In September 2021, we received an inquiry from Mr. Abdullah in Saudi Arabia regarding a continuous foaming machine. The client was planning to establish a PU foam factory to produce products for the local and Yemeni markets. He had some basic knowledge about machine usage and selection.

The client had no prior experience in foam production before, so he was particularly concerned about after-sales support and technical assistance.

We began by analyzing the client's target market (specific industry) and understanding the local product requirements (such as foam density, hardness, etc.) to confirm the client's production needs.

Through video conferences, we guided the client through our PU foam production process, providing the client with a concrete understanding of foam production and highlighting the convenience and efficiency advantages of our machines compared to those of other manufacturers.

Drawing upon our more than 20 years of experience in foam foaming, we shared insights with the client about using the machine and common challenges in the foam foaming process, addressing any technical concerns the client may have had.

We also provided the client with factory layout plans to expedite the setup of the entire foam production line while maximizing production efficiency.

Due to the client's high level of trust in our professional service, he ultimately chose us as his supplier for foam machinery and later made repeat purchases for a rebonded foam production line and foam cutting machines.

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.

When using a batch foam machine for polyurethane soft foam foaming, have you encountered the following situations?

1.Uneven and numerous foam pores,

2. Rough foam texture.

3. Chaotic pore sizes across the entire foam surface, with slight signs of large pores.

Issues like these are quite common. The main reason for the first issue is that the distance between the mixing impeller of the foam machine and the bottom of the mixing barrel is too great; the second issue is that the mixing blades are too short and narrow: the third issue is that the angle of the mixing blades is too large.

Many manufacturers who design and produce foam machines only understand the principles during the design process, without understanding the significant relationship between a different design in foam production and product quality. A reasonable and perfect mechanical design can only be gradually improved in actual work, and only experienced foamers can achieve this.

Here are some experiences we have had with machine modifications and upgrades, hoping they will be helpful:

First, the installation position of the mixing wheel should be as low as possible, closer to the bottom of the mixing barrel is better. In general, the distance between the lowest point of the mixing blade and the bottom of the mixing barrel should be around two centimeters

Second, the shape of the mixing blade should be fan-shaped, with a moderately wide edge. The advantage of being wide is that it increases the contact area with the liquid material, providing sufficient power and also balances the liquid material.

Third, the length of the mixing blade should also be as long as possible, leaving about three to four centimeters from the baffle inside the mixing barrel.

Fourth, the two edges of the mixing blade should be sloped, with the angle of inclination based on the width of one end and two centimeters difference on both sides. After the mixing blade is modified, proper operation is also crucial, especially the mixing speed. Most batch foam machines nowadays are equipped with high-speed timing frequency conversion devices. However, in actual production, this device is often unnecessary. The operating speed mainly depends on the amount of material in the mixing barrel. If there is a lot of material, the speed should be appropriately faster, and if there is less material, then the speed should be lower.

The compressive resistance of a foam is related to many factors such as the structure of various chain segments composing the foam, the chemical bonds between molecules, the crystallinity of polymers, the degree of phase separation, the structure of isocyanates, and the proportion of isocyanates used.

1. Slow rebound foam is formed by the reaction of high molecular weight polyols and low molecular weight polyols with isocyanates. The soft segments formed by high molecular weight polyols have large volumes, low crosslink densities, and high activity. They are easy to compress and quickly recover after pressure is removed. The hard segments formed by low molecular weight polyols have small volumes, high crosslink densities, and low activity. They are difficult to compress and also difficult to recover after external forces are removed. This characteristic gives foams their slow rebound feature and is the basis for manufacturing slow rebound foams.

Because the properties of the soft and hard segments in slow rebound foams are different, there is a certain degree of phase separation between them. If there is no phase separation between the segments, the foam body is a tightly bound whole on a macro scale, leading to the phenomenon of "move one hair and the whole body moves," meaning it shrinks as a whole when compressed and expands when pressure is released. However, the microstructure of the foam determines that this situation cannot be achieved completely. Especially in slow rebound foams, various chain segments have different molecular structures, uneven molecular weight distributions, and unavoidable phase separation. Slight phase separation causes some hard segments, due to their low activity, to have difficulty recovering during the recovery process after external forces are removed. These "escapees" more or less restrain the recovery of soft segments, ultimately leading to shrinking.

2. The crystallinity of hard segments, which is stronger than that of soft segments, is also a reason for poor recovery. Materials have similar compatibilities, which also apply in slow rebound foams. Because the hard segments have closer cross-linking points and higher crosslink densities, the small molecules formed are more likely to aggregate together. Due to the presence of hydrogen bonds, these aggregated hydrogen-containing substances enhance the crystallinity of the material, leading to greater cohesive forces. After compression, external forces change the aggregation state of the chain segments, making it easier for polar groups to fuse together. When the external force is released, the new aggregation state, due to strong cohesive forces, is difficult to return to the pre-stressed state, resulting in shrinkage of slow rebound foams.

