Improve Your Thermal Spray Business by Capturing Re-work Costs Data

If you are in the thermal spray coatings business, then you know the tremendous level of competition that currently exists in the plasma spray industry. With several new thermal spray shops cropping around and the increased emphasis on quality, price and delivery by astute customers, it is imperative that you look for every possible means to improve your competitive edge.

Every step that can improve the bottom line of the thermal spray facility that you are involved in, regardless of what capacity you fit into, be it a business owner, shop foreman, chief engineer, quality manager or production controller can go a long way in getting one step ahead of the competition. This article addresses one such small aspect that is oftentimes overlooked by thermal spray shops both big and small.

That aspect is to do with re-work costs. Being a fairly complicated process with lots of variables and lots of processing steps involved, sometimes errors in processing can occur in the normal course of events. Some of these errors can be linked to operator error and some are not associated with operator error.

Regardless of what the source of the error is, these can result in re-work of the hardware at best and scrapped hardware at worst. If the hardware can be re-worked, then the costs associated with such a re-work must be captured for later analysis. While many thermal spray companies do not even attempt to quantify their re-work costs, out of the ones that do quantify their re-work costs, very few do anything whatsoever with this data as valuable as it is.

Re-work costs data provide valuable information that can improve the bottom line of your operation. For example, if the data is further broken down into source of error, then it can point to ways and means of reducing the re-work. If most of the re-work is the result of operator error, then obviously this points to the need for improved operator training.

 If most of the re-work is the result of equipment malfunction, then this points to the need for improved maintenance procedures. If a major amount of re-work is due to the use of incorrect powder quality then sourcing is the culprit. Thus, identifying the major cost contributors to re-work can lead you to fixing the root cause of the problem.

Additionally, quantifying re-work costs can lead to accurate pricing structures by accounting for these costs during the quotations process. This is important because otherwise the cost of your operation is not clearly reflected in your price quotations to your customers. Thus quantifying and analyzing re-work costs can go a long way in improving the bottom line of your thermal spray coatings facility.

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Troubleshooting CBN Inserts - Definition of Hard Turning

Hard Turning Definition

Hard Turning " as machining hardened steels above 40 HRc, not hard in terms of "difficult". Alloy Steels with a hardness below 40 HRc are not generally machined using CBN inserts because other tool materials work as well or better and cost less. Soft materials often stick to PCBN cutting tools causing "build up" on the cutting edge. This results in poor surface finish and tool life. The geometry of PCBN tools used for machining hardened steel is very blunt with no chip groove geometry to provide swarf control, not ideal for machining soft steels. However, some steels with a high alloy content and 30+ HRc are successfully finish machined with DR-50 because nothing else will do the job. If there is no adhesion, reliable size control and consistent surface finish can more than justify the cost of the tools.

Aluminum Alloy Machining

Aluminium alloys cannot be machined with CBN inserts. PCBN has a trace content of Aluminium nitride. Aluminium builds up on the cutting edge very quickly causing rapid tool wear and poor surface finish.

Cast Iron Machining

Cast iron and Iron based hard facing alloys with a significant ferrite content are not machined with CBN inserts. The soft gooey ferrite sticks to the CBN insert cutting edge causing rapid wear and poor surface finish.

D2 Machining

Interrupted cutting D2 tool steel is very difficult and unpredictable. D2 contains up to 14% Chromium and was designed to be used at 50-56 HRc. If the material is hardened to +60 HRc and not tempered very carefully, Chromium Carbide formation at the grain boundaries makes the material impossible to machine with interrupted cutting.

HSS Machining

Interrupted cutting of High Speed Steel - HSS is temperature resistant and does not soften in the shear zone. Interrupted cutting Nitrided steel is difficult. When continuous cutting, the super-hard surface is machined away by a part of the cutting edge that is not controlling surface finish and size. When interrupted cutting, the entire cutting edge impacts with a superhard surface resulting in poor tool life.

Hard Facing Alloy Machining

Hard facing alloys - Stellite (Cobalt/Chrome Alloys)and Colmonoy (Nickel/Chrome alloy) with more than 20% Chrome is not practically machined with PCBN - Tool life is too short. Chromium cannot be machined using PCBN. PCBN can be used to remove hard Chromed plated surfaces and expose a hardened steel base material, but it is not possible to machine within the Chrome.

High Temperture Alloy Machining

Machining high temperature alloys - Inconel, Hastalloy, Waspalloy, Titanium, Nimonics etc are not machined with PCBN. Tool life is negligible due to chemical affinity.

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Thermal Spray Metallographic Sample Mount Variables

Metallurgical quality control of thermal spray coatings is an important step for any applicator of this family of coatings because unacceptable structure can lead to premature failure. More importantly, spelled hard coatings can lead to secondary damage in critical aerospace applications and as a limiting case in the situation where there is a single engine aircraft as in most military vehicles, failure of the engine can lead to mission failure and even fatalities.

