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.

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.

Looking for ways to improve the sustainability of your bulk bags?

How about reducing their size?

How do you do that?

Do a better job of densifying your product so that it takes less volume for a given weight... and use a shorter bag!

Ideally, the product you put in your bulk bag should be at its maximum packed bulk density when it leaves your bulk bag filler.  If it's not you are using a larger bulk bag than necessary and, more importantly, it may not be safe.

Not all bulk bag fillers do the same job when it comes to compacting or densifying your product.

At Control and Metering we use a 'rule of thumb' that for every 10% you can reduce the height of your bulk bag, the cost reduces by 5%.

So if you can do a better job of densifying your product while it's being filled you're not only lowering your packaging costs you're also improving your packaging sustainability.

A VERY nice win-win!

Unfortunately, Dusting is a Common Problem

While bulk bags can be the most economical package for shipping semi-bulk quantities of dry bulk solids, they often get a bad rap from end-users because the process of unloading them can be dusty.

Excessive dusting during discharge obviously causes a mess requiring additional clean up labor.  However, it can cause significant profit reduction because every pound of product that lands on the floor reduces ingredient yield and increases input costs.

Dusting Can Be Costly!

We know of a food manufacturer whose bulk bag discharging stations create a lot of dusting during unloading.  A plant visit confirmed the mess made during bulk bag discharging, but curiously their floors are always spotless!  

The plant has hose bibs EVERYWHERE, which encourages cleaning.  Seemingly a good thing.  

However, a thorough analysis of their ingredient yield showed that they were losing approximately $300,000.00 annually due to poor yield: TONS of product - along with a good chunk of profit - were being washed down the drain!

While it's true that not all of that waste was directly attributable to dusting from bulk bag dischargers, most of it was.

So, not only is dusting during bulk bag unloading a nuisance and housekeeping issue, it can quickly affect - negatively - the bottom line.

What can be done?

1. Training.  The biggest issue we see with the use of bulk bag dischargers is that operators are not following the manufacturer's operating instructions.  Regardless of the equipment used to unload bulk bags, if it is not used properly optimal dust containment cannot be achieved.  Left to their own devices operators will quickly figure out the easiest way to get product out of the bag - and that often leads to unecessary dust emissions.  Easy operation sounds like a good thing, but the reality of discharging bulk bags is that they require some effort to use properly.  Work with your bulk bag discharger vendor to fully understand how their equipment should be used to best effect and then train and supervise your operators accordingly.
2. Bulk bag design.  We often see situations where fine product sifts through the fabric of bulk bags.  If that sounds familiar your ingredient vendor should be willing to work with you to provide a bulk bag that eliminates this problem.  The easiest solution is to used coated bulk bags that feature a film of polypropylene bonded to the inner surface of the bag fabric.  This should cure most sifting problems.  However, if a coated bag isn't enough your vendor should be using a separate polyethylene liner.
3. Bulk Bag Discharging Equipment.  Bulk bag dischargers come in many configurations.  Some are better than others when it comes to dust containment.  Look for designs that allow easy  and safe access to the bag outlet spout while keeping it enclosed in a hopper that can be connected to a vacuum dust collection system.  However, not all of these designs are created equal!  If the hopper that is under negative pressure is filled with product during discharging, dusting will still be a problem when the hopper door is opened and product that has adhered to the inside of the door drops on the floor.  Ideally, the outlet spout of the bulk bag should protrude out of the hopper during discharge so the only time the hopper sees dust is during the initial stage of product flow and perhaps at the end of the discharge cycle.  Ergonomics are also a key criteria when selecting a bulk bag discharger.  As mentioned above, you don't want your operators circumventing Standard Operating Procedures and creating excessive dusting because the bulk bag discharger is too difficult to use properly.  Carefully evaluate dust containment features and ergonomic design when selecting a bulk bag discharger.

Before we discuss all of the considerations necessary to design a successful high-speed bulk bag filling line, let's first agree on what "high-speed" means!

If you are currently filling four bulk totes per hour, 10 bags per hour may seem to be high-speed.  After all, that's a 250% rate increase!

If you're filling 10 bags every hour, an automated bulk bag filling system that produces 15 - 20 FIBCs in the same time it takes you to fill 10 is a big deal.

However, at least for the purpose of this article, we're going to define high-speed bulk bag filling as producing 30 or more filled bulk bags per hour.

