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Файл:The bases of special methods of biomass processing into prospective materials. Tutorial
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4) Process of casting. The resulting semi-finished products are cut
into pieces for the convenience of placing them in hopper of the casting
machine. There are definite temperature conditions for each polymer which
is determined in accordance with reference data. The process of molding
the product starts from the moment of injection and ends by cooling the
product and opening of the mold.
The technological process parameters (the case of polyethylene):
– temperature in the zones of the cylinder: 1–170 0C; 2–170 0C; 3–150 0C;
– mold temperature: 110 0C;
– velocity of screw: 40 rpm;
– cycle duration: 20 min.
The casting machine is used (fig. 2.7) in the laboratory work for
WPC preparation. The polymeric material plasticized in casting machine is
injected into the cavity of the mold directly through the gate channel.
Fig. 2.7. Casting machine:
1 – material (heating) cylinder; 2 – heating elements; 3 – screw;
4 – cooling channels; 5 – bunker for material; 6 – hydraulic engine; 7– reduction unit;
8 – hydraulic cylinder of injection unit; 9 – pressure gauge; 10, 17 – stationary plates;
11 – column guides; 12 – casting mold; 13 – movable plate; 14 – wheel- lever
mechanism; 15 – hydraulic cylinder of clamping unit; 16 – nuts; 18 – stop bar;
19- nozzle
Casting machine consists of three important units:
– clamping unit;
– plastification unit;
– machine bed with drive system and control system.
Plastification unit. It consists of a screw rotating in a stationary
heated cylinder that at injection point moves like a piston in the direction of
the casting machine nozzle. Then in the plastification process it returns to
its start position due to back pressure of the polymer melt. The rotary
61
motion of the screw is provided by hydraulic or electric engine, as well as
its axial movement by working piston (ram) with a hydraulic cylinder.
Clamping unit. Tasks performed by this unit:
– contact with the casting machine nozzle;
– opening and closing of mold;
– creation of the force required to hold the mold in the closed
position;
– demolding of products.
The force required to keep the mold closed can be created
mechanically with crank-lever or hydraulic mechanism.
Machine bed (frame). The bed is used for placing individual
structural elements of casting machine on it and their secure mounting.
The process is managed using timers or electronic time sensors.
The placement of additional control equipment helps to control mold
filling and feeding (eg. depending on the pressure of the mass in the mold).
For thermoregulation of plastification unit electrical strip heaters are used.
The temperature of the cylinder, as a rule, is controlled by electronic
sensors.
5) Cooling. A cooling (hardening) of the product in the form
happens. The cooling duration is 6 hours. After cooling to room
temperature, the mold is opened and the finished specimen is ejected.
2. Test physical and mechanical properties of the resulting plastics in
accordance with standard methods: density in accordance with GOST
15139-69 «Plastics. Methods for the determination of density (mass
density)», strength according to GOST 25.602-80 «Design calculation and
strength testings. Methods of mechanical testing of polymeric composite
materials. Test for compression properties at normal, elevated and low
temperatures», GOST 25.601-80 «Design calculation and strength testings.
Methods of mechanical testing of polymeric composite materials. Test for
tensile properties on plane specimens at normal, elevated and law
temperatures», GOST 25.604-82 «Design calculation and strength testings.
Methods of mechanical testing of polymeric composite materials. Test for
bending properties at normal, elevated and low temperatures», GOST 465080 « Plastics. Methods for the determination of water absorption».
2.1 Determination of WPCs bending properties.
Similarly to the procedure described in the laboratory work № 5.
2.2. Determination of water absorption.
Similarly to the procedure described in the laboratory work № 7.
2.3. Determination of compressive strength.
62
Preparing the specimens for testing
c
v
Before the test the specimens are conditioned according to GOST
12423-66. The time from the ending of production of molded specimens or
a composite material from which they are cut to the test specimens,
including conditioning, should be not less than 16 hours. The thickness and
width of the sample working part are measured in three places: on the edges
and in the middle. Parts with the size of less than 10 mm are measured with
the accuracy up to 0.05 mm, sized 10 mm and more up to 0.1 mm. The
average thickness and width of the specimen is recorded in the test report
and using them, the cross-section area of the specimen is defined with the
accuracy up to three significant figures.
