FIELD OF THE INVENTION
The invention relates to conveyor belts used in steel manufacturing plants. More
particularly this invention relates to adhesive and a cover rubber for joining two ends of
the conveyor belt.
BACKGROUND OF THE INVENTION
Conveyor belts are used for conveying different kinds of materials for example, coal,
coke, sinter, iron ore, fluxes and waste materials in different industries including an
integrated steel plant. Different grades of conveyor belts for example, M24 & heat
resistant, and ultra heat resistant are known. Ultra heat resistant (UHR) belts are used
mainly in iron ore agglomeration and coke making plant where the material discharged
on the belt can reach temperature between 120 - 180°C in normal operating condition
and sometimes reaches at higher temperature due to plant abnormality. These belts are
generally joined / repaired through splice joining technique by using joining kits
consisting of green cover rubber compound, adhesive, and cleanser. Joining of the belt
is conducted mainly through hot vulcanization process which requires around 12 hour
shutdown for onsite joining and repair.
Performance of a conveyor belt is largely determined by the properties of the belt joint.
Generally the joint portions are the weaker link in a conveyor belt system which initiates
failure at service. Therefore, utmost importance is given on the types of joining
materials, and joint preparation process, while carrying out the joining process. Among
the different kinds of conveyor belts, ultra heat resistance belts are subjected to most
severe service conditions in terms of heat and exhibit higher rate of failure at service.
Detailed analysis of the existing belts and the joining materials indicates a scope for
improvement in the high temperature performance of the adhesive compounds.
Belt conveyors are multilayered composite structure built with alternate layer of
fabric/steel cord and rubber vulcanized together. The end portions of the belt further
bonded to make it a continuous loop before putting into service [1]. The end of the belt
is normally spliced using hot vulcanizing, cold splicing, or mechanical fasteners/clip joints
[2]. Conveyor belt joints are exposed to substantial dynamic loads during the long time
of their operation. Ensuring a high durability of conveyor belt, joints are equivalent to
guaranteeing a reliable operation of the belt. Continuous conveyor belt service is
dependent entirely on the strength and life of the splice joint to hold the two ends

together. Ultimately, belting performance is dependent on the quality, efficiency, and
technique of the splicer [3]. The strength of the splice is always lower than that of the
solid belt because in the spliced areas continuity of plies or steel cords has been
disrupted. Therefore, a zone where the stresses in adjacent plies or cords differ
markedly is formed. It results in different elongation and additional shearing stresses in
the layer of rubber [4]. The strength of the splice joint depends on several factors such
as the parameters of the joined belt, the connecting layer and the technology of splicing,
as well as on the adhesive materials used to make the splice [4]. The strength of the
splice constitutes a criterion for the selection of a belt suitable for the operating
conditions [4].
Different improved splice joint techniques were reported in literature to address the ever
increasing demand for better belting performance and increase in running tensions.
A selection of an effective adhesive compound remained the key interest of research for
conveyor belt joints specifically for high temperature application. Conveyor belt
adhesive-bonded joints generally composed of rubber and a gum rubber adhesive [1].
Various adhesives have been disclosed in different prior patents and prior-published
literatures by researchers [5-8]. Natural rubber (NR) and different synthetic rubber like
diene rubber had been used as adhesive for conveyor belt joint. The adhesive was
applied to strands by exposing a plurality of strands at two belt ends. Two arrays of un-
vulcanized cross-sectionally profiled strips of rubber were provided with one array
substantially parallel with the strand of bottom plurality and the other array on top
strips. The top strip was overlaid the array of bottom strip. It was followed by hot
vulcanization of the strips together thereby forming the spliced joint [5-6], However, no
specific service temperature has been disclosed in these literatures. It described that the
adhesion bond was strong in various cycles as exhibited by a dynamic adhesion rating in
the splice of more than 50,000, 75,000 and 100,000 cycles [5].
Another prior art disclosed a method of preparing the adhesive with neoprene latex
which offers improved adhesive strength of the joint-surface of conveyor belt along with
improved workability and safe sanitation during joining [7]. Splice joining both ends of
the conveyor belt has been disclosed along with rubber formulation to smoothly
separate the canvas layers. The tear strength of the first rubber layer was set larger
than that of the second rubber layer. Thus, when the first rubber layer and the second

