Pc plastic (polycarbonate)
English name: polycarbonate
Specific gravity:1.18-1.20g/cm3 molding shrinkage: 0.5-0.8% Molding temperature: 230-320℃ Drying conditions:10-/20℃ for 8 hours.
The material has high impact strength, good dimensional stability, colorless and transparent, good coloring, good electrical insulation, corrosion resistance and wear resistance, but poor self-lubrication, stress cracking tendency, easy hydrolysis at high temperature and poor compatibility with other resins. Suitable for making small instrument parts, insulating transparent parts and impact-resistant parts.
Moldability 1. Amorphous substance, good thermal stability, wide molding temperature range and poor fluidity. Small hygroscopicity, but sensitive to water, must be dried. Molding shrinkage is small and prone to melt cracking and stress concentration, so the molding conditions must be strictly controlled and the plastic parts must be annealed.
2. For plastic parts with high melting temperature, high viscosity and more than 200g, it is recommended to use a heated extension nozzle.
3. The cooling speed is fast, and the mold gating system is based on the principle of short thickness. It is advisable to set up a cold well, the gate should be large and the mold should be heated.
4. If the material temperature is too low, it will cause material shortage, plastic parts will be dull, and if the material temperature is too high, it will easily overflow and plastic parts will bubble. When the mold temperature is low, the shrinkage, elongation and impact strength are high, while the bending, compression and tensile strength are low. When the mold temperature exceeds 120℃, the plastic parts cool slowly and are easy to deform and stick to the mold.
2. How to inject PC material?
1 The influence of high thermal conductivity of PC is considered. It is difficult to control the processing temperature, which easily leads to the phenomenon of "delamination" during molding. Appropriate temperature control system can improve the temperature rise of melt.
2 carefully control the temperature. Adopt advanced mineral filling heating ring (belt) and automatic tuning controller to improve temperature control; Pay attention to the temperature control of the screw end of the barrel, which can improve the defects such as silver line and scorch mark.
3. Use a new special screw head to improve the shearing phenomenon in the plasticizing process and ensure the linear transportation of materials.
Adopt special injection screw for PC. It is suggested to adopt medium and long feeding section (7 spiral), long screw (8~ 10 spiral) and shallow spiral groove compression section.
5. Use the special screw head check valve (NRV) for PC injection molding. PP check valve (NRV) will cause excessive shearing of molten material, so it must be equipped with a "suction" seat.
It is best to use chrome-plated thread in the feed section of the screw.
7. Wash the barrel and screw thoroughly every time the injection molding machine stops, otherwise the check valve will break and the screw coating will peel off easily.
8 moisture control. When the weather is rainy or humid, the product must be dry.
3. What are the molding processes of 3.PC?
Polycarbonate (PC) is a colorless and transparent amorphous thermoplastic material.
Its name comes from its internal CO3 group. Polycarbonate is colorless, transparent, heat-resistant, impact-resistant and flame-retardant, and has good mechanical properties at ordinary use temperature.
The same performance is close to PMMA. Compared with polycarbonate, polycarbonate has good impact resistance, high refractive index and good processability, and it needs to add inhibitors to reach UL94 V-0 level.
PC can be injection molded, extruded, molded, blow molded, thermoformed, printed, bonded, coated and machined, and the most important processing method is injection molding. Pre-drying must be carried out before molding, and the moisture content should be lower than 0.
02%, a small amount of water processing at high temperature will produce white turbidity, silver lines and bubbles, and PC has considerable forced high elastic deformation ability at room temperature. It has high impact toughness and can be cold formed by cold pressing, cold drawing and cold rolling.
The molecular weight of PC for extrusion should be more than 30,000, and the gradual pressure screw should be adopted, with the length-diameter ratio of 1: 18 ~ 24 and the compression ratio of 1:2. 5. Extrusion blow molding, injection-blow molding and injection-stretch-blow molding can be used to form high-quality and transparent bottles.
