Feeding a Bulk Bag Filler in a Portland Cement Plant: The Great Slidegate Debate

Many cement plant operators turn to us because they’re experiencing difficulty achieving high weight accuracy and high throughput for bulk bag filling. The complaint is the same:  The bag filler isn’t doing the job.

In these cases the first question I ask has nothing to do with the bag filler brand or type. I ask this: “Are you using a slidegate feed system?” There’s a good reason for my question because since 1978 CBE has been manufacturing and servicing bagging equipment for the cement industry. Over the years we’ve learned what works best for cement plants. And that’s why I first asked about the slidegate.

Why Slidegates Appear To Be The Right Choice

A slidegate is a simple and commonly used device for controlling the flow of gravity-fed material from a hopper into a bulk bag filling machine. The slidegate’s opening size is manually set by the operator for the desired flow of material. Simple and fast. No wonder cement plants think, at first, that a gravity-fed slidegate system is perfect for their operation.

slidegate assembly for bulk bag filler

A slidegate makes the right choice if speed is all that matters. However, the speed comes at a cost of accuracy, consistency and cleanliness.  The faster you load the bag, the less control you will have and the more these other things will suffer.

Compelling Reason #1:  Why Slidegates Should NOT  Be Used In Cement Plants – Accuracy

Weight accuracy is equally important to speed. In fact, in high volume operations, weight accuracy is where money is made or lost. Unfortunately, slidegates are not the best choice for accurate bagging of Portland cement. This is because the density of Portland cement fluctuates during production (like most granular powders do).

Density of the material in the holding hopper changes and is less or more fluid depending on the amount that the material is fluidized. As the density varies, so does the flow characteristics of the material resulting in off-weight bags. As the material flows through a gravity gate depending on how aerated it is, its density could be anywhere between 70 Lbs./CuFt (if it is aerated) and 94 Lbs/CuFt (if it is settled or packed). Without a more measured and controllable method of feeding material into the bagging machine, achieving acceptable weight accuracy will not be possible.

Compelling Reason #2:  Why Cement Plants Should Avoid Slidegates – Dust

There’s another issue with slidegate controls – dust. Rapid filling by gravity feed creates a sudden, large amount of displaced air that can expel a quantity of material and dust from the bag, briefly overtaking the capabilities of the dust collection system.

Any plant that insists on using slidegates to control the gravity flow of Portland cement to a bulk bag filler must invest in proper product conditioning and dust collection. However, even with these systems in place the equipment operator will find it necessary to manually adjust the slidegate during the production run as the materials characteristics change due to changes in humidity and density.

Alternative Metering Systems for Bagging Cement

As I have explained, slidegates can be problematic in any cement plant interested in weight accuracy and speed for filling bulk bags. Therefore, we recommend a positive feeder such as an auger or a rotary air lock.  Either of these feed systems is an effective solution for Portland and masonry cement bagging.

When bulk bag fillers are required, rather than valve bag fillers, we frequently specify our Model 510 and Model 520 Bulk Bag Fillers equipped with an auger-feed or rotary air lock. Either model has a capacity to handle bag weights from 1,000 to 4,400 pounds at up to 25 bags per hour.

If weight accuracy and/or improving bag fill cleanliness is important, I recommend you consider either upgrading your existing bulk bag filling system with a positive feed system or making sure that your next system includes a positive feed system.

Bag Filling Machine Basics

Often customers come to us with a specific bag filling machine in mind, but after a few minutes of conversation with us about what they want to accomplish in their production line, a different bagging machine is recommended, often a less costly solution.

This post will describe the three basic types of industrial and agricultural baggers and link to other sources on the CBE website. This is a good place to start if you want to  become better informed about bagging.

The Valve Bag Filling Machine

Valve bags are frequently used for packaging powders, granules and blends of powder and granules. These bags are engineered to self-close after filling, so a separate sealing step is not required in the production line. Furthermore, because the bag opening is small and mostly contained during the filling process, dust is minimized.

An Air Packer in Operation

In video #1, a very typical valve bag filling machine, a CBE Model 730 air packer is being used to fill bags with a blend of barite and bentonite – a very fine powder measuring 200-300 mesh.

In this application a single operator places an empty bag onto the machine’s spout. The machine fills the bag to its proper weight. The bag closes automatically. The bag drops to the transfer conveyor.

The Model 730 uses high-volume, low-pressure forced air to propel the powder into the bag, which is why the generic term for the machine is “air packer”. An air packer is any valve bag filler that uses forced air to feed product into the bag.

Video #1

The Versatility of Valve Bag Fillers

Valve bag fillers can also be belt-fed, gravity impeller, or auger-fed, all depending on the size, weight and moisture content of the product being packaged.

Valve bag filling machines are very versatile. For example, the Model 730 shown in the video can fill bags ranging in weight from 20 – 110 pounds. The fill rate, depending on material, is 6-8 bags per minute.

An air packer can be integrated with an automated bag placer and palletizer for semi-automated or fully automated operation. Most units we sell, however, are for manual operations such as depicted in the video. An advantage of CBE machines is their simple operation. Literally, five minutes of instruction is all that is necessary to train an operator.

Palletizing Filled Bags

The packaging process isn’t complete, of course, until the bags are neatly arranged on a pallet for shipping. This is why we design production lines for our customers that improve productivity all the way down the line.

Notice in the video that filled bags are transferred through a bag flattening conveyor that removes air in the bag and shapes the bag for secure stacking.

