Bin Activators

OMYA lnc., Florence, Vermont Major manufacturer of calcium carbonate used mainly in the plactics, paint, and paper industries as a filler, extender and coating.

The Verpol plant of OMYA Inc. is the, most modern plant of its kind in the world. It processes
both crushed and finely ground calcium carbonate through its completely computerized operation.
Bulk densities of the materials range from 25 to 70 Ibs. per cu. ft. To meet process and excess
storage requirements, the company has 27 bins ranging from 8 ft. to 26 ft. in diameter, of both concrete and steel construction. The bins are filled either pneumatically or by belt conveyor. Some of the bins are discharged through rotary valves to belt feeders or pan feeders, and some to bagging machines filling 50 lb. bags. Discharge rate varies from 4 tons per hour up to 40, depending on the stage of the process. However, calcium carbonate, especially the finely ground product, can be difficult to discharge from storage because it tends to bridge and clog.

27 Vibra Screw Bin Activators of 3 different diameters (4 ft., 6 ft., and -12 ft.), carbon steel construction, most of which have an epoxy coated interior.

To assure reliable flow of material in its computerized operation, where such reliability is critical, the company decided to install Vibra Screw Bin Activators under all its storage bins. This was possible because the Bin Activators work equally well on both concrete and steel bins. Flexibly mounted to the bottom of the bin, the Bin Activator, but not the bin, is subjected to controlled vibration. An integral baffle located just above the discharge outlet directs vibrations high up into the bin, keeping the material free flowing. An important factor in the handling of calcium carbonate, this action rids the material of entrained air, conditioning it to a uniform bulk density, which helps speed conveying and bagging operations.

OMYA Inc. relies on its Bin Activators to help it produce an uninterrupted flow of high quality product In the words of a company official, “It would be difficult to operate the plant without our Bin Activators.”

OMYA BIN ACTI

Can you afford to get caught without a critical part?

You can’t drive your car forever with the same oil, brakes, muffler and tires. Periodically it will need to be serviced. Solids processing equipment is no different. It needs to be properly maintained in order to perform within its design parameters. And, eventually certain parts will need to be replaced. Maintaining a spare parts inventory is often considered a luxury you can’t afford. But stop to consider how much downtown you can afford if a critical part fails. There is no perfect answer but here are some insights into some different types of equipment and parts.

Spare parts for solids processing equipment might include sleeves (elastomer seals), hangers, flight screws, conditioning screws, isolators and wire screws.

In the best of conditions, solids processing equipment like vibrating bins, bin activators, vibrating conveyors and screw feeders, are subject to stresses that will, over time, cause critical part failure. Even if the part in question is a standard item and readily available, you need to gauge the consequence of the downtime resulting from ordering, shipping and installing that part. What if that part requires custom manufacturing? How much downtown is too much? At what point should you consider having a replacement in your spare parts inventory. It is a question you should be asking before a part fails.

Bin Activators have two critical parts that will need to be replaced and we recommend you have spares.

Elastomer seals between the bin and the bin activators
Isolators for your bin activator hangers

After two years of service these parts should be carefully inspected. This inspection should then be repeated every six months. Obvious signs of degradation are checking and cracking. Also examine your isolators for sag. If signs of fatigue or wear are detected, these parts should be replaced. If you have spare parts on hand, be sure to inspect them carefully before installing them. Elastomer parts in extended storage can be compromised. Nevertheless, the cost of the part vs. the cost of the downtime suggests having spares is a wise decision.

You might think that the Gyrators on vibratory equipment are subject to a high rate of failure due to what is perceived as their high-stress function. The fact is, in continuous use situations, they are subject to very little stress. Gyrators are oil lubricated and with proper maintenance they can last years. Simply conduct the recommended inspections every 1000 hours of operation and change the oil every 6000 hours. Like a well maintained car, you can get years of trouble-free service following a simple maintenance routine. When processing is not continuous and Gyrators are frequently started and stopped, stresses on the Gyrators are increased and these inspections become more important.

There are also parts that are custom engineered and built specifically for the equipment they help operate. For example, most feeder screws are unique to the feeder they are shipped with. If the equipment is operated according to manufacturer’s guidelines, the screw can last longer than the feeder. But in real world situations, screw failure is all too common and when they break, there is no quick fix. Again, you have to weigh the cost of having a spare on hand vs. the downtime you will experience having to order a custom-engineered part.

So…to borrow a tried and true motto, be prepared. Consider what equipment you are operating, how it is being used and your tolerance for downtime. Refer to your manufacturer’s recommended spare parts list. If you have questions consult your equipment manufacturers and get their recommendations to help find the balance between the investment you are able to make in spare parts and the risk you are willing to take. Our experience shows that you should have some spare parts on site. It will pay off some day.

Bin Activators Cure Material Segregation

Bin-BinActivator-Comparison 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.

