What’s shore hardness?
When selecting a material for your application, you’ve no doubt seen reference to a Shore Hardness rating. You’re not alone if you find this confusing, but understanding Shore Hardness meaning is key to a successful project. This guide is designed to give you a clear picture of what a material’s shore value means. We’ll cover:
Shore Hardness scales: Rockwell vs Shore Durometer
Shore material: plastics, elastomers and rubbers
How exactly is the hardness of plastics measured?
How to convert Shore A to D
What is rubber Shore Hardness?
Rubber hardness examples and applications
Shore hardness scales: Rockwell vs Shore Durometer
The Shore Hardness test relates to the hardness of a material. A material is usually measured using the standardised Rockwell hardness test or Durometer test – and both can work out how well plastics will fare when it comes to indentation.
Named after its inventor, Albert Ferdinand Shore, Shore offers different Shore Hardness scales for measuring the solidity of different materials. Each scale will result in a value from 0 and 100, with the higher number relating to increased hardness. Shore Hardness Durometer uses either the Shore A or Shore D scale.
What’s the difference between Shore A and Shore D? The Shore D scale measures semi-rigid plastics and rubbers. The Shore A scale measures softer materials.
The Rockwell test also measures a material’s hardness, specifically the resistance of plastics towards indentation. Shore hardness vs. Rockwell comes down to the material you’re testing. The Rockwell test is used for materials too hard for the Shore D hardness scale. If you’re testing metals, for example, you’ll use the Rockwell method, although this can also apply to testing plastic hardness.
Shore material: plastics, rubbers and elastomers
The hardness of plastics and other materials are shown below. Semi-rigid plastics, rubber and elastomer shore hardness can even overlap. Examples of specific materials that undergo shore hardness testing include:
|
Shore A Plastics |
Shore D Plastics |
Shore A Elastomers |
Shore D Elastomers |
|
– Polyurethane (PU) – Polyvinyl chloride (PVC) – Ethylene-vinyl acetate (EVA) – Silicone rubber – Polyolefin |
–Acetal – Acrylic – Nylon – Polycarbonate (PC) – Acrylonitrile butadiene styrene (ABS) – Polyethylene terephthalate (PET) – High-density polyethylene (HDPE) |
– Thermoplastic elastomers (TPE) – Natural rubber – Styrene-butadiene rubber (SBR) – Ethylene propylene diene monomer (EPDM) – Neoprene |
– Epichlorohydrin rubber – Fluoroelastomers (FKM) – Hydrogenated nitrile rubber (HNBR) – Polyacrylate elastomers (ACM) – Butyl rubber
|
Shore D Hardness vs Rockwell is really a question of, when does a material become too hard for the plastic shore hardness scale? Additives can change a material’s chemical composition, for instance. Rockwell Hardness examples for hard plastics include:
● Polycarbonate
● Nylon
● Acetal
● Polystyrene
You’ll see those hard plastics listed in our table, such as polycarbonate shore hardness. But these plastics can also be too hard for Shore D Hardness testing, and are suitable for Rockwell testing.
How exactly is the hardness of plastics measured?
To ascertain the hardness of plastics and elastomers, you’ll need a Durometer reading. Use a Shore Durometer instrument, such as the one shown here. Note:
● The Durometer uses an indenter, which is loaded by a calibrated spring.
● The measured hardness is determined by the penetration depth of the indenter under the load.
● Measuring a flat surface is extremely important – accurate hardness readings can’t be made on surfaces which are rounded, rough or uneven.
● The shore hardness scale – specifically, the indenter – is differently shaped for Shore A and Shore D, as seen in the illustration below. Shore D is rounded, while Shore A is flat.
● For the minimum time of an hour, test pieces will be conditioned immediately before testing, where possible.
How to measure shore hardness
Step 1: To measure hardness, place the test piece on a hard, flat or rigid surface, the pressure will be applied as quickly as possible, but without shock.
Step 2: Record at specific times. Take a hardness measurement at 3 and then 15 seconds.
