Opening machine mixing
Two-roller opener roller speed ratio of 1.2 ~ 1.4: appropriate, fast rollers in the back, the higher the speed ratio leads to faster mixing, low speed ratio can make the film smooth. Rollers must be through the cooling water, mixing temperature should be below 40 ℃ to prevent scorching or loss of vulcanizing agent volatilization. When mixing, the roller distance is small at the beginning (1~5mm), and then gradually enlarged. Charging and operation sequence: raw rubber (wrapped roller) - → reinforcing filler - → structure control agent - → heat-resistant additives - → coloring agents, etc. - → thin pass 5 times - → under the material, oven heat treatment →Return to refining-→Sulfurizing agent-→Thin pass-→Parking overnight-→Return to refining-→Sheets out. Rubber can also not be oven heat treatment, after adding heat-resistant additives, add vulcanizing agent and then thin pass, parked overnight refining, and then parked for several days to refining out of the use of tablets. Mixing time is 20~40 minutes (the specification of the opener is φ250mm × 620mm).
If you use precipitated silica or weak reinforcing filler (titanium dioxide, zinc oxide, etc.), the rubber can not be added to the structure of the control agent. Fillers should be added slowly to prevent the spheres formed by the fillers and raw rubber from floating on top of the stacked rubber resulting in uneven dispersion. If a large amount of filler is to be added, it is best to add it in two or three additions with a knife in between to ensure good dispersion. When a tendency to granularize the rubber is noticed, the roll spacing can be tightened to improve mixing. Rubber particles falling onto the catch tray should be swept and collected with a brush and returned immediately to the rollers of the refiner, otherwise the refined rubber will contain lumps of rubber and result in a poor appearance of the product. The incremental filler should be added after the reinforcing filler has been added, and a wider roll spacing can be used.
Capacity (mixing rubber): φ160mm × 320mm refining machine for 1~2 kg; φ250mm × 620mm refining machine for 3~5kg.
Silicone rubber in the refining machine to join the pack of the slow roller (front roller), mixing is very fast pack of the fast roller (back roller), refining must be able to operate both sides. Because of the silicone rubber rubber is relatively soft, mixing can be used in ordinary fuzi knife operation, thin pass can not be pulled down like ordinary rubber sheet, and the use of steel, nylon or wear-resistant plastic scraper scraping down. In order to facilitate cleaning and prevent lubricant leakage into the rubber, should be used to move the baffle. Gas-phase silica is easy to fly, harmful to the human body, should take appropriate labor protection measures. If the powder peroxide is used directly in mixing, explosion-proof measures must be taken, and it is better to use paste peroxide.
If there are impurities and hard lumps mixed in the rubber, the rubber can be mixed and then filtered through the rubber filter, when filtering, generally use 80-140 mesh screen.
2. Closed mixing machine mixing
The use of this method can improve production efficiency and improve labor conditions. Tests have shown that the performance of closed mixing rubber and open mixing rubber performance is similar. With the laboratory 2L mixing time of 6 ~ 16 minutes, mixing without special difficulties. With φ160mm open kneader, when the loading coefficient is 0.74, the mixing can also be carried out normally. The discharge temperature is related to the type of reinforcing filler: when weak reinforcing filler and precipitated silica are used, the discharge temperature is below 50℃; when gas phase silica is used, the discharge temperature is about 70℃.
3. Rubber parking and refining
Silicone rubber rubber mixing end, should be after a period of parking (generally not less than 24 hours is appropriate), so that a variety of agents (especially structure control agent) can play a full role with the raw rubber. After resting, the rubber becomes hard, plasticity is reduced, before use must be refining. Back to the refining machine, the beginning of the roller distance is larger (3 ~ 5mm), this time the rubber is harder, the surface is wrinkled, wrapped in the front roller (slow roller). With the extension of the refining time, the rubber gradually become soft; slowly reduce the roller pitch (0.25 ~ 0.5mm), soon the rubber that is wrapped in the back roller (fast roller). "To be fully soft, smooth and flat surface of the rubber, can be discharged out of the film. Insufficient refining, the surface of the film has wrinkles; refining excessively sticky rubber and lead to sticky rollers.