Yes, that's a lot, but it can be done consistently, with excellent weighing accuracy and such a rate can be achieved while producing stable - safe - bulk bags.

Sequence of Events

What happens when filling bags at a total rate of over 30 tons - 60,000 lb - per hour?  Well, exactly the same things happen as when filling 3 bags per hour, except they happen in a much shorter period of time.

Here is the timing chart for a bulk bag filling system designed to achieve a rate of 30 bags per hour:

Those are the same five tasks that are required to fill virtually any bulk bag at any rate.  However, as you can see and as we predicted above, the duration of each task is very short if we want to achieve a total cycle time of only 120 seconds!

High Speed Bulk Bag Filling - Critical System Considerations

Bulk Bag Design

The design of your bulk bag must support the overall system required to achieve a high speed bagging rate. 

For example, is the design of the loops compatible with the equipment such that they will be easily released and not hang up when the bag is automatically removed from the filling machine? 

Is the diameter of the inlet spout big enough to accommodate the filling machine fill head - that has been designed to achieve the instantaneous flow rate necessary to fill the bag in the required time?

Bulk Solid Handling System

The system that moves or conveys the dry bulk solid powder, flake, granules, pellets, etc. to the bulk bag filling system must be sized to maintain the gross throughput of the system.  In the case of 30 - one ton bags per hour, that is 60,000 lb per hour.

Instantaneous Bulk Solid Flow Rate

Ensuring that the bulk material handling system upstream of the bulk bag filler can maintain a continuous rate of 30 tons per hour does not necessarily guarantee that bulk bags can be filled to match that rate.

As can be seen in the timing chart above, over half of the cycle time is consumed by tasks unassociated with actually getting the bulk solid product into the bag.

In our example there is only 55 seconds allowed to deposit 2,000 lb of product into the bulk bag.  That means the required instantaneous bulk solid flow rate is roughly 130,000 lb per hour!

If the bulk bag filling machine performs weighing during this time, a 'dribble feed' task is required.  That means that part of the 55 seconds alloted to filling the bulk bag with product is used to dribble the last, say, 50 lb of product into the bulk bag to maximize weighing accuracy. 

Typically, for it to be effective, the dribble feed time is 10-15 seconds in duration.  That leaves only 40 seconds to fill 1,950 lb into the bag.  In that case the instantaneous fill rate is over 175,000 lb per hour!

Surge Capacity

As described in the above section, the bulk bag is actually being filled for only a portion of the total bag fill cycle time.  The rest of the time - called overhead time - is taken up by other tasks. 

During the overhead time bulk solid product cannot flow into the bag.  However, since our bulk material handling system continuously feeds 60,000 lb per hour to the bulk bag filling system, the product conveyed during the overhead time must be stored above the bulk bag filler. 

Typically, a surge hopper or storage vessel of some kind is used to hold the product conveyed to the bulk bag filler during the overhead time.  Calculations can be made to determine the vessel volume necessary to hold the product - commonly called surge capacity.

Bulk Bag Filling System

The bulk bag filling machine must be designed to accomplish the tasks in the time alloted - while maintaining acceptable weighing accuracy and producing stable and safe bulk bags.

Features such as automatic loop release, automatically movable loop attachments, automatic bag removal, etc. are required.

However, the most critical consideration is that because each task duration is so short, each aspect of the bulk bag filler's design must be optimized to not only operate quickly, but to perform its function properly in so short a time.  Weighing accuracy of +/- 1-2 lb and bags that have been filled to their maximum bulk density can be achieved when filling bulk bags in excess of 30 per hour.  However, specialized designs are required.

Filled Bulk Bag Takeaway

Removing one filled bulk bag every two minutes from the bulk bag filling system is no easy task.  Forklift traffic patterns must be considered as well as the round trip distance from the filling system to/from the warehouse storage point or loading dock.

Pushing The Envelope

Bulk bag filling rates in excess of 30 tons per hour can be achieved.  Filling machines that perform weighing can be made to fill up to 35 bags per hour.  Pre-weighing - weighing the product in a vessel above the filler and dropping the 'shot' into the bag as quickly as possible - can reduce the bulk bag filling cycle to the point where it is possible to produce over 40 bags per hour.

As can be seen there are many considerations that must be addressed when implementing a high speed bulk bag filling system.  Careful work conducted in partnership with the bulk bag and bulk bag equipment vendors is a must to ensure success.

