Since I am writing my very first actual engineering post, I believe the foundation is a good topic to start with. Any products such as cars, bridges, houses, and even a chair will require some sort of manufacturing process put into it. Sand-casting is of particular importance to me because it is a method that we use in my Manufacturing Process class lab. It is quite simple when you think about it, albeit the dangerous aspect of it. So what is sand-casting really?
No, I am not going write a report about this but I will try to explain the process. Really, sand-casting is just what it sounds like-sand + casting. Although, you cannot use regular sand; green-sand molds which is not necessarily green, but it should contain a little bit of clay and water for bonding. Patterns come in different forms and sizes but really, it is important to make the pattern slightly bigger to compensate for the shrinkage that occurs when the metal cools down. So we start off with a metal container that could be separated from the middle (becoming two separate parts) with the top part being cope and bottom being drag. So basically, the pattern is attached on the molding board (think of it as the floor) of the drag. Next process is kind of crazy!
We shovelled a bunch of sand on a sieve (aligned on top of the drag) and shook it continuously which causes a bunch of smaller sands to fall onto the drag-process is called riddling. Seriously, I do not know who came up with the term "riddling" but it sure is tiring (especially if have to do it so many times). Fast forward to the fun part, assuming that we rammed the sand as hard as we could every time, the sand should be pretty tightly packed-which is good. Last thing we want is the sand collapsing. We removed the pattern then we created a hole through the sand (should lead to the pattern) so we can pour the metal into it. Has anyone ever seen the process of melting a metal?
For this particular project, we used aluminum which was melted on a furnace. I know this may sound crazy-but, seeing molten metal in person is almost a once in a lifetime opportunity. It was marvelous. Dang, it took a while and it was obvious how powerful that furnace is from the noise it was generating. Seeing molten metal in person was quite astounding. Just the thought of metal not having control over its form at such high temperatures was crazy. Other students were taking videos and pictures with their camera phones but I thought that was a little weird. So we let the metal cool for about thirty minutes.......BIG MISTAKE.
The metal piece that we built had so much deformities that it was not even funny. Thirty minutes was not sufficient and it was probably the amount of water that was responsible. See, the water in the sand did not have enough time to evaporate so it probably reacted with all the high pressure vapors in the casting---->really, ask a chemistry major for the actual explanation because I really do not know. Good news is that 90% of all the metallic parts formed that day were defective. It is always nice when the mistake of a lot of people can quite nicely cover yours =). So, I brought home an actual deformed metallic part. In case you were all wondering about we were going to use these parts for, it is supposed to be for a miniature steam engine which is quite nice. Currently, we are building the piston in lab.
The shortcoming of sand-casting becomes obvious when you try to mold a very detailed pattern. Also, sand-casting itself, is not a very controlled process. Slackers could skip a few rammings and they could end up garbage. A different process would be required for those parts with really intricate details such as die-metal casting. Unfortunately, the actual die-metal casting process is beyond the scope of what we cover in lab although I may talk about it later in future posts if I am in the mood.
No comments:
Post a Comment