A downside to powder coating perhaps?

Does the term ‘Wheeltappers and shunters’ ring a bell?

Back in the day before the likes of ultrasonic testing was available the railway companies employed wheeltappers. They would walk around the railway yard hitting each wheel in turn with a long handled hammer. Sound wheels would ring, a cracked wheel would give a dull sound and not ring true.

Please don’t hit your alloys with a hammer. If you do don’t blame me if the paint chips.

I’m wondering if maybe a rubber mallet or similar might be a suitable implement to tap each spoke in turn listening out for any difference in sound.

What we really need is for someone with a wheel with a cracked spoke to do some tests.

3 Likes

Excellent idea

It’s also a bit like those experts showing how clever they are when testing antique bone china on Bargain Hunt.

To start with, I would try using the smooth well-rounded plastic handle of a small screwdriver (ideally an old yellow plastic PO No1) for a light tap, and a proper plugs-in-the-ears doctor’s stethoscope on the far side of the wheel.

However, I also think it would only be an effective test if no tyre on the rim; the tyre will soak up any ring.

I do remember the spare rim I bought for my NC did have a nice ring, even just with handling.

3 Likes

4 Likes

Now that makes sense looking at what’s left of the wheel where it fractured With areas of black

1 Like

There has been talk that it isn’t actually the coating process which does the damage, it’s the baking off of the old coating which does it as the temps used are much higher. If you do a Google search on Subaru STI wheels you’ll see they’re prone to it. Interestingly they’re a multi spoke design like the NC wheels too.

1 Like

Sought my son’s opinion on powder coating aluminium wheels, he is a metallurgist who has worked for Alcoa forging aluminium components. Age hardening takes around 8 hours at 150C, the exact time and temperature depends on the aluminium grade and size of component to achieve max strength and fatigue resistance. If the powder coater heated the wheel to 200C for 1 hour then in his opinion there will be a significant decrease in ductility and fatigue strength.

2 Likes

That isn’t how they powdercoat wheels though.

From a wheel refurbisher

http://thewheelwizard.ltd.uk/powder-coating/

3 Likes

I wonder if there is a degree of salesmanship to persuade people to powdercoat rather paint wheels.

Agree with the link from PR-Yorkshire.
Manufacturers of wheels “Tend” to have them painted.
For a few reasons perhaps?
I looked at having my alloy wheels from my motorbike powder coated in 2013 and decided against it.
Also powder coating looks nice and thicker, but when it chips/kerbed not easy at all to repair…
Just an opinion, “stick with spray paint”.

2 Likes

This could also be evidence of fatigue failure. The light areas (more shiny areas) could be the initial fatigue induced crack and the darker areas (duller areas) are the result of total tensile failure as a result of the increased stress concentration generated by the reduced material cross section. The light and dark areas are typical of a fatigue failure. Like it has been pointed out in the thread, the powder coating process may have reduced the toughness of the material and as a result fatigue cracks will start and will propagate much faster under cyclic loads. It is possible that the powder coating as it is flexible would hide the cracks. I have had experience of fatigue cracks being hidden by metal spray coatings causing eventual catastrophic failure. The only way to identify the presence of these cracks once the parent/base material is coated is to use X Ray or Ultrasonic NDT methods.

2 Likes

As a retired HGV driver, it was common to be stopped by ‘The Ministry’ who used a small hammer to check for loose wheel nuts (120 or more depending on configuration), just a very light tap - quick, easy and effective

1 Like

Thanks for all your inputs on this thread and an update
I ordered new alloys and replaced the remaining wheels to find the back two had severe hairline fractures through the alloy spindles in the places where the total failure occurred on the front !
Thankfully they chose to hold on otherwise it would have been ‘three wheels on my wagon …then two … then one ! ….’
The lower wishbone nut was ground down on the road surface to about 2 mm … and will need replacing
I count myself as ‘lucky’ on this one despite the hit to the finances which is a small price to pay !

4 Likes

What’s a severe hairline crack look like?




4 Likes

Bloody hell !!! You are one lucky bunny.
:heart:

1 Like

Scary… Very scary.

The one plus is that it’s not hidden under the paint / powder coat.

Think there are going to be a lot of people very carefully examining their wheels this weekend.

4 Likes

Yup.
There goes one definition of a severe hairline crack eh SAZ? :wink: :roll_eyes:
It’s either flawless, ot it’s a lampost waiting to happen.
If that was on an airliner landing wheel…they’d be grounded.

1 Like

I’ve already examined mine, all four off to see what’s on the backside.
Whilst they are absolutely spotless (freshly powder coated last year) I’ll be keeping an eye on them, constantly.:thinking:

1 Like

dude… I have no words to say about this. you were really lucky…