Crack Detecting

[Superspeed]

I have just bought a Molyslip crack detecting kit ( ie.three cans of spray)
and have tried to use it on a set of twink rods and crank.
But i'm not sure if i'm doing it right,
When the rods are very clean,
spray on the red dye,
leave for upto twenty minutes,
spray on developer,
leave for ten minutes,
inspect under good light for red lines,
Thats what the instructions say but i wondered if you have to wipe of excess dye before applying the developer.
Am i doing it wrong or are my rods good
Has anyone had experience with this or other techniques
Cheers

[M100]

You need to wet a bit of (preferably lint free) cloth or paper towel with a small amount of the cleaner and wipe until the surface to be tested is clean. Don't spray the cleaner directly on the surface or use a soaking wet cloth.

Let the item dry for a few minutes so that the cleaner flashes off and then spray on the developer.

To test your technique you could bolt on the big ends and see if you can detect the split line

For testing the crank magnaflux techiques are probably a better solution.

[rgh0]

Your crack detector works by the red dye seeping into cracks and then staining the developer above the crack. Thus good for detecting surface cracks only but most cracks that develop in service originate on the surface good for more testing of used parts. Magnetic and xray techniques can also detect internal faults that may arise during casting or forging or welding of a new component.

Basic process

1. Clean and dry the part to be tested.
2. Spray on the red dye and allow to soak per instructions
3. clean off the dye using the cleaner. This leaves the dye inside any cracks.
4. spray on the developer and wait per instruction. The dye in the cracks will stain the developer showing the line of the crack.

Rohan

[Superspeed]

Excellent thanks fella's
I'll dig out a old casting with a known crack and practice on that.
Does anyone have a idea how much it will cost to x-ray a crank.

[gwnorth68]

Xray of steel components for fatigue cracks is not a very satisfactory approch. The xray shows density variation in the material and the tight cracks would have to be perfectly aligned for the xray to show any indication (or very unrealistically large). Magnaflux or zyglo (die penetrant) are much more reliable.
Tom Moore

[Superspeed]

Thanks all for your help.

[handi_andi]

Hiya

Personally I would consider using Magnetic Particle Inspection which can detect cracks up to a few millimetres below the surface. Essentially, you spray paint the component white, then magnetise it using either a pemanent or electric magnet then spray iron filings over the surface which should only stick to a crack, which is easily visble because of white paint.

The information below might be helpful and I have some more information on MPI which is used extensively in the oil industry as the primary method of crack detection.

The magnetic particle inspection method along with liquid penetrant inspection is one of the oldest and most widely utilized forms of nondestructive testing currently in use today. One of the advantages that a magnetic particle inspection has over some of the other nondestructive evaluation methods is that flaw indications generally resemble the actual flaw. This is not the case with NDT methods such as ultrasonic and eddy current inspection, where an electronic signal must be interpreted. When magnetic particle inspection is used, cracks on the surface of the part appear as sharp lines that follow the path of the crack. Flaws that exist below the surface of the part are less defined and more difficult to detect.

Magnetic particle testing uses magnetic fields and small magnetic particles, such as iron filings to detect flaws in components. In theory, it is a relatively simple concept. When a bar magnet is broken in the center of its length, two complete bar magnets with magnetic poles on each end of each magnet will result. If the magnet were cracked but not broken completely in two, a north and south pole will form at each edge of the crack, just as though the break had been completed. If iron particles were then sprinkled on this cracked magnet, these particles would be attracted not only to the ends of the magnets poles but also to the edges of the crack.

Hope this helps

Andy