Thermoplastic tube extrusion coating molding

- Jul 13, 2019-

Traditional thermoplastic plastics pipe extrusion molding, melt flow direction parallel to the pipe axis, macromolecular chain along the parallel to the wall of the plastic pipe axis orientation, the strength of the pipe wall is more than circumferential, axial and the stress of the pressure pipe is circumferential for axial twice, so the axial and circumferential strength conflicts with axial and circumferential stress.Thermoplastic tube extrusion coating molding rotates the melt flow direction to be close to the vertical axis of the tube, plastic macromolecular chain along the tube circumferential orientation, so that the plastic tube circumferential strength is greater than the axial direction, so that the axial and circumferential strength and force remain consistent.

1, the preface

The invention of thermoplastic pipe material has a history of more than 70 years.

However, the flow direction of the melt is parallel to the axis of the pipe during the extrusion molding of the traditional thermoplastic pipe.The disadvantage of this approach is that the plastic macromolecular chain in the pipe wall is oriented along the axis parallel to the pipe, and the strength of the pipe wall is more parallel to the pipe axis than perpendicular to the pipe axis.This is just the opposite of the wall of the tube when it is subjected to internal pressure.According to the stress analysis of the pressure-bearing pipe, when the pipe is under internal pressure, the stress generated along the circumference of the pipe wall is more than twice that generated by the pipe wall parallel to the pipe axis.

Originally, the strength of plastic is much lower than that of metal. The direction of high plastic strength is not used on the circular pipe wall where the strength of plastic pipe needs to be high, but falls on the axis where the strength is not high. The existence of this phenomenon is undoubtedly a great waste.Different plastic, this kind of anisotropic differences also have different sizes, such as * easy orientation of TLCP, when injection molding is used, the strength of the parallel to the direction of melt flow around three times as high as in vertical direction of melt flow, that is, the strength of 150 mpa TLCP, when using traditional extrusion molding in tubing, the use intensity is less than 50 mpa.

Chinese patent CN101332667A discloses a long glass fiber reinforced plastic tube extruder head, which relates to a plastic circular tube extruder head mounted on a plastic extruder and characterized by long glass fiber online spiral compounding.The device is equipped with glass fiber input device, fiber and melt mixing distribution device and mandrel rotating device. The mixing distribution device of the machine head successfully inputs glass fiber with certain length treated by coupling agent into plastic melt, and makes glass fiber evenly mixed into it to become fiber and plastic mixed melt.The mandrel rotating device of the head realizes the transformation from flow along the axis of mandrel to flow around the spiral direction of mandrel between mandrel and die until solidification.In the plastic tube extruded by the device, the orientation of polymer molecules and long glass fibers along the axis of the spiral direction greatly improves the circumferential strength of the tube.

However, the plastic tubing long glass fibre circumferential configuration is through the mandrel in the mouth mould rotation, require additional drive power and set the corresponding transmission device (such as speed adjusting of rods sprocket, mandrel rotation of sprocket stents, mandrel rotation drive chain, rotating mandrel and driven sprocket drive), not only consumes energy and the nose structure complex;In addition, the device is an insurmountable shortcomings, melt with mandrel spinning and was gradually introduced mouth mold cooling finalize the design in the process of pipe rotation stress exist in the embryo, so pipe besides must be linear motion, added a senseless rotary motion, and the stress rotation will be frozen in the wall, this is all thermoplastic plastics pipe extrusion molding is not allowed;In addition, most of the plastics extrusion processing and the melt temperature is about 200 ℃ or so, some even as high as 400 ℃ or so, the plastic melt in the extrusion process pressure as high as several mpa to tens of mpa, filled with glass fiber polymer melt pressure will be higher, between the mandrel and bearing seal is very difficult and easy to cause the melt leakage, affect the normal operation of equipment, and increase the operator labor intensity, sometimes even lead to the occurrence of equipment damage, and so on and so forth.

2, thermoplastic tube extrusion coating molding

The main thermoplastic tube molding, the traditional method is extrusion molding.As mentioned above, in the extrusion process, the melt flow direction is parallel to the pipe axis, the macromolecular chain is parallel to the pipe axis orientation, and the strength of the pipe wall is parallel to the pipe axial direction than perpendicular to the pipe axial direction.In order to improve the performance of plastic pipes and give them new functions, the outer surface of plastic pipes is often modified and processed to improve the strength, toughness, elastic modulus of plastic pipes, or oxygen resistance, anti-static and electrical conductivity, flame retardant and so on.In the traditional extrusion coating method, the melt flow direction is also parallel to the pipe axis.

In order to change this backward technology, manred automatic systems has applied for a PCT patent, which is authorized by the United States, as shown in figure 2.Use the patent technology, make plastic tubing in the process of extrusion molding, melt flow direction from parallel to the pipe axis is perpendicular to the pipe axis direction, plastic macromolecular chain orientation also from parallel to the pipe axis is perpendicular to the pipe axis, and with the pipe garden weeks tangent, wall strength perpendicular to the pipe axis direction is greater than the parallel to the pipe axis, fiber reinforced thermoplastic pipes will realize the true sense of the enhancement of perpendicular to the pipe axis direction.This patent provides a key technology for changing the direction of melt flow, namely, an extrusion coating head with a guide plate and a plastic tube coating and reforming device with a coating head.

