With the popularization and application of highly flame-retardant PIR B1 grade polyurethane, pentane is used as a foaming agent, and the new foaming machine will become the core configuration of the production line. After nearly 20 years of continuous development and optimization, the customization foaming machinehas fully mastered all core technologies and has been successfully applied to multiple production lines at home and abroad. These technologies include: flow control technology, self-cleaning mixing head technology, high-speed shear mixing emulsification technology, with the successful realization of high temperature control technology, it is now patented and researched by Weihua.
WEIHUA Core Pu foaming machine technology
Source： │ Datetime：2020-04-21
The main points of polyurethane foam technology control
1. Strictly control the physical and chemical properties of the original liquid
The chemical properties of polyisocyanate, combined polyether, blowing agent, catalyst and foam stabilizer in black and white materials directly determine the chemical reaction and foam physical properties of the synthetic polyurethane. It is the basic condition for producing qualified polyurethane foam.
The black and white monomers should be clear and viscous liquids without flocculent insoluble impurities. If there are insoluble impurities, it will block the filter screen of the foaming machine, resulting in unstable raw material flow, and the ratio of black and white materials does not meet the requirements. The mixing is uneven. Even the pipeline blocking the foaming machine is not blanked.
In the case of double-shift production of each line of our company, the black and white filter screens of the foaming machine (and premixer) and the needle valve of the nozzle are thoroughly cleaned at least once a week.
2. Strictly control the proportion and injection volume of the original solution
The proportion of black material, combined polyether and cyclopentane must be strictly controlled. When the total injection volume is unchanged, cavitation occurs when the proportion of black material is too large, soft foam occurs when the proportion of white material is too large, foaming occurs when the proportion of cyclopentane is too large, and cavitation occurs when the proportion is too small. If the ratio of black and white material is out of balance, uneven mixing will occur and the foam will shrink.
The amount of injection should be based on process requirements. When the injection volume is lower than the process requirement, the foam molding density will be low, the strength will be low, and even the phenomenon of incompletely filled cavitation will occur. When the injection volume is higher than the process requirements, foaming and leakage will occur, and the box (door) will be deformed.
3. Strictly control the process temperature and curing time
Polyurethane foaming is a more complicated physical and chemical reaction process. The fluctuation of raw materials, molds, preheating temperature and curing time will directly affect the foaming quality.
A. Black material is a relatively active chemical substance, which easily reacts with water. The storage process should ensure that the container is dry and sealed and filled with dry nitrogen protection. It should not be in direct contact with water during use. Storage temperature below 5 ° C will cause crystallization, so care must be taken to prevent freezing. Once crystallization occurs, it should be heated and melted at 70-80 ℃ before use, and fully stirred evenly. Storage temperatures above 50 ° C will produce an insoluble solid with increased viscosity and changes in chemical properties. White materials also have the same properties.
Therefore, it is required that the black and white materials should be stored in a ventilated, cool and dry place at room temperature (20-25 ° C) to avoid the sun and rain.
B. Black and white materials should be treated with constant temperature before foaming, and the foaming temperature should be controlled at 18-25 ℃.
When the temperature is too low, the viscosity of the black and white material is large, the flow rate is unstable, the fluidity is poor, and the mixing is uneven. When the temperature is too low, the reaction speed of the foam generation is slow and the aging time is long. When the curing time is not enough, the cabinet and door still foam after demoulding, and the appearance is deformed.
When the temperature is too high, the reaction is violent and difficult to control. It is prone to uneven performance of the bubble liquid injected into the larger tank. The bubble liquid injected at the beginning has undergone a chemical reaction, the viscosity rapidly increases, and the bubble liquid injected afterwards has not yet reacted. As a result, the bubble liquid injected later cannot push the bubble liquid injected first to the forefront of the foaming process of the box body, and a partial bubble phenomenon occurs in the box body.
C. The temperature of the preheating furnace should be controlled at 30—50 ° C, the temperature of the foaming furnace should be controlled at 35—50 ° C, and the temperature of the foaming mold should be controlled at 35—45 ° C.
In winter, the temperature of the cabinet and door to be foamed is low, and it must be preheated in the temperature of the preheating furnace. Otherwise, when the hot polyurethane liquid touches the cabinet or door, the chemical reaction will be seriously affected, and the bubble liquid and the shell will not stick.
When the temperature of the foaming mold is too low, the fluidity of the foaming system is poor, the curing time is long, the reaction is incomplete, and cavitation occurs; when the temperature of the foaming mold is too high, the plastic liner is heated and deformed, and the foaming system reacts violently. Therefore, the temperature of the foaming mold and the ambient temperature of the foaming furnace must be strictly controlled.
Especially in winter, it is necessary to preheat the foaming mold, the preheating furnace, the foaming furnace, the cabinet and the door for more than 30 minutes when the line is opened every morning. After foaming for a period of time in summer, the foaming system must be cooled down.
D. The foaming and curing time of the black and white material used by our company must be more than 6 minutes. The aging time is too short, the cabinet and door still foam after demolding, and the appearance is deformed. Especially after the door body is deformed, the door seal gap is large, the leakage is cold, the box is not insulated, and the compressor is frequently started.
4. Strictly control the injection pressure of the foaming machine at 13-16MPa
When the injection pressure is unstable, the ratio of black material to white material is unstable and the mixing is insufficient. The difference between the injection pressure of black material and white material is controlled within 5bar, otherwise, the phenomenon of string material damage to the foaming machine will occur.
During the foaming process, you should always check the injection pressure of the foaming machine and clean the injection system of the foaming machine.
The black, white material and cyclopentane are mixed unevenly, which is manifested by the uneven density of the polyurethane foam, large bubbles in the local area, foam cracking, and local softening of the foam: white, yellow or black stripes appear on the foam, and the foam collapses.
Weihua Machinery is good at researching the technology of pu foaming machine in order to provide customers with more productive pu foaming machine. The technical theory of pu foaming machine has been transformed into our products, all the latest pu foaming technology Can be reflected in our products.
tags: pu foaming technology, polyurethane foaming, pu foaming machine, Weihua machinery