By now, everybody knows how strong bulk bags are. Woven polypropylene sewn together by hand can carry 1000 kg loads around the world with ease. Now to the average person, 1000 kgs might sound like the upper limit of what mini-bulk bags can handle. However, there are techniques and building schematics that allow bulk bags to carry 3,000 kilos, or even more! The only problem you might have with a bulk bag that size is having the heavy equipment to move them around.
So what goes into a bulk bag that can carry that much weight, and how is it different from a standard 1000 kilo bag? There are a number of ways to make a bulk bag more robust. From design to materials, it is an engineering feat to create such a lightweight vessel that can carry so much. In fact, there is an ISO Standard that specifically addresses the proper material, construction, design, and testing requirements to manufacture bulk bags with the best possible methods. Much like UN Rated Hazardous Material bags, regular bags made to this standard are tried, tested and true. Are you getting bulk bags from a supplier that adheres to the ISO 21898 standard? Let’s look at some of the methods used in the manufacturing of an ultra-heavy-duty bulk bag.
Polypropylene - The Wonder-Poly is STILL Wonderful!
If you have been paying attention, you know that bulk bags are made from woven polypropylene that has been extruded into tapes. This woven material is simply known as fabric. Much like the sheets on your bed have a thread count, woven polypropylene fabric has a similar description in terms of how much material there is. The measurement is based on how much one square meter of fabric weighs. GSM (grams per square meter) is the standard unit used to figure out how resilient the woven fabric is. A lower GSM number has less material than a fabric with a higher GSM. If you want to carry more weight, you are going to need a heavier and more durable fabric to begin with.
Another method used to create a very heavy bulk bag involves sandwiching fabric together. This double-wall design gives a bulk bag more resilience to tearing as well as increasing the overall strength of the bag itself. The most common application for a double walled bulk bag is either the mining or aggregate industries. Hauling heavy and jagged granular material can be challenging as the sharp material inside really wants to get out! The double-wall design helps to ensure the contents inside the bag stay inside the bag.
So now that we have a really well built, double-wall, heavy GSM bulk bag in the works, what other part of the bag needs to be reinforced as well? The lift loops are the main point of contact between a bulk bag and the heavy lifting equipment. If you skipped this step in making a heavy-duty bulk bag, let’s just say it’s never going to get off the ground!
Lifting Loops - Cirtical Points of Contact
The lift loops are an integral part of any bulk bag design. A standard bulk bag has lift loops made from woven polypropylene as well, but they are not made like the body fabric is. Instead of a single layer tapes being woven together, the lift loops are made from polypropylene tapes that have been stacked together before being woven into a webbing type material. Much like the fabric, the webbing material created to make lifting loops has a specific weight as well. If you need to carry more weight, you are going to need heavier webbing to make stronger lift loops.
Standard bulk bags usually only have lift loops that extend partially down the side of the bag. As the weight creeps up, the loops creep down. The heavier the load, the longer and stronger the loops. One method to increase the holding power of regular polypropylene loops is to extend the loops down the sides, across the bottom, and then up the other side. This creates a cradle effect as the loops enwrap the entire bag. We call that “Style 104” loops, and they add a lot of extra strength to our already tough bags. We carry a stock bag that is rated for 1850 kilos and they are made with that type of lift loop system. Interesting enough, our stock bag that can hold 1850 kilos weighs only 3.5 kgs itself!
Do not try this at home! Bulk bags should always be lifted straight up with all four loops in contact.
Safety Bands - Music to Your OHS Officer's Ears
Finally, to make a really robust bulk bag, you can add a safety band. A safety band is basically a horizontally positioned polypropylene belt that is sewn around the top perimeter of the bag. This belt is made from the same stacked tape webbing as the lifting loops, so you know they are solid! The safety band essentially ties the lifting loops together on a horizontal plane. Safety bands hold the four lifting loops onto the bag body in case there is a situation where the bulk bags cannot be lifted straight up, like they are designed to be used. This extra piece of webbing material will help to prevent the lifting loops from peeling off the bag if the loops are forced into an angled position under severe tension.
Now what kind of everyday scenario would require a bulk bag with a safety band? Here, for example, is a picture of a 2000 kg bulk bag being lifted and suspended by only two loops. This is an excellent representation of what happens if you receive filled bulk bags that have tipped during transport. This kind of lift is called “righting” the bag, and it exerts a strong angled force on the handles. Without the band, the angled force would peel the webbing away from the bag body, making it impossible to lift. So, the safety band is critical for righting the toppled bags since it addresses the unusual angled force during this operation.
The most common scenario that would require a safety band is a bulk bag that is being handled by multiple people and different equipment along the way. Here is a picture of a 2000 kg bulk bag being filled. Notice the lift loops are splayed outwards instead of being straight up and down. When the forklift picks up the filled bag, the loops will be perfectly straight, evenly carrying the load. However, what about when the bag is shipped to its final destination? Will every single piece of lifting equipment handle them perfectly? Probably not, especially for overseas shipping where cranes, stevedores, and other various lifting gear is implemented along the way. In this case, it would be essential to have a safety band to ensure your product arrives intact.
So there you have it, some excellent background information on how we keep making the best big bags in the biz. If youand your equipment are ready to really start throwing some weight around, let's get started!