Strippers and Dubious Chemicals

My last few blog posts have dealt with a few "issues" that I have encountered, the outcome of which is that I need to redo the powder coating on a number of parts.

One of the main reasons for powder coating the parts in the first place is that the coating is very durable.  In other words, it's a bugger to remove.  I had a couple of attempts with the sandblaster and various sanding discs and wire wheels; these would eventually remove the majority of the coating but would take a heck of a long time. 

If I lived in the US there would appear to be a number of chemical products available to strip powder coat.  However, none of them are available in the UK.

The internet suggested that, after giving the surface a good abrading to remove the top surface of the coating, paint stripper could be used to remove the remaining powder coat.  Well, normal Nitromors paint stripper had zero effect.

Further research suggested that to be effective, the paint stripper needed to contain a particular chemical ingredient, namely Dichloromethane (DCM).  This was a common solvent many years ago and used to be widely used in paint strippers.  But, probably for good reason, in the modern health and safety-conscious era, it is has been removed from most products.

It took some tracking down but I did manage to find some industrial strength paint stripper containing DCM on the well-known internet auction site and purchased 5 litres.

Innocuous packaging, limited H&S warnings (and no data sheet supplied with the product...)

I need to recoat the rear wishbone spacer tubes and the rear wishbone tie.  I gave these parts a quick session with the angle grinder/flappy wheel combo (and in the case of the wishbone tie, some wire brush treatment to get into the recesses) to scratch up the surface of the powder coat finish.  These were them brushed liberally with the professional strength paint stripper and left to soak for a few minutes.

Health and Safety Tip - DCM paint stripper is potent stuff.  Even outside in well-ventilated conditions, I could smell the solvent content!  Make sure you wear gloves, long sleeves and eye protection.  I got some small splashes on my skin when brushing the stripper on and it starts to burn any exposed skin immediately.  Also, work quickly; this stuff burns even through gloves!  After just a couple of minutes of holding the parts while applying the stripper my fingers were starting to tingle!

The potency does mean that the product is extremely effective.  It only took a few minutes for the surface of the abraded powder coat to start wrinkling and using a wire brush I was able to remove the majority of the original coating.

Less than 5 minutes for paint stripper to do its stuff...

After a wire brushing and rinse off with water

Wishbone tie after flappy wheel/ wire brush treatment

After a few minutes of soaking in paint stripper...

...the majority of old coating could be removed with a wire brush

After rinsing and drying

These parts were then re-prepped for powder coating.  I gave the spacer tubes a thorough going over with the grinder and sanding discs to try and remove as much of the surface pitting as I could.  These and the wishbone tie then had another session in the sandblasting tent before an application of Afterblast.

Wishbone tie after sandblasting...

...and after etching with Afterblast

The wishbone tie was then recoated in Satin Black; this time around I made sure to get a good coating of powder all over the part prior to curing.

Ready for coating (again...)

After curing - better than the first time!

For the wishbone spacer tubes, I tried another approach for the application of the candy red topcoat (another technique sourced from internet research...).  The High Chrome coat was applied and cured as before. This time though, rather than allowing the parts to cool and reheat them prior to applying the candy coat, I tried a technique called 'hot flocking'.  This technique involved applying the second coat to the parts as soon as they were removed from the oven after curing the first coat.  Due to the parts being at or just below curing temperature, the second coat of the powder started to cure as soon as it is applied to the part.  This also meant that the powder adhered far more readily to the part and did not get blown off as easily.  The parts were then cured in the oven as normal for 10 minutes.

Extensive sanding to remove surface pitting

High Chrome coating applied and cured as usual...

...before red candy is 'hot flocked' to parts straight out of the oven

After 10 minutes of curing in the oven

No blemishes and no patchy coating...

Nice result!

The results this time were far better.  The spacer tubes were blemish-free and the consistency of the red candy coat was much more even with no patchy bits. The colour is amazing in the sunlight!

So now I am back on track and I can get on with finishing off cleaning up the rear hubs!

Powder Coating Fest - Part 3

Having had some reasonably successful results powder coating various donor parts, using either satin black or gloss black powder, I thought it was time to funk things up a bit.

At the 2019 Stoneleigh Kit Car Show, I was looking at the various powder coat colours on the ElectroStaticMagic stand.  I had been contemplating coating a few pieces in either a candy blue or red which would be similar colours to the anodised aeroquip style hose fittings that we plan to use for plumbing Project Snake.

My original thought was to go for a blue candy colour but they didn't have any in stock at the Stoneleigh show so I went for candy red instead (always one for sticking to a plan).  The candy powder is applied over the High Gloss Chrome powder and I picked up 1/4kg of that at the same time.

The first pieces I decided to apply to funk treatment to were the front axle dust caps.  These got the usual wire brushing, sandblasting and Afterblast treatment prior to coating.

Dust Caps - after initial clean...

...after sand blasting

...and after application of Afterblast

The instructions for appying the candy powder coat require an initial coating with the High Chrome powder, which is then cured for 30mins at 180 degrees and then allowed to cool to ambient temperature.  The red candy powder is then applied over the High Chrome and cured for 10mins at 180 degrees.