There are many kinds of PC alloys, which can improve the defects of high viscosity (processability) of PC melt and easy stress cracking of products. PC and different polymers form alloys or * * * mixtures to improve the material properties. .
4. What is the common sense of injection molding machine?
First, the preparation work before the start of the injection molding machine
1. Wear the safety protective clothing specified in the workshop before taking up the post for production.
2. Clean the environment around the equipment and don't store anything irrelevant to production.
3. Clean up the sundries inside and outside the workbench and equipment, and wipe the guide rail of the injection seat and the pull rod of the clamping part with clean cotton yarn.
4, check the equipment control switch, button, wire, operating handle, handwheel for damage or failure. Each switch and handle should be in the "off" position.
5, check the various parts of the equipment safety protection device in good condition, sensitive and reliable work. Check whether the "emergency stop" of the test is effective and reliable, whether the safety door slides flexibly and whether the switch limit switch can be touched.
6. Safety protection devices on equipment (such as mechanical locking lever, baffle, safety protection switch, etc.). ) Don't move, modify or deliberately make it invalid.
7. Check whether the screws of each part are tightened and loosened. If any abnormality or damage is found in the parts, it should be reported to the foreman, who will handle it himself or notify the maintenance personnel.
8, check the cooling water pipeline, test the water, check whether the water flow is unobstructed, whether it is blocked or dripping.
9. Check whether there are foreign objects in the hopper. Nothing is allowed to be stored above the hopper. The hopper cover should be covered to prevent dust and sundries from falling into the hopper.
Second, open the injection molding machine.
1. Turn on the main power switch of the machine tool, check whether the equipment leaks electricity, preheat the barrel and mold according to the set process temperature requirements, and keep the temperature of the barrel for more than 20 minutes when it reaches the process temperature to ensure the uniform temperature of all parts of the barrel.
2. Open the cooling water valve of the oil cooler, cool the oil return and water delivery throat, and start the oil pump by inching. Only when no abnormal phenomenon is found can the oil pump be officially started, and it can not run until "Motor Start" is displayed on the screen to check whether the safety door works normally.
3, manually start the screw rotation, check the screw rotation for abnormal sound and stuck.
4, the operator must use the exit, such as exit switch failure are not allowed to boot, it is strictly prohibited not to use the exit (cover) operation.
5. Cover and fix the covers and protective covers of rotating parts of various electrical appliances, hydraulic and operating equipment.
6, the operator on duty, without permission, no one is allowed to press the button and handle, no two or more people at the same time operating the same injection molding machine.
7. When placing molds and inserts, they should be stable, accurate and reliable. If any abnormality is found during mold clamping, stop the machine immediately, and notify relevant personnel to eliminate the fault.
8. When repairing the machine or cleaning the mold for a long time (more than 10 minutes), it is necessary to withdraw the injection seat, make the nozzle leave the mold and turn off the motor. When the maintenance personnel repair the machine, the operator shall not leave his post.
9. When someone operates the machine or mold, no one is allowed to start the motor.
10, when the body enters the machine tool or mold opening, the power supply must be cut off.
1 1. When opening the mold, avoid hitting the fixed mold with the injection seat to avoid the fixed mold falling off.
12. Generally, the air injection should not exceed 5 seconds at a time. If two consecutive injections fail, pay attention to inform nearby personnel to avoid the danger zone. When cleaning the nozzle rubber head, it is not allowed to clean it directly by hand. Iron tongs or other tools should be used to avoid burns.
13. The glue melting cylinder has high temperature, high pressure and high power during its operation. It is forbidden to trample, climb and put things aside on the melting pot to prevent soup injury, electric shock and fire.
65438+
15. When abnormal noise, peculiar smell, sparks, oil leakage and other abnormal conditions are found during the operation of the machine tool, it shall immediately stop the machine and immediately report to the relevant personnel to explain the fault phenomenon and possible reasons.
