| In processing plants around the world, ribbon blenders | | | | the shaft that is needed. A balanced design provides |
| are used to mix many thousands of products, from | | | | a system that blends quickly, produces minimal |
| fertilizers and plastic resins to flavored coffees and | | | | resistance as the ribbon/rod assembly moves through |
| cosmetics. The ribbon blender is one of the most | | | | the bulk, and ensures long-term reliability. |
| common mixing devices in service today, because it | | | | For every minute that your blender is committed to |
| is one of the most versatile and cost-efficient mixers | | | | discharging and cleaning, production is sagging. So, |
| ever created. Its simple design makes it relatively | | | | efficient discharge has become another important |
| easy to build. Simplicity also ensures easy | | | | focus in ribbon blender design. Fast discharge is a |
| maintenance. | | | | function of axial pumping action especially the |
| But during the last few years, business conditions | | | | pumping action of the outer ribbon and the discharge |
| have changed in many industries. Competitive | | | | valve design. Complete discharge requires controlled |
| pressures have mounted worldwide to increase | | | | clearances and a clean design in the interior trough.o |
| production, reduce waste, and improve end-product | | | | All interior angles must include generous radius to |
| quality and consistency. Suddenly process managers | | | | prevent material from collecting in corners.o |
| are finding that the "common" ribbon blender isn't so | | | | Clearances should be uniform at the bottom of the |
| simple anymore. | | | | trough.o Welds should be ground and polished, even |
| One by one, the process industries have recognized | | | | for non-sanitary applications. |
| that many small improvements on the process line | | | | 3. Seals and valves. |
| can add up to a big gain in overall production.o Faster | | | | Recent developments in seals, packing systems, and |
| discharge means shorter blending cycles and greater | | | | valves have made ribbon blenders more reliable and |
| production on every shift...o More thorough discharge | | | | versatile. This is a welcome development, since the |
| means less cleaning, greater accuracy, and less risk | | | | shaft and packing in a ribbon blender are submerged |
| of cross-contamination between batches...o A | | | | in the product zone. |
| variable-speed drive allows you to fine-tune the | | | | Improved seal integrity always helps to insure against |
| blending process, so you can intensify blending | | | | batch-to-batch contamination. |
| without fear of product degradation ... | | | | When blending abrasive materials, and when |
| Several years ago, selecting a ribbon blender was | | | | contamination is a critical concern, air-purged seals |
| mainly a matter of matching your drive and ribbon | | | | help to prevent material from attacking the packing |
| design to the bulk density of your product. In most | | | | material and shaft. In industries that require sanitary |
| applications today, this is only the beginning of the | | | | designs, quickly disassembled split seals/glands are |
| design process. In drives, ribbon design and materials, | | | | provided for east cleaning after every batch. |
| seals, packing materials and discharge valves, we | | | | The valve most often specified for a ribbon blender |
| now have many new choices to consider in order to | | | | is a manually operated slide paddle valve. But for |
| boost productivity. | | | | special applications vacuum operation, for example |
| The result is that ribbon blenders are now being used | | | | alternative valves are required. One alternative is a |
| in many applications in plastics, pharmaceuticals, foods | | | | spherical disk valve, which provides a positive seal |
| and other industries that are surprisingly sophisticated. | | | | during vacuum blending, while it also offers a large |
| But the ribbon blender still has its limitations. Often, as | | | | discharge port for fast discharge. |
| we refine the design to make the ribbon blender | | | | What's next? |
| more and more productive, we eventually come to | | | | As ribbon blender engineering continues to evolve, |
| this critical question: Is this an application that would | | | | these workhorses will be used even more widely, |
| really be better served with adifferent design? | | | | and in more demanding applications. But the process |
| Specifically, would a switch to a vertical cone screw | | | | engineer who is determined to maximize blending |
| blender deliver production gains large enough to | | | | efficiency must eventually ask whether the ribbon |
| justify a higher price tag? | | | | blender is really the best design for his application. |
| This is sometimes a hard question to answer | | | | When in doubt, test before you invest in any new |
| theoretically. Testing in a manufacturers test center is | | | | equipment. Compare the capabilities of a ribbon |
| important, because it allows the equipment buyer to | | | | blender and a cone screw blender in an equipment |
| evaluate each blender design and confirm which is the | | | | manufacturer's testcenter, using your own |
| best choice. | | | | ingredients. Ultimately, this is the best way to be sure |
| Ribbon blenders what are the key design | | | | that you will be putting the best possible blender on |
| considerations? | | | | your process line. |
| 1. Drive design. | | | | Do you need a ribbon blender or a vertical cone |
| The first variables to consider in powering the blender | | | | screw blender? |
| are always product density, volume and moisture | | | | Ribbon blenders and vertical cone screw blenders are |
| content. But from that point on we must consider | | | | found in many plants, and in many ways they |
