1、BRITISH STANDARD BS 6043-4.8: 1991 Methods of sampling and test for Carbonaceous materials used in aluminium manufacture Part 4: Cold ramming pastes Section 4.8 Determination of electrical resistivity of baked rammed paste NOTEIt is recommended that this Section be read in conjunction with the gener
2、al information in BS6043-4.0, published separately.BS6043-4.8:1991 This British Standard, having been prepared under the directionof the Chemicals Standards Policy Committee, waspublished under the authorityof the Standards Board and comes into effect on 30September1991 BSI 10-1999 The following BSI
3、 references relate to the work on this standard: Committee reference CIC/24 Draft for comment 90/54848 DC ISBN 0 580 19732 8 Committees responsible for this British Standard The preparation of this British Standard was entrusted by the Chemicals Standards Policy Committee (CIC/-) to Technical Commit
4、tee CIC/24, upon which the following bodies were represented: Aluminium Federation British Ceramic Research Ltd. Chemical Industries Association Institute of Petroleum Refractories Association of Great Britain Amendments issued since publication Amd. No. Date CommentsBS6043-4.8:1991 BSI 10-1999 i Co
5、ntents Page Committees responsible Inside front cover Foreword ii 1 Scope 1 2 Principle 1 3 Materials 1 4 Apparatus 1 5 Sampling 1 6 Preparation of test samples 1 7 Procedure 1 8 Calculation and expression of results 2 9 Test report 2 Publication(s) referred to Inside back coverBS6043-4.8:1991 ii BS
6、I 10-1999 Foreword This Section of BS6043 has been prepared under the direction of the Chemicals Standards Policy Committee to provide a method of test for cold ramming pastes used in the production of aluminium. There is no corresponding International Standard; however, it is intended, upon publica
7、tion of this Section of BS6043, that it be offered to the International Organization for Standardization (ISO) for possible adoption as an International Standard. It is essential to use BS6043-4.1, BS6043-4.6 and BS6043-4.7 in conjunction with this Section of BS6043. This standard describes a method
8、 of test only, and should not be used or quoted as a specification defining the characteristics of a product. Reference to this Section should indicate that the method of test used is in accordance with BS6043-4.8:1991. A British Standard does not purport to include all the necessary provisions of a
9、 contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages1 and 2, an inside ba
10、ck cover and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover.BS6043-4.8:1991 BSI 10-1999 1 1 Scope This Section of BS6043 describes a method for the determination, at a
11、mbient temperature, of the electrical resistivity of test pieces of baked rammed cold ramming paste used in aluminium manufacture. NOTEThe titles of the publications referred to in this standard are listed on the inside back cover. 2 Principle A baked test piece of known dimensions is produced from
12、a test sample of cold ramming paste by ramming under regulated conditions followed by baking according to a defined programme. A constant direct electric current is passed longitudinally through the test piece and the electrical potential is measured between two longitudinally spaced points near the
13、 centre of the test piece using a bridge, potentiometer or voltmeter. 3 Materials 3.1 Copper gauze, approximately two threads per millimetre, bright, annealed. 3.2 Aluminium foil, of thickness approximately20m. 3.3 Metallurgical or regular-grade petroleum coke, as described in5.1 of BS6043-4.7. 3.4
14、Refractory cement, for sealing the lid of the baking box. 4 Apparatus 4.1 Ordinary laboratory apparatus 4.2 Ramming apparatus, and the other apparatus described in clause4 of BS6043-4.7:1991. 4.3 Test-piece holder, having two parallel metal plates electrically insulated from each other and capable o
15、f being clamped in contact with the full area of the end faces of the test piece, with connections for passing an electric current through the test piece. 4.4 Source of direct electric current, capable of being adjusted to pass a direct electric current of the order of500mA through the test piece, a
16、nd capable of indicating and maintaining the set current with an accuracy of 0.5%. 4.5 Potential measuring equipment, comprising a bridge, potentiometer or high-impedance voltmeter capable of measuring the potential developed on the test piece with an accuracy of 0.5%. 4.6 Potential probe, having tw
17、o sharp-pointed electrical contact pins set in an electrically-insulating body, at a fixed spacing of50 0.1mm. The actual spacing shall be checked and recorded at the start of each series of determinations. 4.7 Vernier callipers, capable of measuring lengths of not less than150mm, and having a verni
18、er graduated in0.1mm or smaller units. 4.8 Electric oven, capable of being controlled at110 5 C. 5 Sampling Prepare a representative laboratory sample of cold ramming paste in accordance with BS6043-4.1. 6 Preparation of test samples Prepare at least two test samples from the laboratory sample (see
