Foundry-Basics
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The document provides an overview of the sand casting process in 13 steps: 1. Mix sand and create molds using patterns. 2. Place pattern in bottom mold and compact sand. 3. Add top mold and fill with compacted sand. 4. Remove pattern to leave a cavity in the sand. 5. Pour molten metal into the mold. 6. Allow metal to cool and harden. 7. Break apart mold and remove the new cast part.
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Foundry-Basics
- 1. Foundry-Basics By Mr.B.Ramesh, M.E., (Ph.D.), Research Scholar, CEG, Anna University, Chennai. Associate Professor, Department of Mechanical Engineering,, St. Joseph’s College of Engineering, Jeppiaar Trust, Chennai-119
- 2. What is a Foundry? • Casting is one of the oldest industrial processes • There are different casting processes. The focus here is: “GREEN SAND” CASTING A foundry is: a factory that pours molten metal into molds, producing cast metal objects. Some typical cast metal objects: Turbine blades in jet engines Engine blocks, axles Aluminum pots
- 3. SAND-CASTING Sand, mixed with clay binder & water (so it will hold its shape) plus coal dust to improve surface finish Pattern (a copy of the shape you want to produce, made of wood, plastic or metal) Basic materials & equipment for green sand-casting Container of molten metal (filled from furnace) Top and bottom mold forms (made of metal, open at top and bottom) Rammer (tool to compact the sand; often a pressing machine is used)
- 4. SAND-CASTING MOLDING: Sand placed into bottom mold form & compacted MOLDING: Pattern placed into mold A very basic summary of the sand casting process. . . First of all, mix the sand. 2 1THEN
- 5. SAND-CASTING MOLDING: Add the top mold form 3 4 MOLDING: Fill top form with compacted sand. A tube or pipe provides a path to pour the metal in Pattern is still inside!
- 6. SAND-CASTING MOLDING: Take the top mold off and remove pattern & pipe or post 5 6 MOLDING: Replace the top mold and fasten securely! Pouring hole In the middle of the sand is a cavity shaped like the pattern!
- 7. SAND-CASTING 7 CASTING: Pour the metal (container is filled from furnace immediately before you are ready to pour) 8 Wait for the metal to cool (minutes to days, depending on the size of the casting)
- 8. SAND-CASTING 8 SHAKE OUT: Break apart the two halves of the mold & take out the part—usually requires vibrating or striking the mold to break apart the sand CLEANING. Sand is cleaned off the part, the “tab” where metal flowed in must be removed. 9 A copy of the pattern has now been made in metal 10 Mold forms are reused 11 Sand is broken up, screened to remove debris and clumps, and sent for remixing
- 9. SAND-CASTING Sand-casting is simple in concept, but demanding in execution. It is a process essential to making basic and advanced products. . . it is also hazardous and energy-intensive!
- 10. Sand Casting: Parts of a Sand Mold (expendable mold) Key terms: Flask, Cope, Drag, Sprue, Runner, Gate, Riser, Mold Cavity, Core, Parting Line, Draft (not shown).
- 13. Patterns What is pattern? • Approximate duplicate of product • Patterns are made in the shape of the casting • Pattern Materials: Wood, Plastic or metal. • One piece or multiple piece pattern
- 14. Types of Patterns Types of patterns used in sand casting: (a) solid pattern (b) split pattern (c) match plate pattern‑ (d) cope and drag pattern
- 15. Pattern Making One piece or Solid Pattern Cope & Drag PatternMatch Plate Pattern Split Pattern
- 16. Pattern Allowances Shrinkage Allowance Patterns are made larger than the casting to compensate contraction of the liquid while freezing. For internal cavities the allowances should be negative. Machining Allowance Allowance required to remove the rough cast surface. 2 to 25 mm (0.1 to 1’) Draft Allowance To facilitate ease of removal, usually ½ to 2 deg. Shrinkage allowance Normal shrinkage: Cast iron 0.83 to 1.3% Aluminum - 1.3%
- 17. Cores Cores • Cores are used to create internal cavities. • Should have similar properties as the mold. • Shaken out after casting is produced.
- 18. Process 1 Mould
- 19. 2
- 20. 3 Dolly
- 21. 4
- 22. 5Sprue Pins
- 23. 6
- 24. 7
- 25. 8
- 26. 9
- 27. 10
- 28. 11
- 29. 12
- 30. 13
Editor's Notes
- The pattern must be slightly larger than the finished part you want to produce, as metal shrinks when it cools (about 10mm/meter, depending on the lengh)
- STRONGLY SUGGEST that presenter be prepared with props:
- Note that the top form and bottom form lock together; they always fit together the same way!
- In “dry sand casting,” the molds filled with sand are baked to increase the strength of the sand. In green sand casting, the water with which the clay is mixed is not evaporated.
- Sometimes the molds filled with sand are baked to increase the strength of the sand
- For very large parts, sand set on the shop floor forms the bottom half of the mold. This is “floor molding”
- Key hazards: burns, silicosis (from inhalation of dust), toxic fumes when organic binders are volatilized by molten metal.