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| Fröhlichová M., Fröhlich L., Borovský T. |
| ANALYSE OF TITANIUM EFFECT ON THERMAL STATE IN THE HEARTH OF BF |
| Keywords: Blast furnace|hearth|refractory wear|titanium bearing raw material|titanium carbonitrides|protective layer| |
| No 3 (2007), p. 353-359 |
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| Havlík M., Petrík J., Palfy P. |
| MICROHARDNESS MEASUREMENT CAPABILITY |
Abstract
Microhardness tests are used with loads lighter than 200 g, which typically creates indentation with the diagonal on the order of 50 m. The Vickers test is carried out in a similar manner to the Vickers macroindentation tests with the same pyramid. Due to their specificity, microhardness testing can be used to observe changes in hardness on the microscopic scale. Unfortunately, microhardness values vary with load and work-hardening effects of materials. Additionally, it is difficult to standardize microhardness measurements.
The capability of a process is a measure of its ability to satisfy customer’s requirements. Process capability studies are carried out to compare customer’s requirements with process performance and to identify the stakes-in-the-ground for process monitoring.
The semiconductor grade copper Cu - K3A – 534 EG, delivered as a cylinder ?40 mm was used as an experimental material. The surface for metallographic analysis was prepared by standard way by grinding through a series of gradually finer silicon carbide water cooled papers. The sequence was 220, 240… and 3000 grit (ANSI/CAMI grit size scale). Finally, it was mechanically polished with Al2O3, moistened with water and cleaned with ultrasonic cleaning equipmnent. Polished surface was etched with 4 g FeCl3 - 30 cm3 HCl - 1000 cm3 CH3OH. The material has coarse - grained structure with grain diameter 8 – 15 mm. The samples for microhardness analysis No. 1 – 4 were taken from the grain No. 1, the samples No. 5 – 9 from the grain No. 2 and sample 10 was part of the grain No. 3. The dimensions of samples were 3 5 mm with thickness 6 mm. Before microhardness measurement the samples were mechanically polished as well as before etching.
The optical microscope NEOPHOT 32 with microhardness tester Hanemann, type Mod D32 was used as measurement equipment No 1. The smallest graduation on the scale of the equipment’s measurement system equals 0.3058 m. The measurement equipment No. 2 was optical microscope NEOPHOT 1 with microhardness tester of the same type as with microscope No. 1. The smallest graduation on the scale of the equipment’s measurement system equals 0.2865 m. Both testers were up to standard STN EN ISO 6507 – 2. The microhardness was measured according to standard STN EN ISO 6507 – 1 with load 20 g and loading time 10 s. The linearity requirement for the tester was satisfied between loads of 10 and 50 g.
Discrimination (resolution) is the amount of change from a reference value that an instrument can detect and faithfully indicate. The measure of this ability is typically the value of the smallest graduation on the scale of the equipment’s measurement system. A general rule of thumb is the measuring instrument discrimination ought to be at least one - tenth the process variation. If the measurement system lacks discrimination (sensitivity or effective resolution), it may not be an appropriate system to identify the process variation. The discriminations for both testers and used experimental material are not sufficient.
Grubbs’ test (with significant level ??= 0,05 %) was used for outliers detection. The statistical outliers indicate, that the process is out of statistical control. Again ideally, the causes of outiers are eliminated and new data is obtained. Only one outlier (tester No. 1 and appraiser C) was found. Normal probability is an assumption of the standard methods of MSA (Measurement Systems Analysis). In fact, there are measurement systems that are not normally distributed. When this happens and normality is assumed, the MSA method may overestimate the measurement system error. Therefore, before use, the data should be checked to confirm that its distribution is approximately normal. The normality was evaluated by normal probability plot, using software Freeware Process Capability Calculator by Symphony technologies. The normality of results of both testers and appraisers was confirmed.
One of the MSA methods, periodic GRR studies make it easy to establish and monitor the performance of a tester. A GRR study can quickly establish the short - time performance of a tester, including appraiser influence. The method will allow the measurement system’s variation to be decomposed into two separate components, reproducibility and repeatability, but not their interaction.
The GRR method - combined estimate of measurement system repeatability and reproducibility, with confidence 99 % and coverage 99 % (5,15 ??was used for determination of microhardness (HV 0.02) measurement system capability. The method used 3 appraisers, 10 samples, 3 trials (impressions) on each sample and 2 microhardness testers for quantification of capability (%GRR), repeatability (% EV – the influence of tester), reproducibility (% AV – the influence of appraisers) and part variation (% PV – variation between samples) of the system. Software Palstat CAQ, module MSA was used for calculation.
As the value of capability %GRR has been 56.3 % for the first tester and 77.3 % for the second one, the hardness measurement system and process realized within it are not capable and heavy depends on appraisers, mainly their different image focusing on testers, also in result of their different construction.
On the other hand, the means of results of both testers, compared by unpaired t test (??= 0,05 %) are consider to be not statistically significant (p = 0.3543).
The Z-score and Mandela’s statistics were used for comparison. Z – score show significant sample sensitivity and markedly appraisers and samples variability for tester No. 2. Mandela’s statistics are less sensitive as Z-score.
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| Keywords: MSA|capability|microhardness| |
| No 3 (2007), p. 402-411 |
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| Brehuv J., Magula R. |
| KNOWN AND UNKNOWN MINING-PROCESSING ACTIVITIES OF RISTOCRATIC FAMILY „DE SOÓSO“ |
| Keywords: |
| No 3 (2007), p. 460-464 |
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