Firma Nyheder

PPR-rør øget mekanisk styrke til forbedring af produktionen

2018-11-15

First, the basic principles of plastic extrusion

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.

For det andet, polyolefin rør ekstrudering molding proces kontrol

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. Pretreatment of raw materials

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. temperatur kontrol

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.

Tønde-temperaturfordelingen, fra fødezonen til matricen, kan være flad, inkremental, faldende og blandet. Hovedsageligt afhænger af ekstruderens materialepunkt og struktur.

Head set the temperature, in order to obtain better appearance and mechanical properties, and reduce the melt outlet expansion, the general control of the body temperature is lower, the machine head temperature is higher. The machine head temperature is high, can make the material smoothly into the mold, but the shape of the extruded material is poor, the shrinkage increases. Head temperature is low, the material plastic bad, melt viscosity, nose pressure rise. Although this will make the product too dense, after the shrinkage rate is small,PPR Pipes the product shape stability is good, but the processing is more difficult, from the mold expansion larger, the product surface rough. But also lead to increased backpressure extruder, equipment load, power consumption also increases.

Temperaturen på støbesættet, temperaturen på stansen og kerneformen har en virkning på rørets overfladefinish. I et vist omfang er støbeformen og kerneformstemperaturen høj, og rørets overflade er høj. Generelt må PPR Pipes temperatur på stikkontakten ikke overstige 220 grader, smeltetemperaturen for indgangen på hovedet er 200 grader, og temperaturforskellen mellem indløb og udløb på maskinens hoved må ikke overstige 20 grader. Fordi den højere temperaturforskel mellem smelte og metal vil forårsage hajfænomenet. Overdreven smeltetemperatur fører til at dø. Men den specifikke beslutning til den faktiske situation.

Smeltetemperaturen er den faktiske temperatur af smelten målt ved enden af ​​skruen og er derfor den afhængige variabel. Hovedsageligt afhænger af skruens hastighed og tøndeindstillingstemperatur. Den øvre grænse for smeltetemperaturen af ​​det ekstruderede polyethylenrør er generelt defineret som 230 grader. Generelt styret på omkring 200 grader er bedre. Polypropylenrør ekstrudering smelttemperatur grænsen er generelt 240 grader. Smeltemperaturen bør ikke være for høj. Generelt overvejer nedbrydning af materialer, PPR-rør, mens temperaturen er for høj, vil gøre rørmaterialet vanskeligt.

3. Pressure control

Den vigtigste trykparameter i ekstruderingsprocessen er smeltetrykket, det vil sige, at hovedtrykket i almindelighed øger smeltetrykket, vil reducere ekstruderens udgang, idet produktdensiteten øges, bidrager til at forbedre produktkvaliteten. Men trykket er for stort, PPR Pipes vil medføre sikkerhedsproblemer. Smeltryk og størrelsen af ​​råmaterialer, skrueopbygning, skruehastighed, processtemperatur, maskestørrelse, porøs plade og andre faktorer. Smeltepresset reguleres sædvanligvis mellem 10 og 30 MPa.

4. Vacuum setting

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. cool down

Polyethylene pipe extrusion molding in the cooling water temperature requirements are generally low, usually below 20 degrees, in the production of PPR pipe, the first paragraph of the temperature can be slightly higher, the latter part of the lower, resulting in a temperature gradient. It is also important to adjust the cooling water flow. Flow is too large, the pipe surface rough, resulting in spot pits. Flow is too small,PPR Pipes the surface of the pipe to produce bright spots easy to pull off, such as uneven distribution, pipe wall thickness uneven, or oval.

6. Screw speed and extrusion speed

Screw speed is to control the extrusion rate, yield and product quality of heavy industry parameters. The speed of the single screw extruder increases and the yield increases. The shear rate increases and the apparent viscosity of the melt decreases. Is conducive to the homogenization of materials. At the same time due to good plasticization, so that the interaction between the molecules increased mechanical strength. But the screw speed is too high, the motor load is too large, the melt pressure is too high, the shear rate is too high, from the mold Peng expansion, the surface deterioration, and the amount of instability.

7. Traktionshastighed

Traktionshastigheden har direkte indvirkning på produktets vægtykkelse, dimensionstolerance, ydeevne og udseende, trækhastighedshastighed for at være stabil, og trækkrafthastigheden og rørekstruderingshastigheden matcher. Forholdet mellem trækkrafthastigheden og ekstruderingslinjens hastighed afspejler orienteringsgraden, at produktet kan forekomme, hvilket kaldes trækforholdet og skal være lig med eller større end 1. Trækspændingen øges, og køle-stereotypernes temperatur er konstant, så produktet i dimensioneringsmuffen, køling af vandtanken for at forblive i tiden er relativt kort, efter at kølingen af ​​det færdige produkt også vil være mere inde i restvarmen, vil varmen gøre produktet i færd med at trække Orienteringen af ​​orienteringsstrukturen er sket, PPR-rør resulterer i en reduktion i artiklens orienteringsgrad. Jo hurtigere trækkraften, jo tyndere rørets vægtykkelse, desto større krympning af det færdige produkt efter afkøling. Jo langsommere trækkraften, jo tykkere rørvægtykkelsen, jo mere sandsynligt vil det føre til stuvning mellem matricen og størrelsesmuffen. Destruktion af normal ekstruderingsproduktion. Derfor skal ekstruderingsprocessen i ekstruderingshastigheden og trækkraften styres godt.

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

Polyolefinbaserede krystallinske polymerer, udførelsen af ​​den nedadrettede slange er forskellig fra rørproduktets størrelse og ydeevne, når den leveres. Hovedårsagerne er for det første polyolefin smeltekøleprocessen at forekomme krystallisation, krystallinitet og krystalform og temperatur og termisk historie, tiden til sted. For det andet, lige uden for rørets temperatur er det normalt højere end stuetemperatur. For det tredje, lige udenfor forsamlingslinjen af ​​stress i røret. For at opnå stabilitet i ydeevne og størrelse, skal PPR Pipes det generelle polyethylenrør placeres fra samlebåndet i 24 timer, polypropylenrøret, der skal placeres efter 48 timer i overensstemmelse med de tilsvarende standarder for ydeevneprøvning.