How to Choose a Thermal Spray Coating Company

How Do You Choose a Thermal Spray Coating Company?

Choosing a thermal spray coating company comes down to four checks: does it run the right process in-house — HVOF, D-Gun, plasma or flame spray — rather than selling one process as the answer to every job; can it back a quote with real quality-control data instead of a verbal guarantee; does its equipment envelope actually fit your part's size and volume; and will it recommend a coating based on how the part fails in service rather than whichever coating sits at the top of its price list. Get those four right and turnaround, logistics and communication tend to sort themselves out.

Most buyers start the search with a keyword search and a price comparison, which is backwards. A quote that's a few hundred rupees cheaper per part is a false saving if the process is wrong for the failure mode, or the vendor skips surface preparation and bond testing to hit the price. The sections below work through what to verify before a drawing goes out for quote, and what a vendor selection checklist should cover for pump shafts, hydraulic rods, rolls, valves and other wear- or corrosion-critical components.

Check Process Capability First: HVOF, D-Gun, Plasma — In-House or Subcontracted?

The single biggest differentiator between coating shops is what they actually run on their own floor versus what they broker out. A shop offering only flame spray or basic metalizing will recommend flame spray even when a part's wear duty calls for HVOF or D-Gun — not out of dishonesty, but because that's the only tool in the box. Ask directly which processes are in-house: HVOF, Detonation Spray (D-Gun), atmospheric plasma spray, arc/flame metalizing, and which carbide and ceramic powders (WC-CoCr, Cr3C2-NiCr, stellite, alumina, chrome oxide) each process runs routinely.

Subcontracting isn't automatically disqualifying — some legitimate shops subcontract a rarely-needed process — but it should be disclosed, and it changes the turnaround and quality-chain-of-custody math. If a vendor is vague about what's in-house versus outsourced, or can't name the specific powders it stocks, treat that as a signal to keep evaluating other suppliers before committing a drawing.

Certifications and Quality Control: What ISO 9001:2015 Actually Buys You

ISO 9001:2015 certification is a baseline, not a marketing badge — it means the shop runs a documented quality management system with traceability, corrective-action records and process control, which matters when a coated component goes into a pump, turbine or hydraulic system that can't tolerate an undocumented failure. Ask to see the certificate and ask what it covers (coating processes, or just general operations).

Beyond the certificate, the real test is what QC data ships with the coated part. A competent thermal spray shop should be able to report bond strength (D-Gun coatings commonly exceed 80 MPa), porosity (well under 1% for D-Gun, low single digits for a well-run HVOF process), coating hardness (up to roughly 1,400 HV for D-Gun tungsten carbide), and coating thickness at agreed measurement points — not just a visual pass/fail. If a vendor can't produce this data on request, or treats it as unnecessary paperwork, that's a red flag for any component where coating failure means unplanned downtime.

Equipment Envelope and Part Size Capacity

A vendor's process list only matters if its equipment can actually hold your part. Small precision components (valve stems, seal faces, plungers) need fixturing and masking precision; long components (calendar rolls, paper machine rolls, large shafts) need a machine envelope and part-handling capacity that many job shops simply don't have. Ask for the maximum part length and diameter the shop can coat in its D-Gun and HVOF cells — capacity up to roughly Ø800 mm and 7 metres in length is a reasonable large-format benchmark to check a vendor against if your components run long.

Undersized equipment forced to handle an oversized part usually shows up later as uneven coating thickness or masking failures at the edges, not as an upfront refusal — so verify capacity before quoting, not after the part comes back with a defect.

Match the Coating to the Failure Mode, Not Just the Price

The most common vendor-selection mistake is comparing quotes for "a coating" without first pinning down the failure mode the coating needs to solve. Abrasive wear, adhesive wear/galling, high-temperature oxidation and general corrosion each point to a different material and process, and a vendor that quotes the same WC-CoCr HVOF coating for all four isn't doing its job. A good vendor asks about the failure mode before quoting a material.

• Abrasive wear at moderate temperature (pump shafts, hydraulic rods, general hard-chrome replacement): tungsten carbide (WC-CoCr) via HVOF or D-Gun
• High-temperature erosion and oxidation (boiler tubes, fans, turbine components): chromium carbide (Cr3C2-NiCr) via HVOF
• Galling and self-mated sliding wear, elevated temperature (valve seats, turbine components): cobalt-based stellite via plasma or HVOF
• Long-term atmospheric or marine corrosion on structural steel: zinc/aluminium metalizing (arc spray)
• Dielectric or thermal-barrier requirements: ceramic coatings (alumina, chrome oxide, zirconia) via plasma spray
• Severe duty with a documented history of coating failure under HVOF: D-Gun, for its higher bond strength and lower porosity

What Does It Cost, and How Should You Evaluate Quotes?

Thermal spray coating cost is driven by powder material, process (D-Gun runs a premium over HVOF for the same material), part size and surface area, coating thickness, and post-coat grinding or finishing — not by a flat per-square-inch rate that applies across every part. When two quotes for the same drawing land far apart, the gap is almost always one of these variables, not vendor margin: check whether both quotes specify the same coating material and grade, the same target thickness, and the same post-coat grinding tolerance before assuming the cheaper quote is the better deal.

Reason about cost against the cost of failure, not the quote in isolation. A pump shaft that costs a production stoppage every time it's pulled for reworking is worth the higher-spec coating even at a materially higher price; a low-duty component with no failure history doesn't need the premium process. Ask a shortlisted vendor to walk through why it recommended a specific material and thickness for your part's duty cycle — a vendor that can explain the reasoning is more trustworthy than one that just returns a number.

A Vendor Selection Checklist

Work through this list before committing a drawing to any thermal spray coating company:

• Is HVOF and/or D-Gun run in-house, or subcontracted? Get a direct, specific answer.
• Is the shop ISO 9001:2015 certified for its coating operations specifically, not just general manufacturing?
• Will it report bond strength, porosity, hardness and thickness data for the actual part, not just a general spec sheet?
• Does its equipment envelope comfortably fit your part's size, including any long or large-diameter components?
• Did it ask about the part's failure mode and duty cycle before recommending a coating material?
• Are the quotes you're comparing specifying the same material, thickness and post-coat finishing — genuinely apples to apples?
• What's the realistic turnaround for your part size and volume, including any masking and post-coat grinding?

Common Mistakes When Selecting a Thermal Spray Coating Vendor

The most frequent mistake is treating the lowest quote as the default winner without checking whether it specifies the same material, thickness and process as the other bids — a thinner or lower-grade coating will always look cheaper. The second is picking a vendor based on general manufacturing reputation without confirming its specific thermal spray process capability and QC reporting; a well-known machine shop that also does "coating" as a side service is not the same as a dedicated thermal spray operation.

A third mistake is skipping the failure-mode conversation entirely and asking for "a hard coating" — every material on this page counts as hard, but only one or two are right for a specific wear or corrosion environment. Finally, buyers sometimes assume any coating shop can handle any part size; verify equipment envelope for long rolls, rods or shafts before the part ships, not after it's returned with an uneven coating.

Getting a Recommendation for Your Part

The fastest way to apply this checklist is to send the part drawing, duty cycle and any failure history directly to a shortlisted vendor and see how specific the response is. See the full process and material range on the technologies page, compare the economics in more depth in what drives thermal spray coating cost, and if the part is currently hard-chrome plated, start with hard chrome replacement to see whether HVOF or D-Gun is the better fit. When you're ready, get a quote with the part drawing and duty cycle and expect a process and material recommendation, not just a price.