Testing
Tests are carried out in a room or enclosed space at the temperature
and relative humidity of ambient air or other environment given in the
technical specifications for the test material. If there are no such
instructions, the tests are carried out at the temperature of ambient air
(20 ± 2) 0C and relative humidity of ambient air (50 ± 5) %. If the room
temperature is different from given one, the specimens are held in a heat
chamber at a temperature (20 ± 2) 0C for 2–3 hours before tests.
When the specimens are tested at elevated and low temperature the
time required for a complete heating or cooling of the specimen before
testing should be given by the normative and technical documentation for
the test material. If there are no such instructions, the specimen holding
time at the required temperature is at least 20 min for 1 mm thickness.
The specimen is mounted on base plates of the testing machine so
that its longitudinal axis coincides with the load direction, and end surfaces
are parallel to the bearing surfaces of the plates. Mechanical extensometers
or other devices are installed to measure strain (resistance strain gauges
bonded to the specimen before the installation in the testing machine).
Required stroke speed of active gripping v is installed (recommended
v = 1–15 mm/min).
To determine the modulus of elasticity or Poisson’s ratio, the
specimen is loaded uniformly with a given constant stroke speed of active
gripping within the initial linear part of the strain diagram. The change in
the longitudinal deformation of the specimen l is recorded.
To determine the Poisson’s ratio
the specimen is loaded
uniformly with a given constant stroke speed of active gripping within the
63
initial linear part of the strain diagram. The increments of longitudinal
II
I
c
F
max
hb
F
c
=
max
c
F
max
hb
II
c
I
hb
F
E
=
l
lII
=
c
F
c
v
c
I
c
II
c
v
=
and lateral
strain of the specimen in its given plane are recorded.
While determining the compressive strength, the specimen is
uniformly loaded with a given stroke speed of active gripping. The
maximum load
sustained by the specimen is recorded.
Processing results
Compressive strength expressed in Mpa is calculated by the
formula:
, (10)
where
– the maximum load before to the destruction of the specimen,
N;
– cross sectional area of a specimen, mm2.
Modulus of elasticity in compression E expressed in MPa is
determined by the formula:
, (11)
where ∆Fс – increment of load, N;
I – the base of strain gauge, mm;
– change in the relative longitudinal strain of the
specimen working part measured by resistance strain gauge, when the load
for
changes.
Poisson’s ratio
is calculated by the formula:
, (12)
64
where
c
I
c
F
№ of
the
specimen
The
aggregate
Fraction,
mm
Density,
kg/m
3
Compressive
strength,
MPa
Flexural
strength,
Mpa
Water
absorption, mg
– change in the relative lateral strain of the specimen when the
load for
measured by the width or thickness of the specimen
(depending on the task) changes.
Present the results of the research in the form of the table:
2.5.6. Technology for producing the wood-polymer composite (WPCs)
by flat pressing
Objectives: to conduct experimental study on the preparation and
determination WPCs physical and mechanical properties by flat pressing.
Materials and reagents:
– wood sawdust of different types;
– wood flour of various grades and species;
– thermoplastics;
– antioxidant.
Equipment:
– testing sieve;
– laboratory oven;
– scales with an accuracy of 0.1;
– rolling machine;
– hydraulic press;
– liquid thermostat with an accuracy of temperature control ±1.0
– desiccators
– cans from glass or enameled steel
– ruler
– distilled water;
– phosphorus pentoxide or other dryers
Procedure.
Make specimens of WPCs in laboratory.
