What is Durometer?

Tuesday, April 8, 2008

When new products are being developed, one of the most difficult tasks is to determine the material. Materials are typically selected based on several criteria:

Association - use material that has been used with similar products.
Mechanical properties - Flex Modulus, Tensile strength, Impact, HDT, etc.
Color - Part needs to be clear – Knowing the color can help to narrow the search
Durometer - measure of hardness in polymers, elastomers and rubbers.

I would like to discuss durometer. Durometer can be a very fast way to narrow your search for a material. Durometer is a value that indicates the hardness of a material, defined as the material's resistance to permanent indentation.

There are several scales of durometer, used for materials with different properties. The two most common scales, using slightly different measurement systems, are the ASTM D2240 type A and type D scales.

The A scale is for softer materials

The D scale is for harder materials

Durometer works together with association.

The chart below relates Shore A and Shore D values with production grade and some common materials

Shore A	Shore D	Material
30		Art Gum Eraser
40		Pink Pearl Eraser
50	15	Rubber Stamp
60		Pencil Eraser
70	30	Rubber Heel
80		Rubber Sole
90	45	Typewriter roller
100	55	Low Density Polyethylene
	70	Polypropylene PP
	75	ABS
	80	Polycarbonate PC
	85	GF Nylon
	90	Glass

In the Rapid Prototyping industry there are a number of resins that can simulate different production and common materials.

The chart below relates Shore A and Shore D values with Rapid Prototyping resins. The chart is only a guide to help direct you to a material that closely represents your final product.

Shore A	Shore D	Material
30		Tango Plus Cast Polyurethane
40		Cast Polyurethane
50	15	Cast Polyurethane
60		Tango Black Cast Polyurethane
70	30	Tango Gray Cast Polyurethane
80		Cast Polyurethane
90	45	Cast Polyurethane
100	55	Cast Polyurethane
	70	Cast Polyurethane
	75	Cast Polyurethane
	80	Accura 25 WaterClear Ultra 10122 Cast Polyurethane
	85	Accura 60 ProtoGEN 18420 WaterClear Ultra 10122 Cast Polyurethane
	90	ProtoGEN 18420 SL 5530 Cast Polyurethane

Durometer is a tool to use when selecting a material for a new product design. It’s one of many tools that can aid in the design and material selection process. Once a design is complete and a material has been selected – ProtoCAM will be glad to produce high quality prototypes.

Ed Graham
Engineering Manager
egraham@protocam.com

2 Comments:

L Chrzan said...: Interesting and informative post about this useful measurement. This should be helpful to people who need to describe the relative hardness / softness of the material they want to use in the product that is being prototyped.

Questions:
Is durometer an actual physical tool that is used? If so, what does it look like? Do you have a picture?

Thanks!; April 9, 2008 11:21 AM
RobK said...: Great post Ed. Thanks!; January 4, 2009 12:02 AM