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How Carbide Powder is Pressed

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How Carbide Powder is Pressed

Tungsten carbide shapes are made from a powder which is typically tungsten, carbon, cobalt and wax to bind it all together. 

Carbide shapes are made three ways; pressing in a die, ”whittling” a shape from a green piece of carbide or grinding a shape from a finished piece of carbide.  See our Carbide Articles Index for more information on Carbide, and the different grades of carbide.   

This is a carbide press.  At top is a ram.  The powder is poured into the press cavity (the die) then the ram comes down and compresses the powder.  Once the powder is fully pressed the top ram withdraws.  There is a second ram at the bottom of the cavity that comes up and pushes the part out of the cavity. 

Below are two different dies (seen from the top) to press a diamond shape and a trapezoid respectively.   Next to them is a saw tip seen from the side.  Saw tips are pressed from the side.  This means you can use one die to produce many different widths of the same shape. 

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The pressed parts are then presintered.  In this step the wax is melted out.  This leaves a piece of ”green carbide” or “green state carbide”.  Since the wax has been melted out it is just powder pressed together.  It is actually weaker than side walk chalk.  It can be machined easily in this state although great care is required.   

It is at this step that carbide parts get chipped edges.   Some parts, such as saw tips, are made in large and very large batches.  They are moved by conveyors and often poured into trays for final sintering.  If this not done carefully one square edge impinging on another can cause chipped edges in the carbide parts.    By contrast you can use a .410 shotgun to fire fully sintered saw tips at a concrete block wall without damaging the saw tips. 

The final step is sintering in which the carbon is forced into a relaxed tungsten matrix creating tungsten carbide grains and those grains are enveloped in a binder or matrix of cobalt of similar. 

During the final sintering the parts shrink dramatically.  Exactly how much shrinkage will occur is difficult to predict exactly.  Parts are usually designed to be produced a bit oversize.

 

Various Pressing Defects 

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