The present invention relates to an improved plastometer
for measuring plasticity of coal.
The invention relates more particularly to a plastometer
for measuring plasticity of coal by recording the speed of a
stirrer dipped in coal powder at a short interval of time as the
temperature of the coal powder is increased gradually at a steady
rate from 300°C to 550°C and computing the plasticity of the coal
from the data recorded using a suitably programmed personal
computer (PC). The measurement of plasticity of coal is useful
for predicting its behaviour during carbonization, gasification,
liquefaction and combustion.
The conventional plastometer such as, "Gieseler Plastomete
available from M/s Standard Instrument Inc., U.S.A., comprising
furnace, plastometer head, stand and electronics (not known) used
for determining plastic behaviour of coal is too expensive and
difficult to maintain for regular use in the coking coal sectors
of steel plants.
The object of the invention is to design and fabricate
a plastometer for coal at a reduced cost using durable and
readily available components to ensure its dependable performance
during regular use in steel plants.
The invented plastometer comprises a retort assembly
having a vertically held cylindrical crucible for holding the
sample of coal powder to be tested with the bottom end closed
and top end partly closed with an annular top cover, a co-
axial barrel erected vertically upward from the inner edge of
the annular cover plate with an outlet for gas near its middle
part, a stirrer dipped in the coal powder contained in the
crucible v/ith a rod erected vertically upward through the
central bore of the barrel, a guide sleeve provided at the bottom
end of barrel to guide the stirrer rod within the central bore
of the barrel with sufficient clearance from the barrel inner
wall and a stand to facilitate smooth up/down movement of the
retort assembly; a top assembly, having a motor,located co-axially
above the barrel and coupled to the upper end of the stirrer rod
protruding the bore of the barrel? an electromagnetic brake
connected to the shaft of the motor for controlling the torque
applied by the motor to the stirrer and also to a shaft encoder
which measures the rotational speed of the stirrer; an electrically
heated furnace of cylindrical shape having a solder bath surrounded
with heating coils embedded in a heat insulating medium which is
encased in a metallic housing; a well for mounting a thermocouple
therein and a support block for the furnace; an industrial personal
computer (PC) having within it the peripherals such as?shaft
encoder card which is connected to a shaft encoder interface
card, ADC card which is connected to a room temperature recorder,
a thermocouple in the furnace and a temperature controller card;
and a printer connected to said personal computer (PC).
Thus the invention provides an improved plastometer
for measuring plasticity of coal, comprising a retort assembly
having a vertically held cylindrical crucible . for holding a
sample of coal powder with a closed bottom and partly closed top
by means of an annular top cover, a co-axial vertically errected
berrel on the top cover with an outlet for gas, stirrer with four
rabble arms of its lower part dipped in the coal powder contained
in the crucible and its upper part protruding the central bore of
the barrel through a guide sleeve; a top assembly having a
motor with its shaft coupled with the top end of the stirrer,
and a magnetic brake connected to the motor shaft and also to
the shaft encoder which in turn, is connected to a shaft encoder
interface card; an electrically heated furnace having a solder
bath with inner wall embedded in heat insulating materials,
such as glass wool, a thermocouple well, a stainless steel outer
casing and a support block; an industrial type personal computer
(PC) having within it peripherals such as a shaft encoder card
which is connected to the shaft encoder interface card, an ADC
card which is connected to a room -temperature recorder, a
thermocouple placed in the thermocouple well of the furnace
assembly and the temperature controller card for the furnace,
and a power supply card for converting the 230 V AC mains supply,
received through a transformer which supplies. 16 V AC to the
shaft encoder interface card, into 12-24 V DC variable supply
for the magnetic brake and 24 V DC supply for the motor; and a
printer connected the said personal computer (PC); characterised
in that (a) the solder bath is made of a tumbler shape and heated
with three separate ceramic coated heating coils to prevent
generation of convention current in the bath and to ensure durable
performance of the coils; (b) the temperature controller card is
capable of producing digital signals corresponding to the on-time
and off-time of power supply to the heating coils using solid
state relays (SSR) without the need for using a digital-to-analogue
convertor, allowing thereby the bath temperature to be controlled
directly by the PC; (c) the shaft encoder interface card is
capable of generating 12 V DC supply required by the shaft encoder,
of converting the shaft encoder output signals to be of 5V for
being recognisable by the shaft encoder card in the PC and of
providing visual indication of the rotation of the motor shaft
v/ith LBDS: (d) a stand is provided for the smooth up and dovm
movement of the retort assembly.
