what is Sintering!!!???

Sintering is a method for making objects from powder, by heating the material (below its melting point - solid stage sintering) until its particles adhere to each other. Sintering is traditionally used for manufacturing ceramic objects, and has also found uses in such fields as powder metallurgy. A special form of sintering, not limited the solid state but still considered part of powder metallurgy is liquid state sintering in which at least one but not all elements are existing in a liquid state. Liquid state sintering is required for making cemented carbides or tungsten carbide.

The word "sinter" comes from the Middle High German Sinter, a cognate of English "cinder".

Sintered bronze in particular is frequently used as a material for bearings, since its porosity allows lubricants to flow through it or remain captured within it. In the case of materials with high melting points such as Teflon and tungsten, sintering is used when there is no alternative manufacturing technique. In these cases very low porosity is desirable and can often be achieved.

Sintered bronze and stainless steel are used as filter materials in applications requiring high temperature resistance while retaining the ability to regenerate the filter element. For example, sintered stainless steel elements are used for filtering steam in food and pharmaceutical applications.

In most cases the density of a collection of grains increases as material flows into voids, causing a decrease in overall volume. Mass movements that occur during sintering consist of the reduction of total porosity by repacking, followed by material transport due to evaporation and condensation from diffusion. In the final stages, metal atoms move along crystal boundaries to the walls of internal pores, redistributing mass from the internal bulk of the object and smoothing pore walls. Surface tension is the driving force for this movement.

Metallurgists can sinter most, if not all, metals. This applies especially to pure metals produced in vacuum which suffer no surface contamination. Many nonmetallic substances also sinter, such as glass, alumina, zirconia, silica, magnesia, lime, ice, beryllium oxide, ferric oxide, and various organic polymers. Sintering, with subsequent reworking, can produce a great range of material properties. Changes in density, alloying, or heat treatments can alter the physical characteristics of various products. For instance, the tensile strength En of sintered iron powders remains insensitive to sintering time, alloying, or particle size in the original powder, but depends upon the density (D) of the final product according to En/E = (D/d)3.4, where E is Young's modulus and d is the maximum density of iron.

Particular advantages of this powder technology include:


the possibility of very high purity for the starting materials and their great uniformity
preservation of purity due to the restricted nature of subsequent fabrication steps
stabilization of the details of repetitive operations by control of grain size in the input stages
absence of stringering of segregated particles and inclusions (as often occurs in melt processes)
no requirement for deformation to produce directional elongation of grains
Many literary references exist on sintering dissimilar materials for solid/solid phase compounds or solid/melt mixtures in the processing stage. Any substance which melts may also become atomized using a variety of powder production techniques. When working with pure elements, one can recycle scrap remaining at the end of parts manufacturing through the powdering process for reuse.