ZhangJiaGang Antron Machinery,Co.,Ltd

waste plastic granulation will be smooth and efficient

For the waste plastics directly in the raw and modified regeneration, the processing equipment mainly includes single-screw extruder, twin-screw extruder and multi-stage granulator. The waste material is melt-plasticized by an extruder, and the strip material is extruded, and the pellet is directly hot-cut or cooled to a desired size. The extrusion granulation process is:

1.Extrusion granulation process control

Strict control of process parameters is a must when the entire process is in progress. Process parameters include: processing temperature, extruder speed, working pressure, feed rate and pelletizing speed.

Raw material pretreatment

Waste plastics will leave a lot of water during the cleaning process, which will cause bubbles in the melt and affect the quality of the granulation. Therefore, the waste must be dried before processing, the drying temperature must be set reasonable to prevent bonding into a dough; the drying time is set according to the drying temperature to ensure complete drying.

2. Temperature control

Extrusion temperature is a necessary condition for plasticizing the material and flowing the plastic melt. It has a very important influence on the plasticization and granulation quality and process of materials. To properly control the extrusion temperature, you must first understand the relationship between the temperature limit of the material being processed and its physical properties. Find out the characteristics and laws to choose a better temperature range for extrusion granulation. Therefore, the following aspects should be considered in the temperature setting of each section. One is the properties of the polymer itself, such as melting point, molecular weight size and distribution, melt index, etc.; secondly, the performance of the equipment is considered.

3. Pressure control

The most important pressure parameter in the extrusion process is the melt pressure, which is the head pressure. In general, increasing the melt pressure will reduce the extruder output and increase the compactness of the product, which is beneficial to improve the quality of the product. But if the pressure is too high, it will bring security problems. The melt pressure is related to the properties of the raw material, the screw structure, the screw speed, the process temperature, the mesh number of the filter, and the porous plate.

4. Screw speed and extrusion speed

Screw speed is a rework parameter that controls extrusion rate, throughput, and product quality. The speed of the single-screw extruder increases and the output increases. The shear rate increases and the apparent viscosity of the melt decreases. Conducive to the homogenization of materials. At the same time, due to good plasticization, the interaction between molecules is increased and the mechanical strength is improved. However, if the screw speed is too high, the motor load will be too large, the melt pressure will be too high, and the extrusion amount will be unstable.

5. Impurity filtration

After the waste plastic is cleaned and separated, its impurity content is still high, so it needs to be filtered before the plastic melt is extruded to remove residual impurities and ensure the quality of the particles. Filters are frequently replaced during processing, and filter mechanical replacement devices are required to ensure continuity of production.

Common problems and solutions in the granulation process

problem

the reason

Solution

More black spots

Recycled material itself has more impurities

Strengthen cleaning and screening, increase the number of meshes or layers

Local overheating of the barrel, causing material to char

Reduce extruder temperature and increase filter mesh or number of layers

Extrusion partial shear is too strong, causing material carbonization

Reduce extruder speed and increase filter mesh or number of layers

The pressure on the head is large, which increases the backflow of the material and causes the material to be charred.

Raise the temperature of the head; replace the filter and reduce the mesh number

The equipment is aging and there is too much adherence on the wall of the barrel

Replacement of equipment or parts

Carbonization of the accumulated material in the vent hole is taken out

Clean the vents regularly

The discharge port is not smooth, and the accumulated material is carbonized

Clean or replace parts

Mold cleaning is not clean

Clean up regularly

Screw thread damage, carbonization of dead corner material

Replace or repair the screw

Poor exhaust, causing material carbonization

Clean the vents and keep them open

Frequent broken bars

More impurities

See the solution to the problem particle black spots

Insufficient amount of extrusion

Increase screw speed, increase feed rate or replace filter

The head temperature is too high and the material viscosity is lowered.

Properly reduce the temperature of the head

Poor plasticization

Properly increase the extrusion temperature or speed to promote complete plasticization

Mixture material, large difference in properties

Adjust the temperature or speed according to the actual situation

Poor exhaust, air holes in the strip

Ensure that the vent hole is unobstructed and reduce the extrusion temperature reasonably

Towing too fast

Increase the speed or reduce the traction speed

Particle hollow

High moisture content of the material

Increase drying temperature or time to ensure smooth venting

The extruder has a high temperature and has an auxiliary decomposition

Increase extrusion rate and reduce extrusion temperature reasonably

Low processing temperature, material is not fully plasticized

Reasonably increase processing temperature

The water temperature is too low, the material shrinks, causing shrinkage

Reasonably reduce the temperature of the head and properly increase the temperature of the cooling water

Natural exhaust port, vacuum material

Feed speed does not match host speed

Properly reduce the feed speed or increase the host speed

The temperature of the natural exhaust port area is low, the plasticization is not good, and under the action of extrusion, the raw material is taken.

Improve the temperature of the natural exhaust port area and promote plasticization

The temperature of the natural exhaust port area is too high, the viscosity of the material is seriously reduced, and the clinker is taken under the action of extrusion.

Reduce the temperature of the natural exhaust port area

The natural exhaust ports of the screw and barrel do not match

Select matching screw and barrel

No reverse conveying element or reverse meshing block is provided here

Set reverse conveying element or reverse meshing block

The temperature in this area is too high, the viscosity of the material is seriously reduced, and the material is caused by the extrusion.

Properly reduce the temperature in this area too high

Vacuum gasket is low

Reasonably adjust the gasket position

Low processing temperature, uneven plasticization of materials

Reasonably increase processing temperature

Large head pressure, material return

Check if the die is clogged, change the net or increase the temperature of the head

Hopper bridge

Too much filler, moisture absorption, agglomeration, resulting in increased friction between the mixture and the hopper wall

Appropriate addition of external lubricant to reduce friction between the mixture and the hopper wall and the mixture

Cutting bridge

The processing temperature in the first zone and the second zone is high, the material is softened in the feed silo, and it is difficult to follow the blanking of the equipment wall.

Properly reduce the processing temperature of one zone and two zones

Mixture agglomeration

Reduce drying temperature or high mixing time and reduce the amount of liquid additives

Continuous problem

In some cases, the particles are connected together by end faces of the film or tangentially.

Increase the flow rate of water flow to avoid agglomeration;

Trailing problem

Cutting disadvantage

Replace the cutter

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