The dust caps were given a once over with the Eastwood Prepaint Prep and a wipe over with a tack rag and then the High Chrome powder was applied.  This goes on as a flat medium grey colour.

High Chrome powder applied

These were then brought up to temperature in the oven and cured for the recommended 30mins.  The finish of the High Chrome is very good.  The powder cures to an almost chrome-like finish (as the name suggests....).  If leaving the parts as the Chrome finish it is recommended to gloss clear coat the parts to prevent the powder dulling with time.  I reckon this would give the parts a really good shine and, on a well-prepped surface (unlike my battered and bruised dust caps), I think at first glance it would be hard to differentiate the finish from a real chromed part.

Shiny Dust Caps - shame about the dimples...

I can see my face in this one!

Its like looking in a battered mirror....

Next step was to apply the red candy powder.  I did this the day after applying the High Chrome so obviously the parts had cooled completely.  I gave them another wipe over with Prepaint Prep and a tack rag and then tried to apply the red candy powder.  

Note the word 'tried'.  This proved quite tricky.  The second coat of powder didn't want to adhere to the parts at all.  I'm not sure whether I wasn't getting a good ground contact (because of the first coat), although I had scraped a bit of the coating off on the inside where I had placed the hanging/ground wire, but the powder went on in a very patchy manner and when I tried to fill in the gaps, the powder that had coated the part just seemed to blow off.

I ended up blowing all the powder off with an airgun, re-cleaning the parts and trying again.  The second time I turned the air pressure on the powder coating gun down a bit (to around 4psi) and trying to 'fog' the parts in powder.  This did achieve a better coverage (although not a very economic use of powder and everything in the garage now has a slight red tinge to it....) although care was still needed not to blow the powder off in places.

Eventually managed to get parts completely covered...

These were then popped in the oven at 180degrees / Gas mark 4 for 10mins after the parts had reached curing temperature.  I was quite pleased with the results.  The final colour is quite a deep red and so is more like the colour of 'Ruby' (the AK demonstrator that is current inspiration for this project) which is fine assuming we don't change our mind on the final colour!!

Close inspection of the final pieces did show some areas where the coating was a bit patchy, but only if you look closely (and the dust caps will eventually be hidden anyway - which begs the question why did I bother...).  

Freshly cured Candy Red dust caps...

Final result - some minor blemishes!!

Still, it was a good experiment for some parts which might be more visible and so buoyed by the initial success I attempted to powder coat the rear wishbone spacer tubes.

These needed a good session with the angle grinder and some flap wheels to clean off the surface pitting caused by my leaving them too long in a citric acid de-rusting bath previously.  After an intensive session with 40, 80 and then 120 grit flap wheels, the tubes cleaned up quite nicely.

After some flappy wheel treatment...

These then got a final sandblast, spray with Afterblast and a clean up before powder coating with the High Chrome.  As before these were cured at 180 degrees for 30mins.

Chrome coated spacer tubes

Having scoured the internet for some tips on applying the candy powders, I found a couple of tips on various forums, which suggested that, rather than trying to apply the candy powder to a cooled part, it should be preheated to around 65-75 degrees to aid adhesion of the second coat. 

This technique made a big difference and the candy powder seemed to adhere much more readily to the chrome coat, although there were some areas that needed a bit more persuasion than others. 

However, after curing and cooling, I was a bit disappointed with the results.  The candy coat was still quite thin and patchy in places and where I had obviously not managed to remove all the surface blemishes from the tubes with the grinder/flap wheel combo, the powder had concentrated around these giving some very obvious dark spots on the coating.

Patchy coating...

...and dark spots

I know these tubes (and the dust caps) will be hidden from sight once the car is finished, but I still want these bits to be the best finish that they can be.  So at some point soon, I will probably attempt to redo them all.

Set Blasters to stun.....

Armed with my trusty Budget Blaster Mk2, I had been making good progress with cleaning and prepping many of the donor car parts for powder coating.

However, the change of my blasting media of choice from kiln-dried sand to aluminium oxide soon identified a major issue.  

The aluminium oxide media is far more abrasive than the sand; so abrasive that it actually blew its way through the nozzle of Budget Blaster.  I was starting to notice that it was taking a bit longer to clean off one of the rear hubs and then I spotted the hole in the nozzle...

The additional hole does not improve performance.....

OK I thought, I've managed to do quite a lot of sand blasting with the original nozzle so I'll just order another set of nozzles from a well-known mail-order company that offers next day delivery and that should see me set for a bit longer.  In the meantime, I'll just revert to Budget Blaster Mk1.

A great plan....for less than 5 minutes, by which time Budget Blaster Mk1 had bitten the dust as well.

RIP Budget Blaster Mk1...

Clearly, the nozzles were not going to survive very long with the aluminium oxide media and so I cancelled the order for another set of cheap nozzles and contemplated Plan B.

Plan B involved the purchase of a Clarke SB3 Grit Blasting Gun, the main lure of which was it came with a hardened steel nozzle!  There were fairly mixed reviews of this on the internet, but for £20 I was prepared to give it a go.