The invention is described fully and particularly in
an unrestricted manner with reference to the accompanying
drawings, in which
Figure 1 is a sketch of the retort assembly, top
assembly and the furnace of the plastometer;
Figure 2 is a sketch shov/ing the heating arrangement
of the furnace; and
Figure 3 is a block diagram of the plastometer showing
inter-connection of the various functional units thereof.
Referring to Fig. 1, the retort assembly 1 comprises
a cylindrical steel crucible 2 of inside diameter 21.4mm and
height 35.0mm; an annular top cover 3; a co-axial barrel 4 of
height 121 mm, inside diameter 9.5mm at the bottom part and

12.7mm at the top part with an outlet 6 for gas; a stirrer 5
with its lower part containing four rabble arms dipped in coal
powder contained in the crucible and its uoper part nrotruding
the central bore of the barrel through a guide sleeve 7. The
top assembly 8 comorises a 24V, 0-300 RB»I DC motor 9; an
electromagnetic brake 10 connected to motor shaft to produce a
torque of ^0 gnu Inch "to rotate the stirrer; a shaft encoder 11
connected to the electromagnetic brake for recording the
rotational speed of the stirrer, operating from a 12 V DC
suonly and generating 1000 pulses or 100 dial divisions per
revolution of the stirrer; and a shaft encoder interface card
12 for generating 12 V DC supoly for the shaft encoder 11 from
16 V AC supply received through a transformer, and also for
converting the 12 V output of the shaft encoder to 5V input
required for the shaft encoder interface card. The electrically
operated furnace 13 comprises a solder bath 1^ with inner
wall 15 and heating coils^ thermocouple well 16^ glass wool
insulation 17, casing 18, around the inner wall and support
block 19 and an outer casing 18 of stainless steel.,and of
outside diameter 120 mm and height 130 mm, the inner wall of
the solder bath being of diameter 80 mm and height 100 mm.
Referring to Fig. 2, two heating coils 20 and 21
of 300 Watt each are located around the upper and intermediate
part and one heating coil • 22 of 150 Watt is located around
the lower part of the solder bath wall 18, each coil being
ceramic-coated.
Referring to Fig. 3, the industrial type personal
comouter (PC) 23 is of type PC-AT 486 working at 256 MHZ with
256 KB catch Memory, 4 MB main Memory, 260 MB hard disk drive,
1.2 MB floppy disk drive (130 mm) and 1.44 MB floppy disk drive
(88 mm), SVGA card with 1 MB video RAM, SVGA colour Monitor,
101-key keyboard and easy mouse. The computer contains within
it a shaft encoder card 24 and an ADC card 25, and a suitably
programmed software 30, and is connected to a printer 26.
The shaft encoder card 24 is connected to shaft
encoder interface card 27, which in turn is connected to the
shaft encoder 11 of the top assembly 8 (Fig. 1), and is used
for counting the number of pulses generated by the shaft
encoder 11 at fixed intervals of time of one minute, taking
care of the direction of rotation of the stirrer 5 of the retort
assembly 1 caused by motor 9 through magnetic brake 10. The
shaft encoder card 24 is a PC add-on card based on 16-bit ISA
bus design and provides a 25 Pin D type connector for all its
input signals.
