Breaking Filters on UV lamps

Date 01-04-2013 14:54

Get a large mirror to put in the drip zone and reflect up onto the area of interest?
If possible, make a holder of some sort for the lamp to aim it down, and then you might not need to have three hands...

By CWI555

Date 01-04-2013 23:54 Edited 01-04-2013 23:59

Superflux: "Get a large mirror to put in the drip zone and reflect up onto the area of interest?"
Ding Ding Ding, give the man a cigar.

I've used that method, and it works, but there are some things to keep in mind if you do.

Lets review some standard formula:
F=C/ƛ
F frequency
C speed of light
ƛ wavelength

Snells law written for optic refraction
N2/N1 = ƛ1/ƛ2
N1 index of refraction of air = 1.0
N2 index of refraction of glass = 1.6
http://hyperphysics.phy-astr.gsu.edu/hbase/tables/indrf.html
http://hyperphysics.phy-astr.gsu.edu/hbase/geoopt/refr.html#c2

The index of refraction for glass is the standard for 'crown glass'. Most modern mirrors use that, but remember there are 'flint glasses' and 'barium crown glasses'.

Why does that matter? Because there are multiple frequencies of light involved here. Specifically white light with a full visible spectrum of ~380-700nm, fluorescent bulb central frequency 365nm, and the fluoresced light from the inspection medium at around 525-575nm. Note: The longer wavelength is due to stokes shift caused by energy lost in the process of creating that fluorescence to begin with. More simply put, the shift in spectrum is due to that lost of energy.

That's a general overview of the background.

That is also why you cannot use what you see in the mirror to make a call, but you can use direct light of sight from the examiner to make that call. Simply put a meter on the inspection surface to make sure the mirror is delivering sufficient energy from your lamp, then use direct visual of the part to interpret the indications.

I've made that as simple as I can, but if you want specifics of why you can't use the mirror directly, shoot me a pm.

By Superflux (****)

Date 01-05-2013 13:56 Edited 01-05-2013 14:16

CWI555,
Thanks for pointing out the issues with refraction through the glass. I was just brain storming and "typing outloud" (which is why I placed a ? mark after my response).
That, and another issue is the wavelengths that are absorbed by the (unknown!) reflective material. Some mirrors use aluminum and some are silver and I don't have a clue what other metals are used by mirror manufacturers.
BUT! Indications found by any creative NDT method (such as using red diesel and corn starch for Dye penetrant and developer) can always be considered a "Visual indication", then subjected to further testing and evaluation by approved methods under controlled conditions.
Just like welders, sometimes we in the QC/QA bizz have to get creative in order to "Git'er done". One difference is, is that we are expected to operate under a more stringent set of rules, ethics, to abide by.

By CWI555

Date 01-06-2013 01:26

Aluminum or silver would be irrelevant except where there is a loss of energy due to surface texture. By measuring intensity on the part itself, that variable is mitigated. As mentioned, I've used that method before, it works. If someone is going to use it as well, they need to qualify it to meet those extra rules and ethics you mentioned.

On a side note, I've used red dyed machinist penetrating oil and soap stone scrapings to find a crack when no other material was available. You don't get a traditional bleedout, but you do get an area where the oil is clumped up by the soap stone scrapings.

By welderbrent (*****)

Date 01-04-2013 15:05

Is there a clear plastic you can put around it without causing a problem with the UV? Or at least a plexiglass shield that was between the lamp and the drips?

Have a Great Day, Brent

By eekpod

Date 01-04-2013 20:10

Ive had the same problem, they get so dam hot that one little bit of water and they crack.
Sorry no good ideas other than be careful.