Issue link: https://www.e-digitaleditions.com/i/1242780
26 / May 2020 powderbulk.com with a wide range of materials, such as fly ash and some nonhazardous catalyst materials, and can facil- itate a very fast and efficient means of discharging as long as the material isn't dusty. Conical-bottom bags have a tapered end and help to promote material flow. These bags are typically used for poor-flowing materials like some titanium dioxide grades. Fully opening-bottom bags feature a duffle-style bottom opening that allows the entire bag's bottom to be fully opened. These types of bags are used with extremely poor-flowing materials such as peat and sawdust. Hygiene flaps at the bottom of FIBCs help to protect the entire bottom from getting dirty and experiencing wear and tear. Also referred to as sanitary flaps or diapers, these flaps cover the bottom of the bag and are typically used with food ingredients. FIBC liners FIBC liners, the majority of which are made from poly- ethylene, are usually used for fine powders, food, and pharmaceutical materials to prevent the ingress of contaminants into or the egress of hazardous materials from the FIBC. Polyethylene allows the ingress of mois- ture over a period of time, so typical liners are only rated as moistureproof and not waterproof; although, there are specialized designs that are vaporproof. Liners are normally manufactured from linear-blend polyethylene as it's stronger than low-density polyeth- ylene and reduces the risk of shredding when it's cut open. Typically, liners are generally between 1 and 6 mil in thickness, depending on the material and the protection level required for certain materials. Typical liners are only suitable for holding material at tem- peratures less than 176°F; above this temperature, the liner starts to plasticize. When dealing with material at temperatures at or above 176°F, special liners should be used, such as those made from resins with greater temperature limits or metallized liners. Loose liners are normally extruded from a tube and are then cut to the appropriate length to fit the FIBC in use. The cir- cumference of the extruded liner should be equal to the base circumference of the FIBC plus 2 percent greater to accommodate any liner stretching while filling. FIBC construction and quality FIBCs are designed to be lifted by their loops when filled. Strength is built into the FIBC to give a safety factor ratio of 5-to-1 for single-trip bags and 6-to-1 for multitrip bags, meaning they're used more than once. This safety factor means that a bag with a 5-to-1 capacity can securely hold 5 times the weight of the bag's expected contents. FIBCs designed to hold food each end of the loop is connected to each side of the FIBC's corner walls. The length of a lifting loop is generally 10 inches but may increase to 12 inches if the FIBC is to be picked up and moved by forklift tines. Pop-up loops, which are fabric loops that have plastic strips sewn into them so that they're stiff and stand upright, enable a forklift to engage the loops without additional labor, but they do incur additional bag costs. Filling spouts. The spout on a bag is tailored to fit the filling equipment head. The most common filling spout size is 14 inches in diameter. When FIBC liners are used, some machines clamp onto only the liner, in which case the filling spout diameter can be increased to 20 to 24 inches to allow the material to reach the FIBC's top four corners and not bridge at the inlet spout. This is most important with powders. Outlet spouts. The diameter of the outlet spout should be sufficient to ensure easy material dis- charge. Easily discharging material is also achieved by having the discharge machine correctly designed. Most discharge units can handle poor-flowing mate- rial, depending on the unit's design and choice of flow- promotion method, such as paddle massages, vibrations, and the bulk bag discharger dish angle. Outlet spout diameters tend to vary from 10 to 24 inches and, same as with the filling spouts, a 14-inch diameter is the most common size. Outlet spout length should be sufficient to ensure that the outlet can be tied off and, in most cases, goosenecked. Goosenecking is a method of securing the bag's outlet spout by folding the tied outlet spout over itself and then attaching a wire tie around the folded spout to provide a second level of security. Spout length can vary from 16 to 36 inches but depends on the diameter size. Other FIBC outlet extras. In addition to the tra- ditional round outlet spout, there are various outlet systems and features for FIBCs. All are designed to accommodate a particular material type that can't be dealt with using a standard outlet spout. Flat-bottom bags are for one-time use only, as there's no outlet on the bottom. Instead, a slit is cut in the bag's bottom and the material flows out. These bags are used FIGURE 2 Typical FIBC with lifting loops and sealable filling and discharge spouts with ties