CA1195641A - Conveyor belts - Google Patents
Conveyor beltsInfo
- Publication number
- CA1195641A CA1195641A CA000406666A CA406666A CA1195641A CA 1195641 A CA1195641 A CA 1195641A CA 000406666 A CA000406666 A CA 000406666A CA 406666 A CA406666 A CA 406666A CA 1195641 A CA1195641 A CA 1195641A
- Authority
- CA
- Canada
- Prior art keywords
- rubber
- parts
- astm
- layer made
- oil
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B65—CONVEYING; PACKING; STORING; HANDLING THIN OR FILAMENTARY MATERIAL
- B65G—TRANSPORT OR STORAGE DEVICES, e.g. CONVEYORS FOR LOADING OR TIPPING, SHOP CONVEYOR SYSTEMS OR PNEUMATIC TUBE CONVEYORS
- B65G15/00—Conveyors having endless load-conveying surfaces, i.e. belts and like continuous members, to which tractive effort is transmitted by means other than endless driving elements of similar configuration
- B65G15/30—Belts or like endless load-carriers
- B65G15/32—Belts or like endless load-carriers made of rubber or plastics
- B65G15/34—Belts or like endless load-carriers made of rubber or plastics with reinforcing layers, e.g. of fabric
- B65G15/36—Belts or like endless load-carriers made of rubber or plastics with reinforcing layers, e.g. of fabric the layers incorporating ropes, chains, or rolled steel sections
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B65—CONVEYING; PACKING; STORING; HANDLING THIN OR FILAMENTARY MATERIAL
- B65G—TRANSPORT OR STORAGE DEVICES, e.g. CONVEYORS FOR LOADING OR TIPPING, SHOP CONVEYOR SYSTEMS OR PNEUMATIC TUBE CONVEYORS
- B65G2201/00—Indexing codes relating to handling devices, e.g. conveyors, characterised by the type of product or load being conveyed or handled
- B65G2201/04—Bulk
Abstract
ABSTRACT OF THE INVENTION
This invention relates to conveyor belts, more parti-cularly, this invention relates to conveyor belts suitable for transporting oil sand in open pit mines located in areas which are subject to great changes in atmospheric temperature throughout the year (form about 40°C in summer down to -55°C
in winter), which comprises an outer layer made of a cover rubber and provided on the surface kept in contact with oil sand being transported, a second outer layer made of a cover rubber and provided on the back surface kept in contact with conveyor pulleys, a core layer made of a cushioning rubber and integrally incorporating belt reinforcement having a high tensile strength, and at least one intermediate layer made of a crack-resistant rubber and provided between said core layer and each of the two outer layers.
This invention relates to conveyor belts, more parti-cularly, this invention relates to conveyor belts suitable for transporting oil sand in open pit mines located in areas which are subject to great changes in atmospheric temperature throughout the year (form about 40°C in summer down to -55°C
in winter), which comprises an outer layer made of a cover rubber and provided on the surface kept in contact with oil sand being transported, a second outer layer made of a cover rubber and provided on the back surface kept in contact with conveyor pulleys, a core layer made of a cushioning rubber and integrally incorporating belt reinforcement having a high tensile strength, and at least one intermediate layer made of a crack-resistant rubber and provided between said core layer and each of the two outer layers.
Description
TITLE OF INVENTION
.
Conveyor Belts BACKGROUND OF THE INVE~TION
1. Field of_the Invention This invention relates to conveyor belts. More parti-cularly, this invention relates to conveyor belts suita~le for transporting oil sand in open pit mines located in areas which are subject to great changes in atmospheric temperature through-out the year (from about 40C in summer down to -55C in winter).
.
Conveyor Belts BACKGROUND OF THE INVE~TION
1. Field of_the Invention This invention relates to conveyor belts. More parti-cularly, this invention relates to conveyor belts suita~le for transporting oil sand in open pit mines located in areas which are subject to great changes in atmospheric temperature through-out the year (from about 40C in summer down to -55C in winter).
