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            Slow rebound sponge foaming equipment and process
            Time:2020/4/2 9:28:46    

            一 (1) Equipment

               Slow rebound sponge foaming equipment is basically the same as ordinary sponge foaming equipment. 
               So far two foaming methods are used in China: manual foaming and assembly line foaming. Generally, small sponge factories use manual equipment, and large-scale and well-funded manufacturers use pipeline equipment. 
               When sponge first entered China, most of the production equipment was imported from abroad, and so as the manual foam equipment. The influence is relatively large, such as the semi-automatic foaming machine manufactured by the German company Hennecke.
            The working method of semi-automatic foaming machine is as follows: Polyether and small materials are pumped into a suspended storage tank through a metering pump, and TDI is pumped into another storage tank suspended on a mixing tank through a metering pump. After the mold is prepared, the mixing bucket is lowered to the center of the mold, and the polyether and small materials are discharged into the mixing bucket. Lift the stirring rod and bucket to allow the material to spread evenly into the mold to start milky, hair rise, and gel. After 5 minutes, the mold can be removed, and then the sponge is moved to the curing area to mature. The advantages of this equipment are: the weighing, loading and unloading are all completed by the machine with high accuracy, labor saving, and uniform spread of the material and liquid; the disadvantages are: relatively speaking, the equipment investment is relatively large; in addition, needs to clean the mixing bucket after every foaming, so the work efficiency is not high.
               With the development of domestic sponge foaming technology, the domestic manual foaming machine manufacturing technology has become increasingly mature. Many foam factories now use split foam machines. In this foaming machine, the stirring barrel is directly connected to the motor. The motor is equipped with a larger inverter, which ensures that the stirring speed is raised from 0 to 1000 rpm within 0.5 seconds.
               The operation method is as follows: various materials are manually weighed, polyether and small materials are sequentially added to the mixing barrel, and after stirring at a low speed, the mixing is suspended for about one minute, TDI is added, and the mixing is performed at high speed for 3-5 seconds. The material flows into the mold, spreading, fermenting and turning into gels. The mold is removed in about 5 minutes later, and the sponge is moved to the curing area for curing. The advantage of this equipment is that it is easy to operate. By changing the mixing buckets of different models, large density, small density, large orders and small orders can be done. Disadvantages are the uneven spreading of the material and liquid, the difficulty in controlling the process conditions, the uniformity of the quality of the obtained product, the lack of stability and the big loss.
               Recently I went to some places and found that the semi-automatic foaming machine has a tendency to re-enter the stage which also shows that the development situation of the domestic sponge industry is improving. Assembly line of foaming machines have become popular. There are many domestic manufacturers and each product is similar. The main difference is in the mixing head and the control operation mode. Some use liquid crystal display and some use digital display. It can be said that each has its own advantages.
            (II) Craft

              With the formula, it also depends on good equipment and strict control of process conditions to complete production.


            I. Mixing head type

               The mixing head of the assembly line foaming machine is mostly a mace type, and the shearing force generated is sufficient to meet the stirring needs, and will not be described in detail. The manual foaming machine mixing head is recommended to use the sucker type, which is to drill 4-5 pieces of 3-5cm circular holes symmetrically on a suitable round steel plate according to the model of the mixing bucket. This type of mixing head rotates. It is not easy to get into the air, and it is not easy to fall out after the TDI is added (this will happen with propeller stirring). 

            2, stirring speed

               The manual foaming machine's stirring speed is controlled at about 300rpm before TDI is added. After TDI is added, the speed should be increased to about 900rpm in 0.5 seconds. Do not deviate too much from this speed. The speed is too low or too high, and the diameter of the sponge is relatively rough. The stirring speed of the mixing head of the assembly line foaming machine can be controlled at 4500-5000rpm. Some masters have to foam at a speed of 6 or 7 thousand revolutions, and the effect is not necessarily 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 it does not need too high shear force. If you have to use this speed, you can only use excessive stirring, which is not beneficial to the cell structure.

            3, material temperature

               The temperature of manual foam is controlled at 25 ± 1 ℃, and the temperature of assembly foam is controlled at 22 ± 1 ℃. In the south, the material temperature should be relatively low because the environment temperature is relatively high for a long time; in the north, the material temperature should be moderately high because the environment temperature is relatively low for a long time. Especially for manual foaming, the material temperature must be controlled because there are too many uncontrollable factors in the manual foaming process. If the operator's cooperation is not good, if the operation cycle is prolonged, the material liquid stays in the mixing barrel for a long time. Due to the friction friction heat, the material temperature continues to rise when the material temperature is the same as the room temperature. The heat generated is not enough to compensate the heat loss due to the low ambient temperature, and the material temperature will naturally drop. When the ambient temperature is higher than the material temperature, the material temperature will rise significantly. Regardless of whether the material temperature rises or falls, if the deviation from the predetermined temperature is large, it will affect the foaming. Because the formula is set at a preset temperature. 
               In general, the lower the material temperature, the better the foamed pore size, and the better the performance indicators of the sponge; the higher the material temperature, the more scattered and rough the foamed pores, the worse the performance indicators of the finished product. Some masters said that I was still foaming at over 30 degrees. As everyone knows, each time the temperature rises by 10 ° C, the chemical reaction speeds up twice. Everyone thinks about the controllability of this operation.

