Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
This invention relal:es to conveyor belt devices
for conveying so-called viscous materials such as oil sand,
slurry, and sludge containing water or oil or mixtures of
them by 5~ wt and over.
Fig. 1 is a schemat:ic representation of a belt
conveyor to which the present invention is applicable,
and Fig. 2 shows data plotted, with critical surface tension
as abscissa and asphalt separating force as ordinate.
Fig. 1 shows an example of a conveyor belt device
for conveying the above-mentioned materials, represented
schematically, and comprising a conveyor belt 1 wrapped
around a drive pulley 2 and a tail pulley 3 and travelling
in the direction of arrow A. A head snub pulley 4 is pro-
vided to secure a larger cont(~ct angle for the drive pulley
2, and return rollers 5 are pcovided consecutively on thereturn run to support the bel~. The object indicated at
6 is a cleaner.
In conventional con-veyor belt devices for such
application, as the conveyor belt used for conveying viscous
materials including slurry and sludge has a cover layer
which does not possess a non-adhesive property, viscous
materials such as slurry or sludge will stick to the con-
veyor belt 1 as well as to the outer circumferences of the
head snub pulley 4 and of the return rollers 5, and will
be comp_essed and grow in size irregularly, causing problems
including belt meandering and spillage of the material being
conveyed. Such sticking mate:rial is scraped off by scrapers,
cleaners, etc. provided at appropriate places along the
path of the belt, but their eEfectiveness is rather limited.
Heretofore, conveyo:c belts for such application
have been required to possess sufficient strength and flexi-
bility to perform a long distance conveyance of a viscous
material from a .ocation at which oil sand is drilled, to
a bitumen separation trcatment plant under annually varying
climatic conditions, and from this point of view, conveyor
belts using general purpose rubbers, which bond well to
core cords and duck, have been used. However, as the general
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purpose rubber surface of such belts does not possess a
non-adhesive property, oil sand will stick to the conveyor
belt 1 as well as to outer circumferences of the head snub
pulley 4 and of the return rollers 5, as mentioned above.
Heretofore, the adhesion of oil sand to oil sand
conveyor belts has been counteracted by sprinkling kerosene,
gas oil, etc. over the belt surface. However, for reasons
of fire protection and safety, sprinkling of oil has to
be terminated, and now this measure is prohibited.
The present invention was accordingly contemplated
to provide a solution to the problem of prolonged adhesion
of viscous materials, e.g. slurry, sludge, and oil sand,
to conveyor belt devices.
According to the present invention there is pro-
vided a conveyor device for conveying a material having
a critical surface tension (yc) of A dyne/cm, said conveyordevice comprising a conveyor belt having a cover layer the
critical surface tension lyc) of which is (A - 15) dyne/cm
at-the most, and a head snub pulley having a surface with
a critical surface tension (yc) of (A + 10) dyne/cm.
The present invention further provides a conveyor
belt device comprising a conveyor belt having a cover layer
the critical surface tension (~c) of which is 15 dyne/cm
at the most, and a head snub pulley having a surface the
critical surface tension (yc) of which is 20 to 40 dyne/cm.
Preferably, in order to remove at least a portion
of any of the material sticking to the head snub pulley,
the snub pulley is provided with a cleaner.
The cover layer may comprise at least 30% rubber.
Preferably, the surface of the head snub pulley
is coated with a rubber preparation selected from the group
consisting of butyl rubber, chloroprene rubber (CR), natural
rubber INR), polystyrene-butadiene copolymer rubber (SBR),
polybutadiene rubber lBR), acrylic elastomer and a blend
thereof, the preparation comprising at least 80% polymer
and at least 30~ rubber.
For the measuring method of critical surface ten-
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sion ~c~, c31ycerine, formamic.e, thiodiglycol, ethylene
glycol, and polyethylene glycc,l (mean molecular weight:200)
were employed as liquids of known surface tension values.
The angle of contact (~) of each of these liquids was
measured on a sample for meas~rement at 25C, and yc was
obtained by extrapolatlng cos Q to 1.
In Fig. 2, critical surface tension lyc) is plot-
ted as abscissa (unit: dyne/cm), and asphalt separating
force as ordinate (unit: gms/cm wide); (a) is silicone rubber,
lb) is polytetrafluoroethylene, lc) is fluororubber, (d)
is natural rubber, le) is polystyrene-butadiene copolymer
rubber (SBR), (f) is polyethy:ene, and (g) is polyacrylo-
nitrole-butadiene copolymer rubber (NBR). yC~ is the critical
surface tension of bitumen, which is the main cause of the
adhesive property of oil sand..
