Genel Demir Döküm ( ingilizce ) CHAPTER CONTENTS 1 METAL CASTING 1 Selection of castings of various materials, shapes, and sizes 1.1 Overview of Casting Technology Definitions Casting nomenclature Heating and pouring Solidification and cooling 1.2 Casting Processes Expandable mold casting Permanent mold casting 1.3 Casting quality Casting nomenclature The figure in the right shows the nomencla- ture of mold and castings in sand casting. 1.1 OVERVIEW OF CASTING TECHNOLOGY Advantages Complex shapes Net-shape ability Very large parts Variety of metals Mass production Disadvantages Poor accuracy Poor surface Internal defects Mechanical properties Environmental impact Casting nomenclature Definitions Casting is a process in which molten metal flows into a mold where it solidifies in the shape of the mold cavity. The part produced is also called casting. Mold preparation Metal heating Pouring Processing Cooling Casting technology involves the next steps:Metal Casting 2 Valery Marinov, Manufacturing T echnology The pouring cup, downsprue, runners, etc., are known as the mold gating system, which serves to deliver the molten metal to all sections of the mold cavity. Gating system in sand casting Heating and pouring Heating The total heat required is estimated as the sum of ? Heat to raise the temperature to the melting point  Heat of fusion Ž Heat to raise the molten metal temperature to the temperature of pouring Pouring Major factors affecting the pouring action ? Pouring temperature  Pouring rate Ž T urbulence Some important equations in pouring: Pouring cup Downsprue Gates to casting Runner Runner well Runner extension Downsprue well Velocity of the liquid metal at the base of the sprue: Gravitational acceleration constant Sprue height gh v 2 Volumetric flow rate: Casting’s cross-sectional area Q = vA Mold filling time: MFT = V/Q Mold cavity volume Fluidity Fluidity is a measure of the capability of a metal to flow into and to fill the mold before freezing. It defines to the great extend the quality of casting. Factors affecting fluidity: ? Pouring temperature  Metal composition Ž Heat transfer to the surroundings  Viscosity of the liquid metal Standard testing method Pouring cup Downsprue Spiral mold Limit of flow before freezing In the foundry practice, test for fluidity is carried out for each ladle just before pouring the molten metal into the moldMetal Casting 3 Valery Marinov, Manufacturing T echnology Solidification and cooling Solidification of metals Pure metals solidify at a constant temperature equal to their freezing point Most alloys freeze over a temperature range Chvorinov’s rule TST—total solidification time C m —mold constant V—volume of the casting A—surface area of the casting n—constant, usually n=2 n m A V C TST Solidification time Example: Calculate the total solidification time for a 10/100/200-mm steel plate if C m = 0.2 min/mm 2 Solution:Metal Casting 4 Valery Marinov, Manufacturing T echnology Shrinkage Directional solidification ? By a proper design of the casting  By external and internal chills Several riser designs are used in prac- tice as shown in the figure. The riser must remain molten until after the casting solidifies. The Chvorinov’s Rule is used to cal- culate the riser’s dimensions. Riser design Open Blind Top Side Casting Mold Riser Casting Mold Riser Casting Mold Riser Casting Mold Riser Possible types and positions for risers in sand casting Riser design