The Complete Bulk Bag Unloader Customization Guide

A step-by-step guide to selecting bulk bag unloader components

In the market to upgrade or extend your bulk bag unloading line? Not all bulk bag dischargers are created equal.

Need help selecting bulk bag unloading equipment?

Spiroflow Systems’ Andy Forrester walks us through some of the variations and customizations available in today’s bulk bag unloading market. From standalone, simple frame designs to high-volume semi-automated unloading systems with densifying vibration tables, bulk bagging systems can be custom built to meet a wide range of budget and discharging requirements.

Define Bulk Bag Unloading Requirements

Before starting to specify the bulk bag unloader type, options and customizations, first consider the material, process needs and bag requirements. Some of the most important considerations to ensure you end up with a safe and reliable discharging solution include:

Material properties and flow characteristics

Size and type of bags that will be handled

How the bags will be handled (Fork Truck or Hoist)

Headroom/space constraints

Weighing/batching requirements

Downstream process requirements

Bag removal and disposal

Dust containment

Hygienic requirements

Step 1: Understand the Material Characteristics

There are a wide range of material characteristics that will impact the eventual design of a bulk bag unloader with some of the most critical being:

Material Type – Dust Containment

Some materials can be harmful to both operators and the environment so different levels of dust containment and operator protection can be a major consideration.

If materials are hazardous or corrosive additional seals can be incorporated between the bulk bag and discharger to minimize the risk of any dust escaping. Several different dust seal designs are available depending on the design of the discharger. A rubber membrane dust seal within the base of the unloader and peripheral double dust seal (ideal for single-trip bags that contain dusty materials) can be used to contain dust created as material flows from the bag.

In some cases a completely sealed “Glove Box” untie chamber could be the best solution, in other cases an untie chamber with dust collection and flow control devices may be sufficient. For an additional level of protection an “hygienic spout connection” can be incorporated to better seal the connection between the bulk bag and the downstream process. This is achieved by clamping the bag outlet spout to a custom spigot prior to initiating material flow. All this occurs within an enclosure that can be maintained at a negative pressure throughout critical phases of the discharge process.

Dust collectors can be integrated into the bulk bag discharger frame so that the dust drawn away from the emptying bag can be reintroduced to the system just downstream of the bulk bag outlet, thus minimizing product loss.

Explosion Proof/Hazardous Options

When discharging bulk bags of combustible material or when working in explosion-rated areas, various additional steps can be taken to protect operators and the equipment itself by using a discharger designed specifically for these circumstances. These options are available to meet any area classification and include features like, explosion proof motors, pneumatic vibrators, intrinsically safe sensors and static grounding and monitoring systems.

Material Flow Characteristics

Flowability will determine if flow aids are required and their type. Various designs are available ranging from different types of paddles or massagers to vibration, mechanical agitators or air ‘pads’ and ‘sweep” systems.

Some materials will agglomerate in a bulk bag to the extent that they will still not discharge using typical flow aids. In these cases, a bulk bag conditioner may be required to break the set of material and reduce the size of large lumps thereby allowing a bulk bag discharger to empty the bag. These units can be of a stand alone design or can also be incorporated into some discharger designs.

Step 2: Knowing your Bag Specifications

If you are a high volume consumer of raw materials in FIBC’s you may be able to influence the specifications of the bulk bags that your products are supplied in, however, if your supplier only offers a particular style of bag it is critical to understand certain key parameters.

Dimensions

Determine if the base dimensions are within the typical range of 35” x 35” to 41” x 41”. If the dimensions are outside of this range a smaller or larger bag support (dish) and a larger frame may also be required. In addition to the base dimensions the range of side seam heights of the bags to be handled also needs to be known as this will determine the height of the discharger structure and whether space saving options need to be considered.

Lifting Loops

There are two main styles of lifting loops, lay flat and cross corner and both are normally compatible with standard bag lifting frames but the details should always be confirmed to ensure a safe and reliable fit and if any customization is required.

Liner/Sealing Requirements

Determine if the bags that will be used will incorporate a liner to prevent the ingress of foreign materials or moisture into the bulk bag or to prevent the egress of very fine powders through the fine stitching and weaving of the bulk bag.

The two primary types of liners used in FIBC’s are “From-fit” or “Loose Tubular”. If the bag will have a loose tubular liner there are different types of ‘liner tensioner’ that can be used to either hold the liner in place as the bag discharges or partially wind up the liner as material flows out of it to prevent the liner from exiting with the material and becoming entangled in downstream equipment.

Base Construction

Not all FIBC’s incorporate a discharge spout so knowing the details of the base construction of the bags that will be handled is critical to the design of the discharger.

Outlet spout: If the bag has an outlet spout what is the diameter and length? These details will be critical to ensure the correct operation of features like spout closure bars and hygienic spout connections.

Flat bottom: These types of bags, often referred to as single trip bags, require a purpose-built knife to cut the base as it is lowered into the discharger. Note it is critical safety feature that an operator is not required to reach under a suspended load to manually perform this function.

Conical bottom: Usually, a standard discharger can be used with this type of bag, but care must be taken to ensure that the ties that secure the cone during shipping can be safely released once the bag is lowered into the discharger.

Step 3: Bulk Bag Handling Requirements

Determine if the bag will be placed into the discharger using a forklift or if the bag will be moved to the discharger where a motorized hoist and trolley will be used to load the bag. Depending on the situation, this will determine what type of discharger frame is required.

Bag Weight

The filled weight of the bulk bags must be assessed to confirm the bulk bag discharger frame design will safely handle the upper limit. It will also define the capacity of the hoist and trolley required if a monorail style discharger is being considered.

Step 4: Determining method of downstream Material Transfer

How will the material exiting the bag be handled? There are two common types of feeds for material exiting: gravity feeds and conveyor feeds.

Gravity feed: material falls from the bulk bag discharger into a vessel or container.

Conveyor feed: a mechanical or pneumatic conveyor is fed by the discharger. Many conveyors are not suitable for being flood fed directly from the discharger so the design will need to allow for a metering device such as a rotary airlock valve or similar to be installed between the discharger and conveyor.