1. Mixer Head Design
For automated foam production lines, mixer heads are typically designed in a serrated rod shape, providing sufficient shear force for mixing, so this will not be elaborated further. For manual foam machines, it is recommended to use a suction-disc-style mixer head. This design involves symmetrical drilling of 4-5 round holes (3-5 cm in diameter) on a steel plate sized to match the mixing bucket. Such a design prevents air entrapment during rotation and minimizes the risk of TDI splashing out, which often occurs with propeller-style mixer heads.
2. Mixing Speed
For manual foam machines, the mixing speed should be maintained at approximately 300 rpm before adding TDI. After adding TDI, the speed should be increased to around 900 rpm within 0.5 seconds, with minimal deviation from this range. Excessively low or high speeds can result in coarse foam cell structures. For automated foam production lines, the mixing speed of the mixer head should be controlled between 4500 and 5000 rpm. Some operators insist on using speeds of 6000-7000 rpm, but this does not necessarily yield better results. Slow-rebound polyether used in such formulations has a relatively low molecular weight and viscosity, requiring less shear force. Overmixing at higher speeds can negatively affect foam cell structures.
3. Material Temperature
For manual foaming, material temperature should be controlled at 25±1℃, while for automated lines, it should be maintained at 22±1℃
-Regional Variations: In southern regions with prolonged higher ambient temperatures, the material temperature should be slightly lower. Conversely, in northern regions with extended colder periods, the material temperature should be slightly higher.
-Manual Process Control: Temperature control is critical in manual operations due to numerous uncontrollable factors. For instance, prolonged operation cycles or friction-induced heat can cause material temperatures to rise significantly above room temperature. Conversely, low ambient temperatures can lead to heat dissipation, causing material temperatures to drop if friction-generated heat is insufficient. Deviation from preset temperatures affects foam quality since formulations are optimized for specific conditions.
Generally, lower material temperatures produce finer foam cells with better performance, while higher temperatures result in rougher, inconsistent cell structures and degraded product properties. Although some operators claim successful foaming at over 30 ℃, the reaction speed doubles for every 10℃ increase, significantly reducing process controllability. For example, in tests on automated foam production lines with a feed temperature of 22℃, the material temperature rose to 32℃ within one second of mixing at 5000 rpm, while the room temperature was only 25℃. This highlights the significant impact of mixing on material temperature.
4. Additive Preparation
-Manual Foam: Additives do not require pre-mixing. Accurate weighing and direct addition to the mixing bucket are sufficient.
-Automated Foam: Some additives should be diluted with polyether to match pump operating characteristics.
Recommended Concentrations:
-Amine: 30% with polyether
-D22: 1%
-Cell-opening agent: 50%
If additive concentrations are too high, adjustments can overshoot desired levels, while overly low concentrations may delay adjustments, hindering production efficiency. For example, using a tin catalyst at a 1/400 concentration can result in excessive additions during adjustments, delaying the desired effect.
5. Conveyor Speed
Conveyor speed is irrelevant for manual foaming but critical for automated lines.
Slow-recovery foams require a lower conveyor speed than regular foams. Speeds that are too fast can destabilize the foam. Slow-rebound formulations use less water, have slower reaction and heat generation rates, and exhibit slower gelation. A conveyor speed of approximately 3.8 meters/minute is generally sufficient, though experienced operators may adjust speeds based on their expertise.
6. Gas Injection
To ensure cell-opening in slow-rebound foams, gas injection into the mixer head is necessary for automated production lines. Manual foaming does not involve gas injection.
-Density Considerations:
–Lower foam densities require less gas, while higher densities require more.
–If equipment gas flow meters cannot accommodate desired injection levels, adjustments in formulation may be necessary, such as increasing cell-opening agent amounts, reducing tin and silicone oil levels, or raising material temperatures. These factors should be considered during formulation design and process planning.