METAL 2009 19. – 21. 5. 2009, Hradec nad Moravicí ________________________________________________________________________________

FOLLOWING BRAKE RETRACTION CASTS FROM ALLOYS ALUMIN UM AND ZINC

Pavel Pěnička – Iva Nováková

Faculty of Engineering, Department of Engineering Technology

Technical University of Liberec, Czech Republic

Precis The thesis deals with the dilatation during solidification of cast. There was used special measuring arrangement that makes possible the monitoring of values of dilatation and temperature of cast during solidification alloys of zinc and aluminum. These values were measured by the help of recording unit and were noted down to the computer. Measured values were recorded to charts and given connections brought up to graphs. Evaluation of given dependences, that were brought up to graphs, was next part of this work . In the end of diploma work, there are mentioned calculations of coefficient thermal contractility of cast. 1. Introduction Nowadays, alloys of nonferrous metals are asserted in industrial practice more than in the past, above all aluminum, bristly ox-tongue and zinc, eventually copper, titanium etc. Benefits of dominant characteristics of alloies aluminum and zinc are used especially in car industry.

Relativelly, fractional density (2700 kg.m-3), high heat conductivity (207 W.m1.K-1) and good foundry characteristics are the main characteristics of alloys of aluminium. Alloys of zinc embody low temperature melting (less than 420 °C) and unpr etentious casting. Main technologies of casting of both these materials and their alloies is high pressure way. This technology interlocks high dimensioned accuracy and smoothness of casts. Foundry from alloys of aluminum embody consistence without internal vices (pistons and heads of gas-engines) during gravity casting to the metal forms.

Fig 1.Demonstration of cast piston

2.Basic characteristic of alloys aluminum 1) production of aluminium oxide from alumina cement ores; 2) reduction of oxide on metal aluminum by electrolytic way from electrolyte Physical properties of netted aluminum are: a) density 2700 [kg.m-3] b) thawing point 660 °C c) temperature vaporization 2520 °C d) crystallic grating, cubic and areal centered e) grid constant a = 4,05.10 -10m f) atomic number 13 g) atomic materiality 26,98 The biggest physical properties of aluminum are in high heat as well as in electric conductivity.

And so we can claim that the heat conductivity of aluminum includes for about 235 [W. m1. K-1] at

METAL 2009 19. – 21. 5. 2009, Hradec nad Moravicí ________________________________________________________________________________ temperature of 20 °C. And then the coefficient of e lectric conductivity of aluminum with cleanness of 99,99% (relatively) stands by standard temperature so about 2,6.10-8[�m]. It is possible to arrange it with about 60% of electric conductivity of copper. It is necessary to claim that thanks to influence of ingredient elements, coefficient of thermal expansion lowers extremely with standard

temperatures, it is about 23.106 [K-1]. Aluminum forms with oxygen very stationary oxide AL 2O 3.

2.1 Characterization of casting alloys of aluminum Mostly used alloys of aluminum are silumins (binary alloys Al-Si), which we classify into hypoeutectic, eutectic and hypereutectic according to eutectic poin. In the picture 2- 1, there comes out constitution diagram Al-Si. This binary alloy could also contain next elements, whose occurrence is lower than 0,1%. If we want to use this alloy in grocery and if we need to have it corrosion-proof, we will use 0,05% copper there. If we add titanium there in quantities of 0,1 to 0,2%, we will get dulcification of grains in primary phase � (Al). Prime silumins have good foundry characteristics. Casts have good tightness in the face of gas and liquids, they have also good weldability and tolerance in the face of corrosion. But it is true that workability isn't just best. The higher is content of Si, the better are foundry characteristics. Standardized alloys usually contain 10 to 13% of Si. These alloys is possible to apply for casting to the sand forms, metal forms and also for compressive cast. If we have higher content of silicon, it is good to modify it by natrium or strontium during gravity casting.

melt (L); ��� - stiff solutions

temperature thawing: net aluminum 660°C; net sili con 1412°C Fig 2.Constitution diagram Al-Si (unmodified melt)

2.2 Basic physical properties of zinc

a) density 7130 [kg/m3] b) melting temperature 419 °C c) boiling point 906 °C d) molar materiality 65,37 e) heat conductivity 113 [W/mK] f) specific heat 0,39 [kJ/kgK] g) latent heat thaw 100 [kJ/kg] 2.3 Characteristics of foundry alloys of zinc Zinc isn´t used like independent metal in foundry industry but his alloys are used, because zinc doesn´t embody the best mechanical characteristics. It isn´t also used for production of machine parts. Zinc reaches these characteristics as late as with admixtures with other metals, like e.g . with aluminum and copper. Zinc is linked to the group of heavy nonferrous metals with low smelting temperature (420 °C). It granulates in he xagonal crystallic system.

