ISO 23873:2010

INTERNATIONAL ISO
STANDARD 23873
First edition
2010-11-15
Hard coal — Method for the measurement
of the swelling of hard coal using a
dilatometer
Houille — Méthode pour le mesurage du gonflement de la houille au
moyen d'un dilatomètre
Reference number
©
ISO 2010
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ii © ISO 2010 – All rights reserved

Contents Page
Foreword .iv
Introduction.v
1 Scope.1
2 Normative references.1
3 Terms and definitions .1
4 Principle .2
5 Materials .2
6 Apparatus.2
6.1 Mould and accessories.2
6.2 Dilatometer.3
6.3 Dilatometer furnace.3
6.4 Temperature controller .4
6.5 Temperature recorder .4
6.6 Retort and piston.4
6.7 Means of recording piston movement .4
6.8 Cleaning instruments.4
7 Procedure.5
7.1 Temperature calibration.5
7.2 Preparation of test sample and test pieces .5
7.3 Determination .6
8 Expression of results.7
9 Precision .8
9.1 Repeatability .8
9.2 Reproducibility .8
10 Test report.8

Foreword
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(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
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The main task of technical committees is to prepare International Standards. Draft International Standards
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Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 23873 was prepared by Technical Committee ISO/TC 27, Solid mineral fuels, Subcommittee SC 5,
Methods of analysis.
iv © ISO 2010 – All rights reserved

Introduction
The dilatation of coal has been primarily measured by two different standard procedures: the Ruhr dilatometer
and the Audibert-Arnu dilatometer. Both of the methods were very similar, having the same basic apparatus
and heating rate but using different initial masses of coal arising from the method of pencil preparation.
This International Standard combines the two previous procedures by adjusting the equipment specification to
define a single acceptable method.

INTERNATIONAL STANDARD ISO 23873:2010(E)

Hard coal — Method for the measurement of the swelling of
hard coal using a dilatometer
1 Scope
This International Standard describes a method for the measurement of the swelling of hard coal using a
dilatometer.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
ISO 1213-2, Solid mineral fuels — Vocabulary — Part 2: Terms relating to sampling, testing and analysis
ISO 13909-4, Hard coal and coke — Mechanical sampling — Part 4: Coal — Preparation of test samples
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 1213-2 and the following apply.
3.1
softening temperature
temperature of initial contraction
temperature at which the downward movement of the dilatometer piston is 0,5 mm
NOTE See temperature θ in Figure 3.
3.2
temperature of maximum contraction
temperature at which the dilatometer piston reaches its lowest point
NOTE See temperature θ in Figure 3.
3.3
temperature of maximum dilatation
temperature at which the dilatometer piston reaches its highest point
NOTE See temperature θ in Figure 3.
3.4
maximum contraction
maximum downward movement of the dilatometer piston, measured from the zero point
NOTE 1 Maximum contraction is expressed as a percentage of the initial test-piece length.
NOTE 2 See c in Figures 3 and 4.
3.5
maximum dilatation
maximum upward movement of the dilatometer piston after contraction, measured from the zero point
NOTE 1 Maximum dilatation is expressed as a percentage of the initial test-piece length.
NOTE 2 See d in Figures 3 and 4. The value can be either positive or negative.
3.6
repeatability
maximum acceptable difference between two determinations which are carried out in the same laboratory, by
the same operator with the same apparatus, on test pieces prepared from the same test sample and tested
simultaneously in two different retorts during the same heating cycle or separately in the same retort during
different heating cycles
3.7
reproducibility
maximum acceptable difference between the means of two determinations which are carried out in each of
two laboratories, on representative portions taken from the same gross sample, after the last stage of sample
preparation
4 Principle
A test piece, in the form of a pencil, prepared from powdered coal is heated at a constant rate in a steel retort
positioned in a furnace, the temperature monitoring system having been previously calibrated using two
reference metals of known melting points. The change in level of a piston resting upon the test piece is
observed continuously, and a record is produced which is charateristic of the swelling properties of the coal.
5 Materials
The following materials are required for temperature calibration (7.1).
5.1 Graphite pencils, 30 mm long, base diameter 7,4 mm, top diameter 6,8 mm, with a small cylindrical
reservoir drilled in the narrow end of each pencil.
5.2 Metal balls, of the following reference metals:
a) lead, of analytical reagent grade, assay (Pb) 99,98 % minimum, melting point 327,0 °C;
b) zinc, assay (Zn) 99,87 % minimum, melting point 419,3 °C.
5.3 Water-based blacking.
6 Apparatus
6.1 Mould and accessories
6.1.1 Mould (see Figure 1), made from steel, case-hardened after machining. The bore shall be polished
after hardening and the bore and uniformity of taper (i.e 1 in 50) shall conform to the dimensions given in
Table 1.
6.1.2 Mallet, plastics head, mass about 200 g.
6.1.3 Ram (see Figure 1).
2 © ISO 2010 – All rights reserved

