The grinding air is injected tangentially via Laval nozzles in the nozzle ring into the machine. This causes a spiral jet of air to form in the grinding zone, from which the mill derives its name. A high pressure forms in the mill as a result of the spiral flow of air that can rise to 1 bar overpressure in operation without product. The integrated injector is charged with compressed air which ensures that the product is conveyed into the machine against the overpressure present in the machine. This, however, is associated with a considerable compressed air consumption, which can be as much as 30% of the total grinding air requirement.
The feed product circulates close to the nozzle ring and is thus intercepted repeatedly by the air jets exiting the nozzles. Comminution is the result of inter-particle collision caused by the particles flowing at different speeds in the nozzle jet. Comminuted material is conveyed along with the air to the discharge, the spiral flow subjects the particles to a classification: only fine particles are discharged, coarse particles remain in the mill.
Alpine® AS Spiral Jet Mills are characterized by a special geometry of the mill housing in the area of the discharge, which contributes towards a finer classification effect and a sharp top cut.
The product also has an effect on the air flow within the machine: the more product there is in the machine, the more the spiral flow is braked and the lower is the centrifugal force and the coarser the end product. The relationship of the product to the classifying air flow rate is therefore the most significant parameter for setting the fineness of the spiral jet mill. In principle, different nozzle angles can also be used to achieve the required fineness values, whereby the complete nozzle ring must be exchanged in this case.
The Alpine UPZ Ultraplex Fine Impact Mill are truly flexible. Designed with ultimate versatility in mind, this one unit can accomplish a multitude of size reduction tasks. A wide variety of grinding inserts are available through the entire line of mills. The mill is also offered with a counter-rotating (Contraplex) set of pins for added shear for difficult to mill products. The pharmaceutical version of this work horse has been designed specifically for cGMP compliance from the ground up. Size reduction of soft to medium soft material can be accomplished at rates from 3 to 700 Kg/hr depending on feed material and final size requirements.
Alpine UPZ Ultraplex Fine Impact Mill can also be integrated into Stott Isolators. This arrangement provides a completely integrated system capable of containment levels as low as 1 micro-gram/cubic meter.
Operation of the mill is simple. Material is introduced to the mill via feed device such as a rotary air lock or volumetric/gravimetric feeder through the mill's inlet. The inlet directs the material to the grinding chambers center. The grinding toll rotates at high speed, creating centrifugal force that will accelerate the pharma-powder outwards. The particles outward flow hurls them at high speed against the pins or other grinding media where the impact will cause the particles to fracture.
The Mikro Atomizer® Air Classifying Mill uses air flow to convey materials to the grinding zone. Size reduction occurs when hammers fitted to the rotor impact particles at 4,000 to 8,000 RPMs. A deflective liner returns oversized particles to the hammer impact zone for further reduction. The ground materials are then conveyed to the classifier wheels which are mounted to the grinding rotor. Larger particles are rejected for regrinding as the desired particles are air conveyed by internal fan blades and exit the mill for collection.
While most customers use the air jet sieve to determine the particle size of dry powder ranging from as fine as 20 µm / #635 (mesh) up to 4,750 µm / #4 (mesh), some utilize the particle size analyzer to determine the average particle size below a specified cut point; such as D90 < 50 µm. Others use the air jet sieve to confirm that a powder top size does not exceed product specifications. The Mikro Air Jet Sieve® MAJSx can even be used as a small lab-scale classifier to remove the fine particles out of a sample or as a dedusting system to remove undesirable dust from small batches.
How it Works: The Mikro Air Jet Sieve® MAJSx utilizes test sieve screens and the pneumatic sieving principle to enhance the accuracy and reproducibility of particle size analysis. This method has become the preferred standard for such tasks as quality assurance of incoming raw materials, process control, and verification of final product specifications. While under negative pressure, a positive upward air flow is emitted from the rotating slit wand which continuously disperses particles across the surface of a test sieve screen. Those particles that are smaller then the opening of the test sieve screen pass through and are carried away from the sample, leaving the particles larger than the sieve opening on top of the test sieve screen. Particle size within the range of 20 to 4,750 µm can quickly be determined. The unique rotating slit wand feature also reduces, and in many cases, eliminates the need for tapping or brushing, thus enhancing the analysis reproducibility. The overall
system is designed for cleaner operation and requires less counter space than other types of analytical equipment.
