I think more details especially about the operating conditions and general geometry of the proposed conveyor will be required before any suggestions can be made.

1. You mentioned the crumbs will be fed into a kiln. What is the temperature at the discharge point of the conveyor and how will the crumbs be introduced into the kiln?

2. I doubt the material is free-flowing, so you will quite probably require a mechanical feeder at the base of the hopper to balance the mass flow. Also one would need to know the drop height of the material on the conveyor.

3. Do the steel cords on the crumbs protrude and if so, are they frayed and might become snagged in a steel mesh for instance?

4. Will be conveyor be horizontal, inclined or regenerative (i.e. declining angle)?

5. What is the length of the proposed conveyor and are there any width restrictions?

6. Some photos of the existing equipment and site will be helpful.

We are a company operating out of KL so feel free to call me at the following numbers should you have any questions.

Best regards.

Barry Chung

03-8062 6686

012-386 6812 ■

The chopped rubber pieces have a high wall friction value, high internal friction and strong interlocking characteristics, so an effective design of the interface of the hopper with the belt feeder is crucial to secure reliable discharge from the hopper and a consistent density of the output. It is also desirable to minimise the drag-out forces, which means avoiding a high overpressure on the belt under the hopper outlet. These objectives conflict to some extent, because if the orifice is oversized it will give a high down pressure through the outlet but if undersized the material will arch and not flow out.

Experience would suggest that for a material of this lump size and nature of external surface a fully live outlet of a mass flow hopper with a 500mm minimum width of slot opening would not form either a structural or a cohesive arch. It is normally recommended that the outlet length should be at least three times its width, but in this case I suggest that an opening 1500mm would give useful benefits of a better extraction profile and lower total overpressures.

Turning to the detail, a lower Vee section of hopper with wall angles at about 70 degrees to the horizontal should be adequate to promote wall slip on smooth mild steel. This should extend to a height of 1200mm, where an cross section 1500mm square would give a Vee wall angle of 67.4 degrees. Above this the four wall of the hopper could diverge in a pyramid shape at 60 to provide the require holding capacity because the material will not arch at this transitional cross section and the nom. 51 degree gully angle will self-clear. Should a rat hole develop it could be disturbed with a vibrator fitted with a tuned active reed. A small, side mounted, inverted Vee insert in the hopper would not be amiss in the upper section, to reduce compacting pressures in the transition region and provide hoop stress relief in the upper region, provided that the flow channel was not restricted to less than a meter wide.

A key feature of the interface with the belt is that there should be a diagonal crank in the lower Vee section of the hopper from the back end to a 300 deep outlet at the discharge end. The sides are made up with triangular shaped vertical terminal walls, to form a taper outlet from 500 to a 750 wide opening.

A belt 1000 wide with slightly diverging side skirts would then suffice, travelling at nom. 2.5 to 3 M/min. should deliver the required output. The overall belt length would then be about 3M centers, unless further length transfer was required.

It would be helpful to conduct wall friction tests to verify the slip value. Arching tests are more awkward because of the dimensions involved but the saving grace is that there are many fairly simple rectification options available in the unlikely event that problems arise. I trust these notes are helpful and would give an efficient and economical construction.

Lyn Bates

Ajax Equipment ■