Vulcanization and foaming mechanism of foamed rubber extrusion tube

- May 31, 2019-

Vulcanization and foaming mechanism of foamed rubber extruded tube




1, vulcanization and foaming


The curing speed should match the foaming speed.

One party shall not be substantially faster than the other party.


Vulcanization speed is too fast: due to the strong mechanical force of vulcanized rubber foaming agent can not be successfully decomposed out of the rubber material.


Vulcanization speed is too slow: the foaming agent in the rubber material is completely or nearly and completely unvulcanized state will decompose the gas to foam rubber, but at the same time the surface of the rubber material is also broken by the gas, so that the surface of the rubber tube is not smooth or there are pores.


Comparison of the two speed: generally vulcanization speed needs to be slightly faster than the foaming speed, so as to ensure the smooth surface of the rubber tube, two can make the foaming agent decompose the gas to foam the rubber.




2. Foam process of rubber hose


Microwave: the foam of the rubber tube is mainly completed by microwave heating.

Use the heat radiation of microwave to heat the rubber tube from the inside to the outside. When the rubber tube starts to get hot and froth inside, the relative temperature of the rubber material on the outside of the rubber tube is still relatively low, which will not lead to the failure of vulcanization of the rubber tube.

This from the inside to the outside of the heating method to ensure that the rubber tube can be smooth foam.


The heating of the rubber tube by microwave accompanied with vulcanization, but the vulcanization did not reach the final vulcanization depth.

After coming out from the microwave, the rubber tube is finally vulcanized by entering the hot air heating section.

To finish the vulcanization and foaming of the rubber hose.




Second, formula design




1, raw rubber


In the selection of raw rubber, the vulcanization rate of stiff fluidity should be considered


Stiffness: in order to achieve the required stiffness do not let the rubber in the transmission process of vulcanization cao, because the weight of the rubber material pressure caused by the deformation of the rubber material.

Raw rubber shall be of the higher grade of Mooney.


Fluidity: in order to achieve the fluidity required for extrusion, it is necessary to consider the lower grade of menny when choosing raw rubber


Vulcanization speed: because the vulcanization speed of foaming gum is usually faster, in order to meet the need of vulcanization speed, it is necessary to use the brand with higher content of the third monomer in the selection of raw rubber.


All kinds of factors: we must choose according to the wall thickness and size of the rubber hose.

In general, the use of menni higher raw rubber.

It can also be mixed with a high-bottomed Mooney.




2. Reinforcing agent


Generally, we choose carbon black with better fluidity, such as N550, for the sake of the fluidity of the rubber


Note: in order to improve the fluidity of the adhesive, a certain amount of flow AIDS can be added.




3. Curing system


The vulcanization system of the foam hose is usually required to be quick.

You have to use a lot of ultramicroid and ultramicroid.

The TDEC(TL) effect was better.

It burns very quickly and very quickly.

Its drawback is not safe storage.


In order to make the decomposed gas easier to foaming the rubber, we should pay attention to the crosslinking density when designing the curing system.

Too high crosslinking density is not conducive to foaming.

A better way would be to reduce the sulfur content.




4, blowing agent


In the choice of foaming agent should pay attention to the decomposition temperature and volume of foaming agent.


Too low decomposition temperature of foaming agent: it is easy to lead to foaming before vulcanization, which is not conducive to the smooth surface of the rubber tube.


Foaming agent decomposition temperature is too high: easy to lead to foaming after vulcanization, not conducive to the smooth rubber tube foaming.


Blowing amount: it is advisable to choose the blowing agent with stable blowing amount. If the blowing amount fluctuates greatly due to the change of temperature, the blowing agent is not conducive to the grasp of the size of the rubber hose.


Note: the commonly used foaming agent is AC H OT




Third, rubber mixing




1, clean


The cleaning of rubber refining is particularly important. If impurities or other rubber materials are mixed into the rubber refining process due to the uncleanness of the appliance, the surface of the rubber tube after vulcanization is not smooth or the pores are not even.




2, glue parking


It is better to leave the rubber mixture for 24 hours after finishing mixing (without vulcanization system and foaming agent) and then return to the mixture for adding sulfur.

It is good for dispersing the compound when the compound is kept for a certain time.




Four,




1. Extruder


When starting to feed the extruder, the screw speed should be opened slowly.

In order to avoid the front end of the screw in the machine barrel idling and grinding screw.


Extruder temperature control, generally at about 70 ℃.

The temperature shall be increased from the feeding section to the outlet of the hose.

The temperature of the extruder can increase the plasticity of the plastic material and preheat the plastic material.


The temperature of the extruder has an effect on the rubber tube foaming.

Proper preheating can help the microwave section foam more quickly.

However, if the temperature of the extruder is too high, it will affect the coke burning of the rubber, which is not good for foaming.


The extrusion speed must match the transfer speed of the first vulcanization groove. If the extrusion speed is too fast, the rubber tube will fall to the ground, while if it is too slow, the rubber tube will be pulled by the transfer of the vulcanization groove.




2, the first high temperature


The first section is called high temperature, and this section is shorter than the other three.

Its function is to use this section of high temperature to skin the skin of the rubber tube, but more on the rubber tube internal effect.




3. Microwave section


In the microwave section, there is also hot air, but the main use of microwave radiation is to heat the hose from the inside to the outside.

A large number of microwaves make the rubber material internal rapid temperature rise and cause the decomposition of the foaming agent to foam the rubber tube.

Since this heating is from the inside out, the decomposition foaming is also from the inside out.

Avoid the rubber tube because the outside has been vulcanized caused by the inability to foam.




Hot air


The third and fourth sections are hot air vulcanization.

From the second microwave vulcanization tank out of the rubber tube has been relatively sufficient foam, but the depth of vulcanization is not enough, into the third and fourth section for the final vulcanization.

These two sections are mainly rubber vulcanization, of course, also accompanied by a certain degree of foaming.




5. Cooling and cutting


The rubber hose from the fourth section has finished all the vulcanization and foaming and is put into the cooling tank for water cooling.

After cooling, cut it into required length according to size.

The finished product is complete.




additional




1, the vulcanization groove transmission speed match


From the first section of high temperature to the fourth section of hot air vulcanization, the transmission speed is increasing, because the rubber tube through each section of its size is growing, so the speed is not increasing the rubber tube in the vulcanization groove will be bent and blocked.

The rubber tube is not straight after coming out, even in the vulcanization tank for a long time blocked will also catch fire.

Specifically, the transmission speed should be adjusted according to the actual situation during production.




2, microwave control of the amount of foam


The size of microwave amount can affect the foaming rate of rubber hose directly, general microwave is bigger foaming amount is bigger, conversely smaller.




3. Influence of transmission speed of vulcanizing groove on size of rubber hose


Increase the speed ratio of the vulcanization groove appropriately, can make the rubber tube in the vulcanization groove form pull, can make the size of the rubber tube has a certain decrease.

This method is sometimes used to adjust the size of the foam tube.