Any belt catalogue will get you started. Particular issues will be providing diverter ploughs for each end and the possibility of resin bonding causing accretion along the return rollers. B ■

First task is to secure reliable discharge. Best to design for ‘live’ flow at hopper outlet.

What is capacity of hopper.?

Size of bark chips?

Length of hopper outlet?

any site constraints on height.

Lyn ■

Hello,

The conveyor length is only 35 feet (10.67 m). Therefore, you can just design this conveyor as if unidirectional, and then construct it as below (subsequently you have changed the conveyor length to 70 feet):

1) There is no need for snub pulley.

2) One end pulley will be drive pulley, the other end pulley will be non-drive pulley. Both pulleys size will be as if drive pulley. The conveyor will have DOL starting.

3) Screw take-up at non-drive end.

4) The pulleys will have crowning. The carrying run to have 20 degree or 30 degree trough which will promote aligned running of the belt.

5) The skirt board will be open at both the ends.

6) The belt force on non-drive pulley can be considered 2 x (Belt Tension T1).

7) If conveyor is inclined, then drive size will be considering material movement for uphill situation.

8) Conveyor can have full length decking plate. Accordingly both ends internal scrapers need not be there. I think bark conveying may not require external scraper. In that case, it can result into saving of 2 external scrapers also, if so decided by you.

9) The mentioned procedure is good enough for short reversible conveyor. For long reversible conveyor the design will be as per the rules as applicable for that conveyor (if not familiar with the applicable design procedure, refer to the conveyor designers).

Ishwar G. Mulani

Author of Book: ‘Engineering Science And Application Design For Belt Conveyors’. Conveyor design basis is ISO (thereby book is helpful to design conveyors as per national standards of most of the countries across world). New print Nov., 2012.

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

Email: conveyor.ishwar.mulani@gmail.com

Website: www.conveyor.ishwarmulani.com ■

A long slot outlet usually has progressive extraction, otherwise extracting from the inital section only means that the interface has to shear under a static bed for a large area. Live extraction is provided by raising the side wall clearance to allow an increasing side repose to give progressive increase in outflow. This is further enhanced if the hopper walls are inclined by also increasing the outlet width. However, this construction is not permissible normally with a reversing conveyor as the reducing sidewall gap would not allow progressive extraction in reverse.

To overcome this handicap the hopper outlet must have a parallel neck section on which is mounted a pivoting neck that swings in the direction of feed to give an increasing repose at each side in both directions of discharge. The reversal automatically moves the pivoting neck so the system is self correcting. The side profile should be optimised for proportional increase in both directions. Incidentally, the end plate should be profiled in a parabolic arch to match the stressed arch of the discharge, a feature I believe is rarely included. For further information contact lyn@ajax.co.uk ■