Additional income for your shop
We here at Republic Diesel have been using the thermal spray welding process for many years. I personally applied the coating for my first time in the mid 80’s and we haven’t slowed down yet. This process is something we do every day on a multitude of different components. It has actually become a very important part of our business and a well needed source of income.
Thermal spray welding, also known as metalizing or flame spraying, as it is sometimes referred to, was first performed around the start of the 20th century. In the 1920’s spray welding in the United States was seen mainly in coatings on Navy ships, railroad cars and on coal barges. The process was used mainly as a corrosion resistant coating. Several people believe that World War II gave flame spraying its biggest boost to date. As our Armed forces were sent overseas to protect our country their need to repair equipment and machinery in the field gave many businesses an opportunity to get into the thermal spray market. What followed was, as the old saying goes, necessity is the mother of invention.
For years thermal spray welding had a bad reputation and was considered by many as Black Magic or Voodoo. This negative impact label has been a major hurdle for many shops to overcome. Some of the reasons for this may be due to the number of shops that had gotten into the field without proper training or equipment. The product these shops produced quickly failed and it was easier to find fault with the process than the people applying the coatings. The coating process is just that, a coating. It does not fuse itself to the substrate as conventional welding does. Thermal spray does not have much shear strength but under compression it can withstand a beating.
As I mentioned earlier, we find this process to be a great source of additional income. Some of the parts we apply the thermal coating to are cylinder block decks and main bore saddles. Some OEM’s (including Caterpillar) have actually approved this thermal spray process to restore material previously removed during the repair of components. As examples, crankshaft seal areas and connecting rod bores are also areas we apply the coatings. Some non-engine components we repair are transmission and torque pieces, driveline yokes and large heavy-duty brake parts.
To give you a little deeper understanding of the process I would like to walk you through the repair of a couple of components, a yoke and a crankshaft seal surface. I understand crankshaft seals can be repaired with a wear ring but when it comes to the large diesel crankshafts, the cost of the wear ring makes the application of the thermal spray a very economical, alternative process.
In this first picture you can see where the yoke seal surface has some grooves cut into the yoke. These grooves need to be repaired before the yoke can be put back into service. We have indicated the yoke in the lathe and applied the masking material. The masking material is a water soluble paint type material that will keep excess overspray from adhering in the splines, bolt holes and on non-functional surfaces. The masking material will help with the clean up when all machining has finished. We will next undercut the worn area about .015” per side to remove as much of the groove as possible. This undercutting procedure gives us a good clean line for the thermal spray coating to adhere to and it also prepares the surface for the coating. The surface preparation is extremely important; it needs to be clean and rough. The rough surface gives the coating more contact area to adhere to.
In the next picture we are applying the coating. We use the flame spray system for smaller parts. This system uses oxygen and acetylene as the flame. Once the coating powder is mixed with the flame it turns into a molten stage and air pressure forces it onto the part. While the flame could potentially melt the part, we do not allow the component to reach more than a couple of hundred degrees. There are several factors you need to take into consideration when thermal spraying components. The distance and angle you maintain from the spray gun to the part is as critical as the temperature you maintain, the amount of material you are applying per revolution, the speed the part is rotating and the exact mixture of gas pressures; all are equally important in the coating process.
As you look at the coated part in picture 3 you can see some excess material in the splines and at the base of the yoke. This overspray can be easily removed with nothing more than a good stiff wire brush. The part will need to cool before we can do our final machining as we do not want the temperature to affect the finish size of our component.
Pictures 4 and 5 are simple machine work, turning a part in a lathe. The coating is very abrasive but can be easily machined with several of today’s cutting inserts. On some parts we use a sealer to act as a lubricant for the cutting tool and also to seal any porosity in the coating.
Lastly you see the finished part, cleaned, polished and ready to return to the customer. The total time we spend coating the seal surface on a piece this size is somewhere around 45 minutes. We will use less than ¼ pound of powder to coat the part and the masking material in less than a ½ cup. When you factor in the gases and cutting inserts we will have around $20.00 to $25.00 in consumables. We find this repair to be profitable and when your customer has to replace the part he will find it very economical.
While I understand most shops do not have these yokes sitting around waiting for repair, there are many other components you could look into to increase your shop services. Small water pump shafts were an item we cut our teeth on in the early stages of developing our thermal coating department. Electric motor shafts are another source of small pieces you could consider as a new source of revenue. While there may not be a seal area to repair on these shafts, they are notorious for spinning bearings.
Thermal coating is not Black Magic, it is a very effective repair process used in the repair of heavy duty components. There are remanufacturing facilities using it every day to repair front covers and flywheel housings where pumps or covers have worked loose and fretted into the cover surface. It has become such an important part of our business that we have five machinists/technicians applying the coating every day for their entire shift. Those jobs do not even include the coating process we use in our engine component areas.
Born and raised in Louisville, Kentucky, Steve Edmondson began his 32-year career in 1979 at Republic Diesel, a leading specialist in medium to large diesel engine machining and spray welding. If you have any questions or concerns about spray welding your unique component, feel free to call Steve at (800) 292-5565.
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