Remaking temperature is generally controlled at room temperature. If the rubber section of long-term storage (more than a month) and the emergence of rubber viscous soft, surface wrinkles and other phenomena, you can add 5 to 10 parts of the gas-phase silica, in order to improve the performance of the rubber process, and to ensure the quality of vulcanized rubber.
(B) press out
General silicone rubber is relatively soft, so its press out better, easy to operate. Silicone rubber can be pressed out of a variety of different shapes and sizes of products, the processing equipment and tools are basically similar to ordinary rubber.
Pressing out the machine is generally used φ30mm or φ65mm single thread screw, the length and diameter ratio of 10~12:1 effect is better. Pressing out as much as possible to maintain a low temperature, not more than 40 ℃ is appropriate, so the barrel and screw must be through the cooling water. For products with high quality requirement, 80~140 mesh filter can be installed near the head to remove the impurities in the rubber material and improve the quality of pressing out. Silicone rubber from the mouth out of the type will expand, expansion rate depends on the fluidity of the rubber, the thickness of the blank and the rubber into the realm of the mouth type of pressure. However, increasing or decreasing the ejection rate will change the elongation of the unvulcanized pressed product, thus changing its dimensions slightly. As a rule of thumb, hoses expand about 3% from their orifice size, with very soft compounds expanding at a greater rate and harder compounds at a lesser rate. When pressed out of other shapes of products, the hole of the mouth type is rarely the same as the cross-section of the pressed out products, which is due to the flow of rubber at different points of different friction play a role in the result. Therefore, for a certain mouth type, must be many times after repeated tests, so as to get the desired shape of the product.
Type T head is required on the extruder to press out the coated wires. The mouth shape is mounted on the T-head at right angles to the barrel of the press-out machine. This allows the core wire to be wrapped with a silicone rubber jacket through a hollow ported conduit (core). Reinforced hose can also be used T-head for continuous production, the first general method of pressing the inner rubber layer, and after pre-curing, and then on the outside of the braided reinforced steel wire or nylon, and then make it through the T-head on the outside of a layer of outer rubber, and finally sent to the vulcanization, in the process of molding, if the hose to the inside of the compressed air filling. During the molding process, if the hose is filled with compressed air, it can prevent the collapse of the inner rubber.
Silicone rubber pressed out of the semi-finished product is soft and easy to deformation, so usually must be immediately vulcanized. The most commonly used method is hot air continuous vulcanization; wire and cable industry usually use high pressure steam continuous vulcanization. If the press out can not be continuous vulcanization, in order to prevent deformation. Immediately after pressing out, it should be picked up by disk, drum or conveyor belt, and isolated by talcum powder to avoid mutual bonding. If you find the rubber is too soft and not suitable for the booklet, the rubber can be mixed with 3-5 parts of gas-phase silica.
Generally used to press out of the rubber formula, the amount of vulcanizing agent should be increased appropriately than the molded products. The pressing out speed of silicone rubber is lower than that of other rubbers, and when it is required to achieve the same pressing out speed with other rubbers, a higher screw speed should be used.
(C) calendering
Silicone rubber calender is generally used vertical three-roller calender. Used in the production of film, the middle roller is fixed, the middle roller speed than the upper roller, speed ratio of 1.1 ~ 1.4:1, the lower roller speed and the middle roller compared to the calender when started, the upper roller temperature of 50 ℃, the middle roller should be kept at room temperature, the lower roller cooled with cooling water. The calendering speed should not be too fast, generally 60~300cm/min. first adjust (30~60cm/min) the roller spacing (middle and lower rollers) at a low speed to ensure a certain calendering thickness, and then increase to normal speed (150~300cm/min) for continuous operation. Matting (often polyester film) in the middle and lower dropout between the passage, in the middle and lower rollers should maintain a small amount of accumulation of glue, in order to make the whole cloth and the adhesive material close fit. After calendering, the film take-up roll is tied off and sent into the oven or vulcanizing tank for vulcanization. The mandrel of the winding roll should be a hollow metal tube, and the thickness of the film roll should not exceed 12cm, otherwise full vulcanization cannot be obtained.
