I have to say that YouTube for me has been an education, in mostly how not to do things. There is the odd pearl amidst swine, but the majority is mostly how not to go about doing things. The go to tool seems to be the wire wheel in the bench grinder to clean anything rusty, the vlogger's confidently grind away any patina and finish in their quest to 'restore'. I am not a fan and it is not an approach I advocate or use. That is not to say a bench grinder with a wire wheel does not have a place in the workshop, as it most certainly does, but it should not be the tool of first resort.
One of the methods I use to get heavily rusted parts cleaned or to get apart is to use electrolysis. It is the best method I have found to clean back to bare metal, where you are not trying to preserve the original finish. It is a simple, inexpensive and non destructive method to clean corrosion off steel and cast iron. It doesn't work on aluminium. You will need a tank for holding the electrolyte solution. I use a plastic hot water header tank sold in plumber's merchants for use with a central heating system. It is big enough for most bicycle parts. It will hold the warmed electrolyte without reacting to it - IMPORTANT. The power supply is an old car battery charger, the non-smart type, which doesn't know a battery is not connected to it. If you only have the smart type, connect it to a battery, but take your power feed from the battery.
The type of electrolyte you use is important for two main reasons. The electrolyte allows the electric current to flow through the solution which facilitates a chemical reaction to take place. A by product of that chemical reaction is the release of gas, which is why electrolysis needs to be carried out in a well ventilated area. The electrolyte consists of a liquid and an additive. Most hot plating processes use an acid as the liquid. You can use acetic acid (vinegar) with table salt. It will work, however, two caveats. Firstly, if the metal is pitted by rust before you start, using an acid electrolyte will make the pitting worse, because, although the method is quick, and will do the job, it is aggressive. Secondly, table salt is Sodium Chloride. If you use salt in the electrolyte, the process releases Chlorine gas. Yes, that's right, the stuff that was used to gas troops in the First World War, so it is damaging to your health. A very good reason not to use it in my opinion, as there are other and in my opinion, better methods to achieve the goal.
The electrolyte I use is washing soda crystals, an alkali These are much superior chemically to baking soda, which is much less effective. Washing Soda is an alkali salt which does not appear to corrode the metal aggressively during electrolysis. Using this method also releases gases, which are oxygen and hydrogen. An explosive mixture! So you have to do it in a well ventilated area.
I suspend the part to be cleaned in the electrolyte solution. I use steel wire, NOT copper. I found that the flexible plastic coated wire sold in garden centres is ideal. The plastic has to be stripped off the wire wrapped around the part to make a good electrical contact. A portion of the wire at the other end has to be bare metal for the battery charger to connect to. I use a piece of scrap wood (a non conductor) which is wider than the tank to suspend the part from.
You will also need a piece of sacrificial steel in your tank. This is needed as it will attract all the rust particles. I would recommend that it has a flat surface and secondly that you use as big a surface area as you safely can. DO NOT allow the sacrificial steel to contact the part you are trying to clean. I welded up a frame which fits around the sides of my tank, which is removable for cleaning. (You can use one or more sacrificial pieces, wiring them in series if you prefer.) Cleaning the sacrificial electrode is an important point, as heavily corroded parts will need a longer time in the tank.
You connect the black lead to the part to be cleaned and the red lead to the sacrificial electrode. Once you turn the battery charger on, you will see bubbles coming off the part. I usually set the charger to work on trickle charge. If the charger has an Amp meter you will see the needle move up the scale. As the sacrificial electrode becomes contaminated with rust off the part, the amperage will fall. Turn the power off before removing the part from the tank to check progress. If the part still has surface rust, remove the sacrificial electrode and clean off the accumulated crud. The wire wheel on the bench grinder is good for cleaning the metal after the crud has been scraped off, before you put it back into the tank. The surface of the part will go black as the rust is removed. This is an inert chemical coating replacing the rust, which will clean off.
The electrolyte can be left in the tank for re-use. The plastic hot water header tank has the option of a lid, which is useful for covering it after use. I remove the sacrificial plates before covering up the tank after use. You will have to periodically replace the sacrificial steel electrodes, but you should get a lot of use from them before that happens. Cleaning them after use is also important as the process works better when the sacrificial electrode is clean.
Once you are happy that your part is thoroughly clean of rust, it will need washing in warm soapy water. Brush the part using a brass brush and then clean it with WD40 or Brunox. Electrolysis will take off any plating or paint as well as rust, so electrolysis will get your part back to bare metal. If you use it to clean any cast iron such as old tools, once you have the part cleaned with WD40/Brunox, wipe the cast iron part over with boiled linseed oil on a bit of kitchen roll. Make sure it is evenly coated and put it near a radiator or other heat source to dry. It will seal the cast iron ready for painting and should ensure the porous cast iron doesn't start to rust under the paint. I was told this by an old man who maintained machinery in the workshop during his apprenticeship nearly 70 years ago. I have found that cast iron I had media blasted and immediately primed, then painted has all rusted from below the paint over time. Boiled linseed oil was a component in both old paints, varnishes and of course Japanning laquered finish.
I have used the boiled linseed method on cast iron and found it to work very well. If cleaning old cast iron, any paint residue will likely be lead based paint. Not something you want to inhale as dust through sanding or using a wire brush in an electric hand tool or bench grinder. Once the boiled linseed oil has dried, it will take paint no problem, I generally give the item two coats of boiled linseed oil allowing each to dry before the next application. The item should not rust once coated and will stay stable if there is any delay in painting it.
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