Metallurgical laboratory evaluation of thermal sprayed coatings includes but is not limited to metallographic examination of the sample. Additional tests such as erosion testing, hardness testing, tensile testing, etc may form part of the overall quality control process. While this could be the subject of an entire treatise, we will limit ourselves in this brief article to metallographic examination and in particular to the variables involved in the preparation of the mount itself.

For those that are not familiar in the art, successful metallographic evaluation begins with the preparation of a good quality mount. There are several variables involved in this step as discussed in what follows. The first and foremost variable is in the choice of the mount material itself. Bakelite is a commonly used material. Two-part epoxy compounds are also utilized by many metallurgists. To provide added strength, fine aluminum oxide powder is sometimes added to two-part epoxy compounds. For quick evaluations, hard mounts made of metal are also utilized in the industry.

When utilizing Bakelite as the material, one needs to control the variables of pressure, temperature and time of pressing to reproduce high quality mounts time and again. When two-part epoxy compounds are used, the mixing proportion of the two parts need to be controlled as well as the amount of hardening additives such as aluminum oxide need to be controlled. Mixing time and subsequent hardening time are also variables in the process.

The choice of metal used in the quick mount method is very critical. It is important that the metal be sufficiently hard so smearing of it does not occur during the subsequent grinding and polishing steps. Sometimes hard metal strips can be used juxtaposed to the coating surface during the mounting process for proper edge retention. In such cases, alteration of the edge retention material could producing varying effects during subsequent sample preparation processes.

As one can see, there are several variables even in the sample mount preparation process which if not controlled can lead to erroneous interpretation of coating quality. The best practice to avoid pitfalls and ensure consistent repeatable quality is to document the controlling practice of all these as part of the laboratory manual.

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Turning Recycled Tungsten Carbide Into Tungsten Carbide Blades

Tungsten carbide is an extremely valuable alloy that is used in many industries for different applications. It is also a highly prized alloy because it can be 100% recycled over and over again. Because of its strength, durability, and resistance to both heat and rust, carbide is an ideal choice for surgical instruments, mining and drilling inserts, jewelry, and grips for all sorts of sporting equipment. However, another widespread uses for carbide, especially after it has been recycled, is to make cutting blades with it.

Tungsten carbide is an ideal material to forge blades out of because thanks to its hardness and other properties, a much finer yet more durable edge can be fashioned once the blade has been formed. Carbide blades need far less sharpening than those made of stainless steel or titanium. Moreover, they will not pit, corrode, or break under normal wear and tear.

Why Recycled Material is Used for Blades

The most prominent reason why it makes sense to use recycled carbide for fashioning cutting blades is because of the lack of material that is available domestically. Roughly 90% of all tungsten is mined outside of the United States and since it takes both tungsten and carbon to create tungsten carbide, domestic producers are forced to either import material from overseas or search for recycled sources stateside. Using recycled carbide is the only way to create a viable domestic market for the product and this is why tungsten carbide recycling companies will typically pay between $7 and $11 per pound for scrap that would otherwise be thrown away.

How Carbide Blades are Made

There are many types of blades that utilize tungsten carbide such as rotary saw and planning blades, scalpels, and hunting or fishing knives. There are two ways that any of these tungsten carbide blades can be made. The first way involves creating the blade from 100% tungsten carbide. To do this, the recycled material is melted down, molded, and forged if necessary into the shape of the blade. After the basic shape is in place, it is grinded to perfection, polished, and given its edge. Unfortunately, this is not always the best way to use carbide to make a cutting blade.

Tungsten carbide's incredible hardness (second only to diamond) can actually become its downfall here. This is because the material's atomic structure is woven so tightly together that regardless of what shape it takes, it has no give whatsoever. Whereas stainless steel, titanium, or aluminum blades can bend when under pressure, carbide will actually shatter much like glass. This means that if you were to try and put too much pressure on the blade or even drop it on a hard surface such as tile, the force against the blade from heavy pressure or an impact could destroy it entirely.

To combat this problem, blades using the benefits of tungsten carbide can be made a second way that involves a more practical grafting process. To do this, the base and main structure of the blade is created out of another material with high strength, but more give such as stainless steel or titanium. Only the blade's edge is made of carbide. 

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The Three Basics For Making Money With a Thermal Spray Shop

Thermal spray coatings is an exciting field of business wherein the competition is relatively low compared with other fields of metallurgical and mechanical lines of work such as machining, welding or fabrication. Even as competition in the area of thermal spray coatings is increasing, there is still quite a bit of room available for the would be entrepreneur to start a thermal spray coatings shop and be at least somewhat successful.

While the field itself is quite exciting, dealing with exotic alloys and fanciful applications, the bottom line of the business and for that matter the bottom line of any business is to make money. The purpose of this article is to briefly outline three basics that need to be followed through if you would like to be successful making money in your thermal spray business endeavor.

The first and foremost aspect is price. Starting out as a new thermal spray facility, your price needs to be better than what anyone else is offering. No one wants to deal with a higher priced new entry in this market. Whatever steps need to be taken to keep the price low, must be taken. This may include negotiating with your suppliers of raw material, keeping labor costs low, keeping overheads low, etc. The importance of a low price cannot be overstated in this field.

