View Single Post
Old 8th Feb 2019, 5:48 am   #74
Catkins
Pentode
 
Catkins's Avatar
 
Join Date: Feb 2015
Location: Chepstow, Monmouthshire, UK.
Posts: 234
Default Re: 1938 Murphy A56V television restoration

Quote:
Originally Posted by Ed_Dinning View Post
If home, how easy was it to source the chemicals and what sort of power supply did you use?
Hi,

As my brother said, they were home plating kits, supplied with all the necessary chemicals and plating anodes (copper/nickel/zinc). Each came packed into a white plastic bucket, which later becomes the electroplating tank. Photo 1 shows the copper plating kit in use.

You do have to add a couple of extra things (obviously depending on whether you already have them). In addition to the electrolyte solution, you also make up a degreasing solution, an acid "pickle" solution and a passivate solution (the third only for zinc electroplating), and you need to provide tanks to put them in, preferably sealable for later storage. The solutions will attack some plastics, and so you need to ensure any plastic tanks are of a type that won't be attacked. We found sealable plastic tubs designed for storing food left-overs in the fridge to work very well here.

The chemicals are supplied in plastic bags, and are not the exact amount you need to make up the initial solutions (this is presumably so you can top up the electrolyte and make more degreasing/pickle solutions once they are exhausted, from memory there were enough to make up at least another fresh solution). So you need to have a set of scales which can accurately measure fairly small quantities, to correctly make up the electrolyte and other solutions.

An important addition, as mentioned by my bother, was a bench power-supply. Using this you can accurately control the amount of current being used. The reason for this should become clear later.

But obviously the most important "addition" was time. Websites state you can get good results with home plating kits, but it takes a lot of practise. Something which we found to be very true.

I obviously first started experimenting with odd bits of metal which could be thrown away afterwards. This was to get experience with the process and to get a feel for all the variables at play, there are lot of variables and it is those which make the difference between a good plate and a terrible plate.

Before plating you have to prepare the metal, to make sure it is clean and free from contaminants. First you put it into a degreaser, this is obviously enough to remove grease and other dirt. A couple of minutes is recommended depending on the temperature of the degreasing solution (the hotter it is the more quickly it works), it is better to overdo it than underdo it, but with any powerful alkaline/acid solution there is also too long, which will damage the surface. Next you put it into an acid "pickle" solution, which removes contaminants, this is for about 30 seconds for steel. This is strong acid and will literally eat away at the metal if left in too long. If you're adding an additional plate, it is an easy way to remove your previous plate(s) at this time, as experience tells.

The above times are guidelines and with practise you start to get a feeling for when and why you need to vary them to get a better result.

Next you put it into the electroplating tank and turn on the power. The electroplating solution will take all the current you can give it, at whatever voltage you select. The question is what is the best voltage and current to get the best plate? The guidelines provide a start, which is xxx voltage (this differs between copper/nickel/zinc plating), and so much current per square inch of metal surface (the larger the surface the more current is drawn).

The surface area to be plated, the voltage and the current all ultimately determine the rate (or speed) of plating. The more surface area the slower the plating for a given voltage/current. The higher the current/voltage the faster the plating, irrespective of surface area, but obviously you need to increase this as the surface area increases to get the same rate of plating. There is a sweet spot between too slow plating and too fast plating. Too slow plating results in coarse and dense plating which is not attractive. Too fast plating results in fragile plating, it can often be easily flaked away as it doesn't stick. Even with the right current you can also get plating burns which is uneven plating due to current eddies in the electrolyte (uneven distribution of current). This is often due to poor placement of the component with respect to the anodes, to get perfect even plating all parts of the component need to be the same distance from an anode.

To add to this you have the additional variables of plating time, and electrolyte temperature all of which affect the resultant quality of the plate.

With so many variables at play it is not surprising that the vast number of home platers get poor results. Doing a lot of reading (for pitfalls) and a fair amount of practising, I got better and better, you slowly get a feel for what is right. That is not to say I didn't experience some major disasters, I had plenty of them along the way, but I learnt from my mistakes and started again and again, until I got it right.

While looking for photo 1, I discovered photo 2. Photo 2 shows two metal "backs" from potentiometers that were mounted on the front of the case (providing the contrast, brightness and focus controls - the volume control is different as it also has a double pole switch). The left back is completely untouched, and it can be seen to be extremely rusted and corroded. The right back was orginally similar in appearance, but, it was treated, prepared for electroplating, and then given one plate of zinc electroplating at a carefully controlled current. For one plate, the results are very good, and it looks almost new.
Attached Thumbnails
Click image for larger version

Name:	20161016_222440.jpg
Views:	175
Size:	159.0 KB
ID:	178005   Click image for larger version

Name:	IMG_20170418_213211561.jpg
Views:	168
Size:	75.4 KB
ID:	178006  
Catkins is offline