Gating and running System Presentation.pptx

Gating and running system

1. Knowledge of Gating System Types, Gating Ratio, and Design Principles Academic Training Presentation

2. Introduction to Gating System In sand casting, the gating system directs molten metal into the mold cavity. Proper gating design ensures high-quality casting and reduces metal wastage. A well-designed system controls metal flow rate, prevents turbulence, and reduces defects.

3. Functions of Gating System 1. Fill the mold cavity quickly without overheating metal. 2. Ensure smooth flow and minimize turbulence. 3. Control temperature to avoid shrinkage in casting parts. 4. Filter impurities and gases from molten metal.

4. Design Requirements of Gating System • Smooth and steady metal flow without splashes or oxidation. • Should not carry slag, gases, or impurities into mold cavity. • Must fill cavity efficiently with minimal metal waste. • Allow easy disassembly after solidification and maximize yield.

5. Main Components of a Gating System 1. Pouring Basin: Funnel-shaped entry regulating metal flow. 2. Sprue: Vertical passage guiding molten metal downward. 3. Runner: Horizontal channel distributing metal to ingates. 4. Ingate: Entry point where metal enters mold cavity. 5. Riser: Reservoir compensating for shrinkage during solidification.

6. Types of Gates • Top Gate: Metal enters from top; causes turbulence and poor surface finish. • Bottom Gate: Metal fills from bottom up; less turbulence but risk of early solidification. • Parting Line Gate: Combines both advantages; common in industrial practice.

7. Types of Gating Systems 1. Pressurized Gating System: - Decreasing cross-sectional area toward mold cavity. - Maintains back pressure and reduces air aspiration. - Common for cast iron and high-speed flow applications. 2. Unpressurized Gating System: - Increasing total area toward mold cavity. - Allows smooth flow with lower turbulence. - Common for aluminum and light alloys.

8. Gating Ratio Definition: Ratio of cross-sectional areas of sprue : runner : ingate. Formula: As : Ar : Ag Pressurized Systems → 1 : 0.75 : 0.5 (Gate control system). Unpressurized Systems → 1 : 2 : 2 or 1 : 3 : 3 (Choke control system). Example: Aluminum → 1:2:1 or 1:3:3 depending on alloy.

9. Hydraulic Principles in Gating Design Reynolds Number (Re = ρuL/μ): Predicts flow type (laminar or turbulent). - Re < 2000 → Laminar flow (stable). - Re > 2000 → Turbulent flow (undesirable). Bernoulli’s Equation: Total head remains constant; used to calculate velocity and pressure drop. Avoid sharp corners and maintain full liquid metal flow throughout system.

10. Steps in Designing a Gating System 1. Determine optimal pouring time based on metal and section thickness. 2. Design sprue with proper taper to avoid air aspiration. 3. Calculate choke area to control flow rate. 4. Design runners to maintain steady flow distribution. 5. Design ingates to control entry speed and temperature. 6. Place risers to compensate for shrinkage and gas release.

11. Pouring Time Calculations Gray Cast Iron (<450 kg): t = K(1.41 + T/14.59)√W Steel Casting: t = (2.4335 - 0.3953 log W)√W Ductile Iron: t = K₁√W (K₁ depends on section thickness) Copper Alloy: t = K₂∛W Accurate pouring time ensures complete filling and minimal defects.

12. Riser (Feeder) Design • Supplies molten metal to compensate for shrinkage. • Should remain liquid longer than casting section. • Recommended shape: Cylindrical with hemispherical bottom. • Volume/surface ratio of riser > casting section to ensure feeding efficiency.

13. Testing the Gating System Design 1. Transparent Mold Water Test: Observes flow behavior using colored fluid. 2. High-Speed Radiography: Monitors metal flow using X-rays. 3. Open Mold Test: Direct visual observation of metal flow. 4. Contact Wire Sensors: Detect metal front progression electronically.

14. Common Gating System Defects • Oxidation of molten metal. • Mold erosion due to high velocity flow. • Air aspiration and turbulence leading to porosity. • Uneven cooling causing shrinkage cavities.

15. Conclusion Proper gating system design ensures defect-free and high-quality castings. Selection between pressurized and unpressurized systems depends on alloy type. Accurate calculations of gating ratio, choke, and riser optimize performance. Hydraulic principles guide smooth flow and minimal turbulence. Effective testing validates design efficiency before production.