End-to-end solutions from raw materials to production equipments for PU foam and mattress-Sabtech
What Is Foam Cutting Equipment?
In recent years, foam cutting equipment has become the most popular product of Sabtech Technology Limited. We pay great attention to the product details and we push the design team to make great technical improvements. At the same time, we're concerned about the selection of raw materials and we eliminated quality problems from the source. Only reliable raw material suppliers can cooperate strategically with us.
The trends are constantly changing. However, Sabtech products are the trend that's here to stay, in other words, these products are still leading the industrial trend. The products are among the top recommendable products in the industrial rankings. Since the products deliver more value than expected, more customers are willing to establish long-term cooperation with us. The products are expanding their influence in the international market.
Customization for foam cutting equipment and fast delivery are available at Sabtech Technology Limited. Besides, the company is dedicated to providing timely product delivery.
Manufacturing polyurethane filter foam typically involves two key stages. The first stage involves preparing open-cell or partially open-cell polyurethane foam according to the desired porosity. If the foam is closed-cell, it needs to be subjected to roller compression to rupture the cell walls, thereby creating the necessary porous structure. The second stage is to remove all the cell membranes to form a reticulated structure.
To produce polyurethane filter foam, the size of the pores and the structure of the network of the foam are largely determined by the catalyst, foaming agent, and surfactant.
In practical operations, there are two common methods for forming the network:
First is the alkali hydrolysis method. The steps of this method involve immersing the soft polyester-type polyurethane foam obtained from the first stage in a 10% sodium hydroxide solution at 50 degrees Celsius for about 10 minutes. Then it goes through processes such as washing with water, neutralization with acetic acid, another round of water washing, and drying, resulting in the final product of polyurethane filter foam.
Another method is the combustion method, also known as the explosion method. This method requires placing the soft polyether-type or polyester-type polyurethane foam obtained from the first stage into a sealed container. The container is then evacuated to 13.3 Pa, followed by the introduction of oxygen and natural gas (in a volumetric ratio of 2:1), bringing the internal pressure of the container to a certain level (which increases with the porosity). Next, the gas inside the container is ignited using a spark plug. The heat generated from the combustion process will burn off or melt the cell membranes without damaging the cell struts. Finally, the resulting product after combustion is cleared with air, and the filter foam is removed from the container.
Both of these methods are effective ways to prepare polyurethane filter foam, and the specific choice between them depends on the material of the foam and the desired structural characteristics.
To produce polyurethane filter foam, the size of the pores and the structure of the network of the foam are largely determined by the catalyst, foaming agent, and surfactant.
In practical operations, there are two common methods for forming the network:
First is the alkali hydrolysis method. The steps of this method involve immersing the soft polyester-type polyurethane foam obtained from the first stage in a 10% sodium hydroxide solution at 50 degrees Celsius for about 10 minutes. Then it goes through processes such as washing with water, neutralization with acetic acid, another round of water washing, and drying, resulting in the final product of polyurethane filter foam.
Another method is the combustion method, also known as the explosion method. This method requires placing the soft polyether-type or polyester-type polyurethane foam obtained from the first stage into a sealed container. The container is then evacuated to 13.3 Pa, followed by the introduction of oxygen and natural gas (in a volumetric ratio of 2:1), bringing the internal pressure of the container to a certain level (which increases with the porosity). Next, the gas inside the container is ignited using a spark plug. The heat generated from the combustion process will burn off or melt the cell membranes without damaging the cell struts. Finally, the resulting product after combustion is cleared with air, and the filter foam is removed from the container.
Both of these methods are effective ways to prepare polyurethane filter foam, and the specific choice between them depends on the material of the foam and the desired structural characteristics.
In modern industrial production, polyurethane flexible foam play an important role in various fields such as furniture, automotive seats, and shoe insoles. However, the key technical control points for producing high-quality polyurethane flexible foam plastic products cannot be overlooked. Here are several key technical points in the production process:
Control of Toluene Diisocyanate (TDI):
The optimal isomeric ratio of TDI is 80/20. If this ratio is exceeded, it can lead to the formation of large and closed cells in the foam, prolonging the curing time. Particularly in the production of large block low-density foam products, an excessive isomeric ratio can delay heat release, potentially causing the foam center temperature to remain high for a long time, leading to carbonization and even ignition. If the isomeric ratio is too low, the foam product's density and resilience will decrease, and fine cracks may appear on the foam surface, resulting in poor process repeatability.
