Common Pharmaceutical Mixer Models
Multi Agitator Systems
Equipment strategies for increasing process versatility in the Medical Industry
The best strategy for improving the versatility and efficiency of your mixing equipment will depend upon the parameters of your particular application. But for most applications, these general guidelines will at least provide a springboard to re-examine your equipment and develop a plan to improve production.
Vacuum minimizes the time dedicated to solids transfer and wetting out
Vacuum is widely recognized for its ability to accelerate deaeration and intensify the mixing process. You can also use vacuum to transfer additions, and especially low-density powders. This will hasten the process and prevent dust from escaping into the plant atmosphere - improving operator safety and often reducing the risk of explosion. Applied correctly, vacuum readily collapses (or “densifies”) powder agglomerates floating persistently on the surface of the batch and helps to wet them out quickly.
Accelerate emulsification and dispersion by injecting additions directly into the high shear zone
Additions delivered to the surface of the batch must vortex into the batch and be carried into the high shear zone by the flow of the bulk material. This process is slow and expensive. Numerous batch turnovers are often required before agglomerates are broken down and a uniform distribution is achieved. Sub-surface injection can speed up both the mixing process and subsequent clean-up. But careful control of the vacuum injection process is crucial to avoid creating excessively violent turbulence within the mix vessel - and a long cleaning cycle later.
Sub-surface injection also helps to control heat
Heat is the inescapable by-product of the shearing action necessary to produce emulsions and dispersions. In fact, it is often the critical factor that limits the shear that can be applied to a mix – and the speed with which the mix cycle can be completed. Pharmaceutical/cosmetic mix vessels are usually jacketed to control the temperature of the batch. But the first step in controlling heat should be to minimize heat input – rather than concentrate mainly on removing heat after it accumulates. By shortening the mixing process, and reducing the total energy imparted to the batch, sub-surface injection helps to reduce heat input and avoid thermal degradation.
Choose a combination of agitators that offers a variety of mixing action
Multi-agitator mixers, such as the anchor/rotor-stator/disperser combination offer valuable flexibility. Since they are independently driven, the agitators can work together in an endless variety of combinations. Each agitator can also operate alone at a variety of speeds.
This flexibility allows the multi-agitator mixer to adjust to changing mixing requirements during a single mix cycle. Many products undergo a series of significant changes as reactions occur and the physical properties of the material evolve. With independent, variable-speed drives, the multi-agitator mixer can adapt as the cycle progresses - providing the optimal combination of shear and flow at each stage.
Choose agitator designs to ensure homogeneity – and thorough distribution of heat The centerpiece of a high-performance emulsifier/homogenizer is its high-shear rotor-stator design. But the slow-speed agitators are equally important. In fact, the two systems must work together efficiently to generate flow and permit very high shear rates. With vigorous flow, heat is quickly carried away from the high-shear agitators. This action prevents localized heat from reaching dangerously high levels.
In a multi-agitator mixer like the Ross VersaMix, the anchor generates both upward axial flow and inward radial flow from the vessel wall. This flow feeds material to the high-shear agitators near the center of the vessel. In a co-axial system, the slow-speed agitators turn in opposite directions to generate contrasting upward and downward axial flow, as well as radial flow. All slow-speed agitators should be equipped with scrapers to assist in removing material that would otherwise form an insulating layer on the vessel wall and inhibit heat transfer.
High Shear Mixers
Your choice - Batch or Inline?
The first step in specifying the right mixer for your application is to decide between a batch or continuous inline system. Each type of system offers a unique set of advantages, and the engineers at Ross will help determine which one will provide the most efficient and economical solution for you.
Batch mixing
Batch High Shear Mixers can be permanently mounted to the mix tank or suspended over the vessel with a portable lift. The mobile configuration offers you the flexibility to use a single mixer in multiple vessels. It also allows you to vary the position of the rotor/stator generator in the vessel to fine-tune the process to handle a variety of materials. For many applications, the batch design produces fast particle size reduction and short mixing cycles, but only if the flow pattern within the vessel is optimized. The rotor/stator generator of the batch High Shear Mixer is generally positioned 2-3 head diameters from the bottom of the vessel, and slightly off-center. To promote adequate circulation with heavier solids, the rotor/stator generator may be located in the center of the vessel.
In-line mixing
Whether your system is set up for single-pass mixing or multiple passes with recirculation, the inline mixer allows you to produce an end-product with a predictable particle size distribution and outstanding reproducibility. Because the in-line system is closed, it also minimizes problems caused by air entrainment during processing. Especially when mixing material in large volumes, the in-line mixing system is extremely cost-efficient. Unlike a batch mixer, which requires a high-horsepower motor to generate adequate circulation in a large vessel, a small in-line mixer can handle a 25-gallon batch as easily as it handles a 250-gallon batch. As the vessel size increases, the energy required by the in-line mixer remains low - while the savings grow.
A Ross High Shear In-line Mixer is versatile choice for process lines that require frequent changeover from one product to another. A simple valve can divert finished product downstream or switch instantly from one source vessel to another.
