Lid and Lifter

I had some time this afternoon to get the lid lifting mechanism mounted on the furnace drum body and drum lid.

I started by drilling 1/4-inch holes at the locations already marked with silver Sharpie, and then just pushed the threaded rod through the holes, set fender washers on the rod, and then thread the 10mm washer nuts on.

The pipe-in-pipe mechanism is very securely attached to the furnace shell, and the clamps do not permit the outside pipe to move up and down at all.

I measured the determine how much of the inside pipe had to be cut off so that the lid would sit on top of the furnace body.  It was about 7-1/4 inches to cut off.  Then I smoothed it with the grinder.

I had to adjust the top outside pipe down and I had to back out the adjusting screw to get the lid to lift, but there is just not very much lift - maybe 3/4-inch of vertical travel.  Plus, the lid sags or droops from the pivot point.  This sagging will only become more pronounced when I have the brick and insulation installed in the lid. 

 

For now I will just lift using the handle, but I think I will have to redo the lifting mechanism lever and foot pedal so that I can get about an inch of vertical travel.

To counteract the sagging, I can put washers behind the top pipe clamp on the bottom exterior pipe to tilt it out and away from the drum slightly.  This would have the effect of tilting and lifting the lid up.

 

I could also screw a pipe reducer onto the top exterior pipe and run a 1-inch mast up above the lid.  From the mast I could run threaded rod down to the lid and use turnbuckles to pull the lid back.

Another thing I may try is taking the metal cutting shears and trimming some of the cut rolling ring at the base of the lid back.  This would give a little more clearance

Maybe combination of all of these ideas will get the lid working the way that I expect it to. 

Lid and Lifting Mechanism

The pipe clamps were delivered on Friday and I began working on attaching the clamps to the outside pipe.

I got a 24-inch length of 1/2-inch black pipe and I cut 3/4-inch long spacers from it.  These will hold the clamps off of the side of the drum so that the lifting mechanism will clear the rolling rings on the drum.

On top of the lid I installed two garage door pulls as handles.  These can be used to swing the lid after the lifting mechanism lifts it up, or they can be used to lift the entire lid off of the furnace body for maintenance.

On the side of the drum I have marked the centerline and hole locations.  I will have to unpack the insulation from one side of the furnace body, drill the holes, install the clamps through the holes and fasten them down with fender washers and nuts on the inside of the drum.  Then I will replace the insulation.

On the lid I have marked the hole locations.  I will drill them and install the clamps the same way as the bottom clamps.

After that is done I will assemble the whole thing and then measure how much of the inside pipe has to be cut off so that the lid will close fully.  To take the inside pipe off and cut it, the outside pipe on the furnace body will have to be temporarily removed as well.

I will drill through the outside pipe and through the inside pipe and press a roll pin in so that the inside pipe and outside pipe turn together with the lid.

Farther down, just above the lower outside pipe, I will drill a hole through the inside pipe only.  Then I will file notches in the top of the outside pipe to serve as detents to hold the lid in position.

Once all of this is done, I will pull the lid off and begin installing the insulation inside of it and fastening the bricks and fiberboard down.  I had some 1-inch wide, 1/8-inch thick braided fiberglass gasket and furnace cement delivered today.  These will be used to keep the steel clips covered up.

I know the progress has been slow, but I have been making progress!  I should have this furnace completed in a couple of weeks.

Lid Insulation Work

This morning I cut the ceramic fiber insulation board into a torus.  The furnace ceiling will rest on the fiberboard and be cushioned by it.  The ring of fiberboard will be supported by the perforated steel clips that will be connected to the steel drum by 5/16" screws.

I was going to place another ring of fiberboard over this to cover the clips up, but now I can see that it will be too thick if I do.  

I need to find a 1" x 1/8" fiberglass ribbon that could be laid over the clips and affixed with furnace cement.  

The clips need to be covered so that they are insulated from the furnace heat.  Otherwise, they will conduct heat right to the shell, making the shell very hot.

In the center of the torus the firebrick will be exposed.  A 1"x 1" ceramic fiber rope gasket will be glued in with sodium silicate.  This gasket will seal against the top of the heating chamber firebricks when the lid is closed.  The weight of the firebrick ceiling should help keep the gasket compressed.

Because the outside of the shell did not get hot during testing yesterday (it did warm up after a couple of hours soaking), I am encouraged to put tape and decals right on the side of the shell.

 

I intend to affix warning decals to the lid and body.  The decals will warn of high temperatures and hazardous voltage.

Here you can see that I wrapped safety tape around the lid.

I am going to put a couple of garage door pulls on the lid for positioning the lid when it is lifted up off of the body by the lifting mechanism.

Heat Up Rate Testing

Right now I am in a holding pattern on the furnace while we wait for pipe support clamps to arrive from China.  

The pipe support clamps will support the lifting mechanism.

I cannot assemble the lid until the lifting mechanism is fastened to the side of the drum.

This morning I installed a 3-amp fuse and fuse holder in the power supply line to the PID controller, and I put a spade-type disconnect in the control line to the SSRs.  I put the disconnect inline so that I will be able to easily open the circuit and install the door safety limit switch in the future.

After disturbing all of the wiring, I thought it would be a good idea to plug in the furnace and test it.  I installed ceramic wool insulation in the drum since the last time we heated it up.

When I turned the controller on, it was at 20 °C - room temperature.  I changed the set point temperature to 750 °C and began to monitor the heat up.  I placed two firebrick over the heating chamber as a temporary lid, like before.

With ceramic wool insulation the heat up rate was faster than before.  It is about 27 °C / minute now.  Plus, the steel furnace shell never got hot - it remained at room temperature.  So, now I know that I will not have to rebuild the furnace into a larger steel drum.

It took 27 minutes and 17 seconds to come to 750 °C.  I am sure it will be a little longer when there is a metal charge in the chamber to melt, but the completed furnace will also have a heavy and well-insulated lid to hold in more heat.

I have read about other electric foundry furnaces in online forums and most report very slow heat ups of over an hour.  So, I am pleased that my little furnace performs so well.