Addition of External Blowing Agents:
External blowing agents (water) not only reduce the density of the foam but also improve the softness of the product and help remove reaction heat. To prevent center carbonization in the foaming process of large block foam products, a certain amount of water is usually added. However, as the amount of water increases, the amount of catalyst should also increase correspondingly; otherwise, it may prolong the post-curing time of the foam. Generally, for every 5 parts increase in water, 0.2 to 0.5 parts of silicone oil should be added.
Catalyst Ratio:
Organic tin and tertiary amine catalysts are commonly used to control the NCO-OH and NCO-H2O reactions. By adjusting the ratio of different catalysts, the growth of polymer chains and the foaming reaction can be controlled. Under certain product densities, choosing the appropriate catalyst ratio can control the foam's open-cell rate, cell size, and void load value. Increasing the amount of organic tin catalyst can generally produce foams with smaller cell sizes, but excessive use may increase the closed-cell rate. It is necessary to determine the optimal catalyst dosage through experiments to achieve the best performance of foam products.
Foam Stabilizers:
The role of foam stabilizers is to reduce surface tension of the material, making the foam film wall elastic and preventing foam wall rupture until the molecular chain growth and cross-linking reactions lead to material solidification. Therefore, foam stabilizers play a critical role in the production of one-step polyether sponge and must be strictly controlled in usage.
Temperature Control:
The foam generation reaction is highly sensitive to temperature, and changes in material and foaming temperature will affect foaming operations and physical properties. Therefore, temperature control is one of the important conditions to ensure stable foaming processes. The material temperature is generally controlled at 20-25°C.
Stirring Speed and Time:
The stirring speed and time affect the amount of energy input during the foaming process. If stirring is uneven, a large number of bubbles may appear on the foam surface, leading to defects such as cracking. During mixing of Component A, the speed is 1000r/min; after Component B is added to Component A, the high-speed stirring speed is 2800-3500r/min for 5-8 seconds.
In summary, the key technologies for producing polyurethane flexible foam include controlling TDI, adding external blowing agents, adjusting catalyst ratios, using foam stabilizers, temperature control, and controlling stirring speed and time. Proper control of these technical parameters can ensure the production of stable quality and high-performance polyurethane flexible foam plastic products.
Control of Toluene Diisocyanate (TDI):
The optimal isomeric ratio of TDI is 80/20. If this ratio is exceeded, it can lead to the formation of large and closed cells in the foam, prolonging the curing time. Particularly in the production of large block low-density foam products, an excessive isomeric ratio can delay heat release, potentially causing the foam center temperature to remain high for a long time, leading to carbonization and even ignition. If the isomeric ratio is too low, the foam product's density and resilience will decrease, and fine cracks may appear on the foam surface, resulting in poor process repeatability.
Addition of External Blowing Agents:
External blowing agents (water) not only reduce the density of the foam but also improve the softness of the product and help remove reaction heat. To prevent center carbonization in the foaming process of large block foam products, a certain amount of water is usually added. However, as the amount of water increases, the amount of catalyst should also increase correspondingly; otherwise, it may prolong the post-curing time of the foam. Generally, for every 5 parts increase in water, 0.2 to 0.5 parts of silicone oil should be added.
Catalyst Ratio:
Organic tin and tertiary amine catalysts are commonly used to control the NCO-OH and NCO-H2O reactions. By adjusting the ratio of different catalysts, the growth of polymer chains and the foaming reaction can be controlled. Under certain product densities, choosing the appropriate catalyst ratio can control the foam's open-cell rate, cell size, and void load value. Increasing the amount of organic tin catalyst can generally produce foams with smaller cell sizes, but excessive use may increase the closed-cell rate. It is necessary to determine the optimal catalyst dosage through experiments to achieve the best performance of foam products.
Foam Stabilizers:
The role of foam stabilizers is to reduce surface tension of the material, making the foam film wall elastic and preventing foam wall rupture until the molecular chain growth and cross-linking reactions lead to material solidification. Therefore, foam stabilizers play a critical role in the production of one-step polyether sponge and must be strictly controlled in usage.
