How to guarantee high quality double screw extruder?

The structure of extruder machine

An extruder usually consists of at least three stages. The first section, near the feeding hopper, is the feeding section. Its function allows material to enter the extruder at a relatively steady rate. In general, to avoid clogging of the feed channel, this part will be kept at a relatively low temperature. The second part is the compression section, where the melt is formed and the pressure is increased. The transition from the feed section to the compression section can be abrupt or gradual. The last partial metering section, next to the extruder outlet. The main function is that the material flowing out of the extruder is uniform. In this part, to ensure the uniformity of composition and temperature, the material should have sufficient residence time. At the end of the barrel, the plastic melt leaves the extruder through a head designed to the desired shape, through which the extruded melt stream passes.

PVC Conical Twin Screw Extruder

PVC Conical Twin Screw Extruder

Another important part is the drive mechanism of the extruder. It controls the rotational speed of the screw, which determines the output of the extruder. The power required is determined by the viscosity (flow resistance) of the polymer. The viscosity of polymers is dependent on temperature and flow rate and decreases with increasing temperature and shear force. The extruder is equipped with a filter screen, which can block impurities on the filter screen. To avoid downtime, the filter should be able to be replaced automatically. This is especially important when processing resins with impurities, such as regrind. The screw of the extruder is divided into feeding section, plasticizing and melting section. The temperature is divided into 45, 65, 75, 80, 90, 120…

Quality requirements for plastic extruder barrel manufacturing:

1) The barrel should be made of wear-resistant and corrosion-resistant alloy steel. The barrel blank is formed by forging and then machined to the size required by the drawing. At present, 38CrMoAlA alloy steel is mostly used in domestic manufacturing of extruder barrels, and 40Cr or 45 steel can also be used.

2) After the rough machining of the barrel, it should be quenched and tempered, and the hardness is 260-290HBW.

3) After the semi-finishing of the barrel, the surface of the inner hole should be nitrided, the depth of the nitriding layer is 0.4 ~ 0.7mm, and the hardness is above 940HV.

4) The matching clearance between the barrel and the screw,

5) The wall thickness of the barrel should also be controlled, because the barrel must have a sufficient thickness to ensure that the barrel has a large thermal capacity and thermal inertia. When the working speed of the screw changes, there will be no obvious fluctuation in the temperature control of the barrel, which ensures the stability of the process temperature of the extruder and makes the extrusion production work smoothly.


Trial debugging before delivery

The machines produced by Kairong will be tested according to the materials required by customers before leaving the factory to ensure that the machines can operate normally. When conditions permit, we will send engineers to the customer’s factory for debugging and training.

Customer acceptance & Production

① After the extruder production line is installed, the workshop organizes workers to clean up the environment of the extruder production line and clean the equipment.

Co-rotating Twin Screw Extruder

Co-rotating Twin Screw Extruder

② Process technicians should carefully read the relevant extruder instruction manual, and formulate the process of trial production of plastic products, the operation procedures for trial production, the plan for trial materials, the tools for trial and the production trial time according to the requirements in the manual. Organize the extruder production operators to study the equipment operating procedures carefully, understand and be familiar with the equipment structure and the functions of various parts, and memorize the functions and usage of each switch and button in the equipment.

Preparation before test running

① Check whether the nuts on each equipment of the extruder production line are loose.

② Check whether each safety shield is firm.

③ Check the tightness of the V-belt installation, and adjust the tightness of the V-belt appropriately to suit the operating requirements.

④ Pull the V-belt, the rotation should be relatively easy, the operation of all parts is normal, and the screw rotation is not locked.

⑤ Check whether the grounding protection of the equipment and the control box, electrical wiring, etc. are loose, and whether they meet the requirements.

⑥ Check and test the insulation resistance of the motor and electric heating device should meet the specified requirements.

⑦ Check that the assembly clearance of the screw and the barrel should meet the specified requirements.

⑧ Each control knob should point to the zero position or at the stop position.

The sequence of operations is as follows:

① Check whether the lubricating parts of each equipment and the quality of the lubricating oil in the reduction box meet the requirements, properly supplement or add enough lubricating oil, and the lubricating oil level is at the high line of the oil standard line.

② Control the electric box circuit to close the power supply.

③ Check that there should be no foreign matter in the hopper and barrel.

④ Start the screw drive motor to run at low speed.

⑤ Check whether the pointer of the voltmeter and ammeter of the control box swings abnormally, and the power consumption should not exceed 15% of the rated power.

⑥ Check whether the rotation direction of the screw is correct (if the screw thread is clockwise, it should be clockwise when facing the barrel and the screw is correct).

⑦ Listen to whether there is any abnormality in the working sound of each transmission part, and see if there is friction between the rotation of the screw and the barrel.

Dry running barrel to heat up

① Each section of the barrel is heated and heated, and the temperature control table is adjusted according to the temperature requirements of the extrusion process.

② After the barrel is heated to the temperature required by the process, the temperature is kept constant.

③ Start the driving screw to rotate the motor at low speed, and observe whether the swing of the voltage and ammeter is abnormal; see whether the screw rotates smoothly; whether there is rotational friction between the screw and the barrel; Everything works and stop immediately. Note: The idle running time of the screw should not exceed 3min.

Test run with material

① Test the quality of raw materials. Whether the particle size of the raw material is uniform, whether the material is wet (if the moisture content is large, it should be dried), whether there are impurities in the material, etc. At the same time, verify whether the raw material number plate is in line with the technical requirements of the materials used in the test run.

② The barrel is heated and heated, and the temperature is reached after the process requirement is reached, and then heated at a constant temperature for 1h.

③ Check that there are no foreign objects in the extruder hopper and barrel before driving.

④ The V-belt pulley should be flexibly rotated without blocking.

⑤ Start the driving screw rotating machine at low speed, and observe whether the pointer of the voltage and ammeter swings normally; whether the screw rotates smoothly; whether the working sound of each transmission part is normal. Everything is ready to set up.

⑥ Feeding into the barrel. The initial setting should be small and uniform. It is necessary to observe the swing change of the ammeter pointer and the smooth rotation of the screw while feeding. If there is no abnormal phenomenon, the feeding amount can be gradually increased until the mold is buckled and discharged.

⑦ After the mold is discharged, the incompletely plasticized melt should be removed first.

Note: When adjusting the gap between the die and the mandrel, the operator cannot face the die mouth to prevent accidents.

Counter Rotating Twin Screw Extruder

Counter Rotating Twin Screw Extruder

After the quality of the test product is qualified, the current change of the screw at high, medium and low speed and the output per unit time of the product are tested again.

Stop feeding

The production sequence of stop feeding and test run is as follows:

① Reduce the working speed of the screw to a minimum.

② Cut off the heating power of the barrel and the mold. Start the barrel cooling fan.

③ When the barrel temperature drops to 140℃, stop the barrel feeding. Stop the screw driving the motor until the mold outlet is out of material.

About US

Kairong Group, headquartered in Nanjing, China, is a global manufacturing and trading company in the field of high-performance plastics and rubber processing equipment, extrusion solutions, masterbatch, and compounding, etc. 

Its unit Nanjing Haisi Extrusion Company is a professional manufacturer of twin screw extruder, single screw extruder, two stage extruder,equipment for dryer and its related auxiaries.  We tailor solutions from raw materials, materials processing equipment, to injection for different customers. 



If you are looking for a reliable twin screw extruder manufacturer, then we are your worthy choice manufacturer, you can browse our homepage to learn more about our company and products, and if you have more questions You can contact us directly, we are happy to provide you with high-quality service and excellent products.



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