The 7 Habits of Highly Effective Thermal Spray Operators
Excellent, consistent coatings are not an accident; they are a result of a highly effective thermal spray operator. They are not in isolation; there are other people involved who help them accomplish the task.
If you read this short piece and say to yourself, “this was so basic that it was a waste of time to read”, congratulations! You are a highly effective operator or manager and already understand these fundamentals. With that being said; you can not believe how often I observe that these fundamentals are missing in shops that I visit. The result is wasted time, money, and effort on rework and scrap when it could have been avoided.
If you read this and say to yourself; “sounds nice, but we don’t have time for that stuff”, I would simply ask; how much time do you spend on rework or making excuses for sub-standard results?
What is the cost of rework and scrap in your operation? If you don’t have a specific number that you measure each week, you don’t know! What is the cost of the operator walking around looking for tools, materials, or answers to questions? These are hidden costs that are often not measured resulting in lost profit margin.
The overall description of the highly effective operator is that he is organized, has a procedure for everything, follows the procedure, asks questions for clarity, and cleans up after himself.
The first habit of the highly effective operator is that he is organized.
He has his own tool box with tools that he has confidence in to help him get the job done. They will include hand tools to do minor equipment maintenance and adjustments to a set up. Additionally he will have his own set of micrometers that he knows are calibrated and readily available. This operator never has to wander around the shop searching for tools to get the job done.
I have visited some shops that have tool boards with the specific tools in designated areas so there is a visual organization that is easy to see when something is missing. This is a little more difficult in a area that has multiple operators and multiple processes that occur on a regular basis. A solution for that situation could be the creation of an “Area Czar”. A person is assigned a specific area to keep organized and clean. If anyone disrupts his territory, he will have the authority to correct the situation. The highly effective operator is held accountable to execute the discipline to keep all tools organized, and challenges everyone around him to do the same.
The second habit of the highly effective spray operator is that he keeps his work area clean.
Before he starts a job, he organizes and cleans up the area he is going to work in. He generally can not stand clutter and dirt in the area being used to spray world class parts. Similarly, he cleans the area up after completion of the work or at the end of his shift because he understands that the person following is also a world class operator and he too wants to work in a world class environment.
There are various sources of oil and water in a spray shop. The obvious ones are the machining and grinding lubricants, which can be oil based or water based. These are necessary in completing any pre-spray machining, but are a problem when it comes to getting a good bond with the thermal spray. Our recommendation is to process all parts after machining through a degrease operation before you continue on to the grit blast operation. I have visited shops who are satisfied with using the grit blast as the degreasing operation. It reminds me of kitty litter; it will absorb oil, but once it gets saturated, it will transfer oil to the surface you are grit blasting. Do not use your grit blast cab as a kitty liter tray. Although this is not convenient, it will lead to a better track record for best practice.
By far, the biggest source of oil and water contamination is from the compressed air source. Many shops use the older piston compressors that generate oil into the compressed air. And, unless you are in the desert, you will get water from condensation forming in the normal air. Coalescing filters will do an adequate job of removing the water and oil, but they must be sized correctly. They have to be sized for the maximum output of the compressed air system, not just for the use with the thermal spray. It is best to have a filter isolated for the use of the thermal spray torch and any cooling air that you may need for the operation. Be careful to size the filter for both the thermal spray torch and the cooling air. The highly effective operator will stop all operations if he sees contamination of the compressed air.
The third habit of the highly effective operator is that he has a procedure for everything
and it is the same procedure that all operators in a given shop use. He has a pre-spray inspection procedure so that he has confidence that he knows exactly what needs to be done. When work comes into his area, he is going to complete fundamental tasks that are documented in a procedure.
The effective operator is working in an environment that has some sort of work flow traveler that maps out exactly what is to be done to a part through the entire shop. First, he is going to verify that all proceeding procedures have been completed and documented.
The effective spray operator is going to verify that the starting size he has received is correct. He also will know what the finish spray size and surface finish will be of the part after the finish machine or grind operation. In a job shop environment this is important because operations in the thermal spray area can have a significant effect on the finished part.
The highly effective operator is going to be working from written instructions. Operators who work from verbal instructions and assumptions tend to generate more rework and scrap.
The fourth habit of the highly effective operator is consistency.