Generally out of the sheet to utilize the middle and upper roll can be, the roll temperature is room temperature. There is a way to make vulcanized film or thin film directly on the post-extension machine. At this time, the roll temperature is: the upper roller 60 ~ 90 ℃, the middle roller 50 ~ 80 ℃, the lower roller 110 ~ 120 ℃. Rubber by the upper and middle rollers to remove air bubbles, to obtain the required specifications and preheating, and then transferred to the lower roller by the middle roller for a period of vulcanization can be rolled.
When the three-roll calender is used for silicone rubber lamination and rubbing, the fabric passes between the middle and lower rolls instead of the matting (polyester film). The three-roll calender is only suitable for one-side lamination, and if two-side lamination is necessary, a four-roll calender should be used in the case of long-term production.
The rubber used for calendering must be correctly controlled the degree of refining, it is best not to fully refining on the refiner, in order to get enough refining in the calendering process, which can avoid the rubber in the calendering process due to the refining of excessive and sticky rollers. Rubber formulation also has a certain impact on calendering, the use of reinforcing filler rubber calendering process performance is better.
(D) coating
Coating refers to the silicone rubber paste by dipping or scraping the paste method of uniform distribution in the fabric, to improve the film products and flexural properties of the strength, so that the fabric moisture-resistant to create high-temperature electrical insulating materials, etc..
1. Paste preparation
For the production of paste with silicone rubber rubber, the vulcanizing agent is mostly used vulcanizing agent BP (dibenzoyl peroxide), which is due to the vulcanizing agent BP is not easy to evaporate at room temperature, and fabrics have a better adhesion of the reason. The dosage is slightly more than the general model products. Reinforcement filler if the use of fumed silica, the dosage should not be more than 40 parts, well should be appropriate to increase the amount of structure control agent. Solvent should be used volatile, such as toluene, xylene, etc..
Mixed rubber after sufficient refining under the sheet, and then cut into small pieces, placed in the solvent soaked overnight, using a blender or mixer for mixing, to make a concentration of 15-25% (solid content) of the slurry. The gum paste should be stored in the environment below 40℃ after it is made.
2. Fabric pretreatment
Silicone rubber coating with the bottom fabric, a section of the use of glass cloth, nylon and polyester. Due to the glass cloth heat resistance, high strength, low moisture absorption, so more applications.
Glass fibers in the process of drawing the surface coated with paraffin lubricant (0.2-0.5% of the weight of the fabric), in the vulcanization temperature is not easy to volatilize, affecting the combination of adhesives and fabrics, must be removed before coating. Industry often use the heating method to remove the lubricant. The heating method is divided into low-temperature treatment and high-temperature treatment. The former is the glass cloth at a temperature of 200 ~ 300 ℃, continuous hot baking 20 ~ 30 minutes, or at the same speed through the heat to 275 ~ 325 ℃ hot roller, so that the lubricant thermal decomposition and volatilization of the escape; the latter is the glass cloth at a temperature of 500 ℃ baked 2 ~ 4 hours, or at a speed of 2 ~ 6m/min through the heat to the 600 ℃ of the oven, to get rid of the lubricant. Low-temperature treatment of glass cloth strength loss is small (down 15~25%), but the lubricant is difficult to get rid of the net (content down to 0.2~0.5% or so); high-temperature treatment of the strength loss is large (down 30~70%), but the lubricant content can be removed to 0.2% or less. In order to reduce the loss of strength, generally use low-temperature treatment.
Nylon thermal deformation is large, affecting the rubber and the combination of fabrics, in order to be coated with rubber before the need for heat setting, that is, the fabric in a certain amount of stretch, for a short period of time under the heat treatment. The treatment temperature is 170~175℃.
Polyester and nylon, the same, also need to heat-setting treatment, processing temperature of 215 ~ 220 ℃. The difference is that the polyester surface chemical treatment, that is, with 25% sodium hydroxide aqueous solution at room temperature impregnated for 6 hours, so that the surface is easy and adhesive bonding.
3. glue
Fabric after pretreatment, but also for the surface adhesive treatment, and then can be coated with glue. Adhesive is a solution composed of alkoxysilane, borate, vulcanizing agent and solvent (ethyl acetate or ethanol).