Process for Obtaining Tight Components by Powder Metallurgy

Abstract

The process: includes mixing a metallic powder including iron or nickel or copper or mixtures of two or three elements thereof where the sum thereof defines at least 55% in mass of the metal matrix of the component to be produced, and a molybdenum disulfide powder as a densification agent and as a solid lubricant with a content from 3 to 30% in volume; filling a mold with the mixture and obtaining a compact presenting from 5 to 25% in volume of primary pores; and subjecting the compact to a temperature and time sufficient to allow the reaction of the molybdenum disulfide with the matrix, forming iron sulfide, nickel sulfide or copper sulfide, and the diffusion of the molybdenum in the matrix; and subjecting the compact to temperature sufficient to transform the sulfide into a liquid phase, filling the primary pores before finishing the sintering step of the compact.

Description

FIELD OF THE INVENTION[0001]The present invention refers to an improved process for molding powders by compaction and sintering, with low cost and having a large scale capacity of producing components in tight material, to be applied in the restriction of gas or liquid flows, without requiring subsequent operations after sintering said components. cl DESCRIPTION OF THE PRIOR ART[0002]For several applications, the process of powder metallurgy may be an alternative for the conventional processing, such as casting or machining, of ferrous and non-ferrous materials. It is a process which consists, basically, in obtaining components through raw materials in the powder form. The powder is then mixed, molded and then subjected to a thermal process, known as sintering, in order to provide physical and mechanical properties to the component, by means of the consolidation of the previously molded powder particles.[0003]The powder metallurgy process presents as advantages and in comparison to ...

AI Technical Summary

Benefits of technology

The present invention provides a process for obtaining tight components without the need for additional operations. The process involves compaction and sintering of a metal powder mixture containing molybdenum disulfide and a densification agent to form a reaction product which, from a lower temperature, fills the pores in the matrix, resulting in a higher density component. The process is low cost, produces components with high final density and enhanced mechanical properties, and works with a range of metallic materials. The process allows for large batches of equal pieces with high productivity and easy control of parameters.

Problems solved by technology

When porosity does not have a specific engineering function on the component, such as, for example, filtering or fluid flow control, it is usually harmful to the properties of the components.

However, the increase in the final density of a component produced by powder metallurgy is usually followed by an increase in the processing cost, said relation usually being nonlinear and even being exponential when aiming to achieve a final density close to 100% (totally dense material, free of pores).

However, these processes present some drawbacks.

When the component is under stress this layer may fracture, generating abrasive particles during contact with other components, which may cause premature wear or even failure under operation thereof.

Furthermore, this process presents strict control variables.

A small change in the dew point of the furnace, for example, may cause a layer of oxides having inadequate composition and morphology, thus generating a layer which is more fragile or even more porous.

The methods of forging and of double compaction / double sintering, although being carried out simultaneously with the processing, that is, do not require an additional step, invariably imply in a greater processing cost, added to the fact that the first method is limited in relation to the geometry of the components.

In the first case, it is necessary to carry out the forging of the pre-sintered piece, which is usually carried out at high temperatures, which implies increased costs with tooling and limitations related to productivity caused by the difficulties in producing components in large scale.

This same difficulty is faced by the double compaction / double sintering method, since every component, after being pre-sintered, should be further compacted and then sintered.

Both methods can provide tight components, but they can only be applied to materials which can be easily deformed, since the principle used for reducing the amount of pores is the plastic deformation of the material.

The drawbacks mentioned above limit the application of the components produced by such methods, either due to the high cost and difficulties of large scale implementation or due to geometric or dimensional control limitations.

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