Omfattande guide till matnings- och vakuumanordningar i förpackningsmaskiner

During the packaging process, the product is usually sent to the metering device for metering by means of a feeding device on the packaging machine, and then filled into the packaging container, and then wrapped and packaged.
Here, the feeding device commonly used in the packaging machine and the vacuum pump used in the vacuum packaging machine are introduced. For the quantitative metering device, please refer to the chapter on the loading machine. In the section on the packaging machine, the working principles and some typical structural forms of the packaging container and packaging material feeding device, the filling and pouring device, and the wrapping and packaging device are also introduced.

Feeding device

The function of the feeding device for packaging items is to feed the items to be packaged stored in the hopper to the item metering device for metering according to the packaging process requirements, and then the other devices of the packaging machine implement the packaging operation.
The feeding device for packaging items is generally composed of a hopper, a conveyor, a feeder, an anti-blocking device, a sorting and directional arrangement device, and a driving device. Due to the great differences in the physical and chemical properties, natural forms and packaging process requirements of the items, the feeding device has a variety of structural forms.
According to the driving mode of the supplied items, the supply device can be divided into: gravity feeding device (including gravity conveying of finished items); belt conveyor device (including chain conveyor device); screw conveyor device; pumping device; turntable slide device; vibration feeding device, etc.
The feeding device should have a simple structure, reliable operation, adapt to the physical and chemical properties of the material being fed, and be coordinated with the subsequent packaging process operation.

Gravity feeding device
The gravity feeding device uses the characteristic that the items can flow from high to low under the action of gravity. The items are placed at a high position and flow along the fixed material channel to the low position, thereby realizing the supply operation of the items. When the items flow in the material channel, it is easy to form an arch or bridge, resulting in poor flow or even blockage. Therefore, the flow channel should be smooth and flat, and necessary anti-blocking stirring devices should be set. For items with directional requirements, a sorting and directional arrangement device should also be set. Items that are not convenient for automatic orientation should be manually arranged and stacked in the hopper in advance.
The figure is a working principle diagram of the gravity feeding device for powder and granular materials. The material in the hopper 1 flows continuously to the quantitative rotating disk 4 under the action of its own weight and the agitator 5, and the fixed scraper 2 scrapes off the excess material on the rotating disk metering cup 3, thereby realizing the metering operation.

Piece material feeding device

The figure is a principle diagram of the piece material feeding device. Figure (a) shows a piece material feeding device that can automatically select and orient, which is suitable for the automatic feeding of cylindrical pieces with a relatively small length and diameter. The disorderly pieces of material are stored in the hopper. Under the action of the orienting mechanism 2 and the rejector 6, the pieces of material are arranged in a directional manner in the feed trough 7, and move along the feed trough to the feeder 1 under the action of its own weight, thereby realizing the intermittent feeding of the pieces of material. Figure (b) shows a feeding device for pieces with a relatively large length and diameter that are not easy to automatically select and orient. The pieces of material need to be manually arranged in the hopper in advance. Under the weight of the pieces of material and the action of the agitator 2, the pieces of material move along the feed trough 7 to the feeder 1, and the feeder delivers the pieces of material to the next process.

Belt feeder
Belt feeder can be used for the supply of bulk, block, bagged and pieced items, and can be composed of multiple belts to meet various packaging process requirements.
The figure shows the principle diagram of the belt conveyor. The items are transported from the hopper 5 to the unloading device 6 and unloaded. The tensioning device 8 is used to adjust the tension of the belt, and the steering roller 7 is used to increase the wrap angle to ensure the conveying capacity of the belt.
The conveyor belt in the belt feeder is in contact with the items. According to the physical and chemical properties and hygiene requirements of the conveyed items, the corresponding belt material needs to be selected and the necessary physical and chemical treatment needs to be carried out. The conveyor belt includes cotton canvas belt, chemical fiber fabric belt, rubber canvas belt, nylon sheet belt, steel belt, metal mesh belt, etc. Commonly used physical and chemical treatment methods for belts include impregnation, coating of surface protective layers, etc.

Chain feeding device

The figure shows a schematic diagram of a chain conveyor for conveying toothpaste on a toothpaste cartoning machine. The basic structure of a chain conveyor commonly used for feeding packaged items is shown in the figure. The traction component for conveying items consists of two parallel ring chains. The two chains are connected by a small shaft or a slat to keep the two chains parallel and equidistant. Special chain plates are installed on the chain, or rollers and pallets are installed on the small shaft (slat) between the two chains. Accessories such as push plates are used to drive the packaged items to move forward. The traction chain generally uses a standard sleeve roller chain, or a sleeve roller chain with a special long chain plate, a flat chain, etc. In order to ensure the correct meshing transmission of the chain and sprocket teeth and the position accuracy of the feeding, a chain tensioning device is generally required.

Chain conveyors are suitable for the delivery of pieces and stalks that require accurate delivery of packaged items and certain packaging operations during transportation.

Rotating disc feeding device
When the rotating disc rotates, the materials stored in the disc hopper can move to the outer edge of the rotating disc under the action of friction and centrifugal force, and are arranged in a directional manner along the tangent direction of the disc and enter the conveying channel tangent to the outer edge of the disc. By setting a certain conveying device on the conveying channel, the automatic sorting and directional arrangement of materials can be realized.

The figure shows the working principle diagram of the conical bottom disc hopper feeding device. The conical bottom disc can increase the tendency of materials to move to the outer edge of the rotating disc. The materials are arranged in a directional manner along the tangent direction of the disc and enter the conveying trough in turn. This device has a simple structure and reliable operation. It is suitable for the automatic sorting and directional feeding of various small columns, sleeves, covers, blocks and sheet materials.