The two melt flows generated by the two sides of the flow guide plate flow in a subtractive and counterclockwise direction, and are coated on the outer wall of the tube embryo formed by the core tube.Under the action of axial linear velocity applied by the tractor to the pipe, the two melt flows will form a cross arrangement, and the cross Angle is determined by the traction speed and melt velocity.

Thermoplastic tube extrusion coating and molding device (2. Raw material pretreatment device;5. Coating layer feeding extruder;6, extrusion coating machine head;7. Sizing cooling device;8. Traction device;9. Finished pipe coiling device;10. Core tube extrusion machine)

Thermoplastic tube extrusion coating molding is achieved in this way: the head of the extrusion coating machine 6 is provided with two guide plates, by two extruders feeding.One flow guide plate receives the melt plasticized polymer melt from extruder 10 and extrudes the molded core tube. The other flow guide plate receives the melt plasticized polymer melt from extruder 5 and extrudes the coating outside the core tube. After cooling and shaping, the finished tube can be obtained.

The production process of thermoplastic pipe material is to rely on the traction of the tractor to guide the pipe blank to the exit mold into the sizing cooling device. Under the action of the traction, the melt flow formed by the flow guide plate will be stretched in a spiral path around the mandrel, forming a network, which can be called cross compound.The size of spiral Angle is determined by the ratio of extrusion speed and traction speed, and the ideal Angle is the spiral Angle (cross compound Angle), where the annular strength is equal to twice the axial strength.In figure 6, the finished pipe actually has a four-layer structure, and the macromolecular chain in the four layers is oriented along the circumference of the pipe.

3, thermoplastic tube extrusion coating and molding applications

TLCP has the characteristics of high strength, high modulus, high heat resistance, high impact resistance, high wear resistance, high flame resistance, high barrier resistance, corrosion resistance, low creep, low thermal conductivity, etc.However, its easy orientation of macromolecular chains, serious anisotropy of products, and the great difference between the strength of fusion joints and that of non-fusion joints limit the wide application of this product.Using thermoplastic tube extrusion coating molding technology extrusion coating molding TLCP tube, or TLCP/TP alloy tube, TLCP bar macromolecule will be close to perpendicular to the tube axis orientation, this orientation will be mainly reflected in the tube's circumaxial strength, and the defect of low weld joint strength will be compensated by cross composite.

3.1TLCP steam transmission pipeline

When used for conveying steam with higher temperature, compared with metal pipe, it can save a lot of anti-corrosion cost and heat preservation cost, and has a long service life.Compared with traditional extrusion forming method, the bearing capacity of tube can be increased by more than one time.

3.2TLCP crude oil gathering and transportation pipeline

Compared with metal pipe, it can save a lot of anti-corrosion cost, a lot of heat insulation cost, long service life;Compared with traditional extrusion forming method, the bearing capacity of tube can be increased by more than one time.

3.3TLCP/TPU alloy oil well pumping liner

It can be used for oil production within 5000 meters, far more than 2500 meters of UHMWPE liner and 3500 meters of PEX liner.

3.4TLCP/PO alloy oxygen resistant plastic pipe

Water resistance, heat resistance, barrier performance, mechanical properties and other excellent, two-layer structure, performance than the use of EVOH five-layer structure oxygen resistance plastic pipe, waste recovery easy.(1) finished plastic pipe;2. Raw material handling device;3. Tube feeding machine;4. Tube surface preheating plasma treatment device;5. Extruder;6, extrusion coating machine head;7. Shaped cooling device;8. Tractor;9. Oxygen resistive plastic pipe coated with TLCP/PO alloy layer)

Send machine 3 and 8 equal linear velocity, pipe will be semi-finished products tube surface modification or add a new function for coating oxygen layer tube PEXb PEXc tube, and semi-finished products in semi-finished products such as synchronous crosslinking PEXa tube rolling machine 1 tube, for the machine 3 and pipe rolling, 8 drag and into the tubing on pipe surface treatment, surface treatment plant 4 processing method for plasma treatment, corona treatment, or flame treatment, etc., the surface processing of semi-finished products tube into the coating head 6, compared with raw materials processing plant 2 and 5 molten coating layer extruder plasticizing of polymer melt together.In coating head 6, to melt and semi-finished tube axis vertical, along with the intermediate tube outer wall and tangent good or poor clockwise direction, after being coated to the outer surface of the intermediate pipe into the cooling stereotypes, finalize the design water cooling tank 7 * eventually get the extrusion coating on the surface modification of pipe resistance of oxygen tube, oxygen layer and winding machine 9 are collected to the finished product.