(1) molding process
① ingredients and mixing process. PVC plate preparation quality directly affects the extruder extrusion speed, process parameters and product quality, so that should strictly control the process
Ingredients in the formula when the composition of the material to be accurate measurement, to prevent the measurement of large errors caused by the actual formula changes, thereby increasing the quality of the quality of analysis and quality control. This point in the actual production process is often easy to overlook, should cause enough attention.
Mixed temperature. The mixing is usually carried out in a high speed mixer. Material in the mixer high-speed friction heat, in the mixing process, the temperature control is very important. Temperature control should pay attention to two points: First, PVC resin and additives into the mixer, the immediate mixing, the use of friction heating, when the temperature reaches 120T or so when the nesting to the cold mix machine; Second, the hot mix in the cold Mixing machine for a certain period of time, when the material temperature is lower than 45 in order to open the cold mixed with the gate discharge.
B. Mixing time. Materials in the mixing process has experienced changes in density, uniformity and part of the process of gelation, while excluding the material in the water and volatile matter, take some time to complete. Mixing time is too short, will make the extrusion process becomes difficult, material melting time is long, product quality deterioration; mixing time is too long, the temperature will rise too high, easy to cause the material color decomposition, and energy consumption, production efficiency low.
C. Feed order. RPVC plate components are more important to choose a reasonable feeding order is very important, the choice of feeding order should be conducive to the role of additives play to avoid the confrontation between the additives effect, but also help to improve the dispersion rate.
Typical hot and cold mixing processes are as follows.
(A) the PVC resin in the high-speed mixer to pull up to 60 times.
(B) Put the stabilizer and continue to heat up to 90 °.
(C) into the lubricant, processing aids, impact modifiers, fillers, colorants and so on.
(D) investment outside the lubricant, continue to heat up to 115 ~ 120T.
(E) the material at a low speed is discharged into a rotating coolant with cooling water.
⑴ cold mixed to 40 ~ 45 <C out of material, spare.
The main advantage of powder is the material in the preparation of the heat process is short, the equipment required to use low, short production cycle. Its main drawback is poor material uniformity and poor performance of the forming process, the compression rate is large. Powder can be directly used for extrusion (usually twin-screw extruder extrusion), but also through the plastic granulation into pellets for single screw extruder production plate.
② extrusion molding process. Extrusion molding is one of the most important aspects of the entire production process of extruded sheet. The molding temperature, extrusion speed and other process parameters directly affect the quality of the sheet.
A. Molding temperature. RPVC plate molding temperature is based on the formula, the thickness of the plate and other factors to determine. The barrel temperature of the single screw extruder is: mouth. The ^ ^, ^ The 140, 150 ~ 160t, 170 ~ 180 ^. The temperature of the feeding section of the twin screw extruder is slightly elevated so that the material can be melted at the end of the feed section so as to enclose the rod to prevent the material from being pumped out through the exhaust section. Head connector temperature and head temperature
B. Extrusion speed. The extrusion speed is determined by the screw speed, the screw speed increases, the extrusion volume increases and the extrusion speed is accelerated. Under the same molding temperature condition, the plasticizing quality of the material will decrease and the reasonable extrusion speed (screw speed) To ensure product quality and improve economic efficiency is very important.
C. Traction speed. The linear velocity of the traction roller should be slightly faster than that of the three rollers of the calender to maintain a certain tension so that the sheet does not deform, such as warping during the cooling process. But the speed is too fast when the plate will have a greater internal stress, affecting the quality of secondary processing products.
D. Cooling stereotypes. The main function of the three-roll calender is calendering and cooling. The temperature of the calender tube is shown in Table 5-2. The distance between the three rollers and the die lip should be as small as possible, usually 5 to 10 cm. If too large, the machine out of the board easy to sagging wrinkles, surface roughness, and easy to heat cooling, negative pressure. The roller length should be slightly larger than the head width. Increasing the diameter of the roll increases the roll time and increases the extrusion speed so that the gloss of the PVC sheet is good. The working distance between the upper and middle rollers of the three-roll calender can be slightly larger than the thickness of the plate. Triacent traction speed and extrusion speed of the extruder should be consistent, try to avoid stretching.