After flattening, the transfer conveyor delivers the bag to the palletizing station where a worker (without bending over) simply lifts the bag into place on the pallet. Facilitating this is a pallet jack that automatically adjusts to the proper height.

A Bag Filling Machine for Open Mouth Bags

Some products and industries are not conducive to valve bags. If the material is too course, or won’t flow well enough, an open mouth bag is required. Some markets and customers traditionally prefer open mouth bags sealed by heat or sewing. In these situations you’ll need a different type of bag filling machine, an open mouth bag filler like the one featured in Video #2, the Model GWB (for Gross Weight Bagger) being used to package granulated zeolite.

Open mouth bag fillers require a second stage in the production line for sealing the bag. In the video a heat sealer is being used for the plastic bag. Alternatively, a sewing station can be used for sealing poly woven bags.

Notice in the video that although the packaging operation is very simple, open mouth bag filling requires slightly more attention from the operator than the valve bag filler in the first video. Still, operator training involves mere minutes.

Video #2

Open mouth bag fillers are frequently found in agricultural applications – packaging grain, feed, seed, and fertilizer. Granulated minerals or chemicals, such as the zeolite being packed in  video #2, are common applications, as well. Food products and landscaping products round out the possible applications for an open mouth bag filling machine.

The Model GWB fills up to six bags per minute. However other models offered by CBE can fill 20-110 pound bags at rates up 24 bags per minute. An open mouth bagger can be gravity-fed, gravity plus vibrator-fed, auger-fed or belt-fed.

For fast, easy filling of free-flowing, non-dusty powders, granules, and flakes, it’s hard to beat a CBE open mouth bag filler. But, what if you’re looking to transport and store up to 4,400 pounds of material in a single bag? What then?

The Bulk Bag Filling Machine

Bulk bags or “super sacks” are gaining in popularity as efficient methods of storing and transporting large volumes of material – chemicals, plastics, and minerals being the most common.

In Video #3 a CBE Model 530 bulk bag filler is paired with an automated pallet dispensing system for bagging 5-20 bags per hour of plastic resin.

Bulk bag filling looks simple but precise engineering is required to fill a bag quickly without wrinkling the bag or trapping air pockets inside. A properly designed bag filling machine and process ensures proper filling.

Video #3

Watch carefully in the video how the strap holders rotate making it faster for the operator to hang each bag. Also note that before product flows into the bag, the machine blows air into the bag to open it fully.

This high volume application required an automated pallet dispensing system which enables a single operator to fill up to 20 bags each hour.

For feeding product to the bag filling machine, one can choose belt-feed, auger-feed, rotary-vane feeder, gravity-feed, vibratory feed or air lock feeder.

Today, when manufacturers and distributors are looking at ways to reduce material handling costs, the bulk bag (super sack) is gaining in popularity.

Rest assured that one call to Choice Bagging Equipment will connect you with a bag filler specialist who will be able to recommend the best solution for your production requirements and budget. Request a call back here.

Valve Bag Filling Machine – Kaolin Clay [Model 830]

A Kaolin producer in southern Georgia was interested in a valve bag filling machine capable of filling 50 lb and 55 lb (25 KG) bags of Kaolin Clay at a rate of 12-16 bags per minute. The application presented definite challenges in that the material was easily aerate-able.

An Innovative Valve Bag Filling System

The bagging system CBE designed included:

  • Bulk bag unloading hopper
  • Incline conveyor
  • Surge hopper
  • Model 830 impeller packer
  • Receiving conveyor
  • Bag flattener
  • Palletizing station

A ground level bulk bag unloading hopper discharged into an incline screw conveyor. The screw conveyor inclined the material to a surge hopper above a Model 830 Paddle Flow Impeller Packer which packed out the material at a rate of 6-8 bags per minute (depending on product grade).

Filled bags were automatically discharged onto a specially designed receiving conveyor and transferred on an incline through a bag flattener that conditioned each bag before delivering it to a palletizing station at the end of the packaging line. The system required two operators. One to place empty bags on the filling machine and a second to palletize the filled bags at the end of the line.

Each filling sequence was initiated automatically by a sensor at the spout of the filling machine when the operator spouted a bag on the machine. No button push was required. The bag would then fill to weight automatically to a pre-determined weight selected by the operator.

Valve Bag Filling Machine with Accurate Weighing

The valve bag filling machine had an integrated weighing scale, which worked in combination with a single PLC based control package. The weighing controls were especially designed for valve bag filling applications and featured a gain-in-weight totaling display. The controls were designed with the ability to communicate weigh data to a printer or central management control system.

cbe-clay2-case-study cbe-clay3-casestudy

Bag Clamp System for Higher Productivity

A pneumatic bag clamp sped up the placement and removal of the bags by eliminating the need for the operator to clamp and unclamp each bag from the filling spout at the beginning and end of each bag fill.

The flow of material was automatically started and stopped by a multi-position pinch valve (called a pinch tube cutoff). The system controls signaled the pinch valve to reduce flow at a pre-programmed weight. The pinch valve would actuate to reduce product flow before closing at the end of each weigh cycle. This prevented overfilling of the product.

The system provided a high level of productivity and changeover to different product grades was effortless with the integrated digital weighing scale by which an operator could key in target weight in a couple of keystrokes.

When is Used Bagging Machinery the Right Choice?

Selling, servicing and supporting used bagging machinery has been the heart and soul of our company since my family began in this business some 38 years ago. We began as a service company and worked on everyone else’s machinery long before we began building our own.

