Selecting the ideal conveyor can become a daunting task for the buyer who may not be aware of the advantages of the individual types. A product feasibility test is always advisable to determine the most suitable conveyor for the material concerned, the distance involved, and the throughput required. However, the following guidelines can be used as a starting point.
Flexible Screw Conveyor
The simplest and low-cost solution is the flexible screw type, comprising a stainless-steel spiral rotating within an UHMWPE food-grade tube. This type of conveyor suits materials with a bulk density up to 2.5 kg/l and can carry material to a maximum distance of 20m, although multiple units can extend to greater distances as required. Maximum throughput rate is 20,000 kg/hr.
The term ‘flexible’ means that the tube and the spiral within it can be curved to some extent. This creates installation flexibility to convey around any obstacles between the inlet and outlet.
The spiral itself has a round cross section in most applications, but a flat version can be used for cohesive or fine materials. It is desirable to have a generous head of material in the feed hopper, as this assists the elevation of material when starting. Also, the conveyor is designed to run full of material; empty running will lead to excessive noise and wear.
Flexible Screw Conveyors in Action
Flexible screw conveyors are used at Farley Health Products in Cumbria. The plant is maintained at full pharmaceutical levels demanding stringent operating standards. An intermediate bulk container (IBC) containing blended product is placed above a sealed hopper. Once in place, the valve of the IBC is opened allowing the product to flow into the hopper without any risk of atmospheric contamination or escape of dust.
The conveyor then carries the product at a very steep angle to a packing system. The system fulfils the very highest levels of hygiene and dust containment, despite strict operating parameters.
The main advantage of the flexible screw type is its simplicity. This results in short installation times and low maintenance. USDA 3A-accepted designs for pharmaceutical use are available, and the whole system can be stripped down for cleaning in minutes. Wear is a problem only with abrasive products, and life with other materials is almost indefinite. Tubes and spirals can be easily replaced.
The aero-mechanical conveyor has the alternative and more descriptive name of a rope and disk conveyor. The rope is actually a continuous loop of steel cable with a series of equally spaced disks secured to it. It travels through a tube around a drive sprocket and a number of idler wheels. This type of conveyor is capable of conveying material vertically up to 20-25m. A major advantage of this type of conveyor is that degradation of the product is almost negligible. This is because the material is carried along in moving pockets of air which are created between successive pairs of disks, similar to the effect of a vacuum or pneumatic system but at significantly lower speeds. Another advantage is that the aero-mechanical conveyor does not need a cyclone or filter to separate the product from the air.
Furthermore, the air carrying the material is not expelled at the outlet. The material is separated from the air that carries it, and the unloaded air current is directed down the return section of the tube. It is therefore retained in the tube circuit. Typical maximum rates of throughput are oats 40 tn/hr; milk powder (26% fat) 20 tn/hr; and granulated sugar 80 tn/hr. If installed vertically, the throughput of the aero-mechanical is unaffected, and material can be lifted at the above-stated rates of throughput to 20 or 25m.
Throughput of the flexible screw conveyor, on the other hand, will diminish the steeper the angle at which it operates. The extent of this depends on the nature of the material. The problem is caused by fallback of material back through the center of the spiral, which can be checked by the provision of a central core or tube. Single flexible screw conveyors of 6 to 8m in length can then be used in the vertical.
An aero-mechanical conveyor should always be started empty and stream fed. In some cases, a controlled feed device, such as a screw or flexible screw conveyor, will have to be used. Maintenance needs are moderate to high. The rope must be tensioned occasionally. Rope life depends on conveyor length, the number of starts and stops, solids loading, and whether routine inspection and tensioning are properly performed.
A pneumatic conveyor uses air to convey materials through an enclosed pipeline. It provides a solution for any user requiring a system that is easy to route, has few moving parts, is dust-tight in operation, and completely empties the system of product with minimum residue. Most systems are derivatives of three basic technologies employing some common equipment in terms of filtration, pipeline fittings, blowers, or compressors.
Vacuum conveying is made under negative pressure, but its use is usually restricted to throughputs of around 10 tn/hr over 50m. The motive air force is provided by either a roots pump or side-channel high-efficiency fan sited at the receiving end of the system. Air-powered venturi systems are also used for low-capacity conveying. However, despite their comparative low capital cost, they can prove more expensive to run.
