Kermetico HVAF equipment provides an effective way to protect augers and screws from corrosion and abrasive wear.
Kermetico HVAF thermal spray systems deposit ductile, high-bond, thick tungsten carbide coatings harder than 1,600 HV300.
Our gas impermeable HVAF screw coatings are superior to any other thermal spray technology in wear protection of injection and extrusion screws and transport augers.
Want to know why?
The Abrasive Wear of Screws and Augers
Transport screws are efficient systems for material handling. In addition to conveying of solid, semi-solid, wet and sticky materials, they are also used in production processes for drying, cooling and mixing. These processes cause extensive wear damage to the screw/auger flights and shafts.
Unprotected equipment could fail, causing a loss in productivity and expensive repairs.
Abrasive wear is probably the most common type of wear in the plasticating unit. If abrasion is allowed to continue unchecked, it will result in a gradual decrease in machine performance and, eventually, complete failure. In abrasive wear, the most common culprits are the fillers and additives in the resin.
Corrosion attacks the metal surface even when the machine is not in operation.
It breaks down the metal surface and renders it more susceptible to mechanical wear. Resins that have chlorinated and fluorinated components, such as PVC and PTFE, are very corrosive. Even a material that normally is not corrosive by nature can degrade under inappropriate screw design and a corrosive environment.
The best defense against corrosion and wear is the proper component material selection and the use of wear and corrosion resistant coatings.
A Surface Treatment to Protect a Screw from Corrosion and Wear
Carbide coatings deposited by using different high velocity technologies (HVOF, HVAF and Detonation), are extremely wear-resistant. The industry uses tungsten carbides 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 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.
We recommend WC-CoCr-bound powders because they exhibit the highest wear resistance coupled with an adequate corrosion resistance in any environment except very high pH environments or hydrofluoric acid. Even 100 microns (0.004″) of our WCCoCr coating is gas-tight, protecting a base metal of a screw from corrosive agents as a barrier coating.
Since 2006 we have sprayed numerous different screws and augers for both new and repair work in our job shop, and we have never seen them again. They are still in service.
Our customers and partners in the USA, Europe and China have sprayed many augers and screws.
We also manufacture ID-guns to protect internal diameters of barrels starting from 80 mm (3.15”) and larger up to 1,500 mm (5’) deep.
A Comparison of Abrasive Wear and Erosion Protection Properties of HVOF and Kermetico HVAF Coatings
A slurry erosion test, courtesy of Schlumberger.
This test compares an Economy mode Kermetico HVAF WCCoCr coating to layers of 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 equipment provides such superior results?
A Research of HVAF Coatings Properties
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-10Co4Cr 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-10Co4Cr 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-10Co4Cr 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?
Economic Aspects of Kermetico HVAF Coatings
The list price of our HVAF 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).
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
- apply 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 Augers and Screws with Kermetico High Velocity Equipment
Usually, we deposit auger coatings using robotic blast and spray operations.
We blast an auger 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 conventional air blasting.
Hot grit blasting provides very even surface preparation and induces less stress into the base metal.
Kermetico HVAF Thermal Spray Coating Equipment
Kermetico designs and manufactures three families of HVAF thermal spray equipment.
- Convertible HVOF and HVAF equipment:
- 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 carbide gun to spray a balanced mix of parts in a job shop
- AK5 – a compact gun to spray smaller parts, thin walls and complex surfaces
- 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
- Specialized HVAF S equipment:
- Additional equipment:
Kermetico, Inc. – HVAF and HVOF Material Science Excellence, 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 equipment in action.
We also provide HVAF and HVOF thermal spray coating services to customers in North America – ourselves and through our network of partners.