From Source to Destination, Vacuum Conveying Gets It DoneFrom Source to Destination, Vacuum Conveying Gets It Done
November 27, 2019
Beyond a high-tech solution for transferring materials, pneumatic conveying solves safety hazards, production slowdowns, and material loss with custom and off the-the-shelf engineered systems.
Modern vacuum technology has been at the forefront of manufacturing technology since the beginning of the industrial revolution. From the first manually operated vacuum pumps of the late 1800s, to the first industrial use air-powered vacuum cleaner in 1953, the first vacuum conveying system designed to deliver powders for ordnance in 1962, and current venturi technology, vacuum conveying is the most sophisticated method of handling powders and bulk solids today.
Vacuum conveying has always been used for plant efficiency, material protection and safety, lending to its advancement and wide-spread use across most industries including pharmaceutical, chemical, food processing, additive manufacturing, and the aerospace industry.
Today’s vacuum conveying systems employ essentially the same concepts as the first systems of the 1950s, yet with more sophisticated components and advanced knowledge gained through practical experience.
Each industry poses different problems in terms of materials, regulations, and safety. Materials in the pharma and cosmetics industries utilize materials with particles so small you can barely feel them between your fingers, yet both industries have vastly different regulations, safety concerns, and quality control challenges. Other industries work with highly abrasive powders, hygroscopic materials, or utilize powders that are incredibly heavy at 250 to 350 lb/cu ft, like additive manufacturing.
Some applications with relatively unproblematic materials like sugar, plastic pellets, rice, and coffee are more straightforward and may not need the level of engineering that challenging powders such as iron oxide, zinc oxide, calcium carbonate, or toner demand. However, even unproblematic powders can pose unique challenges, relative to process, that require custom engineered components. Likewise, some difficult powder applications may be suitable for turnkey off-the-shelf systems.
Why Vacuum Technology?
As vast as material behavior is, so are the reasons why manufacturers employ vacuum technology. Some users want more automation, while others are seeking to improve ergonomics or create a cleaner work environment, or manage materials cost. Increased throughput is the primary objective for others.
Seasoned vacuum conveyor manufacturers translate information, passed down through time, between industries to engineer custom and off-the-shelf solutions that work on start-up.
Although the process of conveying wax chips is straightforward, similar in nature to conveying plastic pellets, the melting point of wax poses challenges. Wax that melts at very low temperatures becomes sticky and adhesive requiring provisions to ensure the wax melts in the tank and not in the equipment being used to convey.
Vacuum Technology Applications
When International Converter, a division of Novolex, the leader in foil laminates, multi-web lamination, and specialty barrier and sealant coatings for use in a wide range of high barrier consumer and industrial applications, requested a quote for a vacuum conveying system to eliminate manual transport of wax chips to a raised platform where workers dumped 40-lb bags into a hopper, its ideal solution was a completely automated system that would allow it to change from using 40-lb bags to super sacks.
There are numerous ways to engineer pneumatic conveying systems and previous experience with this type of arrangement, common across most industries, as well conveyor installations with other wax applications at Candle-Lite and HB Fuller, facilitated several design choices on the path to final design that that met the customer’s ergonomic, production and financial needs.
Although all pneumatic conveying systems require some bit of human interaction, the first system iteration proposed the ideal solution to eliminate worker effort and risk, coming as close to a fully automated system as possible, complete with automated super sack unloading equipment and dual material receivers to facilitate the delivery of both gloss and matte wax beads to their respective tanks. The cost, however, was outside of what International Converter had to work with.
Even though the automated bulk bag unloader would have further reduced worker interaction in the process, and therefore worker risk, it did not add much to the package otherwise. Had International Converter--which operates three shifts five days per week--wanted to increase throughput from its average of 1500 lb of wax beads per shift, a bulk bag unloader would have been a more viable option.
Since the volume of pellets through the system was lower capacity, rather than using a bulk bag unloader, a wand was implemented as the pick-up point. Now, workers use a wand to suck material out of the top of the super sack rather than suspending it. Though it is more labor intensive than using a bulk unloader, using a wand to remove material from bulk vessels eliminates the exertion, repetitive motion, and awkward positions that occurred with manual handling of 40-lb bags, and has the same outcome as using a bulk bag unloader.
In addition to backing down the automation in the system design, instead of using two receivers to deliver both matte and gloss chips to the system, the facility’s high ceilings supported the use of one receiver with a gravity diverter valve that acts like a splitter valve. The gravity diverter valve has a blade inside that switches from one direction to another, allowing material to be diverted to the appropriate tank.
To ensure that heat rising from melting tanks didn’t make the conveying equipment hot enough to melt the wax while conveying a sparge ring provided some isolation from the process to the conveying equipment. Sparge rings are transition pieces with small fittings that create positive pressure and used most often with heat sensitive equipment or vapor control.
Still on a mezzanine level, the pellets are transferred, via wand, from a Gaylord up 20 ft to the receiver. Where it used to take two workers per shift, and require equipment to be shut down while loading, a single person can do it, eliminating the risk, which was the primary goal.
