Considerations regarding of basaltic materials usage with mineralizers input in machine building.

Stefanescu, Werner ; Pugna, Adrian ; Pleniceanu, Aristica 等

1. INTRODUCTION

The economic development normally entails important changes in the field of machine building, as well.

The machine building represents a branch of vital importance for the national economy of any country. The increase of the machines park brings abut the imperative of making machines building more efficient through substantially reducing the expenses for raw materials and various other materials, fuels and lubricants.

Such objectives can be attained by maintain the machines park in good technical condition, by using high quality parts, by ensuring high operating reliability.

At present, the endeavor to solve such problems consists in replacing some classical materials, both deficient and energo-intensive, with some new, unconventional materials, such as basalt.

The basalt products cam be obtained through casting, followed by a thermal treatment of recrystalization, this procedure is used for obtaining big parts with simple geometrical shapes, or through sintering method of powders, recommended for obtaining small and medium parts with complex configuration. Molten basalt cam be cast in various moulds, resulting in polyfunctionnal and efficient parts for different industrial fields, machine building included.

Researches have proved that basalt crystalline structures are not submitted to the well-know aging phenomenon, as it happens with most metallic materials and basaltic products obtained sintering are characterized by high stability at the action of strong bases and acids, as well as by high resistance to corrosion and wear.

The test made under operating conditions (Stefanescu & Iancului, 2004) on several parts (gaskets; sleeves; disks; chain-stretching rollers; etc.) manufactured of sintered basalt, along with witness parts from current production have proved the following for the sintered basalt parts:

--a very good resistance to wear, a doubled resistance, as compared to that of classical parts;

--a highly superior value for parts reliability;

--an inferior wear seed, justified by the high hardness of sintered (7,5-8 of MOHS scale of Hardness);

--the presence of hidden crazing due to manufacturing technologies of sintered basalt parts;

--how resistance to dynamic loading.

Improving technology for the elaboration of parts sintered in a basalt assumed a detailed study on the composition of elements of identification at the rock, also for determining the composition, structure and network parameters.

During the sintering experiments depending on the substances included in the recipe and the temperature, the samples have been some structural changes caused by chemical reactions and the results coincided with theoretical determinations. For this reason, the results of the chemical and theoretical methods, have requested an investigation of the structure through a high resolution--X ray diffractometry

Analyzing each diffractogram--figure 1- it was ascertain a big anorthit presence and frequency in the mass of basalt rocks and sintered basalt parts, which confer them an under--cooling stable and rigid state (lack of elasticity).

The under--cooling state it could be also the result of the presence of olivine and magnetite; their presence being more than 10%, which would favor the crystallization process and from here the vitreous state in the parts mass.

Using electronic microscope to examine the texture, contours and the geometrical shapes of the sintered basalt parts the following ascertained:

--existence of amorphous masses in each case due to the presence of olivine and anorthit;

--imperfections in the parts mass (dislocations, micro cracks, cleavages), due to manufacturing conditions and stresses with negative consequences upon mechanical resistance;

--very good compactness, low porosity which demonstrate that the parts were obtained through a "high sintering";

--pore elimination during sintering process determine a lower mechanical resistance due to internal inter--granular stresses. The technological experimental trials done on the samples showed that in the process of obtaining sintered parts one must take in account the following considerations:

--compactness, structure, basalt--leant mixture cohesion and also compactness in sintering process are influenced by the pressuring forces in the mold;

--samples quality are influenced by the pressure on which they were formed and by the sintering velocity ;

--samples which followed the right thermal regime where free of cracks, deformations and have dimensional stability.

[FIGURE 1 OMITTED]

2. METHOD AND EXPERIMENTAL RESULTS

The low resistance to dynamic loading of the parts that are used in machine building proves the existence of inadequate manufacturing technologies for sintered basalt parts and, implicitly, the development of studies and researches of the component elements texture and structure at the rock level, and part, respectively.

X rays diffraction method is one of the most modern and safe means of determining the structural characteristics of basaltic materials (Gheorghies, 1990).

[FIGURE 2 OMITTED]

The comparative study of rocks diffractograms for parts manufacture and those of the basalt parts--figure 2--, proved that, during sintering process, there appeared no new substances, and no significant structural changes have been produced at the level of elementary cell so as to determine changes of physical-mechanical propertiers (Suk-Joong L. Kang, 2005).

Complete sintering (Stefanescu, 2000) with proposed effects over the basaltic granular materials, in solid stage, without liquid stage forming, can be obtained:

--by thermal crystallization treatments, the temperatures rates of which do not change the type of interatomic bond and the atomic structure within the crystalline structure, on which the mechanical, thermal and physical--chemical loading depends;

--by means of small additives and impurities, known as mineralizers, whose role is to inhibit the granules growth and the transfer of pores to the granules limit, where their elimination may continue until the wanted porosity is obtained. The presence of mineralisers (Becherescu, 1982) changes the real structure lattice by disorganizing in and creates holes which favors the transfer of the material from one part of the structure into another part, thus influencing the physical--mechanical characteristics of the basaltic parts used in machine building.

Consequently, experiments have been developed, in laboratories, on witness samples made of basalt and on samples made of basalt and mineralizes based on Ti and Mg oxides, with a 2 % ratio.

[FIGURE 3 OMITTED]

The samples whose number, from and dimensions were established according to STAS 6200'9-91, as function of loading, were obtained by pressing and were thermally treated at temperatures between 900-1100[degrees]C, temperatures required by oxiolic and mineralogical composition of the basalt employed.

[FIGURE 4 OMITTED]

During the experiments there have been evaluated two parameters: the mechanical resistances to compression and volumetrically contractions.

The experimental data--figure 3--showed an increase of the volumetrically contraction for each sample separately, with the growth of temperature. Samples without mineralisers have superior values as compared to those with mineralisers, a fact which explains the presence of interval strain because of the decrease of the crystalline degree and the development of strained granules. By analysing the technical data obtained with respect to mechanical resistance to compression--figure 4--there has been observed that basaltic samples without additions display a weaker mechanical behaviour as compared to those with additions. At inferior temperatures (900-1000[degrees]C), mechanical resistances have low values; significant increases can be observed at temperatures between 1050-1100[degrees]C, justified by the intensified sintering processes.

3. CONCLUSION

The studies and the experimental results revealed the following conclusions:

--mechanical resistances to compression and volume contractions increase with sintering temperature growth;

--the use of mineralisers based on Mg and Ti oxides explains the better mechanical behavior of sintered basalt parts, because of the increase of the crystalline degree and the development of less strained granules;

--the use of mineralisers in the manufacturing technology of sintered basalt parts results in more reliable parts for machine building.

4. REFERENCES

Becherescu, D.(1982). Physical methods used in chemistry, Ed. Stiintifica si Enciclopedica, Bucuresti

Gheorghies, C. (1990). Diffraction spectrum and investigation techniques, Ed. Tehnica, Bucuresti

Stefanescu, W. & Iancului, D. (2004). Studies concerning of basaltic materials in agricultural machinery building, in USAB University from Timisoara, Scientifical Research & Horticultural, pp 325-329, ISSN 1453-1402

Stefanescu, W. (2000). Contribution to the study of structure influence and physical-mechanic properties of basalt based components over the system operational reliability of farm equipments. PhD; Timisoara

Suk-Joong L. Kang (2005). Sintering Densification, Grain Growth and Microstructure, Elsevier Ltd., ISBNS 978-0-7506-6385-4