Plasma Transferred Arc Welding.
Plasma-transferred arc welding (PTA welding) is a thermal process for applying wear and corrosion resistant layers on surfaces of metallic materials. The highly energetic plasma arc melts the surface of the base material. At the same time, the powdery filler material is inserted into the arc and also molten. During solidification, a substance-to-substance bond between the filler material and the base material is created.
Metal parts often fail their intended use not because they fracture, but because they wear, which causes them to lose dimension and functionality. Hardfacing, also known as hardsurfacing, is the application of buildup or wear-resistant weld metals to a part’s surface by means of welding or joining.
Carbon and low-alloy steels with carbon contents of less than 1 percent can be hardfaced. High-carbon alloys may require a special buffer layer.
The following base metals can be hardfaced:
• Stainless steels
• Manganese steels
• Cast irons and steels
• Nickel-base alloys
• Copper-base alloys
Various welding techniques can be used, including metal-inert gas (MIG), tungsten-inert gas (TIG), plasma transferred arc (PTA), submerged arc (SAW) and manual metal arc (MMA). A very broad range of coating materials can be applied.
Wear is such an all-encompassing term. Can it be broken down into more manageable categories?
Many different categories of wear exist—too many to cover in one article—but the most typical modes of wear are as follows (percentages are estimates of total wear):
• Abrasion—40 percent
• Impact—25 percent
• Metallic (metal to metal)—10 percent
• Heat—5 percent
• Corrosion—5 percent
• Other—5 percent
Most worn parts don’t fail from a single mode of wear, such as impact, but from a combination of modes, such as abrasion and impact. For example, a mining bucket tooth usually is subjected to abrasion and impact, and depending on what type of material is mined (soft or hard rock), one mode may be more dominant than another. This will dictate the welding product used.
Determining the wear mode can be challenging and may require trial and error when you select hardfacing products.
It depends on the hardfacing alloy. Many chromium carbide alloys check-crack when cooled to moderate temperatures; this is normal. Others, such as the austenitic and martensitic families, don’t crack when applied with proper welding procedures.
Complex carbides generally are associated with the chromium carbide deposits that have additions of columbium, molybdenum, tungsten, or vanadium. The addition of these elements and carbon form their own carbides and/or combine with the present chromium carbides to increase the alloy’s overall abrasion resistance. They can have all of these elements or just one or two. They are used for severe-abrasion or high-heat applications.
As a rule, you should bring all parts at least to room temperature. You can select higher preheat and interpass temperatures based on the base metal chemistry and hardfacing product you’re using.lications.
Manganese and some stainless steels and similar hardfacing products require no preheating, and welding temperatures should be kept as low as possible. Other steels usually require proper preheat and interpass temperatures. You should consult the manufacturer for the best combination to prevent cracking and spalling.
Limited-layer products usually are in the metal carbide families, such as chromium carbide and tungsten carbide. You can apply martensitic and austenitic products in unlimited layers unless the manufacturer specifies otherwise.
The brittle nature of the metal carbides leads to check-cracking, and as multiple layers are applied, stress continues to build, concentrating at the root of the check cracks, until separation or spalling occurs between the parent metal or buffer and the hardfacing deposit.ns.
The plasma arc welding process, which is very similar to gas tungsten arc welding, was invented by Robert Gage in 1957. Plasma arc welding uses a constricted arc or an arc through an orifice, which creates an arc plasma that has a higher temperature than the tungsten arc. By the 1960’s Plasma Transferred Arc welding (PTAW) was developed by the NASA programme. This is essentially the same technology that is used today.
What’s the difference between PTAW Hardfacing and other technologies?
A number of very important differences exist. The key is that this technology creates a metallurgical bond that penetrates the substrate.
It is important to understand what type of wear issues the mine is experiencing. The more information we obtain at an early stage the easier it is to provide a viable solution. Plasma Hardfacing works with our powder suppliers and the maintenance engineers to select the correct matrix based on how the machinery is wearing. There are many different powder options available which suits a wide variety of wear issues. If none of the powders are suitable our powder suppliers can also blend a customised powder mix to suits your needs.ate.
It is important to understand what type of wear issues the mine is experiencing. The more information we obtain at an early stage the easier it is to provide a viable solution. Plasma Hardfacing works with our powder suppliers and the maintenance engineers to select the correct matrix based on how the machinery is wearing. There are many different powder options available which suits a wide variety of wear issues. If none of the powders are suitable our powder suppliers can also blend a customised powder mix to suits your needs.
If the mine does not have a specific requirement on which powder they require for their machinery Plasma Hardfacing will visit the site and meet with the Maintenance Managers to determine the best wear solution. We provide key data on the powder matrix and how it deals with the wear i.e. corrosion, impact, abrasion etc. How the powder is applied is also discussed so that the key wear points have the protection to ensure the machinery is protected. No work commences until you are satisfied with the powder selection and application design.
This can depend on the particular item we are welding and also the particular type of Hardfacing solution that is required. Our aim is to ensure that we not only increase the lifespan of your product but drastically reduce the cost of GET parts by providing a cost effective price.
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If we do not deliver you cost savings we will refund you money. No questions asked.