6.2 Test specimen surface state Unless otherwise specified, a tests shall be made on clean surfaces; b any cleaning procedure used shall be reported.. The result of a test where a hole
Environmental conditioning
Unless otherwise specified, the test specimens shall be conditioned for a minimum of 24 h at
Test specimen surface state
Unless otherwise specified, a) tests shall be made on clean surfaces; b) any cleaning procedure used shall be reported Wherever possible, the details shall be agreed between supplier and customer
When cleaning the test specimen, it is crucial to avoid contaminants such as dust, dirt, fingerprints, grease, oil, and mould release, as these can affect the results Careful cleaning is essential to prevent issues like swelling, softening, abrasion, or other damage to the material.
Electrodes
The article specifies that two platinum electrodes, with a minimum purity of 99%, must be utilized These electrodes should have a rectangular cross-section measuring (5 ± 0.1) mm by (2 ± 0.1) mm, featuring one end that is chisel-edged at an angle of 30° ± 2° Additionally, the sharp edge must be smoothed to create a flat surface that is approximately 0.01 mm to 0.1 mm wide.
NOTE 1 A microscope with a calibrated eyepiece has been found suitable for checking the size of the end surface
It is advisable to utilize mechanical methods for refurbishing the electrode shape post-testing to ensure that the electrodes adhere to the necessary tolerances, particularly concerning the edges and corners.
At the beginning of the test, electrodes must be symmetrically positioned in a vertical plane, forming a total angle of 60° ± 5° The opposing faces of the electrodes should be nearly vertical on a flat horizontal surface of the test specimen Additionally, the separation between the electrodes along the surface of the test specimen should be set at 4.0 mm ± 0.1 mm.
To ensure accurate measurement of electrode separation, a thin metal rectangular slip gauge will be utilized Each electrode must move freely, applying a force of 1.00 N ± 0.05 N on the test specimen's surface at the beginning of the test The design should guarantee that this force remains consistent throughout the duration of the test.
One typical type of arrangement for applying the electrodes to the test specimen is shown in
Figure 3 The force shall be verified at appropriate intervals
In tests conducted on materials with minimal electrode penetration, electrode force can be produced using springs Conversely, for general-purpose equipment, gravity should be utilized to generate the necessary force.
In many apparatus designs, electrode movement during testing can occur due to specimen softening or erosion, resulting in an arc and altering the electrode gap The extent and direction of this gap change are influenced by the positions of the electrode pivots and the contact points with the specimen The impact of these changes is likely material-dependent and remains undetermined Variations in design may lead to differing results between apparatus.
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Test circuit
The electrodes shall be supplied with a substantially sinusoidal voltage, variable between
The voltage measuring device must accurately display a true root mean square (r.m.s.) value for voltages of 100 V and 600 V within a frequency range of 48 Hz to 62 Hz, with a maximum allowable error of 1.5% Additionally, the power source should have a minimum capacity of 0.6 kVA A suitable test circuit example is illustrated in Figure 4.
A variable resistor must be able to adjust the current between the short-circuited electrodes to a range of (1.0 ± 0.1) A, while ensuring that the voltage indicated by the voltmeter does not decrease by more than 10% during this current flow Additionally, the instrument used to measure the short-circuit current should have a maximum error of ±3%.
The input supply voltage to the apparatus shall be adequately stable
The over-current device shall operate when a current with an r.m.s value of 0,50 A with a relative tolerance of ±10 %, has persisted for 2,00 s with a relative tolerance of ±10 %.
Test solutions
Dissolve about 0.1% by mass of high-purity anhydrous ammonium chloride (NH4Cl), with a minimum purity of 99.8%, in de-ionized water that has a conductivity not exceeding 1 mS/m This solution should achieve a resistivity of (3.95 ± 0.05) Ωm at a temperature of (23 ± 1) °C.
NOTE 1 Select the quantity of ammonium chloride to give a solution in the required range of resistivity
Dissolve about 0.1% by mass of analytical reagent grade anhydrous ammonium chloride, with a purity of at least 99.8%, and 0.5% ± 0.002% by mass of sodium-di-butyl naphthalene sulfonate in de-ionized water, ensuring the water has a conductivity not exceeding 1 mS/m, to achieve a resistivity of (1.98 ± 0.05) Ωm at (23 ± 1) °C.
NOTE 2 Select the quantity of ammonium chloride to give a solution in the required range of resistivity
Solution A is typically the preferred choice; however, for more aggressive contaminants, Solution B is advisable When Solution B is utilized, the CTI or PTI value should be accompanied by the letter "M" to signify its use.
Dropping device
Test solution drops should be applied to the specimen surface every 30 seconds, with a permissible variation of ± 5 seconds These drops must be released from a height of 35 mm, also allowing for a variation of ± 5 mm, and should ideally land centrally between the electrodes.