6.1.4 Press (see Figure 1).
6.1.5 Load cell (see Figure 1), capable of registering a load of 0 to 15 kN.
6.1.6 Pencil gauge (see Figure 1).
Table 1 — Dimensions of mould
Bore
Distance from wide end
(tolerance: −0,00, +0,005)
0 7,4
10 7,2
20 7,0
30 6,8
40 6,6
50 6,4
60 6,2
70 6,0
6.2 Dilatometer
A general arrangement of suitable dilatometer apparatus giving critical dimensions is shown in Figure 2.
6.3 Dilatometer furnace
A furnace capable of heating two or more retorts (6.6) to a temperature of 550 °C at a rate of 3 °C/min is used.
A suitable furnace (for heating three retorts) is illustrated in Figure 2 and consists of a casing fitted with a base
and a top cover. The cover supports a cylindrical block of copper-aluminium alloy CA 104, of 65 mm diameter
and 460 mm long. The block has three holes of 380 mm minimum depth and 15,0 mm ± 0,1 mm diameter,
drilled as shown in Figure 2. The top surface may be insulated by an appropriately shaped piece of board. The
block is heated electrically by an insulated resistance winding, capable of raising the temperature of the block
to 550 °C at a rate of 3°C/min. The space between the block and the casing is filled with a thermal insulating
material. A suitable temperature sensor is positioned in the third retort in such a way that the sensor tip lies
centrally 30 mm above the internal base of the retort. The distance of 30 mm is established by using a
graphite pencil (5.1) as a means of measurement.
The furnace shall comply with the following operating conditions.
Heat the furnace to 400 °C, measuring the temperature at the standard sensing point, i.e. at a position
equivalent to that of the centre of a normally sited test piece 30 mm above the internal base of the sensing
retort. Place a second temperature-measuring device (e.g. a probe), of similar precision, in one of the other
retorts at the same height above its base. If the two devices differ, apply a correction. Heat the furnace at a
rate of 3 °C/min and, when the temperature has reached about 450 °C, measure the temperature over the
lower 250 mm of the retort using the probe. The difference between the corrected probe temperature and the
mean temperature shown at the standard temperature-sensing position shall be not more than:
⎯ 2 °C in the lower 120 mm;
⎯ 5 °C from 120 mm to 180 mm;
⎯ 10 °C from 180 mm to 250 mm.
The instrument used to measure the temperature can be either the temperature recorder described in 6.5
or another of at least equal precision.
6.4 Temperature controller
The temperature controller shall be a separate instrument from that used to record the rise of temperature
during the test. It shall be of the automatic, programmed type capable of maintaining a mean rate of
temperature rise of 3 °C/min ± 0,05 °C/min between 250 °C and 550 °C with a variation of not more than
±1 °C per 30 °C rise in any 10 min period, with a precision of ±1 °C.
6.5 Temperature recorder
A suitable means of producing a complete record of the temperature variation during the test.
6.6 Retort and piston
A cylindrical retort of cold-drawn seamless tube of steel fitted with a gastight threaded plug at its base and a
collar at its top. When inserted in a hole in the furnace, the retort shall be supported only by the collar with the
threaded plug clear of the bottom of the hole.
When new, the internal diameter of the retort shall be 8,00 mm ± 0,05 mm and the external diameter shall be
14,5 mm ± 0,1 mm. Check the internal diameter with a suitable ball gauge when new, and again after 100,
150, 200, etc., tests. If the internal diameter of the lower third of the retort has increased at any point to more
than 8,075 mm, discard the retort.
The p
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