To view Gas flow graphs for sintered bronze click this link
This material is made from tiny metal spheres each having a relatively pure copper core, with a surface relatively rich in alloying element(s), which are normally tin and/or nickel.
It is prepared by sintering close to the melting point of copper in moulds which are often made of graphite or stainless steel. The powder is poured into the mould, vibrated to settle it down, and then the mould and powder is furnaced to sinter the metal balls together. What results is a highly (up to 50%) porous product with strong bonds between the constituent particles. The moulds can be flat to make discs or plates, cylindrical to make tubes, or can also have more complex shapes to make near-nett-shape sinters for special applications.
Applications usually involve controlled gas or liquid flow through the porous metal, and the particle size of the metal is chosen to give the desired pore size in the resulting sinter. Pores can be from 5 microns mean size up to 100 microns. The particles of the metal matrix tend to be about ten times the size of the mean size of the holes.
When the tooling is made of carbon or simple pieces of stainless steel, it is not expensive, but on the other hand it doesn't last forever. Therefore the process allows low startup costs and relatively small batch sizes, but for large batches of 10,000+ components multi-cavity tools are needed which can tend to be quite a lot more expensive to procure and maintain.