METAL 2009 19. – 21. 5. 2009, Hradec nad Moravicí ________________________________________________________________________________ Foundry alloys of zinc Aluminium is employed like a main ingredient element. Constitution diagram of the system Zn- Al (see in the picture 2- 4) is the type of the diagram with primary phase with limited solubility of the ingredient element and with origin of eutectics. Eutectics is created by a phase of Zn-ZnAl. Eutectic temperature of the system of Zn- Al egualed 382°C at concentration 5,5% of Al. Content of aluminum in standardized alloys are at intervals 4 to 27% Al.

Fig 3.Balanced dichotomous diagram of Al-Zn It is obvious that foundry alloys have approximately eutectic up to hypereutectic constitution and solidification usually begins by secretion of primary phase ��Al. The lowest smelting temperature and narrowest interval of solidification have approximately eutectic alloys with the content around 4 up to 5% of Al. The higher content of aluminum we have, the higher temperature of liquidation is. There is also broader solidification range. We can use copper and bristly ox-tongue there in the first place as adjacent ingredient elements. 3. Experiments that we did at the department of KSP - TU in Liberec The experimental part of this work was bent on monitoring the process of free shrinkage during casting of choice alloies of aluminum and zinc. Test gear for examination according to Bočvar and Sviderský was used for that purpose and it was modified for scan dilatacnich changes during solidification and chilling of casts of specific form „sponge – biscuit". Inductive pick was used for scan, dilatometer of Polish production and PC.

Fig 4.Associated diagram of the display for measurement of braked shrinkage of the cast

METAL 2009 19. – 21. 5. 2009, Hradec nad Moravicí ________________________________________________________________________________ 3.1 Characterization of measuring equipment Measuring equipment is formed with arrangement according to Bočvar and Sviderský. Dilatometer is intended for measuring dilatation changes. The temperature dependence on time is here as well as dilatation on time. We prepare thermocouples that we hold on the stand. Then we add it to cable where we have appropriate cables that are marked in red (+) and blue ( - ). We add cable to the measuring apparatus by the help of desinence with pins . We also add dilatometer. Every drawer in a given apparatus is named because of the knowledge of each place of things. This apparatus of Bočvar and Sviderský is connected with Pc and with the technology where we have appropriate software that can communicate with measuring apparatus. Firstly, we set up values in that software and it is ready for casting after activation of the program. I casted clean aluminum (Al) where pre-heating in electric furnace was set up on 720°C. We also casted alloy of aluminum (AlSi7) from that temperature. We preheated the clean zinc on temperature of 720 °C and it was again in electric furnace. We drained it from subsequently. We also drained alloy of zinc (ZnAl4Cu3 (430)) from that temperature. We always waited to a temperature of 50 °C where we chose this parameter in a given software. All casts were made in the shape that remind us the form of sponge - biscuit.

1 - frame; 2 - platen; 3 - cavity for cast; 4 - part sinuses with sand mixture; 5 - movable metal formative board; 6 - compression spring; 7 - nut; 8 - measuring sensor dilatation Diagram of measuring equipment according to Bočvar and Sviderský. Spring will give a power on this arrangement that creates prestress and thanks to that braked shrinkage of congeable(coolings) casts comes.

