Sintering Atmosphere:
The choice of a suitable furnace atmosphere which is governet by the characteristics of the materials and to some extent by the properties desired in the sintered prodect, is of almost importance in practically all sintering processes.
It has been felt that reaction of :-
1- the constituents of atmosphere amongst each other at the sintering temp ( e . g water gas reaction).
2- The atmosphere with the material to be sintered ( e . g reduction of oxides or decarburization).
3- The atmosphere with furnace refractions will lead to different in composition of the atom – sphere before its introduction. This chang affects the properties of the work being sintered.
Thus controlled atmosphere are highly desirable during sintering otherwise the atmosphere will give rise to a large scrap loss and inconsistencies.
In the quality of the end product.
For any case of sintering the functions of sintering atmosphere are :-
1- it must prevent oxidation on the metal surface at the sintering temperature otherwise it would inhibit or interfere with the sintering process.
2- It must a void carburizing and decarburizing reactions and nitriding condition in certain metals.
3- It must have the tendency of reduce surface films such as oxides on powder particles, If they are present, and remove or replace absorbed gases and.
4- It must not contaminate the metal powder compact at the sintering temperature.
The atmosphere which prevails in the various types of sintering furuaces are considered to fall into three groups :-
1- Reducting atmosphere.
2- Neutral atmosphere.
3- Oxidising atmosphere.
H2 cracked NH3 atmosphere are often employed, but carbon monoxide, hydrocarbons, partially combusted hydrocarbon gases, and lithium containing atmosphere may also be used in some cases as the reducing atmosphere. The choice of a reducing atom – sphere is made depending upon the articles to be sintered, the initial and operating cost of the atmosphere generator.
Vacuum sintering is costly and therefore employed, on a small scale in very special cases where it is essential or for research work.
Vacuum, helium and argon are employed for sintering reactive metals at elevated temperature.
المادة المعروضة اعلاه هي مدخل الى المحاضرة المرفوعة بواسطة استاذ(ة) المادة . وقد تبدو لك غير متكاملة . حيث يضع استاذ المادة في بعض الاحيان فقط الجزء الاول من المحاضرة من اجل الاطلاع على ما ستقوم بتحميله لاحقا . في نظام التعليم الالكتروني نوفر هذه الخدمة لكي نبقيك على اطلاع حول محتوى الملف الذي ستقوم بتحميله .
الرجوع الى لوحة التحكم
|