Electromagnetic vibrating feeding device
The vibrating feeding device is a device that uses vibration technology to transport loose powders and small items in medium and short distances. According to the structure of the vibrating body, it can be divided into straight trough type and disc hopper type; according to the type of excitation source, it can be divided into mechanical type, electromagnetic type, hydraulic type and pneumatic type. Here we mainly introduce the electromagnetic vibrating feeding device.

The structure of the electromagnetic vibrating feeding device: generally composed of exciting electromagnets, armatures, vibrating bodies, main vibration springs, vibration damping springs and bases. As shown in the figure, the vibrating trough body (or hopper) is supported on the base by the main vibration plate spring, the iron core and coil of the electromagnet are fixed on the base, and the armature is fixed on the bottom of the vibrating body; there is an angle between the working surface of the vibrating trough body and the horizontal plane (there is a spiral conveying channel with a spiral rise angle of a in the vibrating hopper), and there is also an angle between the main vibration plate spring and the plumb plane. The entire device is connected by bolts, vibration damping springs and the frame.
Obviously, the principles of the disc hopper type and the straight trough type are basically the same, except that the straight trough conveyor channel is changed into a spiral conveyor channel, and the swing vibration is changed into a torsional vibration.
Take the straight trough vibrating feeding device as an example to illustrate the working principle of the vibrating feeding device.

As shown in Figure (a), the object is placed in the trough body. The trough body performs directional forced vibration under the action of electromagnetic excitation force and the main vibration plate spring. When the trough body moves to the upper right, the object is driven by the trough body by the friction force and obtains accelerated movement to the upper right; when the trough body decelerates to the upper right, or accelerates to the lower left under the action of electromagnetic attraction, since the object has obtained a certain kinetic energy when accelerating to the upper right, the object still has a tendency to continue to move to the upper right or slide a distance to the right relative to the working surface of the trough body, or even make a section of oblique throwing motion to the upper right, and then fall back to the working surface of the trough body. When the trough body moves to the upper right again, the object is accelerated by friction again, and the above movement cycle is repeated. In this way, every time the tank body reciprocates and vibrates once, the article moves a certain distance to the right relative to the tank companion body, thereby achieving the requirement of supplying articles.

Vacuum device

The vacuum pump is the main working part of the vacuum packaging machine, and its performance will directly affect the vacuum degree. There are two main types of vacuum pumps used in vacuum packaging machines: one is an oil bath eccentric rotor vacuum pump (also called a slide valve vacuum pump); the other is an oil bath rotary vane vacuum pump. As shown in the figure.

Oil bath eccentric rotor vacuum pump
Working principle: as shown in the figure. A rotor slide valve 9 is installed in the pump 12, which consists of a valve ring and a valve stem. The valve ring on the rotor slide valve is sleeved on the eccentric rotor 10, and the geometric center of the rotating shaft 11 and the pump chamber 13 coincide. The valve stem on the upper part of the rotor slide valve can slide freely up and down in the cylindrical slide bolt 2 and swing left and right. The valve ring sleeve slides along the surface of the pump chamber 13. When the shaft 11 rotates counterclockwise, the rotor slide valve 9 divides the pump chamber 13 into two working chambers, and the volume of chamber A gradually expands, while the volume of chamber B gradually decreases. The gas pressure in chamber A continues to decrease, and the pumped gas enters chamber A through the cavity in the valve stem and the rectangular hole on the side. When the rotor slide valve turns to the top dead center of the pump chamber 13, the suction ends, and chamber A reaches the maximum suction volume, and the rectangular hole is closed at this time. The pump shaft 11 continues to rotate, and the volume of the original working chamber begins to gradually decrease again, the gas is compressed, and the pressure continues to increase. When it exceeds the spring pressure of the exhaust valve 7, the gas pushes it open and is discharged. The two chambers A and B work alternately. When chamber A inhales, chamber B exhausts. Each rotation of the pump shaft is equivalent to completing a suction and exhaust process.

Oil bath rotary vane vacuum pump

Working principle: as shown in the figure. When the eccentric rotor 5 with two vanes 6 rotates clockwise, the vane G slides against the inner wall of the pump body 8 under the pressure of the spring 4 and its own centrifugal force, and the right suction chamber continues to expand, and the pumped gas enters through the suction port l. When the other vane passes the suction port position, the sucked gas is isolated and the suction is completed. The rotor continues to rotate, the isolated gas is gradually compressed, and the pressure increases. When the pressure exceeds the pressure on the exhaust valve 3, the gas pushes open the exhaust valve 3 through the exhaust pipe and is discharged through the oil and the exhaust port of the pump. During the operation of the pump, the vanes always divide the pump chamber into two working chambers, A (suction) and B (exhaust). Every time the eccentric rotor rotates one circle, there are two suction and exhaust processes.

Slutsats

In the packaging process, feeding devices play a crucial role in ensuring the smooth and efficient transfer of materials to metering devices for packaging. The different types of feeding devices, such as gravity feeding, belt feeders, chain conveyors, vibrating feeders, and rotating disc devices, are designed to meet the diverse requirements of various materials and packaging processes. These devices must be tailored to the physical and chemical properties of the items being fed to ensure reliability and prevent issues like blockages or improper alignment.

Additionally, vacuum pumps, such as the oil bath eccentric rotor and rotary vane pumps, are integral components of vacuum packaging machines, ensuring the proper vacuum level for preserving items. The selection of the appropriate feeding and vacuum devices ensures an efficient, reliable, and safe packaging operation, essential for meeting both production and quality standards.