pc plastic (polycarbonate)
English name: Polycarbonate
Specific gravity: 1.18-1.20 g / cm3 Molding shrinkage: 0.5-0.8% Molding temperature: 230-320 ° C. Drying conditions: 110-120 ° C for 8 hours Can be used for a long time under the -60~120 ℃. 120℃ for long-term use
Material properties High impact strength, good dimensional stability, colorless and transparent, good coloring, electrical insulation, corrosion resistance, wear resistance, but poor self-lubrication, stress cracking tendency, high temperature hydrolysis, and other resins with poor compatibility. Suitable for the production of instrumentation small parts, insulation and transparent parts and impact parts
Molding properties 1. Amorphous material, good thermal stability, wide range of molding temperature, poor fluidity. Moisture absorption is small, but sensitive to water, must be dried. Molding shrinkage is small, easy to melt cracking and stress concentration, so the molding conditions should be strictly controlled, the plastic parts must be annealed.
2. High melt temperature, high viscosity, greater than 200g of plastic parts, it is appropriate to use heated extension nozzle.
3. Cooling speed, mold pouring system to coarse, short for the principle, it is appropriate to set up a cold material well, the gate should be taken as a large, the mold should be heated.
4. Material temperature is too low will cause the lack of material, molded parts without luster, material temperature is too high easy to overflow edge, molded parts blistering. Mold temperature is low shrinkage, elongation, high impact strength, bending, compression, tensile strength is low. When the mold temperature exceeds 120 degrees Celsius, the cooling of the plastic parts is slow, easy to deform and stick to the mold
2. How to injection molding PC material
1 Consider the impact of high thermal conductivity of PC. Processing temperature is difficult to control, easy to lead to molding "delamination" phenomenon, the appropriate temperature control system to improve the melt heating.
2 Careful temperature control. The use of advanced mineral-filled heating ring (belt) and auto-tuning controller to improve temperature control; pay attention to the temperature control of the cylinder screw end, can improve the silver lines, scorch marks and other defects.
3 Use new specialized screw head to improve the occurrence of shear during plasticizing and to ensure the flow line delivery of materials.
4 Adopt PC specialized injection screw. It is recommended to use a medium length charging section (7 screws) and a screw with a longer (8 to 10 screws) and shallow fluted compression section.
5 Use a special screw head check valve (NRV) for PC injection molding. PP check valves (NRV) can cause excessive shearing of the melt and must be equipped with a "backsiphon" back to the valve seat.
6 It is best to use chrome-plated threads on the charging section of the screw.
7 Every time you stop, thoroughly clean the barrel and screw of the injection molding machine, otherwise, it is prone to breakage of the stopcock and stripping of the screw coating.
8 Moisture control. Weather rain or humid production must dry material.
3. What are the molding processes of PC
(Polycarbonate, abbreviated as PC) is a colorless and transparent amorphous thermoplastic material.
It gets its name from the CO3 group within it. Polycarbonate is colorless and transparent, heat-resistant, impact-resistant, flame-retardant BI grade, and has good mechanical properties within ordinary use temperature.
With performance close to PMMA, compared to the polycarbonate impact resistance, high refractive index, good processing performance, need to add a retarder to comply with UL94 V-0 level.
PC can be injection molding, extrusion, molding, blow molding, thermoforming, printing, bonding, coating and machining, the most important processing method is injection molding. Must be pre-dried before molding, the moisture content should be less than 0.
02%, trace water processing at high temperatures will make the products produce a whitish color, silver wire and bubbles, PC at room temperature has a considerable forced high elastic deformation capacity. The impact toughness is high, so it can be cold pressed, cold drawn, cold rolled and other cold molding process.
Extrusion PC molecular weight should be greater than 30,000, to use gradual compression screw, L/D ratio of 1:18 ~ 24, compression ratio of 1:2. 5, can be used for extrusion blow molding, injection - blow, injection - pull - blow molding high quality, high transparent bottles.
PC alloy variety, improve the PC melt viscosity (processability) and products prone to stress cracking and other defects, PC and different polymers to form alloys or **** mixtures, to improve the material properties. .
4. What is the common sense of using the injection molding machine
First, the injection molding machine before the start of the preparatory work
1, before going on duty to produce wear a good workshop provisions of safety and protective clothing.
