How do I choose the style of bulk bag unloader frame I need (what Super Sack system is right for my application)?
Bulk bag unloaders come in (3) primary frame configurations – Fork Loaded, Hoist & Trolley, and Half Frame. The decision on which type is best for your application can be tricky. There are cost, configuration, and application influences, as well as ergonomic and flexibility considerations in making the best choice of frame type. Below is a brief description of each, and their advantages and applications, as well as some alternative designs for unusual scenarios.
Half Frame bulk bag unloaders are primarily used in locations were an existing I-beam and hoist are present, but can also be used in tandem with a forklift to create a simple and inexpensive discharging system. Location is an important consideration here, in that the unit will need to be centered under the Beam/Hoist, as well as the down-stream process. When using a fork lift to support the bag, the key is to insure that operators are not in jeopardy of getting pinned between the frame and lift, or run over in the process of untying the bag. A common application for a Half Frame units are for high speed discharging systems via bag piercing systems that cut the bag as it is lowered onto the bag support, and then quickly discharged so the next bag can be loaded/discharged. Often these systems also use a quick-release bag support frame for the forklift.
This style of Super Sack® frame offers full bag support from the top and bottom, and uses a lifting frame (spreader bar, bag lift adapter, etc.) to attach the lift loops of the bag, then lift and nest the bag/adapter on support bars that are adjustable within a structural frame. The primary advantage is the bag is completely supported, but at a lower cost than the Hoist & Trolley system. These are best used when bag sizes changes are rarely if ever required. While it is easy to make a change for a new bag size, due to the location (high position on the unloader frame) it typically requires a man-lift or rolling staircase to accomplish.
Hoist & Trolley
HT units offer all of the support features of the FL frame, but offer a traversing-lifting hoist to insert the big bag into the frame. When handling multiple sized FIBC’s, or if a forklift isn’t available in the area, this system can be extremely advantageous. The only down-sides are cost (hoist and beam are expensive to integrate), and some plant Health & Safety programs will require guarding or lock-out of the lifting area below the bag. This is easily added, but is an additional application consideration. To use this system the operator will extend and lower the bag adapter (spreader bar) just above the bag, then attach the loops, lift the bag up and into the frame, then lower onto the receiver pan for untying/dispensing.
Low Head Room Options
These are typically hybrids of the FL and HT units can be used when application or locations aren’t permissive for standard frames. These include:
- Split-Frame FL unloaders whereby a top frame (bag support) can be moved off a base frame which allows a bag to be inserted without the draft of the forklift backrest interfering. The top frame can then be nested back on the base frame via fork pockets located low on the frame.
- Another Low Head option is a Super Low Draft system where a special carriage on rails moves the bag lift adapter in/out of an extended frame, with cylinders that lower to attach the bag, then raise so that the carriage can retreat back into the main frame and lower the bag onto the bag support.
- Lastly, a Compact FL unit can be used when discharging bags into downstream equipment or hoppers via gravity but must be moved into/out of place. This style of frame is much like the FL unit, but is typically shorter, and with fork-pockets low on the frame or sometimes a crane attachment on the top for indexing to the desired discharge location.
Below are examples of these bulk bag unloader frame types:
There are many other factors that go into selecting the right Super Sack® unloader for your application. Your supplier should be able to help you with the selection and design. You should have the following information available:
- Total Bag Weight
- FIBC Height Range (Lowest – Highest)
- Ceiling Height Available at Application Site
- Bulk Bag Bottom Design (Spout Bottom – Plain Bottom) and Size (spout diameter x length)
- Forklift Backrest Height (best way to measure is to lift the forklift (s) to be used at the application site to the highest height that is reasonable – and measure from the top of the forks to grade)
- Outlet Height of Unloader (or Inlet Height of Application)
- Inlet Design Size/Style (hopper, flange, conveyor, etc.)
- Any Location Specific Limitations – area footprint available, mounting details (concrete, steel mezzanine, etc.), equipment dimensions to straddle, etc.
- Area Electrical Classification (Explosion proof – Class/Div/Group)
- Voltage Available