Temperature Control:
The foam generation reaction is highly sensitive to temperature, and changes in material and foaming temperature will affect foaming operations and physical properties. Therefore, temperature control is one of the important conditions to ensure stable foaming processes. The material temperature is generally controlled at 20-25°C.
Stirring Speed and Time:
The stirring speed and time affect the amount of energy input during the foaming process. If stirring is uneven, a large number of bubbles may appear on the foam surface, leading to defects such as cracking. During mixing of Component A, the speed is 1000r/min; after Component B is added to Component A, the high-speed stirring speed is 2800-3500r/min for 5-8 seconds.
In summary, the key technologies for producing polyurethane flexible foam include controlling TDI, adding external blowing agents, adjusting catalyst ratios, using foam stabilizers, temperature control, and controlling stirring speed and time. Proper control of these technical parameters can ensure the production of stable quality and high-performance polyurethane flexible foam plastic products.
Density:
A. PU flexible foams with high density have many small pores, appearing fuller. However, the higher the density, the poorer the water absorption.
B. Generally, PU flexible foams with high density also have high hardness, but it is not ruled out that some high-density foams may add super soft additives, making the sponge very soft. Therefore, PU flexible foams of the same density may have different degrees of softness or hardness.
C. High-density foams are often used for sound-absorbing cotton, sofa cushions, soft packaging materials, etc. Medium and low-density foams are generally used for protective materials.
Resilience:
A. Slow rebound foams, also known as inert foams, memory foams, zero-pressure feeling foams, etc. Slow rebound foams have a "honeycomb" structure, so they cannot quickly return to their original shape after being compressed.
B. Characteristics of slow rebound foams: good water absorption, sound insulation performance; strong toughness, high tensile strength, good shock absorption and cushioning performance; good heat insulation and thermal insulation, can withstand severe cold and heat.
C. High rebound foams have a mixture of pore sizes, different skeleton thicknesses, and a high open hole rate. When compressed, they produce rebound forces with different supporting forces in different deformation states.
D. High rebound foams have super strong resilience and breathability; excellent anti-fatigue performance and flame retardancy; the feel is similar to latex surface.
A. PU flexible foams with high density have many small pores, appearing fuller. However, the higher the density, the poorer the water absorption.
B. Generally, PU flexible foams with high density also have high hardness, but it is not ruled out that some high-density foams may add super soft additives, making the sponge very soft. Therefore, PU flexible foams of the same density may have different degrees of softness or hardness.
C. High-density foams are often used for sound-absorbing cotton, sofa cushions, soft packaging materials, etc. Medium and low-density foams are generally used for protective materials.
Resilience:
A. Slow rebound foams, also known as inert foams, memory foams, zero-pressure feeling foams, etc. Slow rebound foams have a "honeycomb" structure, so they cannot quickly return to their original shape after being compressed.
B. Characteristics of slow rebound foams: good water absorption, sound insulation performance; strong toughness, high tensile strength, good shock absorption and cushioning performance; good heat insulation and thermal insulation, can withstand severe cold and heat.
C. High rebound foams have a mixture of pore sizes, different skeleton thicknesses, and a high open hole rate. When compressed, they produce rebound forces with different supporting forces in different deformation states.
D. High rebound foams have super strong resilience and breathability; excellent anti-fatigue performance and flame retardancy; the feel is similar to latex surface.
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.
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.
Soft polyurethane foam often encounters various accidents and problems during actual foaming production, each of which is caused by multiple factors. In the analysis of accidents caused by complex factors, it is generally difficult to list all influencing factors and the main factors that actually play a role. Below are 15 frequently encountered problems and their polyurethane foam defects moisture contamination porosity causes, let's take a look together!
1. High closed-cell content
a. Polyether polyols: high proportion of ethylene oxide, high activity, often occurs when switching to polyether polyols with different activities.
b. Process formulation: excessive tin octoate usage, high isocyanate activity, high crosslinking degree, rapid crosslinking speed, excessive amines and physical blowing agents causing low internal pressure of foam, inability to open cells when foam elasticity is high, and high TDI index can also result in high closed-cell content.
2. Shrinkage (gelation speed greater than foaming speed)
a. High closed-cell content, shrinkage during cooling.
b. Process conditions: low air temperature, low material temperature.
c. Process formulation: excessive silicone oil, excessive physical blowing agent, low TDI index.
