Comparative study on stress and stability of spectacle-lenses with different finishing

Transcription

1 LKT - Laboratorium für Kunststofftechnik Ges.m.b.H. LKT Laboratorium für Kunststofftechnik Report PB-Nr. Programme: P626 Title: Search terms: Programme group: Comparative study on stress and stability of spectacle-lenses with different finishing stress, polarised light Microscopy Number of pages: 23 Number of original copies: 3 Client: Lensbond Research & Development GmbH Paris-London-Str Salzburg, Austria Sign and date of the order: Roland Pföss, Programme manager: Programme assistant: Dipl.-Ing. A. Schmidt Dipl.-Ing. I. Bednar Vienna, May 2010 Programme manager A Programme manager B Managing director L-F-5/1-9/92 (replaces GA-5/1-5/92)

2 The following samples have been made available for the comparative study: Conventional models of glasses (metallic earpiece and accordingly binder) Sample 1 Black earpiece Labelling left glass: 1,74 drilled Labelling right glass: 1,67 drilled polarised light: Stress runs vertically in the area of the drilling see schematic diagram:

3 Sample 2 Silver earpiece Labelling: 1,67 slotted (both glasses) monochromatic polarised light: Stress runs vertically in the area of the holes see schematic diagram: Microscopic image, polychromatic, polarised light; left glass, outer face fine hairline cracks run vertically to the colour rings see arrows Haarrisse

4 Sample 3 Black and white patterned earpiece Labelling: 1,60 slotted (both glasses) monochromatic polarised light: Stress runs vertically in the area of the holes see schematic diagram:

5 Sample 4 Green earpiece Labelling left glass: 1,60 drilled Labelling right glass: 1,60 POLYCABONAT drilled monochromatic polarised light: Left glass Stress runs vertically in the area of the holes see schematic diagram: Right glass Stress in the area of the holes; stress in the entire glass, possibly caused by the shaping of the polycarbonate

6 Microscopic image, polychromatic, polarised light; right glass (PC) outer face; fine hairline cracks run vertically to the drilling, which partially branch out

7 Sample 5 Golden earpiece, right glass broken Labelling left glass: ORG.1,74 slotted -3,00 Labelling right glass: ORG.1,74 slotted monochromatic polarised light: Stress runs vertically in the area of the holes see schematic diagram: Microscopic image, polychromatic, polarised light; left glass inner face fine hairline cracks run vertically to the colour rings

8 Right glass (broken) inner face fine hairline cracks run vertically to the colour rings

9 Sample 17 Claret-metallicé earpiece Labelling: drilled monochromatic polarised light: Left glass Stress runs vertically in the area of the holes see schematic diagram: Microscopic image, polychromatic, polarised light; drilling right glass, outer face no apparent hairline cracks

10 Sample 18 Brown striped earpiece Labelling: slotted monochromatic polarised light: Left glass Stress runs vertically in the area of the holes see schematic diagram: Microscopic image, polychromatic, polarised light; drilling in the left glass, outer face fine hairline cracks run vertically to the colour rings see arrow Haarrisse

11 Glasses with Lensbond-technology and earpieces with metal components Sample 6 Lensbond red/black/silver earpiece Lensbond-technology monochromatic, polarised light: barely apparent stresses, only a few stresses in the area where the earpiece and the lens are bonded together

12 Sample 7 Lensbond red/white/silver earpiece Lensbond-technology monochromatic polarised light: barely apparent stresses, only a few stresses in the area where the earpiece and the lens are bonded together

13 Sample 8 Lensbond red/black/silver earpiece; Labelling: 12/52 Lensbond-technology monochromatic polarised light: barely apparent stresses, only a few stresses in the area where the earpiece and the lens are bonded together

14 Sample 9 Lensbond black silver earpiece; Labelling: 8/52 Lensbond-technology monochromatic polarised light: no apparent stress

15 Different glasses before the installation Sample 10 Labelling: 1,59 Polycarbonat drilled monochromatic polarised light: large-area stress state without overlaid preferential direction stress peaks in the area of the drilling Microscopic image, polychromatic, polarised light; fine hairline cracks at the edge of the drilling first cracks already occurred before the installation Hairline cracks

16 Sample 11 Labelling: 1,74 drilled monochromatic, polarised light: Stress runs vertically in the area of the holes see schematic diagram: Sample 12 Labelling 1,67 drilled Stress runs vertically in the area of the holes see schematic diagram: Sample 13 Labelling 1,67 milled Lensbond-technology no apparent stress

