ISO 1432-2021 pdf free download – Rubber, vulcanized or thermoplastic — Determination of low-temperature stiffening (Gehman test).
This document specifies a static procedure, known as the Gehman test, for determining the relativestiffness characteristics of vulcanized or thermoplastic rubbers over a temperature range from roomtemperature to approximately -120°c.
2Normative references
The following documents are referred to in the text in such a way that some or all of their contentconstitutes requirements of this document. For dated references, only the edition cited applies.Forundated references, the latest edition of the referenced document (including any amendments) applies.ISO 18899:2013,Rubber — Guide to the calibration of test equipment
ISO23529,Rubber —General procedures for preparing and conditioning test pieces for physical test methods
3Terms and definitions
No terms and definitions are listed in this document.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:- ISO online browsing platform: available at https://www.org/obp
-IEC Electropedia: available at http://www.electropedia.org/
4 Principle
The torsional stiffness is measured as a function of temperature, starting from a low temperature.Thestiffness is measured by connecting the test piece in series with a calibrated spring wire and measuringthe angle of twist of the test piece when the top of the wire is turned 180°.
5Apparatus
5.1Torsion apparatus, consisting of a torsion head, capable of being turned 180° in a plane normalto the torsion wire.The top of the wire is fastened to the torsion head.The bottom of the wire is fastenedto the test piece clamp. A device for “friction-free”indication or recording of angle by mechanical orelectrical means shall be provided, permitting convenient and exact adjustment of the zero point. Theindicating or recording system shall allow reading or recording of the angle of twist to the nearest degree.This principle is shown in Figure 1.
5.2 Torsion wires, made of tempered spring wire, of a length of 65 mm ± 8 mm, and having nominal torsional constants of 0,7 mN·m, 2,8 mN·m and 11,2 mN·m. In cases of dispute, the 2,8 mN·m wire shall be used.
5.3 Test piece rack, made of material of poor thermal conductivity, for holding the test piece in a vertical position in the heat transfer medium. The rack may be constructed to hold several test pieces. The rack is attached to a stand. It is advantageous to make the vertical portion of the stand from material of poor thermal conductivity. The base of the stand shall be of stainless steel or other corrosion-resistantmaterial.
Two clamps shall be provided for holding each test piece.The bottom clamp shall be attached to thetest piece rack.The top clamp acts as an extension of the test piece and is connected to the torsion wireby a rod.
5.4 Heat-transfer medium, liquid or gaseous, which remains fluid at the test temperature and whichdoes not appreciably affect the material being tested, as prescribed in ISO 23529.
Gases may be employed as the heat transfer medium provided the design of the apparatus is such thatresults obtained using them duplicate those obtained with liquids.
NOTE The following fluids have been used satisfactorily:
a) for temperatures down to -60 °C, silicone fluids of kinematic viscosity of about 5 mm2/s at ambient
temperature, which are usually suitable owing to their chemical inertness towards rubbers, their non-flammability and their non-toxicity;
b)for temperatures down to -73 C, ethanol;
c)for temperatures down to -120 °C, methylcyclohexane cooled by liquid nitrogen (found to be satisfactory
with the use of suitable apparatus).
5.5 Temperature-measuring device, capable of measuring temperature to within 0,5 °C over thewhole range of temperature over which the apparatus is to be used.
The temperature sensor shall be positioned near the test pieces.
5.6Temperature control, capable of raising the temperature as per 8.2 and 8.3 and maintaining thetemperature of the heat-transfer medium to within ±1 ℃.
5.7Container for heat-transfer medium, a bath for a liquid medium, or a test chamber for a gaseousmedium, with means of heating and cooling the coolant to the minimum temperature required.
5.8Stirrer, for liquids, or fan or blower, for gases, which ensures thorough circulation of the heat-transfer medium. lt is important that the stirrer also moves the liquid vertically to ensure a uniformtemperature in the liquid.
5.9Stopwatch, or other timing device, graduated in seconds.
6Calibration
The requirements for calibration of the test apparatus are given in Annex A.ISO 1432 pdf download.