Over time, we developed a deep knowledge of what worked and what didn’t work based upon what we saw and observed in those other machines. I say all that to tell you this; no one knows used equipment and its value better than we do. I do not mean this in a “salesy” type of way. We are one of the only if not the only bagging equipment company I know of that will offer used equipment along with new equipment without any reservations.

At the end of the day, one of our core operating principles is to connect our customers with the bagging machine that is right for them, not necessarily best for us. We do this because we realize that giving our clients good recommendations builds trust and our customers’ trust is what we have built our business on over time.

With that said, it is oftentimes apparent that customers that call searching for used equipment would frequently be better served with new equipment.

Is a Performance Guarantee Important to You?

Many customers require specific results in terms of weight accuracy, filling speeds, cleanliness etc. Although we can and are happy to offer our professional opinion regarding what we think results will be based upon our past experience, there is no way that we can make such a guaranty with used equipment. Even with our new machines, we require our clients that are seeking specific results to send us their product and bags that we can set up and test run in our test lab to determine what combination of features and functions will produce the desired results.

Many customers want the peace of mind of a very inclusive warranty to give them piece of mind that they will not run into operational issues during their first couple of years of operation and if they do, the manufacturer will be quick to respond to their requests for service and resolve their issues quickly.

Is a Full Warranty Critical to Your Decision?

I am sure that it will come as no surprise that used machinery does not come with the same warranty as new equipment. Used equipment might have “no warranty” or a limited warranty depending on its condition (usually on parts / components only). Almost always, used equipment does not include on-site labor or support. New machinery, by comparison, usually includes warranties on performance, parts and labor.

Does Your Application Demand Advanced Bagging Features?

Many customers are looking for features and functionality that were not available when the older bag packaging machinery was manufactured. While very functional, many used machines have designs, weighing scales, valves, sensors, integrated sealers and other parts that have been replaced by newer, more advanced technology. While time tested and dependable, they are not always capable of delivering the same results as current technology.

For instance, our Model 230 Spiral Flow Auger Packer has an available “quick change” auger feature that allows the flighted portion of an auger to be removed for cleanout or replacement within 2 minutes without disassembling and more importantly without un-aligning the drive. This is one example of many features that were not available with older model machines that are available today.

Will Parts be Available?

Some customers need the assurance replacement parts will be readily if not instantly available. Although most bagging machines are supportable many years if not decades after manufacture, most manufacturers make stocking decisions for what replacement parts to carry in stock based upon current sales. As time passes and more and more older machines are taken out of service, demand for parts of older machines decline and thus fewer and fewer parts for those machines are kept in stock. There is no difficulty obtaining parts for used machines as long as users plan maintenance and are not in time sensitive operating environments. We’re one of the few bag filler manufacturers that offers parts for all brands of baggers.

Used Bagging Machinery can be a Great Idea

Utilizing used bagging machinery is a great way to reduce operating costs. However, there are important considerations that should weighed. Used machines make great fits for general purpose applications and applications where high precision results are not necessarily required. The warranty and replacement parts available for used equipment most always is not the same as new equipment and customers should understand this.

The Automatic Bagging Machine, Should the Machines Take Over?

An automatic bagging machine in this day and age is truly a marvel. Even so, an automated system isn’t right for every situation. I’ll explain the pros and cons of automation in the bagging plant.

Not only is it possible to run an entire packaging line with a single operator that used to be staffed by a large crew, but the wealth of data that can be obtained to continuously refine and improve system performance is unparalleled relative to what was possible even a decade ago.

It is possible to access, control and diagnose machinery that is located anywhere on the globe via computer. Automated bagging machinery can tell us what it is doing and when it is doing it with a high degree of precision. It can be programmed to do just about anything that the mind can conceive.

Automation can be an Accelerator for your Business

You see, I believe that automation is an accelerator. By this I mean that an accelerator is a form of lever, something that generates a larger result relative to the amount of force applied to achieve it. Automation as an accelerator can take various forms.

Is Faster Always Better?

It can literally make things go faster, they can pace work so that a consistent level of productivity is maintained over time or it can free a worker’s time so that the worker can being doing literally two things at once. But accelerating a flawed process with automation will not necessarily fix or correct the underlying issues in that application.

Accelerating a flawed process, as I hope to describe to you in the rest of this article, only shines a brighter light on existing issues that plagued productivity before automation came along.  Automating the wrong process can make existing problems bigger faster.

Automated Bagging Systems are Not For Everyone

Over the years of building, supplying and servicing automatic bagging machines I have come to understand that automation is not for everyone. What I am about to say about automated bagging machinery might sound like a rail against it and to attempt to convince you that automating is a bad idea and that everyone keep things manual. This could not be further from the truth. My company is a strong proponent of and advocate for automation.

But too often, we see customers only partially embracing the commitment required to successfully implement and achieve the results that automating promise. This is because, in my opinion, most companies view automation strictly in a transactional or monetary sense. This is to say, if we buy this automated machine then we will be able to reduce our “X” expense by “Y” usually referring to labor as the “X” expense.

When Manual is a Better Choice

But I have learned that the correct conditions for automating a bagging line must exist to ensure the success of the investment. Operating conditions, bags designed for use with automation and availability of personnel with the needed skills to operate the new system are all critical components of a successful installation.

Fatal Flaw #1: Continuously Changing Variables

Most current automation options that are economically feasible for most operations do not lend themselves to change or the introduction of continuously changing variables. Automation likes to do a repetitive task the same way over and over and over. If you have multiple products, multiple bag sizes, multiple products that have changing characteristics or changing environmental conditions might want to put some serious thought into how that automation will perform in your specific application.