2~ DescrLPtlon of the Prior Art Oil sand contains 6 to 18~ bituminous substance and 0 to 10% water. The rest is mineral substances, which consist of 90~ white quarty sand and 10% clay. Usually, oil sand also contains stones and rocks of varying sizes, sometimes measuring 30cm x 60cm x 120cm and weighing about 450Kg. In extreme cases, a big stone of more than one ton is dug out and loaded on a conveyor be~t. Conveyor belts used for transportation of oil sand are 60 inches (1.524m), 72 inches (1.83m) and 84 lnches (2.134m) wide, and several tens of meters to s,everaI
thousand met.ers long. In some examples, the traveling speed r~aches 800 to 1500 ft/min and the transportation capacity ~mounts to 5000 to 10000 ton/hr. When transported under such conditions, oil sand tends to stick firmly to the beltst pulleys and rollers; in fact, if no protective measure is taken, the thickness of oil sand left sticking to conveyor belts reaches , . ~
0.5 to 1 inch (13 to 25mm), thus greatly lowering transpor~ation efficiency. Various methods have been proposed and tested to overcome this difficulty. Of these, the way which has proved most successful throughout the year is to spread kerosene, gas oil or similar petroleum hydrocarbons on conveyor belts and transport oil sand on these oil-applied belts. By this method, transported oil sand can be completely unloaded from the belts with no bits of sand ]eft sticking. Kerosene is also used to clean already attached oil sand off the belt suxface. Therefore, conveyor belts which are resistant to the petroleum hydrocarbons to be spread must be used for successful operationO
The cover rubber composed mainly of natural rubber or SBR, which is commonly employed in ordinary conveyor belts, absorbs petroleum hydrocarbons and becomes swollen, resulting in excessive wear and deterioration with the consequent reduc~
tion itl service life. In addition, stresses developed as a results of swelling often cause the belt to advance in a zig-zag way, necessitating earlier replacement.
The higher the degree of swelling of rubber by lcerosene, the more predominant will be absorption of kerosene by rubber~
as exempli~ied by NBR rubber compositions with lower acrylo-nitrile content. Thou~h better in cold resistance, a rubber in which kerosene is absorbed becomes soft and readily gets worn, or stresses caused by swelling make normal conveyor belt operation impossible.
Normally, conveyor belts are operated on a continuous basis throughout the year, but they have to be stopped in some cases for a considerable period of time because of breakdowns of the conveyor machine or for other reasons~ If this happens, the kerosene, which is absorbed in the rubber and acts as a low-temperature plasticizer, may evaporate to the atmosphere by the action of solar radiation and wind, thus hardening the rubber. The result is lowering of flexural resistance and acceleration of the growth of scores.
The kerosene spread on the surface of conveyor belts also serves to extract plasticizers and antioxidants incorporated in the rubber, adversely affecting the resistance against oxidation and flexural loads.
Each conveyor be]t advances forward and backward conti-nuously turning around a plurality of pulleys, and is therefore subject to bending loads at all times. In addition, the helt is forced to take a trough shape while it is advancing in the forward direction to prevent loaded oil sand from falling down, tllrned 1at when it reaches the head pulley, and forced to talce a reverse trouyh shape in the return path to prevent any 2ig-zac~ advancement of the belt.
~ n this way the belt is alway subject to ~lexural loads both in the longitudinal and lateral directions duriny operation;
hence, any detrioration in flexural resistance causes cracks in the belt, which determine its service life.
Because of the working conditions and belt composition described above, it has been common in areas which are subject to great changes in atmospheric temperature r that the service life of a conveyor belt is determined by crack formation.
Particularly, with a conveyor belt incorporating steel cords as core material, these reinforcements are continuous only in the longitudinal direction and a~e spaced at certain intervals in the lateral direction. If cracks are formed by bending along a longitudinal axis of the belt, these will spread and connect one another in the longitudinal direction, ultimately splitting the belt into two or more pieces (lengthwlse ripping) and making normal operation impossible.
SUMMARY OF THE INVENTION
This i.nvention has been accomplished to overcome the problems associated with prior art as stated above, and relates to novel conveyor be1ts which comprise a core layer made of a cushloning rubber incoxporating reinforcements with high tensile stren~th (steel cords), a top surface layer and a hack surface .1.ayer, both made of an ol.l-.resistant cover rubbe.r, and at least one Lntermediate layer made oi. a craclc-resistant rubber and provld~d betweel1 said core layer and each oE the two surface layers, in wh.ich the three main types of rubber layers have d.li.erent physical properties (compositlons and characteristics of these rubber layers will be detailed later).
An object of this invention is to offer a conveyor belt capable of successful operation over a wide range of temperature and having a volume swell of 10 to 30% (when measured aecording to the method described in ASTM D-471) by designing belt composition as defined above.
A further object of this invention is to offer a conveyor belt having hiyh oil and cold resistance.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a section of a conventional conveyor belt, E~'igure 2 is sections of preferred embodiments of the present 1() i.nvention, and Fi.yure 3 shows flexural properties of various rubber compositions.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Various embodiments may be possible to achieve the afore-mentioned and other objects. It is also possible to provide a p:l.ura1ity o:E crack-resistant layers between the eore layer and eclch of the surface Layers. Rubber composition and characteris-ti.cs o:E each layer of the conveyor belt of the presen-t invention a:rC`! as :Eol1.ows:
~ s the cove:r rubber, a vulcanized rubber composition ~0 I)avi.n(J a Gei~man T1oo sti.ffness value of -49F to 112F' and a VO~ ;wc~1..1. o:E 1() to 30~; (ASTM l~3 oil, 158F' x 22Mrs) must be used. As the cushioning rubber, it is essential to select a vul~anized rubber composition ~hich adheres firmly to steel cords and has a Gehman Tloo stiffness value of -49F to 112F.