19、clause5) by the method described in7.1 and7.3 of BS6043-4.7:1991. 7 Procedure 7.1 Preparation of baked test pieces Prepare two test pieces by ramming the test samples (see clause7) by the method described in8.2 of BS6043-4.7:1991 using the ramming apparatus(4.2). If the cold ramming paste requires p
20、re-curing before baking, pre-cure the test pieces in accordance with8.3 of BS6043-4.7:1991. Bake the test pieces by the method described in8.4 of BS6043-4.7:1991. 7.2 Determination 7.2.1 On each of the baked test pieces (see7.1) carry out the operations described in7.2.2 to7.2.6. 7.2.2 Dry the test
21、piece by heating it for2h in the oven(4.8), controlled at110 5 C, then place it in a desiccator to cool to ambient temperature. Keep the test piece in the desiccator until it is required for testing. 7.2.3 Measure the diameter of the test piece in the central region using the vernier callipers(4.7),
22、 making two measurements mutually at right angles. Measure to the nearest0.1mm and calculate the mean of the two measurements to the nearest0.1mm. 7.2.4 Place the test piece(7.1) in the holder(4.3) with a flat pad comprising several thicknesses of the copper gauze(3.1) or the aluminium foil(3.2) bet
23、ween each end face of the test piece and the corresponding parallel metal plate of the holder. Clamp the test piece in the holder, using the minimum force necessary to ensure reliable electrical contact over the whole area of the end faces of the test piece.BS6043-4.8:1991 2 BSI 10-1999 7.2.5 Pass a
24、n electric current(see4.4) through the test piece, selecting a magnitude for the current which allows the developed potential to be measured by the potential measuring equipment(4.5) with a limit of error in the reading of less than0.5%, e.g.for a digital voltmeter reading to0.01mV, a minimum readin
25、g of2.00mV is obtained. Ensure that the selected magnitude of the current is not sufficient to cause any detectable change in the resistance of the test piece due to electrical heating during the test. Record the current used to a precision of 0.5%. 7.2.6 Using the potential probe(4.6) connected to
26、the potential measuring equipment(4.5), take four readings of the developed potential at approximately90 circumferential spacing, with the pins of the probe positioned longitudinally with respect to the test piece in its central region. Calculate the mean of the four readings to a precision of 0.5%.
27、 7.3 Validation of data If the range of the four potential readings(7.2.6) is greater than5% of the mean value, repeat the measurements in accordance with7.2.6 with the probe positioned at new locations close to the original positions and calculate a new mean value to a precision of 0.5%. If the ran
28、ge of the new set of readings is less than5% of the mean, take the data as valid. Persistently anomalous or fluctuating values indicate the presence of a major inhomogeneity in the test piece; in this case discard the test piece, reject the result and repeat the determination, by following the opera
29、tions described in7.1 and7.2.2 to7.2.6 with a new test piece. Take the mean of the four validated readings of the potential to calculate the electrical resistivity of the test piece. 8 Calculation and expression of results Calculate the electrical resistivity, E, of the test piece, in7m, from the fo
30、llowing equation: where: Calculate the electrical resistivity for each test piece (see7.1) to three significant figures. If the results obtained for the two test pieces differ by more than10% of the lower value, reject the results and the test pieces and repeat the procedure starting with fresh test
31、 samples (seeclause6). Express the mean electrical resistivity of the two test pieces (see7.1) to three significant figures. NOTETypical values generally fall in the range57m to1007m. 9 Test report The test report shall include the following information: a) a complete identification of the test piec
32、es including details of the cold ramming paste and of its compaction, baking and any other treatment; b) a reference to this British Standard, i.e.BS6043-4.8:1991; c) the value of the mean electrical resistivity of the two test pieces, calculated and expressed in accordance with clause8; d) any unus
33、ual features noted during the determination; e) any operation not included in this BritishStandard or regarded as optional. V is the mean validated potential(see7.3) (inmV); D is the mean diameter of the test piece(see7.2.3) (inmm); C is the current passing through the test piece(see7.2.5) (in A); L
34、 is the distance between the pointed tips of the potential probe(4.6) (inmm). E V D/2 () 2 CL - =BS6043-4.8:1991 BSI 10-1999 Publication(s) referred to BS6043, Methods of sampling and test for carbonaceous materials used in aluminium manufacture. BS6043-4, Cold ramming pastes. BS6043-4.0, General in
35、troduction 1) . BS6043-4.1, Methods of sampling. BS6043-4.6, Determination of maximum rammed apparent density. BS6043-4.7, Preparation of baked rammed test pieces and determination of baked apparent density, change in volume and loss in mass. 1) Referred to on the front cover only.BS 6043-4.8: 1991
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