Maximum bulk bagging rates are achieved when using a pre-weigh system. 

Pre-weighing refers to weighing the payload of product to be placed in a bulk bag in a separate bin or hopper above the bulk bag filling machine. 

Doing so eliminates the time required to precisely weigh the product as it flows into the bulk bag on the filling machine.  Rather, the pre-weighed 'shot' can be dropped into the bulk bag as quickly as it can be made to flow through the pre-weigh hopper outlet.

So, instead of a fast feed and dribble feed cycle with weighing conducted on the filler that, at its fastest consumes 50-55 seconds, a pre-weigh system can fill a bulk bag in approximately 15 seconds.

Removing 40 seconds from the bulk bag filling cycle time dramatically increases the bulk bagging rate.

Bulk Bag Filler vs. Pre-weighing

Let's examine the numbers in more detail:

Note that the Filler Weighing cycle time is only 120 seconds - that equates to 30 bags per hour.

That is a very high rate and is possible with many products using high speed bulk bag filling equipment.  However, as can be seen, adding a pre-weigh system to this type of bulk bag filler increases the bagging rate considerably.

A 90 second cycle time means that a properly designed pre-weigh system is capable of filling 40 bulk bags per hour!

Also note that the final densification time has been increased.  This compensates somewhat for the reduced amount of total densification time compared to the Filler Weighing cycle where the bag would be densified for most of the Fast Fill task.

In our next article we will dive into the design issues that must be considered to properly implement a bulk bag pre-weigh system.

Last week I had dialogue with a potential customer who was stumped with a bulk bag problem.  The solution had nothing to do with bulk bag handling equipment; rather it had everything to do with the flexibility of bulk bags themselves.

This customer was faced with having to fill bulk bags with a sludge like material that contained over 20% moisture.  Needless to say, it easily bridged and ratholed.

Specifically, the customer's system was being designed to mechanically convey the product to a small surge hopper, which would in turn empty into a bulk bag.

The customer was searching for a way to ensure that the product would flow easily from the surge hopper into the bulk bag.  However, they had been unable to find a suitable solution to getting the sludge through the bulk bag inlet spout sized at the typical 14" diameter.

The answer required a paradigm shift.  That was: bulk bags do not have to have a spouted top.

As can be seen in the following diagram, bulk bags can be manufactured with many different top and bottom configurations.

In the case of this application the solution was to use the 'skirt top' design shown above - also commonly known as a duffle top bag.

This allowed the customer to design the surge hopper with an outlet large enough to prevent bridging and ratholing while still being able to get the product into the bag. 

All they had to do was open the duffle top to completely expose the inside of the bulk bag and let the sludge fall from the large opening in the bottom of the surge hopper.

Because the product was so heavily moisture laden dusting was not an issue. Therefore, there was no need to have the bulk bag inlet sealed to the surge hopper outlet.

Plus, the duffle top allows the bag top to be tied and closed securely preventing comtamination of the product and spills.

The customer was able to simply, easily and inexpensively solve their problem once they learned that - true to their name - Flexible Intermediate Bulk Containers or bulk bags can be designed to suit almost any bulk solids handling task - flexible indeed!

View this content on Spiroflow's main website.

Often bulk bags require inner liners, usually made of polyethylene, to protect the ingredient.  Care must be taken when discharging lined bulk bags to prevent entanglement with downstream equipment and to ensure 100% product yield.

Liners come in many forms: loose tubular, loose fitted, sewn-in, glued-in.

Loose means that the liner is not in any way attached to the outer bulk bag.

Tubular means that the liner is basically a cylinder of polyethylene film that is stuffed in the bag.

Form fit means that the liner is constructured with sides, top and bottom and usually inlet and outlet spouts - it looks just like a bulk bag only it is made from polyethylene film.

Loose Bulk Bag Liners

Whether tubular or form fit, a loose liner requires some sort of physical means to prevent it from discharging with the ingredient and becoming entangled in downstream equipment.  A device called a liner tensioner is typically attached to the bulk bag lifting frame or rigging frame to prevent this from happening.

Liner tensioners vary in their operation, but the most basic simply hold the liner in place preventing it from moving out of the bag.  More sophisticated tensioners wind up a portion or all of the liner as it is emptied.

Before the bulk bag is lifted into the discharger the inlet spout of the bag is untied to expose the tied liner inlet.  The liner neck is then wound onto the liner tensioner spool piece, which is then either fixed in place or rotated to take up the slack in the liner by activating its actuator (typically pnemuatic).

