Your request is not clear. You note the takeup will move upwards against gravity during starting, when in fact, it will fall when the belt is stretched from the acceleration force. ■

There are many factors that determine the amount of movement that a gravity take-up will go through during a start up.

Your designer should have given your the maximum travel distance of the carriage as well as a positioning of the carriage during startup.

As Larry has already stated the carriage will fall as the belt stretches and then rise again above the (not running) resting point and eventually settle to the running position.

In order to determine the total amount of carriage movement in a vertical take-up a complete analysis would need to be done on your system.

Conveyor belt elongation consists of two type of stretch, permanent & elastic. Permanent is the stretch that occurs during the first few weeks of operation of a new belt and elastic is the normal stretch that a belt undergoes during normal operation of the system. Take-up travel is usually calculated based on a total of these two factors. ■

As per literature i had read, the bottom of the counter weigh box should be at a height of approximately 2.0 mtr from ground level.

But in some cases, the length of belt loop in take up structure is so large, that flapping of belt has been observed.

So, as a thumb rule, the length of belt in take up loop should be equal to 3 times the belt length required for one joint.

All above facts are my own experience.

Please tell me any suggestions regarding this.

Regards,

Dilip Gohil ■

Dear Shri Ramesh babu,

You have 90 m long conveyor equipped with gravity take-up. If you do not wish to go into elaborate design steps, you may adopt following suggestions.

1) The take-up system to be mounted in a 4 legged trestle. The gantry from both ends will be resting on both the sides.

2) The trestle will have top member to provide support to the gantry.

3) The take-up guide will start below the bottom of the top member of the trestle.

4) Locate the upper position of slide frame such that there is clearance of 0.8 m to 1 m along guide at top level.

5) Accordingly, position the take-up slide frame to suit the take-up travel.

After erection, you will find that the clearance at upper level is somewhat more than the above value. The specific design analysis will consider the variation in belt length and take-up travel during operation of the conveyor, belt length elongation / contraction due to daily temperature variation, etc. The belt permanent elongation will tend to lower the slide frame and thereby increasing the clearance at upper level. Therefore the same will not influence the minimum required clearance.

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 thing to consider is the ability to extract the pulley or plough, should the need arise. With the take-up weight chocked up in the framework the bracing can often impede/prevent equipment removal. ■

Further to my earlier reply, the information about thermal expansion coefficients for certain materials concerning belt are as below :

Steel : Thermal expansion coefficient 10.8 x 10 E -6 per unit length per degree centigrade (i.e. 10.8 / (1000 x 1000)).

Polyester : Thermal expansion coefficient 65 x 10 E -6 per unit length per degree centigrade.

Nylon (Polyamide) : Thermal expansion coefficient 80 x 10 E -6 per unit length per degree centigrade.

The value of coefficient for steel is as per engineering books. Polyester and nylon values have been obtained by reference to Polymer Engineer Mrs. Anagha M Khare (Pune). There are marginal differences in stated values for different types of polyester / nylon, but by large the values are as stated for most of the types.

The coefficients are for solid material (without buckling etc.) These materials in belt carcass have twist / waviness which would possibly tend to moderate the effect.

Very exact values can best be informed by belt manufacturer, in accordance with specific type of material being used by the concerned party and the specific values in context of belt. If other readers have more specific information, and if it is not of proprietary nature, the information is welcome.

It would be observed that if the material being conveyed is at ambient temperate and take-up is of floating type, the effect of thermal expansion will be limited to keep certain provision in take-up travel. The take-up force will remain as per counter weight if there is contingency for it to move freely at either end in response to the temperature variation.

Say conveyor length : 500 m

Daily temperature variation : 35 deg C (i.e for the belt proper).

The change in belt length if it is steel cord type : 10.6 x 500 x 2 x 35 / (1000 x 1000) = 0.371 m

The implication at take-up : 0.1855 m.

The take-up total stroke at the rate of 0.35% : 500 x 0.35 / 100 = 1.75 m (this is not take-up travel at a time)

The take-up frame movement due to temperature variation, as a % of total stroke : 10.6 %

The variation in belt length, due to temperature effect : 0.0371% i.e. 1/27th of one percent !

If the belt happens to be of EP construction, the take-up stroke is 11.25 m and the above variation at take-up will be 1.116 m i.e. 9.92% of take-up total travel. The change in belt length will be less than 1/4th of 1% !

If the take-up position is done during evening time (say midway of extreme limits), the implication will become half. The belt will acquire material temperature. Often the material temperature will not acquire the ambient temperature, but will remain fairly stable irrespective of ambient temperature (say material excavated from the mine or stockpile, etc. reducing the actual effect).

If the conveyed material is at artificially created temperature hot or cold, then implication will be as a difference of conveyor running empty (for some time during regular operation, trial, commissioning, etc.) versus when it is at operational temperature.

The information will be of interpolation to readers by large. The use of the information is subjective to the specific application.

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 ■