17 Sample 14 Labelling 1,60 milled Lensbond-technology no stress caused by milling sample 15 Labelling Polycarbonat milled Lensbond-technology irregular stress state possibly caused by moulding Sample 16 Labelling 1,74 milled Lensbond-technology no stress caused by treatment

18 Glasses with Lensbond-technology and earpieces without metal components Sample 19 Lensbond black/red earpiece; Labelling: LB 2 TEST 1,6 GLAS new Lensbond-technology without metallic binder monochromatic, polarised light: no apparent stress Microscopic image, polychromatic, polarised light; fastening bar left glass, inner face

19 Summary of the study and accordingly the stress in the glass The conventional finishing of rimless glasses with bores in the glass and screw connections of the temples already shows first stress during the drilling of the glass. Further stress results from the subsequent screwing. Drilled glasses show less stress than slotted glasses therefore, the form of the drilling is also relevant concerning the stress state of the glasses. On the contrary, glasses with Lensbond technology do not show any stress. In its finished condition there is few, if any stress evident. Mechanical treatments such as drilling, milling and plugging of highly sensitive optical plastic lenses do not meet with the experiences of the plastics technology as optimal jointing technology.

20 Further Analysis Tensile Test: The stability of the fixing of the temples of sample 2, sample 7, sample 8, sample 17, sample 18 and sample 19 have been tested using the tensile test. The tensile test of sample 2 shows a maximum tensile force of 257 N. The tensile test for sample 2 (glasses with slotted drilling) showed that it is necessary to apply the maximum tensile force (ca. 257N) to destroy it. Finally the middle temple has been ripped out. Basically, the stability is defined by the stability of the metal and the tensile force required for the forming.

21 The tensile test of sample 8 shows that it is necessary to apply a maximum tensile force of 113 N. The tensile test of sample 8 did not cause a detachment of the bonded joint. The metallic connecting piece for fastening the earpiece caused the damage of the plastic part which is bonded to the glass (see adjoining picture) The stability of the bonding is in any case higher than it is required for the power transmission by the other spectacle parts. The tensile test of sample 7 shows that it is necessary to apply a maximum tensile force of 107 N. The tensile test of sample 7 also shows (like sample 8) that the bonded plastic part was ripped out by the metallic connecting part. The bonding did not come off. The second tensile test of sample 7 shows that it is necessary to apply a maximum tensile force of 130 N. For this second tensile test of sample 7, both glasses of the spectacles were fixed by clamping the glasses in order to test the stability of the middle piece. One of the glasses was damaged during installation. Nevertheless, the second tensile test of sample 7 still shows a higher strength value than when tested the first time. The plastic part was again ripped out by the metallic part.

22 The tensile test of sample 17 shows that it is necessary to apply a maximum tensile force of 163 N. Sample 17 are glasses with circular bores. The lateral earpiece has been ripped out of the fixation. Basically, the stability is defined by the stability of the metal and the tensile force required for the forming. The tensile test of sample 18 shows that it is necessary to apply a maximum tensile force of 176 N. Sample 18 are glasses with slotted bores. The middle piece has been ripped out. Basically, the stability is defined by the stability of the metal and the tensile force required for the forming. The tensile test of sample 19 shows that it is necessary to apply a maximum tensile force of 108 N. During the tensile test the middle piece of the spectacles has been sheared off. The bonding was mainly disconnected.

23 Summary Tensile Tests To sum up, one can say that according to the tensile test the glass gets damaged at about 250 N, by the metallic components. During the tensile test, the bonding of the glasses with Lensbond technology and metallic components in the earpieces, showed resistance at least as great as the constructional material strength it requires. The bonding of the glasses with the newest Lensbond technology (no metallic components in the earpieces) withstood a tensile force of ca. 108N. In this case, the bonding was sheared off but about 20% of the adherend could withstand the applied force (at this point the glass broke). Resume The subsequent mechanical treatment of glasses causes stress in the material which can even be intensified if the earpiece and the glass are bolted together. The form of the bore is also relevant concerning the stress in the glass. Furthermore, the stress in the glass reduces the resistance against applied mechanical force. Another consequence could be aberrations caused by the stress in the glass which should be avoided generally. The Lensbond-technology shows a good stability regarding bonding. The particular strength of Lensbond technology is the finishing of the glasses without stress.