Vacuum systems are regularly used to transfer material from bag dump units, open containers, drums, silos, and big bag dischargers where longer transfer distances and excellent route flexibility is required. Variants of all the above types of conveyor can be produced in mobile forms for processors who require transfer of materials at several locations.
Wherever materials need to be transferred, vacuum conveying offers distinct advantages in terms of good product flow rates and low maintenance costs.
The main advantage for this type of conveyor is the fact that the product will only come into contact with air throughout the conveying line. Coupled with their dust-free operation and easy-to-clean features, this makes them particularly suitable for transferring food and pharmaceutical materials where the most rigid standards in hygiene and containment need to be met and maintained. The product range for these materials is virtually unlimited and is used for salt, sugar, flour, starch, spices, yeast granules, glucose, talc, and paracetamol. Other industries include the chemical, plastics, water, and minerals.
*This article was first published on Powder Bulk Solids.
Pneumatic Vacuum Conveyors vs. Aero Mechanical Conveyors (AMCs) – which is best?
Are you looking to see which conveyor is best, Pneumatic Vacuum Conveyors vs. Aero Mechanical Conveyors? Spiroflow has been at the forefront of the bulk material handling industry for more than 48 years, selling both types of conveyors. In this short article, we cover how each type of conveyor works, their similarities and differences, and how to best determine the best solution for a particular process.
Which is which?
Pneumatic (Vacuum) Conveyors
In a pneumatic or vacuum conveyor, the product is conveyed in a suspended stream of gas, usually air. When particulate materials are metered into an airstream, at an optimal solids-to-air ratio, the differential air pressure generated via a vacuum pump creates a high enough velocity to move the materials within the conveying tube.
Pneumatic conveying is a simple option to move material across challenging routes. The product is moved hygienically and is a good fit for several applications.
Aero Mechanical Conveyors
Aero Mechanical Conveyors are effectively ‘mechanical’ pneumatic conveyors offering many advantages of vacuum conveyors but at a reduced capital cost. It also has reduced running costs and operates without the hassle associated with the filtration equipment required to separate your product from the conveying air. The movement of the conveyor is so rapid it aerates the product. As a general rule, each pocket contains about 80% air and 20% material.
It is one of the most efficient methods of conveying materials. Its dust-free and clean handling properties make the conveyor a good fit for many applications across several industries.
What are the differences?
What makes each stand out when you compare Pneumatic Vacuum Conveyors vs. Aero Mechanical Conveyors ? One may be a better solution for a particular process than the other. This next section examines the differences between both types.
The addition of a DART Automatic Rope Tensioning device can prevent needless maintenance issues, particularly during the initial breaking-in period of the conveyor or critical 24/7 operation when correct tensioning of the rope assembly is essential to ensure smooth operation.
Regular inspection and maintenance are not always an option if resources are stretched, or if the conveyor is in an inaccessible location, so the DART is a valuable option. Spiroflow offers the DART on AMCs and has seen examples of well-maintained and tensioned aero-mechanical conveyors running for 15 years before spare parts are required.
Is power consumption a priority?
AMCs can convey material at a rate from 400 Cubic Feet per hour to 1840 Cibic Feet per hour depending on the diameter of the tube. These conveyors can achieve this by using a drive motor between 2-7.5 Hp through a gearbox. Pneumatic conveyors require a 20-40 Hp blower to reach comparable rates to an AMC.
Is noise a factor?
Pneumatic conveyors are much louder than AMCs, which operate below 85dBA. Pneumatic conveyors must be remotely installed or have mufflers installed, which adds to the cost of the system.
Does your process require multiple inlets or outlets?
Multiple outlets on vacuum conveyors require a separate receiver, its own pressurized air supply for filter cleaning as well as its own feed control valve and diverter valves. Additional piping is also needed to feed each individual usage point.
Each receiving point requires venting of the motive air as well as filters, valves, diverters, and additional piping to direct product to each use point for pressure systems.
Multiple inlets and outlets can easily be integrated with AMCs. When multiple outlets are used we recommend that the conveyor operates at half speed. This ensures that the material exits the conveyor properly. A tube valve at each outlet provides a smooth path for the ingredient to pass through.
What about venting?
One of the major advantages of an AMC is that it’s a balanced system. Ambient air is drawn into the conveyor along with the material and the material is discharged at the outlet of the conveyor. The displaced air is drawn back into the conveyor creating the balanced system. There are no special venting or filtering requirements because there is no pressurization at the discharge point.
Still have questions?
