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Selecting a Bulk Bag Discharging System

Dust control in material-handling equipment is achieved using a bag spout access chamber.
Pneumatic bag spout clamping system

The popularity of flexible intermediate bulk containers (FIBCs), also known as big bags or bulk bags, has grown significantly over the past few decades. This development is largely the result of advancements in weaving technologies and the widespread use of an extremely durable, recyclable material called polypropylene. Woven polypropylene bulk bags are generally less costly for packaging and transporting bulk materials than traditional methods.

Companies that handle powdered bulk solids on a regular basis likely face the challenge of selecting a bulk bag unloading system that meets their application requirements. Choosing the appropriate system can be a daunting task. While many manufacturers offer basic unloading equipment, only a few can design systems to meet specific
application requirements.

The most critical items to consider when selecting a bulk bag unloading system are the unit’s capabilities and quality. End-users must consider capability thoroughly before investing in new equipment. Because of their great experience, quality suppliers of material-handling equipment know what questions to ask to help users determine their application needs. Most bulk bag unloading systems look the same from a distance, but in general, their benefits and capabilities differ.

The process of bulk bag unloading is much more complicated than simply emptying a bag. For example, how significant is dust control? Many materials are irritating to breathe, hazardous, explosive, or extremely expensive, making proper material handling and dust control not merely desirable, but crucial. The highest level of dust control is achieved by utilizing a dust-tight bag spout access chamber. This feature discourages material spillage; when combined with a rear-mounted dust takeoff stub, it provides more-effective dust control than systems lacking this feature. Optional dust collection systems can collect dust generated at the discharge point, return it to the product stream, and draw dust generated during disconnection of the bag discharge spout away from the operator.

An even more sophisticated approach is to use a bag spout clamping system within the bag access chamber. Although designs vary, some manufacturers have been known to use specially formulated seals and pneumatic cylinders to dock the bag discharge spout to a fixed outlet transition housed within the access chamber. This type of system provides dust-tight unloading, allowing easy discharge of dusty or hazardous materials. Operators often find pneumatically actuated spout clamping systems easier to use than manually actuated versions.
Another crucial equipment feature is the ability to obtain complete product discharge from the bulk bag. Because companies commonly switch to the use of bulk bags to save money, complete product discharge is necessary to maximize cost savings. Several flow-promotion techniques have been used to promote complete product discharge. However, some have worked very well while others have been completely ineffective.

Heavy-duty construction is necessary for ensuring the quality and durability of material-handling equipment.
Heavy-duty massaging systems are used to remove especially challenging materials from bulk bags.

If the end-user’s material is especially challenging, the material-handling equipment should contain an aggressive massaging weldment with an open pipe frame to enable significant bag penetration. If the base of the bag is uniformly compressed using standard bent-sheet-metal massaging plates, flow may be impeded. Some manufacturers offer heavy-duty or hydraulic massaging systems for the most problematic materials.

Many applications require that the handling system be able to stop material flow to partially discharge material from the bag. To achieve partial discharging, manual iris and pinch valves have been used with varying degrees of success. Since the column of material emitting from the bulk bag can be dense, iris or pinch-valve assemblies have been known to fail or have shown that they cannot close on the bag discharge spout. If the bag spout closure is an important part of the process, the user should choose a system that is strong and durable enough to meet application requirements.

Even in relatively simple applications, the bag-unloading unit is generally integrated with other material-handling components. Users should determine whether a new system must be integrated with existing equipment and whether the supplier has the necessary experience to ensure that the controls and features will work properly together. For example, to handle and transport material to the proper point after being discharged from the unit, the user can use a vibratory feeder or gain-in-weight scale system.

Material-handling unit’s discharge spout closure system.

Another factor to consider is a prospective unit’s overall quality. The supplier’s design experience, fabrication expertise, finishing, component selection, and assembly all play an important part in equipment quality. Quality not only affects a system’s long-term durability but also may affect operator safety and the buyer’s return on investment.

Safely unloading containers starts with a strong foundation. The bulk bag frame must be robust enough to ensure many years of service. Some manufacturers try to cut costs as much as possible by reducing a unit’s structural supports. Users should ask suppliers about the size and thickness of the support frames before investing in equipment that may not meet expectations.

When considering quality, it is important not only to look at the unit itself but also the supplier’s reputation. Is the end-user planning to purchase a custom-designed unit or a standard piece of equipment that will function as promised? If the purchaser plans to own the unit for 10 years or more, will the supplier be around to service the account and answer future questions?

There is no universal solution for every application and every set of circumstances. A qualified supplier will be proud to provide examples of custom-designed equipment and will be pleased to offer custom products for unique application needs. The demand for bulk bags will continue to accelerate. When a company plans to invest in a new system, it should carefully consider its capabilities and quality.

Brian Carpenter is a sales representative at Material Transfer & Storage Inc. (Allegan, MI), which custom designs and manufactures material-handling equipment and systems. He can be reached at 800-836-7068 or [email protected]. For more information about the company, visit www.materialtransfer.com.