Hapman’s Joe Zerbel, Tubular Drag Conveyor Product Manager, answers the most commonly asked questions regarding the Tubular Drag Conveyor.
Yes. Conveyor flights can be made of various materials depending on the need, including steel, aluminum, cast iron, polyurethane, etc. However, unless precluded by special circumstances such as high temperature, we generally recommend and supply UHMWPE (ultra-high molecular weight polyethylene) flights. UHMW is an engineered material that is abrasion and impact resistant. It is light weight and has a very low coefficient of friction, so it keeps low the energy required to pull it through the conveyor circuit minimizing the wear to bends and pipes. Additionally, conveyed materials are least likely to stick to it.
The simple fact is that bends allow Tubular Drag Conveyors to do what other conveyors cannot. However, the addition of bends naturally increases chain pull (the amount of energy needed to pull the chain though the circuit); and as chain pull increases, so does the potential for wear. Therefore, minimizing the number of bends is always best. The actual number of bends that can be included depends on where in the circuit they are located and whether the conveyed material behaves as an abrasive or a lubricant. Multiple changes in direction are common but the most reliable circuits contain no more than 270° of bended pipe.
The most frequent maintenance activity of a Tubular Drag Conveyor is to remove excess chain slack. Over time the natural and continuous articulation of the conveyor chain will increase clearances between the links and hinge pins, causing the chain to elongate. A manual jack screw take-up mechanism is included on most machines to change the sprocket location (usually an idler sprocket) and remove the slack. When the slide plate which supports the sprocket reaches the end of its travel, it can be returned to its home position and two links removed from the chain. Flights are wear items, as is the conveyor chain itself. These are individually serviceable.
Flight life is very difficult to predict whereas every application is unique. The wear potential of a conveyor depends on several factors including the length, complexity (number of bends), duty cycle, whether the material behaves as an abrasive or a lubricant and to some extent, proper maintenance. On average a set of flights will last upwards of two years. By design, in most cases, flights are the intended wear component of the system (as opposed to conveyor bends and pipe). Flights are individually serviceable and can be replaced a couple of times before the entire chain assembly is in need of replacement. Every 35,000 hours (or as recommended by the gear box manufacturer) the gearbox lube needs to be changed.
Whether or not a conveyor can have a flooded inlet depends on the material, its bulk density (see our Bulk Density Guide), particle-to-particle friction and its ability to be compressed. Conveyors that have bends experience a narrowing of the distance between flights (discs) at the chain enters and leaves each bend. This articulation compresses and repositions the material within the flight pocket. Some materials are reluctant which can hinder the free movement of the chain, stressing the chain, increasing pull and contribute to nuisance faults. The vast majority of Tubular Drag Conveyors are meter fed at a prescribed rate with the conveyor running at a pace that is slightly faster so as to assure that a 20% freeboard is maintained in the conveyor. This, we know, regardless of material type, results in the most reliable performance and is the basis of our performance guarantee.
The maximum length of a Tubular Drag Conveyors depends on the complexity of the circuit (number of bends), the material weight (bulk density) and the friction factor of the material (whether or not it behaves as a lubricant). In a straight line, whether horizontal or vertical, these conveyors are capable of hundreds of feet of length, but the above factors can significantly shorten the distances these conveyors can cover.
The high-torque/low-speed mode of operation makes these conveyors more energy efficient than screw conveyors and pneumatic conveyors, often times requiring a fraction of the horsepower. Because material is effectively captured between flights and remains captures and relatively static within the flight pocket throughout the travel, material is gently handled with a minimum of particle degradation. This mode of operation tends to enable these conveyors to better tolerate the effects of abrasion than screw conveyors and pneumatic conveyors.
Whereas these conveyors can include bends and change planes, they can potentially do the work of several conveyor and thus can have a lower cost. However, chain type Tubular Drag Conveyors are a premium solution. They are robustly built for superb reliability in demanding industrial environments and any situation where uptime is critical. Chain-type Tubular Drag Conveyors are the last choice for people whose primary concern is the purchase price. People who choose this method of conveying are first drawn to the technology because of its dust tight construction, its ability to convey though bends and convey vertically. However, low energy consumption, low wear and low maintenance translate to a lower cost of ownership. When the lowest possible cost of owning a piece of equipment is most important, we have the best solution.
Chain type Tubular Drag Conveyors and cable conveyors cannot rightly be considered for the same applications. They are different calibers of equipment altogether. While cable conveyors are generally low-torque/high-speed operating and do not have the ability to start and stop while fully loaded, chain type tubular drags are high-torque/low-speed operating – not only enabling them to start and stop while fully loaded but making them more energy efficient and more durable to abrasion. Cable conveyors are constructed of light gauge tubing that is joined together using compression fittings. Meanwhile, chain-type Tubular Drags are constructed of schedule 40 pipe that is joined together using heavy plate flanges. See an in-depth comparison.
Tubular Drag Conveyors naturally clean out very well, that is to say most of what goes into them will come out if allowed to run empty. However, when elevating there is a small heal of material that is left in the lower bend. The amount left there varies according to the size of the conveyor, the condition of the flights (how worn they are) and the flow-ability of the material but rarely amounts to more than a coffee cup or two. When batching, these conveyors are very repeatable, that is to say that the amount of heal from one batch to the next is the same. Occasionally as part of this same conversation, people are concerned about residue or the amount of material that naturally remains on the conveyor chain. We employ various features to address these and improve discharge efficiency, including chain hammers, air knives and motorized brushes, according to the specific material and situation.
Our chain-type conveyors have been used successfully to handle cocoa beans, coffee beans, salt, sugar, peanuts, corn grits, corn starch, wheat flour, xylitol, sodium bicarbonate, and various other food chemical additives and preservatives. Our conveyor design is well suited for dedicated handling of high acid food ingredients when the opportunity for bacterial growth is very low and when there is no expectation of frequent, quick, easy or complete cleaning to the point of being sanitary or having no residue.
Whereas chain-type Tubular Drag Conveyors are high-torque/low speed operating, they tend to me more tolerant of abrasive materials. They are generally a better choice than screw conveyors and pneumatic conveyors. Coupled with the other advantages like dust tight handling and the ability to convey through bends and require less horsepower, they can be the best overall choice. However, it is important to note that, as the name implies, drag conveyors are subject to the effects of sliding and grinding abrasion and care must be taken to apply these conveyors in such a way as to minimize the wear potential, such as keeping the chain pull low.
It is possible to operate Tubular Drag Conveyors under a slight vacuum or positive pressure and they may be purged with inert gases as may be necessary to displace oxygen.
For more information on the Tubular Drag Conveyor, click here or contact Steve Grant at (269) 382-8223.