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Problem: Heavy Duty Wear Protection (Slurry Pumps and Mixer Blades)

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Pumping fluids containing large concentrations solids is extensively practiced in industry. However, this practice can severely erode components that are used to move these materials. Hard materials attached to high wear surfaces, have been used to resist such erosion damage. These hard materials have typically been clad on to surfaces via co-forming, polymer cements, brazing and or welding, depending on the service temperatures and environments. The most widely used technique is welding, but many times welding can crack or distort the underlying components and only yielding Ľ 25 volume % hard particles.

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Mixer parts are similar to slurry pump components in that mixers are move slurries, agglomerate mixes, highly loaded "plastic" compounds, and other particulate media. The mixer blades are exposed to low angle erosive action or abrasion as the mixers run against container walls and high frequency impact from large, hard particles. Thus, other coating/cladding processes are needed to assure improved wear resistance. These new coating must be metallurgically bonded, able to cover contoured flow surfaces, and have a high hard particle content, while being able to coat sharply contoured and re-entered surfaces of components.

Solution: BrazeCoat -M or S

BrazeCoat -M and BrazeCoat -S. mats and suspension coatings are applied to a wide variety of contoured surfaces. The different types of BrazeCoat coatings enable its application in a wide range of environments and on a range of compatible base materials. BrazeCoatģ M (mats) are able to be cut, placed and fused to large and small surfaces. BrazeCoat -S (suspensions) can be sprayed or applied by dipping to cover even the complex surface contours of impellers. BrazeCoat is proven in erosive and abrasion with WC grades being superior to the best flame spray and fuse coatings and having at least 4 times more erosion resistance than white cast iron. BrazeCoat offers tailored thicknesses, hardness and coating thicknesses, dependent on the need. The coatings are easily applied and fused during post application furnace, treatments. The resultant metallurgical bonds assure excellent adherence, even in the most abrasive and erosive environments.

Additional Protection for Drilling Tools

Rock drilling equipment is normally protected against wear via the use of carbide (WC) and/diamond inserts brazed into the cutting edges. During drilling, these cutting edges remove and crush the rock and soils as they pass by the drilling bit’s non-cutting surfaces. Away from the cutting edges, the tool bit surfaces still wear quicker than the cutting edges themselves. This reduces the tool life and limits the useful life of the carbide or diamond inserts. Weld overlays and thermal spray coatings have been applied, but their variable quality and process control lower their reliability as a solution.

Solution: BrazeCoat -M or S

BrazeCoat -M and BrazeCoat -S are very hard, coatings produced from mats and suspension, respectively, consisting of a high volume percent tungsten carbide (WC) and/or chromium carbides (Cr3C2). Either product can be used to coat contoured surfaces. The BrazeCoat process utilizes a mat or suspension of carbide particles that are subsequently infiltrated with an adjacent cloth or suspension of a braze filler powders. The mats, up to 0.120" thick are applied directly onto the fitting surfaces to be protected. While the suspensions, typically sprayed on to Ľ 0.012" thick, coat more difficult tool surface geometries. Infiltration, fusion and metallurgical bonding of the BrazeCoat layers is accomplished in one step by heating in vacuum or H2 atmospheres. Once the fusion treatment is completed, the BrazeCoat coatings exhibit wear behavior near that of cemented carbides and protects longer and more consistently than welded or thermal spray coatings.

Problem: Protecting Turbine Blades (Z-Forms)

Turbine and other turbo-machinery blades, have the tendency to vibrate and therefore require stiffening and support. Many times this is accomplished by providing an integral ring located either at the blade tips and/or mid-span. These rings must be split to reduce fatigue cracking. However, the ring segments, typically machined or cast into each blade, must run and vibrate against the other blades’ ring segment. The segments interlock as "Z" forms where on adjacent "Z" surfaces highly wear resistant coatings are required to prevent premature failure through fretting fatigue or impact fatigue.

These coatings require high hardness, toughness, excellent bonds and good oxidation resistant since, for turbine blades the temperature could exceed 1800įF. These highly stressed coatings and blade areas require high performance and reliable coatings.

Currently, thermal spray and weld claddings are used. These methods perform with varying degrees of success and many times are expensive.

Solution: BrazeCoat -M

BrazeCoat -M using Cr3C2 carbides is a good cladding candidate to replace either thermal spray coatings or weld overlay done by plasma transferred arc or laser. The turbine blade base materials are typically highly alloyed nickel based materials which can easily crack when welded. Hence, welding processes have to localize and minimize the heat effects. Thermal spray, on the other hand is not material efficient due to the narrow edges to be coated and does not readily achieve metallurgical bonds. Thus, thermal spray coatings exhibit high occurrences of coating debond. BrazeCoat -M, eliminates many of these problems. Importantly, the mats can be cut to the size and geometry of any edge, are processed in a thermally and environmentally controlled atmosphere, and metallurgically bond to the blade materials. Compared to either weld overlays or thermal spray claddings, BrazeCoat ’s NiCrBSi matrix Cr3C2 filled claddings exhibit improved wear resistance based on its improved bonds and higher, more uniform carbide distributions.

For additional case histories of how MRi’s BrazeCoat has solved cladding or wear prevention problems: e-mail: rsmith@materialsresources.com

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e-mail: rsmith@materialsresources.com