting has gained approval in both hand-held and automated cutting operations. Some of the most impressive results are achieved in automated systems. Advances in computer numerical controls (CNC), robots, and other automation techniques have offered manufacturers higher cutting speeds achieved through plasma arc cutting. Improved torch designs and more efficient power supplies have made plasma arc cutting increasingly popular.

New areas of technology in plasma arc cutting systems include non-transferred arc plasma, which allows plastics and other nonconductive materials to be cut. Research on cutting plastics is continuing and at least one commercial process is currently available.
Plasma Arc Cutting Advantages



[/url]Automated plasma arc cutting systems provide several advantages over other cutting methods such as oxyfuel and laser.
Rapid Cutting Speeds:
Plasma arc cutting is faster than oxyfuel for cutting steel up to 2 inches thick and is competitive for greater thicknesses. Plasma cutting achieves speeds greater than those of laser cutting systems for thicknesses over 1/8 inch. CNC controls allow speeds of up to 500 inches per minute (ipm) to be achieved on gauge thicknesses. These fast cutting speeds result in increased production, enabling systems to pay for themselves in as little as 6 months for smaller units.
WideRange of Materials and Thicknesses:
Plasma cutting systems can yield quality cuts on both ferrous and nonferrous metals. Thicknesses from gauge to 3 inches can be cut effectively.
Easy to Use:
Plasma cutting requires only minimal operator training. The torch is easy to operate, and new operators can make excellent cuts almost immediately. Plasma cutting systems are rugged, are well suitable for production environments, and do not require the potentially complicated adjustments associated with laser cutting systems.

Economical:
Plasma cutting is more economical than oxyfuel for thicknesses under 1 inch, and comparable up to about 2 inches. For example, for ½ inch steel, plasma cutting costs are about half those of oxyfuel.

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مُساهمة من طرف ENG_3ALIM في الأحد مارس 16, 2008 11:38 pm

Plasma Arc Cutting Applications



Automated plasma cutting systems are being chosen over oxyfuel, hand tools, and laser cutting in the following areas:
Sheet Metals
Plasma cutting is commonly used to cut sheet metals from 24 gauge up to 1/8 inch thick at high speeds on carbon steels, aluminum, and stainless steels.



  • Plasma cutting is widely used in the transportation industry to form the outer skins of tractor trailers, buses, and agricultural equipment.

  • Plasma cutting systems are also used in the heating, ventilating, and air conditioning industry to cut complex duct work.


Plate Thicknesses
Industries involved in cutting plate thicknesses also find many applications for plasma cutting. Plasma systems cut plate thicknesses from 1/8 to 3 inches, but the most common applications are for carbon steel plate ¼ to ¾ inch thick.



  • Steel service centers cut large plates of steel down to size with plasma.

  • Makers of large construction machinery, mining equipment, and material handling equipment utilize plasma cutting to produce cranes, bulldozers, and other large equipment.

  • Plasma cutting also produces structural steel framework for railroad cars, trucks, and other heavy equipment.

  • Other applications include cutting metal for ship building and the production of pressure vessels.


Other Applications
Plasma cutting is not limited to flat sheets of metal. Plasma torches placed on robots are being used increasingly for contour cutting of pipes and vessels, removal of sprues and risers from castings, and cutting of formed shapes, angles, and curves in various planes.
Plasma Arc Cutting Economics


Capital Costs
Plasma cutting equipment includes a power supply, torch, and torch leads. Equipment costs are greater than for oxyfuel cutting, but are offset by the ability to cut aluminum and stainless steels and to achieve high speeds on carbon steels. Additional equipment needed to automate a cutting operation can range from $3,000 for a simple X/Y machine to $350,000 for an entire automated system.

Operating Costs
Operating costs for plasma cutting on ¼ in. steel are approximately 7 cents per foot. This includes power costs, labor costs, and the cost of plasma gases. The nozzle and the electrode in the plasma torch are consumed in the cutting process. The life of these parts varies greatly. When using nitrogen as the cutting gas, part replacement is typically required every 4 to 8 hours of arc time. For air-plasma systems, the nozzle and electrode may need to be replaced approximately every 1 to 2 hours of arc time. The cost of these replacement parts is typically under $15 for low-power, 40 amp systems and up to $40 for high-power, 1000-amp systems. Replacement parts can be installed in minutes by the operator.