               The author has monitored the material temperature of the foam nozzles in the assembly line. The feed temperature is 22 ° C. The residence time in the mixing head is 1 second. The rotation speed of the mixing head is 5000rpm. The room temperature is only about 25 ° C. It can be seen how much the effect of stirring on the material temperature.


            4 、 Auxiliary preparation

               Manual foaming does not require preparation of additives, as long as it is accurately weighed according to the feeding coefficient and added to the mixing barrel.
               The assembly line foam needs to dilute some additives with polyether to meet the working characteristics of the pump. Adjuvant concentration should be appropriate.
               Polyamine can be formulated with polyether at a concentration of 30%, and D22 can be formulated at a concentration of 1%. The porosity agent can be formulated to a concentration of 50%.
               If foaming process needs to adjust the amount of additives and the concentration is too high, the adjustment will become larger, and the result is often overcorrection; too low will cause a serious lag in the adjustment  which is not conducive to production. Some masters have formulated tin into a 1/400 concentration. When the amount of tin needs to be adjusted, the amount of tin is constantly added, or subtracted, but the desired adjustment effect cannot be achieved immediately.

            5.Chain speed

               There is no chain speed problem with manual soaking. Control the chain speed of the pipeline.
               In general, the chain speed of the slow rebound pipeline is lower than that of ordinary bubbles. Too fast will pull the bubble down. Because the slow rebound sponge has less water consumption, slow rise, slow heat generation, and low heat, the gel speed of the foam is much lower than that of ordinary cotton. Therefore, the chain speed is generally controlled at about 3.8 meters / minute. Of course, experienced masters can use whatever chain speed they can control.

            六 、 Gas injection

               To ensure the opening of the slow rebound sponge, injecting air into the mixing head if necessary. Of course, there is no problem with gas injection by hand. Assembly line foaming must consider gas injection. The smaller the density, the smaller the gas injection volume. The larger the density, the larger the gas injection volume. Sometimes it is limited to the range of the gas flow meter installed on the equipment. If you want to increase the gas injection volume, you cannot do it. This must be considered before formulating and determining the foaming process. Dosage, reduce the amount of silicone oil, increase the material temperature to achieve.


            (3) On-site judgment and control

               No matter how good the formula is, only by producing high-quality products can the value of the formula itself be reflected. Therefore, only by accurately judging and calmly controlling the problems in the production process, can the goal of formula design be achieved.
               In most cases, the production conditions are quite different from the pilot conditions. Many formulas has no problem in a small test, but once produced by machines, the problem comes to a lot.
               The problems most likely to occur during the preparation of slow rebound sponges are closed cells, cracks, collapses, sinking, coarse holes, crimps, and local rotten cores. At this time, you cannot hold the formula dead, but you must do it immediately to make judgments, find reasons, and make adjustments.

            A. There are no closed cells. It is easy to find by hand foaming. After removing the mold, pinch the four corners of the sponge with your hands. If you close the cells, you will feel pinched or full of gas. This is mostly due to the lack of opener or tin in the formula. If the surface of the sponge dries quickly, it will decrease tin by 3% -5% when the production is continued; if the surface dries slowly, increase the porosity agent by 3% -10% when it is made again. The assembly line sponge can be inspected only when it exits the drying tunnel. Closed holes problem is solved same as the above.

            B, cracking has horizontal plane cracking and vertical line cracking. Most of the horizontal cracking is because of the insufficient of tin. At this time, it can be seen that the sponge has a very good porosity which can be solved by adding about 5% of tin; vertical cracking is related to insufficient stirring strength and insufficient stirring time which can be adjusted appropriately. Sometimes inadequate TDI can also cause cracking. We need to attention to this problem.

               There are two reasons for the 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. Sinking is usually caused by bad silicone oil or the dosage is just at a critical point: it can only support it not to collapse, but it is not enough to maintain the initial stability of the system.

            D. The problems that can be found after the sponge is cut are: coarse holes, crimps, and rotten cores:

            1) The appearance of coarse pores is related to the quality and dosage of the porosity agent. The second is insufficient of TDI. Third, the material temperature is too high, and fourth, the stirring speed is too low or too high.

            2) The cramps in the slow rebound are mostly related to the incomplete stirring, but also to the milky whiteness too fast.

            3) A rotten core appears inside the sponge, and the core is sticky for a long time which is caused by uneven stirring.

            E. If closed-cell shrinkage occurs in the slow rebound sponge, it can be seen after 30-40 minutes from the mold that the post-processing is needed at this time. Generally available methods are manual treading, wooden board striking, peeling and deflation, and high-pressure injection. The simplest and most effective one is to step on it manually so it is not easy to hurt the sponge, it depends. When the temperature is low, you can come a few times more. It can fully recover as long as the opener is of good quality.

            Personal work experience is for reference only.
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