2, clean up the environment around the equipment, not allowed to store any items not related to production.
3, clean up the workbench and equipment inside and outside the debris, with clean cotton gauze to wipe the injection seat rail and mold part of the tie rod.
4, check the equipment control switches, buttons, electrical wiring, operating handles, handwheels are not damaged or malfunction. Each switch, handle should be in the "off" position.
5, check whether the equipment safety protection devices are intact, work sensitive and reliable. Check whether the test "emergency stop" is effective and reliable, whether the safety door sliding flexible, whether the switch can touch the limit switch.
6, the equipment on the safety protection devices (such as mechanical locking lever, stop plate, the safety protection switch, etc.) are not allowed to move casually, and not allowed to modify or deliberately make it useless.
7, check the parts of the screws are tightened, there is no loosening, found that the parts are abnormal or damaged phenomenon, should be reported to the foreman, the foreman to deal with their own or notify the maintenance staff to deal with.
8, check the cooling water pipeline, try to pass the water, to see whether the water flow is smooth, whether blocked or dripping.
9, check the hopper whether there are foreign objects, hopper is not allowed to store any items above the hopper, hopper cover should be covered to prevent dust, debris fall into the hopper.
Second, the injection molding machine start
1, close the machine's main power switch, check whether the equipment leakage, according to the set process temperature requirements for the barrel, mold preheating, in the barrel temperature to reach the process temperature must be kept warm for more than 20 minutes, to ensure that the barrel of the temperature of all parts of the temperature uniform.
2, open the oil cooler cooling water valve, the return oil and water pipeline cooling, start the oil pump, no abnormalities found, before officially starting the oil pump, to be displayed on the screen "motor open" before running action, check whether the role of the safety gate is normal.
3, manually start the screw rotation, check the screw rotation sound and jamming.
4, the operator must use the safety gate, such as the safety gate travel switch failure is not allowed to boot, is strictly prohibited without the use of safety gate (cover) operation.
5, running equipment, electrical, hydraulic and rotating parts of the various covers, shields, etc. to cover, fixed.
6, non-shift operator, without permission, no one is allowed to press the buttons, handles, two or more people are not allowed to operate the same injection molding machine at the same time.
7, the placement of molds, inserts should be stable and reliable, molding process found abnormalities should be stopped immediately, notify the relevant personnel to remove the fault.
8, machine repair or longer (more than 10 minutes) to clean up the mold, be sure to back up the injection seat so that the nozzle away from the mold, turn off the motor, maintenance personnel repair machine, the operator is not allowed to take off duty.
9, someone is not allowed to start the motor when dealing with the machine or mold.
10, the body into the machine tool or mold open file, you must cut off the power supply.
11, avoid when the mold is open, with the injection seat hit the fixed mold, so as to avoid the fixed mold fall off.
12, to the empty injection is generally not more than 5 seconds each time, two consecutive injection, pay attention to notify the neighboring personnel to avoid the danger zone. Clean up the nozzle tip, not allowed to clean up directly by hand, the application of iron pincers or other tools to avoid burns.
13, the melting tube in the process of high temperature, high pressure and high electricity, prohibited in the melting tube on the trampling, climbing and shelving items to prevent soup injuries, electric shock and fire.
14, in the hopper does not feed the case, do not allow the use of metal rods, rods, rough poke hopper, to avoid damage to the hopper within the sub-screen, screen guards and magnet frame, if the screw rotation state is very easy to occur in the barrel of the metal rod involved in the serious damage to the equipment accident.
15, machine tool operation found in the equipment, abnormal sound, odor, sparks, oil leakage and other anomalies, you should immediately stop, immediately report to the relevant personnel, and explain the failure phenomenon and the possible reasons for the occurrence.
16, pay attention to the safe operation, not allowed to use any reason or excuse, make may cause personal injury or damage to equipment operation.
Third, the shutdown notes
1, close the hopper gate, normal production to the barrel of no material or manual operation of the empty injection - pre-molding, repeated several times, until the nozzle no melt shot.
2, if the production of corrosive materials (such as PVC), stop the barrel, screw must be cleaned with other raw materials.
3, so that the injection seat and the fixed template is detached, the mold is in the open state.
