Lecture-5 ELEMENTS OF GATING SYSTEM.pptx

Elements of gating system ppt

1. ELEMENTS OF GATING SYSTEM

2. INTRODUCTION In casting  process, gating system plays an important role to produce a high quality casting.  The main function of gating system is to lead molten metal from ladle to the casting cavity ensuring smooth, uniform, and complete filling. Gating system can be classified as  Pressurized  System And Unpressurised System .

3. PRESSURISED SYSTEM Pressurized System is referred to as "Gate Control System" , since ingates controls the flow of metal.  It is used for reactive metals like magnesium alloy etc. Pressurized  System consumes less metal and yield is more. In case of Pressurized  System, The system will always be full of liquid metal.

4. UNPRESSURISED SYSTEM Unpressurised System is referred to as "Choke Control System", since the choke controls the flow of metal. This system is used for normal metals such as brass, steel, aluminum alloy, etc. Unpressurised System consumes more metal and the yield will be slightly lowered. In case of unpressurised system, flow is not full.

5. GATING SYSTEM The term gating system refers to all passage way through which the molten metal passes to enter the mold cavity. It basically consists of : Pouring basin Sprue Runner Gates Risers

6. POURING BASIN A pouring basin make it easier or a ladle or crucible operator to direct the flow of metal from crucible to sprue. Helps maintaining the required rate of liquid metal flow, Reduces turbulence at sprue entrance. Helps separating the slag before it enters the sprue. If the pouring basin are made large: Dross and slag formation will tend to float on the surface of the metal and may be stopped from entering the sprue and hence the mould . They may be filled quickly without overflowing and may act as a reservoir for liquid metal to compensate metal shrinkage or contraction

7. Pournig basin

8. SPRUE A sprue feeds the metal to runner which in turn reaches the casting through gates. A sprue is tapered with its biggest end at top to receive the liquid metal. the smaller end is connected to the runner.

9. RUNNERS Runners are connected channels that convey the molten metal to different parts of the mould . A well-designed running system can regulate the speed of the molten metal, avoid shrinkage and minimize turbulence. It is vital that the running system does not have any sharp corners or edges which could restrict the flow of metal and reduce its effectiveness .

10. RISERS These are vertical channels that provide a continuous flow of molten metal to eliminate shrinkage as solidification occurs during the casting process . The design of the risers, including the size and the number, is determined entirely by the casting requirements. The risers must have sufficient capacity to supply the volume of molten metal needed to compensate for shrinkage. The design must also promote directional solidification. This can, in part, be achieved by placing the riser(s) near the thickest and largest part of the casting as this will cool and solidify last. Once the casting process has been completed, the risers and sleeves can be sawn off. The metal can then be recycled to make further sand castings

11. GATES A gate is a channel which connects runner with the mold cavity and through which molten metal flows to fill the mold cavity. A small gate is used for casting which solidifies slowly and vice versa. A gate should not have sharp edges as they may break during pouring and sand pieces thus may be carried with the molten metal in the mold cavity.

12. Types of gates: 1.TOP GATE The top gate sometimes also called as drop gate because the molten metal just drops on the sand in the bottom of the mould . DISADVANTAGE: T here is a lot of turbulence. The dropping liquid metal stream erodes the mould surface.

13. 2.BOTTOM GATES The bottom gate is made in drag portion of the mould . As comparison to top gate ,bottom gate involves little turbulence and sand erosion. Bottom gate produces good casting surface. DISADVANTAGE: In bottom gates liquid metals enters the mould cavity at the bottom . If freezing takes place at the bottom it could choke off the metal flow before the metal flow before the mould is full.

14. 3.PARTING LINE SIDE GATE Middle or side or parting gating system combine the characteristics of top and bottom gating system . In this the gate is provided along the parting line such that some portion of the mould cavity will be below the parting line and some portion will be above the parting line.