We were recently contact by a long time customer who is in the process of replacing five storage silos at their plant. These silos were erected in 1981 and they included (5) 10 ft diameter Vibra Screw Bin Activators.
The bins are in pretty bad shape due to 39 years of exposure to the elements. Our customer, thinking that if the bins were in tough shape, that the Bin Activators would also be on the same condition. So they were planning to replace everything is the system.
We visited the site and checked the metal thickness of each Bin Activator body and collection cone for wear using Ultrasonic Wall Thickness Gauge. No wear was found to exist after all these years. The customer has not replaced any parts of the Bin Activators in 39 years. Not going to replace the Bin Activators and we have a happy customer.
Built to Survive
The Merrill–Crowe Process is a separation technique for removing gold and silver from the solution obtained by the cyanide leaching of precious metal ores. This process is currently used at the 10 largest gold producing mines in the free world. As part of the process, zinc dust is added in small amounts but due to the variation in gold to silver ore ratio the amount of zinc need fluctuates and needs to be precisely fed to maintain steady state process.
Zinc dust has a bulk density at 220 lbs/ft3, with a particle size of 2-9 micron. The feed rates are low between 8 to 35 kg/hr. The material will settle out, de-aerate and become a non-free flowing powder. Over the years Vibra Screw has developed a Loss-In-Weight feeding system which incorporates its vibrated Versi Feeder which uses controlled vibration to assure consistent flow of material from the hopper through the feed screw and into process. The Live Bottom Bin above the feeder stores a shift worth of material and discharges the material to the feeder when the control system requires. Vibra Screw has been providing feeders for over 40 years to gold extraction processes.
Vibra Screw has been designing batch and continuous gravimetric control systems for decades. We were quick to adopt useful technology by incorporating digital and graphics displays, as well as an ever-growing number of I/O interfaces into our products. As expected, customer response to these improvements was overwhelmingly favorable.
However, all gravimetric control systems, no matter how fancy the user interface, measure weight using a transducer called a load cell. (See Figure 1) The load cell converts mechanical weight into an electrical signal. The most common type of load cell employs a strain gauge transducer (See Figure 2) in a Wheatstone bridge and can be found in devices ranging from deli scales to systems designed to process solid rocket fuel.
While computer technology has enabled high tech gravimetric control systems to evolve significantly over the last 40 years, a load cell is still the basic workhorse at their core. And, though it may be hard to believe, the strain gauge load cell technology got its start in the late 1800’s. In 1843 Sir Charles Wheatstone perfected and popularized his Wheatstone bridge. (See Figure 3) A resistance change in the bridge produces a proportional change in voltage across the bridge. Then almost 100 years later, in 1930’s, Edward E. Simmons and Arthur C. Ruge invented a device that could measure strain in an object.
It wasn’t long before the strain gauge and Wheatstone bridge technologies were combined and the “load cell” was born. This transducer changes mechanical energy into a proportional electrical signal. Even with the invention of the transistor following World War II, the load cell still found it’s primary application in laboratory test instrumentation. The small signal created by the load cell wasn’t ready for commercial/process gravimetric control systems. Lever scale and balance remained the preferred method of measuring weight.
Finally, in the computer age of the late 20th century, electronic technology had advanced enough to accurately measure small signal changes and the load cell started to replace the balance and mechanical lever scales used in processing industry. Even in today’s cutting edge technology, over 170 years later, the strain gauge load cell continues to be the preferred transducer used for process weighing and gravimetric control and the one used by Vibra Screw.
Over our 65 plus years of making Bin Activators we have had the opportunity to work on projects that require special designed Bin Activators for a wide range of industries.
The normal material of construction of a Bin Activator (material contact parts) is carbon steel, 304 or 316 stainless steel, depending the customer’s needs. Special applications over the years required aluminum, titanium and Hastelloy with the occasional abrasion resistant liners made from T-1 AR steel, ceramic tiles (like the space shuttle), Tivar™ UHMW-PE and we even made a fiberglass lined Bin Activator.
In 1978 a customer who handles Chlorinated Dry Bleaches asked Vibra Screw to build eight, 5 ft diameter Bin Activators made out of Inconel 600 which we did. These units have been running without issues for 48 years, but even Inconel is not completely unaffected by the corrosive powder. Time took its toll on the units and they needed replacing.
The photo shows the first two replacement 5 ft Vibra Screw Bin Activators, made from Inconel 600, with non-Inconel parts epoxy coated. As we say “Vibra Screw products are Built To Last”.
