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Pulverizing

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Pulverizing is the crushing or grinding down of material into very small or granular-sized particles using a pulverizer. Pulverizers are designed along the same specifications as crushers and are used in the quality reduction of material. They range in type and size and are capable of crushing a variety of materials, including food, aluminum, concrete, plastic, resin, demolition debris, scrap metal, limestone, coal, and even tires.[1] Pulverizing is also used to crush stones, coal, and slag down to a suitable size for use in road construction, as concrete aggregate, and as heating fuel for large industrial furnaces. 

[edit] Process

Pulverizing can be seen as the final stage in the milling process. Milling involves the reduction of a given material. The first phase involves crushing material considered too large to be pulverized. For example, in mining, large lumps of ore can pass through two crushing stages before being pulverized—primary crushing, using a jaw crusher, and secondary crushing, using a cone crusher or gyratory crusher. Crushing can be defined as the reduction of material through the slow application of a large force.

In primary crushing, the crusher is often located in the actual workings of the mine. Broken ore is dropped down a pass and fed directly into the opening of the jaw crusher. The crusher is equipped with metal jaws at the top that crush the ore with quick, short movements similar to the chewing action of human jaws until the ore is broken down into manageable six-inch (15-cm) pieces.[2]

Secondary crushing is used when the ore, after primary crushing, is still too large to be pulverized. The cone crusher, designed to handle smaller pieces of rock, is the most common type of crusher used in North America for secondary crushing.[3] Vibrating screens on the crusher are used to control the size of the crusher building. Undersized ore falls through openings in the screen and is transported by conveyor to a mill. Larger-sized ore pieces too big to fall through the openings in the screen are fed back into the crusher along a separate conveyor for further crushing. This ore is called the circulating load.

The last stage is to pulverize the material into fine granules or shards. Each stage is characterized by the size of the feed material, the size of the output product, and most importantly, the resulting reduction in the ratio of the material.[4] Two types of pulverizing exist. Open-circuit pulverizing entails just one pass of the material through the pulverizer with no removal of fines or recirculation of material. On the contrary, closed-circuit pulverizing is when material is discharged from the pulverizer and passed through to an outside classifier. The finished material is removed at this point and the over-sized material re-circulated back into the pulverizer for additional grinding.[5]

[edit] References

  1. What is a pulverizer? Mill Powder Tech Solutions website. 08-04-2009.
  2. Primary Crushing. Mining Basics. 08-04-2009.
  3. Primary Crushing. Mining Basics. 08-04-2009.
  4. Pulverizing and Crushing. Mill Powder Tech Solutions website. 08-04-2009.
  5. Pulverizing and Crushing. Mill Powder Tech Solutions website. 08-04-2009.