Remember that automation (at least today’s automation) cannot make judgement calls about what to do in a given circumstance. It is programmed to do one thing the same way over and over. So if you have changing variables and flux in your operating environment, it likely isn’t a good environment or automation either.

Fatal Flaw #2: Poor Working Conditions

An automatic bagging machine does not operate well in a dirty environment. Yes, there are some things that can be done to “harden” a robot or other automation for dirty environments (like an air purged jacket for instance) but these things are not a guarantee to fix or solve the problem. And it’s not that necessarily that it won’t operate or that it can’t do the job in dirty environments. But over time, the dust and dirt will get all over the moving parts of the equipment and cause premature wear and tear which can result in higher than expected maintenance costs and downtime if not appropriately planned for.

In my view, adequate dust collection to remove and eliminate all air born dust is critical. A routine cleaning regiment should be implemented to prevent dust and dirt from accumulating on moving parts such as air intakes, air cylinders, rotary joints, rollers and belt drives.

Unlike people, an automatic bagging machine (at least today) does not heal itself. A person goes home at the end of the day perhaps tired and sore. But they relax, they sleep and they recharge on their own before the next step. A machine can’t do that on its own. People must tend and care for it on a regular basis. If this is not a commitment the plant is willing to make, the likelihood of failure of automation in the application will be high and the likelihood that the plant will have an unfavorable experience with their automated bagging machinery will be equally as great.

Bottom line, good to exceptional dust collection systems and housekeeping are critical and essential to making your upgrade to automated packaging machinery a success.

Fatal Flaw #3: Poor House Keeping and Maintenance

An automatic bagging machines must be regularly serviced and maintained to deliver an optimal level of performance. For simple manual equipment, especially if spare parts are kept in stock, it is perhaps not critical if a machine is run to failure (break down).

Usually component failure on manual equipment causes a work stoppage but other than that maintenance personnel can be called relatively quickly, the fixes are easy to diagnose and repair.

Component failure on an automatic bagging machine is a different story. In addition to unexpected work stoppage, with components that move automatically often times at high speed, an automated bagging machine that is not properly maintained can be a hazard to itself and workers in the area. A $5 part could cause thousands of dollars of damage if it causes a crash of two assemblies moving at high speed. To speak frankly, if you think that somehow it is not reasonable to regularly service your equipment and prefer to run to failure of a part in order to keep maintenance costs to a minimum, you should not automate.

Just like you would not ever fly with an airline that was in the habit of only maintaining their airplanes when they broke (if they were able to stay in business that way), automated bagging machinery should be serviced and maintained with a similar level of dedication and commitment. Regular and regimented maintenance is critical and essential to preventing unplanned downtime and keep the equipment running at its peak level of performance.

Fatal Flaw #4: Assigning Unqualified Personnel to Operate and Maintain the System

Automated bagging machines require a more skilled and technically savvy operator than a manual packing line. Manual bagging machines usually can be operated by operators with little to no experience or education. Controls are usually little more than start and stop push buttons. An operator can be taught to use the machine within minutes. The control systems of manual bagging machines are usually limited to motor starters, relays and solenoids. Items that a typical plant maintenance person are very familiar with and work with on a daily basis.

Automated bagging machinery is becoming increasingly more and more sophisticated and requires operators and maintenance personnel with more training and experience. Automated bagging machines often include servos, stepper drives, virtually always a PLC and communicate over Ethernet.

None of this is rocket science, but if your plan to install a machine that is controlled by this type of technology and your personnel aren’t trained and skilled in their operation, you need to be prepared for the learning curve that will follow or consider the possibility that you will need new and different people than those you have traditionally employed to operate and maintain your new packaging equipment.

Finding the Right Home for your Automatic Bagging Machine

In summary, automated bagging machinery certainly offers the ability to increase production and efficiency. Automation offers the possibility to be able to do more with less and the ability to produce more, better, cheaper and faster than ever before.

However, to be successful, a plant must have the right philosophy regarding how to implement automation and enter the project with the right attitude, commitment and mindset.

Automation is an accelerator. It will only produce more of the same quality that was possible before (assuming it is inserted into an old existing process). If there are continuously changing variables in the application, the risk of problems will be elevated. The operating environment needs to be conducive to automation and good and regular housekeeping is a must. A regular maintenance regiment must be put in place and plant personnel properly trained on its operation and maintenance.

If you want to discuss bagging solution options at your plant, we’d welcome the opportunity to offer our expertise.

Bagging Machine Selection Decisions

Often, customers call us looking for a bagging machine as though they were a common appliance. This is understandable since people don’t know what they don’t know and because they are experts at their own specialty and not experts on bagging machines. However, bagging machines are not one size fits all.

Common Bagging Applications for Common Materials

Bagging machines and bagging systems are highly specialized equipment used to fill powders, flakes and granules into bags weighing from ounces to tons. Consider the variety of common bagged materials that you’ve seen before like sugar, flour, pet food, soil, compost, rock salt and concrete and you will begin to get a sense for the diversity of products that go into bags and these are just a few examples.

Bagging of Uncommon Materials

However, most materials we encounter are very uncommon. Things like Sodium Metabysulfite, Chromium Oxide, Zinc Oxide, Attagulite Clay, Barite, Fume Silica, and Vermiculate to name a few. We have seen literally thousands of different materials over our nearly 40 years in the business and each one has its own unique properties and characteristics.

Some flow well. Some don’t flow at all. Some are dusty. Some are relatively dust free. Some are hazardous either in terms of risk of inhalation or ingestion or because they are flammable or explosive.

