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Spray Welding – What, Where and When to spray

In the world of welding, there are many options. We all are at least familiar with the term welding whether we understand what welding truly is or not. In this article, we are going to discuss a metal coating or bonding process that is becoming more useful and common in the automotive industry to salvage castings. Although there is not actual fusion of material to the substrate as would happen with fusion welding, we have coined this process “Spray Welding”.
This is not to be confused with the torch method in which powders are introduced into the torch outlet and deposited into cracks or used to build up a broken segment of casting, as that; truly is fusion welding. As you can see, by generalizing the subject so much, it makes the topic difficult to discern. Spray Arc is a method of applying metal alloy particles to a base alloy of components like shafts, block and head casting surfaces, cylinder bores and so on. The goal is to restore the surface to a diameter or height dimension that allows for continued re-use of the component. Some of the easiest components to spray are shafts. The equipment needs are less than would be required for doing cylinder bores.
This equipment can be effective and efficient when applied with a hand-held spray device. One disclaimer that I want to interject regardless of how simple the process can be is that spray arc should not be done without the proper safety equipment. The most important factor in the safety equipment would be the air filtration as you do not want to inhale or ingest the alloy particles that will be airborne. The process of spraying the shaft typically requires cleaning the part, masking off the areas that you do not want overspray and abrading the surface where you want the spray weld to adhere to. Masking can be a “painted on” material or a tape like product. Masking is usually done where plugs are not an option as they can be installed and removed more quickly than masking and can typically be re-used. Abrading the surface that you intend to repair must be grit blasted to leave an aggressive surface texture to give the spray on alloy a gripping surface to bond to.
The spray arc alloy, as stated earlier, is not fusing with the base material but rather fusing to the other spray particles which are building a sleeve or shim at the prepared surface. This sleeve is gripping the rough surface texture so that the sprayed-on material does not slip during shaft rotation. There is a minimum material thickness that must be maintained for the alloy to produce an effective wear surface. Generally, for a crankshaft seal surface or a camshaft main journal, you will want a minimum of .015” wall thickness.
This is beneficial when oversizing the bore for a camshaft but when you are building up a crank seal surface, you may need to first grind the shaft under size by .030” to .050” then build up enough that you can grind back to standard OD so that you can achieve the correct surface finish for the seal. Depending on the alloy that you are using, you may require more, or less material to ensure proper performance. You will want to consult the alloy supplier and make test parts to ensure that the post grind surface is acceptable for seal surfaces and/or journal surfaces. When spraying gasket surfaces, you will again abrade the surface that you intend to coat for retention and mask or plug the areas that you don’t want sprayed. It is critical to have the proper abrasive surface as in most instances, you will mill the surface to correct the surface finish requirement and establish the corrected height dimension.
Failure to do so can result in the milling operation throwing your sprayed surface across your shop, which can be dangerous and costly. When properly applied, these alloys can improve the wear characteristics of the gasket surface as you can customize alloys to have harder surfaces while yielding very similar thermal expansion and contraction rates. Head and block surfaces are an area that have been improved by the integration of robots to perform the spraying.
The speed and feed rates are going to be consistent, the path is consistent and the need for airborne particle safety can be contained to a room with no people in it. This is a process that is being done in AERA member shops in North America and abroad as is shaft spraying and these are not mass production facilities. Cylinder bore spraying is practiced at OE levels, the motorsport industry and believe it or not at some level in the engine remanufacturing level. It is expensive and doesn’t seem to be plummeting in cost anytime soon. It works very well and gives many options for alloys that have great wear characteristics, hones well and salvages castings.
Currently this seems to be reserved for the R&D, Racing and mass production as the systems are not currently proving to be as flexible as deck and shaft spraying systems. There are many videos online showing these operations. Some videos are shared by AERA member shops. I personally have worked with this within and outside of the automotive industry and can tell you that there are tons of applications and the products work very well if the processes are followed. Many of these products get a bad rap when a product was intended to be used for say a seal surface and ends up getting used to repair a rod journal and the result is catastrophic failure. Just remember the old adage, the right tool for the job.
AERA Technical Specialist Chuck Lynch spent 20 years of his career at Jasper Engines in many roles, including process engineer. He has also worked as a quality auditor, analysed tooling needs, coordinated procurement and training for equipment and tooling, incorporated the use of super abrasives, coordinated failure analysis of components, and more.
Credit to AERA’s Technical Specialist  – Chuck Lynch (AERA – an International Partner to RMI ERA)
RMI – ERA (Engine Remanufacturers’ Association)
The Engine Remanufacturer’s Association (ERA) – was established in the early 1990s, and today serves the engine repair requirements of consumers, Industry and engine remanufacturing professionals in South Africa.
As a proud Association of the Retail Motor Industry Remanufacturers’ Cluster: ERA, SADFIA and ACRA, ERA’s membership comprises the cream of South Africa’s automotive engineers, dedicated to providing consumers with only the best advice, finest components and highest quality workmanship.
ERA members use state of the art equipment, while highly skilled staff perform the full range of automotive engineering operations required to overhaul and repair all components of the modern petrol and diesel engines on our roads.
ERA members take pride in providing warranties against workmanship appropriate to the type of engineering work undertaken.