Flame Spray vs Twin Wire Arc Spray: What’s the Difference?
Flame spraying and twin wire arc spraying (generally referred to simply as "wire arc spraying") are two different types of thermal spraying process. With a great deal of overlap in the capabilities of these two techniques, it can sometimes be difficult to know which one is best suited to a given use case. In this article we take a look at the unique characteristics of each technique, to help you decide which is the best coating solution for your applications.
The term “thermal spraying” encompasses a wide range of different techniques, all of which share the same fundamental operating principle: By heating a feedstock of deposition material – often in wire or powder form – and accelerating molten or semi-molten droplets of it towards a substrate, a coating can be formed. Thermal spray is used to coat structures and components with a diverse range of metals and ceramics to provide protection against corrosion, friction, or other harsh operating conditions.
Flame spraying and wire arc spraying were the first thermal spraying techniques to be invented. They remain the simplest and most common types of thermal spraying.
Operating Principles of Flame Spraying and Wire Arc Spraying
The fundamental difference between flame spraying and wire arc spraying is the means by which heat is supplied to the feedstock material. Flame spraying – as the name suggests – uses a flame to do this, usually a combination of oxygen and either acetylene or propane. Deposition material is introduced to the flame in either wire or powder form, and a stream of compressed air accelerates droplets of the molten deposition material toward the substrate to coat it.
Wire arc spraying, on the other hand, uses an electrical arc to heat the feedstock material. The deposition material is always supplied in the form of two wires (hence the name “twin wire arc spraying”), which are fed into the spray gun by drive rolls. Within the spray gun, a potential difference is applied between the two wires such that electrical arcing takes place. This causes the tips of both wires to melt. A high-speed flow of gas removes molten material from the wire tips and accelerates it toward the substrate, while breaking down larger droplets into smaller ones.
Practical Differences Between Flame Spraying and Wire Arc Spraying
The operational differences between flame spraying and wire arc may seem minor: both techniques involve the application of heat and compressed gas to the deposition material to melt it and spray it toward the substrate. However, the different operating principles have several practical ramifications.
Flame spraying and wire arc spraying offer different performance. Wire arc spraying can offer higher deposition rates (provided equipment is capable of delivering sufficiently high power); lending it to applications where speed is important. However, flame spraying has the advantage in a number of other performance areas: flame spraying can offer better process control leading to more stable quality, less oxidation – especially important in application where conductivity of the metal is imperative (copper, zinc) – and denser coatings suitable for demanding anti-corrosion applications. In addition, flame wire spraying offers higher deposition efficiency than wire arc spraying, meaning less loss of material leading to lower cost per mass of coating and evening out the difference in deposition rate. An important EHS favoring flame spray is the drastically lower amount of fine particle emissions, which are cut down to 1/60th compared to arc spray  directly leading to decreased risk of metal fume fever.
The simplicity of flame spraying typically means it has lower capital costs than wire arc spraying. However, the running costs of flame spraying are generally higher due to the need for fuel gases. Often, the choice between flame and arc spraying can be determined by a lifetime cost analysis and the surface geometry: smaller surfaces benefit from the narrow spray stream and less overspray of flame spray, while larger ones benefit from the speed of arc spraying.
Whether flame spraying or wire arc spraying, Saint-Gobain offers a comprehensive range of coating technologies and materials to help you achieve the result you need. To find out more about our coating solutions, get in touch with Saint-Gobain today.
 Bémer D. et al., Ultrafine Particles Emitted by Flame and Electric Arc Guns for Thermal Spraying of Metals, The Annals of Occupational Hygiene, Volume 54, Issue 6, August 2010, Pages 607–614