Question

13. Describe the process steps in sand casting? Compare to die casting, what are some major advantages and disadvantages of sand casting? 14. A large steel sand casting shows the characteristic signs of penetration defect – a surface consisting of a mixture of sand and metal. (a) What steps can be taken to correct the defects? (b) What other possible defects might result from taking each of these steps? 15. Using an explicit sketch to illustrate and describe the process steps in investment casting. What are the advantages and disadvantages of investment casting over sand casting? 16. What are some the operations required in sand casting after the casting is removed from the mould?

17. What are the most common metals used in die casting?

18. Which die-casting machines usually have a higher production rate, hot-chamber or cold-chamber?

19. What is the difference between true centrifugal casting and semicentrifugal casting?  

Answer 1

13. Before going know the process of sand casting first we discuss about casting. Casting is process which is useful to create a Replica of our physical model with small dimension chanes ( which is greater to original one because it needs machine operations)

Steps Involved in Sand Casting

1. Prepare a modling sand based up on our requirement with standard composition. let us take green sand( Silica sand particles+Clay+Water).

2. Place the drag on flat surface and put the Pattern on drag.

3. Pour the green sand on the drag slowly and ramming the sand slowly with wooden hammer.

4.Fill the Drag box fulley and Remove the excess sand then we get a flat sand.

5.Next flip the Drag box and place Cope box properly and lock it.

6.Place a straight tapered circular cross sectional Piece to Create a Sprue then pour the green sand and again Ramming.

7.In the Next step unlock the cope and drag remove the pattern and spruce part gently.

8. Create a runner for Molten metal passes.

9. then again fix lock the cope and drag in the same position, then Pour the molten metal through Spruce.

After filling the hole setup placed constant for few hours to solidify.

10. After few hours break the mold take out the new pattern and then sent to further maching process.

Advantages over Die Casting:

1. Less complexicity in construction

2. Easy to prepare

3. Easy to handle anyware

4. Good for Small Production.

5. ferrous and non ferrous mould can be prepared.

Disadvantages:

1. Complex Shapes are not produced.

2. Misrun Problems comes.

3. Only single product obtained.

4. Not Suitable for medium and large scale productioins.

14.a. When we preepare large steel sand casting that shows the penetration defect i.e a surface consisting of a mixture of sand and metal to correct this mistakeswe need take some caustions

i.e

1. Preparing the mould snad properly.if it not prepare well it mix with molten metal.

2. after preparing mould cavity check wheather any defects in cast mould ie cracks at edges etc. recorrect the damaged portion.

3. Prepare the proper Runner and in gate to flow the material in laminar flow. if it is turbulent sand particle mix with molten metal.

14.b. Possible defects:

1. Partially filled portions

2. Rat tails at cracks

3. Porosity

4.Hot tearing etc

15. For the procss steps of Investment casting go through with Photo in Below

Advantages and Disadvantages of investment casting over sand casting

Advantages

1. High degree of Dimensional Accuracy and no sand inclusion in mould.

2. High Reliability

3. VArious complex shapes can be produced.

4. Holds the toleranences between +0.005 to -0.005 this much tolerance cannot be obtained in other casting process.

5. good surface finished products.

6. High productivity.

Disadvantages:

1. It prepares only alloyed Products not preferable for ferrous materials

2. preparation of mold cavity is difficult.

16. Post Processing Operatons of Sand casting:

1. Clean the surface to remove the sand particles on surface.

2. Machine the Extra dimensions ie allowaned portions by supported machines.

i.e 1.turning,milling, broaching, grinding etc

3. preapre the surface with required surface finish.