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what is Centrifuge Separation?-Centrifuge manufacturer | ZONELINK

October 14, 2022


How a centrifuge works

A centrifuge is a machine that uses centrifugal force to separate components from liquid and solid particles or a mixture of liquid and liquid. Centrifuges are mainly used to separate solid particles from liquids in suspension; or to separate two immiscible liquids of different densities in emulsions (such as separating cream from milk); it can also be used to remove Liquids in wet solids, such as drying wet clothes with a washing machine; special ultra-speed tube separators can also separate gas mixtures of different densities; using the characteristics of different densities or particle sizes of solid particles in liquids with different sedimentation speeds, some sedimentation Centrifuges can also classify solid particles by density or particle size.

When the suspension containing fine particles stands still, the suspended particles gradually sink due to the action of the gravitational field. The heavier the particle, the faster it sinks, whereas the particle with less density than the liquid will float up. The speed at which particles move in a gravitational field is related to the size, shape, and density of the particles, as well as to the strength of the gravitational field and the viscosity of the liquid. Particles the size of red blood cells, with a diameter of several micrometers, can be observed to settle under normal gravity.

In addition, when the substance settles in the medium, it is accompanied by the phenomenon of diffusion. Diffusion is unconditional and absolute. Diffusion is inversely proportional to the mass of the substance, and the smaller the particles, the more serious the diffusion. The subsidence is relative and conditional, and it needs to be subjected to external force to move. The sedimentation is proportional to the weight of the object, the larger the particle, the faster the sedimentation. For particles smaller than a few microns, such as viruses or proteins, they are in a colloidal or semi-colloidal state in solution, and it is impossible to observe the sedimentation process only by gravity. Because the smaller the particles, the slower the sedimentation, and the more serious the diffusion phenomenon. Therefore, it is necessary to use a centrifuge to generate a strong centrifugal force to force these particles to overcome the diffusion and produce a sedimentation movement.

Centrifugation is to use the strong centrifugal force generated by the high-speed rotation of the centrifuge rotor to accelerate the sedimentation speed of the particles in the liquid, and separate the substances with different sedimentation coefficients and buoyancy densities in the sample.

Conversion between centrifugal force (g) and rotational speed (rpm)

The conversion formula between centrifugal force G and rotational speed RPM is as follows:

G=1.11×10^(-5)×R×(rpm)^2

Among them, G is the centrifugal force, which is generally expressed as a multiple of g (acceleration of gravity).

10^(-5) is the negative fifth power of 10, the square of the rotation speed (rpm)^2, R is the radius, and the unit is centimeters.

For example, with a centrifugal radius of 10 cm and a rotational speed of 8000 RPM, the centrifugal force is:

G=1.11*10(-5)*10*(8000)2=7104

That is, the centrifugal force is 7104g.

And when the centrifugal force is 8000g, its speed should be: 8489 is about 8500rpm

Main classification

Folding 1. According to the separation factor Fr value

Centrifuges can be divided into the following types:

1. Normal speed centrifuge

Fr≤3500 (usually 600~1200), this kind of centrifuge has a low speed and a large diameter.

2. High-speed centrifuge

Fr=3500~50000, the rotating speed of this centrifuge is high, the diameter of the drum is generally small, and the length is long.

3. Ultracentrifuge

Fr>50000, due to the high speed (above 50000r/min), the drum is made into a slender tubular type.

The separation factor Fr refers to the ratio of the centrifugal force of the material in the centrifugal force field to the gravity of the material in the gravitational field.

Folding two, according to the operation mode

Centrifuges can be divided into the following types:

1. Gap centrifuge

Its feeding, separation, washing and slag unloading processes are all gap operations, and manual, gravity or mechanical methods are used to unload slag, such as three-legged and top-suspension centrifuges.

2. Continuous centrifuge

The processes of feeding, separation, washing and slag unloading can be carried out automatically in a gap or in a continuous process.

