Continuous impregnation and granulation line for long fiber reinforced thermoplastic (LFT-G)

As standard, a LFT line consists of a creel which holds and simultaneously unwinds a number of fiber bobbins, a chucking device with combs for guiding and tensioning the fiber strands and an extruder for melt preparation. In addition, there is a die for impregnating the fibers with the polymer melt and a water bath for cooling the coated strands, while a puller as drive unit conveys the fiber strands. The strands are then chopped to length in a pelletizer. A central control module with touch panel controls the individual components of the line, for example automatically coordinating them in the event of a variation in line speed or pellet chopping length.

Technology Introduction

● Long fiber reinforced thermoplastic material is referred to as "LFT", which can be subdivided into: LFT-G, LFT-D, etc.
● LFT-G complete set of equipment jointly developed by Nanjing Chuangbo Machinery Co., Ltd and Beijing University of Chemical Technology, features in the structure optimization and automatic process control technology of die head, which has the characteristics of high infiltration degree, small fiber damage, stable and controllable process and high production efficiency.
● The production line is suitable for PP, PA, PET, PPA, PBT and other thermoplastics
● Suitable reinforcement fiber: glass fiber, carbon fiber, basalt fiber, etc.
● The fiber content is 30%, 40%, 50%, 60% controllable. It can meet the needs of different customers.
● Unwinding of fiber rovings can be selected: inside unwinding and outside unwinding.

Characteristics of LFT - G

● Bending and tensile strength increased by about 100%-300%.
● Impact resistance increased by 2-3 times.
● Excellent high-temperature creep resistance, high impact strength at low temperature, suitable for high and low temperature alternating frequent occasions.
● High size accuracy, small deformation, vertical and horizontal shrinkage rate is small and consistent.
● Simple molding, good fatigue resistance, good molding performance.
● Low warp, little glass fiber exposure, good surface performance.
● Recycling, green environmental protection.

Comparison between LFT and conventional cut short glass reinforced composites

Long fiber reinforced thermoplastics (LFT) are being used in high mechanical injection molding applications. Although LFT technology can provide good strength, stiffness and impact performance, the processing method of this material plays an important role in determining the performance of the final components. In order to successfully shape LFT, it is necessary to understand some unique characteristics of LFT.

The difference between LFT and conventional cut short glass fiber reinforced composites is the length of the fibers. LFT is produced by pultrusion rather than shear mixing. In LFT manufacturing, continuous strands of glass fiber roving without twist are pulled into a die head for coating and impregnating resin. From the die head, this continuous reinforced plastic strip is chopped or pelleted, usually to a length of 10 to 12mm.In contrast, conventional short glass fiber composites contain only 3 to 4mm long chopped fibers, which are further reduced to less than 2mm in a shear extruder.

Long glass fiber reinforced thermoplastic (LFT) is a kind of composite material with light weight and high strength. This kind of composite material is mainly used in the higher requirements than short-cut glass fiber reinforced thermoplastic materials, and has been widely used in the automotive industry, machinery manufacturing, electronic appliances, chemical environmental protection, aerospace communications, construction and other sectors and industries.

The complete equipment process flow chart

1. Feeding system

2. Loss in weight feeder

3. Twin screw extruder

4. Inside fiber unwinding

5. Glass fiber pretreatment system

6. Impregnation and coating mold

7. Cooling water tank

8. Strand shaping

9. Blower

10. Strand arranging

11. Hauling machine

12.Special granulator

13. Vibrating screen

Die Head Design

When designing the die head, we need to consider impregnation, improve infiltration degree, reduce fracture rate, avoid degradation and improve efficiency etc.. Specific requirements will be discussed with potential customers.

Fiber Unwinding

Inside fiber unwinding is provided for LFT-G glass fiber, and outside fiber unwinding is provided for LFT-G carbon fiber.

Pre-treatment of Fiber

If the fiber is pre-stretched before entering the die head, the impregnation efficiency of the die head will be greatly improved. For this, we have developed a long-fiber pretreatment device, and at the same time, the pre-stretch width can be adjusted according to different fibers.

The second function of the fiber pre-treatment device is to preheat the fiber. The purpose is to give the surface of the fiber a temperature close to the melt material, to prevent the cold material from rapidly cooling after the cold fiber enters the die head, which increases the probability of fiber breakage and affects the fiber infiltration efficiency.

PLC Control

● The main interface of the user input: You can choose the polymer material system, the number of fiber bundles, the fiber content, the fiber type (carbon fiber, basalt or glass fiber), the traction speed, and the cutting length (granule size).
● One-key start of the whole unit: After the user input is completed, the device performs automatic inspection, and then optimizes the operation according to the set parameters to increase the speed to the set value.
● It can output the basic parameters that the user cares about, such as the total output of the production line, the output of plastic, and the amount of fiber, and gives the approximate time for replacing the fiber roll and counts down.
● Process adjustment: The operator can adjust parameters according to the running conditions to predict and prevent problems.
● Adjust the traction speed of the production line, which can be controlled independently. The traction speed on the display should be changed accordingly, and the feeding amount should be changed accordingly. Other display parameters are adjusted accordingly. Traction speed needs to be linked with subsequent cutting feed speed.

Specification