3. The structure of isocyanates is also a factor affecting the compression resistance of slow rebound foams. TDI is usually used to produce slow rebound foams. Because the two NCO groups in the TDI molecule are at the 2,4- and 2,6- positions, they have a certain angle between them, making them prone to deformation under stress. Especially under hot pressing conditions, significant deformation and heat loss occur, particularly evident in bra cup foams, making recovery from these deformations difficult.

4. The low NCO index of isocyanates used in the preparation of slow rebound foams is also a reason for poor recovery. The NCO index of ordinary foams is usually above 100, while in slow rebound foams , the NCO index is generally between 85-95. This means that 5-15% of the hydroxyl groups do not participate in the reaction. Therefore, although the surface of the foam appears to be a single entity, internally there is a considerable portion of chain segments that are independent of each other.

Solutions for Improving Compression Resistance of Slow Rebound Foams:

1.Use high EO polyether (so-called blowing agent polyether) to replace some slow rebound polyether.

A. High EO polyether has a low hydroxyl value and a large molecular weight. After reacting with isocyanates, the segments formed have molecular weights greater than or close to those formed when ordinary polyether reacts with isocyanates, reducing the degree of phase separation and crystallinity.

B. High EO content polyether has soft and smooth segments, which can provide good slow rebound effects. Additionally, the addition of high EO polyether can effectively improve the low-temperature resistance of slow rebound foams.

2.Add a small amount of polyether-modified polyester to increase the material's cohesive force.

The polyester segments, due to the presence of ester groups, have high internal cohesive forces and good tensile and compressive properties, significantly improving the compressive resistance of slow rebound foams.

3.Use a small amount of high-functionality and high molecular weight polyether as a crosslinking agent, and replace some ordinary polyether with high-activity polyether for slow rebound.

This disrupts the distribution of chain segments, reduces the degree of phase separation, and increases the reaction degree, reducing crystallinity.

4.Use MDI or add MDI to TDI.

MDI has a different structure from TDI and produces foams with better compression resistance and less heat loss. If using MDI, it is best to use modified MDI (with high branching and easy closure of cells); liquid MDI can also be used, as it is intramolecular cyclization and more resistant to compression. Slow rebound foams made with all MDI have much better compression resistance than pure TDI, and many manufacturers are already using this.

Calculation of foaming distance for continuous foaming machine

Given: Bubble release time for the formula is 108 seconds, conveyor belt speed during foaming is 4.6 meters per minute. Calculate the swinging and trough foaming distances.

Foaming distance when swinging: (108/60) x 4.6 = 8.28 meters

Foaming distance when troughing: [((108-18)/60)] x 4.6 = 6.9 meters

Explanation: For the same formula, continuous foaming machine has a shorter bubble release time than small bubbles. The calculated foaming distance is shorter than the actual foaming distance. This method only provides approximate confirmation of the foaming distance, supporting the adjustment of the settling plate. Troughing: 18" indicates the time in seconds that the raw material stays in the overflow trough.

Calculation of foaming height for continuous foaming machine

Given: Formula flow rate: 80 kilograms per minute for polyether, 20 for white polyether, 60 for TDI, 20 for stone powder, conveyor belt speed 4.5 meters per minute, mold width 1.65 meters, producing foam with a density of 25 kilograms per cubic meter. What is the foaming height in meters?

Total formula weight: 80 + 20 + 60 + 20 = 180 kilograms

Formula volume: 180/25 = 7.2 cubic meters

Base area of conveyor running per minute:

4.5 x 1.65 = 7.425 cubic meters

Foaming height: 7.2/7.425 = 0.97 meters

Explanation: Silicone oil, amine, and tin are not considered here as they offset the amount of carbon dioxide used during the foaming process. Moisture content (MC) is not considered because MC does not increase foam weight when vaporized.

Foaming Daily Operation

Beginners worry that improper adjustment of the settling plate will cause the liquid sprayed from the nozzle to surge forward or backward, affecting foaming. The reaction rate gradually increases within the first two minutes after starting the machine, sometimes requiring corresponding adjustments to the settling plate. Adjustments to the settling plate are more critical in formulas with low density and high MC.

TDI flow rate can be calculated by determining the corresponding scale value for the flow rate, but it is recommended to measure the TDI flow rate during the first foam production. Flow rate is too important; if the flow rate is incorrect, everything else will be a mess. It's best to rely on the simplest and most intuitive method of measuring flow rate.

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

Formulas for foam machines with longer mixing chamber or more teeth on the mixing shaft typically have less amine and lower material temperature. Conversely, formulas for foam machines with shorter mixing chamber or fewer teeth on the mixing shaft typically have more amine and higher material temperature.

For the same formula, when switching between dual spray swing heads and single spray swing heads, if the cross-sectional area of the two nozzles is similar, the requirements for the fineness and number of layers of the mesh are similar.

Correction of small material flow rate can be done by measuring the return flow rate of the small material, or by dividing the total usage by the foaming time for correction. When the values obtained from the two correction methods differ significantly, the data from the second correction method should be used.

Formulas for soft foam with better properties are usually in an unstable range, such as lower TDI index, lower water to MC ratio, lower T-9 dosage, and lower silicone oil dosage. Just like in our jobs, there must be effort before reward.