Are all Loading Spouts the Same?
Loading spouts have increased in use for dry bulk material handling in open trucks, stockpiles, railcars, tank vehicles, barges and ships. Plant managers are witnessing the benefits of capturing fugitive dust, improving air emissions, and preventing material waste in grain elevators, ship ports and cement plants.
But purchasing a standard spout from any supplier may not be cost effective enough. Taking a one-size-fits-all approach or the least expensive option often forces the operator to settle for a product that was not optimized for his application and can become the choke point in the product stream.
For example, why purchase a standard spout that has 12 feet/3.5m of travel when you only need 5 feet/1.5m? The fact that the spout will only be 50% extended during the loading process will develop many issues such as material accumulation and cone cohesion that will become costly later. A custom spout designed for your application needs can save you money.
A spout can be custom made based on three measurements: travel, retracted, and extended length. A spout manufacturer that also considers other parameters such as material, flow rate, and moisture content will help you obtain the ultimate cost effective spout.
SOME PARAMETERS TO CONSIDER:
- Product identification: If multiple products are being loaded through the same spout (common in grain applications), convey this to your designer. Also, sticky, abrasive, or corrosive properties will influence component selections and design features to help ensure a successful installation.
- Product size: As the product size increases, there can be bridging problems. This is especially true for very light-weight materials, such as chaff, wood chips, and rice or cotton seed hulls. Generally, the largest product size should be no larger than ¼ the minimum diameter of the inner cone. Very small product (cement, flour, flyash, etc.), will usually fall turbulently and at high rates through the spout and generate high fugitive dust loading, particularly if there is substantial air entrainment.
- Moisture and temperature: High product temperature can damage or shorten the expected life of various components of the loading spout, especially the flexible outer sleeve and polymer cones, if so equipped. Some electrical components may also be affected. Further, very warm products with moderate moisture content can become agglomerated or sticky as they cool. This can cause flow problems, material hang-up within the sleeve or on the cones, and may affect retracted height over time as the material continues to build up on the cones.
- Flow rate: Obviously, it is essential to establish the expected performance of the spout in terms of the customer’s required flow rate. Flow rates specified in terms of mass properties (tons/tonnes per hour, etc.) must be accompanied by the loose bulk density of the product.
Because the product and service conditions can vary widely, optional choices exist for materials of construction, type of auxiliary devices, and a range of accessories which may be added to the spout. All of these choices may or may not be available from every spout manufacturer, but a majority of them should be in the choice menu to allow the spout to be carefully tailored to the customer’s needs.
Sleeve material and construction: Coated fabrics chosen for compatibility with the product being handled and the service conditions are supported by either rigid or semi-rigid rings or hoops. Individual rings allow the collapsed (retracted) sleeve to stack much straighter than a sleeve supported with a continuous, spiral wire. Further, a structural shape, either a channel or H-beam, will stack better than a round wire or cable sewn inside a pocket on the sleeve. Very long sleeves should be made in sections and spliced together, so that replacement of a damaged portion of the sleeve can be done without having to replace the entire assembly.
Standard sleeve material is commonly a vinyl-coated fabric of either polyester or nylon. This material is serviceable over a wide range of ambient and product temperatures, is UV stable, and is chemically compatible with a majority of dry products.
Optional fabrics include chlorosulfonated polyethylene (common trade names Hypalon™ and Coverlight®) coated fabric for high and/or low temperatures (31°F/-35°C to +225°F/140°C) and UV-sensitive applications; neoprene-coated fabric for certain chemical contact issues; silicone-coated fiberglass for very high temperatures (up to 550°F /288°C); as well as other materials on a case basis.
Most loading spouts have aluminum rings to support the outer dust containment sleeve. The inner and outer support rings are fastened to each other by drilling and riveting the rings together. This method results in metal shavings inside of the sleeve as it is being constructed. The fasteners that hold the rings together can ultimately fail and contaminate the product being transferred through the loading spout. Further, piercing the fabric during the riveting process introduces a starting point for failure of the material due to fatigue.
Another option for the rings is a clamping design to bind the outer ring over the inner ring, performing the same function as the riveted assembly, without the rivets or any penetration into the inner ring. This design is void of any fasteners, bolts, or parts that could be introduced into the product being loaded.
By utilizing low profile inner support rings in conjunction with custom extruded outer support rings that are assembled with a high performance clamping method, the need for mechanical fasteners have been totally eliminated.
Cable System: The industry standard is to fasten u-bolts to an “ear” that is welded to the metal stacking cone. The nuts that hold the u-bolt in place can become loose over time and fall off. Or even worse, the u-bolt itself can fail and in both instances, contaminate the product.
Another cable design option is a custom-machined steel peg which has a precision-drilled hole for the cable to pass through. The cable is held in place by a set screw that is treated with Locktite®. If your spout is handling food or grain, ask your manufacturer for both the ring clamping option and the steel peg option.
Most of the standard spouts have a 2, sometimes a 3, cable system. For maximum stability, a 4-cable lifting design is optimum. The extra cable distributes the workload more evenly and provides security if one cable should become weak, or even break.
Most standard spout cables run through a 2-piece pulley. To reduce cable wear and back lashing as the spout extends and retracts, a special 3-piece CNC-machined pulley that feature chamfered edges and precision cable grooves Because the cables do not fray, cable failure is nearly eliminated and so is costly downtime for repairs.
