Due to its excellent weatherability, low temperature flexibility, and other properties, EPDM foaming materials have been widely used as sealing and heat-insulating materials in the automotive industry and construction industry in recent years. Foam rubber molding methods are mainly molded foam and free foam two. Molded foaming means that the foaming material is filled in the mold cavity, and is heated and pressurized so that it is vulcanized and foamed. The foamed rubber obtained by this method needs to be secondarily vulcanized to reduce the shrinkage. Rate, it is also known as secondary foaming; free foaming is direct vulcanization in the hot air, microwave or salt bath, foaming, free expansion, and more for the continuous production of pipe and profiles.
This topic focuses on EPDM's moulded foaming technology. The choice of foaming agent H (N,N-dinitroso-pentamethylenetetramine) is due to its ease of dispersion, large gas evolution and low cost, and is particularly suitable for moulded expansion processes. Foaming. The core of the foaming technology is the matching of the foaming process and the vulcanization process. The decomposition characteristics of the blowing agent H in the EPDM compound are tested. Different vulcanization systems are selected and combined with the actual foaming effect to select the vulcanization. Process and foaming process matching vulcanization system.
In addition, the formulation and process factors in EPDM moulded foaming were also discussed.
Lecturer, Master, mainly engaged in the development and application of basic materials for rubber and rubber foams.
1 is the effect of the type and amount of calcium carbonate on the properties of the foam. It can be seen that as the amount of calcium carbonate increases, the foaming rate decreases, the density increases, and the hardness increases. Among them, the effect of light calcium carbonate is significantly greater than that of heavy calcium carbonate, when its amount reaches 6 the impact of a serious drum is smaller, the diameter of the filler is larger 2.4 process bar; reasonable art, when a time is used Determine the 2.4.1-times; reduce the density of foamed foams in different temperature ranges, and use a foaming temperature of 150 to a high foaming rate to achieve a uniform sulfurization degree. Table 3 Effect of Fi/Particulate Calcium Type and Quantity of Calcium Carbonates on the Performance of Foams - Heavy Calcium Carbonate; ... After 0 parts of Light Calcium Carbonate, EPDM is difficult to foam, and it will also be O å–½It is advisable to use 20 to 50 servings of melamine tea, indicating that Granule I is beneficial to EPDM foaming.
The design of the choice of the parts must be accompanied by the appropriate processing conditions. The additional processing conditions for vulcanization foaming and secondary vulcanization are the vulcanization temperature and the vulcanization conditions bookmark8. The vulcanization system used can match the wider temperature i. Table 2 shows the different vulcanization temperatures I. It can be seen from Table 2 that when the temperature is increased, the density of the foam after the temperature exceeds 160°C is not low, the expansion rate is small, the cells are fine, and the IJ is not charged. From the perspective of comprehensive performance, curing at 160 °C is appropriate, although the high temperature is beneficial to increase the speed of vulcanization, it is unfavorable to control the degree of manufacturing thick products.
The second time relates to the time when the mold expands when the sulfur content of the rubber material is a time for vulcanization. Table 2 The effect of vulcanization temperature on the performance of the foam. Vulcanization temperature/C density/(Mg°m3) Shore C hardness/ Degree of tensile strength / MPa elongation at break /% Remarks 1380. 52190 Epidermis Shrinkage 1680.185130.50200 Warpage, with blisters Note: The first vulcanization time taken at the corresponding temperature vulcanization time of 50%.
Rubber Industry Table 3 1 'Secondary vulcanization time / min Shore C type Hardness / Degree of tensile strength / MPa Elongation at break /% Remarks Rubber has not yet vulcanized Crust Defects Flat Bubbling Bubbling More Bubbling Severe, warping film effect. With the extension of the mold opening time (ie, the degree of vulcanization of the rubber increases), the product density increases. This is because as the degree of vulcanization increases, the modulus of the rubber increases, and under the same expansion force, it The expansion rate must be reduced. Comprehensive foaming effect, a curing time of 12 ~ 16min is appropriate, the degree of vulcanization at this time is about 50%.
4.2 Secondary vulcanization conditions Since the foams for primary vulcanization have not yet been fully vulcanized, and the mold foaming is performed after the rubber has had a certain degree of vulcanization, the foam walls are stretched and there is a residual stress, resulting in bubbles Shrinkage, poor dimensional stability, so it is necessary to conduct secondary vulcanization setting. The effect of the second stage curing time on the shrinkage of the product. It can be seen that without secondary vulcanization, the product shrinks remarkably; after the secondary vulcanization, the dimensional stability is obviously improved, and the vulcanization time of 15 to 30 minutes is enough to set the product.
3 Conclusion The influence of the process is small; different vulcanization systems have less influence on the decomposition of blowing agent H in the EPDM compound.
In order to achieve the matching between the vulcanization process and the foaming process, a vulcanization system with a vulcanization induction period equivalent to the complete decomposition time of the foaming agent should be selected.
When highly filled, light calcium carbonate severely interferes with foaming, whereas heavy calcium carbonate hardly affects foaming.
Secondary vulcanization increases the degree of vulcanization, significantly reducing the shrinkage of the product.
Rock Drilling Core Barrels with Roller Bits adopt the high-carbon steel and special drilling bits angle to keep the drilling strength and efficiency.
There are tree types of core barrels: 1)Core Barrel with bullet teeth is used for cutting an annular ring in rock or concrete(also reinforced concrete). 2)Core barrel with roller bits is used in very strong rock formations(compressive strength > 100Mpa). 3)Cross cutter core barrel is mainly used to break rock cores which remain in the borehole after using a core barrel, also suitable for drilling hard, jointed rock(<100Mpa) and for penetrating through layers containing boulders. Applicable layers: dense sand, gravel and medium hard rocks, etc.
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