|
| Our
sales department frequently receive customer
enquiries concerning the flexibility or hardness
of materials they require in order to fulfil
certain criteria within their applications.
In view of this and in order to assist our
customers in selecting the most suitable materials
with specific softness or hardness, we have
prepared a short explanatory aid on hardness
and an easy find chart for BSS / Shore conversion. |
 |
| Shore
(Durometer) Hardness Testing of Plastics |
|
| The
hardness of plastics is most commonly measured
by a Durometer test. This test measures the
resistance of plastics toward indentation
and provides an empirical hardness value but
does not necessarily correlate well to other
properties or fundamental characteristics.
Shore Hardness, using either the Shore A or
Shore D scale, is the preferred method for
rubber/elastomer materials and is also commonly
used for 'softer' plastics such as vinyl and
polyolefin. The Shore A scale is used for
'softer' rubber while Shore D scale is used
for 'harder' ones. Shore hardness is measured
with an apparatus known as a Durometer and
consequently is also known as 'Durometer hardness'.
The hardness value is determined by the penetration
of the Durometer indenter ‘probe’
into the sample. Because of the resilience
of rubbers and plastics, the indentation reading
my change over time - so the indentation time
is sometimes reported along with the hardness
number. Test methods include ISO 7619 and
ISO 868; DIN 53505; and JIS K 6253. The ASTM
test method designation is ASTM D2240 00 and
is generally used in North America. The results
obtained from this test are a useful measure
of relative resistance to indentation of various
grades of polymers. However, the Shore Durometer
hardness test does not serve well as a predictor
of other properties such as strength or resistance
to scratches, abrasion, or wear, and should
not be used alone for product design specifications.
Shore hardness is often used as a proxy for
flexibility (flexural modulus) in specifying
elastomers. The correlation between Shore
hardness and flexibility holds for similar
materials, especially within a series of grades
from the same product line, but this is an
empirical and not a fundamental relationship. |
|
| Historically,
within the United Kingdom, manufacturers of
the softer plastics raw materials, processors
and their clients have referred to
British Standard Softness (BSS) and
in order to avoid confusion, it is helpful
to cross reference BSS to Shore A
Scale. This scale closely approximates
to the International Rubber Hardness
and Shore A scales – 15 second indentator
at 23 deg |
| |
| BSS |
0 |
1 |
2 |
3 |
4 |
5 |
6 |
7 |
8 |
9 |
| 0 |
100 |
100 |
100 |
100 |
99 |
99 |
99 |
98 |
98 |
97 |
| 10 |
97 |
96 |
95 |
95 |
94 |
93 |
93 |
92 |
92 |
91
|
| 20 |
90 |
89 |
89 |
88 |
87 |
86 |
86 |
85 |
84 |
84 |
| 30 |
83 |
82 |
82 |
81 |
80 |
80 |
79 |
78 |
78 |
77 |
| 40 |
77 |
76 |
75 |
75 |
74 |
74 |
73 |
73 |
72 |
71 |
| 50 |
71 |
70 |
70 |
69 |
69 |
68 |
68 |
67 |
67 |
66 |
| 60 |
66 |
65 |
65 |
64 |
64 |
63 |
63 |
62 |
62 |
62 |
| 70 |
61 |
61 |
60 |
60 |
59 |
59 |
59 |
58 |
58 |
57 |
| 80 |
57 |
57 |
56 |
56 |
56 |
55 |
55 |
54 |
54 |
54 |
| 90 |
53 |
53 |
53 |
52 |
52 |
52 |
51 |
51 |
51 |
50 |
| 100 |
50 |
50 |
49 |
49 |
49 |
48 |
48 |
48 |
48 |
47 |
| 110 |
47 |
47 |
46 |
46 |
46 |
46 |
45 |
45 |
45 |
45 |
| 120 |
44 |
44 |
44 |
43 |
43 |
43 |
43 |
42 |
42 |
42 |
| 130 |
42 |
42 |
41 |
41 |
41 |
41 |
40 |
40 |
40 |
40 |
| 140 |
40 |
39 |
39 |
39 |
39 |
38 |
38 |
38 |
38 |
38 |
| 150 |
37 |
37 |
37 |
37 |
37 |
36 |
36 |
36 |
36 |
36 |
| 160 |
35 |
35 |
35 |
35 |
35 |
35 |
34 |
34 |
34 |
34 |
| 170 |
34 |
34 |
34 |
33 |
33 |
33 |
33 |
33 |
33 |
33 |
| 180 |
32 |
32 |
32 |
32 |
32 |
32 |
32 |
32 |
31 |
31 |
| 190 |
31 |
31 |
31 |
31 |
31 |
31 |
31 |
31 |
31 |
31 |
| 200 |
30 |
30 |
30 |
30 |
30 |
30 |
30 |
30 |
30 |
30 |
|
|
| |
| Example:
To find the Shore A Scale hardness of BSS
45, line up 40 in the left
hand column with figure 5
along the top row. This indicates a Shore
hardness of 74 |
| |
| |
| Imperial
/ Metric Conversion Chart |
 |
| |