Key Operating Parameters Enhance Repeatability & Reliability:The sieving time plays a major role in determining particle size with an air jet sieve. Excessive sieving time can lead to particle degradation due to attrition. In most dry powder applications, Hosokawa recommends a two-minute sieving time cycle which provides ample time for the particles of the entire sample to pass through the sieve screen or be retained.
Sieving vacuum pressure between 8-16 inches of water column is recommended during a sieve analysis. If the pressure is too low, the air velocity passing through the rotating wand may not be sufficient to evenly disperse the entire sample. If the pressure is too high, the air velocity could generate enough force to further grind material as the sample repeatedly impacts the sieve screen and sieve cover.
A sample volume between 10 and 100 grams is recommended in most air jet sieve particle analyzers, depending on the density of the material being tested. Samples larger than 100 grams have the potential to blind
the test sieve screen and affect the analysis results.
Test sieve screen quality and integrity is critical in any particle size analysis process. Hosokawa provides test sieve screens that are 99% accurate. Test sieve screens with damage such as holes, tears, scratches, waves, or other imperfections are not recommended. Sieve screens should be routinely re-certified to insure accurate analysis results.
Performance at an Economical Cost: Certified pre-owned Hosokawa Air Jet Sieves analyzers start at $4,400. Prices can vary dependent on the number of sieve screens required, vacuum selection, balance type, optional components, taxes, and shipping.
Pre-Owned Air Jet Sieve Particle Size Analyzers – from $4,400
Price Disclaimer: Prices listed are subject to change without warning and do not include taxes, shipping, or import fees or the cost of any accessories or ancillary equipment not included in the quotation.
American Made: A long-time industry leader, Hosokawa developed air jet sieving technology in the early 1960's and has refined and elevated its technology to meet the latest market needs. The Mikro Air Jet Sieve® MAJSx is manufactured in the U.S. and comes with our pledge for performance and dependability. These innovative products have earned a reputation for accuracy and reliability as evidenced by the thousands of installations worldwide.
The wet material is fed through customized feeding systems into the grinding and drying section of the dryer's main body. The grinding rotor disperses the wet material into very fine particles and the fine particles are fluidized in the grinding chamber by temperature-controlled, hot gas coming in from the air heater.
The hot air (or inert gas) can be heated up to 650 °C and as the wet product is dispersed, it is reduced in size in the bottom section of the dryer. The system is kept under a negative pressure by the exhaust fan and the surface area of the product is increased enormously so that water (or other solvents) is evaporated instantaneously.
The dry and fine particles are conveyed with the gas stream to the top section of the dryer where a separator classifies the particles by size. Then the particles pass the classifier at the set cut point and are conveyed with the exhaust air to a powder air separating system like the cyclone, cyclone filter or cyclone scrubbers.
The Micron Dryer flash dryer retains a fluidized bed of product in the drying chamber to ensure a low level of adhesion of wet material on the inside wall of the drying chamber. Moreover, process parameters like classifier speed and outlet temperature can be adapted to control moisture content and particle size of the end product.
Ultra fine regular end product - Due to its specially designed dispersion rotor, our flash dryers are able to produce ultra-fine powders in one step from suspensions, slurries, pastes and dough, filter cakes or wet powders.
High evaporation capacity - Due to the combination of high ?T with a good dispersion of the wet product in the air, our flash dryers can evaporate large quantities of liquids.
Compact design - Compared to other direct drying technologies, the flash dryer requires up to 50% less space.
Multi-purpose - Filter cake or slurry, in the same machine. Therefore with the Drymeister-H unlimited mechanical dewatering is possible previous to the final drying stage.
Easy access - Either for cleaning, inspection or maintenance inside the dryer, our flash dryers offers the best accessibility from the market, regardless which size.
Various systems available - Open, closed- and recycle system concepts.