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Tubular drag conveyors: The petfood processing handling system with double the capacity of belt or bucket systems

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Petfood processors have long sought a safer, more energy-efficient means to convey product with less spillage, breakage, or downtime due to necessary cleaning and maintenance.

Although tubular drag conveyors have offered these desired attributes compared to belt, bucket, or pneumatic systems, many in the industry selected these traditional options to move higher volumes or larger-sized products.

However, eight-inch diameter tubular drag conveyors have now become widely available that essentially double the volumes of smaller six-inch units. This provides comparable volumes and pricing to conventional industrial systems and enables the transport of much larger product sizes than previously possible.

These systems can safely and gently convey volumes comparable to belt or bucket systems with the use of much less power, product loss, damage or downtime. This is achieved by gently moving the product through a sealed tube using a coated, flexible stainless-steel drag cable pulled through on a loop.

Solid circular discs (flights) are attached to the cable, which push the product through the tube without the use of air, enabling them to excel in transporting delicate, precise blends for a wide variety of food types in versatile layouts and configurations.

“Today, eight inch tubular drag cable conveyors can move up to 2,000ft³ and 80,000lb/h depending on the bulk density of materials. The units can transport product as large as whole potatoes and midsized grapefruit, and are increasingly used to convey petfood, cereal, nuts, and whole fruit,” says Clint Hudson, Engineering Manager at Cablevey Conveyors – a mechanical conveyor manufacturer that serves the petfood, specialty food, coffee, nut, powder and produce markets.

According to Bob Owen, Director of Product Performance at Cablevey, the primary reasons why industry professionals are turning to the higher volume tubular drag cable conveyors include improved power use, safety, product preservation, product quality, and production uptime.

Reduced power consumption bills
As energy prices continue to rise, petfood processors are paying more attention to reducing the power required to convey materials. Within plants, the motors needed to convey large volumes of food materials can vary greatly in power consumption.

At the high end are pneumatic conveyors that utilise air to move product at high velocity through an enclosed line by creating air pressure above or below the atmospheric level. High-volume pneumatic conveyors generally require larger, power-hungry motors up to 20-50hp or more that run fans, blowers, and rotary valves.

At the mid-range of power consumption are belt conveyors and bucket elevators. In a typical conveyor belt system, a belt forms a closed loop and stretches across two or more pulleys with a drive pulley that enables it to rotate continually. Bucket elevators move material using buckets attached to a rotating belt or chain.

The buckets pick up material, move it to an endpoint, discharge material, and return to the starting point to pick up a new load. To convey a similar, high-volume amount of material, belt conveyors and bucket elevators would typically utilise approximately 25hp motors, says Owen.

At the low end of power consumption are eight-inch tubular drag cable conveyors, which would usually use a 7.5hp motor to move a comparable, voluminous amount of material.

“The drag cable pulls the solid circular discs (flights) attached to the cable at low speed through a loop, which requires less energy than conventional methods. The ample size and number of the discs on eight-inch units enable conveying a similar amount of material as traditional belt, bucket, or pneumatic units,” comments Mr Owen.

Improved standard of safety
Open systems such as bucket elevators and belt conveyors are common in the petfood industry but have substantial drawbacks in terms of the potential for contamination. With either type of system, any product that is left uncovered can potentially expose it to contaminants and moisture in the surrounding environment.

Open systems also allow product spillage onto the plant floor, which can present a slip and fall hazard if not promptly addressed. Unlike open systems, closed systems like tubular drag cable conveyors and pneumatic units effectively seal off product from the outside environment and any potential contamination from that source.

The enclosed nature of the systems ensures no dust escapes that could lead to an unsanitary and potentially dangerous coating of dust on the floor or process equipment. The result is a safer, cleaner, dust-free work environment and reduced risk of dust explosions if the product is in powdered form.

The enclosed systems also eliminate the inherent risk of slip and fall incidents due to product discharge onto the processing area floor.

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Increased product preservation
Enclosed conveyors prevent the product loss intrinsic to open systems such as belt or bucket utilising units. Once food product is in the enclosed tube, it cannot fall out, and no powdered product is lost in the form of escaped dust.

Preventing product loss can offer considerable benefits to the food processor’s profitability with surprisingly quick return on investment (ROI) in some cases. In the example of an international petfood manufacturer processing dog kibble, a bucket elevator was allowing excessive product loss due to spillage.

“When the petfood manufacturer switched to an eight-inch tubular drag cable conveyor, they minimised product spillage and reported a one-year ROI for the system,” says Mr Owen.

Improved product quality
For product that is delicate or presents a higher value in undamaged form, preserving product integrity is important. However, the rough mechanical action of scooping/dumping product from buckets can cause incidental damage, lowering value.

So can the high-velocity conveyance of pneumatic systems through vertical/horizontal tubing, turns, and sweeps, which can batter product during the process.

In contrast, tubular cable conveyors offer a gentler alternative. When the systems move product through a sealed tube using a coated, flexible stainless-steel drag cable pulled through on a loop, the solid circular discs attached to the cable push the product at low speed through the tube without the use of air, preserving product integrity and minimising waste.

“After a cereal manufacturer turned to a high-volume tubular cable conveyor it was able to reduce product damage,” he says.

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The premium for processing high-value products whole and unblemished can be even greater for some products like nuts.

“One food processor that used almonds in its recipe was only able to sell its product for 40 cents a pound if the almonds were damaged. The same product sold for US$4/lb if the almonds were whole and undamaged,” adds Mr Owen.

He notes that the processor chose to use a tubular cable conveyor to minimise product damage and optimise the sales price.

Extended production uptime
To reduce production downtime, petfood processors also increasingly expect conveyor systems to be designed for easy cleaning and maintenance. In this regard, bucket elevators are particularly difficult to clean in preparation for production line changeovers.

To clean them, each bucket must be time consumingly removed and cleaned inside and out to remove accumulated residue. Belt conveyors are usually cleaned with scrapers, but this can still leave product residue that must be removed with a more thorough method.

If not cleaned properly, the food product conveyed must be discarded due to contamination, which equates to lost profit. Or worse, consumers could be harmed, resulting in costly recalls, damage to brand and reputation, or even potential litigation and liability.

With closed conveyors, cleaning is also a mixed bag. Pneumatic conveyors can still be relatively time consuming to clean and sanitise if any manual procedures are involved.

With regard to maintaining cleanliness, tubular drag cable conveyor systems generally offer more options for dry and wet tube conveyor cleaning. These include brush boxes, urethane wipers, air knives, inline sponges, inline bristle brushes, and multi-step, essentially automated Clean-In-Place (CIP) wet cleaning.

“Using more automated forms of cleaning like inline wipers, sponges, and air knives or CIP wet cleaning can result in hours of additional production uptime after every product change, compared to conventional manual methods,” states Mr Owen.

Petfood processors are generally more familiar with traditional belt, bucket, or pneumatic systems than with tubular drag cable conveyor systems. Previously, processors had selected these familiar systems when they required higher capacity.

Today, however, eight-inch tubular drag cable units can basically match the high-volume output of the traditional systems but with significant advantages in power consumption, safety, product preservation/quality, and production uptime.

Del Williams is a technical writer based in Torrance, California. He writes about health, business, technology and educational issues, and has an MA in English from California State University — Dominguez Hills.

Article contributed by Del Williams, Cablevey Conveyors, US.

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