3. Internal cracking
a. Process conditions: low air temperature, high reaction center temperature.
b. Process formulation: low TDI index, excessive tin content, high early foaming strength.
c. High activity of silicone oil, small usage.
4. Top cracking (unbalanced gasification gelation speed)
a. Process conditions: low air temperature, low material temperature.
b. Process formulation: insufficient catalyst usage, small amine usage, poor quality silicone oil.
5. Bottom corner cracking (excessive amine usage, too fast foaming speed)
Large pore surface: excessive physical blowing agent, poor quality silicone oil and catalyst.
6. Poor low-temperature performance of foam
Poor intrinsic quality of polyether polyols, same hydroxyl value, low functionality, high unsaturation, low TDI index with the same tin usage.
7. Poor air permeability
a. Weather conditions: low air temperature.
b. Raw materials: high polyether polyols, high activity silicone oil.
c. Process formulation: excessive tin or same tin usage, low water and amine content, high TDI index.
8. Poor resilience
a. Raw materials: high activity polyether polyols, low relative molecular weight, high activity silicone oil.
b. Process formulation: large amount of silicone oil, excessive tin content, more water at the same tin usage, high TDI index.
9. Poor tensile strength
a. Raw materials: excessive low molecular weight polyether polyols, low hydroxyl value functionality.
b. Process formulation: insufficient tin causes poor gelation reaction, high TDI index at the same tin usage, low crosslinking degree with less water.
10. Smoking during foaming
a. Excessive amine causes a large amount of heat to be released from the reaction of water and TDI, evaporating low boiling point substances and causing smoking.
b. If not charring, the smoke is mostly composed of TDI, low boiling point substances, and monomeric cycloalkanes in polyether polyols.
11. Foam with white streaks
Fast foaming and gelation reaction speed, slow transmission speed in continuous foaming, local compression to form a dense layer, resulting in white streaks phenomenon. The transmission speed should be increased promptly, or the material temperature should be reduced, and catalyst usage should be decreased.
12. Brittle foam
The formula has excessive water, resulting in many unreacted urea formations that are not dissolved in silicone oil, poor tin catalyst usage, insufficient crosslinking reaction, high content of low relative molecular weight polyether polyols, excessively high reaction temperature, and ether bond breakage which reduces foam strength.
13. Foam density lower than set value
Foaming index is too large due to inaccurate metering, high air temperature, low air pressure.
14. Foam with skin, edge skin, bottom voids
Possible Causes: Excessive tin catalyst and insufficient amine catalyst. Slow foaming speed while gel reaction happens too fast; poor mixing efficiency; unstable material feeding rate.Troubleshooting Steps: Adjust amine‑tin catalyst balance; inspect foaming machine mixing head and metering pumps; check raw‑material temperature consistency.
15. High elongation at break
a. Raw materials: high activity polyether polyols, low functionality.
b. Process formulation: insufficient crosslinking due to low TDI index, excessive tin, and high silicone oil content.
Common scenario：Defects persist after formula modification
Lots of foam manufacturers come across this real‑factory pain point: all raw‑material tests pass, formula parameters follow lab specification, yet finished foam still shows cracks, shrinkage or uneven density.
Very often, this points to hardware limitations: inconsistent component metering, insufficient mixing performance, or unstable temperature control on existing foaming machines.
Sabtech equipment is built for stable long‑run production, not only for perfect lab‑condition test runs. Our batch foaming machines and SAB‑CF13 continuous slabstock foaming line focus on metering precision and mixing homogeneity for daily mass‑production.
Still struggling with unstable foam quality in your daily production? Share your defect phenomenon, target foam type (mattress / HR‑sofa /automotive‑seat /memory foam), current machine model and production capacity. Our PU‑foam technical team can give targeted suggestions.We specialize in flexible polyurethane foam machinery solutions to help improve production efficiency and reduce material waste. Contact us now to get a customized machine configuration and quotation. Our professional engineers will provide one-on-one technical support within 24 hours.
1. High closed-cell content
a. Polyether polyols: high proportion of ethylene oxide, high activity, often occurs when switching to polyether polyols with different activities.
b. Process formulation: excessive tin octoate usage, high isocyanate activity, high crosslinking degree, rapid crosslinking speed, excessive amines and physical blowing agents causing low internal pressure of foam, inability to open cells when foam elasticity is high, and high TDI index can also result in high closed-cell content.
