In December 2021, we received an inquiry from Mr. Hairun in Malaysia. Mr. Hairun is a mattress manufacturer in need of producing rebonded foam. He had limited knowledge about machine usage and selection and had no prior experience with the production process. Therefore, he required guidance from experts who could assist him from the ground up.



We systematically explained the principles of foam production to Mr. Hairun, along with the necessary materials and equipment. We also took him on a tour of our factory to provide a clear understanding of the entire production process.



After understanding Mr. Hairun's preferences for the rebonded foam, including density, softness, and market prices, we offered him the most suitable foam production solution. We also provided him with information on foam production costs and compared raw material prices for his reference.



Based on the client's needs, budget, and existing factory layout, we devised a cost-effective machine configuration and layout plan for his facility, including an assessment of startup costs.



Once the machines were successfully installed, our team of engineers provided Mr. Hairun with one-on-one foam production training. When he successfully produced the foam he desired for the first time, he called us and said, "I am happy with crying, thank you very much!" Afterward, he purchased a batch foam machine from us and continued to reorder foam chemical materials from our company.

Phase One: Gas Nucleation Process

The raw materials react in the liquid phase or rely on the generation of gas substances and gas volatilization during the reaction. As the reaction progresses and a large amount of heat is generated, the amount of gas substance generated and volatilized continuously increases. When the gas concentration exceeds the saturation concentration, fine gas bubbles begin to form in the solution phase and rise. As the reaction nears its end, a milky phenomenon appears in the liquid polyurethane material, known as the "milky time."



Phase Two: Self-nucleation Process

In this stage, the gas concentration continues to increase and reaches a certain level. After that, the gas concentration gradually decreases, and new bubbles no longer form. The gas in the solution gradually reaches an equilibrium saturation concentration. During this stage, the viscosity of the liquid material gradually increases, and the gas continuously merges and expands in the gradually viscous liquid phase. The volume of the bubbles continues to expand. The viscous liquid phase forming the outer wall of the bubbles gradually thins. Due to the surface tension relationship between the gas and liquid interfaces, the bubble volume increases from small to large, gradually transforming from a spherical shape into a three-dimensional geometric shape composed of polymer thin films, finally forming an open network structure of three-dimensional micropores. In the synthesis process of polyurethane foam, this stage exhibits polymer volume expansion and foam rising.



Phase Three:

After the gas concentration drops to a certain level, bubbles no longer form. With the permeation of the gas, the concentration continues to decrease, reaching the final saturated equilibrium in the process of the polymeric foam wall transitioning from a viscous liquid state to a non-flowing solid state.

Foam scorching is a common phenomenon encountered in actual foam production. Below are the reasons behind this issue along with potential solutions:



(1) Issues with the quality of polyether polyols: During production and transportation, the product's water content exceeds the standard, there is an excess of peroxides and low-boiling-point impurities, the concentration of metal ions is too high, and there is improper selection and concentration of antioxidants.



(2) Formulation: In low-density formulations, the TDI index is too high, the proportion of water to physical blowing agents in the foaming agent is improper, the amount of physical blowing agent is insufficient, and there is excessive water content.



(3) Climate impact: In summer, high temperatures lead to slow heat dissipation, high material temperatures, high air humidity, and the temperature at the reaction center exceeds the antioxidant temperature.



(4) Improper storage: When the TDI index increases, the accumulated heat energy during post-maturation causes an increase in internal temperature, leading to scorching.

I. Advantages of Polyurethane On-site Foaming Technology:



The method of on-site foaming, spraying (or pouring) polyurethane foam insulation layer, has the surface as a whole without seams, reducing heat loss, with high construction efficiency, easy to meet quality requirements, reducing construction procedures, and eliminating the need for anti-corrosive coatings on pipe surfaces.



II. Polyurethane On-site Foaming Construction Process Principle:



The principle of polyurethane foam plastic foaming and spraying, pouring process is that polyether isocyanate can undergo a polycondensation reaction to form amine methacrylate, which can generate the required polyaminomethyl ethyl, commonly known as polyurethane foam plastic. Catalysts, crosslinking agents, foaming agents, foam stabilizers, etc., are simultaneously added during the reaction to promote and perfect the chemical reaction.