Inconel Bin Discharger
Volumetric Feeder for Fumed Silica
Fumed silica also known as pyrogenic silica because it is produced in a flame pyrolysis of silicon tetrachloride or from quartz sand vaporized in a 3000 °C electric arc. Fumed Silica consists of microscopic droplets of amorphous silica fused into branched, chainlike, three-dimensional secondary particles which then agglomerate into tertiary particles. The resulting powder has an extremely low bulk density 2.5-11.8 lbs/ft3 (40–190 kg/m3) and a primary particle size of 5–50 nm (which is smaller than the average particle from cigarette smoke) and high surface area.
Because of its very low bulk density and small particle size, fumed silica is extremely difficult material to accurately feed into process. For decades Vibra Screw has been metering fumed silica with our controlled vibration screw feeders. The photo shows a Vibra Screw Live Bottom Bin and 2” VersiFeeder volumetric screw feeder. Both work using controlled vibration to de-aerate the material to a constant bulk density and assure the flights of the feed screw are completely filled with material. Typical feed accuracy of 1-2% can be obtained.
We are very sad to report the sudden passing of Joe LiVecchi.
Joe was an institution at our company, having spent the last 57 years running our parts department which has become an indispensable part of our business. Reps, customers, suppliers, and especially his colleagues knew him for his absolute dedication to the job, his encyclopedic knowledge of our equipment, and, perhaps most of all, his unique personality and wit.
Among the hundreds of people Joe dealt with over the years, many didn’t see his deep devotion to his five children, nine grandchildren, and three great grandchildren. He gave countless hours to helping other people with the challenges he had successfully dealt with years ago and he encouraged and supported the younger people he worked with, much to their benefit.
It’s difficult to imagine the company without Joe. What he’s left behind, though, is an indelible legacy, a constellation of friends, and some of the fondest memories we’ve all had.
Behind our office is a field of irises, planted and tended to by Joe over the last few years, just because he enjoyed seeing things take root and grow. Thank you for this, Joe, and for all that you’ve given us. You will always be in our hearts.
Gene Wahl Sr.
President
Vibra Screw, Inc
Soda Ash is used as a builder or filler in the formulation of soaps, detergents, and other cleaning compounds. In the glass industry it is used to bring down the melting temperature of silica sand (the main raw material of glass).
In the paper industry, soda ash is used in the preparation of the sodium sulphite buffer liquid used in the pulp manufacturing process.
Soda ash even finds an application in the water treatment segment, by adjusting the pH of water when it is acidic.
The photo is a recent installation of a Vibra Screw Live Bottom Bin and Versi Feeder screw feeder designed to help process soda ash. The equipment is handling 425 degree F soda ash. The flexible connections are made from heat resistant silicone. Required feed rate 12 – 100 ft3/hr.
High Temperature Loss-In-Weight Feeder
Curbs segregation of bulk-stored mixes
Recent field experience indicates that segregation of dry mixtures in bulk storage can be eliminated by proper application of vibration to the material in storage. As a result, food processors are adding vibrating bin activators to the bottom of hoppers and bins not only to induce flow, but also to eliminate segregation.
An Indiana miller, for example, cut deviations in composition of a bakery premix by one half. Included in the premix are flour, salt. sugar, soda and cornstarch.
Although these ingredients differ widely in density, particle size and flow characteristics, vibration helps keep composition at discharge very close to that at the inlet.
Less segregation, better quality
Eliminating segregation in dry mixes brings three principal benefits. First, better product quality can be maintained on a consistent basis. Second, downtime and lost production due to rejected batches or remixes, can be reduced. And finally, engineering management gains more flexibility in plant design and operation. Larger quantities can be bulk-stored because the risk of segregation no longer limits storage capacity. It is also possible to mix first and store later in instances where the risk of segregation might previously have ruled out this option. Such added flexibility can lead to improved production and important cost savings.
In the static bin (left sequence) loaded with material of non-uniform particle size. A pipe forms down the center of the outlet. The vibration-assisted bin (right sequence) has a baffle over the outlets. Vibration keeps all material mobile. and the baffle prevents the pipe from forming.
How vibration cuts segregation
Picture what happens when you pour a mixture of stone and sand on the ground. A rough cone forms, with stones mainly around the outside and sand mainly in the center. The stones tend to roll down the surface of the cone as it is formed, while the sand sifts down closer to the center. Segregation has taken place.
If, as usually happens in a conventional storage bin,
material discharges from the center of the bin first, finer material would emerge first and coarse material last.