Fig 5.Diagram of the part of measuring equipment

Fig 6.View of general measuring installation

METAL 2009 19. – 21. 5. 2009, Hradec nad Moravicí ________________________________________________________________________________

300

320

340

360

380

400

420

440

460

480

500

520

540

560

580

600

620

640

660

680

700

0 500 1000 1500 2000 2500 3000 3500

čas(s)

tepl

ota

(°C)

-1,6

-1,4

-1,2

-1

-0,8

-0,6

-0,4

-0,2

0

0,2

dila

tace

(m

m)

teplota

dilatace

Fig 6.Time dependencies of temperature and changes of the proportion of cast that has form „

sponge - biscuits" longitude 157 mm from alloys of aluminum (AlSi12) casted from the temperature of 720 °C

300

320

340

360

380

400

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460

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500

0 500 1000 1500 2000 2500 3000 3500

čas(s)

tepl

ota

(°C)

-1,4

-1,2

-1

-0,8

-0,6

-0,4

-0,2

0

0,2

dila

tace

(m

m)

teplota

dilatace

Fig 7.Time dependencies of temperature and changes of proportion of cast that have form of „sponge - biscuit" longitude 157 mm from alloys of zinc (ZnAl4Cu3), casted from the temperature

of 550 °C

METAL 2009 19. – 21. 5. 2009, Hradec nad Moravicí ________________________________________________________________________________ Calculations coefficient of thermal contractility α.

[ ]1

0 .−

∆∆= K

Tl

lα value l0

= 157 mm. Calculated values � are mentioned in sheets.

Tab 1. Values of coefficient thermal shrinkage �� that was gained on the basis of chilling of the cast from alloys AlSi12, including thermal range and value of dilatation.

Number of measuring

Temperature [°C] Dilatation with given temperatures [mm]

Coefficient of thermal expansivity α[K -1]

1 660 až 680 -0,0007 2,23.10-7

2 640 až 660 -0,0010 3,18.10-7

3 620 až 640 0,0072 2,29.10-6

4 600 až 620 0,0287 9,14.10-6

5 580 až 600 0,0336 1,07.10-5

6 560 až 580 0,0017 5,41.10-7

7 540 až 560 -0,0580 1,85.10-5

8 520 až 540 -0,0965 3,07.10-5

9 500 až 520 -0,1309 4,17.10-5

10 480 až 500 -0,1649 5,25.10-5

11 460 až 480 -0,2055 6,54.10-5

12 440 až 460 -0,2469 7,86.10-7

13 420 až 440 -0,2925 9,32.10-5

14 400 až 420 -0,3449 1,10.10-4

15 380 až 400 -0,4008 1,28.10-4

Tab 2. Values of coefficient of thermal shrinkage � gained on the base of chilling of cast from alloys of zinc ZnAl4Cu3, including thermal range and values of dilatation.

Number of measured

Temperature [°C] Dilatation with given temperatures (mm)

Coefficient of thermal expansivity α[K -1]

1 470 až 480 -0,0002 1,27.10-7

2 460 až 470 0,0002 1,27.10-7

3 450 až 460 0,0007 4,46.10-7

4 440 až 450 0,0010 6,37.10-7

5 430 až 440 0,0015 9,55.10-7

6 420 až 430 0,0021 1,34.10-6

7 410 až 420 0,0035 2,23.10-6

8 400 až 410 0,0062 3,95.10-6

9 390 až 400 0,0085 5,41.10-6

10 380 až 390 -0,0001 6,37.10-6

11 370 až 380 -0,0269 1,71.10-5

12 360 až 370 -0,0654 4,17.10-5

13 350 až 360 -0,1031 6,57.10-5

14 340 až 350 -0,1303 8,30.10-5

15 330 až 340 -0,1534 9,77.10-5

METAL 2009 19. – 21. 5. 2009, Hradec nad Moravicí ________________________________________________________________________________ Cuts given alloies of aluminum and zinc

Fig 8.Refined and fretted exhibits of alloy Zn Al4Cu3

Fig 9.Refined and fretted exhibits of alloy Al Si12

4. Bibliography: GRÍGEROVÁ, T., LUKÁČ, I., KOŘENÝ, R.: Zlievárenstvo neželezných kovov, 1.vydání, Bratislava/Praha 1988 Pěnička P.: SLEDOVÁNÍ BRŽDĚNÉHO SMRŠTĚNÍ TUHNOUCÍCH ODLITKŮ ZE SLITIN ZINKU A HLINÍKU[Diplomová práce],KSP-FS,TU v Liberci, 2007 NOVÁ, I.: Tepelné procesy ve slévárenských formách. [Skripta] KSP-FS, TU v Liberci, 2003 PŘIBYL, J., VETIŠKA, C.: Teorie slévárenství. 1. vyd. Praha, 1963