The claviature of mechanical bulk material handling
Mechanical solutions convey a wide variety of bulk materials horizontally, vertically, or diagonally upwards. The materials can be coarse and abrasive, sensitive or even sticky. Several functional principles have been around for an exceptionally long time. Belt conveyors became popular in the early 19th century, followed shortly afterwards by screw conveyors and bucket elevators. But there are still innovations.
In many industries, bulk goods - as a starting or end product - are indispensable. Grain, sugar, and spices are turned into baking mixes and sauce powders. The chemical industry produces detergents and fertilisers and processes salts and ores. The pharmaceutical industry needs binders and fillers for tablets, capsules and granulates. In the construction and mining industries, the proportion of processed or produced bulk materials is particularly high. All these materials have to be conveyed: to storage containers, to the production plant, between different process steps or at the end of the production chain into various containers and packaging. Given this diversity, it is not surprising that a wide variety of technologies are used.
This is particularly true for mechanical bulk material conveying. Due to the fixed conveying paths, it is considered less flexible than pneumatic conveying, which is also frequently used. However, it can be used to convey larger quantities and save energy at the same time. The wide range of standard products makes it possible to fulfil the most diverse requirements. The characteristics of the products must be taken into account. New bulk solids - such as in the development of new foods or special powders for 3D printing - are constantly challenging the creativity and often also the intuition of system planners.
Above all, the flow behaviour of the material is important. It depends on the particle size, shape of the particles, porosity, and roughness of the material, among other things. The desired conveying distance and quantity as well as the conditions in the production environment, such as the possible installation height, are important criteria when selecting the appropriate technology. Regulations such as hygiene standards or explosion protection must also be observed.
Centuries-old technology principles in innovative variants
Typical conveyor equipment includes belt conveyors and belt conveyors that are suitable for copious quantities and long distances of up to kilometres, such as the systems from Beumer. Compact, closed conveying with low dust generation can be realised with screw conveyors or - for heavy, abrasive materials - with chain conveyors. Bucket chain conveyors (bucket elevators) are often used for vertical conveying.
Tube chain or tube drag conveyors are suitable for numerous powders and bulk materials - from grain and coffee to plastic and mineral powders. They can also be used to overcome winding vertical and horizontal routes - with high capacity, dust-free and gently. One of the suppliers is the Italian bulk goods handling specialist Falcon. Its programme includes two models, one for particularly long distances and a second, particularly compact model with parallel tubes. Both are also available as ATEX versions.
Schrage Conveying Systems also produces tube chain conveyors of this type. And in a distinct way. The supplier has identified a collaborative robot (Cobot) that assists in the assembly of the carrier discs - thousands per year. With over 4,000 references worldwide, Schrage has already realised a wide variety of line layouts. Conveyor lines over 50 metres long and 30 metres high have already been created - dimensions that are typical for pneumatic conveyor systems. The only difference is that conveying requires significantly less energy and is possible with less wear and is gentler on the product. There are also mobile or stationary stand-alone models that make it easier to fill and transfer a wide variety of containers or tankers.
Thanks to the double bearing design, the rotor of this rotary valve can be pulled out on guide rods for cleaning or inspection.Valve feeders as versatile problem solvers
Rotary valves are a speciality in bulk material conveying, popular in the chemical and food industries. They transport bulk material between two rooms with a pressure difference as required and also meter it. They therefore combine mechanical and pneumatic systems. A rotor with several cells is the element that gives them their name. A wide selection is available from DMN Westinghouse, for example, which exhibited at the last POWTECH with versions with an enlarged inlet for powdery products and granulates as well as with USDA-approved dairy rotary valves for dairies, food, pharmaceutical and chemical applications.
Jaudt Dosiertechnik's rotary valves are also suitable for discharging and dosing powdery to coarse-grained bulk materials. The portfolio also includes EHEDG versions as well as knife or crusher feeders, which crush protruding material and thus facilitate discharge from silos or bunkers. Quick-clean rotary valves, such as those offered by TBMA, are specially designed for processes with frequent cleaning cycles and inspections. With these, the rotor can simply be pulled out on guide rods to clean it and the inside of the rotary valve.
