Kayem,

All of the factors you mentioned have an impact on belt life. Unfortunately, I do not know of any empirical formulae for predicting service life for hot belts. The key points will be the temperature of the material, dwell time on the belt, chemical compatibility between the material and the belt, heat dissipation rate, and belt cover thickness.

I suggest that you contact the technical departments of those belt suppliers producing hot belts to establish guidelines of what their belts can withstand. Belt heat resistance is very compound specific and compounded rubber properties will vary from batch to batch, as well as from recipe to recipe. Also, be aware that compounds change over the years and that a belt line that has been successful for a given application in the past may not work well when the belt is replaced.

Good luck with your research. ■

There is certainly a lot of strange arguments about the temperature resistance of rubber belts. The major missunderstanding is that the temperature resistance, indicated by the belt manufacturers is usually an indication of the heat resistance of the to layer. This information is fully sufficient for common troughed belt conveyor applications. The material with the high temperature is just acting on the carrying side of the belt with the running side being cooled by air with normal ambient temperature+cooling further down on the empty return run.

In fully enclosed systems as bucket elevators are in first approach, the rubber belt is exposed to high temperatures from top and bottom side. So the whole belt including the core rubber is heating up, making the quality of the core rubber as important as the quality of the to layers. Usually one does not get any information on that core rubber quality. Hence some manufacturers belts run for more than ten years whereas under the same circumstances other belts fail within less then 12 month!

At Beumer we use high temperatures to speed up the aging of elevator belts in a controlled way in our testing laboratory. An increase of average temperature within the elevator casing nay reduce the belt life by 50%!

Another important factors is the fixing of buckets to the belt. We developped belts with cable free zones. Other than by using steel mesh belts with our belts the steel reinforcement of the belt s not exposed to air and humidity after punching the whole for the bolts in the belt. Rubber strips, vulcanised to the belt for applications in lumpy materials, prevent the belt from being damaged by parts sticking between the belt and the bucket back side after moving around the bottom pulley. etc.

So many factors influence the lifetime of the belt.

Holger ■

fOM YOUR QUESTION YOU MUST BE INTERESTED IN HANDLING PRODUCT THAT EITHER VHAS HOT SPOTS OR THAT IS AT HIGH TEMPERATURE.

yOU CAN FIND EMPIRCAL DATA IN HEAT TRANMISSION IN PACKED BEDS IN AN MC ADAMS HEAT TRANSFER , AN OLD BOOK BUT VERY PRACTICAL.

You can also use the Holman heat transfer book.

from there you can builod up your application.

Some years ago whan handling a difficult product that had hot spots up to 650 degres c.

with average temperature of 65 and with zones or lengths with temperatures at 125 ºC.

the reccomended practice at the time , some 25 years ago. Was to limit the time the product resided on top of the belt to two minutes or so ,before blisters formed on the belt, hence fast belts and mutiple transfer points.

Now to your relations ..

You will find that porous materials (Mc Adams) have low conductivity as a packed bed , ad that the conductivity is ruled by the particle size more than by the actual single particle conductivity. From there you can treat your bed as an infinite pyramid (Holman) with conduction heat transfer on the base and convectuin radiation on the upper faces, the geometry of the faces is ruled by the repose angle at the start , and is a good theoretical approach. in practuce this slope evolve into an arch.

The conductivity of the belt, being a composite structure there are no reliable data, use the conductivity of the rubber compound.

consider only natural convection, radiation in the botton face, this is not difficult with todays resourses.

Good luck.

marco ■

The information mentioned by Mr. Holger W is very important and it really matters as to how much proportion of belt (proportion of belt volume) is exposed to temperature.

The information Mr. Kayem is looking for can only be with belt manufacturers, because it is empirical type of information verified after tests and trials.

When somebody says belt is suitable to handle material of so and so temperature, the statement is highly subjective and in true technical-sense unclear. Because, the temperature effect on belt is subjective to installation conditions. The said temperature of material will affect everything within the belt, including carcass. So, the suitability of belt in totality is to be considered i.e. strength of the carcass, its elongation property, short term stretch in the belt, long term stretch in the belt, frequency of take-up adjustment, frequency of revulcanising, rubber ability to maintain desired physical characteristics, rubber resistance to chemical reactions (within rubber and oxidization etc), etc.

As the information is of business nature, possibly, the belt manufacturers may not divulge such information and will be difficult to get.

Regards,

Ishwar G Mulani.

Author of Book : Engineering Science and Application Design for Belt Conveyors.

Advisor / Consultant for Bulk Material Handling System & Issues.

Email : parimul@pn2.vsnl.net.in

Tel.: 0091 (0)20 25882916 ■