Discussion on Key Problems of Automatic Packaging Technology of Wheat Flour

Recently, automatic wheat flour packaging technology and equipment began to enter China's wheat flour processing industry.With the continuous development of intensive and large-scale production mode in wheat flour industry in China, it is inevitable that automatic wheat flour packaging production line should be adopted to replace the semi-automatic packaging production equipment which still has a large labor capacity.This is not only the result of technological development, but also the demand of market competition.On the one hand, in order to adapt to the fluctuations of the international wheat price, reduce the wheat flour production cost, and gain advantages in the fierce market competition, China's wheat flour processing enterprises have been expanding the production scale in recent years, and at present there are more than 200 wheat processing enterprises with a daily processing capacity of 400-1000t [1].With the increase of production capacity, it is necessary to adopt automatic packaging technology and equipment to improve the packaging speed of wheat flour.As in the past, the application of semi-automatic packaging machine, on the one hand, because each packaging production line needs to manually complete part of the key process, which is bound to lead to the speed of the whole packaging production line is limited.In view of our country, on the other hand, artificial wages presents a significant growth trend and the tense situation of human resources, because of the existing wheat flour semi-automatic packaging technology needs more operators, each of the wheat flour packaging production line generally requires 5 to 7 people, so also will encourage enterprises to reduce labor costs and choose automatic wheat flour packaging technology and equipment.

It can be predicted that the automatic packaging technology will be widely used in large wheat flour processing enterprises in China in the next few years.

1. Difficulty in automatic packaging of wheat flour

Wheat flour produced by flour mills is a fine powder with water content of about 14.5% [2].Therefore, wheat flour particles are particles with very large specific surface area.At the same time, because wheat flour particles are mainly composed of starch, protein, minerals and other components, there are polar groups on the surface.In this way, under the combined action of large specific surface area, water and polar groups, there is a certain adhesion between wheat flour and the surface of the equipment, between wheat flour particles, and between the packaging bag and wheat flour.Therefore, in the process of wheat flour packaging, not only easy to produce dust flying;Moreover, the wheat flour will stick to the hopper wall and the mouth of the packing bag, so that the measured wheat flour can not be all smoothly loaded into the packing bag.This will not only increase the packaging measurement error, so that the packaging wheat flour in sales can not reach the qualified measurement standard, and may affect the normal process of packaging: ① wheat flour attached to the bag mouth will affect the normal work of the packing bag sealing process.② Because the wheat flour is not easy to self-compaction, the top of the wheat flour packing bag is raised, which increases the difficulty of sealing.

The above factors make the packaging process of wheat flour different from that of other powders and granules.It is more difficult to realize the automatic packaging of wheat flour, which puts forward higher requirements for the design of the automatic packaging mechanism and its automatic control system, and for the coordination of the whole packaging line, the coordination between the packaging process, the weighing process and the production line in front.In fact, this is also an important reason why China's packaging equipment manufacturing enterprises involved in wheat flour automatic packaging equipment is less.

2.The form and characteristics of automatic wheat flour packaging technology

At present, wheat flour packaging technology is mainly used in two forms: semi-automatic packaging technology and automatic wheat flour packaging technology.The former has become increasingly mature in technology and operation, and its working performance is basically reliable. Its process flow is as follows:

Automatic feeding → automatic weighing → manual bagging → manual auxiliary filling → manual auxiliary sealing and stitching → automatic conveying → manual auxiliary stacking.

Technically, this kind of process requires manual completion of part of the operation procedure, has not yet reached the requirements of unmanned automatic packaging process, so it belongs to semi-automatic wheat flour packaging.Due to the limited speed of manual bag-taking and bagging, for wheat flour production lines with high output, it is often necessary to equip more than two sets of packaging units, and also need to equip operators for the procedures of bag-taking and bagging.

Automatic wheat flour packing device, including automatic picking and bagging functions, has been widely used in Italy, the United States, Germany, Britain, Canada and other developed countries in recent years.Its technological process is as follows:

Automatic feeding → automatic weighing → automatic bagging → automatic filling → automatic sealing and sewing bag → automatic conveying → robot stacking and stacking bag.

As China's wheat flour automatic packaging technology level still lags behind the developed countries, so at present, only in the relatively low technical difficulty of small bag wheat flour packaging (less than 5kg/bag) used in the bag of automatic wheat flour packaging equipment (as shown in Figure 1).For large bags of wheat flour (more than 5k g/bag of wheat flour), semi-automatic wheat flour packing equipment with manual bag feeding is widely used (as shown in Figure 2). So far, only one enterprise in Tianjin has introduced the Italian automatic bag feeding packing machine.An enterprise in Jiangsu province began to try out a full-automatic wheat flour packing device for feeding bags, which was trial-produced by a domestic packaging machinery enterprise.

