Vulcanization and foaming mechanism of styrofoam extruded tube
1. Vulcanization and foaming mechanism of foamed rubber extrusion tube
1. Coordination of vulcanization and foaming
The vulcanization rate is matched to the foaming speed. No one can be much faster than the other.
The vulcanization rate is too fast: the foaming agent cannot be broken down due to the strong mechanical force of the vulcanized rubber to foam the rubber compound.
The vulcanization rate is too slow: the foaming agent decomposes the gas in the state of the rubber completely or nearly completely unvulcanized to foam the rubber compound, but at the same time, the surface of the rubber compound is also broken by the gas, so that the surface of the rubber tube is uneven or has pores.
Comparison of two speeds: Generally, the vulcanization speed needs to be slightly faster than the foaming speed, so that one can ensure the smoothness of the surface of the hose, and the foaming agent can be smoothly decomposed out of the gas to foam the rubber compound.
2, the foaming process of the hose
Microwave: The foaming of the hose is mainly done by microwave heating. The heat pipe of the microwave is used to heat the hose from the inside to the outside. When the inside of the hose is just beginning to be heated and foamed, the relative temperature of the rubber outside the hose is relatively low and the vulcanized tube is not cured. This heating method from the inside to the outside ensures that the hose can be foamed smoothly.
The vulcanization of the hose is accompanied by vulcanization while microwave heating, but the vulcanization at this time does not reach the final vulcanization depth. After exiting the microwave, enter the hot air heating section to complete the final vulcanization of the hose. To complete the vulcanization and foaming of the hose.
Second, the formula design
1, raw rubber
The choice of raw rubber, mainly need to consider the stiffness, fluidity, vulcanization speed
Firmness: In order to achieve the required stiffness, the rubber is not allowed to be deformed during the vulcanization process because the rubber itself is under pressure. Raw rubber must use the higher grade of Mooney.
Mobility: In order to achieve the fluidity required for extrusion, consider the lower grade of Mooney when selecting raw rubber.
Vulcanization speed: Since the vulcanized rubber usually requires a faster vulcanization speed, in order to meet the vulcanization speed, it is necessary to use a higher number of the third monomer when selecting the raw rubber.
Various factors: We must choose according to the wall thickness and size of the hose. In general, the raw rubber of Mooney is used. Can also be mixed with high-end Mooney.
2, reinforcing agent
Generally, for the sake of fluidity of the rubber, we use carbon black with good fluidity, such as N550.
Note: For the fluidity of the compound, a certain amount of flow aid can also be added.
3. Vulcanization system
Vulcanized systems for styrofoams are usually required to be fast. A lot of super promotion and super promotion must be used. Among them, the TDEC (TL) effect is better. The speed is very fast and the burnt is short. The drawback is that it is not safe to store.
In order to make it easier to decompose the gas to foam the rubber, we also pay attention to the problem of crosslink density when designing the vulcanization system. A too high crosslink density is not conducive to foaming. If the amount of sulfur is reduced, it is a better method.
4, foaming agent
Attention should be paid to the decomposition temperature and gas generation of the blowing agent when selecting the blowing agent.
The decomposition temperature of the foaming agent is too low: it is easy to cause the foaming to precede the vulcanization, which is not conducive to the smooth surface of the hose.
The decomposition temperature of the foaming agent is too high: it is easy to cause vulcanization after foaming, which is not conducive to smooth foaming of the hose.
Gas production: It is advisable to select a foaming agent with stable gas volume. If the gas generating amount fluctuates greatly due to temperature changes, the foaming agent is not conducive to the grip size.
Note: Commonly used foaming agents are AC H OT
Third, the rubber
The cleaning of the rubber is particularly important. If the rubber is mixed in the rubber mixing process due to the uncleanness of the appliance, the surface of the rubber is not smooth or the pores are not uniform.
2, rubber parking
After the rubber compounding is completed (the vulcanization system and the foaming agent are not added), it is better to use it after being parked for 24 hours. After the rubber is parked for a certain period of time, it is advantageous to disperse the compounding agent.
Fourth, the process
When starting to feed the extruder, the screw rotation speed should be slower. In order to avoid grinding the screw due to the front end of the screw idling in the barrel.
Extruder temperature control, generally around 70 °C. The temperature should be increased from the feed section to the hose outlet. The temperature of the extruder can increase the plasticity of the rubber, and the second is to preheat the rubber.
The temperature of the extruder has a top effect on the hose foaming. Proper preheating can help the microwave section to foam more quickly. However, if the temperature of the extruder is too high, it will affect the scorch of the rubber compound, but it is not good for foaming.
The extrusion speed must match the conveying speed of the first-stage vulcanization tank. If the extrusion speed is too fast, the hose will fall to the ground, and too slow will form a pull with the transfer of the vulcanization tank, and the hose will be thinned.
2, the first high temperature
The first section is called high temperature, which is shorter than the other three sections. Its function is to use the high temperature of this section to crust the surface of the hose without excessively affecting the inside of the hose.
3. Microwave section
Micro-bands also have hot air, but the most important thing is to use microwave radiation to heat the hose from the inside out. A large amount of microwaves cause the interior of the compound to rapidly heat up to initiate decomposition of the blowing agent to foam the hose. Since this heating is from the inside to the outside, the decomposition foaming is also from the inside to the outside. It is avoided that foaming cannot be achieved because the outside of the hose has been vulcanized.
4, hot air
The third and fourth sections are both hot air vulcanization. The hose from the second stage of the microwave vulcanization tank has been fully foamed, but the vulcanization depth is not enough, and the third and fourth stages are entered for final vulcanization. These two sections are mainly the vulcanization of the rubber compound, of course, accompanied by a certain foaming.
5, cooling and cutting
The hose from the fourth section has completed all vulcanization and foaming, and enters the cooling tank for water cooling. After cooling, it is cut to the required length according to the size. The finished product is complete.
1. Matching of transmission speed of each vulcanization tank
From the first stage of high temperature to the fourth stage of hot air vulcanization, the transmission speed is increased. Since the size of the hose is increased through each section, the hose will bend and block in the vulcanization tank if the speed is not increased. The hose is not straight after it comes out, and even if it is blocked in the vulcanization tank for a long time, it will catch fire. Specifically, the transmission speed is adjusted according to the actual situation at the time of production.
2, microwave control hose foaming amount
The amount of microwave can directly affect the expansion rate of the hose. Generally, the larger the microwave, the larger the amount of foaming, and vice versa.
3, the effect of the speed of the vulcanization tank on the size of the hose
Properly increasing the speed ratio of the vulcanization tank allows the hose to be pulled in the vulcanization tank, which can make the size of the hose smaller. This method can sometimes be used to adjust the size of the foam tube.