Achieving Accurate Weight Measurement

Most of our bagging equipment include integrated weighing scales and because of their diverse flow characteristics and handling properties, they all feed differently which can make obtaining accurate bag weights a challenge.

The Right Machine Depends on the Right Bag

There are also a wide variety of bags and bag styles to choose from open mouth bags to valve bags to bulk bags. Each one of these bag types can be constructed of different materials such as paper, plastic, poly woven, foil or a combination of these. Bags can be perforated and / or non-perforated depending on the customer requirements.

All of these factors: product, bag and application all come together to create a relatively unique set of conditions that can influence the result of a given bagging machine in a given application. What is the correct bagging machine for a product in one application, might not be the correct bagging machine for the same product in a different application if machine is installed differently, the bag is constructed differently or if the material is somehow processed differently.

Find your Bagging Machine Zen Master

Small differences matter to results. This is why working with someone who understands material flow and material handling is so important. If material handling was all science, you could look up what to do in a book and there would be no need for an expert to guide you through the process. But marrying product, bag and plant conditions is a blend art and science.

The art is not touch and feeling, it is experience and accumulated knowledge gained over years of testing theory and proving how theory applies to reality. As it goes with anything in life, sometimes the right solution is not the one that makes the most sense on the surface. Properly marrying a bagging machine to product, bag and application requires a combination of knowledge, skill and experience.

If at all possible, the next time a bagging application comes up in your operation, I recommend that you seek out the help of someone that demonstrates a mastery of these three competencies. It will probably end up to be the difference between mediocre results or absolute failure and success.

Don’t hesitate to contact CBE for advice on bagging equipment, service or parts.


The Importance of Pressure for Cement Bagging Machine Performance

It’s not surprising that pressure is an important factor in bagging dry bulk powders; for a cement bagging machine or concrete bagging machine it is especially critical to speed and weight accuracy. This article explains how one customer significantly improved productivity and accuracy by following the fundamentals.

Our Model 730 Pressure Flow Air Packer is one of the most popular concrete and  cement bagging machines on the market today. We recently installed a pair of Model 730 Pressure Flow Air Packers to bag concrete and mortar mixes at a dry mix plant in Montreal, Canada.
Shortly after installation, the customer called to say that the weight accuracy was not within weight tolerance and also that the concrete bagging rate was much slower than expected. Additionally, the machine is designed to empty out completely at the end of a production run but for some reason he reported that when these machines would empty down to its last 2-3 bags of material, it would completely stop flowing out of the machines.
This was a problem because the customer made very small batches of product and had very frequent product grade changeovers that required opening and completely cleaning the interior of the machine between batches. This meant that nearly ever batch, the customer would have to open the chamber and dump 100-150 pounds of material creating waste and extra cleanup time. Our customer asked that I come to the plant to evaluate the machines and determine whether they had some kind of mechanical or electrical problem. The presumption was that there must be some sort of internal problems with the filling machines.

Mysteriously Slow

Upon arrival to the plant, it was quickly apparent that there was a problem. Although in that moment, bag weight accuracy was within specification, the bags were taking unusually long to fill. All of the mechanics of the machine and the controls were operating as designed, but product was taking too much time to load into the bag. Looking at the pressure gauge on the side of the pressure gauge on the side of the chamber, I noticed that it registered no pressure. So I began a diagnostic analysis of the chamber and its pressurizing system which consisted of the pressurizing chamber, the air pad and the blower control valve that regulating the inlet of high volume, low pressure air into the machine.

Looking for Obstructions

I looked for obstructions in the flow of air to the air pad the fluidized the material and also the disseminator that provided the pressurizing air to drive the air with force down and out of the machine. Neither had any obstructions but neither were flowing the amount of air needed to fill a bag properly.

Checking the Low Pressure Blowers

Then I asked to see the low pressure blowers that were supplied with the machines. Our blowers are specially designed to provide high volume, low pressure air to provide the pressurizing and fluidizing air required for the machines to operate properly. At this point, I learned that the blowers had not been installed. Instead the old set of blowers from the previous set of baggers that ours had replaced were left in place and used to feed air to our machines. I asked to see them.

The first thing I noticed is that they were exceptionally old and smaller than the blowers that we had provided. Additionally, the relief valves that prevented the old blowers from over-pressuring when not filling bags had been modified by someone at the plant to vent off half of the air that the blowers could generate before that air was even transferred over to our machines.

I asked what it would take to shut the line down to exchange the old blowers out for the new ones. This was not possible as the customer was in the middle of a campaign and this was there busy season. I told the customer that without knowing the exact condition of the old blowers there would be no way to assure that we could generate the volume of air and pressure required to achieve the results he was looking for.

Modified Relief Valves Restricting Air Flow

He asked me to see what I could do. I went back to look at the blowers. I noticed that the reason the relief valves had been modified was that they were worn out and someone had done their best to rig them to keep them going. Replacing them was the first order of business. I asked to see the pumps we had provided. I Compared the relief valves on our pumps to the relief valves on the old pumps. Fortunately, with some simple plumbing changes, our pressure relief valves able to be retrofitted to the old blowers. Once I replaced the reliefs, we were able hold steady pressure at 5 PSI although the volume was still much slower than optimal.

