Bulk bag dischargers for tough applications.

As industries continue to move towards the use of bulk bags, flexible polypropylene bulk containers that carry dry bulk powder in weights of 500-4,000 lbs., there are more choices than ever in bulk bag discharging equipment.

Bulk bag dischargers (BBD) were designed to meet growing needs as more manufacturers in the chemical and plastics industries switch to the bulk bag handling systems for specialized applications. The containers make transporting, storing and purchasing large amounts of powder easier and more affordable without the need for large silos.

Most powder handling companies design and manufacture many different models and sizes of bag dischargers or unloaders. Spiroflow Systems of Charlotte, NC, a manufacturer of powder conveying, discharging and filling equipment worldwide, manufactures eight different bulk bag discharger models, each with an innovative design to fit the specific handling requirements. These models can be custom suited to the material characteristics and facility constraints by adding or modifying proven and dependable discharger designs. The bulk bag dischargers are engineered to safely discharge product into conveyor systems which move the material to a processing area such as a mixer or blender for batching by using a flexible screw conveyor, aero-mechanical conveyor or vacuum conveyor, whichever is most appropriate for the application.

Bulk bag dischargers are said to increase productivity and yield, while reducing wasted materials. Bulk bag dischargers are available with a number of cost effective options such as side, corner and bottom bag massage or bag liner clamps strategically located to increase material flow with minimal product degradation.

Factors to consider in selecting a bulk bag discharger

When selecting a BBD, it is important to research individual needs and how the equipment will be used. By using bulk bags there are the immediate logistical concerns that need to be answered.

Companies may first want to perform a usage analysis of the product they currently want to convey. Determine the annual consumption based on previous years' records, as well as planned consumption.

Once the consumption amount is determined, contact the powder supplier and compare prices of the different containers available, such as bulk bags, Gaylord boxes, drums and 50 pound bags. By purchasing large volumes of material, a significant discount may be offered. At this point, companies may find it feasible to purchase material in other containers that fit their needs.

Another point to consider is the logistical transportation of a material to the processing facility. Contact the carrier for rates based on the different containers to be used.

Design a storage plan that can be augmented as needs change. Bulk bags can be easily stacked to increase inventory, provided the bags are accessible by forklift.

The most important option to look at when converting to bulk bag systems is how the equipment and product will be used. The addition of bulk bag dischargers will greatly reduce manpower usage, as well as waste from used containers. Review the costs for waste disposal and employee time for a more accurate cost savings analysis.

Eight types of BBD models are available, each of which is designed to fill a particular need. All eight models can be custom designed with interchangeable options to handle specific product applications. These can be included during the initial production or can be retrofitted on site.

Bulk bag discharger models detailed

Type 2 - basic discharger

The Type 2 is the base discharger for general discharging applications. This type can be fitted with other options to meet customer demands.

Type 3 - loss in weight discharger

The Type 3 model is designed with strategically placed accurate load cells. A team of engineers developed this innovative discharger after field tests and to meet customer demands. Instead of placing the load cells on the bottom of the legs, they are placed near the middle section of the discharger. This decreases the chances of load cell damage and inaccurate weight readings.

Type 4 - knife model discharger

The Type 4 discharger is used for single trip bags. A pneumatic knife slices through the bottom of the bag which empties into a chute. Even though there is dust associated with this process, a polychloroprene liner has been incorporated on the bag dish to provide a better seal.

Type 5 - low overhead discharger

The Type 5 discharger is for use in low overhead applications where the raising and lowering of the bag using most forklifts would not be possible (figure 1). The Type 5 has a special dish assembly that allows the forklift tines to lift the bag with lower height requirements. This removable top dish is designed with a dust tight docking seal that eliminates material waste and contamination. A Type 5 bulk bag discharger with a flexible screw conveyor attached is shown in figure 2.

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Type 6 - hoist discharger

The Type 6, which is a hoist model, is perfect for applications where a forklift is no$. available to lift the bulk bags, or where a designated staging area is not suitable for maneuvering forklifts (figure 3). The unique `T' beam construction is said to guarantee a worry-free discharging station, since the lifting frames are fully load tested and are available to suit existing hoist systems.

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Type 7 - rigid bin and Gaylord discharger

Many European countries utilize the Type 7 discharger, which is designed for rigid bins. The system employs a pioneering docking station that ensures the process will be dust-free, thus reducing product waste. It can also be adopted for use with Gaylord boxes, by incorporating a knife attachment.

Type 9 - total dust containment discharger

For total containment of dust and product, the Type 9 BBD uses a patented spout sealing and stretching system that eliminates dust and ensures all the bag contents are completely discharged. Clamping the bag liner during discharging is said to ensure that no product loss or dust problems occur. The bag spout connection is a 304 stainless steel tube that clamps and holds the bulk bag neck to decrease the possibility of product loss. It contains a pneumatic rubberized seal that fits over the bag spout opening that is clamped. If a bag liner is used, the liner is clamped directly onto the metal spout. Once the connection is secured, the assembly is then pneumatically lowered to stretch the bag neck and to promote material flow.

Bulk bag discharger options detailed

Pneumatic massagers are designed to gently push the bag sides, comers or bottom to increase the angle of repose of the material, which promotes product flow.

Traditional vibration massage often causes further compaction of material, thus reducing the flowability and discharge rate.

The actual massagers are steel paddles that cannot bind or turn like the often used "V" bottom massage system. Depending on the cohesiveness of the product, the "V" massage system may bind and increase tension on the moving parts of the discharger.

The bottom massage system includes an integral bag dish which fully supports the bulk bag, while allowing the pneumatic paddles to massage it for safety. Unlike the "V" system, it securely holds the bags, up to two tons, in place. Since the bag lies directly on the dish, even if the bag loops break, the bag would be supported.

Another available option is the liner clamp system. In some cases, bulk bags have a polypropylene liner which is often a hindrance when discharging material. The liner binds and wraps in the bottom of the bag or it may bunch up and hold material needing to be discharged. A liner clamp system has been developed that holds the liner in place for the total period needed to discharge material. Since the liner is not allowed to flow with the material, there is less material waste, dust and manpower used to shake out remnants.

In spite of the existance of a specific model with load cells, the Type 3 loss in weight discharger, the company can provide them as an option for other models. In contrast to competitors, who may have their load cells at floor level, where contamination or physical damage is likely, Spiroflow engineers have placed the load cells between the bulk bag frame and the hopper frame where they are safe from pollution and possible damage by forklifts and other machinery. By doing this, the chances of receiving an inaccurate reading is said to be greatly reduced, thus decreasing material loss.

By researching individual needs, selecting a bulk bag dishcarger can be easier than expected.