For many small-scale enterprises, although the continuous production line of polyurethane flexible foam offers high output, the costs are also very high, and the target market may not require such large quantities. As a result, non-continuous production lines for polyurethane flexible foam have become their preferable choice. The following is an introduction to the non-continuous production line for polyurethane flexible foam:

1. Box Foaming Process Equipment

The box foaming process and equipment have been developed as a new technology to accommodate the needs of small-scale polyurethane foam production facilities. It builds upon laboratory and manual foam production techniques, essentially an upscaled version of laboratory foam methods. This process has gone through three development stages. Initially, all component materials were sequentially weighed and added to a larger container, followed by the addition of TDI. After rapid mixing, the mixture was immediately poured into a large box mold. This method had high labor intensity, emitted high concentrations of toxic gases, and posed significant health risks to operators. Additionally, the splattering of materials during pouring would entrain a large amount of air, leading to the formation of large air bubbles within the foam structure and even causing foam cracking. Furthermore, there was a significant amount of leftover waste, resulting in substantial material waste and high production costs.

Later on, the process incorporated metering pumps to convey materials to a mixing barrel with an automatically opening bottom. After high-speed mixing, the bottom plate of the mixing barrel would open, and compressed air would swiftly expel the material into the mold for foam expansion. However, this approach suffered from uneven foam pore structures due to the rapid material flow, leading to swirling foam structures and quality issues like crescent-shaped cracks. The third stage of process improvement is the box foaming device that is mostly adopted today. Its fundamental foaming principle is illustrated in Picture



(a) Raw Material Metering and Mixing (b) Foaming (c) Foam Rises to Limit Height

1 - Elevatable Material Mixing Barrel; 2 - Assemblable Box Mold; 3 - Floating Box Top Plate; 4 - Foam Body

Picture 1: Schematic Diagram of Box Foaming Principle

The industrial production equipment for box foaming primarily consists of raw material tanks, metering pump units, elevatable mixing barrels, and assemblable wooden box molds. As depicted in the schematic diagram of the box foaming equipment manufactured by Hennecke (Picture 2), the foaming raw materials are stored in tanks and regulated by control devices to attain the required processing temperature range, typically maintained at 23°C ± 3°C. Sequentially, the metering pump injects polyether polyols, catalyst, surfactants, foaming agents, etc., into the mixing barrel for a stirring duration of 30 to 60 minutes. Next, according to the formulation, TDI is introduced, either directly or through an intermediate container with a bottom switch. Immediate mixing follows TDI addition. Depending on the materials and formulation, the stirring speed is usually controlled at 900 to 1000 revolutions per minute (r/min), with a stirring time of 3 to 8 seconds. After stirring, the mixing barrel is swiftly lifted. The lower part of the barrel lacks a bottom and is placed on the mold box's bottom plate upon lowering, utilizing a sealing ring at the barrel's bottom edge to prevent material leakage.

When lifted, the well-mixed slurry can be directly spread and dispersed on the bottom plate of the box mold, allowing natural foam rise. To prevent the formation of a domed surface on the upper part during foaming, an upper mold plate that matches the mold area and allows for upward limit movement is equipped. The mold box primarily comprises rigid wooden panels, with the bottom plate fixed on a movable mold transport carriage. All four side panels are assemblable, featuring quick-opening and closing locking mechanisms. The inner sides of the panels are coated with silicone-based release agents or lined with polyethylene film material to prevent adhesion. After 8 to 10 minutes of forced maturation within the box, the side panels of the mold box are opened, allowing the removal of block-shaped flexible foam. Following an additional 24 hours of maturation, these foam blocks can undergo cutting and other post-processing procedures.





1 - Raw Material Tank; 2 - Metering Pump Unit; 3 - Control Cabinet; 4 - Mixing Barrel with Elevating Device; 5 - Foaming Box; 6 - Foam Finished Product; 7 - Floating Plate

Picture 2: Box Foaming Equipment Manufactured by Hennecke (BFM100/BFM150)

Box foaming process and equipment exhibit characteristics such as simple operation, compact and straightforward equipment structure, low investment, small footprint, and convenient maintenance. These features make it particularly suitable for small enterprises engaged in intermittent production of low-density block foam. However, its drawbacks are also quite evident: lower production efficiency, less favorable production environment, high concentration of emitted toxic gases on-site, necessitating the use of highly effective exhaust and toxic gas purification systems.



To enhance mixing efficiency, some companies have added several vertical and equidistant baffles to the inner walls of the mixing barrel. These baffles, combined with high-speed spiral-type agitators, facilitate high-speed mixing. This approach can to a certain extent reduce laminar flow effects in the mixing liquid and improve mixing efficiency. An example of this is our product, the SAB-BF3302. For the product's appearance and technical specifications, please refer to Picture 3.



Picture 3: Fully Automatic Box Foaming Machine (Sabtech Technology Limited)

This production line comes with both fully automatic computer control and manual control modes. It's suitable for producing flexible polyurethane foam with densities ranging from 10 to 60 kg/cm. Maximum foam output: 180L. Foam height: 1200mm. Mixing power: 7.5kW. Total power: 35kW.

