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Feeding a Bulk Bag Filler in a Portland Cement Plant: The Great Slidegate DebateValve Bag Filling System for Calcium Carbonate [Model 830]Fully Automatic Model 230 Valve Bag Filler for PowdersBulk Bag Filling System for Powdered Carbon Black [Model 520]Bulk Bag Filling System for Kaolin Clay [Model 510]Model 530 Demonstrational VideoModel 510 Bulk Bag Filler

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.

Valve Bag Filling System for Calcium Carbonate [Model 830]

A construction material supply company in Monterrey, MX wanted to install a valve bag filling system for various grades of calcium carbonate into valve bags from 25-50 KG (55-110 Lb.) at a rate of 400 bags per hour. The client was looking for a system solution to convert bulk bags of material into 25-50 KG (55-110 Lb.) bags. The target rate for the system was 9,000-13,000 KG (20,000-30,000 Lb.).

Valve Bag Filling System for Calcium Carbonate

The system CBE designed included a ground level bulk bag unloading hopper that 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, dependent upon 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 prior to 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.

Valve Bag Filling System for Calcium Carbonate | Model 830Designed for Productivity and Control

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 automatically fill to a pre-determined weight selected by the operator. The 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 totalizing display. The controls were designed with the ability to communicate weigh data to a printer or central management control system.

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 as to prevent overfilling of the product.

The valve bag filling system for calcium carbonate 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 easily key in target weight with a couple of keystrokes.

Fully Automatic Model 230 Valve Bag Filler for Powders

Bulk Bag Filling System for Powdered Carbon Black [Model 520]

A carbon black manufacturer in southern Ohio required an automated bulk bag filling system for a new packaging line for filling granulated activated carbon. Their project had several requirements. First, the client needed to fill bags weighing 500 – 2,200 pounds with a large variety of dimensions and little to no change-over time. Second, they requested a system that could fill one bag directly on top of another (double-stacked) to minimize the amount of motions it would take a forklift to load a two bag consolidated pallet into a truck for transport.

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Bulk Bag Filling System for Kaolin Clay [Model 510]

A client in Guyana was seeking a bulk bag filling system to fill metric ton bulk bags of Kaolin Clay. Kaolin clay is a very fine, free flowing powder that is easily aerated. If mishandled, aerated Kaolin can prematurely fill the volume of a bulk bag causing slow bag fills and the potential for product spillage. Additionally, loose filled into the bag would have made the bag unstable and difficult to transport once disconnected from the support structure of the filler.

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Model 530 Demonstrational Video

Model 510 Bulk Bag Filler