4. Start up production
A. When heating each section, it should be heated in stages, that is, first heating the temperature of each section to 120 ℃, holding it constant for 30 minutes, then heating it to 160 ℃, holding it constant for 15 minutes, and heating it to the process temperature.
B. After the temperature of each section reaches the process temperature, maintain a constant temperature for at least 30 minutes, and continue to extrude for another 15 minutes until the material starts to discharge from the mold. Drain the gas from the original empty screw, stop extruding, and prepare to start the machine. When starting up the PP-R production line, it is necessary to clean the raw PP-R material of the extruder with PE natural resin. After cleaning, the machine can be started up.
C. Recheck the working condition of each equipment, personnel situation, and various preparations. Once everything is ready, start the machine.
D. Start the extruder, first turn on the color line co extruder to extrude at a speed of 20 rpm for 15-30 minutes, and then start extruding at a basic speed of 5-10 rpm. Reduce the co extruder speed to the process speed, observe the material blank, confirm the heating situation, whether there are bubbles in the material blank, and whether the material blank is smooth and flat. Adjust the process temperature reasonably according to the observation situation. After the material blank meets the requirements, start making the startup joint. For large-diameter pipes, use a traction pipe to directly connect with the material blank to reduce the production of a large number of special-shaped pipes during startup. When starting up, apply lubricating oil to the core rod first to prevent the billet from sticking to the core rod and causing quality defects on the inner wall; Start the main engine at a speed of 5-10 revolutions per minute, wait for the discharge billet to meet the joint requirements, stop the main engine, compact the billet from the outside to the inside towards the core rod, and timely pour the traction pipe into the billet at a slower speed. After cooling for 2-3 minutes, start the main engine first, then turn on the traction, follow the extrusion molding procedure, and promptly turn on the cooling water and vacuum pump after the joint enters the sizing sleeve. Special attention should be paid to the occurrence of cracks and openings during the production of joints, which may result in delayed vacuum extraction.
E. After starting production, pay attention to observing the joints of each traction pipe and take timely measures to prevent collisions between the joints Collision Top phenomenon; After each traction pipe joint passes through the traction machine, the traction rope should be promptly and quickly released to guide the pipe into the cutting saw until it reaches the turntable; Turn on the vacuum pump and vacuum box cooling water pump in a timely manner. The cooling water in the cooling water tank must be opened after the traction joint exits the cooling water tank to prevent cooling water from entering the pipes, affecting the quality of the pipes, and even affecting the temperature of the mold head, leading to startup failure.
F. Vacuum sizing. The size of the vacuum degree directly affects the outer diameter size of the pipe. The vacuum degree is generally controlled between 0.02-0.07 MPa. Generally, under the premise of meeting the appearance quality of the pipe, the vacuum degree should be as low as possible, so that the internal stress of the pipe is small and the deformation of the product during storage is small. Vacuum degree is quite important and mainly plays a role in sizing. The vacuum degree should be higher, as described in the second section The vacuum degree in the third section can be lower to ensure the roundness of the pipe. In general, the larger the outer diameter of the produced pipe, the higher the required vacuum degree. Timely measure the outer diameter of the pipe behind the vacuum tank, adjust the vacuum degree after reasonable judgment, and record relevant data for future normal production reference. For large-diameter pipes, drilling and measuring are carried out after the cooling water tank to facilitate timely adjustment and prevent the generation of large quantities of waste. There is also an important data that needs to be adjusted and measured in a timely manner during production, which is the out of roundness of the pipes. After the qualified pipes are released from the vacuum tank, they should be clamped in a timely manner, and the out of roundness of the pipes should be measured and adjusted in a timely manner to ensure the quality of the pipes. Due to the excessive out of roundness of the pipes, there is a large docking deviation during welding, which seriously affects the welding quality; In the national standard factory inspection items, although there is no mandatory requirement for out of roundness, it is increasingly valued during use and has caused more and more quality complaints. Therefore, out of roundness indicators must be given more attention.
