Heat resistant belt

This invention supplies an insulating conveying belt composed of a belt carcass having at least one embedded reinforcing ply, a pulley cover and a top cover, said top cover having a heat resistant member adhered to said top cover, said heat resistant member being selected from the class consisting of fibers of aramid, glass, ceramic or mixtures thereof. This member may be woven or non-woven such as a punched felt mat. Preferably the fibers of the heat resistant member are woven rather than being of the non-woven type. The elastomer preferably is EPDM or blends of EPDM and silicone rubber with carbon black or silica filler.

FIELD OF THE INVENTION 
This invention relates to a conveyor belt containing an insulative layer 
adhered or attached to the cover layer of said belt. More particularly 
this invention relates to a conveyor belt that receives hot loadings and 
which has a fibrous mat or felt of insulative material to insulate and 
protect the underlying belt from the excessive heat, in isolated places of 
roughly 538.degree. C. to 983.degree. C. for short times. 
This invention supplies an insulating conveying belt composed of a belt 
carcass having at least one embedded reinforcing ply, a pulley cover and a 
top cover, said top cover having a heat resistant member adhered to said 
top cover, said heat resistant member being selected from the class 
consisting of fibers of aramid, glass, ceramic or mixtures thereof. This 
member may be woven or non-woven such as a punched felt mat. Preferably 
the fibers of the heat resistant member are woven rather than being of the 
non-woven type. The elastomeric content preferably is EPDM or blends of 
EPDM and silicone rubber with carbon black or silica filler. 
PRIOR ART 
The current state of art employs high temperature resistant elastomers such 
as EPDM & EPR with fillers, low volatility plasticizers and usually with 
sulfur donor or peroxide cure systems. The reinforcement is usually nylon, 
aramid, glass or steel fabrics. Some manufactures have also included burn 
shields made of very high temperature resistant fabric embedded well 
beneath the top cover's surface and above the fabric reinforced 
carcass--to prevent the payload from burning through the rubber top cover 
into the carcass, destroying the belt. This invention, instead, puts the 
fabric onto the top surface to protect both the top cover and the carcass 
as well. 
Japanese Pat. No. JP 244 452 provides a heat-resistant conveyor belt having 
a surface of EPDM or EPR rubber containing 60 or less percent 
diorganopolysiloxane silica, a hardener and a small amount of maleimide 
which allows the cover to be subjected to direct heat of the loadings and 
to experience heat cracking.

Referring specifically to the figure, numeral 1 designates the belt in 
generally having a body carcass 2 composed preferably of one or more 
fabric layers 3 such as the polymeric fibers, glass or wire embedded in or 
covered with elastomer 4 and plied together to form a belt carcass body. 
The body carcass 2 preferably has an elastomeric pulley cover 4 adhered or 
plied thereto with a top elastomeric cover 4 adhered or plied thereto with 
a top elastomeric cover 5 on top of the body. My invention provides an 
insulative layer 6 of a fabric or belt either woven or non-woven to 
separate and insulate the elastomer of the top cover 5 as well as the body 
carcass from the hot pay load 7 to thereby increase the temperature 
resistance of the belt and to increase the service life of the belt. 
The nature of the belt is well known where the elastomers may be any of the 
rubbers known for their heat resistance such as EPDM rubber or EPR rubber. 
NBR, SBR and neoprene may be used, but usually are EPDM and EPR rubbers. 
These rubbers are usually loaded with relatively high loadings of fillers, 
50 to 150 parts per hundred of rubber. Suitable fillers are carbon black, 
hydrated precipitated silica and hydrated alumina to mention those well 
known and preferred. Low volatility plasticizers such as ASTM-D-2226, Type 
104B paraffinic oil, such as Sunpar 2280, polysiloxane oils, polysiloxane 
rubbers, polyisobutylene isoprene rubber and polyisobutylene may be used 
to give the desired degree of flexibility. These rubbers are cured with 
the usual sulfur donor or donors or with a peroxide at the usual 
temperatures--about 135.degree.-180.degree. C. and pressures of 0.3 to 
14.0 MPa. The fabric layers 3 can be at least one or more and usually are 
made from polyamides viz nylon or aramid types, glass or metal fibers in 
any of the types used in making belts. The cover stocks for covers 4 and 5 
are made of the usual elastomeric materials such as the EPDM or EPR 
rubbers compounded with a curative, low volatility plasticizer, various 
fillers and burn-resistant materials such as the silicones. 
The preferred belt body is composed of a blend of about 85/95% EPDM 
rubber/15/5% silicone rubber, a peroxide curative, about 15 to 30 parts of 
carbon black, some antioxidant preferably up to 10 parts, and no liquid 
plasticizer. Also, this composition can be used to impregnate the burn 
resistant member to aid in bonding it to the belt. Finely divided silica 
may be used as well as carbon black for filler in the elastomer used 
either in the carcass or the cover stock. 
The specific and general advantages of this invention are further 
exemplified and represented by the following examples: 
EXAMPLE 1 
A project was established to evaluate the effect of adding a burn shield to 
the surface of a conventional heat belt for improved service life in 
severe heat applications. 
The fabrics evaluated were: (1) glass scrim, (2) Kevlar scrim, and (3) 
square woven fabric nylon warp/glass fill. 
The test procedure used is as follows: a metal punch was rounded off to a 
point with a 0.635 centimeter radius. The punch was welded to a metal 
plate. The samples to be evaluated were supported on a tripod and the 
heated punch was placed on the sample for a one minute dwell with 89 
newtons force on the probe. The penetration into the belt was then 
recorded. 
The metal probe was heated in a baffel furnace and tests were made at two 
temperatures, 538.degree. C. and 983.degree. C. 
The sample used was a 2 ply 0.70cm thick heat belt having a burn shield or 
cover thereon as shown. 
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Burn Shield 538.degree. C. 
983.degree. C. 
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No burn shield 0.37 cm 0.70 cm 
penetration penetration 
(completely 
through sample 
Nylon/glass fill 
0.18 cm 0.53 cm 
penetration penetration 
Kevlar scrim 0.18 cm 0.28 cm 
penetration penetration 
Glass scrim 0.07 cm 0.18 cm 
penetration penetration 
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Based on the results obtained, a glass scrim offered additional protection 
to belts exposed to applications where hot shots are expected.