rubber layer were separated from each other during the work for joining the both ends
of the conveyor belt, the separation took place at the interface or in the vicinity of the
interface and making the separation face smooth. Then cement was applied for hot cure
adhesion of the both ends and carried out vulcanization joining [8]. Resorcinol-
formaldehyde (RF) based adhesive resin with low-sulphur silane cross linking and silica
filler was added in high-tack rubber mixture which was used as intermediate rubber for
hot vulcanization splice joint specifically for fabric belts. The Rubber formulation acted as
a direct bonding mixture due to the presence of Resorcinol-formaldehyde bonding agent
in it which helped to avoid the generally used assembly solution [9].
Cai et al. reported the use of NR/SBR (styrene-butadiene rubber) as interlayer adhesive
and cover adhesive added with a proper amount of tackifier for splice jointing of nylon
conveyor belt constituted with NR as main-body [10].
Other adhesive compounds are also reported to be used as an alternative to rubber
based adhesives. Urethane based system was reported to be used for conveyor belt joint
where the first and second reinforced urethane layers having extended plurality of
fingers at end portions were connected together by an adhesive [11].
Another patent disclosed a technique which could be applicable at operation site with
strong effective splice. Here, the ends of conveyor belt comprising urethane
reinforcement strands could be spliced together where filler was completely removed
from each end sections to form new belt ends. The ends were overlapped to make the
strands aligned and the opposite new ends were molded by pouring urethane to
encapsulate a portion of the overlapping aligned strands followed by pouring more
urethane on either side of the centre belt section to complete the splice [12]. Resin
based adhesive were used for conveyor belts to obtain flexible splice joint comparable to
the belting material where the top and bottom surfaces of the two ends of the belt were
cut away and then butted and laced together. The ends urged apart to stress the lacing
cord and to avoid it, resin based adhesive was applied to the ends to embed the lacing
cord and made the ends up to their original level before curing the resin [13]. Ultrahigh
molecular weight polyethylene containing 100,000 or greater of molecular weight was
used to facilitate joining and repairing conveyor belt in a short time [14]. Here,
polyethylene film manufactured by a deleting system was interposed on one connecting
surface of an endless conveyor belt. The other end of the belt was polymerized, heated

and pressurized at a temperature around 160-170°C for 5-30min when the polyethylene
melted and integrally adhere with high strength the two ends of the conveyor through
thermal vulcanization.
As per the analysis on the past conveyor belt failure cases, it can be established that an
inadequate high temperature performance of the adhesive compound used for joining is
one of the critical reasons for premature failures.
References:
[1] Mazurkiewicz D. Lublin Univ Tech, Poland; Archives Of Civil And Mechanical
Engineering; 2009, 9 (2); 75-91
[2] Friedrich A.J. Soc Mining Metallurgy & Exploration Inc, USA; Conference: 2000 SME
Annual Meeting, Salt Lake City; Bulk Material Handling By Conveyor Belt III; 2000, 79-85
[3] Rengifo, P.E. Goodyear Tire & Rubber Co, Marysville, OH USA; Bulk Material
Handling By Conveyor Belt 5; 2004, 15-24
[4] Hardygora M; Madziarz, M; Wojtylak, M. Wroclaw Univ Tech, Poland; Mining Sci &
Tech. 1999, 661-666
[5] Goodyear Tire & Rubber; Patent No. US2004154903; 12-Aug-2004
[6] Goodyear Tire & Rubber; Patent No. US2005031825; 10-Feb-2005
[7] Bando Chemical Ind; Patent No. JP2001329232; 27-Nov-2001
[8] Bridgestone Corp; Patent No. JP2008050074; 6-Mar-2008
[9] Continental Ag; Patent No. DE3906740; 6-Sep-1990
[10] Cai J; Sheng X. Beijing Xiangjiao Gongye Yanjiu Sejiyuan; 1997, 44(5), 303-306
[11] B F Goodrich Co; Patent No. EP0134545; 20-Mar-1985
[12] B F Goodrich Co; Patent No US4548663; 22-Oct-1985
[13] Ross W. H; US3546054; 8-Dec-1970
[14] Yokohama Rubber Co Ltd; Patent No. JP6134863;17-May-1994