Aerodynamic powder conveyors, which are also available in a hygienic design, are suitable as ascending conveyor systems for sensitive products.Aeromechanics for sensitive bulk materials
Fresh solutions are constantly emerging, especially for sensitive bulk materials. Aeromechanical powder conveyors are among the innovative alternatives to bucket elevators and tube chain conveyors. They were presented at POWTECH 2023 by Gough and Idealtec, among others. The flexible inclined conveyor systems transport both fine powders and granulates and do so very gently. They can be used to feed silos, big bags, or mixers or to load tankers. Dust and product losses as well as wear on the machine are significantly reduced. The principle is based on negative pressure, which is created by pulling a conveyor disc through a pipe at a speed of approx. 4 m/s using a rope. Free-flowing bulk material is sucked into the resulting suction with virtually no frictional forces. Aeromechanical conveyors can be used to comply with strict hygiene standards and realise applications in potentially explosive atmospheres.
Effective vibration
Vibratory conveyors are also used for easy-flowing, sensitive materials. Numerous different basic designs can be customised to suit the product properties and specific features of the process. Netter Vibration, which specialises in this type of conveyor technology, offers the Powerpack conveyor system, for example: a conveyor trough mounted on springs is vibrated by a compressed air piston vibrator. The bulk material on it is repeatedly thrown forwards a tiny bit. Frequency and amplitude can be regulated separately. The system is easy to clean and can also be used for applications in the chemical industry. Instead of compressed air, nitrogen can also be selected as the drive medium. Stainless steel versions are also suitable for the pharmaceutical and food industries.
Rosehips are conveyed towards a coarse sieve inside a metal chute that is open at the top.Transport is particularly energy-efficient if the conveyor systems oscillate in natural resonance and therefore consume little compressed air. This is the case with the Flexilink from Netter. It enables oscillation widths of up to 30 mm. Long conveyor systems and high conveyor speeds can therefore be realised. It can also be used to drive spiral conveyors.
For extremely gentle horizontal conveying of light, fragile bulk goods such as potato crisps or tablets, you can also use the LineDrive conveyor systems from Netter or the Vibra Schultheis adhesive glide conveyors. Their central elements are a conveyor trough or conveyor trough and a linear drive that causes the trough to vibrate in the conveying plane. In this way, the holding and gliding phases alternate and the conveyed goods move in the desired direction. As with belt conveyors, the conveying direction can therefore be reversed. Unlike conventional vibratory conveyors, the product to be conveyed is not subjected to vertical acceleration.
By adjusting the conveying capacity and speed, the height of the product in the conveyor trough, the angle of the vibrators to the trough floor and other parameters, systems can be optimally fed with a wide variety of products, whereby the planner's extensive experience pays off. When designing the system, he can ensure that wear is largely avoided. Even highly adhesive products such as strips of ham can be conveyed evenly and gently using this technology.
New products and applications are constantly creating new challenges for mechanical conveying, for example in the field of battery mass production. WAM has recently started offering a special version of its screw conveyor for this purpose. The stainless steel TXB screw conveyor has been optimised for this application. There is also a version for the food industry: the TXF tubular screw conveyor, also made of stainless steel, is characterised by the traceability of all components and materials used and certification in accordance with EC 1935/2004. Like all TX conveyors, it prevents product contamination; the particularly smooth inner surface minimises product residues. The TXF conveyors are optionally available with ATEX certification for zone 22 or 21. There are also numerous options for them to ensure optimum material flow, whether in the production of baked goods or pasta, in cocoa or salt processing and even in the production of baby food.
Conclusion and outlook
Whether belt conveyors, bucket conveyors, screw conveyors - or newer variants such as vibratory conveyors: solutions for mechanical bulk material handling are just as diverse as the material to be transported. Selection and design are anything but simple. Hardly any conveyors are available ‘off the shelf’. However, experienced planners design systems for a wide range of conditions and safety requirements. Expert knowledge of measurement and control technology, mechatronics and automation complements the mechanical engineering expertise to create truly safe, high-performance conveyors that are customised to the application.