I then switched my attention to the Model 730’s. They were designed to divide the flow of incoming air from the low pressure blowers and direct the bulk of the air to the upper half of the pressurizing chamber to utilize as pressurizing air and the remainder down to the bottom of the machine to provide fluidizing air to lift and convey the material into the bag. Realizing that the old pumps were not capable of generating the volume of air required to both pressurize and fluidize simultaneously, I shut off completely the pressurizing air and directed the entire air flow to the air pad to fluidize the material. Although this solution had its own drawbacks, the machines were now capable of filling bags at a respectable pace and bag weight accuracy was improved.

Puzzling Weight Fluctuation

We began to run and check weigh all of the bags coming down the line to the bag palletizing system. We would see that the bag weights would begin good but then the weights would begin to drift after a period of time. At this point, I asked what the minimum level of product was required to be maintained above the machine for it to be allowed to run. I was told that there was no minimum standard. I then asked what type of level controls were in the bin to indicate to the operator how much material was in the bin at a given time. I was told there were level sensors in the bin but they were not visible to the machine operator and were only used to signal the blending system when there was room in the bin for the next batch of product.

Maintaining Head Pressure

I told the client that especially without the blower capable of generating pressurizing air to generate artificial head pressure in the filling machine, that maintaining product head pressure of product above the machine would be imperative to maintaining good filling speed and weight accuracy. Varying head pressure is very important as changing head pressure changes how the product flows and how the product flows (and at what rate and consistency) directly affects bag weight accuracy. I then trained the system operators to manually monitor the level of product in the supply bin and to stop filling bags when the level of product in the bin got low. This did not cause a production problem as the Model 730’s were capable of bagging much faster than the blending process was able to make new product.

With these changes in place and the customer now aware of how to compensate for the lack of air pressure and head pressure, the results improved dramatically. Bag fill times averaged 5 seconds per bag per spout on 30 KG (66 Lb) bags and weight tolerance averaged +/- .25-.5% depending on the grade of material packaged.

Paying attention to how to properly install and setup a cement bagging machine (or any other application) is critical. Installing a bagging machine is not simply a matter of sliding it under a supply bin and connecting it to utilities. It must be supplied with a good and consistent flow of material and especially if this is not possible, then assuring that the machine has good access to an adequate air supply is even more critical. And if these fundamentals are not fully understood, then it is advisable to seek the help and advice of someone who can help get the fundamentals right. Failing to pay attention to the details or work with someone who will can be costly and cause results to suffer.

The Difference an Experienced Bagging Equipment Service Technician Makes

We recently supplied one of our auger fillers to a producer of specialty sugar in central New Jersey. Shortly after startup, the customer began calling our bagging equipment service department complaining of poor bag weight accuracy that was way out of range of tolerance.

The initial assumption was that there must be a problem with the weight indicator or load cell, so replacements were sent to the plant to change out. Neither of these solved the problem and the weight problems continued. After a few more attempts to solve the problem over the phone, we decided that a technician be sent to the plant to diagnose the problem. The immediate presumption being that since the weight accuracy was poor then there must be some problem with the machine.

Upon arriving to the plant, our technician first calibrated the machine and then checked it for repeatability. Repeatability means starting with the scale at 0.00 then adding a known weight (50.0 pounds as an example) and making sure that the scale climbs to that weight and returns to zero several times in immediate succession. The scale passed this test.

Next, our technician had the customer load product into the machine. The first two bags came off the machine within the specified weight tolerance and then soon after the weights began to become erratic and get progressively worse. Our technician again used the known test weight to check the calibration of the machine. This time, the scale would not repeat. The only difference between the first calibration and scale check was that product had been loaded into the machine.

The Case of the Melted Sugar

At this point, our technician made the assumption that somehow, the product itself must be influencing the scale. Knowing that one of the characteristics of sugar is its tendency to melt when heated or pick up moisture from the air and get hard, our technician wondered if this could be the problem.

So he removed the filling spout of the machine and noticed that it had hardened material caked up on its interior walls. This is a problem for an auger valve bag filler as the auger within the filling spout is rigidly mounted to the framework of the machine and is not part of the weighing scale. Yet the filling spout that surrounds it is what the bag hangs from to be weighed and is part of the scale. Any solid contact between auger and spout which was the core problem in this case would make results suffer greatly. Because once the material hardened inside the spout, every time the auger would rotate it would push against that hardened material and thus the spout and wreak havoc on bag weight accuracy. We alerted the customer so that he could adjust his cleanout procedures to make sure that product would not build up on the inside of the spout.

bagging equipment serviceNext, our technician looked to the controls of our machine to see what could be adjusted to prevent the sugar from heating up inside the machine. First, he looked at the variable speed auger drive and slowed its speed down so that auger would not generate as much heat and friction as it rotated. Then, he turned the auger reverse time in our motor control panel to zero. The auger reverse function is designed to provide a sharp stop to material product flow by reversing at the end of the bag fill and pulling the material back away from the end of the filling spout. Based on his considerable experience, our technician made the assumption that the auger reversing function could be contributing to the compacting the material inside the machine because as it reverses, it reverses the product in the spout into product in the housing. The thought was that if the material was hot or sticky, that reversing the auger might exacerbate the problem. So he turned the reverse function off.

With the spout cleaned of buildup and these two changes in place, our technician asked for the customer to try filling some more bags. The results were markedly improved. Bag weights averaged within 0.3 pounds of the target weight. Fill times were still within expectation. However, our technician knew that the machine was capable of better.

Next, our technician began looking at the feed system of the machine. It was being poorly fed. First, it only had the capacity to hold a couple of bags worth of material. Second, it had no level controls to indicate when there was sufficient material above the machine to fill a bag. Third, the bin was built such that the material bridged within it, so that only a small portion of the material within it would empty down into the filler and the rest would stay stuck inside the bin. And finally, the bin was being fed by a screener that could not screen the material as fast as our auger filler could bag it.

