How to Make a Simple Sand Mold

Transcription

1 4/8/2015 Metal Casting How to Make a Simple Sand Mold Kevin Bakey ENGL 202C

2 Introduction Sand casting is a metal forming process that uses sand as the molding material, allowing unique metal shapes to be cast for a low cost. Sand casting is one of many casting processes, but it has some unique attributes. Sand can be re-used for many castings since the sand is not damaged during the process, and only one pattern is needed to create a large number of sand molds. Recycling casting components makes this process a very economical option for both high and low volume production. With sand molding, you can cast almost any shape you can think of. This instruction set will take you through steps to make a successful metal casting using a sand mold. This document is limited to the making of the sand mold itself. Additional instructions are required to pour the molten metal and extract the shape. It assumes the reader has a basic understanding of the casting process and engineering terminology. This procedure should take place in a well ventilated area due to dust from the sand and fumes from molten metal. Time to make the cast will vary depending on size and complexity. Materials Pattern Chalk dust Sand (moist) Cope flask Drag flask Mold jacket Sprue Sand compactor Sand sifter Note: If you are not familiar with these terms, see the glossary at the end of this document before proceeding. Safety Equipment Safety glasses Gloves Boots Long pants Face Mask Note: Additional safety equipment may be required if working in a plant with other processes or close to the molten metal.

3 Instructions A pattern (in the shape of the desired metal object) is covered in sand, which is tightly compressed over it. The pattern is removed, leaving a cavity in the sand with the desired shape. Molten metal is poured into this cavity, taking on the shape of the pattern. Part 1: Making the Mold CAUTION: Heavy metal objects. Watch where you put your hands at all times so you do not pinch your fingers. 1. Secure the pattern between the cope flask and the drag flask. Lower both ends of the cope flask at the same time to fit on the connecting rods 2. Lightly coat the pattern with chalk dust This is so the sand does not stick to the pattern during removal 3. Pour sand into the sifter, filling the flask half-way with sand. Get rid of clumps by pushing them through the sifter 4. Compress sand with sand compactor Start at the edges and work your way to the middle Important to remove or crush all clumps of sand near pattern for a good product

4 5. Fill the rest of the drag with sand so that it is overflowing, and press sand firmly with hands Make sure the corners are packed tight 6. Remove excess sand to level with the flask ends Ensure all the sand is packed tight at this point If it is not, add more sand, compress again, and re-level the sand. Repeat as needed. 7. Flip the flask over. The empty cope flask should be facing up. 8. Repeat steps 2-6 for cope flask

5 Part 2: Preparing and Removing the Mold Note: Before moving on, sand should now be packed in both the drag and cope flasks. Make sure the drag flask is on the bottom. 1. Use a sprue to make a hole leading into the cavity Twist the sprue back and forth while pushing down firmly Keep digging the hole until you are sure you have reached the pattern. This is where the metal will be poured during casting 2. Remove the cope flask from the pattern and drag flask, lifting upwards slowly Place cope aside, the pattern should be face up You should now be able to see the imprinted pattern in the drag flask 3. Carefully remove the pattern from the drag flask, lifting upwards slowly. You should be able to see the other half of the pattern in the drag flask.

6 4. Put the cope flask back on top of the drag flask They must be aligned in the same fashion as they were with the pattern Fasten the flasks together at the corners to ensure a perfect match 5. Remove both flasks together by slowly lifting upwards Take your time, be very careful not to break the mold while doing this 6. Place the jacket over the completed sand mold. Do not over tighten the jacket as this may deform the sand The Jacket is only there to give some added stability to the mold

7 Congratulations! You have successfully created a sand mold. You are now ready to pour molten metal into your mold to create your shape! Take extreme caution when handling molten metal. Be sure to reference a guide for pouring hot metal before attempting to do so yourself. Once the metal has cooled, all you need to do is break the cast open and you will have your finished part. Glossary Pattern: A flat metal plate which has the form of the object you wish to cast. Cope flask: The cope is the top part of the mold. The cope flask is a box that keeps sand in place while it is compacted over the pattern. Drag flask: The drag is the bottom part of the mold. The drag flask is a box that keeps sand in place while it is compacted over the pattern. Mold jacket: Metal box that fits over the sand mold to add structural support and make sure the mold does not break during transport. Sprue: Metal cone used to cut a hole in the sand mold, allowing access to the internal cavity of the mold. This hole is where the molten metal will be poured during casting. Sand compactor: Any sort of ram or shovel can be used to compact the sand. Sand sifter: A mesh screen used to break up clumps of sand and make the sand finer.