Values, durometer hardness

Plastisols are not "air dry systems, i.e.y they require fusion temperatures of at least 250°F for the copolymers and 300°F for the homopolymers. Plastisols enable us to obtain very low durometer hardness, thick fused sections, and excellent chemical resistance. High durometer hardness values are difficult to obtain. 

The volatile component is usually selected from true non-solvents for PVC resins such as the aliphatic hydrocarbons. The main purpose of the volatile ingredient is to lower the viscosity of the paste by contributing more liquid to the formulation. Very low plasticizer levels are then possible and higher durometer hardness values are attainable (as compared with plastisols). 

Plastisols enable us to obtain very low durometer hardness, thick fused sections, and excellent chemical resistance. High durometer hardness values are difficult to obtain. 

Durometer hardness An arbitrary numerical value that indicates the resistance to indentation of the indentor point of a durometer. 

Durometer hardness - A value that indicates the indentation or resistance to indentation of the indentor point of a durometer. High values indicate harder materials. See ASTM D2280-Test Method for Rubber Property-durometer Hardness. 

The various silicone sealants now available provide a broad spectrum of physical properties. For example, ultimate elongation (as measured by ASTM-D-412) varies from 50% to 1200% and one commercially available silicone sealant- has a typical value of >1200% with almost 100% recovery. Tensile strengths vary from 100 to 1000 psi, while moduli at 100% extension range from <50 to >500 psi. Durometer hardnesses can range from 15 to 80 (Shore A). 

The two most common types of durometers used for plastics are the Shore Type A and Shore Type D. They differ in the spring force and the geometry of the indentor, as shown in Figure 3.45. Due to creep, readings should be taken after a fixed time interval, often chosen as 10 sec. Typical hardness values of some of the common plastics measured by different test methods are shown in Table 3.4. 

Tear resistance was measured at 22°C using a trouser tear specimen described in ASTM D 470-82. The crosshead speed was 500 mm/min. The data reported are averages of results for six specimens. A hand-held Shore Durometer, hardness type "A-2" was used to determine the hardness of the samples, according to ASTM D 2240-75. Specimens were rectangular, 25 mm in length by 13 mm wide. Four plies of sample were used to achieve a thickness of 6.4 mm. Three readings were taken, 6 mm apart on the surface of the four plies. Hardness values measured on the blocks tended to be as much as five units lower. 

The 30% glass-reinforced polypropylene resin has a unique decrease of approximately 25% in work-to-break with increasing test speed above the 0.05 in./min range (Fig. 3-4). An extremely large work-to-break value is demonstrated by the 40% glass-reinforced polyurethane resin (55D Shore Durometer Hardness Base Resin) at the 0.05 in./min straining rate (Fig. 3-9). 

The hardness of plastics (and coatings may be considered to be very thin plastics) is most commonly measured by the Shore (durometer) test or Rockwell hardness test. Both of these hardness methods measure the resistance of plastics toward indentation. This provides an empirical hardness value. Shore hardness most often uses either the Shore A or the Shore D scale. These methods are best used for rubbers or elastomers and are also commonly used for softer plastics such as polyolefins, lluoropolymers, and polyvinyls. The Shore A scale is used for softer rubbers while the Shore D scale is used for harder ones. This method works better for thicker coatings, as with all hardness tests on coatings. The hardness of thin coatings can be influenced by the substrate, that is, an artificially hard measure may be measured. A picture of a durometer is shown in Fig. 2.23. 

Because the seals are supplied on belts, it is imperative that they be as close to the same hardness or durometer as possible. For example, if a belt of seals with different hardness values goes into the same penetration and the same torque is applied to each link, they will not expand uniformly and the seals can be compromised. 

D urometer hardness An arbitrary numerical value that measures the resistance to intention of a blunt indenter point of the durometer. The higher the number, the greater indention hardness. 

Shore hardness It is the indentation hardness of a material as determined by the depth of an indentation made with an indenter of the Shore type durometer. The scale reading on this durometer is from zero (corresponding to 0.100 in. depth) to 100 for zero depth. The Shore A indenter has a sharp point, is spring-loaded, and is used for the softer plastics. The Shore B indenter has a blunt point, is spring-loaded at a higher value, and is used for harder plastics. 

The shore durometer is a simple instrument used to measure the resistance of a material to the penetration of a blunt needle. In the Barcol approach, a sharp indentor is used to measure the ability of a sample to resist penetration by the indentor (Figure 14.18). The values given in Table 14.3 are for one specific set of conditions and needle area for the Barcol and Brinell hardness tests. 

Plasticizer efficiency n. (1) The parts by weight of plasticizer per 100 parts of resin (phr) required to produce a plasticized PVC resin of a particular hardness on the Durometer A scale. (2) Taking dioctyl phthalate as the industry standard of comparison, one may express the efficiency (in %) of another plasticizer as 100 njni), where n is the phr of DOP required to achieve a particular Durometer value (or other desired property) and ni is the phr of the alternate plasticizer required to reach that same value. 

The hardness of the UDPNCs (uniformly dispersed polymeric nanocomposites) was measured according to ASTM D-2240 with a shore durometer. Specific gravity of the composite for respective loading was calculated from the density values of the compounds. 

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