The crack-resistant rubber used must be a vulcanized rubber composition having a Gehman T1oo stiffness value of -49F to 112 F, a volume swell of 20 to 100% (ASTM #3 oil, !v 158F x 22Hrs~, capable of firmly adhering to the cushioning and cover rubbers through vulcanization to produce an integral laminate, and also having other properties favorable for the intended use of the conveyor belts of the present invention.
Preferred embodiments of this invention are explained below by referring to the accompanying drawings.
Fig. 1 is a section of a conventional conveyor belt, and Figs. 2A and 2B are sections of preferred embodiments of this inventionO
To simplify explanation, same numerals are put to those parts common to these Figs~ Compositions and properties of each rubber layer are listed in Table 1 and 2.
Xn Fig. 1, numerals 1 and 3 represent the cover rubber layer, numeral 2 denotes the core layer (cushioniny rubber layer), and numeral 4 stands for steel cords. In this case, if the rubber compositi.on Cl or C2 (Table 1) is use~ for the cover rubber layer, and the compositi.on Cu-l or Cu-2 (Table 2 is employed for the cushioning rubber layer, that is, rubber compositions of similar oil and cold resistance are provided ii64e~
throughout the entire thickness of the conveyor belt, a crack formed on the surface of the cover rubber layer (numeral 9) will grow rapidly in the downward direction, resultiny in lengthwise ripping of the belt and ma~ing its normal operation impossible in a short time.
Figs. 2A and 2B represent belt compositions of preferred embodiments of this invention, in which numerals 5, 6 and 7 are crack-resistant rubber layers (rubber composition Al in Table 2).
Th~se con~gurations are laminates consisting of rubber layers of different oil resistance; in this case, the crack 9 formed on the surface of the cover rubber 1 grows straight in the downward direction inside this layer, but goes oblique after entering the crack-resistant rubber layers 5 and 7. With a multiple crac]c reisstant layer structure, as shown in Fig. 2B, the growth and spread of cracks will require more time than in the case of Fig. 2A, further prolonging the service life of the belt.
In the helt structure of Fig. 1, if Cl or C2 is selected or the cover rubber layers (1 and 3) and Cu-l is used for the aore layer (cushioning rubber layer, 2) the interlaminar str~ngth between the two types of rubber layers is rather low and delamination is li.kely to occur. However, adding crack-resistant rubber layers at least lmm in thickness, as shown in Figs. 2A and 2B of the preferred embodiments of the present invention, will result in extremely high adhesion between the core layer 2 and the cover rubber alyers 1 and 3, producing an integral belt composition of high strength.
The rubber compositions and properties of the cover rubber, cushioning rubber and crack-resistant rubber layers are listed in Table 1 and 2.
Table 1 _ _, Compositions and Properties C-l C-2 ~ .
N~R (AN 26%) 85 . _ _ _ _ __ . _ NBR (AN 22%) 100 __ .___ (Styrene-butadiene rubber) ~ _ ~_ Zinc oxide 5 5 _ _ _ Stearic acid 1 Antioxidant 4 Synthetic plasticizer 30 30 Vulcanization accelerator 1.1 1.0 Sulur (S) 2 2 _ __. __~__ ~
Furnac~ carbon blaclc 60 65 __ _ . _ _.
Gehman value T2 tRM~2) -ll.l~F ~16.6F
T5 (RM=2~ -34.6F _45,4F
(D-1053) Tlo (RM=10) -43~6F _54.4F' Tloo (RM=100) 63,4F -G8~8E' _ _ ~ ___ _ ___ ~ _ _ R~slstance to oil (~STM ~3 o.il, 158F x 22EIrs) Volume increase V~ 16~ 20%
Kerosene 17~ l8~o Normal temperature x 1 Day Tensile strength (rb) 2133 Ib/in2 2346.3 Ib/in2 - $~g3 56~
Elongation (Eb) 450% 480%
Hardness (Hs) (SHOREA) 62 60 Wear 90 110 _ Table 2 . _ . ._ .
Compositions and Properties A 1 Cu-l Cu-2 _............... _ _.
Natural rubber 60 Polybutadiene rubber ~
NBR (AN 20~) 60 100 ~_ ............... . _ _ _ .
SBR 1500 40 40 .
