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!

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.

Many producers of dry bulk solids, who have traditionally shipped their products in drums, boxes or rigid totes, want to take advantage of the financial benfits of converting to bulk bags. 

However, it is often difficult to convert every customer at once.  That means that for at least some period of time bulk bags and the legacy package(s) must be filled.

The problem is how do you handle having to fill multiple packages with multiple packaging machines? 

Changeover can be a significant challenge particularly if your current packaging machine is not portable.  Production scheduling and the time required to simply change from the existing packaging machine to the bulk bag filler can be barriers that prevent companies from benefiting from bulk bags.

What's the answer?

A multiple-package filling machine.  Purchasing a bulk bag filler that also fills drums or boxes or rigid totes - or ALL of these packages - is feasible and economically very attractive.

Filling multiple packages on one machine requires more up front capital as compared to a machine designed to fill only bulk bags.  However, the operational benefits of using a single machine that automatically changes its configuration to fill up to four different packages are significant.

Just think, no delays for changeovers AND you can satisfy those customers who have not yet converted to bulk bags.  A good deal I think.  Plus, there's the financial benefits that immediately hit your bottom line from converting to bulk bags... but that's another story! 

We often run across bulk bag users who subscribe to the idea that bulk totes MUST be inflated before filling.

Not true!

It's understandable why this common practice exists and why it persists: through-pallet densification FIBC fillers.

A through-pallet bulk bag filler is characterised by the bag resting on a pallet throughout the fill cycle.  As you can imagine, if a bulk bag is attached to the filler and left to drape randomly on the pallet prior to filling, it is possible - perhaps likely - that the bag will become twisted or folded on itself and not fill properly.  Hence, bags are often inflated prior to filling when a through-pallet filler is used.

While inflating a big bag is generally a good idea with this kind of bulk bag handling equipment, it takes time during the filling cycle and adds capital cost.  However, there is an alternative.

If you use a filler that features hang filling - the bag hangs from its loops for about half the time it is being filled - you don't have to inflate your bulk bags.

A key characteristic of this type of filler is that a pallet is NOT in the machine while it is filling bulk bags.  Because the bag is not in constant contact with a pallet and because the bag is hung from its loops, you don't have to worry about poor performance from not using inflation.

With a hang filling bulk bag loader the ONLY time you need to use inflation is if your bags contain loose tubular liners.

Stacking bulk bags CAN be done safely.  There are a few things to carefully consider before attempting to stack FIBCs, but if you do your homework and if testing conducted with your product and bulk bags proves they can be safely stacked, the increase in warehouse efficiency can be a remarkable financial benefit.

Here are the things to consider before attempting to stack bulk bags:

1. Is the nature of your product conducive to stacking?  Some dry bulk solids are easily fluidized and behave like a liquid, others densify like a brick.  Where does your product fit within this spectrum?
2. Are your bulk bags properly designed to facilitate stacking?  Unique bulk bag designs exist with features specifically aimed at aiding stacking stability such as stand up loops, strategically placed gussets, etc.  Do you need these features?
3. Is your filling equipment up to the task?  Does your filling equipment densify your product enough to produce a safe and stable FIBC capable of being stacked?

The best way to determine the answers to the above questions is to work with your big bag and filling equipment vendors.  They should be able to conduct tests that will prove that your product can be stacked safely in bulk bags.

Regarding benefits, double stacking doubles your storage space utilization.  Triple stacking improves warehouse efficiency by another third.  And, quadruple stacking - yes it can be done! - reduces your bulk bag storage footprint by a factor of four compared to not stacking at all.

As you can see stacking bulk bags can provide a huge improvement in warehouse efficiency and profit improvement.  If you're interested contact your bulk bag and equipment suppliers and get stacking!

Bulk bags, FIBCs, bulk totes - call them what you will - are usually sized to contain one ton or metric ton of dry bulk solid material.

However, we've seen bulk bag payloads as small as a few hundred pounds and as big as 5,000 lb and more.  That being said, you may be surprised at how often we are asked the size of 'standard' bulk bags - as if there is only one size.

The fact that bulk solids have different bulk densities - usually expressed in pounds per cubic foot - means that for a bulk bag to contain a specific weight it has to be sized accordingly.  For a given weight, a bulk bag filled with a lower bulk density product will be bigger than one filled with a higher bulk density product.

That means that bulk bags end up being whatever size is required to contain the weight of product you want to package.  I.e. there is no 'standard' size!