This article was written by Dan Schnaars, President of Ameriglobe LLC, one of North America's premier FIBC manufacturers.

When to Use Liners vs. Laminated Fabric vs. Fabric for your Bulk Bags

When you are in the process of designing your bulk bag packaging specifications, one of the key issues to consider is the kind of environmental protection the bag must provide to your product.

The best answer for you can sometimes be quite detailed.  Here we will consider the three basic types of protection.

Uncoated or Breathable Fabric Bulk Bags.

Bulk bags are made of woven polypropylene. While the weaving makes a fabric that appears quite solid, it is, in fact, breathable.  Air and ambient moisture pass quite easily through plain fabric.  Dusty products contained within can ‘dust' through the fabric and/or the seams of the bag.  For the majority of applications, breathable or plain fabric does not provide enough containment.  Any product contained in a breathable fabric bag will likely reach ambient humidity levels within a few days.

But, some products such as soy bean seeds or peanuts require a breathable container.  The airflow retards germination and mold and is, therefore, a necessary feature.  Many minerals travel in breathable fabric bags due to cost.  The mineral products often have a low cost per ton and the packaging cost is quite a significant factor in the final product cost.  Coating the fabric does add cost to any fabric.

Laminated (coated) Fabric Bulk Bags 

The most common method of environmental protection for your bulk bagged product is to use a bag that has a thin layer of film laminated to the inside of the bag.  This lamination eliminates most of the air flow through the bag. Most products travel well in this type of bulk bag.  Dusty products do not pass through the lamination and dust from the outside does not enter the bag through the weave.  Ambient humidity transfer is greatly limited by the lack of air flow as well.  If small amounts of sifting are not an issue and small amounts of contamination are not an issue, then this bag is most often the right choice.

Lined Bulk Bags

The need for extreme cleanliness, moisture control, or oxygen flow is what generally dictates the need for liners. 

Contamination Issue - Bulk bags are made from a manual sewing process. The fabric itself is often charged with static electricity that causes small pieces of sewing thread to cling to it.  Some companies are vacuuming the insides of the bag and working in clean environments, but this is only a reduction of the opportunity and amount of contamination.  Over the course of time, a loose thread or two will occur.

Sifting issue - In the sewing process, a needle punctures the fabric and carries a thread through the hole with it.  In order to do this the needle has to be bigger than the thread it leaves behind. Powders will often pass through this extra space.  To reduce this, bulk bag manufacturers offer to add ‘sift-proofing' materials to the seams.  Again, while this greatly reduces the amount of product that can sift through the seams, it can never be 100%.  If it were, then bulk bags made in this way would be able to hold water and not a single one can do this.

Only the proper use of a liner can ‘100% guarantee' that there will be NO contamination in your product.

Moisture control - If sifting cannot be prevented, then you can easily see why strong moisture control cannot be attained without a liner as well. The selection of the specific liner is just as important as the selection to have any liner at all. 

Most applications will use a 2 to 3 mil polyethylene liner.  This liner will work for almost all food applications, general moisture control, all sifting and contamination issues.

Specialized liners can be used when there is an absolute and special need.  For absolute moisture control, a liner with foil laminated to it can be used.  Liners with special gas transmission rates are selected when odors need to be contained or oxygen must be kept out.

Hazardous materials almost always require the use of a liner.

Liner attachments - The final piece to this discussion would be the connection between the liner and the bag itself.  Although many companies simply put the liner into the bag with no connection, this will often create problems for the end user during the discharge process. 

If the liner is unattached, it simply falls out with the product and becomes a contaminate in the receiving hopper.  Liners should be physically attached to the bag so that it will stay in the bag as the product leaves the bag.

There are three methods for attachment; sewing, tape tabbing and gluing.  Different products need different strengths of holding power. 

Some products like pellets will flow very easily from the bag.  It takes very little attachment support to hold the liner within the bag.  In this case, any of the attachment methods will work well. 

Other products tend to clump together such as powders.  These products can grab the liner more intensely.  It takes much more holding power to keep the liner attached to the bag. 

While opinions may vary, the method of attachment that involves the greatest number of square inches of the liner for its strength is a good gluing method.  Done well, this method can generate the most holding power possible for the most difficult applications.

Whatever your need, when you are designing a bulk bag package, involve your bulk bag supplier in the decisions.  They should be able to recommend the best product protection for your application.

-Dan Schnaars, President Ameriglobe LLC