Casting the Keel bulb

 Over the last week or so, I cast the bulb for the keel.  As I mentioned in a previous post, Chad (http://i550knotracing.blogspot.com/) created a "community" bulb plug that I used in creating the concrete mold for the bulb.  I decided to cast the bulb in one piece rather than in halves like some of the other builders.  

 The photo to the left shows the mold and the stainless steel pot that I used to melt the lead. The light weight ladle shown was just used for skimming scum off the top of the lead.  For the actual casting, I bought a Rowell #6 casting ladle from Amazon.  The handle of the  casting ladle is just visible on very left of the photo.  I highly recommend this ladle.  It has excellent size and strength.  My wife actually likes its appearance and wants to use it for decorations later.  I also used a Bayou Classic propane cooker (also bought through Amazon).  This cooker is designed for crawfish boils and puts out a lot more BTU's than your average turkey fryer.  


You can also (barely) see in the photo above that one end of the mold is sitting on a 4X4 and the other end is supported by a hydraulic car jack.  This turned out to be a pretty good idea because it allowed me to tilt the mold a bit so that the molten lead flowed either forward or backward to the ends.  One change that I definitely would have made to this set up is that I would have put the mold closer to the molten lead pot.  Not only would this have reduced the lead drips on the driveway, it also would have made the process faster, eliminating some of the problems that I'll describe below.

The picture to the right shows the plug after I dumped it out of the mold and after I dug out the insert for the keel foil.  A comment about the insert - I made a mold for the insert by wrapping fiberglass around the keel foil with plastic between the glass and the foil.  After the epoxy set, I then removed glass form and then shaped one end so that it fit inside the bulb mold.  Before pouring concrete into the form, I drilled holes in the bottom of the mold and inserted a section of wire coat hanger  in a U shape.  The coat hanger was for two purposes 1) to make the foil insert hold together and 2) to hold it down so that it doesn't lift off and float in the lead.  If I had it to do over again, i would have added a lot of sand to the concrete mix that I poured into the foil insert form, to make the insert almost like a sand casting mold.  It was a lot of work getting the insert out of the bulb, and I think that extra sand would have made the concrete much weaker and easier to remove.  


The final picture here shows the bulb with fairing compound on it next to the original mold plug that was made by Chad.  


Here were some of the problems that I ran into in creating the casting:  First, as mentioned above, I did not work fast enough in pouring the lead and there was noticeable layering of the lead in the casting.  Secondly, if I were to make the mold again, I would have added at least one more pouring hole that was away from the keel foil insert.  The two holes that I had were on top of the keel foil insert which substantially slowed down the pours and I ended up with some voids on the top (really the bottom) of the plug.  I later filled these voids by pouring additional lead onto the plug.  This left a very uneven surface on the bottom of the plug.  I filled in these irregularities with fairing compound.


The final change that I would make if I were to cast this bulb again is that I would have melted all of the lead at once instead of adding to the pot as I went along.  I'm not sure why I didn't do this, although I was thinking that I didn't need all of the lead that I bought (I bought about 200 pounds), and that it would be easier to not melt the unneeded lead.  This was a mistake which again slowed down the process and resulted in some of the layering in the lead.  I ended up with a 30 or 40 pound ingot at the end of the process anyway.


My next step for the bulb is to wrap the whole thing in either carbon fiber or glass cloth.  I'm pretty sure that this step isn't necessary, however with the visible layers in the bulb the last thing I want is for a chunk of the bulb to fall off some day.