Bags, bulk, flexible intermediate bulk containers

Intermediate bulk containers (IBCs) are intermediate between smaller packages, such as shipping sacks and drums, and the larger bulk truck and railcar quantities. IBCs fall into two general categories: Flexible and Rigid. Filled IBCs occupy about the same space as a typical palletized unit load.

Flexible intermediate bulk containers (FIBCs) are very big bags, made from fabric sewn into shape. They are often called bulk bags or SuperSacks (a registered trademark). Usually they contain about 1 ton of dry bulk product such as grains, powders, and pellets. There are also rigid IBCs, which may be called Gaylords (a registered trademark) when made of corrugated board or Tote Bins (another registered trademark) when they are made of stainless steel or plastic.

They are usually filled from the top, lifted from the top or bottom, and dispensed through the bottom (see Figure 1). Many are reused.

Flexible intermediate bulk containers (FIBCs), have been popular since woven polypropylene arrived on the scene in about 1963. Prior to that, bulk bags were made from PVC or rubber-coated cloth and were mainly used for shipping carbon black in 1- to 4-ton loads in each ‘‘bladder’’ to rubber manufacturers. They were filled to capacity and then weighed on a truck scale before loading onto a flatbed truck. They were usually lifted by overhead crane, and then discharged into hoppers through narrow inlets to reduce dust. They were reused over and over for many years, and they were shipped back to the carbon black manufacturer for repair, patching, and refilling. These huge ‘‘balls of black’’ needed no protection from the elements and weren’t even covered with a tarp. They were just tied down securely, 6–8 to a flatbed truck.

Soon afterwards, FIBCs were adopted in other industries in Japan and Europe as an economical way to ship intermediate quantities in logistical systems where shippers and their industrial customers cannot handle a whole bulk tank truck or bulk railcar of product and prefer not to manually handle multiple shipping sacks or drums. Bulk bags have become increasingly popular for replacing 50- to 100-lb (25- to 50-kg) paper and plastic bags. Growth is expected to continue, especially given (a) the present trends of legislation to reduce the maximum weight that a person may lift and (b) the lower cost (and natural resource conservation) compared to smaller sacks or drums.

The advantages of bulk bags, compared to buying smaller packages, include reduced costs for package purchase (from about $8 per bulk bag), filling, and handling. They offer a customer service in handling savings because of the ease of dispensing the product. Bulk bags can also promote safety when handling hazardous materials, because they can be incorporated into sealed material handling systems where smaller bags that have to be cut open and shaken to be emptied cannot.

Another advantage of FIBCs is that they can be customized for the exact amount needed by their customers for a batch. Unlike other types of shipping containers, they can be made in any size and in heights from 24 in. up to the limiting height of a truck/container door.

TYPICAL USES

Bulk bags are used for a wide variety of dry products, primarily for ingredients intended for further processing. Typical products include chemicals, minerals, dyes, resins, feed, seed, grain, flour, sugar, salt, nuts, detergents, sand, clay, cement, hazardous materials, building materials, pharmaceuticals, fertilizers, and other commodities in powder, pellet, flake, crystal, or granular form. Liquid products need more support than a flexible bag alone can provide, so intermediate quantities (200 gal) of liquids can be packaged in a ‘‘composite’’ IBC, with the bag supported by a metal frame, or in rigid IBCs, such as pallet boxes or small tanks that may be lined with a bag. However, some ‘‘flexible tanks’’ for over 5000 gal of liquid, without rigid supports but with transport restraint attachments, have been introduced in Europe.

The filled bag weight depends on the size of the bag and the density of the product. The heavier the product, the more strength is needed. The standard FIBC holds 1100– 2200 lb, and bags from heavier fabric can contain up to 5 metric tons. FIBC manufacturers offer bags with a volume of 10–100 ft³. Footprint sizes range from 29 in. × 29 in. to 41 in. × 41 in., with heights of ≤88-in. empty size. When bags are filled, they have a tendency to settle into a more circular shape. Examples of bulk bag use can be found in many industries. Sugar and flour are shipped to food processing plants in FIBCs. Sandblasters can receive sand in 5500-lb FIBCs. Plastic resin is shipped to converters in 1-ton FIBCs. About 80% of fertilizer in the United Kingdom currently goes into FIBCs. One of the largest markets in the United States is for exported commodities.

MATERIALS

Bulk bags are made of plastic fabric or films with a very high tensile strength. Most are made from densely woven polypropylene (PP) fabric and have sewn seams, but they can also be made from circular-woven fabric (see Film, nonoriented PP; Film, oriented PP). Other materials include high-density polyethylene (HDPE) and polyester. Some European FIBCs are made from fiber-reinforced paper or polyvinyl chloride (PVC) (see Film, rigid PVC). The most heavy-duty FIBCs are usually made from PVCcoated PE fabric. Bulk bags can be printed to identify the contents. Filled bulk bags are usually cube-shaped with a square footprint, but some have a circular footprint. Some designs have antibulging ‘‘baffles’’ as reinforcement features.