Do you still have questions about Pneumatic Vacuum Conveyors vs. Aero Mechanical Conveyors? It’s difficult to say which conveyor will truly work best for your process without an engineer knowing more about your operation. Not all processes are the same. At Spiroflow, we have a team of engineers in the United States and the United Kingdom that can help you. Feel free to contact us if you have any more questions.
Increasingly, manufacturers are recognizing the advantages of transporting dry bulk ingredients in flexible intermediate bulk containers (FIBCs or bulk bags). The savings in ingredient costs, material handling, warehousing and transportation requirements can be substantial.
These benefits can only be realized when appropriate bulk bag filling equipment is applied. Properly designed FIBC bulk bag fillers deliver a dense, stable package that can be safely and easily stored, transported and discharged. The savings that properly filled FIBCs deliver can be augmented by automating the filling system to increase filled bag output.
Depending on the application, automated bulk bag filling systems can range from a single, microprocessor-controlled machine filling 10 bulk bags per hr, to multiple units each outputting 20 bags per hr, to a single, multistation filler production 70 one-ton bags per hr.
First, Fill Bulk Bags Properly
Any benefits from filling FIBCs in greater volume must be qualified by careful analysis of the quality of the resulting filled bag. For example, if you use one filling machine to fill 20bags per hr without proper densification, but then have to store them unstacked or in racks because the bags are leaning and unstable, you are paying a premium for storage space, transportation and labor.
It is most effective to specify a bulk bag filling machine that maximizes the ingredient in the bag and produces a straight and stable package. Then, once you can stack, convey and transport the filled bag efficiently, you can investigate automation techniques to best match your production rates and secure the highest efficiency for your operation. Look for a bulk bag filler designed to hang fill the bag to produce straight sides and to fill the corners of the bag first to maximize stability. A fill should also densify and compact the ingredient and weigh the bulk bag accurately and reliably.
Bulk Bag Filler Automation Opportunities
Filling a bulk bag comprises three main operational steps: rigging the bag, filling the bag and taking the filled bag away from the machine. Automation of an FIBC filling machine can be approached on four levels: 1) adding an automatic control system to a manual machine, 2) automating the removal of the filled bag and placing of the pallet (if necessary), 3) preweighing the ingredient to reduce overhead time associated with bag rigging and ingredient feeding, and 4) providing a multistation machine to simultaneously perform the three operational steps.
A typical filling operation requires the rigged bag or liner to be inflated, the weight of the machine or part of the machine to be tared out, the fill to be initiated, the densification and compaction to be cycled, and the fill rate to be slowed by some method in order to successfully achieve the target weight.
A microprocessor-based controller can automate almost all of these steps. Once the operator has rigged the bag and inflated it, taring the weighing system initiates the automated fill cycle, whereby the controller takes over the sequencing of starting and stopping ingredient flow into the bag, densification and weighting. A typical bulk bag filling system of this sort can achieve an output of up to 10 bags per hr depending on the maximum flowrate of ingredient into the bag. A manual system may be only capable of six to eight bags per hr.
Automatic Bulk Bag Removal
Typically the filled bulk bag is removed from the filling machine by a forklift truck. Providing a means of quickly freeing up the space inside the filling machine to rig a second bag, once the first is full, can increase the output rate and reduce the need for a dedicated forklift truck. Roller or chain conveyors can be positioned in the filler to remove the filled bag automatically. Conveyors, either motorized or gravity type, can be added to allow filled bag accumulation for later transport by forklift truck.
Pallet and slip sheet dispensers can be added to the system, along with additional motorized conveyors, to automatically position a pallet in the machine or to pick up the filled bag on a pallet. This eliminates the need for an operator to manually place the pallet in the machine.
Automatic bulk bag removal can increase the output of a stand-alone, microprocessor-controlled filler to 12 to 14 bags per hr. Filled bags with specially designed lifting loops can be handled easily with fork trucks. This may further increase system output as pallet need not be accommodated.
Preweighing Bulk Bags
The final step to increase the output of a single station filler is to reduce the time required to feed ingredient into the bag to meet a target weight. This can be done by preweighing the ingredient in a weigh hopper located directly above the filler. The “charge” of ingredient is fed into the hopper to the target weight while the system or operator removes the previously filled bag and rigs the next.
