Hardness of Plastics - Rockwell & Burnell scale

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carter
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Hardness of Plastics - Rockwell & Burnell scale

Post: # 12390Unread post carter
Thu Jan 27, 2011 2:15 pm

This has been touched on elsewhere, but I want to get some clarification.

Taken from the commonly available Properties of Plastics Chart, the hardness characteristics (Rockwell & Burnell):

Acetal: R120
PVC: R112
Poly: R118
Acrylic: M93

Is the higher number on the scale harder or softer? How does acrylic compare to these other three given the M-rating.
Last edited by carter on Thu Jan 27, 2011 3:13 pm, edited 1 time in total.
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carter
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Post: # 12391Unread post carter
Thu Jan 27, 2011 2:16 pm

Sorry that last message lost formatting, but I think anyone can see the ratings:

Acetal: R120
PVC: R112
Poly: R118
Acrylic: M93
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mratx
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Post: # 12404Unread post mratx
Thu Jan 27, 2011 8:58 pm

A higher number means harder, although the M scale and R scale use different test weights and aren't equivalent. But those scales measure hardness in terms of indention/deformation, not in terms of resistance to cutting or scratching, so they don't relate perfectly to how easy a plastic may be to cut. Some type of scratch hardness rating would be more applicable, but I have never seen a chart for plastics.

Mark
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carter
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Post: # 12422Unread post carter
Fri Jan 28, 2011 5:40 pm

mratx - thanks for this insight.

so i guess the real question is, what is the order of resistance to cutting of those four materials.
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JuanPabloCuervo
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Post: # 14271Unread post JuanPabloCuervo
Sat Apr 16, 2011 3:09 pm

http://en.wikipedia.org/wiki/Polycarbonate

Polycarbonate M70
Speed of Sound 2270m/s
melting 267°C
Termal conductivity .19 - 22
Heat Capacity 1.2 - 1.3

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http://en.wikipedia.org/wiki/Polymethyl_methacrylate

acrylic glass
Melting 160°C
PMMA was used in laserdisc optical media. (CDs and DVDs use both acrylic and polycarbonate for higher impact resistance.)

http://en.wikipedia.org/wiki/Vinyl_polymer

http://en.wikipedia.org/wiki/Thermoplastic
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http://en.wikipedia.org/wiki/Copper
Speed of Sound 3810m/s
Melting 1084°C
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