Ground Calcium Carbonate / Limestone

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            [post_content] => 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.

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            [post_content] => Mikro ACM® Air Classifying Mills were invented by HMPS in the late 1960’s and are one of the most versatile types of size reduction equipment available in the market. These units while being capable of producing fine, medium and coarse grinds for a wide variety of materials for Food, Pharmaceutical, Chemical and Mineral industries, require very little maintenance over their life span. The basic design of these mills is the impact size reduction that is coupled with an internal dynamic classifier which controls the outlet (product) particle size via recirculating the coarse particles back into the grinding zone.

 There are seven main factors which determine particle size distribution for the Mikro ACM® Air Classifying Mill. When varied, the rotor type and speed combined with the liner and hammer count affects the production of fines. The separator type and speed affects the top size of the product. And lastly, the airflow governs the throughput as well as top size and fines generation. With the endless available options a machine can be configured to process just about any material that is below MOH’s hardness of 5.

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            [post_content] => 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.

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Limestone, which is primarily calcium carbonate, is a sedimentary rock made from the minerals calcite or aragonite. A large portion of limestone is made from the skeletal remains of sea creatures and organisms. Ground Calcium Carbonate (GCC) differs from Precipitated Calcium Carbonate (PCC) in that the GCC is formed directly from grinding limestone rock into a powder, while PCC is chemically produced and precipitated out as powder.

Ground Calcium Carbonate is used in paper and plastic fillers, coatings and paints. It is also used in cement, is converted to quick-lime (calcium oxide) and slaked lime (calcium hydroxide). Ground calcium carbonate is slightly basic and can be used to neutralize combustion vapors or increase the pH in water or soils.

Pure calcium carbonate is a relatively soft mineral/compound, with a Mohs hardness of 2.5 – 3.0. However, mined limestone may have a minor portion of abrasive impurities such as quartz / sand.

One of the standard methods of milling Limestone/Calcium Carbonate is with the Mikro ACM Air Classifying Mill. The ACM has a rotating rotor disc with hammers which rotates with speeds up to 23,000 feet per minute. The particle size is controlled by the internal air classifier, to provide sharp particle size distributions. Various classifier designs are available, to produce from coarse (100 mesh) product down to a fineness of 635 mesh (20 µm) product or a D50 of less than 5 µm. Abrasion resistant options are available, including tungsten carbide tipping, Ni-Hard or Ceramic liners to assist with abrasive impurities and to assist with long life of mill components. Hot air can also be used to dry the product while milling.

An alternate to the ACM for coarser grade Calcium Carbonate is the Mikro Pulverizer Hammer & Screen Mill. The Pulverizer uses swing-hammers with interchangeable screen liners to produce a variety of products from 50 mesh to 150 mesh products. The Mikro Pulverizer Hammer & Screen Mill needs less air (less ancillary equipment) than the ACM and is a lower cost options for the coarser grind Calcium Carbonate products.

For ultra-fine (D50 < 5 µm) milling, the Hosokawa Alpine Super Orion Ball Mill and Air Classifier are the best option. These units come in a variety of sizes to meet your application needs.

Wet milling with Hosokawa Alpine Agitated Ball Mill ANR is used to produce ultra-fine calcium carbonate slurries from 60% to 99% < 2 µm, at relatively low specific energy.

For plastic fillers, stearic acid coating on ground calcium carbonate is often performed. Very uniform coatings are produced using Hosokawa Alpine’s Contraplex (CW) pin mill coating system or Mikro LGM Long Gap Mill for flash drying and coating at the same time.

Contact Hosokawa’s mineral applications department to learn more about Limestone / Calcium Carbonate Milling.

Products
Resources

Mikro^® Crusher

Alpine AS Spiral Jet Mill

Mikro ACM^® Air Classifying Mill

Polymer Systems Press Side Granulator