The takeup unit has to do with belt stretch and adjustment after splicing. If you calculate the total belt lenth and divide it by two that tells you the length of belt subject to stretch. This is usually near enough equivalent to the length between head pulley and tail pulley.

Then you ask your belt Vendor how much will the belt stretch under a given load (your return belt tension T2). That will give you one end of the required stretch. As you repair the belt you will cut bits out of it and reduce its length. So the required adjustment will vary from time to time.

Note - the belt will also stretch on the tight side (under the pull of T1). ■

John- is he referreing to the stretch distance length on the hydraulic or gravity take up at start up and operating weight with load?

leon Z ■

I can give you a proper answer to this question.

The required tension length has to do with the elastic elojgation as well with the permanent elongation.

The elastic elongation of a belt depends on the kD factor.

A belt with an elongation of 12,5% before breking hads a kD factor of 100/12,5=8

In the situation that the conveyorbelt operates with a safety factor of 12,5 the elastic elongation is 12,5% / 12,5 is 1%.

This value is the maximum tension that is in the area close to the drive pulley.

The evarage tension over the entire length of the conveyor including the return part of the belt might be for instance 3% of the breaking strength.

In tis case the elongation is 12,5%*3%=3,75 promille of the entire length of the rubber belt.

The travelling length of the tension trolley is half that length.

Not only the elastic elongation is a factor to take into acount. Teh permanent elongation of a belt even is a grater factor. This value is appox. 1% but strongly depends on the quality.

Normally 1,75% should be sufficient for a EP belt as long as the vulcanising has been taken place under the conditions with correct a pre-tensioned belt.

Your questions both with respect to the elongation and required pulleys are very basic.

There wil be a lot more questions to be answered before you have the desingn criterae to build a conveyor that will satisfy your requirements.

I can be of help if you give me all the available information.

Kind regards

Johan Brands ■

In addition to all other earlier answers, when calculating a take-up distance, especially with short conveyor systems where the belt will not stretch too much, please allow enough room in the tail end tension to allow for a good transition distance. This is the distance from the tail end to the first set of rollers. The area of belt in the centre stretches at a dfferent rate than the belt on the edges (it has less distance to go) and so if the transition distance is too small, various things can happen. The edges of the belt will be over stretched and so tracking of the belt will become more difficult in time, you can get a 'w' effect in the centre as the belt edges try to push down into the centre where the route is shorter and all this leads to a shorter life of the belt. There are various things you can do to counter this such as reduce the degree of trough for the first set of rollers, or raise the tail drum a little to make the distance the same for the middle of the belt as it is for the edges, but far easier to just make sure that you actually allow for this in the design stage.

if you require further info on this, just get in touch.

Stan Holcroft,

Regional Sales Manager,

Fenner Dunlop B. V.,

The Netherlands.

stan.holcroft@fennerdunlop.com

www.fennerdunlop.com/europe

Tel (office) +31 512 585 565

(mob) +31 620 49 88 29 ■

The length of take-up(TUP) also depends on if you wish to allow TUP motion without hitting the end stop. A conveyor can accumulate significant quantities of belt along its length due to vertical geometric depressions that can cause large belt sag between idlers in transient low tension zones. The sag comes from belt stored in the TUP tower.

This extra travel can easily exceed the elastic and thermal stretch previously eluded to.

If you let the belt hit the stop or limit its travel, you will introduce a shockwave that will amplify normal belt line forces. The degree of amplification will vary with the degree of sag and TUP velocity.

This amplification can be many times the force at steady-state.

Let out too much belt and you get spillage, misalignment, and belt entanglement in the idlers. ■

For the general information of the readers.

The earlier respondents have already given most of the information about the take-up stroke etc. I would like to add following information, which has certain relevance to the take-up stroke and also for the belt length to be considered for estimation / procurement.

The present day belt conveyors are designed mostly for 1% sag of belt. The belt conveyor design for 1.5% or 2% are also not uncommon. The belt in conveyor installation will have the actual length depending upon the sag being adopted. The increase in belt length attributed to the sag % values are as below :

For 1% sag : 0.008% (i.e. nearly 125th part of 1%).

For 2% sag : 0.08775% (i.e. nearly 11th part of 1%).

For 3% sag : 0.2208% (i.e. nearly 4th part of 1%).

For 4% sag : 0.407% (i.e. nearly 3rd part of 1%).

The stated increases are with reference to geometrical length without considering the sag.

The calculations are based on arc and chord length as per American handbook.

In a belt conveyor installation, if there is gravity take-up, then say belt tension will be same as take-up tension, in entire length of conveyor. This will result into certain sag %. Now, when the belt is running, the tension particularly on carrying side will become more. This means the average sag % on carrying run will reduce. Similarly, the average sag % on return side will also slightly differ. The situation as above will result into release of certain belt length, which is to be absorbed by the take-up.

If the conveyor is equipped with fixed location winch take-up, then the implication on belt extra length to be taken care by winch take-up tension setting.

I had made the analysis as above very long time back to understand the implication of this situation for the procurement of belt length, effect on take-up stroke etc.

It is very difficult to give generalized opinion but as it appears if the belt sag fluctuation remains within 2% then this issue does not have practical effect on take-up stroke. The usual take-up stroke being adopted as certain % of centre to centre distance, by various standards and practices, seems to be adequate inclusive of above phenomenon.

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 ■