The easiest method to move bulk bags is on pallets (or skid sheets) using fork trucks or pallet trucks. Listed below are considerations when using pallets.
- The ideal size of the pallet should allow the rounded section of the bag to overlap the edges of the pallet so that when the two palletized bags are placed side by side the bags can touch without the pallets touching. This will minimize the risk of damage the pallet and greatly assist in the stability of the bags in stacking and inside trailers and containers.
- As most pallets are rectangular this is not always easy if using a square based bag but, the ability to locate the bag centrally on the pallet, especially after filling is critical. A wide range of mechanical devices to assist the fork truck driver to achieve this are available plus side shift on the truck itself will help.
- If bags are to be stacked, the pallets need to be close slatted both top and bottom to stop "pinching" of the bag. The bag must not protrude through the slats of the pallet above and be damaged by the fork tines when unstacking. Also close slatted pallets give much greater stability in the stack, this reduces damage, time in unstacking and generally makes it easier for the fork truck driver.
- Close slatted pallets are costly and may only be financially justified for in- plant use unless return can be guaranteed. For shipping out, the bags can be transferred to a non-returnable pallet. Or two bags can be placed on top of each other on one pallet for trailer or containerized shipment as long as the filled height of the bag is less than 42 inches. This is labor intensive, but needs to be considered as part of a costing exercise. If no stacking is needed then standard single trip pallets can be used. However, the risk of bag damage from fork tines when poorly constructed pallets are used should be considered.
If the plant handling bags already has skid sheet handling facilities available, these can be used instead of pallets with certain caution.
- When stacking with skid sheets, stability is reduced. We do not advise three high stacking for bulk bags with a filled height in excess of 40 inches, or two high stacking for bags with a filled height of more then 54 inches. With bags higher then these dimensions, racking should be considered.
- The same caution concerning pallets and bag sizing apply to skid sheets.
Well filled bags that have been properly sized are stable and safe to handle and stack. What constitutes a well fitted bag is discussed below, but stability must be retained not just after filling but during stacking, unstacking, transportation and restacking.
To do this a good fork truck driver should always try to restack bags in the same sequence that they were originally stacked. The bottom bag, which is more compressed, will best be repositioned at the bottom of the new stack or be part of the lower tier in a trailer/container where double stacking can be achieved.
Bags which lean to one side or become banana-shaped cannot be corrected once filled. They are dangerous and expensive to handle.
Bags which contain ingredients which have not been compacted, during or after filling, are unstable, dangerous and expensive to handle. Such ingredients tend to be those which have fluidizing air entrained in the material prior to filling. The air must be removed if the filled bag is to remain stable. This applies particularly to powered ingredients.
The use of bulk bags to transport minerals, chemicals, grain and other dry solids by sea rather than in ISO Containers is a growing market. Lower shipment costs and the ability to ship value-added products not suitable for bulk is becoming popular, particularly with end-users who are unable to receive bulk shipments.
There are several points worth noting before planning this method of shipment.
- Bulk bags require loading and unloading "on the hook". This means that the choice of vessel is all important. Wide hatches and small wing spaces with minimum flaring in the forward hold will enable the bags to be loaded and unloaded by ships craneage or dockside cranes without moving the bags into the corners of the hold by forklift.
- Stacking of bags in the ship’s hold without pallets requires using the correct size of crane spreader bar so that the bags are touching when lifted over the ships side and that the loops are vertical.
- Bulk bags for this type of shipment usually have loop extenders added to the lifting loops to enable the four loops to meet in the center for single hook pick up. Tying the loop extenders together with elastic assists the stevedores at unloading time hence a reduction in the damage costs.
- It is worth the extra bag cost to ensure that the quality/weight of cloth used in the make-up of the bag is increased slightly higher than normal as this will reduce the chance of damage at the docks where rough handling is usually encountered. Some overseas ports reject poor quality bags or unsafely filled bags.
Handling At Discharge
To discharge a bulk bag it must be lifted. Therefore, it is advisable to ensure that the bag to be discharged is located within reach of the discharge hoist or fork truck fitted with a rigging frame.
Rigging frames are a lifting device to which the bag lifting loops can be attached so that the lifting loops are kept vertical. These rigging frames can be made for both crane hoist or fork truck use. They are usually supplied as part of any discharger and should be made to suit the size of bag being discharged.
It is bad practice to allow operators to stand under a hanging bag when it is being hoisted and dischargers should have facility to allow an operator to discharge the bag without the need to go under the hanging bag.