3. Geotechnical centrifuge

Folding 3. According to the slag discharge method

Centrifuges can be divided into the following types:

1. Scraper unloading centrifuge

The process is indirect and the operation is automatic.

2. Piston pusher centrifuge

The process is semi-continuous and the operation is automatic.

3. Spiral discharge centrifuge

The process is continuous and the operation is automatic.

4. Centrifugal discharge centrifuge

The process is continuous and the operation is automatic.

5. Vibrating discharge centrifuge

The process is continuous and the operation is automatic.

6. Tilt unloading centrifuge

The process is continuous and the operation is automatic.

Four, according to the process use

Centrifuges can be divided into: filter centrifuges, decanter centrifuges.

Five, according to the way of installation

It can also be divided into vertical, horizontal, inclined, hanging and three-legged.

6. According to national standards and market share

for the following four

1. three-legged centrifuge

2. Horizontal Spiral Centrifuge

3. Disc Separator

4. Tubular Separator

How to buy?

There are many models and types of centrifuges, and the price is relatively expensive. When purchasing, you should measure according to the work. Usually the following factors should be considered:

(1) The purpose of centrifugation, analytical centrifugation or preparation centrifugation;

(2) The type and quantity of the sample, whether it is cells, viruses, or proteins, and the size of the sample. Based on these factors, the decision to purchase an analytical or preparative centrifuge; low-speed, high-speed, or ultra-speed; high-volume, constant-volume, or micro-volume centrifuges.

(3) Economic capacity: When the model is determined, the manufacturer and price should be considered. The price and the performance of the product are synchronized.

(4) Other details: such as whether the centrifugal operation is simple, whether the maintenance is convenient, whether the design is outdated, whether the supply of wearing parts is convenient, etc.

(5) Matching problem: it is impossible for a centrifuge to operate under low speed, high speed and overspeed at the same time. Generally speaking, ultracentrifuges are limited to ultracentrifugation, not suitable for high-speed centrifugation, nor low-speed centrifugation, and also high-speed centrifuges are not suitable for low-speed centrifugation. Therefore, when buying an ultracentrifuge, it is necessary to consider a high-speed centrifuge, otherwise the advantage will not be exerted. Generally speaking, low speed and high speed are used more frequently, while the utilization rate of ultracentrifuges is low. Ultracentrifuges are only purchased in laboratories that are often used or consider regional public settings.

After the model of the centrifuge is determined, it is what kind of centrifugal rotor to choose. The main consideration is the capacity of the sample and the conditions of centrifugation. Usually, there are one horizontal rotor and one angular rotor, or one large-capacity (relatively low-speed) rotor and one small-capacity high-speed rotor each to meet different needs in work. The more complete the better, the better. Because there are many types of centrifugal rotors, many of which are similar, and the rotors of overspeed machines are quite expensive. If they are all matched, the price is several times higher than that of the centrifuge host, and it is not necessary. Due to the different rotor speed, the price varies greatly. In terms of rotational speed, it is not advisable to pursue as high as possible, but there should be a rotor with the highest rotational speed allowed by the centrifuge, otherwise it will be a waste for the centrifuge. Units with two centrifuges may consider complementary rotor models to save money.

Management of centrifuges, according to the use of centrifuges in China for many years, all types of centrifuges should be managed and maintained by special personnel. High and ultracentrifuges require regular inspection and maintenance. Users should record the experimental status and maintenance conditions in detail to ensure the safe use of the centrifuge. The high and low speed centrifuges are easy to operate, so you can use them by yourself after reading the instructions and training the operating procedures of the centrifuges. The ultracentrifuge has a complex structure and complicated working procedures. Improper use is prone to accidents. Especially, the centrifugal rotor should be carefully maintained and used. Judging from the domestic use and management for many years, the custody and operation of the instrument is the guarantee that the instrument is in good condition. The management and operators should be trained so that they are not only familiar with the operation, but also have an understanding of the instrument.


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