Hoist Drive System: The drive components together form the winch, or hoist, which raises and lowers the spout. The assembly consists of: a motor close-coupled to an enclosed, sealed, gear reducer; a drive shaft; support bearing(s); and lift pulleys which wind and release the lift cables. The power requirements are specific to the application: longer travel spouts may require up-sized motors and gear units, and are engineered accordingly. The components of the winch which directly handle the lift cables should be chosen and/or manufactured for ease of maintenance and to cause minimal wear on the cables themselves: sharp edges on lift pulleys can abrade the cables and break the individual wires; turning sheaves which are undersized will fatigue the cables. Both situations can cause premature cable failure, requiring replacement of the cables. The components of the winch assembly should be robust as befits a piece of industrial machinery.
Compact Inline Filter System: Airborne fugitive dusting is a leading concern for companies and local governments. Installing a loading spout in your operation can contain the flow of material into a confined area reducing the radius of debris and dust. In a properly fitted spout, fugitive dust can be greatly reduced or eliminated, thereby creating a clean work environment free from air pollutants and floor spills.
Additional equipment such as a blower and an integral filter can send the fugitive dust to draft back through the sleeve of the loading spout, trapping material dust temporarily in the filter cartridges.
An inline filter system is more cost effective than a free standing dust collection system, which often includes the cost of additional duct work and a discharge airlock. A compact filter system can utilize cartridge filters, have a high air to cloth ratio, and can be equipped with an exhaust fan. A maintenance friendly design allows easy access for filter change by simply removing the filter cap and panel bolts.
Installed in-line with the spout, a filtration system equipped with an automatic pulse jet filter cleaning system can reintroduce dust particles back into feed stream during the entire load-out process, eliminating the need for disposal. The pulse jet cleaning system continuously purges the pleated filter cartridges of dust particles. This prolongs the life of the filter cartridges significantly.
Scavengers: The outlet assembly (scavenger) and associated parts and control devices, are configured to optimize the loading of various configurations or situations.
Cones: A discharge cone can control the flow in enclosed loading. The cone can be self-sealing and seats directly into railcar hatches and semi tankers to minimize fugitive dusting. Sensors attached to the inside of loading spouts automatically measure product levels. The sensors also provide a signal that automatically stops the flow of materials to prevent overfilling and/or plugging within the spout.
Flexible skirt: For open vehicle loading or stockpiling, the open vehicle scavenger includes a flexible skirt, usually multiple strips of rubber, which lays on and conforms to the pile of product. This helps to contain fugitive dust as the product pile builds. Sensors included with this design can be used to automatically raise the spout to maintain optimum contact with the product.
Barrier skirt: A secondary skirt which may be installed on open loaders and stockpiling chutes. This is usually a canvas or other fabric which covers the rubber strip skirt, and closes the gaps which emerge as the skirt flairs on the pile. Useful with very dusty materials, or when the scavenger may become positively pressurized while open loading.
Vent-through design: Specifically designed for attachment to an in-line filter, spout positioner, or both, this allows dust extraction through the main frame or “pan” without the need for an external pipe or hose connection to a nozzle.
INCREASE PRODUCTIVITY WITH ADDITIONAL LOADING ACCESSORIES:
- Positioner: A loading positioner can help minimize spills when loading. The positioner is used with standard volume loading spouts to facilitate and speed up the loading of open or enclosed trucks and railcars at loadout stations. They eliminate the need to reposition a vehicle once it has entered the loading station.
- Level sensor: Material detection probes of various types to signal the operator that the vessel or container is full to the desired level, and also trigger the automatic-raise function in an open vehicle or for stockpiling. The most common type is a tilt probe, which may be a mercury switch or a mercury-free type. Other types include tuning-fork, paddle, and RF or capacitance probes.
- Control pendant: A hand-held pendant, similar to crane control, allows the operator to raise and lower the spout, start and stop the material flow, and control other operations as appropriate. These can be custom-tailored to the requirements of the customer.
- Control panel: Wall-mount or pedestal-mount control panels and free-standing cabinets can provide point-of-use operator interface. These options are built to order, and can contain a variety of functions, as well as motor starters, VFDs, PLCs or I/O racks. The panels can be qualified to the environmental rating required.
- Product trimmer (spinner): A powered device which uses a rotating disk to distribute material laterally to overcome the natural angle of repose, facilitating complete filling of the vessel. Usually applied to railcar loading of light materials like plastic pellets, the vessel is normally loaded by volume, not weight.
- Vibrator, pneumatic or electric: Located on the scavenger, a vibrator can be activated to help clean residual dust and product that may be lodged within the spout, before the vessel or vehicle is removed.
CARE FOR YOUR SPOUT:
Without proper regular maintenance, the loading spout, like any other piece of equipment, will fail to perform the intended function. Periodic inspection of the wear parts, as called for in the manual and adjusted for local conditions, will keep the spout functioning for many years. Highly abrasive products like sand, flyash, certain grains, and minerals, will produce wear on the cones, requiring replacement. The outer sleeve is subject to damage from repetitive use, rough handling, or from contact with the product if the cones are worn. Lift cables can become vulnerable to abrasion and fatigue due to contact with the various parts of the drive system, especially if basic design practices are allowed to slip in the interest of cost. Contact an experienced manufacturer willing to supply a custom a spout, which will save you time and money.
Article Featured in the November edition of Solids & Bulk Handling: