Function and measurement method of sieve hole size of air-screen cleaner

In the practice of recommending the cleaner to customers, we find that some customers have not yet known the configuration and usage of the sieve of the cleaner. Here, I will give you some explanation and suggestions, hope it can help the customers who use the air-screen cleaner.

IFunction and structure of sieve

Generally speaking, the sieve of air-screen cleaner (also called the sizer, screening machine, pre-cleaner) uses punched galvanized sheets. According to the purpose of the processed materials, there are 2-6 layers of structure, which can be used to remove large impurities, small impurities and grading according to the shape of seeds or grains.

Commonly used punching screens mainly have round holes and slit holes. In order to fully ensure the effective use of the sieve area, there are various arrangements. The more holes of the sieve, the higher availability rate. But it is not absolute. The density of the punching holes also depends on the thickness and strength of the sieve.

The picture below is our company's conventional round hole and slit hole screen.

The screening of round hole sieve is mainly realized by limiting the width of seed; while that of slit hole sieve is limited by the thickness of seed.  Please see the three-dimensional size of the seed in the figure below, which is convenient for you to understand the length, width and thickness of the seed.

Some crops seed (such as sunflower seeds, rice, etc.) may need to be screened according to their length, so need use a indented cylinder cleaner. This is another category of equipment and will not be repeated here. This article mainly explains the cleaner how is screened according the width and thickness of the seed.

Take wheat seed screening as an example. Generally speaking need a three-layer sieve structure cleaner. The first layer uses 5.6mm round holes, the second layer uses long holes 3.8mm, and the third layer uses long holes 2.0-2.4mm. (For the above values, the round hole refers to the diameter, and the slit hole refers to the width of the sieve hole). The first and second layers of sieves are used to remove large size of impurities in the wheat, while ensuring that the wheat can smoothly fall into the third layer of sieves. The third layer of sieve is to ensure that the wheat do not fall, and some small impurities can continue to fall down smoothly.

The Transmittance of the slit hole sieve is higher than the round hole. Such as soybean screening, using the same 11.0mm slit-hole and round-hole sieves, and the material and impurities leaked from the slit hole sieve are significantly more than those go through the round hole sieve,because the area of the slit hole is larger than the round hole. Some rod-shaped objects(like straw) can be dropped by slit hole sieve, but can not be removed by round hole sieve. Therefore, for most of seeds, we usually choose the slit hole sieve for the bottom screen, which can let some small rod-shaped materials leak down, while the upper screen often chooses to use the round hole to prevent the large rod-shaped materials from falling into the next layer along with the seeds or grains.

The accuracy of the sieve’s hole size is very important. Its accuracy directly determines the cleaning rate of seed screening and the neatness of grading, the hole size usually reaches the level of 0.1mm. For some small type seeds, it needs to be accurate to the level of 0.01mm.

II Some suggestions about the sieve’s hole size test

Some friends who have been engaged in seed or grain processing, since they are familiar with the equipment and the characteristics of their own seeds, when buying a cleaning machine, they can clearly tell us the sieve hole size they need, we only need to make the sieve according to the user's requirements. However, this part of the customer is a small number. Most of the customers are not clear know about the sieve’s hole size, so need to send us some seed samples. We will use a small sieve to accurately determine the required sieve hole size.

Some customers always said: You are a professional manufacturer of seed cleaning equipment. You should know the hole size of the sieve for the equipment. Why do I need to send seeds to you testing?

Everyone know that different kinds seed use different hole size of sieves. But for us, it is not enough, and even the same kind of seed, because of the different planting region, the seeds’ size will be different. Even the same kinds seeds and in the same region, due to their different years harvest (temperature, humidity, sunshine time, etc.), will cause different size of seeds. Therefore, we only can recommend sieve hole size range of common seeds, cannot provide absolutely accurate hole size of sieve. So the most scientific way is that you can send the seed samples and let our technicians test it. 

There are also some customers who want to buy the machine before the harvest season, So they don’t have seeds at present; and some foreign customers considering the cost of express delivery and time，so we ask them to send some photos of the seeds, and mark the size so that we can understand the shape and size of the seed and we suggest that customers prepare more sieves with similar hole sizes.

The picture below is photos of beans taken by a friend from Tanzania in Africa. He want us to suggest the sieve hole for his 4-layers screen. His requirement is to remove large, small impurities and grading seeds at the same time.

We understand that this friend has done his best to complete the seed measurement and photographing, but from this picture we still find some problems:

1. The seed size is inaccurate. They are all expressed in centimeters and are only accurate to the single digits of millimeters. We guess that the customer uses a meter ruler to measure and estimate. The correct method should be use a vernier caliper to accurately measure the size at least to the level of 0.1mm.

2. The customer only measured the size of one seed, which is not representative. Generally speaking, we need to measure the size of at least two seeds (one largest seed and the other on was the smallest seed), and measure their width and thickness separately. The larger seed’s size will be used to determine the hole of the upper sieve, while the smaller seed, We will use the size to determine the hole of the bottom sieve.

3. It is necessary to provide photos of original materials, and to determine the hole of the sieve, not only need the size of the seed , in fact, we also according to the impurity content and impurity properties in the material. Some customers send to us are the finished products after screening. This will cause judgment errors for us to determine the hole of the sieve, especially the sieve on the upper layer.

4. The beans of this customer need to be classified by size. Then we also need to know how many grades and the percentage of each grade, so that we can determine the hole of the grading screen.

In summary, choose hole of the sieve looks simple, but it actually contains a lot of knowledge. In view of its importance to the cleanliness of the cleaner, I hope that customers attaches great importance to this issue.

Other commonly seeds and grain sorting equipment

1) Air suction: Mainly use negative pressure wind to suck out light impurities in seeds.

2) Vibration screen: screening according to the external dimensions, using sieves to remove large and small impurities in the crop seeds, and grading according to the width or thickness. (Commonly use punching sieve)

3) Positive gravity table: According to the difference density of seeds or grains, it removes lighter seeds, like moth-eaten seeds, mildewed seeds, and underdeveloped shattered seeds and other bad seeds. (Commonly used stainless steel woven mesh screen table)

4) Negative gravity separator: The principle is the same as Positive gravity table, except that the air source uses negative pressure, which is mainly used in rice and wheat crops. (Commonly used punching sieve)

5) Combination seed cleaner: It integrates air suction, gravity table and vibration screen. However, the specific gravity module is a simplified version of the positive gravity table. (Its screen of gravity table usually uses chaffer sieves)

6) Positive gravity De-stoner: According to the different density of seeds or grain, heavier impurities such as stones are removed. (Commonly used stainless steel woven mesh screen table)