FAQ — HVAF Technology, Equipment & Coating Services

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Q: What is HVAF and how is it different from HVOF?
A: HVAF (High Velocity Air Fuel) is a thermal spray process that uses air and fuel gas instead of oxygen and fuel. Compared to HVOF, HVAF operates at lower flame temperature, producing denser, low-oxide, low-porosity coatings with higher deposition efficiency and lower operating cost. It also eliminates the need for oxygen handling and reduces environmental and safety risks.

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Q: How is the Uniquecoat HVAF process controlled and monitored?
A: Our HVAF process is controlled via mass flow controllers (MFCs) for air and fuel, and gravimetric powder feeders for precise powder delivery. Key parameters—air and fuel flow, powder feed rate, and gun standoff distance—are carefully set and recorded to ensure repeatable coating quality. For development and diagnostics, we also use tools such as particle temperature/velocity measurement systems and coating property testing (hardness, porosity, roughness).

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Q: What are the main advantages of your M5™ dual-stage combustion system?
A: The M5™ system uses dual-stage combustion with independently controlled air and fuel in each stage. This allows higher particle temperatures without sacrificing particle velocity, especially for standard HVOF-grade (15–45 µm) WC and CrC powders. In practice, this means higher deposition efficiency, denser and harder coatings, and improved ability to process coarser powders that are difficult for conventional single-stage HVAF guns.

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Q: Is a dual-stage combustion HVAF gun always required?

A: No. Standard and ultra-fine HVAF powders (e.g., 2–15 µm, 5–30 µm) can be effectively sprayed with single-stage combustion guns such as the M5F™ or the M5™ in single-stage mode. However, when spraying standard HVOF-grade WC- and CrC-based powders (15–45 µm), the dual-stage M5™ configuration provides higher particle temperature, higher deposition efficiency, and denser, harder coatings.

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Q: Can your equipment process both fine HVAF powders and standard HVOF powders?
A: Yes. Fine and ultra-fine powders (e.g. 2–15 µm, 5–30 µm) can be effectively sprayed with our single-stage combustion configuration (for example, the M5F™ or M5™ in single-stage mode). When spraying standard HVOF-grade powders (15–45 µm), the dual-stage M5™ configuration provides improved particle heating and higher DE, making it suitable for both HVAF-specific powders and conventional HVOF feedstock.

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Q: How stable and repeatable is the HVAF process with your equipment?

A: Process stability and repeatability are achieved through:

• MFC-controlled gas delivery,

• gravimetric powder feeders with precise weight-loss control, and

• standardized spray procedures (standoff distance, traverse speed, overlap, etc.).
  This combination ensures consistent coating quality from batch to batch and makes it straightforward to transfer parameters from development runs to production work.

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Q: Can you do sample or trial coatings before we invest in equipment?
A: Yes. We regularly spray sample coupons and customer parts to demonstrate coating properties and help customers evaluate HVAF technology before purchasing equipment. Trial runs can be tailored to your material, geometry, and service conditions.

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Q: What HVAF equipment do you use in your coating shop?

A: In our in-house spray shop we use our own Uniquecoat HVAF systems, including M-series guns (such as the M5™ and M5F™), gravimetric G-series powder feeders, and MFC-based control systems. This allows us to test and refine the same equipment we supply to customers and to validate coating procedures under real production conditions.

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Q: What kind of coatings can you apply in your spray shop?
A: We apply a wide range of carbide, alloy, and metal coatings using HVAF, including:

• WC- and CrC-based coatings of various compositions

• Corrosion-, erosion-, and wear-resistant alloys

• High-temperature alloys

• Pure metals

For each job, the coating system is selected and optimized to match the substrate material, part geometry, loading conditions, temperature, and service environment.

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Q: What types of parts do you typically coat?
A: We routinely coat:

• Brush rolls

• Separating screens

• Compacting rolls

• Pump shafts, plungers, and sleeves

• Wear sleeves, bushings and sealing surfaces

• Various test coupons and prototype components

If needed, we can review drawings or photos and confirm whether a specific part is suitable for HVAF coating.

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Q: What substrates can be coated with your HVAF process?
A: Our HVAF coatings can be applied to most engineering metals, including:

• Carbon and low-alloy steels

• Tool steels and hardened steels

• Stainless and duplex steels

• Cast irons

• Nickel- and cobalt-based alloys

• Selected aluminum and copper alloys (within temperature and distortion limits)

Surface preparation and process parameters are adjusted to ensure strong adhesion and minimal substrate heating.

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Q: What is the maximum size and weight of parts you can coat in your spray booth?

A: Our HVAF spray booth can handle fairly large industrial components. We can coat parts up to 40" (about 1,020 mm) in diameter, 180" (about 4,570 mm) in length, and up to 5 tons in weight. If your part is close to these limits or has an unusual geometry, we can review a drawing or photo to confirm handling and fixturing options.

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Q: Can you apply Flash Carbide coatings in your shop?
A: Yes. We offer Flash Carbide and other thin, near-net-shape WC-10Co-4Cr coatings as a service. These coatings are typically 15–30 µm thick, dense, low-porosity, and can be polished to a very smooth surface, making them suitable as hard chrome and conventional HVOF alternatives on precision components such as rods and rolls.

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Q: What is the maximum coating thickness you can apply with your HVAF process?

A: The achievable coating thickness depends on the material and application. For conventional WC-based wear-resistant coatings, we have successfully applied layers in the range of 1.5–2 mm on customer parts.

For Fe-based materials used in 3D build-up / additive-style manufacturing, we have experience applying very thick layers up to approximately 2–3".

For any specific job, we review the part geometry, material, and service requirements to recommend a suitable coating thickness and buildup strategy.

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Q: Do you have ID spraying capabilities for internal surfaces?

A: Yes. In addition to OD coating, we offer ID HVAF spraying for internal bores and cylindrical surfaces, using dedicated internal guns and extensions. This allows us to coat the inside of parts such as cylinders, sleeves, housings, and liners with the same wear- and corrosion-resistant materials used on external surfaces. We evaluate each part based on its internal diameter, length, and access to confirm fixturing and process feasibility.

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Q: What are the minimum internal dimensions you can coat with HVAF (ID spraying)?

A: Our ID HVAF spraying is suitable for relatively small bores, but there are practical limits for access and gun manipulation:

• For a minimum internal diameter (ID) of 65 mm, we can coat internal surfaces up to 1 m in length.

• For larger IDs exceeding 120 mm, the reachable coating length increases to 1.5 m.

For parts close to these limits, we normally review a drawing or sketch to confirm accessibility. In special cases, custom solutions for longer lengths may be possible and can be evaluated on request.

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Q: What information do you need to quote a coating job?
A: Typically we need:

• Part drawings or basic dimensions

• Substrate material

• Desired coating material or required properties (hardness, wear/corrosion resistance, etc.)

• Coated area and required thickness

• Operating environment (temperature, medium, load, speed, etc.)

​​With this information, we can recommend a coating system and provide a technical and commercial proposal.

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