The same basic thing happens in mixtures of dry ingredients having differing physical characteristics. Differences in particle size are the principle contributors to segregation. Differing flow characteristics and density may also influence the situation; however, the combination of a vibrating bin bottom with a built-in baffle over the final outlet substantially reduces the segregation problem.
Vibration keeps the material mobile and free-flowing, particularly at points of potential bridging, and the baffle directly over the outlet prevents material from emptying down a pipe in the middle first, and then off the walls as often occurs in static bins.
Because of the baffle. the pipe never gets a chance to form. Instead, the material draws evenly across the cross section. Moreover, the final discharge is a combination of materials from the center and those from nearer the walls. So even if there were segregation from the center out, there is re-mixing just before discharge. This flow pattern is called mass flow, or first-in, first-out flow.
Mass flow of bulk materials from a bin has been demonstrated in experiments in which layers of different-colored materials are loaded into a bin equipped with a bin activator, developed by Vibra Screw Inc.
Achievement of true mass flow from a bin eliminates risk of dead areas, spoilage and contamination among products processed on the same equipment.
Case in point
The Indiana miller’s experience underscores most of these points. The plant produces dough for dinner rolls and sweet rolls. The basic operation is to blend the dry ingredients into a dry premix. It is stored in a pre-mix bin, and discharged at a controlled rate to a scale hopper, then to a mixer where wet ingredients are added and the dough is developed. The bin is 7-feet- diameter by 15-feet-high and holds more than 10,000
pounds.
Originally, all feeding and dispensing of dry ingredients were by gravity. But a disparity in physical properties of the dry ingredients led to segregation within the storage bin. Densities ranged from 38 to 75 pounds-per-cubic-foot. and particle sizes from 30 to 400 mesh. As a whole. the mixture has a density of 55 pounds-per-cubic-foot and a moisture content of 5 percent.
To minimize segregation, a 7-foot-diameter bin activator was installed on the premix bin.
Closer control also was maintained over the quantity of material stored in the bin. This kept retention time of material in the bin close to 50 minutes. The bin activator mounts to the bottom of the bin in place of the standard bin bottom. Special hangers isolate it vibrationally from the bin. A patented gyrator on the bin activator generates vibratory forces up to 6,000 pounds to vibrate the entire bin bottom and its contents, but not the bin itself. In addition, an integral dished baffle mounted horizontally in the bin activator above the outlet vibrates to induce mass flow from the bin. It also prevents packing at the outlet due to static head loads.
Result of the installation was immediate reduction in segregation. This company measures composition of the premix by monitoring pH of the dough after blending.
Too high a pH means excess alkaline ingredients such as soda. A low pH indicates that level of acidic ingredients, such as salt, is running too high.
With the activator generating controlled vibration into the premix and inducing true mass flow in the bin. the number of samples falling within specifications rose from 68 percent to 78 percent. Moreover, deviations one percent below specifications dropped from 22 percent to 10 percent, deviations two percent below stayed constant at five percent, and deviations on the high side increased from three percent to only five percent.
In addition to improved quality control, the company reports that eliminating segregation improved line machinability of the product as it moves through the process. Based on this experience, it has installed another activator on a second process line.
Inconel Bin Discharger
Over our 65 plus years of making Bin Activators we have had the opportunity to work on projects that require special designed Bin Activators for a wide range of industries.
The normal material of construction of a Bin Activator (material contact parts) is carbon steel, 304 or 316 stainless steel, depending the customer’s needs. Special applications over the years required aluminum, titanium and Hastelloy with the occasional abrasion resistant liners made from T-1 AR steel, ceramic tiles (like the space shuttle), Tivar™ UHMW-PE and we even made a fiberglass lined Bin Activator.
In 1978 a customer who handles Chlorinated Dry Bleaches asked Vibra Screw to build eight, 5 ft diameter Bin Activators made out of Inconel 600 which we did. These units have been running without issues for 48 years, but even Inconel is not completely unaffected by the corrosive powder. Time took its toll on the units and they needed replacing.
The photo shows the first two replacement 5 ft Vibra Screw Bin Activators, made from Inconel 600, with non-Inconel parts epoxy coated. As we say “Vibra Screw products are Built To Last”.
Vibra Screw is known for our powder handling equipment, but we also provide liquid Loss-In-Weight feeders. The two feeders pictured are getting ready to be shipped to a long time customer (over 30 years) who has purchased several sets of these feeders for the energetics industry. One feeders is metering polymer and the other is metering a plasticizer.
In the static bin (left sequence) loaded with material of non-uniform particle size. A pipe forms down the center of the outlet. The vibration-assisted bin (right sequence) has a baffle over the outlets.