You can always count on the work that you give him will have the same outcome. He always has a written procedure on how he is going to perform the job and it is the same procedure any other operator would use in the shop to do the same job.
It is very typical for operators to have their “own way” of doing things, that is a disaster waiting to happen! The complete information of how the job is going to be done should be with the part at all times. Specific detailed operational procedures should be at specific operation areas, but the total job scope information must stay with the part.
He also has documents that clearly define the order in which operations are to be completed. He also verifies that each previous step of the process has been completed before he begins his operations. Each step of the operation that he completes has documentation that verifies he has completed his steps.
Clearly there are several documents that are required for him to complete the job:
- Traveler, this is a document that follows the job throughout the shop that describes what operations have to be completed on the job. The order is clearly defined along with any special instructions for individual operations.
- Operational instructions, these are specific instructions for specific operations. They include details of what the parameters are for the specific operation.
- Inspection instructions, specifying the requirements for the completed operations, finish dimensions, surface finish requirements, or any measurable characteristic of the part or operation.
This operator is trained in the proper procedures and has complete documentation to support what he does
The fifth habit of the highly effective operator is the preparation of the surface to be sprayed.
The surface preparation and the cleanliness of that surface is one of the most critical steps in the process. This is especially true with the repair of components that have been in service. Very often a cast and
The surface preparation and the cleanliness of that surface is one of the most critical steps in the process. This is especially true with the repair of components that have been in service. Very often a cast and machined component that is used in an industrial environment, oil will be absorbed into fine porosity that is inherent in castings. This porosity is so fine that normal degreasing operations will not remove this oil. The porosity can be deeper than .015”, so even if you pre-machine before spray, you may still have some trapped oil.
During the thermal spray process, the casting will commonly heat up to 200 °F or 300 °F and the oil will weep out of the porosity because of the normal expansion. This can cause delamination of the coating. Elimination of this problem is fairly straight forward; heat that part to about 650 ° F, and any oil that is trapped will weep out and burn up. An indication that you have achieved that is there will be no more smoke coming off the part. As an operator I know well says and I quote, “torch her til she stops smokin”.
The grit blast operation is a critical step for successful thermal spray operation. A typical surface finish from machining is a 63 RA. This is too smooth for good adherence for most thermal spray processes. A 300 to 400 RA is far more suitable for good grit blast surface. You want to achieve a “white metal” finish. This finish has enough “nooks and crannies” to give a good bond.
Important blast parameters are:
- Grit size
- Grit type
- Service life of the grit
- Blast working distance
- Nozzle size
- Air pressure
- Blast angle
The sixth habit of the highly effective operator is following the specific spray parameters for that operation.
Every time this job comes into his area, it will be sprayed the same. No matter which operator in the facility sprays the job, he will use the same parameters as defined on the operational instructions for that specific part.
Spray parameters are any measurable attributes of the spray operation. If you define the speed of rotation in rpm’s, plus or minus x rpm’s, this would be a spray parameter. If your instruction is “turn it pretty fast”, this would not be a spray parameter.
Some other examples of spray parameters are:
- Spray distance
- Rotation speed
- Feed rate
- Power settings, which will vary depending on the thermal spray system, but it will define the total energy of the system. It may include voltage, current, gas type, gas flows, gas pressures, or any other parameter that affects the total enthalpy of the “flame”
- Powder feed rates
- Wire feed rates
- Coating thickness pre pass
- All gas and air pressures
- All gas and air flows
In all cases, the parameters are clearly defined and are measurable
The seventh habit of the highly effective thermal spray operator is that he holds himself accountable.
He inspects his own work and documents the results before it leaves his area. The correct finish spray size is verified and documented after the work has cooled down and before it leaves the area. If there are any questions or issues with the spray, they are addressed before the job leaves the area. There is no doubt in his mind that when the part leaves his area that it is correct and there is documentation supporting that statement.
By now you have probably figured out that the highly effective thermal spray operator has highly effective management and he has had extensive training. You might say the eighth habit of a highly effective thermal spray operator is to work for highly effective management. Many of the specifics that we outlined above can only come from the management of the job shop. If they are sloppy with how they are managing the operation, how can they expect any different from their operators.
It is a competitive industry in an unpredictable economy, only the best will survive.