Although similar in functionality for food processors, tubular chain and cable disc drag conveyors have distinct differences in components and operation.
A closer look at these systems will help food manufacturers better understand which system would best support their dry food processing requirements.
What are tubular drag conveyors?
Tubular drag conveyors are mechanically driven conveyors that drag material along the inside of a tube. They are designed to transfer flowable bulk materials from in-feed points to discharge points through an enclosed conduit. Using either a cable or a chain, with close-running discs spaced along its length, the ends of the tubular drag conveyor are connected to form an endless loop, which is pulled by a motor-driven sprocket within an enclosed tube.
Bends facilitate changes in direction in the tubing or by corner housings for tighter turns. Discharge of the product is achieved through outlet boxes and discharge funnels.
Tubular drag conveyors are flexible and designed for versatility in gentle material handling operations. Modular components allow changes in conveyor routing, length and the number, and position of inlets and outlets. They can move material vertically, horizontally, around corners, and at an angle.
Chain And Disc Conveyors
Tubular drag chain conveyors gently move food products through a sealed tube with a drag chain pulled through it on a loop. Solid circular discs (flights), which push the food through the tube, are attached to the chain.
Two types of chains can be used in tubular chain conveyors, link chain and roller chain.
The link chain can act as a universal joint during the movement of the product in the tube, which enables a single conveyor to achieve directional changes in multiple planes.
A roller chain, consisting of interconnected plates held in place with pins and bushings, is capable of one-dimensional movement. Both chains are typically manufactured from type 316 stainless steel, rated for acid and corrosion resistance, but carbon steel is also an option.
Because chains exhibit friction at points of direct contact, most noticeably at system start-up, and particularly in food processing applications where lubricants are not being used, wear can occur at these contact points throughout the length of the chain.
As with all tubular drag conveyors, the chain-drive components need to be regularly adjusted to keep the system in registration and minimize the wear and tear of the conveying discs, chain, and tube. A tension turnaround unit is used to maintain the proper chain tension.
Cable And Disc Conveyors
Like tubular drag chain conveyors, tubular cable and disc conveyors gently move food products through a sealed tube. Instead of the chain, however, cable and disc systems use a coated, flexible stainless steel drag cable pulled through on a loop. Solid circular discs (flights) are attached to the cable, which pushes the food through the tube.
Tubular drag cable conveyors can transport up to 80,000 pounds of product per hour at low speed – similar to chain and disc conveyors – and practically eliminate product degradation.
The cable used in most tubular drag conveyors is WSC (wire strand core), also known as aircraft cable, because it is used in control functions for aircraft. Under normal conditions, these high-tensile aircraft cables will not break. The core is type 316 stainless steel. Surrounding it are stainless steel stranded ropes, an assembly of several strands of steel laid helically in one or more layers around the core. The very high strength of the rope wires enables these cables to support large tensile forces with relatively small diameters.
Historically, wire rope (cable) evolved from wrought iron chains, which had a record of mechanical failure. While flaws in contemporary chain links can lead to catastrophic failure, defects in the wires making up a steel cable are less critical, as the other wires easily take up the load. While friction between the individual wires and strands causes wear over the life of the cable, it also helps to compensate for minor failures in the short run.
The tubular cable and disc conveyor operates on low horsepower, utilizing energy-efficient variable-speed motors of 1-5 HP each, effectively consuming minimal power compared to other conveyor systems used in food processing.
The system’s production flow can be adjusted to variable speeds to modify throughput. A drive unit provides power to move the cable and disc assembly through the conveying tubes. The system components are connected with compression couplers and gaskets, making the system totally enclosed and dust-free.
Like tubular drag chain conveyors, maintaining the required cable tension by the installer and operator is necessary for the system’s proper function and to eliminate the remote possibility for cable strand breaks at cable connection points. A tension turnaround unit maintains the proper cable tension while the system is in operation. The entire cable is nylon sealed, ensuring that no food directly comes in contact with the stainless steel cable and that no potential strand breaks come in contact with the conveyed food products.
The conveyor system’s flexibility allows it to connect with any food production process, from receiving raw materials to weighing and filling, grinding, and packaging.
They are critically applicable where food components can become damaged, where contamination is prevalent, or dust accumulation can be excessive, such as filling and packaging.
Product contamination is a key issue in food production conveying. In every step of the process keeping foreign matter from entering the process stream, maintaining system sanitation, and keeping the system free from unwanted allergens are critical objectives.
The importance of preventing product contamination is magnified with increasingly stringent government and industry product track and trace mandates and consumer demands for maintaining product integrity and safety.
Line changeovers have become a focal issue in food production relative to cleanliness and the speed of conversions. Companies are increasingly running different product lines within a single shift or day.
Every minute spent disassembling a conveyor system for cleaning consumes valuable production time. Yet, if not cleaned properly, a batch of conveyed food products needs to be discarded because of contamination, which leads to lost profit. Or worse, consumers could be negatively impacted, resulting in potential injury, illness, costly recalls, and impacted brand reputation. Food processors are charged with administering line changeovers as quickly as possible to resolve these issues while maintaining 100% system cleanliness.
Tubular drag conveyors, chain and cable systems, transport dry bulk food products gently to discharge points in totally enclosed, dust-free conveying tubes. This prevents foreign substances from contaminating the product stream and keeps dust from the transported product from escaping into the production environment, reducing both the incidence of health hazards and the potential for dust explosions.