OBJECTS OF THE INVENTION
In view of the foregoing limitations inherent in the prior-art, an object of the invention is
to propose a product comprising an adhesive and a cover rubber for joining conveyor
belts operating at high temperature of 180-200 deg. C.
Another object of the invention is to propose a product comprising an adhesive and a
cover rubber for joining conveyor belts operating at higher temperature of 180-200°C,
which maintains the properties of the composition even at high service temperature.
SUMMARY OF THE INVENTION:
Accordingly, there is provided a product comprising an adhesive and a cover rubber for
journey conveyor belts operating at higher temperature of 180-200°C. The adhesive
and the cover rubber comprises (in Parts per Hundred of Rubber) as follows:

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING:
FIGS. 1(a)-1(b) shows an arrangement for joining of two ends of a conveyor belt.
FIGS. 2(a)-2(d) shows graphical representation of variation in belt joint properties
before and after ageing at high temperature for the commercially available cover rubber.

FIGS. 3(a)-3(d) shows graphical representation of difference in physical properties
before and after heat ageing of the commercially available cover rubber after curing for
an extra 5 min over and above the optimum curing time at 160°C.
FIGS. 4(a)-4(d) shows graphical representation of comparative change in original
properties of the commercially available and developed adhesive after curing before and
after accelerated ageing.
FIGS. 5(a)-5(d) shows graphical representation of the change in physical properties
before and after heat ageing of the commercially available adhesive after curing for an
extra 5 min over and above the optimum curing time at 160°C.
FIG. 6 shows an adhesion property of the cover rubber and adhesive.
FIG. 7 shows graphical representation of comparison between the compound of the
invention and that of a commercially available conveyor belt joint material.
DETAILED DESCRIPTION OF THE INVENTION;
Various embodiments of the invention provides a product comprising an adhesive and a
cover rubber for joining conveyor belts operating at higher temperature of 180-200°C.
The adhesive and the cover rubber comprises (in Parts per Hundred of Rubber) as
follows:


Shown in FIG. 1 is an arrangement for joining two ends (El and E2) of a conveyor belt
(100) known as splice joining method. Each end of the conveyor belt (100) comprises a
top cover (104), a bottom cover (108), and plurality of fabric plies (112) between the
top cover and the bottom cover (108). To join both the ends (El and E2), each ends are
sliced in such a manner so as to expose fabric plies (112), the top cover (104) and the
bottom cover (108) of their respective ends El and E2.
Shown again in FIG. lis the application of an adhesive (116) and a cover rubber (120)
over a trapezoidal section (124). The adhesive (116) and the cover rubber (120) are
configured to join the conveyor belt. The adhesive (116) is applied on fabric plies (112)
of both the ends (El and E2) of the conveyor and within the trapezoidal section (124).
Heated steel plates (128) and (132) are pressed from top cover (104) side and from the
bottom cover (108) side (shown by arrows) so that the vulcanization of the cover rubber
takes place. During the vulcanization process adherence between cover rubber - top and
bottom cover of conveyor belt and cover rubber-fabric plies takes place.
To restrict the outflow of the adhesive (120) from the conveyor belt (100) and maintain
proper alignment of the both the ends of the conveyor belt (100), a side plate (136)
from both the sides (top side and the bottom side) are applied.
It should be appreciated that the trapezoidal section (124) can be in any other suitable
shape as per the requirement and should not be construed to be limitation of the
invention.
The composition of the adhesive (116) is shown in Table 1:


The composition of the cover rubber (120) is shown in Table 2:

The preferable composition of the adhesive and the cover rubber is EPDM=80 phr (M-
class), Bromobutyl=20 phr keeping rest of the composition as same as that of Table 1
and Table 2.
Following are the full form and the specifications of the composites mentioned in Table
1 and Table 2 in Table 3.