Single-stage rotor/stator mixer
All rotor/stator mixers are comprised of a rotor that turns at high speed within a stationary stator. In a “single-stage” unit, the rotor includes a single set of four blades. As the rotating blades pass each opening in the stator, they mechanically and hydraulically shear particles and droplets, and expel material at high velocity into the surrounding mix. As fast as material is expelled, more is drawn into the rotor/stator generator, which promotes continuous flow and fast mixing.
Multi-Stage Rotor/Stator Mixers
Multi-stage rotor/stator generators include multiple rows of rotating blades that nest inside a matching stator. The mix material enters the center of the generator through an inlet pipe and is accelerated outward by centrifugal force. During each transit through the rotor/stator generator, the material is subjected to a quick succession of increasingly intense shearing events - until it finally exits the generator and is either piped downstream or recirculated for another pass through the mixer.
New technology for high speed powder induction
Powders like gums and thickeners are notorious for driving up processing costs. Even with a strong vortex in an open vessel, they resist wetting out and often float on the surface for an hour or more. Once they submerge, they often form agglomerates with a hard outer surface that is difficult and costly to break. Ross has developed new technology that enables you to mix and wet out powders almost instantly. Available in either a batch or in-line configuration, the SLIM (Solid/Liquid Injection Manifold) system injects solids directly into the high shear rotor/stator, where they are immediately pulverized and mixed with the liquid stream. The SLIM system accelerates the mixing process dramatically, while it virtually eliminates dusting – minimizing the volume of airborne particles released inside the plant atmosphere.
Dry Blenders
Which design is best for your application?
Ribbon blenders, vertical cone screw and tumble blenders are found in many plants, and in many ways they perform a similar function on the process line. But the differences in their design - and in the advantages they offer - are far more important than their similarities. The ribbon blender is generally less expensive than a vertical cone screw blender or a tumble of comparable capacity. So, in practical terms, you should determine which your application requires in order to achieve the product quality and processing efficiency that you need.
To decide which type of blender will work more efficiently in your application, ask yourself these questions
1. How much room is available on your plant floor? If floor space is tight, you may have to go up - with a vertical blender - since a vertical blender requires a much smaller footprint. If overhead space is limited, you may be forced to use a horizontal ribbon blender, which allows you to use a low-profile loading system. A multi-level operation is generally unnecessary.
2. Does the friability of your product require gentle blending? If so, you will probably need a vertical cone screw or a tumble blender. The blending action of these designs is extremely gentle.
3. Is complete discharge essential? The cone screw blender or a tumble blender gives you virtually 100% discharge through the lower cone.
4. How tight is your budget for power? Since the ribbon blender consumes more power, over long blending cycles this can add up.
5. Is contamination a critical risk? With a packing gland in the product zone, the ribbon blender poses a greater threat of contamination. New seal designs have reduced the risk dramatically, but if your application requires the best protection available, you will have to switch to a cone screw or tumble blender.
6. Is your product heat sensitive? The blending action of a ribbon can generate more heat than that of a mixing screw or a tumble blender.
7. Will you always operate with the blender at least half full? If you need the flexibility to operate with smaller batches, choose the cone screw blender. Because of the geometry of the cone, this blender can operate efficiently with batches as small as 10% of blender capacity. The ribbon blender generally requires a minimum of 40-50% of full capacity.
8. How fast do you want to finish the batch? A fast blending cycle is not always the most important concern, but it is always a factor you should consider carefully. Cone screw blenders are usually about 30% faster than ribbon blenders in similar applications.
9. Are you concerned about blending accuracy? All produce a well-blended product. If accuracy is critical, be sure to test the blender in the equipment manufacturer's laboratory before you buy it - to prove that it can deliver the product quality you need.
10. Will you need complete cleaning between batches? The cone screw blender is easier to clean, especially since you will never have to disassemble a packing gland in the product zone. Just make sure that the cone screw blender you select does not require a bearing at the lower end of the screw. A screw supported entirely from the top end will give you faster, more thorough discharge, easier cleaning, and fewer maintenance headaches.
Storage Vessels
CUSTOM SANITARY TANKS, STORAGE VESSELS, REACTORS AND TRANSFER VESSELS
During the last two decades, Ross has grown to be one of the best-equipped and most highly respected custom fabricators in North America. Ross offers a combination of engineering and manufacturing resources that few fabricators can match.
Ross builds polished storage tanks, mixing vessels, reactors, pressure vessels and atmospheric tanks, columns and custom transfer tanks to meet the special needs of the pharmaceutical and medical process industries.
Our state of the art production machinery and design facilities at each of our fabrication plants give us the control necessary to offer flexible service and air-tight quality assurance. Our fabrication plants are ASME code certified and can provide the ASME stamp when required. Our engineers, machinists and fabrication specialists routinely meet such code requirements as USFDA, BISC, ABS, API and UL as well as ASME.
We regularly work with a broad range of materials, including 304 and 316 stainless steel, Monel, Hastelloy, Titanium, Inconel and aluminum.
We have the capability to polish to your exacting requirements.