16. Pay attention to safe operation. Do not perform any operation that may cause personal injury or damage the equipment for any reason or excuse.
Third, the downtime considerations
1. Close the gate of the hopper, normally produce until there is no material in the barrel or manually inject air for preforming, and repeat for several times until there is no molten material ejected from the nozzle.
2. If corrosive substances (such as PVC) are produced, other raw material cleaning machine cylinders and screws must be used when stopping.
3. The injection base is separated from the fixed template, and the mold is in an open state.
4. Close the cooling water pipeline, put all switches in the "off" position, and turn off the main power switch of the machine tool when the last shift stops on holidays.
5, clean up the machine tool, workbench and ground sundry, grease and dust, keep the workplace clean and tidy.
5. Basic knowledge of injection molding
Injection molding is an engineering technology, which involves transforming plastics into useful products that can maintain their original characteristics. The important technological conditions of injection molding are temperature, pressure and corresponding action time, which affect the plasticizing flow and cooling.
I. Temperature control
1, barrel temperature: The temperatures to be controlled during injection molding include barrel temperature, nozzle temperature and mold temperature. The first two temperatures mainly affect the plasticization and flow of plastics, while the latter temperature mainly affects the flow and cooling of plastics. The flowing temperature of each plastic is different, and the flowing temperature and decomposition temperature of the same plastic are different because of its different source or brand. This is because the average molecular weight and molecular weight distribution are different, and the plasticizing process of plastics in different types of injection molding machines is also different, so the temperature of the barrel is also different.
2. Nozzle temperature: The nozzle temperature is usually slightly lower than the highest temperature of the barrel, which is to prevent the "salivation phenomenon" that may occur in the straight-through nozzle. The nozzle temperature should not be too low, otherwise the molten material will solidify prematurely, blocking the nozzle, or the product performance will be affected because the solidified material is injected into the mold cavity.
3. Mold temperature: Mold temperature has a great influence on the internal performance and appearance quality of products. Mold temperature depends on the crystallinity of plastics, the size and structure of products, performance requirements and other technological conditions (melt temperature, injection speed and pressure, molding cycle, etc.). ).
2. Pressure control: The pressure during injection molding includes plasticizing pressure and injection pressure, which directly affects the plasticization of plastics and product quality.
1. Plasticizing pressure: (Back pressure) When a screw injection molding machine is used, when the screw rotates reversely, the pressure on the melt at the top of the screw is called plasticizing pressure, also known as back pressure. This pressure can be adjusted by the safety valve in the hydraulic system. In injection, the plasticizing pressure and screw speed are constant, so increasing the plasticizing pressure will increase the melt temperature, but will reduce the plasticizing speed. In addition, increasing the plasticizing pressure can often make the melt temperature uniform, the pigment mixed evenly, and the gas in the melt can be exhausted. In general operation, the plasticizing pressure should be as low as possible under the premise of ensuring good product quality. Its specific value varies with the type of plastic used, but rarely exceeds 20 kg/cm2.
2. Injection pressure: At present, the injection pressure of almost all injection molding machines is based on the pressure exerted by the top of the plunger or screw on the plastic (converted from oil pressure). The function of injection pressure in injection molding is to overcome the flow resistance of plastic from the barrel to the cavity, give the melt the speed of filling the mold and make the melt dense.
Third, the molding cycle
The time required to complete an injection molding process is called molding cycle, which is also called molding cycle. It actually includes the following parts:
Forming cycle: the forming cycle directly affects the labor cycle rate and equipment utilization rate. Therefore, in the production process, all relevant time in the molding cycle should be shortened as much as possible under the premise of ensuring quality. In the whole molding cycle, injection time and cooling time are the most important and have a decisive influence on product quality. The mold filling time in injection time is directly proportional to the mold filling rate, and the mold filling time in production is generally about 3-5 seconds.