| the needs of each application individually. Specifying | | | | perform a similar function on the process line. But the |
| the right drive requires effective communication | | | | differences in their design - and in the advantages |
| between the equipment manufacturer and buyer to | | | | they offer - are far moreimportant than their |
| identify key process needs. | | | | similarities. |
| Slow-speed starting Over the years, many ribbon | | | | Of course, one very important difference to consider |
| blenders were built without any provision for starting | | | | is price. The ribbon blender is generally less expensive |
| at slow speed. Unfortunately, a dead load start | | | | than a vertical cone screw blender of comparable |
| presents many disadvantages, all of which increase | | | | capacity. So, in practical terms, you should determine |
| costs. The buyer must choose between using an | | | | whether your application requires a vertical cone |
| over-sized motor and agitator shaft that are capable | | | | screw blender in order to achieve the product quality |
| of providing the peak horsepower and strength | | | | and processing efficiency that you need. |
| needed to get the batch moving or a smaller motor | | | | To decide which type of blender will work more |
| that is appropriate for operating the blender once it is | | | | efficiently in your application, ask yourself these |
| running. The first choice is wasteful, the second | | | | questions. |
| choice is risky, since the high torque at start-up can | | | | 1. How much room is available on your plant floor? |
| overstress the system and eventually causes | | | | Before we even start talking about your blending |
| maintenance problems. | | | | needs, you can answer the first important question |
| The best solution is to provide for a slow-speed start | | | | with a tape measure. If floor space is tight, you may |
| that protects the system. Electronic starting systems | | | | have to go up with a vertical blender since a vertical |
| are a great choice to solve this problem. Electronic | | | | blender requires a smaller footprint. If overhead |
| soft start controllers can be programmed to allow a | | | | space is limited, you may be forced to use a |
| slow start under full load and protect the system | | | | horizontal ribbon blender, which allows you to use a |
| against a spike in start-up torque and amperage. | | | | low-profile loading system. A multi-level operation is |
| Variable speed blending The ability to blend at varying | | | | generally unnecessary. |
| speeds can be advantageous in many circumstances. | | | | 2. Does the friability of your product require gentle |
| Certainly, it is important for R&D applications. It | | | | blending? If so, you may want to consider a vertical |
| can also be useful in any plant where numerous | | | | cone screw blender. The blending action of the |
| products are blended and product changeover is | | | | slowturning mixing screw is very gentle. |
| common. By adjusting the peripheral speed of the | | | | 3. Is complete discharge essential? The cone screw |
| ribbon, you can "tune" the blender to reach the | | | | blender gives you virtually 100% discharge through |
| greatest possible efficiency for each product. When | | | | the lower cone. Even the best ribbon blenders fall |
| blending friable materials, in particular, the variable | | | | short of this goal. |
| drive allows you to blend at a speed just below the | | | | 4. How tight is your budget for power? The ribbon |
| threshold at which the material will start to degrade. | | | | blender consumes more power, over long blending |
| 2. Ribbon design and interior finish. | | | | cycles this can add up. |
| At first glance, ribbon design appears to have | | | | 5. Is contamination a critical risk? With a packing gland |
| changed very little in recent years. | | | | in the product zone, the ribbon blender poses a |
| But the ribbon/rod/shaft design has actually been the | | | | greater threat of contamination. New seal designs |
| object of considerable evolution in design during the | | | | have reduced the risk dramatically, but if your |
| last decade, and it certainly represents a critical | | | | application requires the best protection available, you |
| element in blender design. The ribbon, support rods | | | | may need to switch to a cone screw blender. |
| and shaft must be correctly matched to the physical | | | | 6. Will you always operate with the blender at least |
| properties of the product to boost blending efficiency | | | | half full? If you need the flexibility to operate with |
| and prevent mechanical failures. | | | | smaller batches, choose the cone screw blender. |
| Naturally, the ribbon is specified to provide sufficient | | | | Because of the geometry of the cone, this blender |
| surface area and peripheral speed to move the bulk. | | | | can operate efficiently with batches as small as 10% |
| An equally important measure is the differential | | | | of blender capacity. The ribbon blender generally |
| between the inner and outer ribbons in the double | | | | requires a minimum of 40-50% of full capacity. |
| spiral ribbon set. This differential determines the axial | | | | 7. Will you need complete cleaning between batches? |
| pumping action that ultimately moves the material | | | | The cone screw blender is easier to clean. Just make |
| toward the discharge. The challenge is to induce | | | | sure that the cone screw blender you select does |
| vigorous agitation without over-stressing the ribbon, | | | | not require a bearing at the lower end of the screw. |
| rods and shaft. For this reason, the system should be | | | | Modern designs support the screw from the top end |
| designed fromthe ribbons inward. Ribbon design | | | | will give you faster, more thorough discharge, |
| determines the rod design, which in turn determines | | | | easiercleaning, and fewer maintenance headaches. |