The same thing can happen in storage bins with a material mixture of differing particle sizes. In a conventional bin [Fig. 1], materials separate as it is loaded. On discharge, finer material emerges from the center of the bin first, down a pipe and coarse material last. In a production process requiring a uniform blend, product quality suffers and the downtime from rejected batches can be costly.

When storage bins are equipped with Bin Activators, the segregation problem can be eliminated. [Fig. 2]. Vibration keeps material mobile and free-flowing, particularly at points of potential bridging. An integral baffle directly over the outlet prevents material from emptying down a pipe in the middle first and then off the walls as in conventional bins. Because of the baffle, the pipe never gets a chance to form. Instead material draws evenly across the bin cross section. And the final discharge is a combination or remix of materials from the center and those from nearer the walls. This flow pattern is called mass flow.

Vibra Screw Bin-Activator With Bin Activators, larger quantities can be bulk stored because the risk of segregation no longer limits capacity. Management gains more flexibility in plant design for example with fewer bins and conveyors required. That can lead to improved production and important cost savings.

Since its introduction over 50 years ago, the Bin Activator has become the most widely used bin discharge device in the process industries. It can be used on new or existing bins, and it will discharge virtually any dry material. In most cases, a successful Bin Activator installation is simply a matter of picking the right size Activator for a given bin diameter.

There are over 100,000 Bin Activators in service worldwide and we have a tested materials data base of 8000 dry solids. This experience enables us to properly size Bin Activators by measuring a few basic characteristics. If we know bulk density, moisture content, slide angle, particle size, compressibility, and cohesiveness, we can place the material in one of four general classifications. Then with bin dimensions we can select the proper size Bin Activator.

Class I materials are granular and would normally flow unassisted. But with changes in moisture or temperature they may become flow resistant and require a small Bin Activator. Granular salt, whole grains and plastic pellets fall into this category. Bin Activators should be 1/4 to 1/3 of the bin diameter.

Class II materials are the sluggish powders which would not normally flow by gravity alone. Examples would be flour, starch, powdered sugar, and most plastic powders. Bin Activators should be 1/2 to 2/3 the diameter of the bin.

Class III materials are some of the most challenging to discharge. They can be either readily adhesive or easily fluidized. Sometimes, in the case of cement or hydrated lime they can act either way. A product that that is too easily fluidized will be nearly impossible to control after it leaves the bin. The job of the Bin Activator, then, is to overcome the strong tendency of this material to bridge and pack while at the same time de-aerating it on discharge. Bin Activators for Class III materials should be ½ to 2/3 the bin diameter.

Class IV materials are fibrous or flaky with a relatively low bulk density. They typically have a large particle size and tend to interlock and absorb vibration. Examples of Class IV materials would be wood chips, shavings, plastic scrap and chopped fiberglass. Bin Activators should be as large as the bin will accept.

This information is summarized in the table below. The table also indicates expected discharge rates for a given outlet size with each of the 4 material classifications.

So if you know the bin diameter and the material class for the product you are storing, you can easily and confidently select the proper size Bin Activator for your application.

material-classification-table

Attaching a Bin Activator To a Silo … More Than Just Nuts and Bolts

Bin Activators are one of the most successful devices for ensuring flow of bulk material from storage. They can range in diameter from a couple of feet to 18 feet. Bin Activators can be extremely heavy, and while being subjected to vibration, must support the head load created by additional tons of material in the silo. Making a mistake in the design or material used in the hangers that support them can have catastrophic consequences.

Hangers perform two critical functions. First, they must safely carry the Activator and silo head load. Second, they must provide flexibility of movement under vibration and prevent transmission of that vibration to the stationery silo structure. Accordingly, they must be incredibly strong in tension yet free to move horizontally. Our experience has proven that forged steel hangers combined with isolator bushings provide the best uniform tensile properties and strength. At Vibra Screw we produced both with our own dies and molds.

Smaller Activators use smaller forged hangers combined with a lower durometer isolator. Larger activators use larger forged hangers and progressively higher durometer isolators. The critical calculation is to design for each specific load situation with the right choice of forging size and isolator stiffness. The correct design will maximize strength while minimizing vibration transmission. It may sound simple but for Activators to operate within optimal parameters hangers are a critical component.

When applications require even more load carrying ability, simply adding additional standard hangers is not always possible. Our R&D engineers have designed a cable hanger similar in design to the cables used on the world’s largest suspension bridges. The cable hanger provides excellent horizontal flexibility and vibration isolation, and up to 10 times the load capacity of our strongest regular hangers.

Our experience has shown the hanger designs we’ve described here are far superior to those using ordinary bar stock, threaded rod or even castings for vertical support combined with rudimentary off-the-shelf isolators.

Beyond the nuts and bolts of installing a Bin Activator, a carefully designed hanger system is essential. Vibra Screw’s 60 years of experience, from invention of the Bin Activator to development of its present design, ensures the safety and integrity of each system.

Vibra Screw large forged hanger for Bin Activator — Large forged hanger

Vibra Screw cable hanger for Bin Activator — Cable hanger

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