The sequence of the specimen making process:
0
С;
65
– prepare the components: dry wood flour and sawdust to a moisture
Thermoplastics, %
Wood sawdust, %
40
60
30
70
20
80
Thermoplastics, %
Wood flour, %
40
60
30
70
20
80
content of less than 1%;
– weighing components. The components ratio is presented in the
tables 2.6 and 2.7;
Table 2.6
Table 2.7
3) Calendering. The ingredients are put into the machine one by one:
polyethylene, then wood flour with additives. The mixing process takes
about 10 min. The result is a tape, semi-finished WPCs;
4) Process of pressing. The resulting semi-finished WPCs are cut to
pieces for the convenience of filling the molds. Each polymer has its own
temperature in accordance with reference data. The approximate
temperature is 150–170 0С, the time of pressing is 20 min.
2. Test physical and mechanical properties of the resulting plastics in
accordance with standard methods: density is tested in accordance with
GOST 15139-69 «Plastics. Methods for the determination of density (mass
density)», strength is tested in accordance with GOST 25.602-80 «Design
calculation and strength tests. Methods of mechanical testing of polymeric
composite materials. Test for compression properties at normal, elevated
and low temperatures», GOST 25.601-80 «Design calculation and strength
tests. Methods of mechanical testing of polymeric composite materials. Test
for tensile properties on plane specimens at normal, elevated and low
temperatures», GOST 25.604-82 «Design calculation and strength tests.
Methods of mechanical testing of polymeric composite materials. Test for
66
bending properties at normal, elevated and low temperatures», GOST 465080 «Plastics. Methods for the determination of water absorption».
2.1 Determination of WPCs bending properties.
Similarly to the procedure described in the laboratory work № 5.
2.2. Determination of compressive strength.
Similarly to the procedure described in the laboratory work № 6.
2.3. Determination of water absorption.
Preparing the specimens for testing
The specimens from the sheet material and the laminate are cut to the
shape of a square with sides of (50 ± 1) mm. Its thickness equals to the
thickness of the material. The cut surface should be smooth. The specimens
of bars, rods and pipes are cut perpendicular to the longitudinal axis. They
should be (50 ± 1) mm in length and no more than 50 mm in diameter. If
the testing specimens of bars and rods are larger in diameter they are
ground so that the linear dimensions in all directions do not exceed 50 mm.
If pipes diameter is more than 50 mm the specimens are cut from
the pipe wall. Note that the length, width and thickness of the specimens
should not exceed (50 ± 1) mm. If the wall thickness exceeds 50 mm, it is
ground up to 50 mm.
Testing
At least three specimens are tested. First the specimens are dried at
50 ± 2 0С for 24 ± 1 h and cooled at 23 ± 2 0С. After cooling the specimens
are taken and weighed in no more than 5 min. At least 8 cm3 of water is
taken for 1 cm2 of the specimen surface. Boiling water should be added
regularly to keep its original volume when testing. The specimens should
not be in contact with each other and with side walls of the can. They
should be completely covered by water. The liquid should be mixed up by
rotating the can at least once a day while testing at (23 ± 2) 0С. While
determining the maximum water absorption to equilibrium the balance state
is considered to be achieved if the difference between the mass of the
specimen calculated at 24 h interval do not exceed 0.1 %.
Method of calculating water absorption in cold water.
The prepared specimens are quickly immersed in distilled water and
kept at (23 ± 2) 0C for (24 ± 1) h. Then the specimens are taken from water,
wiped dry with a clean cloth or filter paper. They are weighed in no more
than 1 min.
Method of calculating water absorption in boiling water.
The prepared specimens are immersed in boiling distilled water and
kept there for 30 min. Then the specimens are taken from the can, cooled in
67
distilled water at room temperature (23–2) 0С for (15 ± 1) min. After that
12
mmm −=
S
mm
m
s
12
−
=
100
1
12
−
=
m
mm
x
№ of
the
specimen
The
aggregate
Fraction
, mm
Density,
kg/m
3
Compressive
strength,
MPa
Flexual
strength,
MPa
Water
absorption, mg
the specimens are taken from water, wiped dry with a clean cloth or filter
paper. They are weighed in no more than 1 min.
Processing results
The water mass absorbed by the specimen expressed in mg for each
specimen is calculated using the formula below:
, (13)
where m1 – the mass of the specimen before immersion into water, mg;
m2 – the mass of the specimen after immersion into water, mg.