Zinc oxide 5 5 5 Stearic acid 1 2 2 Antioxidant 1 2 2 Vulcanization accelerator 1.2 1.2 1.2 Cobalt octoa-te 7.5 7.5 Sulfur (S) 1.5 1.5 2 Synthetic plasticizer 30 30 E'urnac~ carbon black 65 70 85 ._ _ __ ... _~__ ~ . _ ~_ Aromatic softener 5 __ _ _ _ _ _ _ _ . . _ . __ Gehman value T2 -43.6F-:13.0F _13,0F
(~STMD-1053) T5 ~67.0aF_45.4F -43.6F
_74.0F-56.2F -52.6F
Tlo0 86.8F73.0F _73.0F
Resistance tv o~].
(ASTM #3 oil, l58F x 22~rs) Volume i.ncrea~e V% 32%140% 17.1%
Normal temperature x 1 Day 40% 160% 33~5%
Tensile strength (Tb) Ib/in 2061.9 2133 2250 ¦ Elonga-tion (Eb) ~ ¦ 550 ¦ 550 ¦ 485 (Hs) (SHOREA) ~ 59 ¦ 65 ¦ 65 FigO 3 shows the flexural properties of the rubber materials listed in Tables 1 and 2, in which length of grown cracks is plotted against number of flexings (in kilocycles).
It is apparent from these curves that Cu-l and A-l show excellent resistance to flexural loads.
Conveyor belts of laminated structure using C-2 for ~he cover rubber, Cu - 1 for the suchioning rubber and A-l for the crack-resistant rubber were explained above as preferred embodiments, but they are not to be considered as a limitation upon the present invention. As stated earlier, the conveyor belts for transporting oil sand are used with kerosene applied on the surface; hence, the surface layer must be made of an oil~resistant polymerO The most typical oil-resistant polymer :is NBR. This is a copolymer consisting of acrylonitrile and butadi.ene, and the content oE acrylonitirle determines its oil and cold resistance. NBR polymers commercially availahle today contain 18 to 50~ acrylonitrile (82 to 50~ butadiene).
Of the.se, those grades having an acrylonitrile content of 18 to 35~ are suitable for use in the conveyor belts because colcl resistance is too low with higher acrylonitirle contents.
Rubber compositions generally incorporate plasticizers to enhance processability and improve physical properties.
Synthetic plasticizexs are most suitable for NBR, which include various synthetic liquid polymers and esters of dibasic acids, such as trioctyl phosphate, dibutyl sebacate, dibutyl phosphate, dioctyl adipate, dioctyl phthalate and di(butoxyethoxyethyl) adipate.
The pre~erred oil-resis~ant rubber materials used in the present invention comprise 100 parts of a rubber component consisti.ng of NBR alone or in combination with other types of rubbers, 10 to 40 parts of a synthetic plasticizer~ 30 to 70 parts of a reinforci.ng filler such as carbon black, 2 to 10 p~rts oE an antioxidant and 3 to 10 parts of vulcanizing chemicals. In addition/ materials commonly used in the rubber industry, such as processing aids and bulking fillers, may also be added. These oil-resistant rubber materials should preferably have a Gehman Tlo~ stiffness value of -49~F
to ~112F (ASTM D-1053) and a volume swell of 10 to 30%
(ASTM ~3 oil, 1S8F x 22Hrs, A5TM D-1053).
As stated earlier, the belt surface is always exposed to kerosene (including gas oi].)~ The oil tends to penetrate the surace layer through the flaws formed by stones or roc]cs con-ta.ined :i.n the oil sand being carried, and the growth rate of cracks, accele.rated by the bending, tensile and compressive forces exerted on the conveyor belt during operation, i.s hi.gher compared with the case when no kerosene is app]..ied.
At the same time, the rubber swells through absorption of kerosene and the plasticizer contained in the rubber tends to be extracted by the absorbed oil. When a rubber is kept ln contact with an oil, the apparent degree of swelling of the rubber is determined by the balance between the entry of the oil into the rubber and extraction of the plasticizer from the rubber.
When the rubber swells l~ss~ extraction of the plasti-cizer will predominate. This is the case observed with N~R
compositions with high acrylor.itrile contents.
Extraction of the contained plasticizer will harden the rubber and adversely affect its cold resistance, resulting in poor 1exural resistance.
The conveyor belts proposed in the present invention have compositions and characgeristics as detailed above.