From these data, it is understood that in order
to keep the critical surface tension of the cover layer
surface of the conveyor belt at 15 dyne/cm and under, it
is sufficient to form an integrated conveyor belt by bonding
silicone rubber, by some means" to the rubber for bonding
core cords or duck. It has aLso been found that it is suf-
ficient to set the rubber con1ent of silicone rubber at
30% and over, and preferably at 40% and over. Furthermore,
that in order to maintain the critical surface tension (yc)
of the surface of the head snub pulley 4 within a range
of from 20 to 40 dyne/cm, and preferably within a range
of from 25 to 35 dyne/cm, it .is sufficient to coat the outer
circumference of the pulley 4 with butyl rubber, chloroprene
rubber (CR), natural rubber (~R), polystyrene-butadiene
copolymer rubber (SBR), polybutadiene rubber (BR), acrylic
elastomer, or a blend of them. As for these rubbers, it
is sufficient to keep their rlbber content at 30% and over.
While the critical surface tension of bitumen,
the main constituent of oil sand of Fig. 2, is 30 to 32
dyne/cm, the critical surface tension ~yc) of the surface
of the cover layer of the conveyor belt 1 is set at 15
dyne/cm and under to weaken the adhesion of the belt to
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oil sand, and on the other hand, the critical surface ten-
sion (yc) of the sur~ace of th.e head snub pulley 4, which
encounters the belt portion having just completed chuting,
is set at 20 to 40 dyne~cm and. preferably at 25 to 35 dyne/cm
to approximate it to that of oil sand., and in turn, to maxi-
mize said pulley's adhering property to oil sand. As a
result, oil sand which is not removed at the time of chuting
and which remains stuck to the belt will be transferred
to the head snub pulley by the difference between two cri-
tical surace tensions. In this way, since the quantityof oil sand sticking to the surface of the conveyor belt
1 is reduced every turn of the belt, this quantity will
not grow beyond a certain limi.t. On the other hand-, the
oil sand transferred onto the head snub pulley 4 can be
continuously removed by the cleaner 6 provided for the snub
pulley.
Experimental condit:ions which led to the present
invention were as follows:
(I) Materials tested.
Conveyor belts 1
350 mm wide duck core conveyor belts 1 were pre-
pared by using two plies of duck of 150 kg/cm2
strong nylon warp and weft as a core in rubber,
and vulcanizing to bond the duck rubber plies,
4 mm thick on the front side and 2 mm thick on
the rear side, to the following surface cover
rubbers:
yc (unit: dyne/cm)
(X) Silicone rubber 5
(Y) Polyacrylonitrile-
butadiene rubber (NBR) 36
(Z) Natural rubber (NR) 32
Head snub pulleys 4
Pulleys with follow:ng surface coatings were
prepared
yc (dyneJcm)
(A) Silicone rubber 5
(B) Butyl rubb~r 28
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~C) Chloroprene rubber 33
[D) Steel strip ~SS41) 45
~II) Dimensions of tested conveyor belts and test conditions.
Center-to-center distance between
pulleys 2 and 3 4000 mm
Center-to-center distance between
pulleys 2 and 4 200 mm
Diameter of drive pulley 2 200 mm
Diameter of head snub pulley 4 100 mm
0 A total amount of 180 gms of oil sand, consisting
of 10% bitumen, 0.5~ water and 89.5~ oil sand,
W8S loaded over an area of 300 mm wide by 300
mm long at the poin1: B of Fig. 1, and compressed
with a pressure of 0.2 kg/cm2 for 1 minute to
stick to the belt surface. Then the belt was
operated at a belt velocity of 45 m/min for five
cycles. After thatr theamounts of oil sand re-
maining on the surface of the belt 1 and on the
surface of the head snub pulley 4 were measured.
The pressure of the head snub pulley 4 on the
belt 1 was adjusted at 1 kg/cm2.
(III) Test Results
The test results were as shown in the following
table.
Classi Kind of Rind of Amount AmDunt Amount Differ-
fication conveyor head snub remain- remain- of ence
belt 1 pulley 4 ing on ing on chute (gms)
the the head (gms)
belt 1 snub
(gms) pulley 4
(gms)
X A 69 19 50 42
Present X B 8 123 24 25
invention
Present X C 13 122 22 23
invention
X D 52 53 40 35
Y C 145 27 0 8
Y D 162 7 9 11
Z B 153 12 10 5
Z D 159 14 0 7
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ri~e ~ f~renc-e of ~he 7th column of the taL):Ie
i~ the d fference betweell the -total amount
180 gms and the s~ of the adhering amounts,
or the amount of oil sand dropped off the belt
due to vibration cluring travelling. In the
cases of the embocliments of the present invention,
it is natural that: the amount of dropped ore
is small since the surface of the conveyor belt
is non-adhesive. When this point is taken into
consideration, it can be seen that 90% and over
of the oil sand was removed from the conveyor
belt 1. It can a so be seen that when the
critical surface t:ension (yc) of the surface
of the conveyor belt was large, almost no oil
sand was chuted, and that when the critical
surface tension (~c) of the head snub pulley
~ was excessive, 1:he efficiency of the removal
dropped.
As set forth hereinabove, the present invention
provides a conveyor belt device which counteracts adhesion
of adhesive materials in viscous materials including slurry,
sludge and oil sand, which does not require sprinkling of
oil and the like to maintain non-tackiness of the belt to
oil sand, which can be operated safely without any trouble
for a long period of time, and which can be manufactured
at a relatively low cost.
