D: Spectacle Frame Materials - Week 2 Flashcards
List 5 types of spectacle frames (note: there are others)
- Plastic Frame
- Metal Spectacle Frame
- Metal/Nylon cord
- Composite/Combination Frame
- Rimless Mounted Frame
(alternatively; 6. Half Eye Frame, 7. Semi-rimless, 8. Numount Mounting)
What 2 types of materials do composite/combination frames consist of?
Metal and Plastic
What are Half eye frames useful for?
used for near vision in a half visual field (useful for presbyopes)
Explain the design of semi-rimless frames
Mounting lenses held only by a top rim
How many attachments do numount mounting frames have?
Only 1 attachment per lens (at nasal edge)
List 5 parts of a frame seen from the front
- Bridge (in the middle, over nose)
- Shield (where the hinge is attached to the spectacle)
- Nose pad (either side of nose)
- Rim
- Endpiece (at corners)
List 6 parts of the frame seen from the side
- Butt portion (around hinge)
- Shield
- Dowel hole
- Temple/shaft
- Bend
- Earpiece
Name 5 designs for sides of spectacle frames
- normal ‘skull’ arm
- convertible arm
- library arm
- ‘bow’ or curl arm
- ‘full curl’ arm
What 2 frame side designs look like a candy cane?
‘bow’ and ‘full curl’ arms
What’s the difference between a convertible arm and library arm?
A library arm is almost completely straight. A convertible arm starts as library but can be bent around the ear or vice versa.
What is a ‘full curl’ arm usually made of? What about a ‘bow’ arm?
full curl: sprung wire, sometimes plastic coated
bow: plastic before bend then plastic covered wire
Name the ideal requirements of a frame material (8)
- Lightweight
- Strong, but flexible
- Retain its shape
- Adjustable
- Inert to body fluids
- Inert to external compounds
- Cosmetically attractive
- Inexpensive
**silicari
What is the difference between ‘thermoplastic’ and ‘thermosetting’ materials?
thermoplastic: capable of being reformed under heat; good for adjusting shape after initial manufacture
thermosetting: set or hardened in final stages of adjustment, which fixes its shape; will not soften much when reheated, but will burn or melt
Describe the 2 main techniques for manufacturing plastic frames.
- Injection Moulding: liquid monomer or polymer pumped into mould.
- Machining: eye shape is cut from steel material
In injection moulding, when are joints usually placed into the mould?
prior to moulding
In Machining, how are the joints handled?
Joints are either heat sunk or riveted
Can both moulding and machining be applied to make a frame?
Yes. moulding, then machining
In what 3 ways can joints be applied in plastic frames?
- Heat inserted into mould
- Riveted into front and side
- Soldered onto the reinforcing wire
How can the half joint be used to secure the front of the frame to the temple?
The half joints can be riveted to or heat inserted into the front
List 3 cellulose based plastic materials for spectacle frames, in order from least to most commonly used.
- Cellulose Nitrate: No longer used due to flammability
- Cellulose Proprionate: increasingly used b/c lower costs
- Cellulose Acetate: very common (most common plastic material in frames)
Name 4 plastic materials for spectacle frames with the name ‘poly’ in them
- Polyamides (“nylons”)
- Co-polyamides (e.g. SPX)
- Polymethylmethacrylate (acrylic/PMMA/perspex)
- Polycarbonate
Name 3 other plastic materials for spectacle frames
- Epoxy resin (e.g. Optyl, which is thermosetting)
- Rubber
- Composite materials (consist of 2 material sset in another plastic, e.g. carbon fibre, kevlar, fibreglass)
Are the 3 cellulose based materials thermoplastic or thermosetting?
thermoplastic
(note: however, c.acetate needs to be blended with certain plasticisers and melt compounded into c. acetate granules first)
Are nylons, polyamides, co-polyamides thermoplastic or thermosetting?
thermoplastic
(note: nylon is just a noteworthy type of polyamide)
Of the thermoplastic frame materials, list the temperatures needed to soften them from lowest to highest
C. acetate: 57 deg
C. proprionate: 67 deg
poly/co-polyamides: over 95 deg
(note: nylon is a polyamide, so same temp)
List 3 advantages of cellulose acetate
- easily polished
- colours fast
- easily repaired
List 3-4 disadvantages of cellulose acetate
- will blister if over-heated
- use of plasticizers can cause frame to become brittle over time
- frames tend to retain flat state if overheated
- frames may be damaged by solvents
Are composite materials thermoplastic or thermosetting?