Selection of the appropriate materials and structure depends on the properties of the product and the distribution system. Waterproof FIBCs are coated with PVC or latex and have heat-sealed (rather than sewn) seams. If the bags will be stored outside, the fabric is formulated to resist ultraviolet degradation. Some products generate static electricity when they flow, and antistatic (or static conductive/dissipative) fabric or liners are available. If bulk bags are intended to be reused, they are usually stronger than those intended for a single trip.

Many bulk bags have plastic liners. Often the liner is disposable (for sanitation reasons) and the outer bag is reused. The choice of liner material depends on the barrier properties needed or the tendency of the products to dust or leak. Products that attract moisture, or are sensitive to water, require moisture vapor transmission resistance. Polyethylene (2–4 mils) is common, but it is not a complete moisture or gas barrier. Saran and aluminum foil laminate liners are better barriers and can be vacuum-packed. Liners are available in single or multiple plies. The liner construction matches the outer bag construction with respect to dimensions and placement of filling and dispensing ports. Liners come in tube shape or are custom-made to fit, with fill and discharge spouts. The liner can be designed to be manually or mechanically inserted.

There are various lifting and dispensing features available. For example, the most standard European FIBCs are for fertilizer, with single-point lifting and no discharge spout. The most common U.S. FIBCs have four lifting points and a spout. The choice of features depends on the application.

FILLING AND DISPENSING

Bulk bags are usually filled from the top and discharged from the bottom. Most bulk bags have a spout at the top and one on the bottom. The spouts are closed with a tie, clamp, tape, or stitching. Clamps or ties can also be used to tie off a partially discharged bag or to regulate the rate of discharge. Intermittent flow controls are also available. However, some bags have no spouts and are simply filled or emptied through an open ‘‘duffle’’ that is gathered and tied to close. Some single-use FIBCs have no discharge spout, and they are simply slit to empty.

Bulk bags normally require special filling and dispensing fixtures and equipment. Gravity directs the flow. Filling and discharge procedures and efficiency are influenced by the product’s angle of repose and flow characteristics. During filling, the bag needs to be suspended from the top so that the product will completely fill the corners. Some filling systems incorporate a vibrating or settling device, deaeration and dust control measures, or a bag squaring method (although they rarely stay square once they are handled). Most are filled to weight using either a batch weigh hopper above the bag or a load cell to monitor the bag’s weight as it is filled. Bulk bags are quick to fill; a two-operator filling station can fill a 2200-lb-capacity bag in about 30 s with a dense free-flowing product. But a light powdery product, which may require extra handling or vibration to compact, may take up to 30 min to pack.

A typical discharge fixture positions the bulk bag above the awaiting hopper, conveyor, pump, or tank receptacle where the bottom is opened so that the product can flow out. Special discharge equipment has been developed to reduce dust, improve flow, meter, and reclose, and improve sanitation (especially important for food products).

SAFE HANDLING, TRANSPORT, AND STORAGE

Bulk bag handling and transport require special systems to ensure safety and efficiency. FIBCs are very heavy and can be unstable during handling, storage, and transport. This instability can result in danger to materials-handling workers and can cause damage to the bag or its contents.

Bulk bags are lifted from the top or handled on pallets. The most common top-lifting design incorporates four loops at the cube-shaped bag’s four top corners. These loops may extend from the top to cradle the bottom like a sling, sewn onto the fabric. There are also center-lift designs that incorporate (a) a single sleeve or loop on the top center and (b) two-sleeve designs with sleeves along two top edges. One-loop bags are more popular in the United Kingdom and France, especially for fertilizer. Some bags have a combination design with center-lift features to aid in discharge and corner lifting to aid in filling. The most heavyduty FIBCs have steel lifting devices.

The loops or sleeves are lifted by the two forks of a forklift (or a single bar, in the case of the center-lift bags) that may be inverted to shorten the height of the lift. For most bags, it is necessary for one worker to position the loops onto the forks and a second worker to maneuver the forklift. Several can be lifted simultaneously by a ship’s tackle and the appropriate stevedore fixtures. It is important for the loops or sleeves to be strong enough to support the weight during handling, including jerks caused by the lift equipment. Correct handling procedures are often printed on the bag or label.

Bulk bags can be transported by flatbed trucks, enclosed trailers, boxcars, flatcars, ship, or barge. Some restraint may be necessary to prevent shifting in transit. Typical restraints are made from straps and fabric, attached to the trailer and boxcar walls. Bulk bags must be strongly restrained if stacked in transit.

Stacks of bulk bags can be unstable. They can be stacked on pallets, but stacks more than 2-high should be supported by retaining walls. Even stacks of 2 should generally be pyramided (the top load spanning two lower ones) to lend stability. Handling a stack of two with a forklift is not recommended. One reason there are stability problems with stacking FIBCs is because they are often not filled with equipment that produces proper settling and material distribution to make the bag form a stable. FIBCs can also be used for temporary storage within a plant, and some can be used for outdoor storage.

