Calculating Deposition Efficiency: Reducing Material Waste in Zinc Arc Spraying

For any fabricator, EPC contractor, or galvanizing alternative shop running twin wire arc spray equipment, zinc wire is one of the largest recurring line items on a project budget. Yet a surprising number of metallizing operations never measure how much of that wire actually ends up as usable coating versus how much is lost as overspray, rebound, and oxidation fines. This article walks through exactly how to calculate deposition efficiency in zinc arc spraying, what drives material loss, and the practical adjustments that reduce zinc wire waste on the shop floor. CeeDee Metalloys supplies zinc wire and zinc aluminium wire to metallizing shops across India, and this guide reflects the same process variables our quality assurance team reviews with customers during technical support calls.

1. What Is Deposition Efficiency in Zinc Arc Spraying?

Deposition efficiency describes how much of the zinc wire fed into a twin wire arc spray gun actually ends up bonded to the substrate as usable coating, compared to the total wire mass consumed during the run. In the arc spray process, an electric arc melts the tips of two converging zinc wires, and compressed air atomises the molten zinc into a stream of fine droplets that are propelled toward the part. Not every droplet reaches the surface in a useful state. Some droplets cool and solidify in flight, some bounce off the substrate on impact, and some drift away as airborne overspray before they ever make contact.

Deposition efficiency is therefore not a measure of coating quality or adhesion strength in isolation, but a measure of process economy: how efficiently raw zinc wire is being converted into finished coating thickness on the part. A shop running at 70 percent efficiency uses roughly 30 percent less wire than a shop running at 49 percent efficiency to achieve the same coating build on the same surface area.

2. How Deposition Efficiency Is Calculated

The calculation itself is straightforward, but it depends on accurate mass measurements taken before and after a spray run. The standard formula used across thermal spray operations is:

Worked Example

Consider a structural steel bracket weighing 12.400 kilograms before metallizing. After a single spray pass targeting 100 microns of zinc coating, the part weighs 12.487 kilograms, a coating gain of 87 grams. During that same pass, the wire feeder consumed 150 grams of zinc wire, measured by spool weight difference. Applying the formula gives a deposition efficiency of (87 / 150) x 100, which equals 58 percent. This means 42 percent of the wire fed into the gun during that pass did not end up as coating on the part.

Why Batch Measurement Beats Single Part Measurement

On a production run with many similar parts, it is more reliable to measure total wire consumption against total coating mass across a batch rather than a single part, since this averages out small weighing errors and edge effects on individual components. Many shops track this as a recurring KPI alongside the process parameters logged for each job, which also supports traceability during quality assurance audits.

3. Types of Material Loss in Arc Spray Metallizing

Understanding where the missing material goes is the first step toward recovering it. Material loss in zinc arc spraying generally falls into four categories.

Overspray

Overspray is molten or semi molten zinc that misses the target area entirely, typically because the spray pattern is wider than the part, the gun is angled incorrectly, or the operator is spraying past the edge of the component during pass transitions.

Rebound

Rebound occurs when droplets strike the substrate but bounce off rather than bonding, usually because the droplets have cooled too much in flight, the surface profile is too smooth, or the impact angle is too shallow.

Oxidation and Fume Loss

A portion of atomised zinc oxidises in flight and is carried away as fine particulate fume rather than landing as coating. This is more pronounced with excessive atomising air pressure or excessive stand off distance.

Wire Feed Inconsistency

Uneven wire feed speed, caused by feed roller wear, wire diameter variation, or contact tip wear, disrupts the stability of the arc and increases the proportion of large, poorly atomised droplets that are more likely to rebound or fall as spatter.

4. Where Deposition Efficiency Matters Most

Deposition efficiency is not equally critical on every job. It becomes a significant cost factor on large surface area work where wire consumption scales directly with project size, such as bridge girders, storage tanks, wind turbine towers, and offshore structures. On these projects, even a modest efficiency improvement compounds across tonnes of zinc aluminium wire or pure zinc wire consumed over the contract duration.

