Structural Principle and Application of 120°QS Type Pressure DSM screen

This paper expounds the structure, performance, principle, characteristics and precautions of 120°QS type pressure DSM screen, and introduces the application of 120°QS type pressure DSM screen in starch industry filtration & screening.  
Description 120°QS type pressure DSM screen is an advanced, modern, static and high-efficiency screening equipment that can be widely used in solid-liquid separation, screening, filtration, washing, etc.


DSM screens are widely used in the starch industry in my country and are well received by factories and workers in the starch industry. 
DSM screen can usually be divided into gravity DSM screen and pressure DSM screen. 
The pressure DSM screen is called the 120° DSM screen because the earliest type of DSM screen was first popularized and used by the Dutch National Mining Company (DSM).  

SIEVE BEND SCREEN STRUCTURE

The curved screen machine is mainly composed of a feeding pipe, distribution pipe, U-shaped pipe, pressure gauge, ball valve, nozzle, DSM screen, screen surface support, seal, screen body, underflow port, overflow port, and so on. 

  • The feed pipe is connected with the feed pipe and the pressure pump, and the underflow port and the overflow port are connected with the relevant pipes and the storage tank, respectively. 
  • The DSM screen is the most important and critical component in the machine. 
  • The quality of the screen determines the running quality of the DSM screen and the quality of the starch milk after being processed by the DSM screen. 

EQUIPMENT SCREEN

The most important part of the screening equipment is the wedge wire screen

The screen surface is composed of about 1,600 acid and alkali-resistant high-strength stainless steel screen wires with a wedge-shaped cross-section evenly arranged. 

  • The gap between the wedge wires is the screen gap.  
  • The working surface of the screen is treated by special processing methods, highly polished, round and smooth, as smooth as a mirror. 
  • The wedge wires have sharp edges and are work hardened for high wear resistance. 
IDENTIFY THE SCREEN
According to the different manufacturing process of DSM screen surface, there are basically three screen surfaces in the world at present, welding screen surface, ring screen surface and aggressive screen surface. There is not much difference in performance between a welded screen and a ring screen, but there is a big difference in price. The performance of the laser screen surface is better than the other two screen surfaces, and it is more conducive to the deep processing of starch, and its price is twice that of the ring screen surface.

In the technical parameters of the screen, the screen slot width is particularly important.  
However, other technical performance indicators that measure the quality of the screen surface often do not attract enough attention and attention. 
For example, the material of the wedge wire, the uniformity of the screen slit, the sharpness of the screen wire edge, the sharpness uniformity of the screen wire edge, the roughness (finishes) of the screen surface working surface, etc.  
These performance indicators are more critical and important than the technical parameters listed in Table 1, but these performance indicators are difficult to measure and measure, and there is even no uniform, specific and clear standard. 

NumberItemUnitTechnical Parameter
1Radian°120
2Radiusmm762
3Arc lengthmm1596
4Screen widthmm312 462 587 712
5Slot sizemm50 75 100 125 150
Table 1

These technical indicators are indeed very important, for example: 
The material of the wedge wire determines the quality and service life of the screen, the uniformity of the screen slit affects the screening performance and the quality of the material after the screening, and the sharpness and uniformity of the edge of the screen wire determine the screening effect and screening efficiency. 
Therefore, in the manufacture, inspection, identification, and selection of screens, full attention and attention should be paid to these technical indicators that are difficult to measure and measure but are very important. 
Otherwise, it will directly affect the use of curved sieves, the quality and yield of starch milk, and the economic benefits of enterprises.  

DSM SCREEN PERFORMANCE

NumberItemUnitTechnical Parameter
1Radian°120
2Screen Widthmm312 462 587 712
3Nozzlespcs2 3 4 5
4Work pressureMpa0.25-0.4
5Screening efficiency%>=60
6Throughputm3/h10-116

The Principle of DSM Screen

The schematic diagram of the DSM screen is shown in Figure 4. 
The starch milk is sprayed from the nozzle to the screen surface. 
With a certain pressure and a certain injection speed, the starch milk is shot towards the screen surface along the tangential direction of the arc screen surface, and then quickly forms the undersize. 
Part of the liquid layer and coarse particles flow through the sieve surface and become oversize. 
The particles are classified and separated by the centrifugal force which is conducive to the separation of fine particles and coarse particles. 

DSM SCREEN FEATURES

The DSM screen is compared with other screening equipment such as cylindrical screen, wedge wire screen panels, and centrifugal screen for several items, see Table 3 for details. 

  • The DSM screen is the same as other screening equipment (except flat screen) in that the screening force is centrifugal force. 
  • But the difference is that the screen surface of other screening equipment is moving, while the screen surface of curved screen is static and immobile. 
  • This determines that the DSM screen has no vibration and noise during operation, saves energy, requires less equipment maintenance, is simple to operate, and is safe and reliable. 