This invention thus offers conveyor belts with prolongecl service life. This means less cost for belt replacement, for repair work tbonding cost, etc.), and minimized operation loss due to reduction in transportation capacity. ~he cost of conveyor belt itself is also less because high oil resistance is not essential for the cushioning rubber layer. For example, an ordinary diene-type rubber may be used as the core layer becc~use it can be firmly bondecl to the surface layers by ~corporatinc~ crack-resistant rubber layers between them.
thousand met.ers long. In some examples, the traveling speed r~aches 800 to 1500 ft/min and the transportation capacity ~mounts to 5000 to 10000 ton/hr. When transported under such conditions, oil sand tends to stick firmly to the beltst pulleys and rollers; in fact, if no protective measure is taken, the thickness of oil sand left sticking to conveyor belts reaches , . ~
0.5 to 1 inch (13 to 25mm), thus greatly lowering transpor~ation efficiency. Various methods have been proposed and tested to overcome this difficulty. Of these, the way which has proved most successful throughout the year is to spread kerosene, gas oil or similar petroleum hydrocarbons on conveyor belts and transport oil sand on these oil-applied belts. By this method, transported oil sand can be completely unloaded from the belts with no bits of sand ]eft sticking. Kerosene is also used to clean already attached oil sand off the belt suxface. Therefore, conveyor belts which are resistant to the petroleum hydrocarbons to be spread must be used for successful operationO
The cover rubber composed mainly of natural rubber or SBR, which is commonly employed in ordinary conveyor belts, absorbs petroleum hydrocarbons and becomes swollen, resulting in excessive wear and deterioration with the consequent reduc~
tion itl service life. In addition, stresses developed as a results of swelling often cause the belt to advance in a zig-zag way, necessitating earlier replacement.
The higher the degree of swelling of rubber by lcerosene, the more predominant will be absorption of kerosene by rubber~
as exempli~ied by NBR rubber compositions with lower acrylo-nitrile content. Thou~h better in cold resistance, a rubber in which kerosene is absorbed becomes soft and readily gets worn, or stresses caused by swelling make normal conveyor belt operation impossible.
Normally, conveyor belts are operated on a continuous basis throughout the year, but they have to be stopped in some cases for a considerable period of time because of breakdowns of the conveyor machine or for other reasons~ If this happens, the kerosene, which is absorbed in the rubber and acts as a low-temperature plasticizer, may evaporate to the atmosphere by the action of solar radiation and wind, thus hardening the rubber. The result is lowering of flexural resistance and acceleration of the growth of scores.
The kerosene spread on the surface of conveyor belts also serves to extract plasticizers and antioxidants incorporated in the rubber, adversely affecting the resistance against oxidation and flexural loads.
Each conveyor be]t advances forward and backward conti-nuously turning around a plurality of pulleys, and is therefore subject to bending loads at all times. In addition, the helt is forced to take a trough shape while it is advancing in the forward direction to prevent loaded oil sand from falling down, tllrned 1at when it reaches the head pulley, and forced to talce a reverse trouyh shape in the return path to prevent any 2ig-zac~ advancement of the belt.
~ n this way the belt is alway subject to ~lexural loads both in the longitudinal and lateral directions duriny operation;
hence, any detrioration in flexural resistance causes cracks in the belt, which determine its service life.
Because of the working conditions and belt composition described above, it has been common in areas which are subject to great changes in atmospheric temperature r that the service life of a conveyor belt is determined by crack formation.
Particularly, with a conveyor belt incorporating steel cords as core material, these reinforcements are continuous only in the longitudinal direction and a~e spaced at certain intervals in the lateral direction. If cracks are formed by bending along a longitudinal axis of the belt, these will spread and connect one another in the longitudinal direction, ultimately splitting the belt into two or more pieces (lengthwlse ripping) and making normal operation impossible.
SUMMARY OF THE INVENTION
This i.nvention has been accomplished to overcome the problems associated with prior art as stated above, and relates to novel conveyor be1ts which comprise a core layer made of a cushloning rubber incoxporating reinforcements with high tensile stren~th (steel cords), a top surface layer and a hack surface .1.ayer, both made of an ol.l-.resistant cover rubbe.r, and at least one Lntermediate layer made oi. a craclc-resistant rubber and provld~d betweel1 said core layer and each oE the two surface layers, in wh.ich the three main types of rubber layers have d.li.erent physical properties (compositlons and characteristics of these rubber layers will be detailed later).
An object of this invention is to offer a conveyor belt capable of successful operation over a wide range of temperature and having a volume swell of 10 to 30% (when measured aecording to the method described in ASTM D-471) by designing belt composition as defined above.
A further object of this invention is to offer a conveyor belt having hiyh oil and cold resistance.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a section of a conventional conveyor belt, E~'igure 2 is sections of preferred embodiments of the present 1() i.nvention, and Fi.yure 3 shows flexural properties of various rubber compositions.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Various embodiments may be possible to achieve the afore-mentioned and other objects. It is also possible to provide a p:l.ura1ity o:E crack-resistant layers between the eore layer and eclch of the surface Layers. Rubber composition and characteris-ti.cs o:E each layer of the conveyor belt of the presen-t invention a:rC`! as :Eol1.ows:
~ s the cove:r rubber, a vulcanized rubber composition ~0 I)avi.n(J a Gei~man T1oo sti.ffness value of -49F to 112F' and a VO~ ;wc~1..1. o:E 1() to 30~; (ASTM l~3 oil, 158F' x 22Mrs) must be used. As the cushioning rubber, it is essential to select a vul~anized rubber composition ~hich adheres firmly to steel cords and has a Gehman Tloo stiffness value of -49F to 112F.
