Kermetico HVAF and HVOF provide effective erosion, corrosion and abrasive wear resistant coatings for pump impellers and casings.
Kermetico HVAF thermal spray systems deposit ductile, high-bond tungsten carbide pump coatings harder than 1,600 HV300.
We would like to share our experience in wear protection and repair coating of pump impellers.
Abrasive Wear, Cavitation and Corrosion of Pump Impellers
Media flowing through pumps is frequently loaded heavily with abrasive substances, like sand or silt. In the pump, these substances move through all the fluid channels, the sidewalls of the impellers and all the close running clearances.
Areas with high flow velocities, such as the narrow labyrinths, are exposed to the most severe abrasive wear.
If the size of the particles is less than the labyrinth clearance, the particles move freely and impact the wall at a shallow angle. The result is erosive wear.
If the particles are of the same size as the close running clearances, they jam between the two walls which cause severe three-body abrasion (abrasive particle and two walls making three bodies).
Under unfavorable circumstances of corrosive media, the combined effect of corrosion, cavitation and erosion can lead to dramatically increased wear rates.
Surface Treatment to Protect Centrifugal Pump Parts from Wear
Carbide coatings deposited by using different high velocity technologies (HVOF, HVAF, Detonation), are extremely wear-resistant. Industry uses tungsten carbide in combination with cobalt, nickel or cobalt-chrome matrices preferably.
The erosion and corrosion behavior of thermal spray coatings is a major factor for the assessment of the pump coating application.
We use our Kermetico HVAF equipment to deposit tungsten carbide coatings that are wear-resistant and tough enough to be used at all angles of impingement. Unlike epoxy coatings, even 100 microns (0.004”) of our tungsten carbide coating is gas-tight, protecting an impeller base metal from corrosive agents as a barrier coating.
WC-CoCr-bound powders exhibit the highest wear resistance coupled with an adequate corrosion resistance in any environment except very high pH conditions or hydrofluoric acid.
Since 2006 we have sprayed many different impeller and case rings for both new and repair work, in our job shop, and most of them have never been returned to us. They are still in service.
Our customer and partners in the USA, Europe and China have sprayed many pump impellers.
Why do we think that a pump impeller could work for ten years or more?
Because our Kermetico HVAF equipment lets us spray superior coatings.
A Comparison of Abrasive Wear and Erosion Protection Properties of HVOF and Kermetico HVAF Pump Coatings
Slurry erosion test, courtesy of Schlumberger.
This test compares an Economy mode a Kermetico HVAF tungsten carbide coating to the same material deposited by industry-leading HVOF and detonation systems.
The two following charts are courtesy of the Central Power Research Institute of India.
Could the reason for this result be that we are comparing ourselves to less than the best available coating equipment?
You may also be interested in a comparison of Kermetico HVAF WCCoCr coatings with one of the most advanced HVOF systems on the market.
Are you interested in how our HVAF Balanced and Ultra modes provide such superior results?
A Scientific Research of Wear and Corrosion Properties of Kermetico HVAF Coatings
As Prof. Wang has shown in his article “Wear and corrosion performance of WC-10Co-4Cr coatings deposited by different HVOF and HVAF spraying processes”:
“Three WC-10Co-4Cr coatings were deposited by HVOF and HVAF processes, and their microstructure and properties were investigated in this study. The following conclusions were drawn as a result.
(1) The WC-10Co-4Cr coating deposited by the HVAF spraying process exhibited nearly the same phase composition as its initial feedstock powder, which included mainly the WC and some Co3W3C and crystal Co phases with nearly no decarburisation. The JK coating sprayed with Jet Kote III-HVOF equipment exhibited the most severe decarburisation with high-intensity W2C and even metallic W phase. The phase composition of the JP coating deposited by the JP8000-HVOF system was composed of main WC and minor W2C peaks and exhibited a light degree of decarburisation.
(2) The wear resistance and mechanism of the HVOF/HVAF-sprayed coatings were influenced not only by their hardness but also by their fracture toughness. The high hardness of carbide coating could effectively hinder the cuts caused by the abrasives, and their high toughness could make the binder absorb some of the energy caused by abrasive attacks with some degree of plastic deformation.
(3) The WC-10Co-4Cr coatings, which had different degrees of decarburisation, exhibited different dominant wear mechanisms.
(4) The electrochemical corrosion resistances and mechanisms of HVAF- and HVOF-sprayed WC-10Co4Cr coatings were influenced by their phase compositions and microstructures.”
Scientists tell us that HVAF provides better wear and erosion resistance than HVOF. But a lot of companies still use HVOF to protect pumps and other equipment.
Why is that?
Maybe HVAF is too expensive?
The Economic Aspects of the Kermetico HVAF Coatings
The list price of equipment is lower than the price of good HVOF equipment.
A comparison of HVAF and HVOF cost per kilogram of deposited WC-10Co-4Cr (prices in Texas, USA, the price of tungsten carbide is $81 per kg).
With Kermetico HVAF thermal spray systems we are not limited to the “best coating possible.”
We can choose how to spray a tungsten carbide coating:
- save money spraying in HVAF economy mode, getting HVOF quality with lower costs;
- spray the highest coating quality in HVAF Ultra mode to achieve high hardness, ductile, non-porous, abrasion and cavitation resistant coatings;
- or choose HVAF Balanced mode to gain a competitive edge in both cost and quality.
But it’s not the end of the story.
Blast and Spray Pump Impellers with Kermetico HVOF and HVAF Equipment
We recommend depositing pump impeller coatings using robotic blast and spray operations.
We blast an impeller surface with a Kermetico HVAF gun (it is extremely fast and uniform) and spray with the same gun after switching the powder feed hose and perhaps changing the nozzle
It is much faster, more accurate and consumes much less grit than manual blasting.
Hot blasting also provides very even impeller’s surface preparation and induces less stress into the base metal.
Kermetico HVAF Thermal Spray Coating Equipment for Impellers
Kermetico designs and manufactures three families of HVAF and HVOF thermal spray equipment.
Convertible HVOF and HVAF equipment:
- C7 – an HVAF/HVOF gun for large parts
- C6 – a general purpose HVAF-HVOF gun
- CID – internal diameter HVAF-HVOF system recommended for pump sleeve coatings
Multi-purpose HVAF AK systems, with a variety of spray guns:
- AK7 – a high-power gun for the thermal spray of large parts
- AK6 – a gun to spray tungsten and chromium carbide – recommended for pump impellers
- AK5 – a compact gun to spray smaller parts, thin walls and complex surfaces – recommended for wear rings
- AK-ID – an 80 mm (3.15”) and larger internal diameter spray gun
- AK-IDR – a rotating ID gun to spray 4” (100 mm) and larger bores
- AK-HH – a handheld gun for on-site coating
- A Grit Feeder for the grit blast preparation of parts to reduce coating cost
- A Gas Permeability Tester for an instant check of a coating’s through porosity
- A Powder De-Duster to screen fine particles from a metallic powder
Kermetico, Inc. – Material Science Excellence, HVAF and HVOF Equipment Manufacturing and Thermal Spray Coating Services Since 2006
We create equipment that helps material scientists, engineers and business managers achieve their goals.
We have installed more than 60 Kermetico HVAF and HVOF systems in the USA, Europe, Japan and China.
Some of the systems are at work in Universities and National Labs, but most of them work in production thermal spray shops.
We proudly design and produce our thermal spray equipment in California and install it all over the world.
You can visit our R&D center in Benicia to meet our designers and see our HVAF and HVOF equipment in action.
We also service customers in the U.S.A. with HVAF and HVOF thermal spray coatings – ourselves and through the network of our partners.