Attached Liners

Even though liners that are attached to the outer bulk bag are designed not to discharge with the ingredient, it sometimes happens anyway.  Often a basic liner tensioner that holds the liner in place is used to guarantee that the liner cannot move.

Liner Tensioner Conisderations

1. Liners 'grow'. Loose liners and liners attached to the top of the outer bulk bag will extend out of the bulk bag outlet spout during ingredient discharge.  Particularly in the case of loose tubular liners, care must be taken to ensure that even if a liner tensioner is used, the liner cannot extend or grow out of the outlet spout enough to foul downstream equipment.
2. Too much liner winding.  If a liner tensioner that winds continuously is used typically the liner outlet is clamped to prevent it from winding all the way up onto the spool piece.  If this is allowed to happen, and the ingredient is at all dusty, dust will be sprayed into the surrounding area when the empty liner is rapidly wound up through the empty bulk bag and then spins around the spool piece.
3. Liner length.  When a liner tensioner is used the liner inlet must be long enough to reach the tensioner spool piece.
4. Ensuring 100% yield.  A liner tensioner that winds up a loose liner - partially or completely - can assist with ensuring that all of the ingredient is dishcarged from the liner.  The act of winding up the liner helps to get the last pounds of ingredient out of the bag.

Increasingly, bulk bags are used to ship 'hazardous' dry bulk solid materials.  This post investigates what you need to know to handle them.  Note that we will address the topic of how bulk bag manufacturers make bags to meet relevant regulations related to robustness and package integrity in a subsequent post.

First, let's discuss what hazardous means.  The United Nations defines hazardous goods as follows:  "Definition of 'dangerous goods' covers articles or materials capable of posing significant risk to people, health, property, or environment when transported in quantity."

That's a broad definition, but for the purpose of this discussion we'll focus on three potential hazards that can arise during bulk bag handling:

1. Static discharge.  Bulk solids that within a bulk bag may generate enough static charge to iginite flammable vapors, gases or dust.
2. Explosive dust.  Bulk solids whose dust, if allowed to accumulate in a high enough concentration, may explode if exposed to a suitable ignition source.
3. Health hazard.  Bulk solids that present a health hazard to humans via direct contact.

Dissipate Static

There are two ways to mitigate the risk of static discharge: bag and equipment design.

Of the four types of bulk bag (Type A, B, C and D), typically only types C and D are used to prevent static discharge leading to explosions. 

Type C bulk bags feature conductive fabric or conductive threads or filaments woven into non-conductive fabric.  The key factor is that Type C bags must have a grounding point to which all fabric, threads or filaments are connected.  The grounding point must then be connected to an external ground point duing filling and discharging of the bulk bag.

Type D bulk bags are constructed from fabric that allows static charge to be dissipated without being connected to ground.  The advantage of Type D bags is that operators are not required to making a ground connection with the bag prior to filling and unloading - a task that can be forgotten sometimes resulting in disaster.

Equipment used in situations where static discharge could ignite flamable substances must, as a minimum, have ground lugs.  Depending on the Area Classification electrical components may have to be explosion rated.

Contain Dust

If the product you are filling or discharging can cause an explosion if a high enough concentration of dust is exposed to an ignition source, dust containment is critical.

Bulk bag fillers must have 'twin-tube' fill heads and provide a tight seal with the bulk bag inlet spout.  The outer tube of the fill head must then be connected to dust collection system so that dust laden air that is displaced during the filling process is safely extracted.

Bulk bag dischargers must have dust containment features suitable for the hazard level.  There are different levels of dust containment available (discussed in another blog post).

All equipment must feature electric components rated for the Area Classification.

Isolate Human Contact

Bulk solids that are health hazards include various refined metals that are carcinogens, chemical compounds that cause respiratory problems and so on.  When dealing with these products maximum dust containment is required.

Specialized bulk bag discharging equipment is available for this application.  It is critical that such equipment contain dust at the following critical steps in the bulk bag unloading process:

• Initial onset of product discharge.  The point in time when product begins to flow from the bulk bag can create a large amount of dust.
• Throughout bulk bag emptying.  Of course, dust must be contained as the bulk bag is emptying.
  
• End of discharge. Near the end of the discharge cycle the bulk bag will loose its shape.  Equipment must be designed to maintain dust containment integrity at this crucial stage.
  
