Home>ASTM Standards>ASTM D991-89(R2020) pdf free download

ASTM D991-89(R2020) pdf free download

ASTM D991-89(R2020) pdf free download.Standard Test Method for Rubber Property—Volume Resistivity Of Electrically Conductive and Antistatic Products
5. Apparatus
5.1 Electrode Assembly—The electrode assembly (Fig. 1) shall consist of a rigid base made from an electrically insulat- ing material having a resistivity greater than 10 TΩ·m (for example, hard rubber, polyethylene, polystyrene, etc.) to which a pair ofcurrent electrodes and a pair ofpotential electrodes are fastened in such a manner that the four electrodes are parallel and their top surfaces are in the same horizontal plane. Another pair of current electrodes identical with the first pair shall be fastened to a second piece of insulating material so that they can be superimposed on the specimen directly above the first pair. The current electrodes shall have a length at least 10 mm (0.4 in.) greater than the specimen width, a width between 5 and 8 mm (0.2 and 0.3 in.), and a height uniform within 0.05 mm (0.002 in.) between 10 and 15 mm (0.4 and 0.6 in.). The potential electrodes shall have a length and height equal to the current electrodes and shall be tapered to an edge having a radius of 0.5 mm (0.02 in.) maximum at the top surface. The distance between the potential electrodes shall not be less than 10 mm (0.4 in.) nor more than 66 mm (2.6 in.) and shall be known within 62 %. The current electrodes shall be equidis- tant outside the potential electrodes and separated from them by at least 20 mm (0.8 in.). The electrodes shall be made from a corrosion-resistant metal such as brass, nickel, stainless steel, etc. Insulation resistance between electrodes shall be greater than 1 TΩ. 5.2 Resistance-Measuring Device—Resistance may be mea- sured by any electrical circuit that enables the current through the current electrodes and the potential across the potential electrodes to be measured within 2 %. Suitable devices for measuring current are: (1) a precision milliammeter, or (2) potential measurement across a reference resistor (resistance value known within 2 % in series with the current electrodes. Suitable devices for measuring potential are: (1) a galvanom- eter having a sensitivity of 1 µA or less per scale division in a null-voltage circuit; (2) an electrostatic voltmeter having a d-c resistance greater than 19 TΩ; or (3) an electrometer such as a multirange voltmeter having an input d-c impedance greater than 0.1 TΩ (Note 1). In any case, the current through the potential electrodes during measurement must be less than 1 % of that through the current electrodes. A stable source of d-c potential shall be provided that can be adjusted to limit the power dissipated in the specimen between potential electrodes to approximately 0.1 W. Because of the large range of resistances covered by conductive and antistatic rubbers, sepa- rate equipment for measuring resistances above and below approximately 50 000 Ω is generally desirable.N OTE 1—Schematic diagrams of a typical apparatus that have been found to be satisfactory are shown in Figs. X1.1 and X1.2. 5.3 Electrode Contacts—Masses shall be provided to pro- duce a uniform contacting force across the width of the specimen of approximately 300 N/m (4.5 kg (10 lb)) on the standard sheet, 150 mm (6 in.) wide, by the current electrodes and 60 N/m (0.9 kg (2 lb)) on the standard sheet, 150 mm (6 in.) wide, by the potential electrodes.
6. Specimens
6.1 Size—The width of the specimen shall be between 10 and 150 mm (0.4 and 6 in.) and the length shall be between 70 and 150 mm (2.8 and 6 in.). The width shall be uniform within 61 %. The thickness of cut specimens is specified in 6.3. Molded specimens are specially prepared as described in 6.2 and therefore have a thickness of 2.0 6 0.2 mm (0.08 6 0.008 in.). 6.2 Molded Specimen—Standard sheets prepared in accor- dance with Practice D3182 may be used, provided the surface of the uncured rubber is kept free of soapstone or other contamination, and the surface of the vulcanized sheet is not contaminated with mold lubricant. To avoid surface contami- nation and minimize distortion of specimen prior to test, sheets may be molded between sheets of moisture-sensitive cellophane, which can be readily removed after brief immer- sion in warm water. After removing the cellophane, the surface of the sheet should be patted dry, taking care not to bend or stretch the sheet.

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