Plasma Arc Cutting Technical Considerations



Although plasma cutting is desirable for many metal-cutting applications, analyze your specific application before choosing a cutting method. This decision depends primarily on the material cut, thickness, desired cutting speed, intricacy, and quality.
Material Type
Carbon steels, aluminum, and stainless steels are most commonly cut with plasma arc. Many other metals may be cut with plasma including nickel alloys, brass, bronze, tungsten, copper, cast iron, titanium, and zirconium.
Material Thicknesses and Cutting Speeds
Workpiece thickness determines whether plasmas cutting speeds will be cost effective for your application. However, the maximum cutting speed depends not only on thickness but also on power supply and material type. The table shown here illustrates representative cutting speeds on various thicknesses of aluminum, stainless steels, and carbon steels.

Cut Quality
Cut quality is affected by type of metal and cutting speed. Process variables, such as cutting gas, power, and cutting speed are adjusted to provide the optimum cut for each metal type. Although the size of the power supply is also a factor, cuts in metals up to 2 in. thick tend to be smooth while cuts in thicker sections may be rougher but still clean.
Cutting Specifications
For applications where high-quality cuts are needed, determine your requirements for a) tolerances, b) amount of bevel, c) dross, and d) heat-affected zone

Plasma cuts to closer tolerances than flame processes like oxyfuel because of the faster cutting speeds heat the workpiece less, resulting in less distortion. Plasma is capable of tolerances to 1/32 in. in materials under ½ in., but the tolerances achieved depend on material type, thickness, and power supply.

Plasma cutting produces a beveled cut, forming a wider cut at the top of the workpiece than at the bottom. The bevel can easily be corrected or reduced with special techniques or equipment. Generally the amount of bevel is less for thinner materials. The amount of dross or oxidation on the surface of the workpiece depends mainly on cutting speed, type of gas, and arc voltage. Using the manufacturers guidelines for these variables can produce dross-free cuts. The high speeds of plasma cutting minimize the amount of distortion and heat-affected zone (HAZ). HAZ width is affected by material type and thickness, conductivity, and torch design.
[
[/url]Cutting Gases
The cutting gas selected depends on the speeds and quality of cut desired. Several cutting gases can be used in a plasma system to improve cut quality and speed. Nitrogen is widely used because it is relatively inexpensive and can be used on many materials and thicknesses. Special mixtures of argon and hydrogen can improve cutting speed and quality on thicker metals and those other than carbon steels. Oxygen is used in combination with other gases to improve cut quality by increasing heat, improving cutting speed, and/or reducing power requirements. Compressed shop air is popular for many applications because it is inexpensive and provides good quality cuts on thicknesses under 1 in., especially on carbon steels.
Power Supply
The power supply required depends on the material thickness and cutting speeds desired. Increasing the power increases the cutting speed or enables thicker metals to be cut without slow down. Power ratings are commonly between 20 and 200 kW.
Plasma Arc Cutting Environmental Concerns



Ultraviolet radiation, particle matter, and noise are hazards of plasma arc cutting, but these are manageable with the proper equipment. Water is often used to control these hazards, in the form of a water table, a water muffler, or underwater cutting. One of these devices is recommended for most automated applications.
Submerged Arc Welding



[/url]Submerged Arc Welding (SAW) shields the weld arc using a granular flux fed into the weld zone forming a thick layer that completely covers the molten zone and prevents spatter and sparks. It also acts as a thermal insulator, permitting deeper heat penetration.

The process is obviously limited to welding in a horizontal position and is widely used for relatively high speed sheet or plate steel welding in either automatic or semiautomatic configurations. The flux can be recovered, treated, and reused.

Submerged Arc Welding provides very high welding productivity....4-10 times as much as the Shielded Metal Arc Welding process.
Gas Tungsten-Arc Welding



[Gas Tungsten-Arc Welding (GTAW), also known as Tungsten Inert Gas or TIG welding, uses tungsten electrodes as one pole of the arc to generate the heat required. The gas is usually argon, helium, or a mixture of the two. A filler wire provides the molten material if necessary.

The GTAW process is especially suited to thin materials producing welds of excellent quality and surface finish. Filler wire is usually selected to be similar in composition to the materials being welded. Atomic Hydrogen Welding (AHW) is similar and uses an arc between two tungsten or carbon electrodes in a shielding atmosphere of hydrogen. Therefore, the work piece is not part of the electrical circuit

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رد: أنواع لحام القوس الكهربيِ بطريقه مختصره

مُساهمة من طرف Argon في الإثنين مارس 17, 2008 4:06 pm

موضوع جميل يا احمد منك كالعادة Very Happy

Argon
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رد: أنواع لحام القوس الكهربيِ بطريقه مختصره

مُساهمة من طرف ENG_3ALIM في الإثنين مارس 17, 2008 8:19 pm

شكرا يا ارجون على مرورك

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رد: أنواع لحام القوس الكهربيِ بطريقه مختصره

مُساهمة من طرف حسن المهندس في الثلاثاء مارس 18, 2008 12:02 pm

وكما عودتنا
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تسلم

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