• Bag removal.  Removing the empty bulk bag - still full of dust laden air - must be done safely without exposing operators to dust.

View this content on Spiroflow's main website.

In previous posts we have discussed reducing shipping costs and the benefits of replacing or eliminating pallets.

In this week's post let's discuss all of the ways that the cost of bulk bag packaging can be reduced.

1. Reduce bulk bag size.  Reducing the height of a bulk bag by 10% decreases its price by roughly 5%.  Maximum densification, for example using the cone table densification system, can almost always decrease bag height by 10% - sometimes by as much as 40% or more.
2. Eliminate baffles.  If your bulk bags have internal baffles and they are being used to enhance stability, it is highly likely you can eliminate them by using a densification system designed for maximum results.  Getting rid of baffles can save as much as $5 per bag.
3. Use coated bulk bags.  If you use liners in your bulk bags you may be able to eliminate them and use coated bulk bags instead.  See the blog post "Bulk Bag Liners - When To Use Them... or Not!" for an excellent review on when to use liners and when not to.  Switching from a liner to a coated bulk bag can save as much as $2 -$3 per bag.
4. Replace wooden pallets with plastic channels.  Using plastic pallet replacement channels can reduce direct packaging cost and logistics related costs too.  See the blog post "Eliminate Wood Pallets - Ship Bulk Bags Without Wood Pallets" for details.
5. Eliminate wooden pallets.  Properly designed and filled bulk bags can be handled only by using their lifting loops thereby eliminating pallets - and their cost - completely.  See the blog post "Pallet Free Bulk Bag Handling" for details.

As you can see from there are numerous ways to significantly reduce the cost of your bulk bag packaging.

Are Pallets Necessary?

Pallets are used to move heavy objects. Forklifts or pallet trucks are used to move them. In the case of bulk bags however, there is a built-in alternative to using a pallet or bottom located lifting device to move them: bulk bag lifting loops.

Every bulk bag has lifting loops that are designed to safely lift the bag and its contents. They can be used to move the bag from the filling station to storage into and out of a shipping container and everywhere in between.

So, technically, a bulk bag does not require a pallet or equivalent.

Checklist for Handling Bulk Bags Without Pallets

Bulk bag filling equipment. Before you can safely handle bulk bags without pallets you must ensure that your equipment is designed to allow the bag to be removed from it without a pallet. Bulk bag fillers can be designed to release the lifting loops while still supporting the bulk bag thereby allowing the bag to be removed by threading the fork tines through the loops. Note that you must have a forklift to remove the bulk bag from the filler - a pallet truck won't work.

Bulk bag design. The bulk bag loops must be 'cross corner' design and the must be designed to stand up right on their own. Both of these features make it easy to thread the fork lift tines through the loops without assistance. Cross corner refers to loops that are sewn on side of the bag and looped over the corner and sewn on the adjacent side. This provides a 'tunnel' for the forklift driver to aim for. Of course, the loops must stand up on their own to make the tunnel. This is done by sewing a strip of plastic within the loop to give it rigidity.

Sanitary considerations. Since the bottom of the bulk bag comes in direct contact with the floor - of your plant or warehouse and the shipping trailer/container - it is often advisable to add a protective flap across the entire bottom of the bag to minimize contamination and provide an extra layer of fabric for added robustness. The flap is sewn along one edge, drawn across the bottom of the bag and attached to the opposite side using Velcro or loops and ties.

End user capabilities. While shipping bulk bags without bottom support has many benefits for the producer, it is a catastrophe for an end user without a forklift. Your customers have to be prepared, willing and able to work with your product in bulk bags without pallets.

Shipping Bulk Bags without Pallets - Is It Really Feasible?

Short answer: yes. Although a small percentage overall, there are many bulk bags being shipped without pallets. For example, export shipments of various products that travel via shipping containers are often shipped without any kind of bottom support. In North America, one of the resin industries converted from boxes to bulk bags now all domestic production of this type of resin is shipped in bulk bags without bottom support.

Palletless Bulk Bags - Benefits

Shipping without a pallet or any bottom support is a lucrative proposition. A number of operatic cost saving opportunities immediately occur:

1. Eliminate pallet cost.
2. Reduce shipping cost. Removing the weight of the pallet from each shipped package means you can increase the payload weight of each bulk bag. This can significantly reduce the shipping cost per pound of product.
3. Reduce handling labor. Not having to manage the handling of heavy pallets increase productivity and reduces packaging labor cost per pound.
4. Increase warehouse efficiency. Not having to store pallets can significantly increase available warehouse space.
5. Eliminate border crossing delays. Borders crossing delays often occur because palleted shipments may be inspected. Additional time (money) can be lost if documentation has to be resubmitted or modified.
6. Improve sustainability.  Eliminating pallets and any kind of bottom support clearly improves sustainability by reducing the use of material and waste.