The crack-resistant rubber used must be a vulcanized rubber composition having a Gehman T1oo stiffness value of -49F to 112 F, a volume swell of 20 to 100% (ASTM #3 oil, !v 158F x 22Hrs~, capable of firmly adhering to the cushioning and cover rubbers through vulcanization to produce an integral laminate, and also having other properties favorable for the intended use of the conveyor belts of the present invention.
Preferred embodiments of this invention are explained below by referring to the accompanying drawings.
Fig. 1 is a section of a conventional conveyor belt, and Figs. 2A and 2B are sections of preferred embodiments of this inventionO
To simplify explanation, same numerals are put to those parts common to these Figs~ Compositions and properties of each rubber layer are listed in Table 1 and 2.
Xn Fig. 1, numerals 1 and 3 represent the cover rubber layer, numeral 2 denotes the core layer (cushioniny rubber layer), and numeral 4 stands for steel cords. In this case, if the rubber compositi.on Cl or C2 (Table 1) is use~ for the cover rubber layer, and the compositi.on Cu-l or Cu-2 (Table 2 is employed for the cushioning rubber layer, that is, rubber compositions of similar oil and cold resistance are provided ii64e~
throughout the entire thickness of the conveyor belt, a crack formed on the surface of the cover rubber layer (numeral 9) will grow rapidly in the downward direction, resultiny in lengthwise ripping of the belt and ma~ing its normal operation impossible in a short time.
Figs. 2A and 2B represent belt compositions of preferred embodiments of this invention, in which numerals 5, 6 and 7 are crack-resistant rubber layers (rubber composition Al in Table 2).
Th~se con~gurations are laminates consisting of rubber layers of different oil resistance; in this case, the crack 9 formed on the surface of the cover rubber 1 grows straight in the downward direction inside this layer, but goes oblique after entering the crack-resistant rubber layers 5 and 7. With a multiple crac]c reisstant layer structure, as shown in Fig. 2B, the growth and spread of cracks will require more time than in the case of Fig. 2A, further prolonging the service life of the belt.
In the helt structure of Fig. 1, if Cl or C2 is selected or the cover rubber layers (1 and 3) and Cu-l is used for the aore layer (cushioning rubber layer, 2) the interlaminar str~ngth between the two types of rubber layers is rather low and delamination is li.kely to occur. However, adding crack-resistant rubber layers at least lmm in thickness, as shown in Figs. 2A and 2B of the preferred embodiments of the present invention, will result in extremely high adhesion between the core layer 2 and the cover rubber alyers 1 and 3, producing an integral belt composition of high strength.
The rubber compositions and properties of the cover rubber, cushioning rubber and crack-resistant rubber layers are listed in Table 1 and 2.
Table 1 _ _, Compositions and Properties C-l C-2 ~ .
N~R (AN 26%) 85 . _ _ _ _ __ . _ NBR (AN 22%) 100 __ .___ (Styrene-butadiene rubber) ~ _ ~_ Zinc oxide 5 5 _ _ _ Stearic acid 1 Antioxidant 4 Synthetic plasticizer 30 30 Vulcanization accelerator 1.1 1.0 Sulur (S) 2 2 _ __. __~__ ~
Furnac~ carbon blaclc 60 65 __ _ . _ _.
Gehman value T2 tRM~2) -ll.l~F ~16.6F
T5 (RM=2~ -34.6F _45,4F
(D-1053) Tlo (RM=10) -43~6F _54.4F' Tloo (RM=100) 63,4F -G8~8E' _ _ ~ ___ _ ___ ~ _ _ R~slstance to oil (~STM ~3 o.il, 158F x 22EIrs) Volume increase V~ 16~ 20%
Kerosene 17~ l8~o Normal temperature x 1 Day Tensile strength (rb) 2133 Ib/in2 2346.3 Ib/in2 - $~g3 56~
Elongation (Eb) 450% 480%
Hardness (Hs) (SHOREA) 62 60 Wear 90 110 _ Table 2 . _ . ._ .
Compositions and Properties A 1 Cu-l Cu-2 _............... _ _.
Natural rubber 60 Polybutadiene rubber ~
NBR (AN 20~) 60 100 ~_ ............... . _ _ _ .
SBR 1500 40 40 .
