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There are several feeding methods in the feeding hopper of the extruder, and small extruders generally use manual direct feeding. The feeding method of a large extruder or a parallel production hopper with multiple extruders can adopt methods such as spring feeding, vacuum feeding, and compressed air pipeline transportation for feeding.
1. Spring feeding device
It is a spiral spring installed inside a rubber tube, which is directly driven by an electric motor and rotates at high speed inside the rubber tube.
When the hopper needs to be fed, the electric motor is started to drive the spring to rotate and the raw materials are driven up by the spring spiral. The upper end of the rubber tube is aligned with the hopper and a discharge port is opened. The raw materials that rise to the discharge port are thrown out of the discharge port by the centrifugal force of the spring rotation and enter the hopper. This type of feeding device has a simple structure, easy operation and maintenance and is suitable for conveying granular and powder materials.
2. Vacuum feeding device
Mainly composed of components such as fan, suction pipe, storage bin, suction pipe, filter screen and electric control box.
When the hopper needs to be fed, fan starts and creates negative pressure in the intermediate storage bin through the suction pipe and filter screen. At the same time, the suction pipe connected to the intermediate storage bin and raw material box sucks the raw materials from the raw material box into the intermediate storage bin. When a certain amount is sucked in, the feeding relay acts, the fan stops working and the suction work stops.At this point, the discharge valve opens to feed the extruder hopper.
3. Compressed air pipeline transportation for feeding
The method of using compressed air pipelines to transport materials is often applied to several extruders working in parallel to produce and supply materials. In such a large-scale extrusion product workshop, the conveying system consists of a main feeding pipeline, which is then divided into several branch pipelines to feed materials to each extruder hopper. This method relies on compressed air and uses air ducts to transport materials which occupies a small area, requires fewer people, and has a relatively clean environment. It can be used to transport granular and powder materials.
The commonly used structural forms of the feeding hopper for the twin screw extruder barrel include ordinary feeding hopper, forced feeding hopper and vibrating feeding hopper.
1. Ordinary hopper
This type of hopper has a simple structure, low cost and is mostly used for feeding the feeding barrel of small extruders. The feeding method of this hopper relies on the weight of particles freely falling into the bucket. Therefore, during work, attention should be paid to avoiding the phenomenon of “bridging” of raw materials in the hopper, which affects the continuous feeding of the extruder.
2. Forced hopper
The forced feeding hopper is often used for large extruders or when the extruded raw materials are in powder form. The screw is decelerated by the worm gear and rotated by the motor. The upper spring applies a certain pressure to the screw, causing the raw material to be pressed into the barrel when the screw rotates. When the material inside the barrel is full, the back pressure of the pressed material pushes the screw upwards, causing the barrel to stop feeding. When there is no raw material in the barrel, the screw is pressed down by the spring force and continues to rotate to feed the barrel.
This forced feeding method avoids the “bridging” phenomenon caused by raw materials in the hopper, ensuring continuous feeding in the machine hopper and continuous feeding in the extruder production. The materials mixed by the high speed mixer generally do not need the forced hopper. The materials mixed by the high speed mixer generally have a low water content, and the powder has a certain degree of fluidity.
3. Vibration hopper
The structure of the vibrating feeding hopper is relatively simple, but an electromagnetic vibrator is added to the ordinary hopper. When it is necessary to feed the material inside the barrel, start the vibrator to vibrate the hopper in the horizontal direction, so that the raw materials inside the hopper slide downwards in the hopper.