2. Equipment for Open-Cell Foam Preparation

Open-cell polyurethane foam is a functional foam product developed in the 1980s. It possesses a high porosity, a distinct network structure, softness, breathability, and good mechanical strength. It finds wide application as excellent filtration and shock-absorption material in transportation, instrumentation, medical material filtration membranes, and as catalyst carriers in the chemical industry. Filling it into aircraft fuel tanks can suppress oil agitation and reduce the risk of explosions. Impregnating it with ceramic slurry and high-temperature sintering results in a novel open-cell ceramic filter material used in the metallurgical industry.

The preparation of open-cell polyurethane foam involves methods such as steam hydrolysis, alkaline soaking, and explosion. In industrial production, the explosion method is predominantly used. Initially, polyurethane foam of a specific pore size is prepared using the box foaming process. Subsequently, it's placed in dedicated explosion network equipment, filled with explosive gas, and ignited after completely filling the foam body. By utilizing the impact energy and high-temperature heat generated by the explosion parameters, the cell walls of the polyurethane foam are ruptured and fused onto the cell walls, forming a distinct network structure, as shown in Picture 4.



Picture 4: Clearly Networked Open-Cell Foam

Methods like steam hydrolysis or alkaline soaking are used to prepare open-cell foam. However, there are issues of low efficiency, poor quality, and environmental pollution with these methods. They are mainly employed for small-scale production such as laboratory sample testing. Large-scale production primarily uses the explosion method.



ATL Schubs GmbH, a German company, specializes in the research and development of polyurethane reticulated foam and manufactures the ReticulatusTM foam explosion machinery. The explosion chamber of the reticulated foam explosion equipment comes in two forms: cylindrical and rectangular. The former is suitable for cylindrical foam, while the latter is more versatile. It can be used not only for square foam but also for processing reticulated foam from cylindrical foam, as shown in Picture 5. The explosion chamber is constructed from high-quality 100mm-thick steel plates. Operation is controlled by a computer modem, offering features like automatic opening and closing, automatic locking, automatic operation, and automatic alerts. Additionally, remote program design and modification can be facilitated through data transmission sensors.



Picture 5: Polyurethane Foam Reticulation Processing Equipment (ATL Schubs)

During production, foam bodies measuring 3 to 6 meters in length that are intended for reticulation are pushed into the explosion chamber. The chamber's door is closed hydraulically, and the air inside the chamber is evacuated using a vacuum pump. Under computer control, a precise proportion of oxygen and hydrogen gases is introduced, and the gas mixture's ratio is mechanically adjusted based on factors such as foam sample type and network size requirements.

Sensors continuously monitor the process, ensuring that all process parameters are within the specified conditions before controlled detonation is initiated. The explosive force and flame intensity generated by the explosion penetrate through the entire foam body, creating a distinct network structure. After forming, the foam body is cooled, residual materials and waste gases are purged using nitrogen, and the pressure chamber can then be opened to retrieve the reticulated foam. The entire process takes approximately 8 to 10 minutes. The pore diameter of the reticulated foam falls within the range of 10 to 100 pores per inch (ppi) (Note: ppi refers to the number of pores within one inch).

The above provides some insight into the non-continuous production process of polyurethane flexible foam. I hope this information proves helpful to you.

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.

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.

What to do when the chain stitch quilting machine fails to pick up the thread?

First, check whether the upper and lower threads are correctly threaded and if the thread tension is appropriate. Then, push up the light axis and check if the needle and hook are in the correct position, approximately two millimeters apart.

If the pattern jumping stitch is not picking up the thread, you can adjust the parameters on the computerized control interface to increase the thread length parameter, but be careful not to increase it too much.



What to do when the quilting machine produces imperfect circles?

First, reduce the stitch length appropriately, ideally between 4.8 and 5.2. Then, set the backstitch to 4 and slow down the speed. This should result in a nicely formed small circle.



How to quilt a standard and even pattern?

First, identify the root cause of the problem. Uneven patterns can be related to the thickness of the sponge. If the base material is too thin, it can also cause pattern distortion, uneven sizes, and disproportion. Adjust parameters according to different patterns and material thicknesses.

For continuous patterns, if there is horizontal overlapping, reduce the x-axis parameter; if there is vertical overlapping, reduce the y-axis parameter. Conversely, if horizontal and vertical lines are separated, increase the x and y parameters accordingly.

For jumping patterns, adjust the GX and GY parameters. When quilting diamonds, if the diagonal separation is too wide, increase the diagonal pull parameter; if the diamond diagonals intersect, reduce the diagonal pull parameter.

How to Solve the Issue of Thread Breakage or Dropping in a Quilting Machine?

First, check if the thread clamp is rusty or has debris. If such issues are found, clean the thread clamp with a cloth. Additionally, push up the optical axis of the quilting machine and check if the distance between the hook tip and the needle is around 2 millimeters. If there is a deviation, adjust the hook left, right, up, or down accordingly. Regular maintenance and cleaning of the equipment are also essential.



How to Maintain a Quilting Machine?

Clean the equipment at the start and end of each work shift to remove debris and dust, ensuring smooth operation of the needle and hook. Regularly lubricate areas with significant wear using machine oil or grease to facilitate smooth high-speed operation. Bearings with oil nozzles should be greased at least once a year to prevent excessive machine wear. Insufficient air pressure or unopened cylinders can cause temporary loss of some functions, so ensure the cylinders are activated before turning on the machine. When shutting down, do not turn off the machine power directly; first, turn off the computer, then the power.