(1) Talk about equipment
Slow rebound sponge foaming equipment is basically the same as ordinary sponge foaming equipment.
Two foaming methods are currently used in China: manual foaming and assembly line foaming. Generally, small sponge factories use manual equipment to make sponges, while large-scale and well-funded manufacturers use assembly line equipment to make sponges.
When sponges first entered our country, most of the production equipment was imported from abroad, and manual foaming equipment was no exception. The semi-automatic foaming machine manufactured by Hennecke Company in Germany has a relatively large impact. (In 2012, the author saw in Indonesia that a machine manufactured in 1983 was still in normal use, and was quite shocked!)
The semi-automatic foaming machine works as follows: polyether and small materials are pumped into a suspended storage barrel through a metering pump, and TDI is pumped into another storage barrel suspended on the mixing barrel through a metering pump. After preparing the mold, lower the mixing barrel to the center of the mold, unload the polyether and small materials into the mixing barrel, lower the stirring rod, stir the materials evenly at low speed, then quickly unload the TDI, stir at high speed for 3-5 seconds, and quickly Lift the stirring rod and bucket, let the material spread evenly into the mold to start milking, rising, and gelling. After 5 minutes, the mold can be removed, and then the sponge is moved to the curing area to mature. The advantages of this kind of equipment are: weighing, loading, and unloading are all done by machines, with high accuracy, labor saving, and the material liquid spreads evenly; the disadvantages are: relatively speaking, the investment in equipment is relatively large; in addition, every time one is delivered Soaking, the mixing barrel needs to be cleaned once, and the work efficiency is not high.
With the advancement of domestic sponge foaming technology, domestic manual foaming machine manufacturing technology is also becoming increasingly mature. Many sponge factories now use split foaming machines. For this kind of foaming machine, the mixing barrel is directly connected to the motor, and the motor is equipped with a larger frequency converter to ensure that the stirring speed can be raised from 0 to 1000rpm or above within 0.5 seconds.
The operation method is as follows: various materials are weighed manually, polyether and small materials are added to the mixing barrel in turn. After stirring at low speed, pause stirring for about one minute, add TDI, stir at high speed for 3-5 seconds, and turn over the mixing barrel. , let the mixture flow into the mold, spread, milky, rise, and gel. Remove the mold in about 5 minutes, and move the sponge to the curing area to mature. The advantage of this kind of equipment is that it is simple to operate. By replacing different types of mixing barrels, it can handle large and small densities, large orders, and small orders. The disadvantages are that the material liquid spreads unevenly, the process conditions are difficult to control, the quality of the resulting product is uniform, the stability is not strong, and the loss is large.
I recently visited some places and found that semi-automatic foaming machines are on the rise again, which also shows that the development situation of the domestic sponge industry is improving. Assembly line foaming machines have become relatively popular. There are many domestic manufacturers, and the products of each are similar. The main difference is the mixing head and control operation method. Some use LCD displays, and some use digital displays. It can be said that each has its own merits. No more details.
(2) Talk about craftsmanship
With the formula, production must be completed with good equipment and strict control of process conditions.
1. Mixing head type
Most of the mixing heads of assembly line foaming machines are mace-shaped, and the shear force generated is sufficient to meet the mixing needs, so I will not go into details. For the manual foaming machine mixing head, the author recommends using a suction cup type. According to the mixing barrel model, symmetrically drill 4-5 3-5cm round holes on a suitable round steel plate. This type of mixing head rotates. , it is not easy to entrain air, and it is not easy to fall out after TDI is added (this will happen with propeller-type stirring).
2. Stirring speed
The mixing speed of the manual foaming machine should be controlled at about 300rpm before adding TDI. After adding TDI, the speed should be increased to about 900rpm within 0.5 seconds. Do not deviate too much from this speed. If the speed is too low or too high, the diameter of the emitted cotton will be relatively rough. The mixing speed of the mixing head of the assembly line foaming machine can be controlled at 4500-5000rpm. Some masters insist on using 6 or 7 thousand rpm to foam, but the effect may not be good. Because the molecular weight of the slow rebound polyether in the slow rebound formula is relatively small, the viscosity of the material is not large and does not require too high shear force. You have to use it like thisPore agent. The assembly line bubble can only be inspected after it has exited the drying tunnel. If closed cells appear, the treatment method is the same as above.
B. Cracks include transverse plane cracks and longitudinal line cracks. Transverse cracking is mostly caused by insufficient tin content. At this time, you can see that the sponge has very good pores, which can be solved by adding about 5% tin. Longitudinal cracking is related to insufficient mixing intensity and insufficient mixing time, and it can be adjusted appropriately. Sometimes insufficient TDI may cause cracking, so be aware of this issue.
There are two reasons for foam collapse: one is forgetting to add silicone oil or the amount of silicone oil is seriously insufficient; the other is forgetting to add tin or the amount of tin is seriously insufficient.
C. Subsidence usually occurs because the silicone oil used is not good or the amount is just at a critical point: it can only support it from collapsing, but it is not enough to maintain the initial stability of the system.
D. Problems that can only be discovered after cutting the sponge: rough holes, pressed ribs, and rotten core:
1) The appearance of rough pores is related to the quality and dosage of the pore opening agent, which has been mentioned in the previous articles. Second, the amount of TDI is insufficient. The third is that the material temperature is too high, and the fourth is that the stirring speed is too low or too high.
2) The tendons in slow rebound are mostly related to insufficient stirring, and also to the milk whitening too quickly.
3) There is a rotten core inside the sponge, and the core is still sticky after a long time. This is caused by uneven stirring.
E. If the slow rebound sponge has closed-cell shrinkage, it will be visible 30-40 minutes after it is removed from the mold. At this time, post-processing is required. Generally available methods are manual stepping, wooden board beating, peeling and deflation, and high-pressure gas injection. The simplest and most effective method is manual trampling, which is not easy to damage the sponge and can be used to gain momentum. When the weather is cold, if it doesn’t work just once, you need to do it several times, step on it, step on it, step on it, step on it, and step on it. As long as the pore opening agent is of good quality, it can be restored.