The time for 50 drops to fall on to the specimen shall be (24,5 ± 2) min
The mass of a sequence of 50 drops shall lie between 0,997 g and 1,147 g The mass of a sequence of 20 drops shall lie between 0,380 g and 0,480 g
NOTE 1 The mass of the drops may be determined by weighing with the appropriate laboratory balance
The mass of the drops shall be checked at appropriate time intervals
For Solution A, thin-walled stainless steel tubing, such as hypodermic needle tubing with an outer diameter between 0.9 mm and 1.2 mm, is recommended for the tip of the dropping device, depending on the dropping system In Solution B, tubes with outer diameters exceeding 0.9 mm are also considered suitable.
3,45 mm have been found to be necessary with the different dropping systems in use
NOTE 3 The use of a drop detector/counter is recommended to ascertain whether there are any double drops or whether drops are missing
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Test specimen support platform
A glass plate or plates, having a total thickness of not less than 4 mm and of a suitable size shall be used to support the test specimen during the test
To prevent the hassle of cleaning the specimen support table, it is advisable to use a disposable glass microscope slide directly beneath the test specimen.
NOTE 2 The use of thin metal foil conductors around the edge of the glass plate to detect electrolyte loss has been found useful.
Electrode assembly installation
The specimen and its immediate electrodes shall be mounted in an essentially draught-free space in an enclosure
To maintain a low fume concentration in the chamber, it is essential to establish a slight airflow across the test specimen and between the electrodes, particularly for certain materials An air velocity of approximately 0.2 m/s is recommended before and during the test In other areas of the enclosure, higher air velocities can be utilized to enhance fume removal The air velocity can be accurately measured using a properly calibrated hot wire anemometer.
A suitable fume extraction system shall be provided to allow safe venting of the enclosure after the test
General
In cases where the material exhibits significant anisotropy, testing should be conducted both along the features and perpendicular to them The results obtained from the direction yielding the lower values will be utilized, unless stated otherwise.
Test shall be made at an ambient temperature of (23 ± 5) °C
Tests shall be made on uncontaminated test specimens, unless otherwise specified
The validity of a test result is determined by the formation of a hole, regardless of the thickness of the test specimen It is essential to report both the formation of the hole and its depth, which corresponds to the thickness of the test specimen or stack.
Preparation
After conducting each test, it is essential to clean the electrodes using a suitable solvent, followed by rinsing them with de-ionized water If needed, reshape the electrodes and perform a final rinse prior to the subsequent test.
Immediately before the test ensure, if necessary by cooling the electrodes, that their temperature is sufficiently low so that they have no adverse effect on the specimen properties
Ensure freedom from visual contamination and ensure that the solution to be used conforms to the conductivity requirements either by regular testing, or by measurement immediately before the test
To ensure accurate test results, it is crucial to clean the dropping device before each use, as residues from previous tests can contaminate the solution and lead to increased concentration due to evaporation It is recommended to mechanically clean the exterior and flush the interior with a conforming solution, typically by dispensing 10 to 20 drops, to eliminate any non-conforming liquid that may affect the outcome.
In case of dispute, the cleaning procedures used for the electrodes and dropper tube shall be agreed between purchaser and supplier
LICENSED TO MECON LIMITED - RANCHI/BANGALORE, FOR INTERNAL USE AT THIS LOCATION ONLY, SUPPLIED BY BOOK SUPPLY BUREAU.
Position the test specimen horizontally on the support table with the test surface facing up Adjust the height of the specimen and electrode assembly to ensure that when the electrodes are lowered, they achieve the correct orientation with a separation of 4.0 mm ± 0.1 mm Confirm that the chisel edges make full-width contact with the specimen surface with the necessary force.
NOTE 2 It may be helpful to place a light behind the electrodes when making this check visually
Set the test voltage to an integer multiple of 25 V and adjust the circuit parameters to ensure the short-circuit current remains within the allowed tolerance.
Test procedure
Initiate the dropping system to allow drops to fall onto the test surface, and continue the test until one of the following conditions is met: a) the over-current device activates; b) a continuous flame is observed; or c) at least 25 seconds have passed after the fiftieth (or hundredth) drop has fallen without either a) or b) occurring.
NOTE If there is no requirement for the determination of erosion, the 100 drop tests may be made ahead of any
After completion of the test, vent the chamber of noxious fumes and remove the test specimen
Specimens that have not failed at the 50 drop point must be cleaned of debris and loosely attached degradation products before being placed on the platform of a depth gauge.
The maximum erosion depth of each specimen will be measured in millimeters with an accuracy of 0.1 mm, utilizing a 1.0 mm nominal diameter probe with a hemispherical end The final result will be the highest value obtained from five measurements.
Erosion depths of less than 1 mm are reported as