Now considering Table 1 and Table 2, composition level of the Bromobutyl is kept high
compared to conventionally used adhesive and the cover rubber. This is due to its
majorly amorphous nature which amounts the flowability. The flowability helps in
bonding with various surfaces of the trapezoidal section (124), top cover (104), the
bottom cover (108) and the fabric plies (112). Further the higher amorphous improves
the heat resistance of the adhesive (116) and the cover rubber (124). This improvement
in heat resistance makes the cover rubber and the adhesive less prone to heat
deterioration at high temperature working conditions.
To ascertain the compatibility with the higher bromobutyl content, EPDM is kept at
between 70-90 phr. EPDM which is conventionally 50:50 amorphous and crystalline has
been substituted with 65:35 amorphous and crystalline respectively.
Since excessive amorphous content leads to lower crystalline content subsequently
lowers the strength of the adhesive and the cover rubber. This reduction in strength is
compensated with the GPF 30 phr and FEF 15 phr content for adhesive and the cover
rubber respectively mentioned in Tables 1 and 2.
To improve the bond formations on side chains of the adhesive (116) and the cover
rubber (120), coated Sulphur (S) content is kept at 1.40 phr and 1.00 phr in the
adhesive and the cover rubber respectively.
It should be noted that sulphur (S) content in the adhesive is more than that of the
cover rubber. The reason being that the adhesive is thinner and needs more bonding
contact with the various parts of the conveyor belt as compared to the cover rubber and
hence needs more active side chains.
This bonding is achieved by curing (the formation of the bonds between sulphur (S) and
various polymeric chains of cover rubber, the top cover and the bottom cover) while
vulcanization affected by means of the steel plate (128). This curing also increases the
internal strength of the cover rubber and the adhesive as sulphur of both bonds
internally with their internal polymeric chains also.
The optimum cure time for the adhesive (116) and the cover rubber (124), while joining
two ends of the conveyor belt together, is 32-35 min at 160°C and pressure of 260 bar.
The pressure of 260 bar is applied by means of the steel plates (136).

Curing characteristics of the adhesive and the cover rubber
Curing characteristics of the adhesive and the rubber compound can be done with
Rheometric study using a Mooney viscometer. Rheometric analysis is done to
understand flow characteristics during vulcanization of the developed adhesive and the
cover rubber. Optimum cure time for both is 32-35 min at 160°C and pressure of 260
bar. The curing characteristics of the cover rubber and adhesive as obtained with the
developed formulations indicated no mismatch in strength between cover rubber and
adhesive while used in splice joint during actual conveyor belt joining.
Physical properties of the adhesive and the cover rubber at room and high
temperature
Room and high temperature physical properties of the commercially available and
developed adhesive and cover rubber compounds are assessed before and after
accelerated ageing tests conducted at 125°C for 96 hours as per ASTM standard in
laboratory followed by measuring the in change in original properties in terms of tensile
strength and tear strength and hardness.
Shown in FIGS. 2(a), 2(b), 2(c), 2(d) and Table 4a and 4b are the variation in
properties due to ageing at high temperature for optimally cured cover rubber and the
commercially available cover rubber. FIG. 2(a) is for tensile modulus, FIG. 2(b) is for
ductility, FIG. 2(c) is tear strength and FIG. 2(d) is for hardness.



A1 & A2: Commercially available B1 & B2: Developed
The comparative change in original properties of the commercially available and
developed cover rubber compound after optimum curing followed by accelerated ageing
is hereby described in FIG. 2a to FIG. 2d.
Fig. 2(a) and Table 4(a) shows the comparative change in tensile strength of the
cover rubber. It reveals more or less similar characteristics of the commercially available
and developed cover rubber formulations before and after ageing. The commercially
available cover rubber does not show much deterioration, after heat ageing. The current
result showed that the changed formulation of the cover rubber matched closely with
the commercially available cover rubber performance.
FIG. 2(b) and Table 4(a) shows that the original ductility of the cover rubber is better
than commercially available but the ductility after ageing is similar to the existing
commercially available.

FIG. 2(c) and FIG. 2(d) and Table 4(a) show improvement in tear strength and
hardness both before and after ageing for the cover rubber compared to the
commercially available.
FIG. 3(a), FIG. 3(b), FIG. 3(c) and FIG. 3(d) and Table 4b shows the change in
physical properties due to heat of the cover rubber after the formulation is over cured
for an extra 5 min over and above the optimum curing time at 160°C. It reveals over
curing leads to higher change in tensile strength and ductility for commercially available
compared to the developed one (FIG. 3(a) & FIG. 3(b)). Higher stability in tensile
properties of the developed formulation even after over curing indicated better heat
resistance properties of it compared to the commercially available. Developed
formulation also shows higher stability in terms of change in tear strength and hardness
under optimum and over cured condition compared to commercially available (FIG. 3(c)
& 3(d)). Developed cover rubber under over cured condition also retained the starting
properties after accelerated heat ageing. Whereas, large change in physical properties
like tensile strength, ductility, tear strength and hardness is observed in case of over
cured existing cover rubber formulation after accelerated ageing tests. The results
indicate that the developed cover rubber formulation though having similar original
physical properties but heat resistance properties are superior compared to the
commercially available.
The comparative change in original properties of the commercially available and
developed adhesive after optimum curing followed by accelerated ageing are shown in
FIGS. 4(a), 4(b), 4(c) and 4(d) and Tables 5a and 5b.