Zinc oxide 5 5 5 Stearic acid 1 2 2 Antioxidant 1 2 2 Vulcanization accelerator 1.2 1.2 1.2 Cobalt octoa-te 7.5 7.5 Sulfur (S) 1.5 1.5 2 Synthetic plasticizer 30 30 E'urnac~ carbon black 65 70 85 ._ _ __ ... _~__ ~ . _ ~_ Aromatic softener 5 __ _ _ _ _ _ _ _ . . _ . __ Gehman value T2 -43.6F-:13.0F _13,0F
(~STMD-1053) T5 ~67.0aF_45.4F -43.6F
_74.0F-56.2F -52.6F
Tlo0 86.8F73.0F _73.0F
Resistance tv o~].
(ASTM #3 oil, l58F x 22~rs) Volume i.ncrea~e V% 32%140% 17.1%
Normal temperature x 1 Day 40% 160% 33~5%
Tensile strength (Tb) Ib/in 2061.9 2133 2250 ¦ Elonga-tion (Eb) ~ ¦ 550 ¦ 550 ¦ 485 (Hs) (SHOREA) ~ 59 ¦ 65 ¦ 65 FigO 3 shows the flexural properties of the rubber materials listed in Tables 1 and 2, in which length of grown cracks is plotted against number of flexings (in kilocycles).
It is apparent from these curves that Cu-l and A-l show excellent resistance to flexural loads.
Conveyor belts of laminated structure using C-2 for ~he cover rubber, Cu - 1 for the suchioning rubber and A-l for the crack-resistant rubber were explained above as preferred embodiments, but they are not to be considered as a limitation upon the present invention. As stated earlier, the conveyor belts for transporting oil sand are used with kerosene applied on the surface; hence, the surface layer must be made of an oil~resistant polymerO The most typical oil-resistant polymer :is NBR. This is a copolymer consisting of acrylonitrile and butadi.ene, and the content oE acrylonitirle determines its oil and cold resistance. NBR polymers commercially availahle today contain 18 to 50~ acrylonitrile (82 to 50~ butadiene).
Of the.se, those grades having an acrylonitrile content of 18 to 35~ are suitable for use in the conveyor belts because colcl resistance is too low with higher acrylonitirle contents.
Rubber compositions generally incorporate plasticizers to enhance processability and improve physical properties.
Synthetic plasticizexs are most suitable for NBR, which include various synthetic liquid polymers and esters of dibasic acids, such as trioctyl phosphate, dibutyl sebacate, dibutyl phosphate, dioctyl adipate, dioctyl phthalate and di(butoxyethoxyethyl) adipate.
The pre~erred oil-resis~ant rubber materials used in the present invention comprise 100 parts of a rubber component consisti.ng of NBR alone or in combination with other types of rubbers, 10 to 40 parts of a synthetic plasticizer~ 30 to 70 parts of a reinforci.ng filler such as carbon black, 2 to 10 p~rts oE an antioxidant and 3 to 10 parts of vulcanizing chemicals. In addition/ materials commonly used in the rubber industry, such as processing aids and bulking fillers, may also be added. These oil-resistant rubber materials should preferably have a Gehman Tlo~ stiffness value of -49~F
to ~112F (ASTM D-1053) and a volume swell of 10 to 30%
(ASTM ~3 oil, 1S8F x 22Hrs, A5TM D-1053).
As stated earlier, the belt surface is always exposed to kerosene (including gas oi].)~ The oil tends to penetrate the surace layer through the flaws formed by stones or roc]cs con-ta.ined :i.n the oil sand being carried, and the growth rate of cracks, accele.rated by the bending, tensile and compressive forces exerted on the conveyor belt during operation, i.s hi.gher compared with the case when no kerosene is app]..ied.
At the same time, the rubber swells through absorption of kerosene and the plasticizer contained in the rubber tends to be extracted by the absorbed oil. When a rubber is kept ln contact with an oil, the apparent degree of swelling of the rubber is determined by the balance between the entry of the oil into the rubber and extraction of the plasticizer from the rubber.
When the rubber swells l~ss~ extraction of the plasti-cizer will predominate. This is the case observed with N~R
compositions with high acrylor.itrile contents.
Extraction of the contained plasticizer will harden the rubber and adversely affect its cold resistance, resulting in poor 1exural resistance.
The conveyor belts proposed in the present invention have compositions and characgeristics as detailed above.
This invention thus offers conveyor belts with prolongecl service life. This means less cost for belt replacement, for repair work tbonding cost, etc.), and minimized operation loss due to reduction in transportation capacity. ~he cost of conveyor belt itself is also less because high oil resistance is not essential for the cushioning rubber layer. For example, an ordinary diene-type rubber may be used as the core layer becc~use it can be firmly bondecl to the surface layers by ~corporatinc~ crack-resistant rubber layers between them.