The water mass absorbed by the specimen per unit surface area for each
specimen expressed in mg/cm2 is calculated using the formula below:
, (14)
where S – the surface of the specimen, cm2.
The mass fraction of water absorbed by the specimen expressed in
percents for each specimen is calculated using the formula below:
. (15)
The result of testing is the arithmetic mean from three parallel
definitions. The permissible deviation between them should not exceed
10 %. The result is rounded up to the first decimal place. If the permissible
deviation exceeds 10 % the test is repeated with twice the number of
specimens.
Present the results of the research in the table:
68
2.5.7. Technology of thermo-chemical modification of wood
Objectives: to conduct experimental studies on the preparation and
testing of physical and mechanical properties of wood modified by thermochemical method.
Materials and reagents:
– billets of wood of various species;
– thermosetting resins.
Equipment:
– мiscometer;
– unit for thermo-chemical modification;
– scales with an accuracy of weighing less than 0.001 g;
– drying chamber;
– glass laboratory cups with lids or beakers for weighing (weighing
bottles);
– desiccators;
– distilled water;
– filter paper;
– testing machine.
Procedure.
1. Prepare wood specimens modified by thermo-chemical method.
The unit diagram is shown in fig. 2.8.
Fig. 2.8. The unit for thermo-chemical modification:
1 – sealed chamber, 2 – vacuum pump, 3 – capacitor; 4 – mesh holder;
5 – input device for reciprocating motion with a rod; 6 – chamber cover;
7 – pressure gauge; 8, 9 – valve; 10 – processed lumber, 11 – thermosetting resin,
12 – thermoelectric heater, 13 – paddle mixer
69
Thermo-chemical modification of wood consists of the following
operations: resin impregnation, drying and curing of impregnating
compound in wood according to GOST 24329-80 «Modificated wood.
Modification methods». The initial billets with moisture content of 10 –
15 % are subjected to modification. Phenol-formaldehyde, urea, furan,
vinyl, acrylic, polyester, silicone, melamine-urea resins monomers and
oligomers having at least the duration of viability of the technological cycle
of impregnation and the ability to cure in the wood under the temperature
influence are used for impregnating. Relative viscosity of impregnating
solutions measured by viscometer VZ-4 should be 11–14 s at 20 0C.
Impregnation of billets is carried out by the method of vacuum-pressure or
vacuum-pressure-vacuum at the temperature not below 20 0C or not higher
than the temperature which reduces the viability of the impregnating
compound. The residual pressure in the vacuum must be at least 0.06 MPa.
The pressure should be equal to 0.8 – 1.2 MPa. The amount of absorbed
impregnating compound should be 30 – 80 % by weight of the original
wood. The impregnated billets are dried with a step rise in temperature from
40 to 120 0C and moisture less than 12 %. The curing of impregnating
compound input into the wood is carried out at the temperature of 150 –
170 0C, then the temperature in the chamber reduces to 40–50 0 C without
forced cooling, after that the wood is maintained at the temperature of 18 –
23 0 C for at least 12 hours.
Determination of the modified wood properties is carried out in
accordance with GOST 21523.5–77 «Modified wood. Method for
determination of water absorption», GOST 21523.8-93 «Modified wood.
Method for determination of modulus of elasticity in compression».
Determination of water absorption
The specimens are dried in the drying chamber at the temperature of
(103 ± 2) 0C until constant weight. The specimens are placed in the
desiccator with distilled water so that one of the frontal surfaces remained
dry, closed with a lid and kept at the temperature (20 ± 2) 0C. After 2 hours,
counting from the moment of immersion of specimen into water, their first
weighing is conducted with an error less than 0.01 g. Before weighing the
specimens surfaces are dried with filter paper. Subsequent weightings are
carried out sequentially every 10 days. The minimum duration of specimen
storage in the desiccator is 30 days. Tests end when the difference between
two successive weightings is not greater than 0.05 g.
The amount of water absorbed by a specimen W expressed in
percents is calculated with an error less than 1 % by the formula:
70
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