1. Normal Cured 2. Over cured
2. A1 & A2: Commercially Available; Bl & B2: Developed
FIG. 4(a) and Table 5a shows the comparative change in tensile strength of the
adhesive. It reveals higher original tensile strength and negligible change in strength
after ageing compared to commercially available adhesive. FIG. 4(b) and Table 5a
shows similar original ductility for both the formulations but change in ductility due to
heat ageing is lower in case of the developed formulation compared to the commercially
available. FIG. 4(c) & 4(d) and Table 5a report higher original and after ageing tear
strength and hardness for the developed adhesive compared to the commercially
available. These results indicate that the developed adhesive is much superior in terms
of their original as well as heat ageing properties. However, the heat ageing properties
are further tested after over curing of the adhesive and the comparative results with
existing adhesive is discussed below.
FIG. 5(a), FIG. 5(b), FIG. 5(c), FIG. 5(d) and Table 5b shows the change in
physical properties due to heat ageing of the commercially available and developed
adhesive after over curing for an extra 5 min over and above the optimum curing time at
160°C. FIGS. 4(a) to 4(d) and FIGS. 5(a) to 5(d) reveals that over curing do not
lead to significant change in original physical properties in comparison to optimum cured
condition for both commercially available and developed adhesive compounds. However,
the tensile strength (FIG. 5(a)), ductility (FIG. 5(b)), tear strength (FIG. 5(c)) and
hardness (FIG. 5(d)) properties after accelerated ageing in over cured condition were
also observed to be higher with the developed adhesive compared to the commercially
available.

Splice joining of the conveyor belt consists of bonding/adhesion of the cover rubber with
the top cover and the bottom cover and fabric plies. Performance of the joint is
determined by the adhesion strength between the cover rubber to the top and the
bottom cover of the conveyor belt and cover rubber to the fabric plies. The vulcanization
of the cover rubber is conducted with single layer of top cover or bottom cover of the
conveyor belt and fabric plies after using the adhesive at the interface between the two
layers. Subsequently these vulcanized samples are peel tested to determine the cover
rubber-top cover / bottom cover and cover rubber-fabric plies adhesion. Fig. 6 and
Table 6 shows the comparative adhesion test results for commercially available and
developed formulations (cover rubber and adhesive).

FIG. 6 and Table 6 show higher cover rubber-fabric plies adhesion strength than cover
rubber to top cover and the bottom cover adhesion strength for both existing and
developed formulations. Developed formulations showed higher cover rubber to top
cover / bottom cover (average separation force 150N against 75N) and cover rubber to
fabric plies (average separation force 300N against 250N) adhesion than existing
formulations.
FIG. 7 and Table 7 shows developed cover rubber-fabric plies joints showed 10%
higher initial adhesion strength as well as lower drop (12% against 26%) in strength
after accelerated heat aging compared to the commercially available products.


Adhesion of the cover rubber to the top cover and bottom cover is in the range of 158 to
183 N as per peel adhesion test at 180 degree angle.
Adhesion of the cover rubber to the fabric plies is in the range of 266 to 311 N as per
peel adhesion test at 180 degree angle.
Adhesion of cover rubber to the fabric plies decreases maximum upto 12% as per peel
adhesion test at 180 degree angle after accelerated ageing tests conducted at 125°C for
96 hours.
Advantages of the adhesive and the cover rubber of the invention offer better service life
to joints of conveyor belt even at high working temperature 180-200 deg. C. Stability in
the adhesive and the cover rubber achieved is high as compared to the commercially
available adhesive and the rubber cover. Initial and after aging adhesion strength
achieved is high as compared to the commercially available formulation.