The ADC card 25 reads the milli volt signal output of
the thermocouple 28 placed in well 16 of furnace 13, the room
temperature from the room temperature recorder 29 and controls
the currents in the heating coils 20, 21 and 22 of the furnace
through temperature controller card 2-7 and is used for
generating isolated analogue DC suoplies and controlling the
temperature of the solder bath 14 of the furnace 13.
The ADC card is a PC add-on card based on the 8-bit
ISA bus design and provides a 37 pin D-type connector using
flat cables.
The temperature controller card 27 has been developed
to raise the temperature of the solder bath 14 at a controlled
rate of 3°C/min by operating an on-off control of the current
supplied from 230 V AC mains to the heating coils 20, 21 and 22
of the furnace through solid state relays SSR controlled by the
digital output of the ADC card.
The transformer 31 is used to supply electrical power
from a 230 V AC source to a pov/er supply card 32 which feeds 24 V
DC to motor 9, 12-24 V DC variable voltage to the magnetic brake
10, and a 16 V AC to the shaft controller interface card 12.
The method of operating the invented plastometer
comprises the following steps :-
Coal sample in powder form is packed inside the retort
containing a stirrer. The retort is placed in the furnace
containing molten solder, maintained at 300°C. The temperature
of molten solder is gradually raised at controlled rate (nominally
3° C/min.) and also the stirrer is rotated by a constant torque
(40 gm-inch) motor. Coal sample inside the crucible is allowed to
undergo destructive distillation leading to the formation of plastic
mass whose viscosity is inversely proportional to the speed of the
stirrer. By increasing the temperature further the fluid is
allowed to polymerize to solid semi-coke. The coal sample is thus
changed from an initial solid state to an intermediate viscous mass
and finally to solid state again. Temperature and stirrer speed
are continuously measured through the PC based Data Acquisition
system developed. When the movement of the circular drum reaches
1.0 Dial Division Per Minute (DDPM) the temperature at the instant
is known as Initial Softening Temperature (Tist). Both
temperature and DDPM are measured continuously till no change in
DDPM value is observed. From the temperature vs. stirrer speed
(DDPM) graph the plastic behaviour of coal is determined.
The performance of the plastometer has been studied
by measuring the plasticity of a number of coal samples of
known plasticity values in terms of 'Dial Divisions Per Minute'
(DDPM) computed from the number of pulses generated by the shaft
encoder 11 when the torque applied by the motor 9 on the
stirrer 5 is maintained at 40gm.Inch and tlse temperature of
the solder bath 14 is increased at a steady rate of 3°C per
minute from 300°C to 550°C. The test results are presented in
Table I.

The test results presented in Table I show that the
agreement between the values measured on the Invented
plastometer with the known values is close.
The invented plastometer is constructed at a cost
of Rs. 8.00 Lakhs whereas the cost of the conventional
Plastometer is Rs. 30.00 Lakhs.
We Claim :-
1. An improved plastometer for measuring plasticity of
coal, comprising a retort assembly 1 having a vertically held
cylindrical crucible 2 for holding a sample of coal powder with
a closed bottom and partly closed top by means of an annular top
cover 3, a co-axial vertically errected berrel 4 on the top cover
3 with an outlet 6 for gas, stirrer 5 with four rabble arms of its
lower part dipped in the coal powder contained in the crucible and
its upper part protruding the central bore of the barrel through a
guide sleeve 7; a top assembly 8 having a motor 9 with its shaft
coupled with the top end of the stirrer, and a magnetic brake 10
connected to the motor shaft and also to the shaft encoder 11
which in turn, is connected to a shaft encoder interface card 12;
an electrically heated furnace 13 having a solder bath 14 with
inner wall 15 embedded in heat insulating materials 17, such as
glass wool, a thermocouple well 16, a stainless steel outer casing
18 and a support block 19; an industrial type personal computer
(PC) 23 having within it peripherals such as a shaft encoder
card (24) which is connected to the shaft encoder interface card 12,
an ADC card 25 which is connected to a room temperature recorder 29,
a thermocouple 23 placed in the thermocouple well 16 of the furnace
assembly 13 and the temperature controller card 27 for the furnace,
and a power supply card 32 for converting the 230 V AC mains supply,
received through a transformer 31 which supplies 16 V AC to the
shaft encoder interface card 12, into 12-24 V DC variable supply
for the magnetic brake 10 and 24 V DC supply for the motor 9; and
a printer 26 connected the said personal computer (PC);
characterised in that (a) the solder bath is made of a tumbler
shape and heated with three separate ceramic coated heating coils
20, 21, 22 to prevent generation of convection current in the
bath and to ensure durable performance of the coils; (b) the
temperature controller card is capable of producing digital
signals corresponding to the on-time and off-time of power supply-
to the heating coils using solid state relays (SSR) without the
need for using a digital-to-analogue convertor, allowing thereby
the bath temperature to be controlled directly by the PC;
(c) the shaft encoder interface card is capable of generating 12 V
DC supply required by the shaft encoder, of converting the shaft
encoder output signals to be of 5V for being recognisable by the
shaft encoder card in the PC and of providing visual indication of
the rotation of the motor shaft with LEDS; (d) a stand is provided
for the smooth up and down movement of the retort assembly.
