Hi Puneet,

Gravity loads are easy to calculate - what you see is what you get - belt weight, plus product cross section area with surchage times estimated bulk density.

Impact loads are more complex. That is because you are dealing with dynamic forces and trying to relate those back to static load design criteria. Mass times drop height will give you an estimate of the energy being dissipated. Mass times acceleration will give you force. To do that you need to know the acceleration at the point of impact.

Look at the free conveyor design spreadsheet on www.cospire.com / Engineering Tips / Bulk Solids. There is a worksheet page which allows you to estimate acceleration down a slope. Once you have a fair estimation of that then

---- Force = Mass X Acceleration

You need to look at the design of the transfer chute to decide how acceleration due to gravity is reduced by friction. I doubt you are looking for a very precise value for your design decision. A reasonable estimate should be adequate.

Regards - John.Rz

www.cospire.com / Browse / Engineering Tips / Bulk Solids ■

Dear Shri Puneet,

Generally one needs to find out the load on usual carrying rollers, return rollers and impact rollers. These loads are to be found out on following basis :

- Carrying Idlers : The load value considering idlers vertical alignment is perfect. That means vertical up/down misalignment is zero. In this situation, the load on idler set would be gravity load due to belt, gravity load due to material, and self weight of the idler rollers. The load on middle roller and load on side roller would be different. For 3-rollers of equal length, the load on middle roller happens to be the largest and bearing and spindle sizes requirement is governing.

The idler set vertical placement can never be perfect. There would be certain up/down misalignment as a part of tolerance in manufacturing of idler set, tolerance in fabrication and erection of supporting structure. In this case, the load on the idler set and thereby the rollers will be of higher magnitude. This load is to be found out considering the expected up/down misalignment value and the forces occurring accordingly.

The load on middle roller will be approximately proportionate to the cross section area intercepted by middle roller. The load on side rollers would be due to vertical downward gravity force of belt weight and roller weight. The load due to material will be as a result of gravity force on material plus material spread thrust in horizontal direction. The material side thrust calculation has been described in my book on belt conveyors. These forces action points are to be decided and then force shared by each of the bearing is decided.

- Return roller : The return roller could be single roller type or two roller V type. The return rollers will be subjected to belt gravity force and roller self weight. This is to be also analysed considering no vertical misalignment and alternatively considering idler vertical up/down misalignment in accordance with the tolerance of the idlers, structural fabrication tolerance and installation tolerance.

- Impact idler : The force coming on the impact idler has to be decide on two considerations (1) Gravity force acting on material layer and the self weight of the roller. In addition it is subjected to material pressure force arising due to change of momentum. (2) When the material being handled is lumpy, the extreme force may arise due to impact by lump and force arising in arresting its velocity. This will be related to the effective stiffness at belt surface as a result of belt, rollers and deflection of the structure.

The exact method to calculate these forces is complex and it is not possible to do further narration here in this matter. In fact, I am writing a book on idler design wherein the calculation procedure to decide the idler loads, selection of bearing, spindle size etc. would be described. This is likely to be in market by year end.

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.

Pune, India.

Tel.: 0091 (0)20 25871916 ■

Dear Puneet,

We require some datas to calculate load (CIL: calculated idler load) on rollers, such as: belt weight, capacity, belt speed, belt tension, spacing of roller (carry, impact and return), and impact load for impact roller.

If the above data are already known, we'll get material weight and idler misalignment and finally load on conveyor roller.

Regards,

Endri ■