The small bin coupled with the lack of level sensors and the fact that the bagger was faster at emptying the bin than the screener was at filling it meant that our filler was at times being starved for material. Our technician pointed this out to our customer and helped them to install a vibrator on the side of their hopper to knock the material loose from the walls of the hopper and improve its feed to the machine. Our technician also trained the operators to make sure that the hopper was full before beginning a bag fill on the machine.

With this simple adjustment and no further adjustments having been made to the bagger itself, weight accuracy further improved to within 0.1-0.2 of the target weight. The presumed problems (the machine) turned out to be a combination of educating the customer on the importance of cleanout and product flow and assisting them with finding the ideal set of operating parameters to make the machine run at its peak capability.

A good technician can considerably shortcut learning curves with his vast knowledge of machine and applications. Sometimes subtle clues that may seem unimportant turn out to be the things that help identify the solution to the problem. Sometimes these things can be divined over the phone. But sometimes, these clues do not come through the phone either because the customer disregards what he is seeing as unimportant or doesn’t understand what they are seeing. Sometimes, there is no substitution for experience, a trained eye and a skilled hand.

The Fundamental Pillars of Smart Industrial Bagging

Regardless of which type of bag an operation uses – valve, open mouth or bulk bag – the ultimate goal of virtually every industrial bagging operation is to fill and seal as many bags as possible cleanly and accurately within a specified time period. Yet while the goal is simple, bagging dry bulk solids can often be tricky in implementation.

There are interrelated factors that must be in balance in order to ensure a successful operation. Three of these factors work together like the legs of a three-legged stool. If one is missing or not in balance with the others, the stool will not set right or possibly topple over. These three factors are:

  • Product
  • Bag
  • Machine

A Corollary Relationship

There is a direct and corollary relationship between these three aspects in every bagging application and the right combination can mean the difference between success or failure. The concept is simple; if one pillar is out of balance with the other two, the results of the entire installation will suffer. Furthermore, a small change to any one of them – the product, bag or machine – necessitates a change in one or sometimes both of the others.

The Cause of Many Problems

It’s very common to blame poor results on bagging machinery, but often times bagging equipment is not the largest problem. It’s just as likely that product characteristics have changed (or in some cases continuously change). Working in partnership with a competent bag supplier and machine manufacturer can help to steer clear of common pitfalls and avoid hazards that might otherwise produce in poor results.

An Example of a Powder Bagging Problem

As an example, consider a producer of a powdered material that decides to upgrade its packaging machines. The producer’s representatives search for and find a machine that has the combination of features they are looking for at a price they can afford. They conduct testing on the machine prior to purchase and all projections look excellent.

The new machine is installed and put into operation. At first glance, all appears well. But soon operators complain that the machine is spilling a large amount of product during the filling process or dusting excessively. Or perhaps the bag weights are out of specifications for weight tolerance. Any of these problems could be caused by the bagging machine itself. But they could just as easily be caused by a bag that is too small (one that fills to volume before it fills to weight) or the bag could be sized right and the bagging machine could be performing properly and the product is being over-aerated by upstream process equipment or somehow the product is being inconsistently fed to the filling machine. The point is that many times the cause and effect of problems within a bagging application might or might not be what they appear to be. There is a balance that must be achieved between bag, machine and product to make good results possible.

Pillar #1, The Product

The installation of any new industrial bagging equipment should begin with a thorough analysis of the product and its properties as well as a careful review of the environment that the machinery will be installed in. Crucial traits such as flow property, bulk density, moisture content, de-aeration characteristics, compaction properties are all important factors in choosing the correct machine for the application.

Additionally, the design and construction of the silo / supply bin and the product feed system should also be reviewed to ensure that the bagging machine is being supplied with material that is consistent and is not being subjected to influences of upstream equipment that will change the products density, flow characteristics and consistency.

Finally, sometimes product manufacturers will change the formulation of their products after their equipment has been operating for a period of time. When this happens, it’s important to test and analyze the new material mix to determine what the ideal bagging machine settings and bag characteristics should be to use with the new product formulation.

Pillar #2, The Bag

Although it does not seem difficult, choosing a bag that is engineered correctly for a given application is not as straight forward as it may appear. Frequently when a producer experiences poor results, the root cause of the problem is a bag that is not appropriately designed for that specific application.

This is not to say that the problem is the quality of the bag or the producer of the bag for that matter. For instance, a common problem we see on a regular basis is that bags are sized to fit the packed (non-aerated) bulk density of a given material while most times those same materials are fed into the bag at their loose (aerated) bulk density. In practical terms what this means is that when the product is moved mechanically or pneumatically, it is entrained with air and when that air is mixed with the material the bulk density is temporarily lowered.

The problem is that most people sell their products by weight, not volume. The dilemma they face is that if they sized their bags to fit the loose (aerated) bulk density of their material, the bag would look like a raisin when the product settled and returned to their non-aerated state. But to make matters worse, frequently they will use the bag and the bagging machine as a mechanism for compacting the material into as small a space as possible.

valve bag for industrial baggingOn the surface, it makes sense. A dense package looks better. It travels well and is less susceptible to load shifting during transit. And the more material that can be fit into a smaller space, the less it will cost to ship. Yet, the simple fact is that a bag that fills to volume before it reaches the target weight will produce a list of negative and unwanted side effects. The bag will be full but the bagging machine that is designed to fill by weight will continue to attempt to deliver material into a bag that has no more room to fit it. The result is product spillage and dusting and bag weights that are out of tolerance.