Clarke SB3 Grit Blast Gun - photo courtesy of MachineMart

Some of the reviews cited issues with media delivery and volume of media used.  I found one review that said to ensure the delivery tube was fixed facing forwards and to angle the gun downwards in use - which I did and had no problems in use.

However, the speed at which the gun uses blasting media is quite high.  The pot takes has a litre capacity so around 1-1.5kg of media.  My initial experiments with the gun managed to empty a full pot in a couple of minutes.  The results were impressive but clearly, some means of capturing and recycling blast media would be required otherwise 25kg was not going to last very long!

My solution was to buy a large tarpaulin and a cheap gazebo with sides, from the well-known internet auction site, to make a supersize blasting 'cabinet' by laying the tarpaulin on the floor and sitting the gazebo on top.  The theory being that the gazebo would help to contain the excess blast media and this could be swept off the tarpaulin and reused.

For the first full-scale test of this set-up, I reverted to using the kiln-dried sand since a) the damp bag that I bought previously had now dried out a bit and b) if the set-up failed I was only wasting a £3 bag of sand rather than expensive aluminium oxide.  

I have to say the results using the SB3 gun and sand were pretty amazing.  The gun is pretty effective and I managed to strip and clean some of the rear axle parts in less than 30 minutes.  It does go through the media at a phenomenal rate!  But the tarpaulin/gazebo combo did a reasonable job of containing the excess media and with some frequent sweeping up, I did manage to recycle a fair amount of the sand and finished with almost as much as I had started with!

Lifes a Beach - After 5 minutes of blasting...

Initial results...

A quick blast with the aluminium oxide should see these parts finished and ready for powder coating.

So a big thumbs up for Plan B (although unfortunately, the 'B' does not stand for budget...)

Powder Coating Fest! - Part 1

With the good weather at the end of May / beginning of June I was expecting to be able to get some more garage time and progress the build.  However my wife had other plans and I received a long list of jobs for the garden and around the house.....

Still I did manage to find some time to get a few of the donor parts powder coated ready to compete the front end build and commence fitting of the differential unit.

First part to be coated was the second front hub.  This was tackled in exactly the same manner as the first hub (Front Axle Part 5 - Front Hub Refurb), although the overall process went much quicker second time round now that I had a better idea of what I was doing!  As with the first hub, I needed to spend a couple of hours reblasting and cleaning up the hub to remove the flash rust that had formed after the first clean.  Thankfully this process was achieved without further personal injury!

Second hub coated in glossy black

Now I could turn my attention to some of the parts to allow me to start on the rear axle rebuild and installation of the diff.  First piece to be tackled was the wishbone tie. 

Followers of this blog will recall that I had to obtain a second wishbone tie as the original one was missing a couple of the bushes and that these particular bushes are not available as a replacement part.  I spent a lot of time cleaning up the original wishbone tie, as well as the replacement, and now the reason for that effort can be revealed!!

Since the bushes can not be replaced, I was worried about damaging them while pressing them out to enable the wishbone tie to be powder coated.  I was also concerned that trying to powder coat the wishbone tie with the bushes in-situ would result in the bushes melting during the curing process!  Jon at AK had assured me that I could powder coat with the bushes in place, but I was still a bit nervous and decided to do a trial run on the original tie.

I followed the same process as for the hubs, pre-heat to "degas", degrease and clean, coat and cure.  The test was pretty successful although as a result I did make a few adjustments to the process.

Wishbone Tie - test

The wishbone tie is a pretty substantial lump of metal and during curing took around 50 minutes for the surface to get up to temperature.  Although the bushes didn't melt as I had feared, during the pre-bake and curing there was a pretty distinct smell of hot rubber; as result, for the actual tie, I lowered the temperature for the pre-bake to 200 degrees C and used Satin Black powder from ElectrostaticMagic which only requires 10 minute curing time at the lower temperature of 180 degrees C.  

Wishbone Tie - Final Result

Wishbone Tie - close-up of finish

Next up was the rear pendulum bracket - another substantial chunk of metal casting!  Although I have obtained new bushes for this part, I coated it with the satin black powder to match the wishbone tie.  In fact I did all the parts for the rear diff in satin black.  The process for all these parts was as previously described.

More sweeping of the drive required...

Pendulum after blasting and cleaning

Powder coated and reading for curing

Fresh out of the oven..

After cooling and removal of masking tape

Close-up of finish

Next up was the rear diff mounting bracket and the compliance buffers (which for the PowerLok differential are solid metal spacers as opposed to the rubber ones for the normal differential units).  The donor rear bracket was quite corroded and very pitted in places.  It needed some considerable work with the sand blaster, the angle grinder / flappy wheel combo and a dremel to get it cleaned up.  I still couldn't quite remove all the pitting though and final finish was not as great as I would have hoped.

Rear Bracket after some initial grinder / flappy wheel action...

Pitting needed a lot of grinding to remove...

After blasting and some treatment with the angry end of the Dremel

Coated parts for rear diff mounting

Some pitting still visible on final coated bracket

So with all those parts coated I am now in a position to finish off the front hubs and start mounting the rear differential.  Just need a wet weekend now then....