The second aspect is quality. Quality in the thermal spray coatings business is expected without even saying. Operators must be trained well to keep a close watch on coating parameters, equipment maintenance, close attention to shop operation sheets and technical plans. Every effort must be put forth in optimizing coating parameters such as gas flows, power settings, feed rates, powder quality control and such to ensure the highest in coating quality.

The third aspect is delivery. It is imperative for a start up operation to quote the lowest in delivery cycles and keep the promised delivery time. On time deliveries account for a lot of repeat business and every effort must be made to keep to the scheduled delivery times. Many times, thermal spray operation is the last in hardware manufacturing sequencing and any delays in delivery can significantly impact end user operations.

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Chromium Carbide Overlay - Built to Last in the World of Metals

Chromium carbide is a compound that is composed of various combinations of chromium and carbon. Its outstanding strength, its ability to retain that strength under even high - temperature exposure, and its ability to resist corrosion render it an ideal additive material in the steel industry. When steel plating (or any other metal alloy) is overlaid with it, it becomes extremely hard and durable.

These advantages add up to chromium carbide enjoying a wide range of applications and uses, including the surface treatment of steel components. Steel plates that are overlaid with it "are meant to be welded onto existing plate structures or machinery in order to improve performance," Wikipedia explains.

Materials World, the member magazine of the Institute of Materials, Minerals and Mining provides a long list of applications. Among them are the following:

    Wear Resistant Coatings - The hardness of chromium carbide helps it to protect parts that are coated with it. Two of the advantages of these coatings are that they are inexpensive and easily applied via welding or thermal spraying. Cutting tools are just one of the items that are formed with chromium carbide overlay.

    Welding Electrodes - More and more often chromium carbide welding electrodes are taking the place of outdated carbon - containing electrodes. That is because they produce better and more consistent results. They also provide a wear - resistant layer to the electrode, up to 250% superior to the earlier carbon - containing electrode, and result in less variation between welds. The application in which the electrodes are most often seen is the "hardfacing of conveyor screws, fuel mixer blades, pump impellers." They are also found in more general applications where "erosive abrasion resistance is required."

    Thermal Spray Applications. - Thermal spraying is the process whereby chromium carbide is applied as a coating to some other metal like steel. As with other applications, the high corrosion resistance that results from this bonding is the greatest advantage. In the steel industry, this coating virtually eliminates rusting. Depending on what substance it is mixed with before it is bonded to the steel, it can also act as a barrier against high temperatures of up to 700 to 800 degrees Celsius. For this reason, steel that is thermal sprayed with it is often used in the aerospace industry. Other typical uses are "as coatings for rod mandrels, hot forming dies, hydraulic valves, machine parts, and wear protection of aluminum parts."

    Chrome Plating Alternative - More wear resistant than hard chrome plating, steel that is overlaid with chromium carbide results in a similar surface finish at a much lower price point. In addition, disposal of chrome plated with the overlay is much more environmentally friendly.

    Cutting Tools - Toughness and durability are obvious must - haves when it comes to cutting tools. Chromium carbide improves both of these qualities. Its main advantage as an additive is that it prevents grain growth during sintering (a form of grain refinement), thereby rendering the cutting tool ultra hard.
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Mining Equipment - Prevent Wear With Thermal Spray Coatings

Thermal spray used for mining equipment? You bet! But before you choose a thermal spray coating (also known as 'hardfacing'), you must first understand the type of wear. The answers may surprise you.

Abrasive wear can include lower impact, lower stressed conditions. Here, there will be no fracture, no sudden loss of parent material. Rather, material removal is the result of scratching, filing, a consistent loss in metal at some micro-level. Of course, wear rates will be more dramatic when the mined abrasives are sharp, angular in nature. Proper material hardness, such as an abrasion-resistant steel or ceramic, is key.

Adhesive wear is more of a tearing or material separation between interacting surfaces. It begins with rubbing, and ends with phenomena known as scoring, galling, or seizure. Their occurrence is typically associated with like materials and structure, under an applied load, without lubrication. Here, material choices should consider attributes like ductility, for impact strength. These "softer" alloys available can actually work harden with impact or deformation. The result is increased strength and resistance to abrasion.

Have you already identified the wear mechanism? Made the proper material selection? Well, now it is time to consider thermal spraying. Hardness is the normal measurement for material choice. Again, keep in mind that, under abrasive conditions, harder material choices, like tungsten carbide or ceramic coatings are ideal. But for adhesive wear, where impact strength can be crucial to success, softer, more ductile choices are the answer.

Did you know that how (or where) the thermal spray coatings are applied can also slow down rates of wear? Depending on mined material type and shape, the success of a hardface deposit will be in how it is aligned on the surface. Parallel, perpendicular, even coating spacing and overlap can mean the difference between success and failure. Dissimilarity in thermal expansion characteristics between the coating and parent metal is also something to consider.

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