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PPR Pipes Increased Mechanical Strength To Improve Production


Zunächst die Grundprinzipien der Kunststoffextrusion

Plastic processing industry is a highly integrated technology industry. It involves the polymer chemistry, polymer physics, interface theory, plastic machinery, plastic processing mold, formula design principles and process control and so on. The theory of extrusion mainly studies the movement and change of plastic in the extruder. The relationship between the three physical states of the polymer,PPR Pipes the relationship between the screw structure, the plastic properties and the processing conditions of the polymer in the different temperature range under the action of a certain external force in the extruder. So as to carry out reasonable process control. In order to achieve the purpose of improving the production and quality of plastic products. Plastic polymer materials, heated at constant pressure, in different temperature range, there are glass, high elasticity, viscous flow of three physical state. General plastic molding temperature above the viscous temperature.

Second, polyolefin pipe extrusion molding process control

The control parameters of the extrusion process include molding temperature, extruder working pressure, screw speed, extrusion speed and traction speed, feeding speed, cooling and so on.

1. Vorbehandlung der Rohstoffe

Polyolefin is a non-absorbent material, usually very low moisture content, can meet the needs of extrusion, but when the polyolefin containing absorbent pigments, such as carbon black, the humidity sensitive. In addition, when the use of materials and fillers, the water content will increase. Moisture not only causes the inside and outside of the pipe to be rough, but also may cause bubbles in the melt. Often the raw materials should be pretreated. General use of drying, can also be added with a corresponding dehumidification function of the additives. Such as defoamers. PE dry temperature is generally 60-90 degrees. At this temperature,PPR Pipes the yield can be increased by 10% to 25%.

2. temperature control

Extrusion molding temperature is necessary to promote the plasticization of molding materials and plastic melt flow. The material of the plastic and the quality and yield of products has a very important impact. Plastic Extrusion The theoretical temperature window is between the viscosity flow temperature and the degradation temperature. The temperature range is wide for polyolefins. Usually above the melting point, 280 degrees or less can be processed. To correctly control the extrusion molding temperature, we must first understand the temperature limit of the material being processed and its physical properties of the relationship. To find out its characteristics and laws in order to choose a better temperature range for extrusion molding. Therefore, the temperature setting should take into account the following aspects: First, the polymer itself, such as melting point,PPR Pipes molecular weight size and distribution, melt index and so on. Followed by the performance of the equipment. Some equipment, the feed section of the temperature on the host of a great impact on the current. Again, by observing the tube die extrusion tube surface is smooth. Whether the bubble and other phenomena to judge.

The extrusion temperature includes the set temperature of the heater and the melt temperature. The heating temperature is the temperature provided by the external heater. The melt temperature refers to the temperature of the material between the front of the screw and the head.

The barrel temperature distribution, from the feed zone to the die, may be flat, incremental, decreasing and mixed. Mainly depends on the material point and the structure of the extruder.

Kopfeinstellung der Temperatur, um ein besseres Aussehen und mechanische Eigenschaften zu erhalten, und die Expansion des Schmelzeaustritts zu reduzieren, ist die allgemeine Kontrolle der Körpertemperatur niedriger, die Maschinenkopftemperatur ist höher. Die Maschinenkopftemperatur ist hoch, kann das Material glatt in die Form bringen, aber die Form des extrudierten Materials ist schlecht, die Schrumpfung nimmt zu. Die Kopftemperatur ist niedrig, der Werkstoff Kunststoff schlecht, Schmelzviskosität, Nasendruck. Obwohl das Produkt dadurch zu dicht wird, ist die Formstabilität der Produkte nach einer geringen Schrumpfungsrate gut, aber die Verarbeitung ist schwieriger, da die Formexpansion größer ist und die Produktoberfläche rauh ist. Aber auch zu erhöhtem Gegendruck-Extruder, Gerätelast, erhöht sich auch der Stromverbrauch.

The temperature of the die set, the temperature of the die and the core mold have an effect on the surface finish of the pipe. In a certain range, the die mold and the core mold temperature are high and the surface finish of the pipe is high. Generally speaking,PPR Pipes the temperature of the die outlet should not exceed 220 degrees, the melt temperature of the inlet of the head is 200 degrees, and the temperature difference between the inlet and outlet of the machine head should not exceed 20 degrees. Because the higher temperature difference between the melt and the metal will cause the shark skin phenomenon. Excessive melt temperature leads to die. But the specific decision to the actual situation.

