Beginners are concerned that if the settling plate is not adjusted properly, the liquid flowing out of the nozzle may cause front surging or back surging, affecting the foaming process. Within two minutes after starting the machine, the reaction speed gradually increases, sometimes requiring adjustments to the settling plate. Adjustments to the settling plate are more critical in low-density and high-moisture-content (MC) formulas.



TDI (Toluene Diisocyanate) flow rate can be calculated to correspond to the scale value, but it is recommended to actually measure the TDI flow rate during the first foaming. Flow rate is too important; if the flow rate is not accurate, everything else will be a mess. It's best to rely on the simplest and most intuitive method of measuring the flow rate.



When mixing powders, the mixed stone powder should be left overnight and production should start the next day. For ingredients containing melamine and stone powder, it is recommended to first mix melamine with polyether for a period of time before adding the stone powder.



Foam machine formulas with long mixing chamber in the machine head or more teeth on the stirring shaft usually have less amine and lower material temperature. Conversely, foam machine formulas with short mixing chamber in the machine head or fewer teeth on the stirring shaft usually have more amine and higher material temperature.



For the same formula, when switching between dual-spray swivel heads and single-spray swivel heads with similar nozzle cross-sectional areas, the requirements for mesh thickness and layers are similar.



For the calibration of minor material flow, one method is to measure the return flow of the minor material, and the other is to calibrate it by dividing the total amount used by the foaming time. When there is a significant difference between the two calibration methods, rely on the data from the second calibration method.



Formulas for high-quality soft foam are usually within an unstable range, such as a low TDI index, low water-to-MC ratio, low T-9 dosage, and low silicone oil dosage.

Polyurethane soft foam plastic is one of the important products in the polyurethane industry. Its production necessarily involves the use of organic amine catalysts, especially organic tertiary amine catalysts. This is because organic tertiary amine catalysts play a significant role in the main reactions of polyurethane foam formation: the reactions of carbon dioxide and molecular polymerization, promoting rapid expansion of reaction mixtures, increased viscosity, and sharp increase in polymer molecular weight. These conditions are essential for the formation of foam bodies, ensuring that soft foam plastics have advantages such as low density, high strength-to-weight ratio, high resilience, and comfort for sitting and lying. There are many types of organic amine catalysts that can be used for polyurethane soft foam plastics. Among them, the highly efficient catalysts recognized by various manufacturers are: triethylene diamine (TDEA) and bis(dimethylaminoethyl) ether (referred to as A1). These are also the most widely used organic amine catalysts in the world today, with the highest consumption among various catalysts.



Due to the molecular structural differences between TDEA and A1 catalysts, there are significant differences in their catalytic performance, particularly in their reactions to carbon dioxide gas and molecular polymerization. If the user does not pay attention to these differences in production, not only will they fail to produce qualified foam products, but it will also be difficult for foam bodies to form. Therefore, understanding and mastering the performance differences between these two catalysts in polyurethane foam production is of great significance. TDEA exists in a solid state under normal conditions, making its application less convenient. In actual production, low molecular weight alcohol compounds are commonly used as solvents, formulated into 33% solutions for ease of use, commonly referred to as A33. On the other hand, A1 is a low-viscosity liquid that can be directly applied. Below is a comparison of the catalytic performance differences between A1 and A33 in the production of polyurethane soft foam plastics.



A33 has a 60% catalytic function for the reaction with carbon dioxide gas and a 40% catalytic function for molecular polymerization. It has a low effective utilization rate of carbon dioxide gas, resulting in lower foaming height and higher foam density. Since most of the catalytic function is used for molecular polymerization reactions, it is easy to produce closed-cell foam bodies, which are stiff with low rebound, and the adjustable range of tin catalysts becomes narrower. To achieve the same catalytic function, the amount used is 33% more than A1. Both the bottom skin and outer skin of the foam body are thicker. Increasing the amount can increase the reaction speed, but the amount of tin catalyst must be reduced accordingly, otherwise closed-cell foam bodies will be produced.



