Does anyone have an easy way to describe and identify these common errors? I thought these were a result of bad/old polish but I never have worked in surfacing so maybe a lab manager could add his/her wisdom on this.
Does anyone have an easy way to describe and identify these common errors? I thought these were a result of bad/old polish but I never have worked in surfacing so maybe a lab manager could add his/her wisdom on this.
Waves - waves are physical abberation in the lens, similar to a knot in a piece of wood. It's usually caused by too much heat during the surfacing process, usually during fining/polishing. If you hold a lens with a wave in it up to a light and move it, you will see the light jump and bend around the wave.
Orange Peel - usually a break down in the hard coating (can be either front or back) or A/R coating, again usually caused by too much heat. The physical appearance is that of, well, an orange peel (though it's usually clear, not actually orange).
Other surfacing errors - broad catagory, consisiting of everything else that can go wrong in surfacing. Appearance varries.
There are rules. Knowing those are easy. There are exceptions to the rules. Knowing those are easy. Knowing when to use them is slightly less easy. There are exceptions to the exceptions. Knowing those is a little more tricky, and know when to use those is even more so. Our industry is FULL of all of the above.
Waves can also be caused by the surfacing machine -- the oscillation and/or stroke break-up set wrong or not working properly: the lens essentially stays in one small area on the tool and does not cover the entire surface area. You will most likely see this occur in the center of the lens.
Been a while since I was surfacing but I remember some of what I used to see...
I've seen orange peel defects happen when a coating unit goes bad. Had this happen a lot with hard coaters for polycarb lenses when I was in the lab side. Usually caused by water in the air line or a bad/dirty coating filter. Coating marks, bubbles, streaks are also symptomatic of a coater problem or a tech that doesn't carefully prep lenses prior to coating.
Waves can also be caused by not enough water or polish and the heat buildup can cause lenses to warp slightly.... too much pressure on the pin clamps can cause waving or excessive material reduction causing lenses to be too thin which can make waving even worse. Waves can also be attributed to bad lens coatings although it is rare.
Generator marks were a common thing I saw when I would float around to different office locations to monitor lab operations. Usually these were seen because the generator wasn't calibrated properly or wrong laps were pulled. Sometimes happened on real high minus lenses because the edge thickness made it difficult to get water/polish onto the pads. They usually look like a concentric set of shallow grooves or pits on the outer edges of the lens... most commonly found in minus lenses.
Back when the surfacing data had to be entered manually, I used to see a lot of hourglass-shapes on the back surfaces where they wouldn't be polished. That was because usually a tech either didn't block the lens correctly or mis-entered an axis value into the generator.... I was so happy when I started working in integrated labs since the data was all handled over the network and there was no need to enter anything other than a job/tray number and hit start and never saw this kind of thing again.
this is likely to be a late post, but I believe it is important to look at the first steps of the surfacing process and then work from there. Are you blocking with alloy? If so, a minimum cool down and cure period of at least 30 minutes is required and 45 minutes would be even better. The other comments pertaining to heat in the process of generating, polishing, fining can all be contributors to waves and aberation. Rule out each step first before moving on to processes farther down the line.
how does a wave looks like?Can anyone plz explain using a photograph?
why does scratch occurs in ophthalmic lens? It would be of great help if anyone could tell me the reasons and suggest solutions for it.
Last edited by Diopterman; 09-07-2011 at 06:48 AM.
The organic lenses are made in plastic polimer, in general these substrates are esy to scratch, in general the "hardness scale is this:Originally Posted by smita.naskar
+hard cr39-1.6-1.56-1.66-1.74-Trivex-poly (less hard)
The only solutions is hard coat the lenses by hard varnishes (based on Polysilossae).
A good explanations of the Hard coat troubles you can found with this link, see at page 14
http://www.bimas.lt/akys/literatura/lesiai_dangos.pdf
my dear friend i am interested in looking at the waves that occurs on ophthalmic lens due to surfacing errors
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