SINTERING
Idroenergy on-site high-purity hydrogen and nitrogen generation systems are widely used in metallurgy, where the use of high purity atmospheres that keep a consistent quality over time is essential. Sintering is particularly important among thermal treatment of metals done through high-purity nitrogen or hydrogen produced on-site with Idroenergy generators.
We will now see what the sintering process is; which the main sintering methods are; which products are obtained through sintering systems and which are the main sintering applications, which is the contribution of purified gases like nitrogen and hydrogen produced on-site through Idroenergy generators in the sintering process. For any further information on sintering process or on-site nitrogen and hydrogen production please contact Idroenergy qualified staff by phone or e-mail.
Sintering: what is it?
The sintering process, which derives from the German word ‘Sinter’ and hence from English ‘cinder’, is a metallurgical process consisting in the compaction and processing of metallic powders in an indivisible compound: sintering is in fact also called powder metallurgy. The material to be treated is heated and brought to a temperature under its melting point to ensure that the particles adhere to one another.
Sintering is a process widely used in ceramic manufacturing, and it finds many uses in the field of powder metallurgy. There is also a form of sintering applied to the liquid phase of materials, with a procedure in which at least one of the elements is found in liquid state. Sintering with the help of the liquid phase is particularly useful in the production of tungsten carbide or other types of carbides.
Parts made by sintering are characterised by extreme surface hardness. This thermal processing procedure for metals is widely used and convenient due to the relatively inexpensive procedure that allows serial production of a large number of pieces.
Sintering: which products?
As explained, sintering is an extremely profitable and versatile metallurgical process, since it allows obtaining different processes and, therefore, different types of materials, polymers and products. Particularly, the sintering process enables the production of compact material, hard and resistant: mixing two or more powders of different materials, of which at least one is found in liquid phase, sintering allows obtaining a compact material, which is afterwards taken to a temperature close to its melting temperature. Therefore, materials with excellent strength and resistance characteristics are obtained by applying the sintering process with liquid phase.
Moreover, sintering enables the production of objects with a specific shape that can be afterwards subject to other processes like extrusion or forging. In this case, the powders are compressed and then heated (always at a temperature under the material melting point) within a mould with the desired shape. The heating process allows compacting the metallic powder grains, to shape a body able to be subjected to other processing procedures.
Another important sintering application regards the possibility to obtain special alloys with excellent properties that could not be generated using other processing techniques, as in case of objects with a specific form that can be processed through sintering of powders welded together by means of temperature increase rather than through material casting into a mould. Sintering is one of the most productive and safe thermal treatments for metals.
Sintering is also used with materials having a high melting point (such as Teflon and tungsten), as a technique that allows their processing when no other processing technique can be applied. Sintering thus makes it possible to process materials that would otherwise be difficult. Sintering is now possible with most of the metals, if not all. Particularly, it is possible to sinter any metal produced under vacuum without surface contamination. It is even possible to sinter non-metallic substances such as glass, alumina, zirconium oxide, silicon dioxide, magnesia, calcium oxide, beryllium oxide and other organic polymers.
Sintering and subsequent processes allow obtaining a wide range of materials with different properties. Thanks to the change in density, to the formation of alloys and thermal treatment of metals it is in fact possible to affect physical properties to obtain new compounds with the physical characteristics required by different processes. The application of hydrogen and nitrogen produced on-site through high purity atmosphere gas generators manufactured and installed by Idroenergy allow obtaining substantial savings on sintering procedures, which also reduce air pollution and risks for the personnel.
Sintering process: detailed description
To obtain the necessary powders for the sintering process, specific physical-chemical and mechanical processes must be applied. Powders can be obtained through:
- mechanical processes: to obtain the powders fragile material must be crushed through hammers positioned within rotating tumblers with spheres, or through rotating knives able to pulverise burr of melted material. In the thermal or mechanical-thermal sintering, temperatures of about 0.7 and 0.9 times the melting temperature must be reached.
- physical-chemical processes: to obtain the necessary powders for the sintering process the next procedures can be followed:
o saline baths for electrolytic action: the collision allows obtaining the powder, dried after being deposited in sponge form;
o atomisation of molten material burrs through a powerful jet of inert gas;
o oxide reduction through high pressure hydrogen;
o dissociation of volatile carbonaceous compounds of iron or nickel through high pressure carbon monoxide;
o through electric spark;
o by the oxidation of finely ground burrs that are made into fine powder; vacuum evaporation and condensation of the material through a plasma torch.
The application of high-purity high-pressure hydrogen and nitrogen to metals is therefore an extremely practical, safe and economical method to grind metals into powder and then process them through sintering and subsequent procedures. Particularly, in the sintering process it is essential to avoid metal oxidation that reduces the powders aggregation rate and could compromise the sintering process success.
Thanks to nitrogen and hydrogen at high purity atmospheres, produced on-site by the high-purity gas generators manufactured and installed by Idroenergy throughout Italy and abroad, we guarantee complete protection against metal oxidation, which is eventually eliminated through redox reactions to obtain pieces characterised by superior mechanical qualities and brightness.
Sintering: the contribution of hydrogen and nitrogen
As explained, sintering is a serial production process for metallic products, mechanical or metal-ceramic parts from premixed metallic powders pressed into the desired shape, by heating and compaction in a high temperature furnace. Parallel to the heating process, the metal particles are welded to each other providing particularly solid metal pieces with the required mechanical specifications.
The sintering process is generally done in continuous furnaces where different phases take place, each one with a specific atmosphere:
1. the first sintering phase, that totally removes lubricants, must have an oxidising atmosphere;
2. the second sintering phase, which is a heating phase, needs a reducing and not decarburising atmosphere;
3. the third sintering phase, which prevents oxidation and allows obtaining a bright surface occurs in the furnace cooling area, in a not-oxidant atmosphere.
To obtain a correct and productive sintering process it is essential to know and control the exact composition of the atmosphere in each area of the furnace and to be able to adjust it according to the characteristics of the material being treated.
Thanks to the use of hydrogen and nitrogen at high-purity atmospheres produced on-site through Idroenergy generators, costs can be reduced and the sintering process metallic powder treatment procedures can be simplified. Idroenergy qualified personnel is able to provide complete installations and customer service in the decision of treatment parameters for sintering or any other thermal treatment of metals.
Thanks to on-site nitrogen and hydrogen production systems the process safety is maximised as well as the application of atmospheres, reducing the need for maintenance plants and simplifying the control and supervision systems of metal processing. Nitrogen and hydrogen generators provided by Idroenergy allow simplifying and accelerating industrial processes, maximising safety of operators and facilities involved.