These raw materials are divided into two groups, fully mixed, and then pumped into a special spray gun by metering pumps in proportion. They are fully mixed and sprayed on the surface of pipelines or equipment in the spray gun or pouring mixer, react, foam, and form foam plastic within 5-10 seconds, which then cures and solidifies.



III. Polyurethane On-site Foaming Construction Methods:



Spraying Method: According to this formula, two groups of solutions are stored in two barrels respectively. The materials are filtered to the metering pump, driven by a pneumatic motor, and input into the gun body through the material tube. Compressed air regulates the material into the mixing chamber, mixed, and then sprayed onto the pipeline or equipment to foam and form.



Pouring Method: The prepared two groups of solutions are stored in barrels, filtered to the metering pump, driven by a pneumatic motor, and input into the pouring mixer through the material tube. Compressed air is introduced into the pouring motor, driving the stirring shaft to mix the two groups of materials, which are then injected into the mold for foaming and forming.



Precautions for Polyurethane On-site Foaming Construction:



Stir the material at room temperature to mix and react, then quickly pour it into the space that needs to be formed. During construction, control the reaction foaming time so that the mixed material after stirring is in a liquid state when poured into the gap. During the foaming process, significant expansion forces will be generated, so proper reinforcement should be made to the pouring interlayer or mold.

1. Adjust Formulation:

Control the amount of water to not exceed 4.5 parts, and if necessary, use low-boiling-point liquid compounds as auxiliary foaming agents to replace some water. Pay attention to the amount of water in the formulation, which must not exceed 5 parts. The highest safe temperature rise point for low-density foam is 160°C, and it must not exceed 170°C.



2. Strictly Control the Accuracy of Component Measurement:

During continuous block foam production, adjust the discharge speed of the mixing head material and the conveyor belt speed to coordinate them. Avoid phenomena such as under-foaming materials flowing into the bottom of already foaming materials due to slow conveyor belt speed or excessive discharge, which can prevent normal foaming, resulting in collapse. Collapsed materials are not easily able to produce localized "gas species," leading to localized heat accumulation and increased risk of scorching. In actual production, poor process parameters may result in small yellow scorching lines appearing at the bottom of foam blocks.



3. Avoid Compressing the Newly Produced Foam:

This is because compressing the foam before it is fully cured affects the foam network and structure. It also prevents heat accumulation due to compression, increasing the risk of self-ignition of new foam. Especially during the most sensitive stage of foam rising, any operational errors and vibrations, such as sudden movements caused by tight conveyor belt chains or excessive folding of isolation paper and belt shaking, can cause compression of immature foam, leading to scorching.



4. Strictly Observe the Curing and Storage Process of Foam:

For the production of polyurethane soft block foam, the curing process of new foam is a high-risk period for fire accidents. Due to the high internal temperature and long duration of heat dissipation in large block foams, the time to reach the highest internal temperature is usually about 30 to 60 minutes, and it takes 3 to 4 hours or longer for it to slowly decrease. During this time, the new foams have left the production line and entered the curing and storage phase, which is easily overlooked. Without proper monitoring measures, it can easily lead to fires. There have been reports that when producing block soft foam with a density of 22kg/? using a polyol with a molecular weight of over 5000, 4.7 parts of water, and 8 parts of F-11 with a TDI index of 1.07, a small amount of light yellow smoke was observed 2 hours later. Although the external temperature of the foam was not high, the interior was in a very dangerous initial stage of decomposition, with a temperature of around 200-250°C, already beginning to self-ignite.



5. To Prevent Self-Ignition of Foam:

Newly produced foam should be cured and stored, not exceeding 3 layers when stacked, with a spacing of more than 100mm between layers, preferably placed separately. The curing and storage phase should have dedicated personnel for enhanced monitoring, such as measuring the internal temperature of the foam every 15 minutes for at least 12 hours, or even longer, before normal storage. For foams that may generate high temperatures, large foam blocks should be cut horizontally (e.g., with a thickness of 200mm) to facilitate heat dissipation. When smoke or self-ignition is detected, use water spray or fire extinguishers, and do not move the foam or open doors and windows indiscriminately to prevent increasing airflow and exacerbating the fire.