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In praise of tubular drag conveyors

10 December 2021

Karl Seidel sets out to debunk some common misconceptions about tubular drag cable and disc conveyors. 

Even food industry veterans can be challenged to distinguish whether a conveyor tubes is screw (augur), pneumatic, vacuum, aeromechanical, tubular drag chain and disc or tubular drag cable and disc, unless they are the plant engineer or maintenance crew.  Indeed, many specifiers, engineers, and other professionals lack technical or hands-on experience with such conveyor and this can pose problems when delicate materials or precise blends need to be reliably conveyed. 

Tubular drag cable conveyors gently move 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. These conveyors can offer a good solution to transport delicate, precise blends for a wide variety of food types in versatile layouts and configurations.

Tubular drag conveyors are not the same as a screw systems: One of the most common misconceptions is that tubular drag cable and screw conveyors are identical, which is far from true. 

Screw systems – also known as auger conveyors – typically utilise a helical blade that moves granular materials within a tube. However, augers can cause product damage and compromise blends.  So, the units tend to be an option when material integrity is not critical, such as when conveying food waste.

The key difference to look for is that augers convey material with a helical screw. The transfer speed is directly proportional to the rotation speed of the screw.  On the other hand, tubular drag cable conveyors transfer material between two discs pulled by a sealed cable and are designed to protect delicate products and blends.

Tubular drag conveyors are designed to protect blends and mixes: When transporting a blend of product with a conveyor system, maintaining a consistent mix ratio is essential, whether a fine powder, coarse mix, or larger variable-sized amalgams of different weights and shapes.

However, conventional conveyor systems are not specifically designed to precisely transport blends without changing the mix ratio. Various product material weights, sizes, and shapes can shift and disperse in open systems like bucket conveyors, and vibration can cause the blended product to shift throughout transport.  Vacuum and pneumatic systems can cause smaller lightweight particles in a blend to move at different speeds than heavier or larger particulates, resulting in significant blend restructuring when the product reaches its discharge point.

In contrast, tubular drag cable conveyors are engineered to maintain precise blend ratios. Not unlike an endless succession of train cars, each space between solid circular discs holds a predefined volume of product.  Based on the manufacturer’s specifications and requirements, engineers can calculate the optimal speed of the system, the most appropriate tube angles, and the proper construction design to guarantee their blended product remains consistent from input to discharge, even at high volumes.  

Tubular drag conveyors can carry moist, hot, or frozen material: Tubular drag cable systems are able to convey food materials in a wide variety of forms and states including powdered, pureed, chopped, moist, hot, and frozen. The systems are able to convey material with a high moisture content – such as soaked beans and chickpeas when some water is being conveyed along with the product.

Tubular drag conveyors have no footprint or expansion limitations: Some in the food industry do not consider tubular conveyors because they mistakenly believe that the systems cannot fit within their facility’s available space or accommodate its layout, which may include significant inclines or elevation changes. However, this is not the case and modular systems such as tubular drag cable conveyors can offer a good solution for complex layouts that could require curves or changes in direction.

Tubular conveyors do not have to be installed at 90° and can use angles so can go in between, around, above or below existing equipment or other obstacles. This is an important consideration for existing facilities that may not have the flexibility to move something out of the way. In addition, tubular conveyors are space-efficient. To conserve space, the conveyor turnaround and its inlet can stand on end. 

Cleaning tubular drag conveyors does not require dismantling and extended downtimes: Between product changeovers, many traditional conveyor systems need to be disassembled, cleaned, or soaked, and then reassembled – a labour and time-intensive process.  However, this is not necessary for tubular conveyors which will have dry, wet, and in-line cleaning options available. Among dry options, brush boxes and air-knives can clean the cable.  Brushes and wipers can wash the tubes.  To sanitise, a sponge soaked in sanitizer can be used without getting the system fully wet.  

For the most thorough cleansing, the cable conveyor’s wet cleaning process internally washes the tube in several steps, starting with a water rinse followed by a foaming agent, a sanitising rinse, and a final water rinse.  Once the system is thoroughly flushed out, drying is achieved by attaching wipers to the tubular conveyor’s discs which remove any residual water.

Karl Seidel is marketing director at Cablevey Conveyors.


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