2. Shrinkage (gelation speed greater than foaming speed)
a. High closed-cell content, shrinkage during cooling.
b. Process conditions: low air temperature, low material temperature.
c. Process formulation: excessive silicone oil, excessive physical blowing agent, low TDI index.
3. Internal cracking
a. Process conditions: low air temperature, high reaction center temperature.
b. Process formulation: low TDI index, excessive tin content, high early foaming strength.
c. High activity of silicone oil, small usage.
4. Top cracking (unbalanced gasification gelation speed)
a. Process conditions: low air temperature, low material temperature.
b. Process formulation: insufficient catalyst usage, small amine usage, poor quality silicone oil.
5. Bottom corner cracking (excessive amine usage, too fast foaming speed)
Large pore surface: excessive physical blowing agent, poor quality silicone oil and catalyst.
6. Poor low-temperature performance of foam
Poor intrinsic quality of polyether polyols, same hydroxyl value, low functionality, high unsaturation, low TDI index with the same tin usage.
7. Poor air permeability
a. Weather conditions: low air temperature.
b. Raw materials: high polyether polyols, high activity silicone oil.
c. Process formulation: excessive tin or same tin usage, low water and amine content, high TDI index.
8. Poor resilience
a. Raw materials: high activity polyether polyols, low relative molecular weight, high activity silicone oil.
b. Process formulation: large amount of silicone oil, excessive tin content, more water at the same tin usage, high TDI index.
9. Poor tensile strength
a. Raw materials: excessive low molecular weight polyether polyols, low hydroxyl value functionality.
b. Process formulation: insufficient tin causes poor gelation reaction, high TDI index at the same tin usage, low crosslinking degree with less water.
10. Smoking during foaming
a. Excessive amine causes a large amount of heat to be released from the reaction of water and TDI, evaporating low boiling point substances and causing smoking.
b. If not charring, the smoke is mostly composed of TDI, low boiling point substances, and monomeric cycloalkanes in polyether polyols.
11. Foam with white streaks
Fast foaming and gelation reaction speed, slow transmission speed in continuous foaming, local compression to form a dense layer, resulting in white streaks phenomenon. The transmission speed should be increased promptly, or the material temperature should be reduced, and catalyst usage should be decreased.
12. Brittle foam
The formula has excessive water, resulting in many unreacted urea formations that are not dissolved in silicone oil, poor tin catalyst usage, insufficient crosslinking reaction, high content of low relative molecular weight polyether polyols, excessively high reaction temperature, and ether bond breakage which reduces foam strength.
13. Foam density lower than set value
Foaming index is too large due to inaccurate metering, high air temperature, low air pressure.
14. Foam with skin, edge skin, bottom voids
Possible Causes: Excessive tin catalyst and insufficient amine catalyst. Slow foaming speed while gel reaction happens too fast; poor mixing efficiency; unstable material feeding rate.Troubleshooting Steps: Adjust amine‑tin catalyst balance; inspect foaming machine mixing head and metering pumps; check raw‑material temperature consistency.
15. High elongation at break
a. Raw materials: high activity polyether polyols, low functionality.
b. Process formulation: insufficient crosslinking due to low TDI index, excessive tin, and high silicone oil content.
Common scenario：Defects persist after formula modification
Lots of foam manufacturers come across this real‑factory pain point: all raw‑material tests pass, formula parameters follow lab specification, yet finished foam still shows cracks, shrinkage or uneven density.
Very often, this points to hardware limitations: inconsistent component metering, insufficient mixing performance, or unstable temperature control on existing foaming machines.
Sabtech equipment is built for stable long‑run production, not only for perfect lab‑condition test runs. Our batch foaming machines and SAB‑CF13 continuous slabstock foaming line focus on metering precision and mixing homogeneity for daily mass‑production.
Still struggling with unstable foam quality in your daily production? Share your defect phenomenon, target foam type (mattress / HR‑sofa /automotive‑seat /memory foam), current machine model and production capacity. Our PU‑foam technical team can give targeted suggestions.We specialize in flexible polyurethane foam machinery solutions to help improve production efficiency and reduce material waste. Contact us now to get a customized machine configuration and quotation. Our professional engineers will provide one-on-one technical support within 24 hours.
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