Step 3: Take a total of five measurements at varying points on the test piece. Record the mean value.
Step 4: If the needle has entered the plastic as far as it can – and the gauge has been pressed firmly on the material – the needle used to measure the plastic will show a corresponding measurement relating to its hardness.
The indentation reading all comes down to how flexible the rubber or plastic is. This reading may change and it’s why it’s important to write down the time the measurement is taken, along with the number which correlates to its hardness.
In the example above, Shore A and Shore D scales use different loading forces to measure material hardness. Specifically, the loading force for the Shore A Hardness scale is 822 g, while for Shore D, it’s 10 lb 4536 g. The possible range of Shore Hardness values is 0 to 100, with a maximum penetration of 2.5 – 2.54 mm for each scale. The minimum Shore Hardness value of 0 corresponds to a maximum penetration of 2.5 – 2.54 mm, while the maximum hardness value of 100 corresponds to zero penetration.
How to convert Shore A to D
Is there a Shore A to Shore D conversion formula? No, as the Shore scale measures the hardness of materials based on different factors, such as the shape and size of the Durometer indenter foot and the force applied. However, it is possible to estimate shore values using empirical conversion charts. These charts are developed by comparing the hardness values of the same material tested with both Shore A and Shore D instruments and are specific to the type of material being tested.
Note, these conversion tables are only approximations and may not be accurate for all materials.
Conversions: Shore Hardness chart
|
Shore A |
30 |
35 |
40 |
45 |
50 |
55 |
60 |
65 |
70 |
75 |
80 |
85 |
90 |
95 |
100 |
|
Shore D |
6 |
7 |
8 |
10 |
12 |
14 |
16 |
19 |
22 |
25 |
29 |
33 |
39 |
46 |
58 |
What is rubber Shore Hardness?
It depends on the type of rubber, or elastomer. Measuring rubber hardness involves a Durometer. That is, determining the Shore Hardness of rubber is carried out in the way in which you measure plastics. If you’re working with a bendable material, you can get the Shore value of rubber using a Shore A Hardness scale. If it’s stiff, you can get your rubber hardness reading using a Shore D scale. There is no specific rubber hardness scale.
Rubber hardness examples and applications
To give you an idea of how a Shore number relates to different materials, a measurement of 0 could be applied to chewing gum and Shore A 55 for pencil erasers. For a car tyre, you’re looking at around a 65 Shore A Hardness. It’s worth knowing that once a material reaches a Shore A 95 range, it will resemble a plastic versus a flexible material.
Other examples of products with elastomer and rubber Shore Hardness include:
Silicone rubber shore hardness 50 A. This strap can be stretched and wrapped around cable bundles up to three times. It grips the cables and uses a latch pin to prevent movement.
EPDM Shore 60 Hardness, A. The wire passes through the grommet at a maximum 45-degree angle.
PVC, 80A shore hardness. Ideal for general protection. The tab provides quick removal from a tight fit. Also available in red, in softer Shore 60 A.
Nitrile rubber, 90 Shore A Hardness. Suited to SAE flange standard. Forms a tight seal to prevent contamination and leakage of fluid.
EPDM shore 30 A Hardness. Provides a secure hold, and shock and vibration protection.
Silicone shore hardness A 65. Forms a tight seal around the cable or tube, preventing the ingress of water, dust, and other contaminants.
Wire clip – screw/adhesive mount
Neoprene rubber Hardness Shore A 80. Suitable for attaching cables to panels. Serrated buckle provides a tight grip to the bundles.
Download free CADs and try before you buy
Free CADs are available for most solutions, which you can download. You can also request free samples to make sure the material you’ve chosen is exactly what you need. If you’re not quite sure which solution will work best for your application, our experts are always happy to advise you.
You might also find it helpful to check out:
A Comparison: TPE vs TPR Material
Whatever your requirements, you can depend on fast despatch. Request your free samples or download free CADs now.
Questions?
Email us at sales@essentracomponents.co.uk or speak to one of our experts for further information on the ideal solution for your application 0345 528 0474.