Greetings from the soon to be frozen "Eastern Wilderness" @1140 feet above mean sea level,

The quickest way to tell is with amperage measurement, as this will tell you if there is a build up of fines under the drive unit or a buried tail pulley etc.

You have to remember that the drive motor or motors are just plain dumb and all they are doing is converting electrical power into mechanical force. All the idlers are doing is moving from friction and the more friction the more load/amperage.

You need to establish a base line measurement as far as amperage with no load and a measurement with a full load. ■

Here are a couple of articles that talk somewhat about the affects. In addition to Leon's comments, seized idlers can cause belt mistracking, premature belt wear and is also a possible fire risk.

http://www.saimh.co.za/Beltcon/Beltcon4/paper419.html

http://www.saimh.co.za/Beltcon/Beltcon9/paper918.html

Regards,

Gary ■

OZbos,

There are many affects;

a) Belt Tracking: Particularly if the jammed idler is in the low tension zones, result belt edge damage and spillage

b) Belt Rip: If the jammed idler is there long enough the belt will abrade a hole in the shell, this in turn becomes an excellent sharp knife for slitting the belt end for end

c) If you have enough it can affect whether the drive can start the belt. I have had one extreme example on a regenerative belt (4000 HP motors installed) which was designed to start under its own inertia and totally failed to do so causing enormous problems all because of seized or sticky idlers

Col Benjamin ■

Probably the main reason for stalled idlers is carry back from the conveyed material. To reduce the frequency of return idler failure, it is imperative to provide the best belt cleaning possible at the head pulley. ■

Dear Mr. Ozbos,

The jammed idler will certainly affect the conveyor performance. This will depend upon how many percentage of rollers are to be considered for jamming. In general, conveyor maintenance and operation should ensure that the large scale jamming of idlers should not occur.

In short if all idlers are jammed then motor will get over loaded, motor will trip, conveyor will stop. If conveyor doesn’t stop the belt and jammed rollers will get worn out and it will lead to replacement of many items. Even belt will start slipping on drive pulley. So it is all round damage.

If very small percentage of idlers (rollers) are jammed, then this should get detected at least in one shift operation. Then these jammed idler (rollers) are to be replaced. As for the conveyor operation with jammed rollers, the belt will suffer some degree of wear and jammed idlers will be further damaged.

It is understood that jamming implies stalling of the idler (zero rotation).

Regards,

Ishwar G Mulani.

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

Author of Book : Belt Feeder Design and Hopper Bin Silo

Advisor / Consultant for Bulk Material Handling System & Issues.

Email : parimul@pn2.vsnl.net.in

Tel.: 0091 (0)20 25882916 ■

Another point or two:

How much power will a frozen roller consume given the contract coefficient of sliding friction to be cf= 1.00?

Assume a belt 1200mm wide, running at 3 m/s, handling 2500 t/h with a bulk density of 1.6 tons/cm, idler spacing of 1.4 m, surcharge of 20 deg., and center roll load of 70% of crossectrion. Then, the power of a frozen center roll is approximately:

= 2.509 kN/m x 1.4m spcg x 0.7 ctr roll x cf=1.0 x 3 m/s = 7.4 kW

Other carry and return rolls will have lower values.

We can quickly see a frozen center idler roll will have a greater influence on short conveyors when the effective demand motor power is below 75 kw or the roller drag becomes greater than 10% of demand.

Longer conveyors with greater than 100 kW will suffer, but can still run under the same center roll seizure.

Wing and return roll seizures will have less influence on power but more on belt mistracking and may shut the conveyor down from off-center belt travel. ■