What is the best mechanical conveyor for fragile materials?

President Bill Gorsline was asked by Powder Bulk Engineering to provide insights on what the best mechanical conveyor for fragile materials is for their Supplier’s Tips feature in the July issue of their magazine. Below is an unedited version of what appeared in the magazine.

Whenever a customer describes their product as “fragile” we will first establish exactly what they mean by “fragile”. We find the best way to do this is by understanding the nature of the damage that the material may be susceptible to.  Although simple breakage of the material is common, surface damage such as scoring and degradation, causing dusting in dry particles, are also frequent concerns.  Once we establish what the customer is needing to avoid we can pretty quickly make an equipment choice and recommendation.  Here’s how we do it.

For practical purposes, there are two causes of damage to materials while being conveyed.

1. The free fall of product or more specifically the sudden stop when it hits something solid, this is usually found:

• Where product is being fed into the conveyor and/or
• Where the material is be being discharged from the conveyor and
• Transfers between conveyors

2. The occurrence of relative motion between particles and/or between the particles and a stationary conveyor component  as a part of the conveying process i.e. while in the conveyor.  Three examples of this would be

• Drag type conveyors where the material is being pushed through a tube by a continuous flexible flighted driving component (usually chain or wire rope)
• Vibratory conveyors with short  amplitudes and high frequency
• Vertical bucket elevators where product is being fed into the casing and scooped out of the boot by the buckets and then discharged by a combination of gravity and centrifugal force at the top.

Conveyor types that are going to provide the gentlest possible horizontal and incline conveying for fragile materials are:

1. Belt conveyors including flat belt conveyors, troughed belt conveyors, corrugated wall belt conveyors, cleated belt conveyors (inclined), here’s why:

• Free fall at the infeed can usually be brought to an acceptable minimum
• Once the materials are on the belt there is no further relative motion generated so no degradation during conveying
• Just as at the infeed, free fall at the discharge can usually be controlled.

2.Long amplitude and low frequency “vibratory” conveyors where the product is gently move forward by the conveyor and then the tray is quickly brought back to the starting position without bringing the product back with it and without damaging the material as well. Limited to horizontal conveying only.

• As with belts, free fall at the infeed can usually be brought to an acceptable minimum.
• Just as at the infeed, free fall at the discharge can usually be controlled.

3. “Z” type bucket conveyors including “C” configuration conveyors, interlocking bucket and pivoted bucket designs, where the conveyor is capable of carrying materials both horizontally and vertically without transfer. (some conveyors are capable of travelling  in three planes without transfer).  For horizontal and incline use, only the horizontal sections are used.

• As with belts, free fall at the infeed can usually be brought to an acceptable minimum
• Once the materials are in the bucket there is no further relative motion generated so there is no degradation during conveying
• Just as at the infeed, free fall at the discharge can usually be controlled and some interlocking bucket designs use a cascading discharge further reducing free fall.

For all the reasons given previously, when it comes to vertical  conveying, the “Z” type of bucket conveyor will be the best choice to handle fragile products whether in a “C” configuration, whether using  an interlocking bucket design or a pivoted bucket, the product can be elevated without damage, degradation or spillage. For more information on how we can handle your fragile materials, please contact our application specialists.