Paper bag and plastic bag can be used in small automatic wheat flour packing.At present, there are two forms of full-automatic wheat flour packaging technology for large bags of wheat flour: valve bag packaging (as shown in Figure 3) or open bag packaging (as shown in Figure 4).In the valve pocket packaging technology, the paper packaging bag with good stiffness is mainly used, and the material with too low rigidity is not suitable for use.In the open bag packaging process, three kinds of packaging bags can be used.But because of the high cost of paper packaging bags, so, China's wheat flour enterprises rarely use, is widely used at present is laminated woven bags and non-woven bags.

3.Key to automatic packaging technology of wheat flour

Although the automatic packaging process for large bags of wheat flour, whether valve pocket or open bag packaging process, can achieve automatic and unmanned operation, but due to the need to complete automatic bag picking, bagging and filling packaging operations, so its complexity and technical difficulty increased significantly, especially the automatic open bag packaging technology.

3.1 Automatic packaging of wheat flour in valve pocket

Since the valve pocket is the valve mouth on the top of one side of the packing bag as the wheat flour filling inlet, one of the technical keys is how to cover the valve mouth to the discharge pipe of the electronic scale accurately.For the single discharge pipe, the manipulator is required to be able to accurately coordinate with the electronic scale and the packing bag conveying device, and to move quickly under the command of the sensor and the control program.But for the multi-station, rotary electronic scale unloading device, it is necessary to make the manipulator and the rotary unloading hopper accurately cooperate.Otherwise, due to the accumulation of errors between the manipulator and the rotary discharge pipe mouth, it will soon lead to the filling and packaging error of wheat flour, and it is difficult to work continuously.

The other key of valve pocket packing technology is that the air in the bag causes the unsmooth filling of wheat flour and the low compaction of wheat flour.The former compresses the air in the bag because of the wheat flour filling, and at the same time, the air flows upward, which brings unfavorable factors to the wheat flour filling smoothly.The latter is caused by the convection between the rising and falling air of wheat flour in the bag, which leads to the decrease of the bulk density of wheat flour in the bag, which may result in the false impression of insufficient volume of the bag.The above two problems are the key problems to be solved in the valve pocket automatic wheat flour packaging.

3.2 Open pocket automatic packaging

In the production of open bag automatic packaging, because our country is widely used laminated woven bags and non-woven bags, and these two kinds of packaging bags rigidity is very low, so automatic bag, bagging is more difficult.At the same time, in the process of wheat flour filling, the problem of wheat flour flying outward and the problem of wheat flour being solid should be solved.

Because many bag making factories use hot cutting to make bags, the adhesion phenomenon of the bag mouth is more serious.This is very difficult for the manipulator to open the bag mouth when packaging, and may even be difficult to open the bag mouth.Moreover, there is also adhesion phenomenon between the adjacent packaging bag mouth, which leads to the manipulator may grab more than one bag at a time, so that the automatic packaging can not be carried out normally.This problem needs to be solved in the open pocket automatic packaging.

Similar to the valve pocket packaging process, when the manipulator will cover the packaging bag to the electronic scale discharge port, the packaging bag and discharge port form a closed space, the air in the bag to the wheat flour filling whereabouts block, and make the packing of wheat flour in the bag density decreased.Similar to the valve pocket, this problem needs to be solved by adjusting the air pressure of the discharge port appropriately.

After the packing bag is covered to the unloading port, the elastic clamping mechanism should be adopted to tightly clamp the packing bag on the outside of the unloading port to ensure that the wheat flour will not fly outward during the filling process.

3.3Other key technical issues

In terms of automatic wheat flour packaging, in addition to the above problems, the weighing device is fast and accurate, the automatic bagging device is fast, stable and reliable, the control system, the controller, the sensing element is sensitive and reliable,High-speed palletizing robots and their reliability are also the key technical issues that need to be studied by technicians and enterprises in China.The domestic automatic bagging technology has just started research and development, technology is not mature, bagging speed, reliability and so on is not high enough;Domestic palletizing robots, sensors, controllers and other key control components technology is not stable.

4. Conclusion

With the continuous increase of wheat flour processing capacity in China and the competition and development of the industry, it is undoubtedly necessary to accelerate the research and development of automatic wheat flour packaging technology in China.Technically, the open pocket packaging technology is more difficult than the valve pocket packaging technology, but because the cost of paper packaging bags is higher than the film woven bags and non-woven bags, for wheat flour processing enterprises with very low profit margins, or more willing to use the latter.Therefore, China needs to step up research and development of the use of film woven bags and non-woven bags open pocket automatic packaging technology, in-depth and full research palletizing robots, sensors, controllers and other key control components, in order to adapt to China's wheat flour processing industry to the integration, scale, high efficiency direction of development needs.

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