Perhaps the more critical of the two is the bag’s ability to release air pressure, and that depends largely on the materials used to fabricate the bag. Many factors must be considered here, including whether the bag is made with traditional paper, high performance paper, plastics or a combination. The weight of the material and the number of layers also need to be considered. The ability of a bag to release internal air pressure is greatly impacted by the inside mechanics of the bag, like whether there is a layer of polyethylene (PE), to what extent the PE is perforated or sliced, and where in the layer sequence the PE is inserted. The ability of the bag to release air pressure subsequently impacts filling speed and overall machine performance. For instance, in the case of an air packers which work by creating an imbalance of air pressure between high pressure (the pressurizing chamber) and low pressure (the bag), if the air pressure inside the bag equalizes with the pressure in the pressurizing chamber of the machine, the product will stop flowing or flow slowly.
The second factor, consistency in the quality of the bag’s construction, can impact the filling process in three ways. First, in automated applications, if bag tolerances vary from bag to bag due to loose manufacturing tolerances of the bag manufacturer, the machine might have issues consistently placing the bag on the spout for filling. This could also affect the way they stack in the magazine, which can lead to misfeeding in the system. Finally, if there are issues with the quality of the bag or inconsistency in characteristics like perforation, efficiency can be compromised due to poor de-aeration.

Sometimes a bag change may have nothing to do with a supplier, but is instead the result of a well-intentioned machine operator who sees an opportunity to save a penny or two per bag by making a change. Or perhaps the company’s purchasing department decides to switch to a bag with fewer layers.

Regardless of the reason, the company needs to step back and consider how the change will impact efficiency and make adjustments to the other two points of The Bagging Triangle to compensate.

Pillar #3, The Machine

The key to machine selection is to work with a manufacturer who understands the three pillars of bagging. A tell-tale sign of a manufacture that understands the relationship of these three elements within a packaging process is one that offers to test product bag and machine together in order to make competent equipment recommendations.

Test Samples of the Product on the Machine

Although there are some straight forward applications that do not require up front testing (like bagging corn or rice), the process typically starts with the machine manufacturer requesting a small product sample from the customer to analyze.

If the manufacturer’s initial analysis of the product matches with his understanding of the application, customer requirements and the customer’s available budget, it is then a best practice to have a larger sample of the material sent to the manufacturer so he can set up a simulated product run of the material under a load of the customer’s actual product tested on the customer’s actual bag.

Testing the product is a critical step that helps define the product characteristics, the bag’s filling behaviors and additionally to identify any previously unforeseen issues that were not considered in the original analysis of the application. From there the machine manufacturer can identify and define the proper filling technology to achieve the ideal productivity level. In addition, this testing helps determine optimal filling rates, how many spouts are needed to hit those rates, and what settings will need to be maintained on the machine to achieve them.

The initial setup is only the beginning. As a machine operator or company makes changes to the bag or the product, it is imperative that they evaluate the effect of those changes and adjust parameters on the machine to maintain balance. Before making the machine adjustments, it’s always wise to consult the manufacturer. Even well intentions changes can produce negative results if consideration is not given to how product and bag must also be altered to balance those changes.

In conclusion, it is the sum of product, bag and machine that creates the conditions for optimal efficiency, productivity, and profitability. Working in partnership with competent bag and equipment manufacturers to find the right combination of product, bag and machine is imperative to the success of the application and ensure that high quality results are achieved.

Rebuilt Bagging Equipment Service

Rebuilt bagging equipment is a great option for many companies Let’s take a look at how Bagger ER.™  Equipment Rebuilding Service brings new life to old work horses.

Time, wear and tear eventually take a heavy toll on a machines ability to operate at peak performance. Original tolerances are lost. Valve efficiency decreases and seals begin to leak. Over thousands and thousands of bags produced even the best machines can become unreliable.But as long as the machine is still in reasonably good physical condition, it might be a good candidate for rebuilding and /or upgrading.

The Hidden Costs of Installing New Bagging Equipment

Replacing exiting machinery with new machines can mean costly projects requiring extensive engineering, modifying or rebuilding supply bins, utilities, dust collection, conveyors, etc. Additionally, time spent that a packaging line is down and not producing is time that an operation cannot make product and more importantly money. Rebuilding the machine you already have can both keep costs down and reduce potential downtime.

Rebuilding the Bagging Equipment On-Site or in Our Facility

Rebuilding the machine can be done in either in position in the production area or removed from service in the maintenance shop in an area that is more conducive to working on and repairing equipment. Rebuilding the machine can be simply be bringing the machine back to its original specifications or it can be upgrading and updating it for new service or with capabilities that are enhanced above the specifications of the original design.

What can Rebuilt Bagging Equipment Include?

A typical rebuild will include new controls (both pneumatic and electrical) and weighing systems and bought up to date with current technology. It can include replacing all major wearable parts, air cylinders, rubberized parts, switches, hoses and fittings. If the rebuild is done at our facility, we can also disassemble, sandblast and repaint the machine to return it to as close to new condition as possible.  Additionally, in the process of rebuilding the machinery we can catalog the machine and detail all of the specifications we rebuilt it to so that on-going support and service are quick and easy.  Before deciding to replace your machinery with new equipment, please consider that you do have options.  Rebuilding existing bag filling machinery can considerably extend the service life and support-ability of equipment you already have and allow it to provide you with many more years to come while saving your thousands of dollars in the process.