Conveying Considerations When Transferring Up and In

Transferring powders and other bulk materials from floor level up and into a hopper, feeder, mixer, reactor, or other destination ranks among the most common material transfer applications. Yet selecting the ideal solution to move the material from point A up and in to point B from the wide variety of conveying options available often confounds even experienced powder handling professionals – especially those under pressure to place safety, throughput, automation, dust control, contamination prevention, ease of use, and cost all among the top priorities. Each conveying approach offers distinct capabilities and characteristics that either support its use for a given up and in application or disqualify its use as inefficient, ineffective, or even outright dangerous.

Conveyors Support Safety

In many food, chemical, pharmaceutical, and other manufacturing plants, the most common up and in type of installation still involves a worker carrying bagged powders, pellets, and other bulk materials up stairs onto a mezzanine, or up a ladder, then dumping the dry solids into a surge hopper, feeder, or directly into a tank, mixer, or reactor. Though simple and seemingly inexpensive, this manual approach invites serious health and safety risks proven to cause expensive workers' compensation claims and exposes the company to liability.

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Hauling 50-lb bags of flour or sugar over the shoulder and up stairs creates a high risk of slips, trips, falls, back injuries, and a variety of other ergonomic concerns. Emptying the bag and loading the materials into the hopper or port by hand often exposes workers to contact with the material as a cloud of airborne dust and/or as a dusty layer blanketing his or her clothing. If ignitable powders and combustible dusts are involved, then a static discharge caused by the sliding action of emptying powders from bags becomes a real threat to trigger an explosion. Loading the material into an existing mixture or liquid also invites vapor exposure and may generate a hazardous splashing effect. Any conveying approach that automates this material transfer process naturally eliminates the numerous safety concerns that inherently plague manual handling approaches for a vastly safer work environment.  

A pneumatic vacuum conveyor transfers coffee beans up and into a hopper for grinding. Volkmann conveying systems use stainless steel as standard to excel in food, pharmaceutical, and other sanitary processes (Volkmann USA).

Conveyors Support Consistent Quality

In addition to protecting workers from exposure to the material, it may be equally important to protect the material from exposure to workers and to the workplace. Many materials are highly sensitive to contact with air or moisture and even short-term exposure during the up and in transfer process may compromise their material properties. For example, ascorbic acid (vitamin C) loses its antioxidant capabilities, pectin loses its gelling ability, some polymers begin curing prematurely, and powders such as corn starch, whey protein, lecithin, and dry milk clump very easily, which may adversely impact flowability and alter how the ingredients interact in the recipe.

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Some applications call for metering or dosing materials into a process and this can pose an especially challenging task for workers emptying the materials from bags by hand. Loading minor and/or micro-ingredients into a mixer, for example, often requires attention to proper dispersal to ensure the targeted homogeneity is achieved. Erratic loading or imprecise manual measurements may leave key ingredients unmixed in a finished product that ultimately needs to be discarded as waste. The diversity of materials, recipes, production targets, and of the myriad up and in applications, along with the challenges of manual powder handling, have led to the development of a diverse range of conveying solutions to match the ideal conveyor to the application. 

While worker safety and contamination control often factor into the decision to upgrade from a manual material transfer process to an automated conveying system, the primary driver justifying the investment is often throughput. As companies grow and need to scale, or as consumer demand for a niche, regional product takes off nationally, the manual method simply cannot deliver the increased production volume required. Consider the process engineer for a nutritional products manufacturer, for example, who needs to transfer large amounts of a protein powder from the discharge under a mixer or dryer up and in to the nearby hopper above a vertical form fill seal machine on a packaging line. Several different conveying methods may be suitable:

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Belt Conveyor

The traditional belt conveyor can be used to transfer powders at up to 100 tn/hr, given a wide enough belt running at a high enough belt speed. It excels when transferring materials with a high bulk density such as cement, aluminum, and salt in mining operations. In this protein powder case, to raise it from the floor level under the mixer up to the hopper of the nearby filling machine, a belt conveyor would require a steep incline that would allow the powder to slide down and off of the belt. Or, to prevent this, a very long conveying length could be used to allow for a gentle incline, but this would require far too great a distance to suit this application.

Bucket Elevator

A bucket elevator excels in transferring bulk materials vertically and is, therefore, often specified to accommodate tight space constraints. It consists of a series of open buckets attached to a belt or chain that lifts the material up to the desired height and discharges at the top. Like open belt conveyors, bucket elevators expose the material being transferred to the open-air environment during the entire operation. This doesn't immediately disqualify its use for all food products, but the risk of contamination due to humidity, contact with air, workers, or chain lubricants, plus issues with pest control and product spillage suggest that it may not be ideal for a sanitary process. In this case when transferring a protein powder for human consumption, the process engineer needs to consider this lack of containment in the context of the required level of cleanliness and sanitation. Further, cleaning each, individual bucket for product changeovers poses a time-intensive challenge.     