Once the new bag is rigged, the preweighed charge is dropped into the bag quickly. As soon as the charge has left the preweigh hopper the system begins to fill the next bag’s charge in the weigh hopper. In this configuration, the bulk bag filling machine itself does not perform weighing and, therefore, does not require a weighing system. However, the overall control system must be expanded to simultaneously perform weighing in the preweigh hopper while controlling the other functions associated with densification, automatic bag removal and pallet and slip sheet dispensing. Pre-weighing, in association with automated controls and automatic bag removal, can increase the output of a single filling station to 20 bags per hr.
Multiple Bulk Bag Fillers Increase Bulk Bagging Rate
For production rates greater than 20 bags per hr, multiple bulk bag fillers can be used. The capital cost versus production rate must be assessed to arrive at the most effective total system configuration. For example, if 30 bags per hr are required, two automatic bag removal systems would be most appropriate. If 40 bags per hr are required, two preweighed, automatic bag removal systems would be selected.
More bulk bag filling machines can be added and sequenced to further increase bag output. If more than 50 bags per hr are required a decision must be made based on available space, operator availability and associated labor costs and capital cost. A high-capacity system may be justified in this case.
If more than six bulk bags per hr are needed to be filled, it is worth considering automation possibilities. A single machine’s output can be enhanced by filling-specific controls, preweighing, and integrating conveyors and pallet and slip sheet dispensers. Further, increases in output can be achieved by applying multiple units as long as sequencing of the operator functions is carefully reviewed.
View our bulk bag filler solutions here.
Two potential hazards that can arise during bulk bag handling:
- Explosion: During filling or discharging some bulk solids can generate enough static charge to ignite flammable vapors, gases or dust. Also, various bulk solids, if allowed to accumulate in a high enough concentration, may explode if exposed to an ignition source.
- Health hazard. Bulk solids that present a health hazard to humans via direct contact.
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/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 during 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 easily forgotten resulting in disaster.
Equipment used in situations where static discharge could ignite flammable substances must, as a minimum, have ground lugs. Depending on the Area Classification electrical components may have to be intrinsically safe and/or explosion rated.
If the product being filled or discharged 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 an appropriately designed 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.
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 lose 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.
Further, bulk bags must be designed to prevent the escape of product particles during handling – otherwise referred to as ‘sifting’. Coated or lined bags can be specifically designed to suit the product and the hazard.
This is only a brief overview of handling hazardous goods in bulk bags. Any potentially hazardous bulk bag handling application must be carefully assessed relative to Standard Operating Procedures, standards and regulations, Area Classification and other factors. Bulk bag and bulk bag handling equipment manufacturers must also coordinate closely to ensure safety.
High Speed Bulk Bag Filling – Pre-weighing
Maximum bulk bagging rates are achieved by using a pre-weigh system. Pre-weighing refers to weighing the payload of product to be placed in a bulk bag in a separate bin or hopper above the bulk bag filling machine instead of weighing the product as it enters the bag.
Pre-weighing eliminates the time required to precisely weigh the product as it flows into the bulk bag on the filling machine. The pre-weighed ‘shot’ can be dropped into the bulk bag as quickly as it can be made to flow through the pre-weigh hopper outlet.
Instead of a fast feed and dribble feed cycle with weighing performed on the filler that, at its fastest consumes 50-55 seconds, a pre-weigh system can fill a bulk bag in as little as 10- 15 seconds.
Removing 35-40 seconds from the bulk bag filling cycle time dramatically increases the bulk bagging rate.
Bulk Bag Filler Weighing vs. Pre-weighing
Let’s examine the numbers in more detail:
|Rig Bulk Bag||30||30|
|Remove Filled Bag||15||15|
|120 seconds||90 seconds|
Note that the Filler Weighing cycle time is only 120 seconds – that equates to 30 bags per hour.
That is a very high rate and is possible with many products using high speed bulk bag filling equipment. However, as can be seen, adding a pre-weigh system to this type of bulk bag filler increases the bagging rate considerably.
A 90 second cycle time means that a properly designed pre-weigh system is capable of filling 40 bulk bags per hour!
Also note that the final densification time has been increased. This compensates somewhat for the reduced amount of total densification time compared to the Filler Weighing cycle where the bag would be densified for most of the Fast Fill task.
If you are looking for more information get in touch with us today to discuss pre-weighing.
3 Ways To Reduce Dusting When Discharging Bulk Bags
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?
- 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 unnecessary 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.
- 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.
- 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.
Read more about how Spiroflow can help you reduce dust with bulk bags in our blog: Common Challenges – Dusting