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Understanding
Plastic Lens Polish |
With the rapid advancement of lens material substrates over the last several years, the performance criteria of Plastic Lens Polishes have been pushed to new heights. In particular, polycarbonate lenses place a critical demand on overall performance. Cut rate, surface quality, lens luster, suspension, life and AR compatibility are just a few of the needs under consideration during polish development, testing and general laboratory use.
Developing a quality lens polish requires several key components involving raw materials, thermal treatment, particle size reduction of the aluminum oxide and finally the complete
formulation that is distributed in gallons and five-gallon pails. The complete formulation is a delicate balance of processed alumina particles, removal accelerants, antifoaming agents and suspension agents. Modern lens polishes perform with alumina mechanical polishing and chemically aided acceleration.
Do not dilute or concentrate the polish as this balance will be disrupted resulting in poor performance and degraded surface quality.
Preparing the lens prior to the polishing process is as critical as the polishing step itself. Whenever possible, crib the lenses in the generator to the minimum useable diameter and apply
an ample bevel at the edge of the lens to allow adequate water flow during fining and polish flow. A smooth surface finish should be achieved after the fining process which removes all generator marks and sub-surface stress fractures.
A very good guide to use in understanding the life of your
polish is as follows. Using proven process methods and routine maintenance guidelines, you can expect to polish up to 400 lenses per gallon. As the mix of high index and polycarbonate goes up, this number will start to decrease. Properly maintaining the polish through temperature control and filtration will help insure good surface quality throughout the normal life expectancy. When turning on the slurry/chilling system prior to processing lenses, it is recommended to let the polish circulate for 20 to 30 minutes to insure proper suspension and operating temperature. Chill and maintain polish at an operating temperature of 55 – 60 degrees if using alloy and 60 – 65 degrees if using wax. Check polish temperature every four hours at the point of delivery to the lens. Check Baume at the start of each shift and at four-hour intervals. Maintain manufacturer’s minimum for that particular polish chemistry. The industry standard for polish times is 6 minutes for all resin materials including polycarbonate. This time is necessary to achieve the proper stock removal and for superior lens finish.
Clean or change filter at the beginning of each shift and at four-hour intervals. This will remove any lens swarf, pad nap or other contaminants that may have been introduced into the polish reservoir and allow the aluminas to stay in suspension. At the end of the production day, clean the polishers and drain all polish from the feedlines and return lines. Close off the
polish tank and flush the system completely with hot water. Allowing polish to stay in the lines will cause the aluminas to build up inside the system reducing polish flow and causing potential contamination.
When it is time to change the polish, thoroughly clean out
slurry tank, filter, filter housing and polish lines by flushing and rinsing thoroughly with hot water. Be certain that all water is removed from the system prior to the introduction of new polish. Water in the polish will cause dilution, which will lower Baume and reduce overall surface quality.
Following these guidelines and working with your polish
distributor will insure your success in Understanding Plastic Lens Polishes while producing great lenses.
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