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Thread: Spots after surfacing and polishing

  1. #1
    Bad address email on file quality's Avatar
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    Question Spots after surfacing and polishing

    We are looking to solve a problem, which keeps on recurring on an on-and-off basis in our RX surfacing proces: after deblocking surfaced and polished lenses, quality control encounters spots on 1.5 and 1.6 plastic lenses. Most days start off without any problems, however, some days these spots occur from the very first run and create quality problems from the first minute onwards. On this particular surfacing line we employ LOH PRA blockers with alloy (47C) at 55° C, LOH V100 cutting machines and LOH TORO polishers. Measures already tried: lowering the alloy temperature, lowering the blocker cooling fluid temperature, replacing the alloy, calibrating the cutting machines and thoroughly cleaning and replacing cylinders of the polishing devices. Still no real result. Any ideas or thoughts? Thanks.

  2. #2
    Rising Star
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    Sounds like you may have an unbalanced cutting wheel on the V100. Replace with new wheel and blades. Also check coolant flow and position of the coolant jets in generator.

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    Bad address email on file quality's Avatar
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    Many thanks. However, spots occur on the surface of the foiled side of the lenses, not the cut side? Will an unbalanced or faulty cutting wheel and blades e. g. influence this side?

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    OptiBoardaholic
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    Could we have a better description of what "spots" are ? Is the lense surface pitted ? Do the spots look like the scratch coat has been "pulled" by the surface tape ? Have you tried putting the lense in very hot water ?
    Joseph Felker
    AllentownOptical.com

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    Bad address email on file quality's Avatar
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    Spots look like pits. We have not as yet tried deblocking in very hot water; define very hot?

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    OptiBoardaholic
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    I mention the very hot water as a method to remove some surface flaws that appear on transition and clear 1.53 index material. The temp would be about 160 F.
    I assume you are using a surface saver tape before blocking with alloy? Not trying to be a smart a.., just never know.
    Joseph Felker
    AllentownOptical.com

  7. #7
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    We do use a surface saver tape, which goes on before blocking. We did use an alternative one for some time, but returned to our original one.

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    OptiBoard Professional Mike Fretto's Avatar
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    Is there any kind of pattern to which lenses are affected high plus, high minus, sv, st28, or progressives. Ive seen the alloy leak down out of the block if not blocked properly, creating a cavity in the alloy that can cause a warpage in the front side of the lense. You did say this is a front side issue correct?
    Mike

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    This is a front side issue. There is no apparant difference with relation to 1.50, 1.60 or 1.70 lenses; the problem persists. We have no alloy leaks neither.

  10. #10
    OptiBoardaholic
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    It may be your deblocker or deblocking procedure. Melt a few lenses off the block in a reclaim tank and check for surface problems. Get a digital camera, take some pictures of the problem and post them.
    Joseph Felker
    AllentownOptical.com

  11. #11
    OptiWizard OptiJim's Avatar
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    Have you changed lens manufacturers? Have you asked the lens or surface tape manufacturers if they have changed their coatings or adhesives? How do you normally deblock? Melt or knock off the blocks? I am wondering if somehow the alloy is penetrating the surface tape and actually pitting the front surface of the lens.

  12. #12
    Master OptiBoarder
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    All this talk about surface tape got me thinking. Way back when, we use to use a type of blue "paint" on glass lenses as a surface saver. Is there something like this for plastic type lenses? Maybe worth a shot?



    Fezz
    :cheers:

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    Master OptiBoarder optical24/7's Avatar
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    Not sure if this pertains to todays techniques in surfacing. (been out of it for years..) But even with chilled blocks we had to let the lens sit and cool down for 30-60 mins. before generating. Solved lots of problems for us.

  14. #14
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    Have you cleaned out your filter in your tape dispenser, there could be dirt in it and when applying tape under pressure dirt could get trapped under the tape. Also test some jobs with 2 layers of tape this would eliminate deblocking problems.

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    had problem with h.i. and started double taping b ut our problem was on back side. change tape and try double taping just to see.

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