Impact Resistance

Question 1

how can crown glass lose its impact resistance?

Answer 1

scratches

Question 2

what is more impact resistant to large slow moving objects?

Answer 2

chemically tempered crown glass

Question 3

what is more impact resistant to small, high velocity objects

Answer 3

CR-39

Question 4

weight comparison to CR39 to crown glass

Answer 4

CR39 half the weight of crown glass

Question 5

polycarbonate has UV absorption up to

Answer 5

380nm

Question 6

impact resistance of high index is similar to

Answer 6

CR39

Question 7

lens of choice for drill mounted lenses

Answer 7

trivex

Question 8

how are glass lenses made impact resistant?

Answer 8

must be tempered either with heat or a chemical bath

Question 9

thermal or air tempering can be used for what materials?

Answer 9

crown glass only

Question 10

chemical tempering can be used for what materials?

Answer 10

crown or high index glass only

Question 11

what materials are inherently impact resistant?

Answer 11

all plastics

Question 12

drop ball testing requirements?

Answer 12

height of 50 inches with a 5/8th inch steel ball (0.56 ounce)

Question 13

when do glass lenses have to be drop ball tested?

Answer 13

after edging and hardening and before it is placed in the frame

Question 14

when do plastic lenses have to be drop ball tested?

Answer 14

can be tested in uncut finished form, and in batches

Question 15

minimum thickness for basic impact

Answer 15

3.0 mm

Question 16

impact resistance for basic impact lenses

Answer 16

1 inch steel ball dropped from height of 50 inches

Question 17

basic impact must be marked with

Answer 17

a manufacture’s ID or mark or logo and carry a warning label

Question 18

high impact lenses thickness must be

Answer 18

2.0 mm

Question 19

impact resistance test for high impact lenses

Answer 19

high velocity impact test- 1/4 inch steel ball traveling at 150 ft/sec

Question 20

scratches on what surface will impact resistance more?

Answer 20

back surface scratches (80% decrease)

-would be 20% decrease if on front

Question 21

will coatings reduce impact resistance? which coatings?

Answer 21

AR and scratch resistance coatings will reduce impact resistance

Question 22

what material is weakened more for scratching

Answer 22

glass is weakened more by scratching than CR39

Question 23

frame test requirements for high velocity impact test?

Answer 23

a series of 1/4” steel balls traveling at 150 ft/sec is directed at 20 points on the frame

Question 24

frame test requirements for high mass impact test?

Answer 24

a pointed 1’ diameter (17.6oz) projectile is dropped from height of 50 inches onto a frame mounted face up

Question 25

if the frame passes the high mass impact test, it is marked with:

Answer 25

the manufacturer’s marking and Z87 on the front and temple

Question 26

Z87 =

Answer 26

3mm thickness and basic impact lenses

Question 27

Z87-2 =

Answer 27

2 or 3mm thickness for basic or high impact lenses

Question 28

requirements for side shields are:

Answer 28

10mm behind the corneal vertex