Course detail
Fundamentals of Foundry Theory
FSI-POB Acad. year: 2021/2022 Summer semester
The course makes students familiar with the physical properties of molten alloys, their flow in mould channels, and the interactions between the melt and the mould. Models of the nucleation phase of crystallization and of the growth phase form the necessary basis for a purposeful control of the crystallization of castings. The analysis of the processes taking place in a cooling casting is focused on the appearance of stress in the casting and on the effects and possibilities of reducing it.
Supervisor
Department
Learning outcomes of the course unit
Students will have become familiar with the basic processes taking place while the mould is being filled with molten alloys and when the latter crystallize and cool down to room temperature. Emphasis is on a purposeful control of these processes in order that castings or required properties can be obtained.
Prerequisites
Students must have the knowledge of the thermodynamics and kinetics of phase transformations (diffusion, phase equilibrium diagrams, phase transformations and their effect on structure and properties), thermomechanics (stationary and non-stationary transfer of heat by conduction, internal sources, transfer of heat by convection), and hydromechanics (properties of fluids, equilibrium of forces in fluids at rest, motion of fluids in fields of force).
Planned learning activities and teaching methods
The course is taught through lectures explaining the basic principles and theory of the discipline. Exercises are focused on practical topics presented in lectures. Teaching is suplemented by practical laboratory work.
Assesment methods and criteria linked to learning outcomes
Awarding the course-unit credit is conditional on attendance at exercises. The examination consists of a written and an oral part. In the written part the knowledge of sets of topics is tested, which the students were made familiar with in lectures. The oral part serves to test individual items of knowledge and to provide for correct marking.
Language of instruction
Czech
Aims
The course objective is to make students familiar with the basic processes taking place while the mould is being filled with molten alloys and while these alloys crystallize and cool down to room temperature. The emphasis is on a purposeful control of these processes so that castings of required properties can be obtained.
Specification of controlled education, way of implementation and compensation for absences
Attendance in lectures is recommended, attendance in exercises is obligatory.
Attendance at the exercises is required, being checked by the leader of practicals. In the case of absence from exercises, the leader assigns a topic for independent written work.
The study programmes with the given course
Programme N-SLE-P: Foundry Technology, Master's
branch ---: no specialisation, 6 credits, compulsory
Type of course unit
Lecture
39 hours, optionally
Teacher / Lecturer
Syllabus
1. Hydraulic relations in castings, free flow, flow in sprues and runners of the gating system.
2. Physical properties of molten alloys, laminar and turbulent flow, running quality, melt-wetting of moulds, melt penetration into the mould.
3. Thermodynamics of crystallization, three distinct zones with different grain structures in the macrostructure of castings, a survey of the theories explaining their appearance.
4. The nucleation phase of crystallization, nucleation rate, model of homogeneous nucleation, heterogeneous nucleation on a planar substrate.
5. Models of heterogeneous nucleation in the cavities of refractories.
6. The phase of crystal growth, heat transport at the interface and in the mould/casting system.
7. Transport of mass at the interface, appearance of segregation
8. Constitutional supercooling, morphology of phase interface.
9. Control of metal crystallization, dynamic methods, melt modification, crystallization control in the phase of crystal growth, single crystals.
10. Crystallization of the basic types of foundry alloys.
11. Volume changes during casting solidification and their consequences, heat nodes, concentrated and scattered shrinkage cavities.
12. Cooling of castings from the solidus temperature, volume changes during phase transformation in solid state, metal shrinkage, changes in mechanical properties, appearance of thermal and phase stresses in castings.
13. Effects of state of stress in a cooling casting, appearance of cracks, ruptures and warping in castings, potential reduction of state of stress in castings.
Laboratory exercise
14 hours, compulsory
Teacher / Lecturer
Syllabus
1. Practical tests of running property (the Curry spiral, platelets of varying thicknesses), aluminium, cast iron
2. Modelling the flow in the gating system – plexiglass model, flow in the pouring basins + simulation
3. Thermophysical properties of the mould, establishing experimentally the heat accumulation coefficient of mould
bf
4. Solidification of castings, experimental determination of the solidification constant
5. Experimental measurement of temperature fields in the casting and in the mould, condensation zone
6. Experimental measurement of temperature vs. time in the casting and in non-insulated, insulated and exothermal risers
7. Solidification vs. time in an experimental casting
Exercise
12 hours, compulsory
Syllabus
1. Introduction to metal flow, theory of running property, basic tests of running property
2. Gating systems, their types, calculation of simple gating systems (underpressure, overpressure)
3. Introduction to the measurement of temperature fields, possibilities of measuring by thermocouples, optical pyrometers and thermocamera
4. Casting risering, calculation of modules, evaluation of experiments
5. PC simulation of solidification, prediction of shrinkage cavities, comparison of simulation and experiment
6. Stress and casting deformations, PC simulation of stress