While wax and plastic pellets are free-flowing materials, hygroscopic materials are not and tend to gum up and clog the system. Additionally, fugitive dust of hygroscopic materials, when released into plant environment, makes housekeeping a time-consuming task.
Pneumatic Conveying System Replacement
When Ramsey, NJ-based Okonite Co., a producer of premium insulated wire and cable since 1878, needed a pneumatic conveying system for its Orangeburg, SC plant, its goal was to replace its in-house system designed to reclaim super absorbent polymer (SAP) and control the environmental end of its proprietary process.
The proprietary three-step process coats wire cable with SAP. The SAP serves as a blocking agent so water cannot run inside the conductor if the cable or wire insulation system is breached in an underground or wet environment.
While the fine powder is responsive to moisture and effective at protecting wires, and therefore systems from shorts, in production it is prone to gumming up with exposure to moisture. Exposure of SAP to the humid air of South Carolina alone can cause clumping affecting efficiency and productivity.
The process at the South Carolina plant runs between 400 and 600 ft of cable per minute through a 4-ft-long atomizer chamber that blows the SAP around in a cloud which coats the wires. The original system used a single filter housing to capture product for reuse. However, each time the filter needed cleaning the chamber would switch from negative pressure to positive pressure and powder would escape into the plant atmosphere through the openings where cable entered and exited the chamber.
Based on previous applications with hygroscopic materials--and SAP in particular--information about how much powder they were moving, the CFM, and the amount of powder wasted on overspray is what led to the design of a dual conveyor system with automatic changeover and a filter large enough to recover material.
The dual-conveyor system works essentially like that of a pumping heart. First, cable enters a chamber at about 400-600 ft/min, while an atomizer simultaneously injects positive air and SAP into the chamber wherein it coats the cable fibers. At that same time, the dual-conveyor system sucks air out of the chamber at a faster rate than enters into the coating chamber, creating the negative pressure system wherein SAP cannot escape into the air external to the coating chamber.
From there, material enters the first of two valve chambers for a programmed amount of time. After that the first valve closes while opening the second valve and chamber. When the first valve closes, air is blasted into the filter to release particulates to the bottom of the system where another routing system returns the SAP back into the hopper for reuse. This filtration cleaning process is repeated for a few seconds until the first filter is entirely clean, and then the second valve closes for its own identical process.
Where Okonite was losing about 7 percent of its material per shift with their original system, the dual-conveyor system has brought loss to nearly zero.
In addition to the dual-conveying system, a bag unloading station with enough negative pressure to remove the SAP before it has a chance to enter the air around the operator and plant environment further eradicates moisture from the system and reduces housekeeping.
Automation does not always require complicated or custom-designed solutions. In many industries, even those with difficult powders like the pharmaceutical industry, long-term experience has led to the development of complete ready-to-operate systems.
Pharmaceutical materials tend to be very fine and prone to segregation, especially during manual transfer of materials in containers and from machine to machine throughout the production process. The vibration--caused by moving containers--promotes segregation, threatening batch quality. It is this reason that pharmaceutical manufacturers primarily use mass flow methods that move all particles at the same velocity, minimizing segregation.
Blenders, mixers, and reactors are common types of equipment used in pharmaceutical processing facilities. Just like many other types of equipment, they require a mezzanine level for manual loading or specialized equipment like drum loaders or vacuum conveying equipment.
Although drum loaders are better than manual loading, limitations--such as the ability to load only one drum at a time--make the delivery of materials to the blender or reactor time-consuming. In some circumstances, it may also be necessary to load multiple ingredients into drums prior to loading blenders and reactors, further slowing the process by increasing processing steps.
Packaged Conveying Systems
One of the most efficient advances in loading blenders, mixers, reactors, or any vessel capable of withstanding vacuum, is packaged conveying systems designed specifically for the direct charge loading of blenders. With a drug processer’s blender or mixer as the primary receiver, the conveyor manufacturer provides the rest of the system: power source, filters, controls, and adapters.
Configured specific to each application with standard equipment, direct charge blender loading systems come with the option of either floor standing, or suspended blender loaders designed to significantly reduce the amount of carry over, eliminating product loss and ensuring batch integrity.
Standing units are readily accessible for cleaning and can be equipped with casters, allowing them to service more than one blender. In addition, once the blender is loaded and equalized, carry over releases into an airtight vessel that preserves product integrity allowing for reuse or safe disposal.
With suspended units, once the blender is loaded and equalized, material automatically discharges back into the blender eliminating the need to handle product manually.
Because the units are easy to take apart without tools, clean up between batches and products takes only 30-45 minutes to wash down equipment and change out bags, filters, and hoses (when using different hoses for every product).
From fully automated custom systems, to more economical plug and play solutions pneumatic conveying solves safety hazards, production slowdowns and material loss while moving product gently and quickly from point to point, with nothing in the way to impede the efficiency of movement.
Vac-U-Max (Belleville, NJ) designs and manufactures pneumatic conveyor systems and support equipment for the conveying, weighing, and batching of dry materials. For more information, call 973-200-6619 or visit www.vac-u-max.com.
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