Tungsten Carbide burrs are one of the most popular powder metallurgy products in the world. They come with a perfect combination and blend of toughness and hardness as compared to all other cutting materials. Tungsten carbide burrs have a lot of applications in many popular industries. Some of them are the aerospace industry, automotive industry, rock and mining industry and the wood industry.
Tungsten Carbide is known for its tensile strength and unique features as a metal compound. Tungsten like most metals arranges themselves just like a chain-link fence. This is why whenever carbide is heated or under pressure, the carbon atoms pack themselves inside the tungsten atoms instead of moving beside the ordinary compounds.
The production of tungsten carbide in forms like carbide burrs is a very delicate production process. And it requires a great deal of precision.
Materials Involved in the Production of Carbide Burrs
The following are materials that are important in the production of tungsten carbide burrs
- Tungsten Carbide balls
- Cobalt powder
- wax
The Manufacturing Process of Tungsten Carbide Burrs
There are a lot of processes involved in the production of tungsten carbide burrs. Some of them include producing raw powder, milling and mixing powders to form agglomerates, dewaxing, post-sintering and pre-sintering, sintering and the finishing processes.
When producing carbide burrs, it is observed that all the steps in the manufacturing process are linked. It is a difficulty faced during the production process. This means that a change in the manufacturing processes will automatically lead to a modification in the end product.
In this section, we will give you a brief explanation of all the steps involved in the production of tungsten carbide burrs.
The Production of Raw powders
One of the raw materials needed for the manufacture of carbide burrs is the powders of binder metals and hard refractory carbides. The commonest ones for refractory carbides include WC, TaC, TiC, NbC and their respective mixed carbides. TiN and Ti are also used in the production of graded hard metals.
Cobalt is also a raw material used in the production of cemented carbides as a metal binder. In the past, they produced cobalt powders by reducing cobalt oxide in hydrogen. Today, we make cobalt powders through the pyrolysis of a cobalt salt. An example is cobalt oxalate. After the production of the raw materials, the next stage is milling.
Milling
The milling step has to do with getting a homogeneous mix of the powders in step one. A tool known as Cylindrical rotating ball mills is used to mix these powders. WC-co is commonly used as milling balls. The milling process takes up to 24 hours. Some manufacturers also make use of attritor units to mill carbide powders. Irrespective of the milling method used, the powder must be homogeneous as this helps to get a uniform structure in the end product.
Milling is usually done with the addition of additives. This helps to prevent oxidation and binding wax which is very important in the compaction of the powders. Here, carbides are crushed to the desired grain size. This reduction in size helps to ease material transport in the solid-state sintering. The milling phase ends with the production of some oxygen which is later reduced in the sintering step.
Granulate
The next step after the milling phase is granulation. Here, the powders are dried and moulded in a spherical shape that allows them to flow easily during pressing. In this step, we use a spray dryer with a temperature of 200 degrees. During the drying phase, additives including alcohol, hexane and acetone will evaporate leaving spherical granules.
Pressing
Pressing is the next step after granulation. Powder compaction is a determinant of how good the end product is. The compressed powder is known as the green body and most times has the same quality as the final product. The compaction must be homogeneous as this affects the quality of the product.
In this step, the carbide products are compressed through uniaxial pressing. Here, the powders are introduced into a rigid die and pressed using a lower and upper punch. The compressed product is green in colour and has a porous body with the binder agent. Then binder agent and the pores have to be removed in the sintering step. The completion of these processes shrinks the compressed product into its final dimensions
Sintering
This step is called the sintering step. It is a key process in the production of tungsten carbide burrs. During sintering, densification occurs in a bid to create and poreless microstructure and the final dimensions of the component. The Carbide burrs are produced in the liquid phase sintering. There are 4 steps in the sintering phase.
- First Step
The first step is where shrinkage occurs. It is majorly due to the reduction of oxides and the degassing of impurities and binders.
- Second Step
In the second step of this phase, the temperature increases and this is when solid-state sintering comes into action. Though the binder phase remains solid, transport and dissolution of material will only happen by bulk transport and solid-state diffusion. As the temperature increases, the porosity decreases and the material that is dissolved in the binder metal begins to re-precipitate on the undissolved grains. The arrangement of the particles also helps to enhance densification.
Third step
The third step is known as the eutectic point. This is where the liquid phase sintering starts. Here, the grains dissolve in the binder phase until it is saturated. This is controlled by the solubility product. The small grains dissolve preferentially while the larger grains are not completely dissolved but grow at the expense of the small grains. This step leads to coarsening and complete densification.
Fourth step
The fourth step is the final step of the sintering step. It is where cooling down occurs. Here, the component reverts to solid. After this, you will find out that there is some left re-precipitation from the last step. It leads to further coarsening. Sintering occurs in a sintering furnace where you can control the temperature, atmosphere, pressure, heating, cooling and sinister times.
During the final sintering process, the parts can shrink up to 15% in any dimension and about 35% in volume. About 15 to 30 tons of pressure is applied to form tungsten carbide into a tool shape such as tungsten carbide blanks.
In the formation of tungsten carbide burrs, there are four methods. They include:
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- Moulding
- Green State Machining
- Grinding
- Brazing Carbide to Carbide
There are different shapes and sizes of Tungsten carbide burrs. They include cylindrical shape (type 5A), Spherical shape (type 5D), oval shape (egg), tree shape (pointed), tree shape radius (type 5F), flame shape (type 5H), 60 degrees cone shape (type 5J).
The type of burr shape created is majorly dependent on the manufacturing process for the burr was created.
Having more of the cutting edge engaged in the material will improve the part finish. There is a flute cut style shape that is also dependent on the type of material being machined, the type finishing required, the amount of stock removal. The harder the material being machined, the finer the cut or shape is.
Conclusion
As described in the article, the process of development for the manufacture of tungsten carbide burrs largely depends on the process optimisation in the industrial furnaces. These optimizations are however based on the technical knowhow of the engines of each production line. For a quality end product, a lot of things have to be taken into consideration including the quality of the initial raw powders, the manufacturing conditions and the final application of the sintered grade. Another very important factor to consider is the carbon balance control. These described processes are perfect for the production of high-quality tungsten carbide burrs.