Flexible Screw Conveyor

If exposure to the open air needs to be avoided, how about an enclosed approach that reduces the risk of contamination? A flexible screw conveyor is one example of an enclosed material transfer approach. This bulk material handling system transfers the materials from a hopper at floor level up a rotating screw conveyor set inside a plastic tube to discharge at the top. This helps prevent exposure to contamination during transfer, though loading the material in the hopper is typically performed manually and may generate a dust cloud depending on the material. It can move materials horizontally or at an incline to navigate space constraints but often needs to be set at a particular angle near 45 degrees to achieve efficient transfer at any reasonably high throughput. The steeper the pitch, the more this type of conveyor struggles when transferring mixtures and/or materials with wide particle size distributions. Further, a given amount of the material must remain in the screw after the hopper has been emptied and material discharged. Though the product loss may be minimal, this creates an issue with cleanup and sanitation that needs to be avoided.

Tubular Drag Conveyor

What about a conveyor alternative that's enclosed for contamination control but can also handle transferring materials at a variety of angles including vertically, and even around corners, if necessary? A tubular drag conveyor offers an enclosed conveyor system that uses a continuous loop of cable or chain with attached discs set inside a tube. As the cable or chain moves, it pulls the discs, which carry the bulk materials up and into the destination.

This mechanical conveyor provides gentle transfer for sensitive products, it can accommodate several curves and bends, and can be used in sanitary operations. Though it checks several critical boxes in our protein powder transfer system, as a mechanical approach, the tubular drag conveyor may struggle to reach the speed and throughput required.

A plant engineer watches as a pneumatic vacuum conveying system from Volkmann automatically transfers powder up and into a stick pack machine. Transferring finished products up and into filling and packaging lines automatically speeds production, prevents contamination, and promotes a clean, sanitary work environment (Volkmann USA).

Pneumatic Vacuum Conveyor

A pneumatic vacuum conveyor uses a vacuum pump to create negative pressure that draws powders, granules, pellets, and even small components from the pickup point up through enclosed tubing and into the discharge. As a sealed system, vacuum conveying provides containment to safeguard against product contamination, prevent worker exposure to and contact with the material in process, and eliminate the risk of nuisance dust in the work environment. Without any belts, chains, cables or other mechanical parts, this approach reduces friction to allow for high-speed material transfer and high throughput rates in a choice of dense phase or dilute phase. The material flows automatically and consistently as a continuous stream or with gentle pulses to protect particle integrity. Line downtime for mechanical wear part maintenance is also eliminated, along with any concern for product contact with lubricants, greases, or metal parts.

Vacuum conveyors that use flexible tubing can fit into compact spaces and effectively transfer materials up vertical inclines and through a number of curves and bends into the discharge. For the example case transferring protein powder from a mixer up and into a hopper, pneumatic vacuum conveying offers the high throughput, gentle conveying, and product containment required, and accommodates steep angles and vertical configurations that fit tight spaces. It excels in sanitary processes and vastly improves efficiency and worker safety versus manual methods. Any risk in transferring dangerous combustible dusts and ignitable powders is virtually eliminated.

In addition, off-the-shelf vacuum conveying systems suit a wide variety of applications with little to no customization. Workers with little technical expertise can typically manage the installation process and operate the system without outside engineering assistance.

Positive Pressure Pneumatic Conveying

Vacuum conveying's alter ego, positive pressure pneumatic conveying, uses compressed air to push materials through the piping or tubing from one point to another rather than draw it from the discharge end with a vacuum pump. This approach offers smooth, gentle, contained conveying in either dense phase or dilute phase comparable to vacuum conveying. It is often specified when materials need to be transferred long distances at high throughputs, when space allows for the large sending vessels, and when energy-efficiency is not a top priority. This air conveying approach would likely be deemed overengineered when considered for the protein powder installation.    

Conveyor Return on Investment

From this review of conveying systems for transferring bulk materials up and in to process or packaging equipment, it is clear that several different approaches could be used to meet the application's requirements, though some are more efficient and effective than others. Thinking an automated approach is too costly, it is easy for many managers to overlook the hidden expenses involved with a labor-intensive, manual process. The disbursements of a single workers' compensation claim for a slip, trip, or fall in the US, for example, average $49,971, according to the National Safety Council. The cost of just one injury could easily exceed the investment needed to upgrade to nearly any of the conveying systems described, depending on the specific application. When also considering the immediate improvements in efficiency, productivity, and quality, and the cost savings in labor, automating the material transfer process is proven to deliver a return in a relatively short payback period.

David Nichols is vice president of sales and marketing for Volkmann USA. The company designs and manufactures pneumatic vacuum conveying systems, vibratory weigh feeders, and other process equipment. For more information, call 609-265-0101, email [email protected], or visit www.volkmannusa.com.