Claims (5)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A conveyor belt suitable for transporting oil sand in cold districts, capable of operating over a wide range of tem-perature and resistant to liquid hydrocarbons containing up to 30% aromatics, which comprises an outer layer made of a cover rubber and provided on the surface which, in operation, is in contact with oil sand being transported, a second outer layer made of a cover rubber and provided on the back surface which, in operation, is in contact with conveyor pulleys, a core layer made of a cushioning rubber and integrally incorporating belt reinforcement having a high tensile strength, and at least one intermediate layer made of a crack-resistant rubber and provided between said core layer and each of the two outer layers.
2. A conveyor belt as defined in claim 1, wherein a plurality of crack-resistant rubber layers are provided between said core layer made or a cushioning rubber and said outer layer made of a cover rubber and provided on the top surface.
3. A conveyor belt as defined in claim 1 or claim 2, said two outer layers on the top and back surfaces being made of a rubber composition consisting of NBR of 18 to 35% acrylo-nitrile content alone or in combination with other types of rubbers, also containing, based on 100 parts of said rubber composition, 10 to 40 parts of a synthetic plasticizer, 30 to 70 parts of a reinforcing filler such as carbon black, 2 to 10 parts of an antioxidant and 3 to 10 parts of vulcanizing chemicals, and having a Gehman T100 stiffness value of -49°F
to -112°F when measured according to the method of ASTM D-1053 and a volumne swell of 10 to 30% when immersed in ASTM #3 oil at 158°F for 22 hours according to the method of ASTM D-471.
to -112°F when measured according to the method of ASTM D-1053 and a volumne swell of 10 to 30% when immersed in ASTM #3 oil at 158°F for 22 hours according to the method of ASTM D-471.
4. A conveyor belt as defined in claim 1 or claim 2, wherein said core layer is made of a cushioning rubber incorporating metal cords arranged parallel in the longitudinal direction, said cushioning rubber being a blend of natural rubber, poly-butadiene, SBR and other types of rubbers, or an NBR rubber containing 18 to 35% acrylonitrile, also containing, based on 100 parts of said rubber composition, 10 to 40 parts of a syn-thetic plasticizer, 60 to 90 parts of a reinforcing filler such as carbon black, and 5 to 10 parts of an agent for rubber-to-metal adhesion, and showing a bonding strength to said metal cord of at least 782 Ib/in2 and a Gehman T100 stiffness value of -49°F to 112°F when measured according to the method of ASTM
D-1053.
D-1053.
5. A conveyor belt as defined in claim 1 or claim 2, wherein said crack-resistant layer is made of a vulcanized rubber compostion consisting of a blend of NBR with an acrylonitrile content of 18 to 35% and other types of rubber, also containing, based on 100 parts of said rubber composition, 10 to 40 parts of a synthetic plasticizer, 30 to 70 parts of a reinforcing filler such as carbon black and 3 to 10 parts of vulcanizing chemicals, and showing a Gehman T100 stiffness value of -49°F to 112°F when measured according to the method of ASTM D-1053, a volume swell of 20 to 100% when immersed in ASTM #3 oil at 158°F for 22 hours according to the method of ASTM D-471, and a bonding strength to the adjacent rubber layers of at least 142 Ib/in2.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP10786081A JPS5811404A (en) | 1981-07-10 | 1981-07-10 | Conveyor belt |
| JP107860/1981 | 1981-07-10 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1195641A true CA1195641A (en) | 1985-10-22 |
Family
ID=14469899
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000406666A Expired CA1195641A (en) | 1981-07-10 | 1982-07-06 | Conveyor belts |
Country Status (2)
| Country | Link |
|---|---|
| JP (1) | JPS5811404A (en) |
| CA (1) | CA1195641A (en) |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS59182109A (en) * | 1983-03-31 | 1984-10-16 | Bando Chem Ind Ltd | Cold and oil-proof conveyor belt |
| JPS60157710U (en) * | 1984-03-28 | 1985-10-21 | 東海ゴム工業株式会社 | conveyor belt |
| JPS6225041A (en) * | 1985-07-26 | 1987-02-03 | シバタ工業株式会社 | Composite body in which chain is buried in rubber and manufacture thereof |
| CN102275712B (en) * | 2011-05-23 | 2013-08-28 | 兖矿集团有限公司 | High-temperature resistant conveyer belt |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5215865A (en) * | 1975-07-24 | 1977-02-05 | Yoshito Haramaki | Extracting method of food extract |
-
1981
- 1981-07-10 JP JP10786081A patent/JPS5811404A/en active Pending
-
1982
- 1982-07-06 CA CA000406666A patent/CA1195641A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| JPS5811404A (en) | 1983-01-22 |
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