We Claim:
1. A product comprising an adhesive and a cover rubber for joining conveyor
belts operating at higher temperature of 180-200°C, comprising an adhesive
and a cover rubber, wherein the adhesive consisting of (in Parts per Hundred
of Rubber):
70 to 90 phr Ethylene propylene diene monomer (M-class) rubber;
10 to 30 phr Bromobutyl Rubber;
2 phr Polymerised Tri hydro Quinoline Antioxidant;
5 phr ZnO;
1 phr Stearic Acid;
30.00 phr Furnace Black;
20.00 phr Ultrasil VN3: Silica;
10.00 phr Paraffin Oil;
01.40 phr Coated Sulphur;
01.40 phr N-Oxydiethylene-2-benzothiazole sulfonamide as Curing
accelerator;
02.00 phr Resorcinol Formaldehyde Resin; and
03.00 MD IV (HMMM) 50 %: Hexamethoxy Methylol Melamine (HMMM)
Resin coated with Inert Carrier in free flowing powder form, and wherein
the. cover rubber consisting of (in Parts per Hundred of Rubber (phr):
70 to 90 phr Ethylene propylene diene monomer (M-class) rubber;
10 to 30 phr Bromobutyl Rubber;
3 phr Polymerised Tri hydro Quinoline Antioxidant;

5 a Vulcanization activator in rubber formulation;
1 phr Stearic Acid;
15 Fast Extruding Furnace Black;
20.00 Ultrasil VN3: Silica;
10.00 Paraffin Oil;
1.00 Coated Sulphur;
2.20 phr N-Oxydiethylene-2-benzothiazole sulfonamide as Curing
accelerator;
5 phr Cumarone Indane Resin;
02.00 phr Resorcinol Formaldehyde Resin; and
03.00 MD IV (HMMM) 50 %: Hexamethoxy Methylol Melamine
(HMMM) Resin coated with Inert Carrier in free flowing powder form.
2. The product as claimed in claim 1, is enabled to join two ends of the
conveyor belt.
3. The product as claimed in claim 1, wherein curing time is in the range of
32 to 35 minutes at 160°C at pressure upto 260 bar.
4. The product as claimed in claim 1, wherein the tensile strength of the
adhesive changes maximum upto -9.27% as per accelerated ageing tests
conducted at 125°C for 96 hours.
5. The product as claimed in claim 1, wherein total elongation of the
adhesive decreases maximum upto 45.30% as per accelerated ageing
tests conducted at 125°C for 96 hours.
6. The product as claimed in claim 1, wherein tear strength of the adhesive
decreases maximum upto 15.00% as per accelerated ageing tests
conducted at 125°C for 96 hours.

7. The product as claimed in claim 1, wherein hardness of the adhesive
increases maximum upto 12.06% as per accelerated ageing tests
conducted at 125°C for 96 hours.
8. The product as claimed in claim 1, wherein tensile strength of the cover
rubber decreases maximum upto 3.3% as per accelerated ageing tests
conducted at 125°C for 96 hours.
9. The product as claimed in claim 1, wherein total elongation of the cover
rubber decreases maximum upto 33.70% as per accelerated ageing tests
conducted at 125°C for 96 hours.
10. The product as claimed in claim 1, wherein tear strength of the cover
rubber increases maximum upto 5.49% as per accelerated ageing tests
conducted at 125°C for 96 hours.
11. The product as claimed in claim 1, wherein hardness of the cover rubber
increases maximum upto 17.30% as per accelerated ageing tests
conducted at 125°C for 96 hours.
12. The product as claimed in claim 1, wherein adhesion of cover rubber to a
top cover and a bottom rubber cover is in the range of 158 to 183 N as
per peel adhesion test at 180 degree angle.

13. The product as claimed in claim 1, wherein adhesion of the cover rubber
to a fabric ply of the belt is in the range of 266 to 311 N as per peel
adhesion test at 180 degree angle.
14. The product as claimed in claim 1, wherein adhesion of the cover rubber
to the fabric ply decreases maximum upto 12% as per peel adhesion test
at 180 degree angle after per accelerated ageing tests conducted at
125°C for 96 hours.

15. The product as claimed in claim 1, wherein preferable composition of the
adhesive is 80 phr Ethylene propylene diene monomer (M-class) rubber
and 20 phr Bromobutyl Rubber.
16. The product as claimed in claim 1, wherein preferable composition of the
cover rubber is 80 phr Ethylene propylene diene monomer (M-class)
rubber and 20 phr Bromobutyl Rubber.