2. The plastometer as claimed in claim 1, wherein the
solder bath is of diameter 80 mm and height 100 mm.
3. The plastometer as claimed in claim 1 or 2, wherein
the upper (20) and intermediate (21) heating coils are each of
300 W and the lower (22) heating coil is of 150 W.

An improved plastometer for measuring plasticity of coal,
comprising a retort assembly 1 having a vertically held
cylindrical crucible 2 for holding a sample of coal powder with
a closed bottom and partly closed top by means of an annular top
cover 3, a co-axial vertically errected barrel 4 on the top cover
3 with an outlet 6 for gas, a stirrer 5 with four rabble arms at
its lower part dipped in the coal powder contained in the crucible
and its upper part protruding the central bore of the barrel
through a guide sleeve 7; a top assembly 8 having a motor 9 with
its shaft coupled with the top end of the stirrer, and a magnetic
brake 10 connected to the motor shaft and also to the shaft
encoder 11 which in turn, is connected to a shaft encoder
interface card 12; an electrically heated furnace 13 having a
solder both 14 with inner wall 15 embedded in heat insulating
materials 17, such as glass wool, a thermocouple well 16, a
stainless steel outer casing 18 and a support block 19; and an
industrial type personal computer (PC) 23 having within it
peripherals such as a shaft encoder card (24) which is connected
to the shaft encoder interface card 12, an ADC card 25 which is
connected to a room temperature recorder 29, a thermocouple 28
placed in the thermocouple well 16 of the furnace assembly 13,
and the temperature controller card 27 for the furnace, and a
suitably programmed software 30, the PC being connected to a
printer 26; and a power supply card 32 for converting the 230 V
AC mains supply, received through a transformer 31 which supplies
16 V AC to the shaft encoder interface card 12, into 12-24 V DC
variable supply for the magnetic brake 10 and 24 V DC supply for
the motor 9; characterised in that (a) the solder bath is made
of a tumbler shape and heated with three separate ceramic coated
heating coils 20, 21, 22 to prevent generation of convection
current in the bath and to ensure durable performance of the
coils; (b) the temperature controller card is capable of
producing digital signals corresponding to the on-time and
off-time of power supply to the heating coils using solid state
relays (SSR) without the need for using a digital-to-analogue
convertor, allowing thereby the bath temperature to be controlled
directly by the PC; (c) the shaft encoder interface card is
capable of generating 12 V DC supply required by the shaft encoder,
of converting the shaft encoder output signals to be of 5V for
being recognisable by the shaft encoder card in the PC and of
providing visual indication of the rotation of the motor shaft
with LEDS; (d) the software is menu-driven and written in C
language, having a graphical interface with extensive use of
windows and mouse for simplifying the operation thereof; and
(e) a stand is provided for the smooth up and down movement of
the retort assembly.