A1 has an 80% catalytic function for the reaction with carbon dioxide gas and a 20% catalytic function for molecular polymerization. It has a high effective utilization rate of carbon dioxide gas, resulting in higher foaming height and lower foam density. Since most of the catalytic function is used for gas generation reactions, it is easy to produce open-cell foam bodies, which are soft with high rebound, and the adjustable range of tin catalysts becomes wider. To achieve the same catalytic function, the amount used is less than A33. Both the bottom skin and outer skin of the foam body are thinner. Increasing the amount can increase the reaction speed, but the amount of tin catalyst must be increased accordingly, otherwise over-foaming and cracking may occur.



In terms of overall performance between TDEA and A1, A1 has a higher comprehensive catalytic performance than triethylene diamine. Its actual application effects are also better, although not as convenient as triethylene diamine in terms of transportation and storage. Currently, the vast majority of mechanical continuous foam production facilities almost exclusively use A1, while all box-type foam production facilities use TDEA. However, this is not absolute. With a clear understanding of the differences between the two and appropriate formulation adjustments, they can be interchangeable and both can produce excellent foam products.

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.

Surfactants used for foam stabilization, also known as foam stabilizers, are a crucial additive in the production of polyurethane foam plastics. When selecting surfactants, what factors should be considered?



Surfactants can be divided into two types: soft foam surfactants and hard foam surfactants. Let's examine each:



Soft Foam Surfactants:

During the initial foaming stage, soft foam surfactants can dissolve to form polyurea, and in the later stages, they can assist in cell opening and bursting. Therefore, when selecting soft foam surfactants, the following factors need to be considered:



1. The activity of the surfactant;

2. The relationship between the operating range of the surfactant and the required dosage range;

3. The impact of the various components of the surfactant on the operating range.



Hard Foam Surfactants:

Hard foam surfactants have a higher degree of cross-linking, making bubbles more stable. They are commonly used for molded products or foaming in restricted cavities. When selecting hard foam surfactants, the following factors need to be considered:



1. Strong emulsification capability of the raw material components;

2. Ability to control the size of the foam cells effectively;

3. Ability to improve material flowability and ensure uniform density distribution.



Surfactants not only play a role in foam stabilization but also affect foam density, elasticity, tensile strength, and other properties. Therefore, when choosing surfactants, factors such as the activity of the raw materials, operating conditions, and foaming process need to be considered.

In polyurethane flexible foams, dichloromethane (MC) is often used to adjust the density and hardness of the foam. With a boiling point of only 40.4°C, during foaming, the reaction of water and TDI generates a large amount of heat, causing MC to evaporate into gas, thus expanding the foam body and reducing foam density.



The vaporization of MC consumes a lot of heat, which can affect the foaming process of the foam in some cases. The following two figures show the changes in the maximum foam temperature and the time to reach it after adding different amounts of MC to a specific formula.



From the charts, it can be observed that after adding MC, the maximum foam temperature decreases significantly, and the time to reach the maximum temperature also increases.



These are just changes in data, but how do they manifest during the actual foaming process? To understand this, let's briefly look at the polyurethane reaction process.



The main reaction in polyurethane foaming is the reaction of water and isocyanate to produce carbon dioxide and amine, and the reaction of polyether polyol and isocyanate to produce polyurethane. However, there are many secondary reactions, summarized as reactions generating urethane and reactions generating urea.



Secondary reactions change the molecular structure of the polymer from linear to cross-linked. Due to different reaction conditions and raw materials, the structure of polyurethane can vary greatly. In general, the more secondary reactions, the more complex the cross-linked structure, resulting in increased hardness and improved tear strength. Of course, the resistance to yellowing also improves, but that's another topic. Increasing the foaming index will strengthen secondary reactions.



Having said so much, what does this have to do with MC? Secondary reactions are all endothermic reactions, requiring heat absorption. However, the vaporization of MC also requires a large amount of heat, thus creating a competitive relationship. Adding a large amount of MC will significantly weaken secondary reactions, increasing the proportion of linear structures in the foam, making it softer, and decreasing thermal plasticity.



Even in colder temperatures during winter, attention should be paid to this issue. Properly increasing the water content in the formula to generate more heat helps maintain the physical properties of the foam without significant changes.