Chain and Disc Systems Sanitation
Tubular chain and disc conveyor systems are designed to meet sanitation specifications as mandated by the FDA. These systems’ core is the polished stainless steel conveyor link chain or roller chain, rated acid and corrosion-resistant.
Because the entire chain is directly immersed within the food being conveyed, cleaning the chain – in addition to the tubing itself – requires more care than what is needed for the cable in a tubular cable and disc conveyor. This is particularly true with a roller chain, where food particles can pack into spaces between plates, pins, and bushings and where water can remain trapped after cleaning, resulting in potential product contamination.
Chain and Disc Conveyor Cleaning Mechanisms
Cleaning mechanisms are available that minimize or eliminate the build-up of food particles from the chain, conveying tubes, and associated equipment. These mechanisms include brush boxes, chain knockers, and wet clean-in-place (CIP) systems.
Dry cleaning mechanisms available for tubular chain conveyors:
- Brush Box – a line insert that mechanically brushes accumulated fines off discs.
- Chain Knockers – a line insert that dislodges particles from the chain.
The wet cleaning CIP (self-cleaning) mechanism available for tubular chain conveyors consists of a 3-step internal tube cleaning process:
- Foam Cleaning/Sanitizing – foam cleaning agent is introduced into the tube environment to cleanse and sanitize all internal parts of the system.
- Rinse – a water rinse is run through the system to flush out debris and the foam cleaning/sanitation agent.
- Dry Air – warm, dry air is pumped throughout to dry the system and make it ready for the resumption of operation.
Cable and Disc Systems Sanitation
Tubular cable and disc conveyors for food-grade applications are better designed to eliminate places for fines to accumulate. Solid discs are used, with no screws or bolts, and attached directly to the cable. Stainless steel connectors are used throughout the system, and equipment is removable for easy cleaning.
One of the key advantages of tubular cable and disc conveyors over the tubular chain and disc conveyors is the significantly reduced possibility of trapping food residue on the cable compared to a chain. As with both link chain and roller chain, the cable is fully immersed within the food being transported through the tube. But the chain has significantly more surface area exposed to the food.
Further, the cable is completely uniform and smooth throughout its entire route within the tube. However, the chain itself has many 90-degree turns and connections link to link, where food residue can more easily collect. The most hygienic food processing equipment designs minimize or eliminate 90-degree angles where food contact is present.
Supporting this is the stainless steel cable used in tubular cable conveyors, which is nylon sealed, ensuring that no debris accumulates within the cable strands.
Cable and Disc Conveyor Cleaning Mechanisms
Compared to tubular chain and disc conveyors, tubular drag cable and disc conveyor systems offer more options for dry and wet tube conveyor cleaning. These include brush boxes, urethane wipers, air knives, inline sponges, bristle brushes, and multi-step CIP (self-cleaning) wet cleaning.
Dry cleaning mechanisms available for tubular cable conveyors:
- Brush Box – a line insert that mechanically brushes accumulated fines off discs.
- Urethane Wiper Disc – a disc insert that wipes away accumulated fines and particles while the system is in progress.
- Air Knife – strategically located at product discharge locations in the line, air knife inserts use compressed air to blow accumulating fines off discs and the cable.
- Sponge Disc and Sanitizing Cleaner – a disposable sponge disc that is run through the system with an applied cleaning agent.
- Bristle Brushes – a brush that is run through the system to remove accumulated fines off the tubing.
The wet cleaning CIP (self-cleaning) mechanism available for tubular cable conveyors consists of a 3-step internal tube cleaning process:
- Foam Agent – foam cleaning agent is introduced into the tube environment to cleanse all internal parts of the system.
- Sanitizing Rinse – a sanitizing rinse is run through the system to flush out debris and the foaming agent.
- Water Rinse – a second rinse of hot water flushes out sanitizing rinse, rendering the tube environment-production ready.
Benefits of Cable vs Chain
- Decreased system downtime
The cable has no moving components like links, plates, pins, and bushings integral to chains that cause friction and wear. With chain and disc systems, if just one part breaks, complete system shutdown occurs.
However, excessive system stress on cables results in localized strain breaks – loads are redistributed, maintaining cable integrity and system uptime.
- Minimized direct contact with food
A nylon-coating prevents direct contact of the stainless steel cable with transported food. The nylon’s smooth surface is void of crevices or sharp-angled components where food particles could be collected, such as is the case with chain links, plates, pins, and bushings where food particles can gather in chains.
- Improved performance for food safety, sanitation, and changeovers
In addition to a 3-step, clean-in-place wet-cleaning process for internal tubing, cable and disc systems provide a considerably more comprehensive set of five mechanisms for inner tube dry cleaning than chain and disc systems.
These processes ensure sanitation and enable faster changeovers than chain systems, which must contend with trapped water deposits within components after cleaning.
Tubular drag conveyor systems installed in facilities 10 to 15 years ago may have been adequate at that time. Still, better technology in conveying system design, controls, and automation has brought a whole new generation of conveyors for use in food processing.
The bottom line of our detailed analysis is that tubular chain and disc systems are simply not as efficient, cost-effective, or easy to clean as cable and disc conveyors.
If you are looking for the next conveyor for your food processing facilities, you may want to consider tubular cable and disc systems. Contact us at Cablevey to learn more about how we can help you choose the best type of tubular conveyor system for your plant.