The traditional extrusion board production line is a kind of foaming material made of polystyrene by high temperature blending using Freon as foaming agent. Because of its excellent thermal insulation, high compressive resistance, low water absorption, lightweight and other characteristics, it is widely used in building external wall insulation, cold storage, water conservancy engineering, central air conditioning pipeline, cold highway, airport runway, high-speed railway subgrade and so on. However, the production and use of freon will be stopped in the whole industry in 2026 according to the Montreal Protocol, because freon, the blowing agent of extrusion board, is ozone-destroying substances and is listed as a banned product by the international community. Moreover, the market price of freon is over 20,000 yuan per ton and keeps rising. Through years of continuous exploration and research and development, carbon dioxide instead of Freon foam production extrusion board technology has been mature, truly achieved the complete elimination of freON, pure carbon dioxide foam thickness of 100mm, bulk density as low as 27kg/m³.
From an environmental point of view, the elimination of CFC-11 is urgent. From the cost point of view, carbon dioxide per ton of about 800 yuan price, an annual output of 150,000 square meters of carbon dioxide extrusion board production line can save 10 million yuan for the manufacturer of blowing agent cost. Choosing carbon dioxide foam extrusion board production line is now and the only future development direction.
Carbon dioxide foam extrusion board production line, including carbon dioxide front constant pressure pump, carbon dioxide supply device, accelerator supply device, material conveying device, the first static mixer, the first melting screw, the second static mixer, the second extrusion screw, the third static mixer and molding die head.
Firstly, the liquid CO2 is stored in the low-pressure tank (the pressure is about 2MPa, the temperature is constant at -20℃), and transported to the second-order high-pressure buffer tank through the booster pump. The second-order high-pressure buffer tank maintains the liquid CO2 at a higher pressure, and it is injected into the extruder at a quantitative and constant pressure through the metering pump pressurization and flow control unit.
The computer system monitors the environment required by the CO2 foaming process and the working state of the injection system, continuously calculates and feeds back the working data. The system automatically adjusts the parameters according to the fluctuations of the data. Through the high precision mass flow control device equipped with the injection system, the CO2 foaming agent with accurate measurement ratio is transported to the injection point of the production line.
The injection process is to stabilize carbon dioxide in a supercritical state through a constant-pressure pump. Carbon dioxide in the static mixer and mix accelerator, the carbon dioxide with high pressure metering pump mass flowmeter stable injection screw, the first order by the static mixer, third static mixer with polystyrene (PS) plastic grade mix, achieve the goal of stable carbon dioxide injection and smooth foam. Carbon reduction is achieved by using carbon dioxide instead of Freon as a blowing agent to avoid high-potential GHG emissions.
The equipment adopts two stage cooling extrusion mixing element to improve the mixing and cooling effect and the compatibility of CO2 and resin; High mass distribution, dispersion and dissolution of CO2 in polymer melt. The pressure required by extrusion can be quickly adjusted by the pressure regulator, and the temperature required by each area is strictly controlled by automatic temperature control. The system adopts intelligent control of man-machine interface.
Key Technologies:
(1) Carbon dioxide modification technology, the use of alcohol, alkyl phosphate ester, distilled water fully mixed after the generation of promoters and carbon dioxide synergic foaming, significantly improve the compatibility of carbon dioxide and PS plastic and foaming rate;
(2) High pressure mixing technology, under the action of 20MPa high pressure, carbon dioxide and promoters in the high pressure mixer, by shunt → confluence → rotation → re-shunt → re-confluence, repeated action, so that carbon dioxide and promoters (gas, liquid) fully mixed;
(3) Supercritical control technology: carbon dioxide constant pressure system is composed of carbon dioxide constant pressure constant temperature device and carbon dioxide steady pressure injection device, so that carbon dioxide can be stably kept in supercritical state for a long time in the process of injection, and its dissolution power is 100 times that of liquid and gas;
(4) Melt static mixing technology in order to prevent mixing material in the process of transportation and extrusion of carbon dioxide escape phenomenon, developed a two-stage static mixer installed on the screw, so that the material always maintain sufficient mixing state.
