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To remove the rust on my Clausing mill, I tried several different methods. Here are the results of the derusting.
Rust Converting and Dissolving Solutions
For non-imersable parts (column and base) I tried 2 different products "All Rust Remover" and "The Must For Rust", both were purchased from the local hardware store.
1. "All Rust Remover" worked great! The disadvantage is that it leaves a film on the surface, so it can not be used on mating precision surfaces. The former rusted area are left with a black finish. This was used on the parts that were too big to reasonably be dunked for electrolysis (the column, base, and knee). The part was cleaned precision surfaces masked, and then sprayed with the remover. After 24 hours I painted the parts. To prevent the converter from seeping through the masking taped I removed the tape after a few minutes.
2. "The Must For Rust" was disappointing!! It is a type that does not leave a film, but it also did not do much in the way of rust converting!!
There are a couple other methods that I plan to try. I'll report on them later.
Electrolysis
For most of the rest of the parts (painted and unpainted) I am using electrolysis. This coverts the rust back into iron, leaving a black finish. Un-rusted area are not affected, and remain shiny. The process does not fill in the pits, but the rust is gone.
One bad after effect of this process, is that once the part is removed and cleaned it will almost immediately start to rust from the moisture in the air! I'm not fluent in chemistry so do not know the exact reaction, but natural iron and steel have a thin clear oxide layer on the surface that slows rusting down. The electrolysis converts this layer along with the regular rust. Once the part is exposed to air the iron starts rusting right away! I do not know how the cleaned surface differs from say a freshly ground or cut area, but it does.
I have had good results with using WD-40 to rid the part of the water film left after washing. I then clean it with electrical parts cleaner (zero residue type) and wipe it down with way oil. If the part is to be painted I the remove the way oil (electric parts cleaner) mask and paint. After the paint has dried to the touch, I re-oil any non-painted areas. There are some solutions that will replace this oxide film, but I have not been able to get hold of any of them. More on this at a later date.
The basic electrolysis process is simple and safe, no harmful substances left. A container is filled with a water and Washing Soda solution (1 or 3 tablespoons of washing soda to 1 gallon of water). The rusted part is the immersed. A sacrificial piece of steel (many stainless steels do not corrode in this process so they are better when used as this piece), Is also placed in the solution. This piece MUST NOT touch the workpiece unless you like sparks due to shorting!!! The POSITIVE terminal from a battery charger is connected to the sacrificial piece and the NEGATIVE terminal to the workpiece. This is critical!! If you reverse the connections your workpiece will rapidly rust even worse!! DC voltage only!
I have used both a standard 12 volt automotive battery charger and a small plug in the wall 12 volt type. For smaller parts I use the plug in the wall charger this generally starts out at about 1 1/2 Amps of current draw at the start of the conversion and trails down to almost 0 when all the rust is converted. For larger pieces, therefore, with a lager surface area I use the automotive charger. The larger surface area is a better conductor to the solution and the current with be higher. My plug in the wall charger would overheat at the higher current levels. Why not just use the automotive charger exclusively? Well if somehow the sacrificial piece and the workpiece touch, the plug in the wall is a lot cheaper to replace, and also as its' current is lower the short is less likely to destroy it if caught quickly. Also you are working with electricity and water so be careful!!! Even at low voltages you can get shocked!!
The sacrificial piece will have to be cleaned (to remove rust coating), or replaced as you use this process. Generally I can get many pieces cleaned before having to worry about it. If the current is low when you start clean the piece and start over.
The washing soda is available in the laundry department of most grocery stores. The box I got (which should last a lllong time), is made by Arm and Hammer. The box is labeled "Washing Soda" so was easy to find. It normally added into the washing machine along with the regular detergent. (No I do not know why, my knowledge of laundry is put in clothes and detergent, start machine). So it is as safe as regular detergent. Once done with the solution it can be disposed of in the same way as dirty wash water. This assumes regular steel is treated. Galvanized steel may be a different beast due to the possibility that zinc may be dissolved in the solution after treatment. It will be grungy with suspended rust particles (from sacrificial piece, and may have foam on top, but it is still safe to dispose of, just like rusty water. Do not spill it on anything, because the rust could stain the surface. Also use a non metal container
Generally I leave the parts in overnight. As this process is somewhat line of site between the pieces, you may have to turn the workpiece around halfway through. Most of my parts were "done" on both sides the next morning.
After the part is removed from the solution, it is scrubbed both with dish soap and warm water. As state above once it comes out of this cleaning it will rapidly form a red rust coating, unless protected!
Figure 1 shows the setup using a 5 gallon bucket
for the container. Figure 2 shows the water during the process.
If let sit after you are done the foam will go away and the rust settle
to the bottom.
To preserve my charger clamps I bough a set of just the clamps at Wallmart, and connect the charger to them with a couple of test leads.
Figures 3 & 4 show the before and after shots of the piece. Note, that this piece was not cleaned up much before or after. It is an internal support piece that will never be seen, so I just painted it, as is, after these pictures were made.
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