It matters less, in relative terms, on small precision components where wire consumption per part is already low, though consistency still affects coating thickness control and rework rates on those parts.

5. Industry Applications of High Efficiency Zinc Arc Spraying

Industries that rely heavily on zinc arc spraying for corrosion protection have the most to gain from tight deposition efficiency control. Infrastructure projects involving bridges and structural steelwork, marine and offshore platforms, renewable energy structures such as wind towers, and railway infrastructure all consume large volumes of zinc wire as a galvanizing alternative, making material yield a direct line item in project margins. CeeDee Metalloys works with fabricators across these sectors, supplying wire alongside the zinc metallizing spray machines used to apply it. A full sector breakdown is available on our applications page.

6. Commercial and Project Level Benefits of Higher Efficiency

Beyond raw material savings, improved deposition efficiency reduces several secondary costs that are often overlooked in project budgeting. Fewer spool changeovers mean less downtime per shift. Reduced overspray means less cleanup, less particulate to manage, and lower housekeeping overhead in the spray booth. Tighter, more consistent coating builds also reduce rework rates caused by under thickness areas that need a second pass. On contract metallizing work priced per square metre, these secondary savings can be as significant as the wire cost reduction itself.

7. Speciality and Niche Applications

Some applications call for tighter efficiency and purity control than general structural metallizing. Sacrificial anode and cathodic protection work, where coating uniformity directly affects service life predictions, benefits from consistent, well documented deposition efficiency records. Specialist products such as Bio-Zinc are formulated for applications where coating consistency and environmental considerations are equally important, while tin zinc wire is used in electronics and capacitor related coating work where deposition control affects functional performance rather than just corrosion resistance.

8. How to Choose Wire and Spray Parameters

Selecting the right wire diameter, alloy, and spray parameters for a given job starts with the target coating thickness and the substrate geometry. Thicker, more consistent wire with tight diameter tolerance feeds more predictably through the gun, which directly improves arc stability.

Wire Selection

For general structural corrosion protection, pure zinc wire remains the standard choice. For projects requiring extended service life in marine or high corrosivity environments, zinc aluminium wire typically delivers better long term performance per micron of coating, which can offset a slightly different efficiency profile compared to pure zinc.

Parameter Selection

Stand off distance, atomising air pressure, voltage, and wire feed speed should be set according to the gun manufacturer’s recommended range for the wire diameter in use, then fine tuned on a test panel before production spraying begins. Spraying a calibration panel and weighing it before committing to a full production run is the single most effective way to confirm expected efficiency before wire is committed to a large job.

9. Performance, Maintenance and Best Practices

Sustaining good deposition efficiency over time is as much about equipment maintenance as initial setup. Contact tips wear with use and should be replaced on a defined schedule rather than run to failure, since worn tips destabilise the arc gradually and efficiency drift can go unnoticed until a batch weighing check is performed. Feed rollers should be checked for wear and correct tension regularly, since slipping rollers cause inconsistent wire feed speed even when the feeder display shows a steady setpoint.

Operator Technique

Consistent gun travel speed, correct overlap between passes, and maintaining the recommended stand off distance throughout the pass, including around edges and corners, all contribute meaningfully to measured efficiency. Operator training and periodic technique audits are a low cost way to recover efficiency losses that have nothing to do with equipment condition.

10. Who Uses Deposition Efficiency Calculations?

Deposition efficiency tracking is most actively used by metallizing contractors, structural steel fabricators, EPC contractors managing corrosion protection scope, and shipyards running large scale arc spray operations. CeeDee Metalloys supplies zinc wire to fabricators and contractors across India, including teams working on infrastructure and industrial projects in the regions below.

Beyond geography, our technical service support helps customers troubleshoot deposition efficiency issues directly, drawing on metallurgical data referenced in independent thermal spray literature such as the Thermal Spray Society guidelines and process notes published by TWI Global on arc spray parameter optimisation.

11. Related Reading

12. Frequently Asked Questions