The melt temperature is the actual temperature of the melt measured at the end of the screw and is therefore the dependent variable. Mainly depends on the screw speed and barrel setting temperature. The upper limit of the melt temperature of the extruded polyethylene pipe is generally defined as 230 degrees. Generally controlled at about 200 degrees is better. Polypropylene pipe extrusion melt temperature limit is generally 240 degrees. Melt temperature should not be too high. Generally consider the degradation of materials,PPR Pipes while the temperature is too high will make pipe material difficult.

3. Pressure control

The most important pressure parameter in the extrusion process is the melt pressure, that is, the head pressure, in general, increase the melt pressure, will reduce the output of the extruder, leaving the product density increased, is conducive to improving product quality. But the pressure is too large,PPR Pipes will bring security problems. Melt pressure and the size of raw materials, screw structure, screw speed, process temperature, the mesh mesh number, porous plate and other factors. The melt pressure is usually controlled between 10 and 30 MPa.

4. vakuumeinstellung

Vacuum stereotypes mainly control the vacuum and cooling speed of the two parameters. Usually in the appearance of the quality of the pipe to meet the premise, the vacuum should be as low as possible, so that the pipe stress is small, the product in the storage process deformation small.

5. abkühlen

Bei der Herstellung von PPR-Rohren sind die Anforderungen an die Kühlwassertemperatur bei der Kühlwassertemperatur im Allgemeinen niedrig, üblicherweise unter 20 Grad. Der erste Absatz der Temperatur kann etwas höher sein, der letzte Teil ist niedriger, was zu einem Temperaturgradienten führt. Es ist auch wichtig, den Kühlwasserstrom einzustellen. Der Durchfluss ist zu groß, die Rohroberfläche ist rau und führt zu Flecken. Durchfluss ist zu klein, PPR Pipe die Oberfläche des Rohrs, um helle Stellen zu erzeugen, die sich leicht abziehen lassen, z. B. ungleichmäßige Verteilung, Rohrwanddicke ungleichmäßig oder oval.

6. Screw speed and extrusion speed

Die Schneckendrehzahl regelt die Extrusionsgeschwindigkeit, den Ertrag und die Produktqualität von Parametern der Schwerindustrie. Die Geschwindigkeit des Einschneckenextruders steigt und die Ausbeute steigt. Die Schergeschwindigkeit nimmt zu und die scheinbare Viskosität der Schmelze nimmt ab. Fördert die Homogenisierung von Materialien. Gleichzeitig aufgrund der guten Plastifizierung, so dass die Wechselwirkung zwischen den Molekülen die mechanische Festigkeit erhöhte. Aber die Schneckendrehzahl ist zu hoch, die Motorlast ist zu groß, der Schmelzedruck ist zu hoch, die Schergeschwindigkeit ist zu hoch, durch die Form Peng-Expansion, die Oberflächenverschlechterung und die Instabilität.

7. Traktionsgeschwindigkeit

Traction speed directly affects the product wall thickness, dimensional tolerance, performance and appearance, traction speed ratio to be stable, and the traction speed and pipe extrusion speed match. The ratio of the traction speed to the extrusion line velocity reflects the degree of orientation that the product may occur, which is called the draw ratio and must be equal to or greater than 1. The traction speed increases and the temperature of the cooling stereotypes is constant , Then the product in the sizing sleeve, cooling the water tank to stay in the time is relatively short, after the cooling of the finished product will also be more inside the residual heat, the heat will make the product in the process of pulling the orientation of the orientation structure has occurred ,PPR Pipes Resulting in a reduction in the degree of orientation of the article. The faster the traction speed, the thinner the wall thickness of the pipe, the greater the shrinkage of the finished product after cooling. The slower the traction speed, the thicker the pipe wall thickness, the more likely to lead to stowage between the die and the sizing sleeve. Destruction of normal extrusion production. Therefore, the extrusion process in the extrusion speed and traction speed must be well controlled.

8. On - line quality control and post - processing of pipe

Polyolefin-based crystalline polymers, the performance of the down-line tubing is different from the size and performance of the pipe product when it is delivered. The main reasons are, first, polyolefin melt cooling process to occur crystallization, crystallinity and crystal form and temperature and thermal history, the time to place. Second, just off the pipe temperature is usually higher than room temperature. Third, just off the assembly line of stress in the pipe. In order to achieve the stability of the performance and size,PPR Pipes the general polyethylene pipe should be placed off the assembly line for 24 hours, the polypropylene pipe to be placed after 48 hours, according to the corresponding standards for performance testing.