Here's the basic procedure to size a bulk bag: 

1. Determine the method by which your bulk bags will be shipped: truck, rail, shipping container, etc.  This will determine the maximum width and depth of the bulk bag (and the pallet size if you're using them - you don't have to!).
2. Once the base dimensions have been determined calculate the bag volume required to hold the payload and then calculate the height using the known cross sectional area of the bag (base x width).

So, remember that there is no such thing as a 'standard' size bulk bag and that yours needs to be sized to your specific requirements.  Any reputable bulk bag vendor will be able to quickly determine the right size bag for your application - and then test it with your actual product to fine tune their calculations.

Conceptually, reusing bulk bags is a good thing.  However,  you have be careful that the way YOU reuse bulk bags preserves the 'goodness'.

Let's explore what that means.

Bulk bags - or FIBCs, bulk totes, big bags, Super Sacks® - are an amazingly versatile and economical method of shipping semi-bulk quantities of dry bulk solids.

In every case, the economics of using bulk bags vs. small containers (50 lb bags, drums, etc.) and rigid bulk containers (corrugated boxes, metal or plastic bins, etc.) is advantageous.  The price per lb of shipped product is almost always lower and the financial return from using bulk bags is even further enhanced when handling labor, yield, warehousing efficiency and other factors are included.

Sounds like a winner, right?  Well, it is.

However, the picture can improve greatly if a bulk bag is reused.  Suddenly, the cost per lb of the packaging drops by half every time a bulk bag is reused.

Obviously, that is a financially compelling reason to reuse bulk bags... but it's gets even better!

Think green.  Even if you recycle your bulk bags (yes, it can be done!), reusing your bags has a tremendously beneficial impact on the energy footprint of the package.  Delaying the demise of the package stretches out its use so that the environmental impact of the packaging on a per lb basis is drastically decreased.  Another VERY good thing.

So, those are compelling reasons to reuse bulk bags, right?  Of course.  Then why might bulk bag reuse NOT be a good thing?

Safety.

Plain and simple: if you do not take great care to ensure that each reused bulk bag is safe before it is used again, you have created a potentially deadly time bomb.

Bulk bags, like ANY package, need to be inspected and, if necessary, repaired before reuse.  Skipping this step can result in problem bulk bags being directed back into production.  Frayed lifting loops, loose stiching, fabric tears, UV fabric damage and many other 'small' problems can result in the total failure of a bag posibly resulting in injury or death.

There exists a growing market for used bulk bags.  Brokers can easily be found who sell used bags.  While this is, on the surface, a useful service, you Must take GREAT care to confirm that the bags in question are safe.

For example, photos abound on the Internet showing used bags for sale that are shown bundled and sitting on loading docks or wharfs - outside in direct sunlight.  Woven fabric made from polypropylene tape degrades when it comes in contact with sunlight.  It takes some time to damage the fabric to the point where handling the bag within its safe load limit would cause failure, but it does happen and it is a very real concern.

That's just one way that a used bulk bag can be unsafe for use.  A thorough inspection by a knowledgeable person is required to confirm that a bulk bag can be safely reused.

So, while reusing bulk bags can be hugely beneficial, care must be taken to guarantee the safety of each reused package. 

The safest, easiest and least costly method of safely reusing bags is to insitute a closed loop system whereby the bags are returned to the producer who filled them - where they are inspected and repaired if required prior to being reused.  Often, a third party is involved who performs the inpection and repair service.

Interested in safely reusing bulk bags?  I suggest that you contact a FIBCA member who can advise you on how to implement a financially rewarding - and safe - bulk bag reuse program.

Super Sack is a registered trademark of B.A.G. Corp.

As a manufacturer of bulk bag handling equipment and a provider of bulk bag handling optimization services, we often challenge ourselves with what it is we need to do to meet all of our customer's expectations.

While it's easy for us to take an insular view of what it takes to design equipment with unique functionality, the 'game' is much larger than just that.

Bulk bag filling and bulk bag unloading equipment is perhaps only a small portion of what we provide our customers.  For example, analyzing their current situation, devising customized ways to solve nagging problems and uncovering operating cost saving opportunities that support an attractive ROI all contribute to creating a valuable customer experience.  Then, of course, there is how well we deliver on those promises.

We know that these are critical pieces of the puzzle that lead to Control and Metering - or any vendor - being seen by their customer's as a valuable partner.

However, it occurs to me that the only way to validate the exact set of 'partner criteria' is to actually ask those whom we serve what's important to them.

To that end you'll soon see Control and Metering reaching out to its customers to find out what we REALLY should be focussing on to enhance our ability to be a good partner.

Can't wait!