DSM SCREEN CHARACTERISTICS

Compared with other screening equipment, the DSM screen has one of the most significant features: 
Those particles whose particle size is about one-half of the screen wire gap (slot size) of the DSM screen will quickly pass through the screen gap and enter the underflow, that is, the particle size of starch milk after screening by the DSM screen is not determined by the width of the screen gap. 
The starch milk particles sieved by the DSM sieve are smaller than the sieve slit, generally about half the width of the sieve slit. 
Therefore, the particles of starch milk sieved by the DSM sieve are smaller than those of other screening equipment with the same mesh number, so the screen slits on the screen surface of the DSM sieve are not easily blocked by particles to achieve the purpose of self-cleaning. 

USE OF CURVED SIEVE

According to the length of the screen surface width of the DSM screen and the size of the screen gap, it can be combined into various types and specifications of DSM screen series products to meet the needs of users due to different requirements of materials, processing capacity, particles, etc. 
Curved sieves can be used in a single unit or in multiple units. They can be used in parallel or in series with the same type of curved sieves, or in series with different types of curved sieves with different specifications, or with other screening equipment, such as centrifugal sieves. Sieves are used in combination. 

SCREENING AND WASHING PROCESS

The screening and washing process of corn starch is a very important and critical process in the processing and production of corn starch. 
The screening and washing process of corn starch is the process of extracting starch and washing fine slag. 
Separating as much fine slag as possible, and at the same time minimizing the starch in the fine slag, not only improves the starch yield but also reduces the slag content in the starch and reduces the powder content in the fine slag.
The 120° DSM screen can meet the production needs of the 10,000-ton cornstarch factory. 
According to the flow chart of corn starch screening and washing, the starch milk slurry after determination enters a 50-micron DSM screen.  
It is divided into two parts after being sieved by a curved sieve, and one part, the undersize material, is directly sent to a starch separator for separation. 
The other part is the material on the sieve that enters the milling equipment for pulverization.  
The finely ground starch milk is sent to the six-stage curved sieve screening and washing system to extract the starch and wash the fine residue. 
Under normal circumstances, corn starch factories use six-stage curved sieves to screen and wash starch chairs in countercurrent, so it is called: six-stage curved sieve countercurrent screening and washing method.  
Corn starch plants generally use two kinds of DSM screen, 50 microns, and 75 microns. The DSM sieve can also be used in starch factories that use sweet potatoes, potatoes, cassava, etc. as raw materials, but the specifications of the curved sieve used and the technological process of sieving and washing are different. 

CLEANING THE DSM SCREEN

During the use of the DSM screen, especially the domestic screen surface has the phenomenon of accumulation of stains. 

When corn starch factories use DSM screen, they will encounter such problems: starch, protein and other particles will block very fine and narrow sieve gaps on the sieve surface, and they cannot be completely removed. In the long run, the sieve gaps will be completely blocked, and the sieve surface will be blocked. Shaped like a steel plate, it completely loses the function of the screen surface. 

Therefore, the screen surface of the DSM screen must be cleaned frequently to ensure that the screen slits are unobstructed so that the screen surface can maintain the special function of screening or washing. 

CONTROL CONCENTRATION 

The concentration of corn starch milk entering and exiting the countercurrent screening and washing system of the DSM screen should be strictly controlled. 

On the one hand, the starch milk sieved by the DSM sieves is sent to the starch separator for separation of starch and protein, and the starch separator has strict requirements on the starch concentration. 

On the other hand, if the starch milk concentration is too low or too high, it will also affect the screening and washing effect of the DSM screen.  

Therefore, the concentration of starch milk entering and exiting the curved sieve screening and washing system should be effectively and strictly controlled. 

Under normal circumstances, the concentration of corn starch milk entering the DSM screen system is about 7~8 Baume degrees, and the concentration of corn starch milk sieved by the curved sieve should be Baume degrees. 

引号—

The special performance and principle of the curved-screen fully reflect the advanced nature of the curved-screen  

In the process of corn starch processing, DSM screens are increasingly replacing other widely used screening equipment such as flat sieves, centrifugal sieves, etc., and are also widely used in the processing of three-potato (sweet potato, potato, tapioca) starch. 

The practice has proved that the sieve bend screen is an advanced, modern, and promising static and high-efficiency screening equipment. 

Foreign DSM screens are first used in other industries, and then in the starch industry.  

The domestic DSM screen was first used in the starch industry, so the curved screen is not only widely used in the starch industry. 

It can also be used in high-capacity solid-liquid separation, filtration, screening, washing, dehydration, and deslagging, such as pulp treatment in papermaking, and environmentally friendly sewage treatment. 

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