DISPOSAL AND REUSE

Empty bulk bags can be discarded in landfills or incinerated if they have no hazardous residue, or they can be recycled (shredded and re-extruded) with compatible materials. But most bulk bags are returned and reused.

FIBCs have excellent return and reuse properties because they are strong when filled, and yet they are lightweight (usuallyo10 lb) and can be folded small when empty. The life of a reusable FIBC depends on its construction, the nature of the contents, and the handling and transportation method used, but is typically 5–10 trips. Many shippers reuse the outer bag but discard the liner. Reusable FIBCs are usually stronger than one-way bags. Returnable packages add costs for return shipment, cleaning, tracking, and inspection. Most are reused in a closed-loop system. They require a close relationship with customers to ensure their timely return in order to minimize the packaging investment.

A hidden cost that is often discovered after a reuse system is put into place is that the filler of the FIBCs must inspect, clean, and repair the bags. This situation has spawned opportunites for third-party businesses to perform these functions.

In some cases, there is a market for used bulk bags, similar to the market for reconditioned drums. But an FIBC is usually designed for a specific type of product and use, and it is best reused for the same type of product. Buyers and sellers of used shipping containers should certify the identity and compatibility of previous contents and document that the package was cleaned, inspected, and certified as to its safe reuse capacity. For example, lime for steelmaking can be packed in used bags because the residue is burned up and vaporized (along with the whole bag, which is not emptied but is added to the furnace intact).

TESTING AND STANDARDS

Safety and performance standards have always been a concern of the FIBC industry, evidenced by the creation of the industry’s self-policing associations such as the Flexible Intermediate Bulk Container Association (FIBCA) and the European Flexible Intermediate Bulk Container Association (EFIBCA). These associations work with other standards groups like the British Standards Organization (BSO), the International Standards Organization (ISO), the American Society for Testing and Materials (ASTM), the American National Standards Institute (ANSI), the United Nations (UN), and the European Technical Committee for Packaging Standardization (CEN/TC261/SC3/ WG7 covers IBCs) to better control FIBC safety and quality. Performance standards for FIBCs vary by country and regulatory agency. The first performance standards were developed in the United Kingdom by the EFIBCA and were later incorporated into the British Standard Institute’s BS 6382 (BSI/PKM 117). These form the basis for later standards adopted by other countries, including the United States, Australia, Japan, and throughout the European Economic Community (EEC). It is also the basis for the International Standards Organization’s ISO TC 122/SC 2 N 238. The EFIBCA has also standardized the information that appears on each bag to include name, date, and address of manufacture, construction identification, standard to which the bag is produced, test certification, class of bag (e.g., single-trip), safe working load, safety factors, handling pictograms, and the contents’ identification.

FIBCs used for hazardous materials are the most highly regulated. In 1990/91, the UN Chapter 16 for the carriage of dangerous goods accepted bulk bags for UN Class 4.1 flammable solids, Class 5.1 oxidizing substances, Class 6.1 toxic substances, and Class 8 corrosives, provided that they conform to the particular modal requirement and have passed drop, topple, righting, top-lift, stacking, and tear tests. In the United States, FIBCs have been accepted by the U.S. Department of Transportation (DOT) for Groups II and III hazardous materials, and performance specifications are given in HM 181-E (1). (See also Transportation codes.)

FIBC materials vary, so most standards are based on performance. Weight-bearing performance tests usually specify testing the bag’s safe rated capacity with a much heavier weight—6 times more heavy for standard FIBCs, 8 times for more heavy-duty FIBCs, and 5 times for singleuse FIBCs—than the expected contents. Filled bag performance should also be judged with respect to tear resistance, stacking, toppling, dropping (2–4 ft), dragging, righting (by one or two loops), and vibration. The most prevalent forms of damage are split side seams, broken loops, torn fabric, abrasion, and sifting. Damage can also be dangerous, if hazardous materials are spilled or if a stack topples onto a worker. In addition to performance tests, there are relevant material tests for the bag fabric and liner, including tensile strength and moisture vapor transmission. Material tests are used primarily for quality control.

CONCLUSION

Flexible intermediate bulk containers (FIBCs) provide a safe and cost-effective system for handling and transporting a wide range of bulk materials. They are ‘‘intermediate’’ between bulk handling and using shipping sacks for dry flowable commodities. FIBCs offer advantages compared to bulk handling and require a low initial investment compared to the special transport and handling equipment used for bulk handling. Some can be stored outdoors without the need for a warehouse or silo. They reduce product waste, and the contents can be easily and accurately metered. An FIBC can perform the function of a mobile hopper. Compared to conventional 50-lb bags, FIBCs are less labor-intensive and do not involve manual handling that can cause back injuries. They are less expensive and require less space to pack. They are quicker to fill, handle, and discharge. And they reduce the risk of product loss, contamination, and pilferage.

DIANA TWEDE

Michigan State University School of Packaging, East Lansing, Michigan

BOB DRASNER

Senior Consultant, Packaging Equipment Specialists (Retired), Rockport, Texas