It has been quite a while since I last posted on my blog due to lack of time and other things I have been doing. I have changed some of my equipment since I was last on here, including experimenting with waste oil burners and just recently homemade K-Bond casting sand. As a result of the WMO (waste motor oil) experiments, I have built two new oil fired furnaces, and will post details of them and the K-Bond sand later on. I will now continue on from where I left off and describe some of the larger items I have made.

Ball Mill
              When I first started out in metal casting, I was unable to get powdered Bentonite to mix up green sand. I was able to get granular Bentonite from a local rural supplier (it is used in cattle feed supplements) but had to find a way of turning it into powder. Some people on YouTube used blenders or coffee grinders to process granular Bentonite into powder, but I found although this worked, it was slow. I also tried an old corn cracker I had (used to crack corn for chicken feed). This is basically a couple of  serrated rollers that the corn passes through and has a large flywheel that was turned by hand. This worked better than the blender, but the Bentonite had to be put through several tines to get it fine enough. Also it was bloody hard work turning the handle. After thinking about the situation some more, and some research, I decided a ball mill would be the way to go. A ball mill is usually a drum shaped container containing ball shaped weights and the material to be broken down. This is then rotated slowly and the balls break down the material as they rotate in the drum. I had a suitable drum with a clip on lid, and made a frame to suit with a washing machine motor and pulleys to gear it down. I mounted the drum on four small wheels from the hardware shop and run a belt from the lower pulley around the drum itself, which gave the final reduction in speed needed. I couldn't find any suitable balls to use, but found some heavy cast iron weights that would do the job. It was then a matter of putting the Bentonite in with the weights,closing the lid and turning on the motor.
The longer it was left on the finer the Bentonite became. This was the easiest method I found to reduce the bentonite to powder. I also used the ball mill to mix up the clay and sand to make my green sand before I built my muller. After shaking out my moulds, the lumpy green sand was also put in the ball mill to recondition the sand. It could also be used to then mull the sand by adding the required water to the sand. This worked OK in place of a muller, although the green sand tended to stick to the drum. It was still better than using an electric drill and stirrer, but not as good as a proper muller.
            The only problem I have had is that the drum I had was a bit rusty and developed a couple of holes.
Also the drum is a little thin and the "balls" are pretty heavy so they tend to dent the drum. This hasn't been too much of a problem, but if I was doing it again, or using it more often, I would use a thicker drum. Maybe a section of an old hot water tank would work well. The thicker drum would probably help the bentonite break down quicker, as the balls would not dent the drum as they turned. Below are some photos of the ball mill and they should be enough to get an idea how it was made and give someone enough info to make something similar. I basically made it up as I went along and probably the only thing to watch is that the drum doesn't turn to fast as the balls will tend to turn with the drum. It must turn slow enough so the balls roll over the material and break it up.

This is the ball mill as it was first constructed with a steel drum turning on caster wheels.The motor is run to a counter shaft and the final reduction is achieved by running a belt around the drum itself. The drum is only a steel drum the same as oil or paint drums, it is only thin and has some small holes. 

             This side view shows the drive belt around the drum,
the caster wheels the drum rotates on, the chute that sends the contents into a container and on the ground are the cast iron weights used to crush the contents.

 This is the rear of the ball mill showing the counter shaft  using an old washing machine pulley. The belt around the drum is tightened by a air conditioner jockey pulley out of a car. The ply was put on the bottom of the drum to cover some holes.

This is a shot with the drum removed showing the A/C jockey pulley for tightening the belt around the drum.The electric motor is pivoted to tighten the counter shaft belt.

These are the cast iron "balls" used in the mill. They aren't quite round, but do the job!

This is the gas bottle I cut to make a new drum for the mill. The old drum was too thin, and had some holes that I couldn't fix. A thicker drum should work better as the balls will be working against something more solid.

Here is the new drum, the bottom of the gas bottle with a plate welded on the cut end, and a hinged door to add and remove the contents.

Here is the plate welded on to the end of the drum, the opening will be closed by a hinged door.










This is the door in place. It is hinged on the top and is held closed by a bolt welded to the outside of the drum and a tongue welded to the lid.

Here is the lid open showing the bolt and tongue for holding it shut and some felt glued around the edge to seal it when it is shut.

Here is the drum mounted on the rollers. I had to find a shorter drive belt and shift the rear rollers to level up the drum as they run in the groove in the drum.

Here is a side view showing the mounted drum and the rear wheels in the groove. This helps to keep the drum from shifting when it is turning.

 



The other side of the ball mill. All it needs is a coat of paint to tidy it up.










Next up I will feature the sand riddle (sieve) I made to sift my sand. I have two different ones, one does the sand for my green sand and is very fine, and another to screen the sand after it has been mulled to get it ready for use. Hope this will be a little quicker than my last post.