G. Cooling and shaping. The temperature of the cooling water for shaping is generally between 15-25 ℃. If the temperature of the cooling water is too high, it will prolong the cooling time and slow down the cooling speed, which means that the time for the molten raw material to be at high temperature will also be extended, especially for the inner wall of the pipe. This will accelerate the decomposition of additives such as soothing reactions in the raw material, reduce the soothing aging performance of the pipe, and also have adverse effects on the shaping of the pipe. On the contrary, if the cooling and shaping water temperature is too low, it will cause the cooling and crystallization rate of the outer surface of the molten PE pipe to be too fast, resulting in a large temperature difference between the inner and outer surfaces of the pipe and causing significant internal stress after shaping, reducing the mechanical properties of the pipe Physical properties (intuitively reflected as high brittleness of the pipe). The cooling water flow rate can be controlled through a flow meter. Excessive cooling water flow rate can easily cause the surface of the pipe to become rough and produce spots Pit; Being too small can also cause a decrease in the surface quality of the pipe, resulting in spots. Uneven distribution of cooling water can also cause the pipe to become out of round.
H. The various data for start-up production are very important and must be truthful Integrated recording of various data, including process temperature Using raw materials Extrusion speed Fixed diameter sleeve model Vacuum degree Cooling water temperature The diameter of the pipe after the vacuum tank Cut pipe diameter and traction speed Pipe wall thickness Out of roundness, degree of pipe clamping, etc.
I. When cutting pipes, there should be a dedicated person to observe the cutting situation, and if there is any clamping or top cutting, it should be dealt with in a timely manner to avoid the entire line being shut down due to the unadjusted tail size. After cutting the pipe, due to the high temperature of the pipe compared to room temperature, the pipe will cool and shrink, and internal stress will be released. After cooling, the size of the pipe will change, especially the outer diameter and length of the pipe. The main reasons are: firstly, crystallization occurs during the cooling process of polyolefin melt, and the crystallinity and crystal form are related to temperature, thermal history, and the time of release. Secondly, the temperature of newly produced pipes is usually higher than room temperature. Thirdly, the stress inside the newly produced pipes is relatively high. In order to achieve performance and dimensional stability, general polyethylene pipes should be left offline for 24 hours and performance tests can be conducted according to corresponding standards. Therefore, the size data of the pipe after cutting and complete cooling shrinkage should be measured and recorded in a timely manner, and corresponding to various data during the process. This is the reference basis for normal production in the future, and must be sorted, summarized, and fully saved.
5. Product inspection and testing
Process product inspection is the assessment of the surface quality of a product during the production process Control of external dimensions (outer diameter, wall thickness, out of roundness, etc.). The control of the outer diameter of pipes can generally be approached from the following aspects:
- Measurement of outer diameter data after vacuum tank;
- Measurement of outer diameter data after cutting;
- Measure the outer diameter data after a period of almost complete cooling and solidification.
At present, more advanced production lines are equipped with online wall thickness measurement devices and automatic die alignment systems. If these devices are not available, tools need to be used to measure the outer diameter of pipes. If the wall thickness and ovality indicators do not meet the requirements, the mold should be aligned in a timely manner, and the vacuum sizing should be adjusted until a qualified product can be stably produced. The inspection of products is necessary before leaving the factory. In addition to the surface quality and external dimension inspection mentioned earlier, the static hydraulic strength of pipe products should also be tested Elongation at break Testing of physical performance indicators such as thermal stability
6. Startup Summary
During the startup process, various abnormal situations will inevitably occur, and corresponding adjustments should be made in a timely manner to ensure the quality of the pipes is qualified. Adjustment measures during startup Measurement data, experimental data The various good methods for starting up must be summarized and summarized in a timely manner. This is the information for our company’s production of HDPE pipes, which is particularly important. After analysis and summary, it should be properly stored And form relevant information for future production reference.