The problem

The requirement was for a big bag discharge system that could transfer a specified weight of silica sand from a bulk bag to be mixed with liquid ingredients and fed into the production system. The batch measurement had to be extremely accurate and ran alongside a liquid feeder for very precise recipe formulation.

It was important that production didn۪t stop when the bag was empty.  Therefore a buffer capacity۝ was required to ensure that the feed was continuous even when the bag ran out and was in the process of being replaced.

In addition, the customer needed to be able to swap bags from one material type to another before the bags were completely empty.  A facility that would enable the bag to be closed, tied securely and replaced was a necessary part of the system.

The solution

Guttridge sales engineers and designers worked closely with the customer to create a custom-built bulk bag discharge system comprising an FIBC with bulkflo to elevate the material into a small loss-in-weight weigh hopper.  A small tubular discharge screw then transferred the specified weight of material from the weigh hopper into the mixer.

Guttridge specialise in using state of the art technology alongside our 50 years of experience to successfully define material properties such as angle of repose and bridging dimensions.  In this example such data dictated the ideal hopper angles and the exact requirement in terms of vibrators and massagers to ensure that the correct material flow was maintained from the bag and from the bulkflo hopper into the weigh hopper.

The FIBC is loaded by means of a hoist that lifts the bag onto the frame.  Massagers and vibrators ensure that the bag is agitated sufficiently so that flow is maintained and the bag empties correctly into the bulkflo hopper.

 The bulkflo hopper is also fitted with vibrators to ensure that the material doesn۪t bridge or stick to the sides of the hopper.  The hopper serves to act as buffer۝ to ensure that flow to the weigh hopper and the production line is maintained even if the bulk bag empties.

The bulkflo also comprises a sack tipping point if a smaller amount of product is required to top up the hopper.

The weigh hopper is filled from the bulkflo and operates on a loss-in-weight basis to supply small and extremely accurate batch sizes into the mixer to a weight specified and entered by the machine operator.  If the batch required is greater than the amount in the weigh hopper, the weigh hopper stops feeding out and the bulkflo starts and refills, feeding the weigh hopper the extra material required to meet the required batch size.  The weigh hopper then restarts and continues to complete the precise batch weight.  The weigh hopper can weigh to an accuracy of +/- 1% and the exact weight of each batch is recorded for future reference

The machine also features a throttle bag closer that closes onto the bulk bag above the bag ties.  This holds the material in the bulk bag securely while it is tied closed.  Once the bag has been sealed, the access doors are closed and the throttle bag closer is released so that the bulk bag can be removed from the FIBC.  This is extremely useful to the customer because bags are often changed prior to emptying completely.  The throttle bag closer ensures that this can be carried out easily and without any spillage.

Benefits to the customer:

• The process stream is maintained and not halted when the bag runs out of chemical.
• Very accurate batch weighing, including batch weight recordings for future reference.
• The system is built specifically for the chemical it is required to handle to ensure optimal flow.
• Bags can be interchanged and removed safely and easily from the discharger without spillage.