Can be either. Depends on what is used
Is rubber thermoplastic or thermosetting?
Can be either. Depends on kind of rubber
List 3-5 advantages of C. proprionate
- lighter than acetate (75% weight)
- can be made thinner than acetate
- cheaper than acetate
- hypoallergenic (b/c acetate)
- easily polished (more glossy than acetate)
List 3-5 disadvantages of C. proprionate
- will blister if overheated
- plasticisers often added to increase flexibility .. but frame more brittle over time
- less colour-stable than acetate (can buff out colour)
- frames may be damaged by solvents
What types of frame materials are considered hypoallergenic?
- c. acetate
- c. proprionate
- polyamide/copolyamide
- nylon
- optyl frames (a kind of epoxy resin)
- stainless steel (metal)
- titanium (metal)
(note: c. nitrate is NOT hypoallergenic)
List 3 advantages of Nylon:
- Light-weight 2. Strong + flexible 3. Not affected by heat or cold
List 2 disadvantages of Nylon:
- Poor surface quality
- Very difficult to adjust
Define polyamide and define co-polyamide
polyamide: an organic compound of the nylon family
co-polyamide: mixture of different polyamides and/or plastic
List 3-4 advantages of poly/co-polyamides
- Lighter than acetate (70% of weight)
- Hypoallergenic
- Very hard, durable surface
- Thinner than other plastic frames
List 3 disadvantages of poly/co-polyamides
- will shrink if overheated
- difficult to adjust or repair
- cold glazing (is required because frame shrinks at 80 deg, which is lower than the over 95 deg needed to soften it)
List 3-4 advantages of Epoxy resin
- 30% lighter than acetate
- hypoallergenic
- very hard, durable surface
- will not age (lack of plasticisers)
List 2 disadvantages of Epoxy Resin
- Thermosetting
- Cannot be repaired easily
List 3-4 advantages of Composite materials
- carbon fibre is 80% lighter than acetate
- good shape retention
- very strong
- can be made much thinner than acetate frames
List 3-5 disadvantages of Composite materials
- cannot be repaired eadily
- better to cold glaze (just like poly)
- difficult to adjust
- not available in transparent colours
- brittle to adjust
What is the advantage and disadvantage of rubber frames?
adv: flexible! disadv. not adjustable
Is polycarbonate impact resistant?
Yes!
Which frame is considered to be “close to the ideal spectacle frame material”?
Titanium
Name 5-8 advantages of titanium frames
- extremely light weight (48% lighter than nickel-silver)
- very strong (good for thin frames)
- high corrosion resistant
- hypoallergenic
- flexible
- low conductivity (thermal + electrical)
- holds adjustment well
- great surface hardness (3x gold plating) = abrasion resistant
Name 2 disadvantages of titanium frames
- very expensive
- welding is more difficult (needs argon gas, so needs specialist welding equipment)
Name 3-5 advantages of aluminium
- lightweight
- hypoallergenic
- stain/tarnish/corrosion resistant
- soft + cold to touch
- holds adjustment well
Name 1 disadvantage of aluminium frames
- due to softness, aluminium frames are thick
Why is rolled “rolled gold” highly resistant to corrosion?
Because “the gold is inert”
What are the 2 types of plating on metal frames?
- Electrolytic plating : pure metal or alloy is deposited on base metal as a solution
– commonly used for plating gold, and other metals like palladium, rhodium and ruthenium - Mechanical plating: best known for “rolled gold” frames