The holding time in injection time is the time to pressurize the plastic in the cavity, which accounts for a large proportion in the whole injection time, generally about 20- 120 seconds (for ultra-thick parts, it can be as high as 5- 10 minutes). Before the melt at the gate is frozen, the holding time has an effect on the dimensional accuracy of the product, but it has no effect later. The holding time also has an optimal value. Mold temperature and the size of main runner and main runner. If the dimensions and process conditions of sprue and gate are normal, the pressure value with the smallest fluctuation range of product shrinkage is usually taken as the standard. The cooling time mainly depends on the thickness of the product, the tearing and crystallization properties of plastic and the mold temperature. The end of cynicism time should be based on the principle of ensuring that the product will not change when demoulding. Generally, the cooling time is about 30~ 120 seconds, so it does not need a long cooling time, which not only reduces the production efficiency, but also makes it difficult to demould complex parts, and even produces demoulding stress when forced demoulding. Another time in the molding cycle is related to whether the production process is continuous and automated and the degree of industrialization.
6. Who has a detailed introduction of injection molding PC?
1.PC polycarbonate is an engineering plastic with excellent mechanical properties and heat resistance.
1) Features:
? PC is a non-toxic, highly transparent amorphous engineering plastic. Shrinkage rate "0.5 ~ 0.7%";
? Hard plastics with good mechanical properties and high impact strength. It is resistant to heat radiation, light stability and weather resistance.
? Good electrical performance, insulation and corona resistance. High oil resistance, low temperature resistance and thermal deformation resistance. "The product can be used at+130℃ and -80℃.
? The melt has high viscosity, is not resistant to strong alkali and ultraviolet rays, and is easy to hydrolyze and crack.
2) Processing performance:
PC has general formability and is suitable for injection, extrusion, molding, thermoforming, printing, metal cutting and bonding.
Injection molding:
? PC amorphous plastic has good thermal stability, wide molding temperature range, serious decomposition over 300℃, and no toxic or corrosive gas during decomposition.
? Water sensitivity is strong, and it is easy to hydrolyze at high temperature. When molding, the water content is controlled below 0.02%, otherwise silver lines, bubbles and hydrolysis are easy to appear.
? The fluidity of PC is poor, and the edge overflows when the gap is 0.06mm during molding. Fluidity is sensitive to temperature, and the cooling speed is fast.
? Products with small shrinkage and high precision are easy to process, but the internal stress of the products is large, so it is best to carry out post-treatment to eliminate the internal stress.
? High viscosity, insensitive to shear and fast cooling. The sprue and gate of the molding die should be thick and short. The mold temperature is 70 ~ 65438 020℃. The die has low temperature, high shrinkage, high elongation and impact strength, but low bending and compressive strength.
3) Main uses:
Electronic industry "connector, coil skeleton" instrument lampshade, medical surgical instruments and other fields.
7. What is PC plastic and what are its main products?
Suitable for making small instrument parts, insulating transparent parts and impact-resistant parts. The formability is 1. Amorphous materials have good thermal stability, wide molding temperature range and poor fluidity.
Small hygroscopicity, but sensitive to water, must be dried. Molding shrinkage is small and prone to melt cracking and stress concentration, so the molding conditions must be strictly controlled and the plastic parts must be annealed.
2. For plastic parts with high melting temperature, high viscosity and more than 200g, it is recommended to use a heated extension nozzle. 3. The cooling speed is fast, and the mold gating system is based on the principle of short thickness. It is advisable to set up a cold well, the gate should be large and the mold should be heated.
4. If the material temperature is too low, it will cause material shortage, plastic parts will be dull, and if the material temperature is too high, it will easily overflow and plastic parts will bubble. When the mold temperature is low, the shrinkage, elongation and impact strength are high, while the bending, compression and tensile strength are low.
When the mold temperature exceeds 120℃, the plastic parts cool slowly and are easy to deform and stick to the mold.