Studies regarding manufacturing technologies of natural basalt sintering parts.

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

1. INTRODUCTION

In the actual stage of the society development, characterized by the acute demanding of materials and energy, the natural resources are not unlimited; in this case recycling it's not a feasible option on the long term.

Basalt parts cam be obtained through casting, followed by a recrytalization heat treatment, or by the method of powder sintering. The basic raw material is the natural basalt rock. The basalt improves its main chemical, physical and mechanical characteristics through melting and recrystallization. Molten basaly cam be cast in various moulds, resulting in polyfunctionnal and efficient parts for different industrial fiels, machine building included (Apostolescu, 1982)

The elaboration of modern making techonologies of basalt parts having superior physical and mechanical qualities implies study and research on substances the basalt rock is made of. After having apllied the heat treatments, the structure parameters and Miller indices of parts are measured. Heat treatments result in structural changes and the occurance of new substances as an outcome of sintering chemical reaction.

Following chemical analyzing, it was ascertain that basaltic materials are mixtures of binary oxide with a variant perceptual structure containing between a maximum 52% for Silicon oxide and a minimum of 2% for Titanium oxide, as shown in Table 1, similar values than pit his estimations by Chais (Becherescu, 1982; 1987), and a diversified of structural links of covalent--ionic type for Si and Al elements, of ionic type for alkaline metals (Na; K) and alkaline (Mg; Ca), and metallic type (Fe; Ti).

The presence of the three types of chemical links is influencing the structure and the properties of the chemical compounds.

During the experimental processes of sintering depending on the included substances in recipe and the temperature, in the weigh of the samples has took place some structural changes, determined by the chemical reactions, and the results have not coincide with the one determined theoretical.

Because of this the results obtained thru chemical and theoretical method, have required an investigation of the basalt material structure, thru a highly resolution method--X ray diffraction.

2. MATERIALS AND METHOD

X rays diffraction method is one of the most modern and safe means of determining the structural characteristics of basaltic materials (Gheorghies, 1990); (Ekstrom, 1986).

Considering the diffraction patterns recorded with the rocks collected from the four representatives basins in Romania, presented in figure 1, it resulted that they consist of the following substances: anorthite (CaO[Al.sub.2][O.sub.3]2Si[O.sub.2]), magnetite ([Fe.sub.3][O.sub.4]), olivine [(MgFe).sub.2]Si[O.sub.4], dolomite (CaC[O.sub.3]-MgC[O.sub.3]) and ilmenite (FeTi[O.sub.3]) (Stefanescu, 2000).

From the analysis of the basaltic rocks diffraction patters, resulted a homogenous structure with very little variation. Which denotes that the structural homogeneity of the basaltic rocks cannot generate physical-mechanical properties well differentiated.

In this case the main role of obtaining basaltic pieces with high physical-mechanical properties is due to elaboration technology and thermal treatment

3. EXPERIMENTAL RESULTS

Turning basalt as raw material, into a product or finished part, implies several operations: choosing the raw material and its processing till it results into powder (washing, drying, sorting, crushing, screeminig, preparation and screeming of powder-binder mixture, shaping and pressing of parts), drying and calcinations, machining and sintering. When elaborating the execution technologies for the parts to be used in machine-building, the parameters of the shaping, calcinations and sintering regime were established experimentally (Stefanescu & Iancului 2004) considering the shape, dimensions and weigh of parts.

[FIGURE 1 OMITTED]

Technological experiments (Stefanescu & Sandru, 1995) on test pieces of various shapes and dimensions demonstradet that when marking basalt parts the following aspects should be considered:

1. The compactness, structure, cohesion of basalt--binder mixture and the compacting during sintering process are influenced by the force employed to press the material into the dies.