Shipping bulk bags without bottom support is feasible, is already being done and can dramatically reduce operating costs.

Wikipedia describes ISPM 15 as the:

"International Phytosanitary Measure developed by the IPPC that directly addresses the need to treat wood materials of a thickness greater than 6mm, used to ship products between countries.  It affects all wood packaging material (pallets, crates, dunnage, etc) requiring that they be treated with heat or fumigated with methyl bromide and marked, often branded, with a seal of compliance. "

Wood Pallet Cost Rising

As a result, the total cost of wood pallet usage has escalated dramatically.  Not only has the cost of ISPM 15 compliant pallets increased, shipping documentation preparation and possible border crossing delays consume additional time and resources. 

That coupled with historic problems related to mold growth, damage to shipped product from pallet defects (splinters, nails, etc.) and the outright refusal of some countries and/or customers to accept wood pallets has caused a strong desire to find a wood pallet alternative.

Bulk Bag Solution

If you ship your product in bulk bags there are two solutions that Control and Metering can recommend:

1. Plastic pallet replacement channels.
2. Shipping bulk bags without any kind of pallet-like support.

Plastic Pallet Replacement Channels

We have had extensive experience with BagPal channels.  These are designed to slip into sleeves attached to the bottom of specially made bulk bags allowing the bulk bag to be handled by a forklift just like a bulk bag on a wooden pallet.

BagPal channels are robust, compare favorably price-wise with treated wood pallets and can be reused and recycled.

Also, they provide a traditional means of moving bulk bags with a forklift - any forklift with standard tines can be used to move a BagPal equipped bulk bag.

Plus, a pair of BagPal channels weighs less and is much smaller than a wood pallet.  These features provide two significant financial benefits:

1. Reduce shipping costs by increasing your bulk bag payload by the difference in weight between a pallet and the channels - roughly 30+ lb. Higher payload per bag equals more product in a truck or container.
2. Increase warehouse efficiency by using MUCH less space to store empty channels vs. empty pallets.

Bulk Bags Minus Bottom Support

Bulk bags can be shipped without bottom handling support of any kind.  This has been done in a number of industries for both domestic and export delivery to customers.

Without bottom handling support bulk bags must be lifted using their loops.  Preventing damage and contamination of the bag bottom is also required.

Specially designed bulk bags with unique lifting loops and protective bottom panel barriers solve these issues. 

Shipping bulk bags without bottom handling support is a topic by itself and will be the topic of next week's blog post.

Ever heard of a 'porthole' style bulk bag?  If you haven't we'll fill you in.  If you have, and you're having problems with them, we'll list what you need to know.

A porthole bulk bag has a porthole in its bottom.  A flat bottom liner is inserted into the bag and filled.

Porthole syle bags are discharged using a bulk bag unloader that features a 'knife' to cut the liner through the porthole. 

1. Stuff the liner properly.  One of the key benefits of using porthole style bags for in-house use (you fill and empty the bags within your plant) is that the outer bulk bag can be reused by simply discarding the old liner and stuffing a new one into the bag.  However, unless the liner is properly reinserted, twists or folds can occur that will prevent the liner from being easily cut by the discharger.  This can lead to shredding of the liner - resulting in downstream product contamination - or a badly twisted or folded liner can seriously impede or even prevent easy product discharge.  Work with your bag/liner supplier to develop a Standard Operating Procedure to ensure the liner is properly inserted.

2. Keep the knife sharp.  This advice might seem counter intuitive from a safety perspective.  However, unless the bulk bag discharger knife is sharp you run the risk of tearing the liner instead of cutting it cleanly.  Tearing through the liner can sometimes result in shredding, which in turn can deposit liner material in the product flow.  Product contaminated with liner shreds is a serious problem to be avoided at all costs.

3. Use the bulk bag discharging equipment properly.  A knife style discharger will have a particular procedure that needs to be followed to ensure trouble free cutting of the liner and complete discharge of the product.  Make sure you confer with your equipment supplier to develop a proper procedure for unloading porthole bulk bags.