1. Ben Paton Guest

## Belt Weigher Inclination

Hi all,

I have a question about effective weighing length of a Belt Weigher on an inclined conveyor belt.

The weigher is a single idler mounted midway between the lead in and lead out roller, with a spacing of 1200mm. If the belt was flat this would give an effective weigh length of 1200mm.... no problems. The belt however, is on an incline of 12.5 deg.
Does this change the effective weigh length of the beltweigher?

The load cell is mounted perpendicular to the conveyor, but the test weight (185.3kg) hangs vertically from the weigh frame.

Any help would be appreciated.

Regards,
Ben Paton
Technician, BHP Steel
Port Kembla, AUS

2. ## belt weigher

This is seen as a matter of mechanics rather than involving any feature of weighbelt mechanism. The inclination will influence the effective force acting on a measuring device that is responsive to forces measured at 90 degrees to the belt.

The weight on the belt acts vertically, so the normal load of a uniformly distributed run of material that acts on the cell at 90 degrees to the belt will be the resolved force, at this angle of slope, of the value that would act were the belt to be horizontal.

The measured resultant weight acting on the cell therefore should be multiplied by inverse of cos 12.5 degrees, or 1.0196.

The difference is relatively small at this angle, but is significant, so it may be useful to load the belt with a run of weights to check the stiffness of the system if this is practical.

Lyn Bates

3. p w chase Guest
there is also the problem on an inclined conveyor that belt tension arising from the material transported by the belt can have an effect on the weighing system. That effect is primarily from the last fixed idler to the first weighing idler and from the last weighing idler to the next fixed idler. With a single idler scale all of that effect is transmitted to the load cell---with a multiple idler scale the effect is smaller because the belt only enters and leaves the weighing area one time.

P W Chase

4. Hello Mr. Ben Paton,

Mr. Lyn Bates has already explained about the effect of inclination of belt weigher. The belt weighers installation on inclined belt conveyor is a routine matter, and it doesn’t cause any problem. The belt weighers are also installed on luffing boom where inclination is varying. The belt weighers on such booms, automatically take into account the inclination value as applicable and gives the correct result.
Only precaution to be taken for belt weigher is, it should not be installed in concave / convex curvature of the conveyor, where it’s result shall be affected by tension in the belt.
I suggest you may interact with the belt weigher manufacturers.

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

5. ## RE: Inclination

There is still another consideration when weighing material on an incline. By changing the inclination, the angle of repose of the material must not be exceeded. The belt scale can accurately determine the speed of the belt, and the material travelling on the belt must settle to the same speed. Material slip can make a terrible mess on a conveyor, but it is even harder to weigh material that is not stationary relative to the moving belt.

6. I appreciate the issue mentioned by Mr. Todd Dietrich. The material slippage on belt is prohibited except as occurring at loading point. The material continuous slippage on belt signifies non-operative or highly objectionable system.

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

7. I am not sure answering a 1.5 year posting is sound. However, others raise points that are debatable in accepting in as factual.

Hendrik Colijn submitted much of his Delft Master's Thesis, with support from the weigh scale community on this subject, through Dr. Wolbier's Bulk Solids Handling publishing company with a tome on Weigh Scale design in 1980's. I am sorry that I cannot bring the title details to mind. I believe a search of BSH publishings will reveal the references. He later published articles in BSH journal on the same. He dealt with incline belt and weigh scale errors from theory and field measurements. Some of these are related to:

1. Material (product) apparent velocity that differs with belt on higher inclinations with mass flow errors from internal friction and cohesive friction.

2. Material apparent velocity that differs with belt due to product shape such as prill like material or areated material like cement that may be a combination of internal rolling and sliding properties and belt to product kinematics.

3. Belt line shape between idlers on inclines are not simpe catenary but a complex hyperbolic shape with many parameters that alter the belts deflection and scale readings at the weigh scale monitor point such as: trough angle influence, belt orthotropic structural elastic stifness properties, and so on.

4. Idler shape errors and pulley shape (buildup) errors that cause logitudinal vibration that can induce errors in mass flow between scale point (carry side) and belt velocity measured point (usually on return strand).

Henk has many references to site studies and others have referenced in this area. THerefore, I recommend to be cautious in using the general comments of accuracy in this or similar applications. Much more needs to be evaluated.

Lawrence Nordell
Conveyor Dynamics, Inc.
www.conveyor-dynamics.com

8. I've just joined the forum and I see this question was placed some time ago... however. I always reduce the effective length of the weigh area by multiplying the length of the weigh area by the cosine of the angle of elevation of the conveyor.

Regards
Jon