2. The dimensional differences and the dispersions, between the test pieces formed at low pressures (0,5-1tf) as compared to the test pieces achieved at high pressures (1,5-2tf) are important

3. The quality of the parts made of basalt through sintering is influenced by the pressure they have been shaped at and the sintering temperature. The parts made at pressures of 1.5-2tf are more compact, the dimensional deviations are smaller, and as the shaping pressure in dies rises the contraction coefficient decresses, also with the improvement of the parts quality.

The sintering technologies (Stefanescu, 2000); (Stefanescu & Sandru, 1999) are conditioned by the shaping regime, the calcinations regime and the sintering regime:

1. The shaping regim is established according to the proportion of mixture component and the parts shaping pressures.

2. The calcinations regime depends on the heating speed and on the calcinating temperature.

3. The sinterimng regime as well as the calcinations regime depends on the heating speed and on the sintering temperature. The sintering regime of differently shaped and dimensioned parts has been established on the basic of sintering parameters with speeds of 85[degrees]C/h, 125[degrees]C/h and 140[degrees]C/h: the heating time, the duration of one impulse, the number of impulses, the time afforded to the keeping of parts in the sintering process have been calculated for the specified speeds and the cooling time, as shown in Table 2.

To emphasize the changes of crystalline phases evident, during the elaboration process of parts destined to machines building, substances where identified through X--ray diffractometric methods and sintered basalt parts.

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 properties.

Analyzing each diffractogram 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.

[FIGURE 2 OMITTED]

4. CONCLUSION

The studies and the experimental results revealed the following conclusions:

--regarding the basaltic rocks collecting place from the chemical composition point of view there is no significant differences which confer homogeneity and identical properties to basalt sintered parts;

--by comparison analysis of the component substances from basalt rocks and sintered basalt parts resulted that no new substances appeared;

--high-frequency of anorthite in basalt rocks and sintered basalt parts offers them an under--cooling state characterized by a total lack of elasticity;

--further studies should concentrate on trying to obtain the so called "complete sintering" with positive effects on sintered basalt parts by using new thermical treatments in order to modify the crystalline structural arrangement, or by using mineralizers in order to inhibit granules growth and pore transfer to the granules limits.

5. REFERENCES

Apostolescu,.D.(1982),Cristallography, Mineralogy, Ed. Didactica si Pedagogica, Bucuresti;

Becherescu, D.(1987), Solid State chemistry, Ed. Stiintifica si Enciclopedica, Bucuresti;

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

Ekstrom, H. (1986) X-ray powder diffraction techniques in the studies of high performances ceramics, Chem. Scr. 26. A;

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.& Sandru A. (1995), Utilization of some basalt parts for sprinklers, in U.P.T University from Timisoara, Bul. St. Mecanica Agricola & Metalurgie, nr.40(54), pp 5-8, ISSN1224-6050;

Stefanescu, W.& Sandru A. (1999), The utility of basaltic materials usage with mineralizers input in machine building, in U.P.T University from Timisoara, Bul. St. Mecanic, nr.44(58), pp 333-338, ISSN1224-6077;

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.

Tab.1. Chemical composition oxides of the basalt

 Extreme values (%)
Nr. Chemical
Crt. composition Romania Optimal

 1 Si[O.sub.2] 44-52 43,5-47
 2 [Al.sub.2][O.sub.3] 14-16 11-13
 3 [Fe.sub.2][O.sub.3]+FeO 9-14 5-8
 4 CaO 9-12 10-12
 5 MgO 7-10 8-11
 6 [Na.sub.2]O+[K.sub.2]O 3-8 3-5
 7 [Ti.sub.2]O 2-3 2-3,5

Tab. 2. The basic parameters of sintering

 Speeds values
Sintering
parameters 85[degrees]C/h, 125[degrees]C/h, 140[degrees]C/h,

Heating 13,2 8,9 8,0
time [h]

Duration of 43 29 26
1 impulse
[s]

Number of 1093 1093 1093
impulses [-]

Maintaining 1,7 1,2 1,0
time [h]

Cooling 9,1 6,1 5,5
time [h]