Crusher - Crusher

Japanese: 粉砕機 - ふんさいき（英語表記）crusher

Grinding is a type of mechanical unit operation that reduces the size of solids to reduce their particle size and increase their specific surface area (surface area per unit volume of a particle). In a broad sense, grinding also includes crushing, coarse crushing, and medium crushing, but in the narrow sense it is often limited to processes that aim for particle sizes of about 1 cm or less. In English, size reduction can also include the atomization of liquids, and comminution is usually used when limiting the division of solids.

[Toyohiko Hayakawa]

Purpose of grinding

There are various purposes for grinding, such as making solids finer to make them easier to handle and increasing the uniformity of solid mixtures consisting of multiple components, but more importantly, it is to increase the specific surface area of the solid to increase the rate of reactions such as sintering and dissolution, and the rate of material transfer. In particular, when it comes to fine powders and ultrafine powders with large specific surface areas, not only physical changes but also chemical changes cannot be ignored, and it becomes mechanochemistry, which is no longer a simple type of mechanical unit operation.

[Toyohiko Hayakawa]

Crusher type

As the materials, particle sizes and conditions to be ground are extremely diverse, there are also a wide variety of grinding machines and their operating methods: wet and dry, batch, continuous and closed circuit grinding.

The ratio of particle sizes that can be reduced by a single crusher, i.e., the crushing ratio = particle size of the raw material to be crushed (material to be crushed) / particle size of the product (particle size of the crushed product), is limited depending on the machine, and in many cases several types of crushers are used in series.

Four types of external force are used to apply to solids for crushing: compression, shear, impact, and friction, and the actions of a nutcracker, scissors, hammer, and file correspond to these four types. Compression is used for coarse and medium crushing, shear is used for fine grinding and the refinement of tough materials, impact is used for medium grinding, fine grinding, and ultrafine grinding, and friction is used for fine grinding and ultrafine grinding. The actual crushing mechanism for individual particles is complex, and they may be subjected to several of these types of forces simultaneously.

[Toyohiko Hayakawa]

Wet and dry grinding

Grinding is usually done in air as a dry type, but there are some cases of ball mills and wet mills such as colloid mills, where grinding is done in liquid (usually in water). Wet milling is preferable when the final product is a suspension in liquid, and is generally said to be more efficient than dry milling. Most wet mills can also be used as dry mills, but conversely, there are many that cannot be used in wet mills due to their mechanism, such as impact mills, crushers, and jet mills.

[Toyohiko Hayakawa]

How to use

Grinding mills can be operated in batch and continuous operation, most often in continuous operation. Ball mills are widely used in both batch and continuous operation.

Continuous milling can be further divided into open-circuit milling and closed-circuit milling. Closed-circuit milling is a method in which the powder product from the continuous mill is passed through a classifier, and any particles larger than a certain particle size are returned to their original size (called returned powder), which is then crushed again in the mill, and only the product removed as fine particles from the classifier is fed back to the mill as new material. Closed-circuit milling is said to prevent over-pulverization, sharpen the particle size distribution, and increase the efficiency of milling.

[Toyohiko Hayakawa]

[Reference] | Batch operation | Classifier

Crusher type
©Shogakukan ">

Crusher type

Principle of the pulverizer
©Shogakukan ">

Principle of the pulverizer

Crusher structure (jet crusher)
©Shogakukan ">

Crusher structure (jet crusher)

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

Japanese:

固体を細かくして粒径の減少と固体の比表面積（粒子の単位体積当りの表面積）の増加を図る機械的単位操作の一種を粉砕grindingという。広い意味の粉砕には破砕、粗砕、中砕なども含めるが、狭義には1センチメートル程度以下の粒度を目的とするものに限ることが多い。英語でsize reductionというと液体の微粒化まで含めることもあり、固体の細分化に限る場合にはcomminutionを使うのが普通である。

［早川豊彦］

粉砕の目的

粉砕の目的は種々あるが、固体を細かくして取り扱いやすくし、多成分からなる固体の混合物の均一性を高めるなどであるが、より重要なのは、固体の比表面積を増加させて焼結や溶解などの反応や、物質移動速度を高めることである。とくに比表面積の大きい微粉、超微粉になると、物理的変化のみならず化学的変化も無視できなくなり、メカノケミストリーmechanochemistryとして単なる機械的単位操作の一種ではなくなってくる。

［早川豊彦］

粉砕機の種類

粉砕する物質、粒径、条件がきわめて多種多様なので、粉砕機もまたその操作方法も多種多様である。湿式と乾式、回分、連続、閉回路粉砕などに分類される。

　粉砕機は一台の機械で細かくしうる粒径の割合、すなわち粉砕比＝粉砕する原料（砕料）の粒径／製品（砕製物の粒径）は、機械によって限度があり、多くの場合に幾種類かの粉砕機が直列に用いられる。

　粉砕のため固体に加える外力としては圧縮、剪断(せんだん)、衝撃、摩擦の4種が用いられ、クルミ割り、鋏(はさみ)、金槌(かなづち)、やすりの作用がこの4種に対応している。圧縮は粗砕、中砕に、剪断は微粉砕、靭(じん)性材料の微細化に、衝撃は中間粉砕、微粉砕、超微粉砕に、摩擦は微粉砕、超微粉砕に用いられる。実際の個々の粒子の粉砕機構は複雑で、これらの幾種類かの力を同時に受ける場合がある。

［早川豊彦］

湿式粉砕と乾式粉砕

粉砕は普通には空気中で行う乾式粉砕であるが、ボールミルの若干の場合やコロイドミルのように液体中（水中が多い）で粉砕を行う湿式粉砕がある。湿式粉砕は最終製品が液体中のサスペンジョンの場合が望ましく、一般には乾式粉砕より粉砕の効率が高いといわれている。たいていの湿式粉砕機は乾式粉砕機としても用いられるが、逆に衝撃式粉砕機、破砕機、ジェット粉砕機のように機構上湿式で使えないものも多い。

［早川豊彦］

操作方法

粉砕機は回分操作と連続操作で運転され、多くの場合連続操作である。ボールミルは回分と連続の両方に広く使われる。

　連続粉砕はまた開回路粉砕と閉回路粉砕に分けられる。閉回路粉砕は連続粉砕機からの粉製物を分級機にかけ、一定粒径より大きい粒径のものを元に戻し（戻し粉という）、ふたたび粉砕機で粉砕を行い分級機の細粒側として取り出した製品分だけを新しい砕料として粉砕機に供給する方法である。閉回路粉砕は過粉砕を防ぎ、粒度分布を鋭くさせ、また粉砕の効率を増大させるといわれている。

［早川豊彦］

[参照項目] | 回分操作 | 分級機

粉砕機の種類

粉砕機の原理

粉砕機の構造（ジェット粉砕機）

出典　小学館　日本大百科全書(ニッポニカ)日本大百科全書(ニッポニカ)について　情報 | 凡例

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