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DUROMETER TECHNICAL INFORMATION AND FAQ |
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What is a durometer ? A durometer is an instrument used for measuring indentation hardness of rubber, plastics and other materials. Durometers are built to various standards from ASTM, DIN, JIS and ISO. There are a number of brands of durometers, all of which must conform to the same ASTM specifications if they are to be known as genuine Durometers. Sometimes a Durometer Scale may be referred to by its' brand name such as Shore. The "A" scale is the Durometer A scale (or type A) and all brands will give the same results. What materials may be tested with a durometer ? Durometers are used to measure the indentation hardness of a large range of materials. Rubber, elastomers, plastics, foam rubber, wood, leather, sponge rubber, printing rollers, roller blade wheels are all typical durometer applications. Other applications include composite foams, crab shells, thread on bobbins, rolled plastic films and countless other applications and materials. Hard metals such as steel, brass and aluminum should be tested with a metal hardness tester. How do I use a durometer ? In use, a durometer is pushed against the sample and the hardness is read from the dial. How do I choose the correct durometer ? The ASTM D2240 standard covers type A, B, C, D, DO, E OO and OOO durometers. The most popular durometers are types A and D. Type A is often used for rubber and soft plastics while type D is used for harder materials such as bowling balls and thermo plastics. If your application is not covered by a type A or type D durometer, one of the others may be used. Please see Tech Notes for a full listing of the different types of durometers and suggested applications. What is the difference between the different types of durometers ? Each type of durometer has a different combination of indenter shape and spring force. This allows a wide range of material hardness to be tested from very soft foams to hard thermoplastics. What is the difference between the different styles The choice of style depends on both the application and personal preference. The most popular style for general use is the 'classic' which features a large stable base which is great for general use as well as printing rollers. The 'ergo' style features a medium base ( 1x1 inch) and a wine glass shaped body which allows access to smaller areas than a 'classic'. The 'e2000™' is the choice for stability in a Digital or Analog Durometer with a 1.25" base. Finally there is a 'pencil' style which features the minimum size base ( 1/2 inch diameter) allowed by the ASTM D2240 standard and although not as stable as a 'standard' or 'ergo' it allows access to the more restricted areas. How do I measure thin materials ? Thin materials ( less than 1/4" ) may be stacked to form a thicker sample. If the sample is too thin the durometer will read too high as it will measure the surface under the sample. Always make sure that adding another layer of material will not change the reading, you then are assured of not reading through the material. In addition to sufficient thickness for testing, sufficient material around the sides of the indenter must be present.
Hardness and Related Characteristics Durometer Hardness test is non-destructive and does not require specimen preparation, which makes it an ideal method for checking materials under any condition with accuracy and reliability. All durometers have a spring loaded indenter which applies an indentation load to the specimen, thus sensing the "hardness", which can be related to other material characteristics. Use of a Durometer provides a quick yet accurate way to indirectly measure other material properties, such as tensile modulus, resilience, plasticity, compression resistance, and elasticity. Test Blocks PTC® recommends test blocks be used as a field check of the durometer. It gives the user an indication as to whether the durometer is mechanically sound prior to use. The block is designed using aircraft aluminum, precision ground and hard anodized. The value of the block is assessed using the durometer at the time of calibration. ASTM D2240 specification states that test blocks are not to be relied upon as calibration standards and the durometer should be calibrated per ASTM D2240 which includes mechanical, dimensional and force curve measurements. Durometer Calibration and Certification PTC recommends sending your durometer in for an annual calibration. The calibration procedures for the durometer includes mechanical, dimensional and force curve measurements as stated in ASTM D2240 and F1957. All Calibration Standards are Traceable to the National Institute of Standards and Technology (NIST). The durometer calibration services and reports provided by PTC Metrology® will meet your A2LA, ISO, ANSI, MIL, DoD, EuroNorm and other customer/supplier requirements. Please contact PTC® at sales@ptc1.com for any assistance you might need in selecting the best durometer for your application. There's no charge for recommending a durometer for your application or evaluating a material sample. PTC® also builds custom durometers and accessories to meet many hardness testing applications. |
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