4, close the cooling water pipeline, turn the switch to the "off" position, the last shift of the holiday shutdown to turn off the machine's main power switch.
5, clean up the machine tool, workbench and ground debris, grease and dust, keep the workplace clean and tidy.
5. Basic knowledge of injection molding
Injection molding is an engineering technology, which involves the content of the plastic into a useful and can maintain the original performance of the product. The important process conditions of injection molding is to affect the plasticizing flow and cooling temperature, pressure and the corresponding time of each role.
First, temperature control
1, barrel temperature: injection molding process needs to control the temperature of the barrel temperature, nozzle temperature and mold temperature. The first two temperatures mainly affect the plasticization and flow of plastic, while the latter temperature mainly affects the flow of plastic and cooling. Each kind of plastic has a different flow temperature, the same kind of plastic, due to different sources or grades, its flow temperature and decomposition temperature is different, this is due to the average molecular weight and molecular weight distribution due to the different plastic in different types of injection molding machine plasticization process is also different, and thus the choice of barrel temperature is not the same.
2, the nozzle temperature: the nozzle temperature is usually slightly lower than the maximum barrel temperature, which is to prevent the melt in the straight-through nozzle may occur "salivation phenomenon. Nozzle temperature can not be too low, otherwise it will cause early condensation of the melt and the nozzle blocked, or due to early condensation of the material injected into the mold cavity and affect the performance of the product
3, mold temperature: mold temperature has a great impact on the intrinsic properties of the product and the apparent quality. Mold temperature is determined by the presence or absence of plastic crystallinity, product size and structure, performance requirements, and other process conditions (melt temperature, injection speed and injection pressure, molding cycle, etc.).
Second, the pressure control: injection molding process pressure, including plasticizing pressure and injection pressure of two kinds, and directly affect the plasticization of plastic and product quality.
1, plasticizing pressure: (back pressure) the use of screw-type injection machine, the top of the screw melt in the screw rotation back when the pressure is known as plasticizing pressure, also known as back pressure. The size of this pressure can be adjusted by the relief valve in the hydraulic system. In the injection, the size of the plasticizing pressure is with the screw speed are unchanged, then increase the plasticizing pressure that will increase the temperature of the melt, but will reduce the speed of plasticization. In addition, increasing the plasticizing pressure often makes the temperature of the melt uniform, the color mixing uniform and the discharge of the gas in the melt. General operation, the decision of the plasticizing pressure should be in order to ensure good quality products under the premise of the lower the better, the specific value is with the varieties of plastics used, but usually rarely more than 20 kg / cm 2.
2, injection pressure: in the current production, almost all of the injection pressure of the injection machine is to the plunger or the top of the screw on the plastic applied pressure (converted from the oil pressure) prevail. The role of injection pressure in injection molding is to overcome the resistance to flow of plastic from the barrel to the cavity, to give the melt filling rate and compaction of the melt.
Third, the molding cycle
The time required to complete an injection molding process is called the molding cycle, also known as the molding cycle. It actually includes the following parts:
Molding cycle: the molding cycle directly affects the labor rate and equipment utilization. Therefore, in the production process, should be under the premise of quality assurance, try to shorten the molding cycle of each relevant time. In the entire molding cycle, the injection time and cooling time is the most important, they have a decisive impact on the quality of products. The mold filling time in the injection time is directly inversely proportional to the mold filling rate, and the mold filling time in production is generally about 3-5 seconds.
The holding time in the injection time is the pressure time of the plastic in the cavity, which accounts for a large percentage of the total injection time, generally about 20-120 seconds (up to 5-10 minutes for extra thick parts). The amount of holding time has an effect on the dimensional accuracy of the product before the melt seals at the gate, but not afterward. The holding time also has an optimum value, which is known to depend on the material temperature, the mold temperature and the size of the main runner and gate. If the dimensions of the main channel and gate as well as the process conditions are normal, the pressure value that minimizes the fluctuation of the shrinkage of the product is usually taken as the optimum value. The cooling time is mainly determined by the thickness of the product, the thermal and crystalline properties of the plastic and the temperature of the mold. Cold irony but the end of the time, should ensure that the products do not cause changes in the principle of demolding, cooling time is generally about 30 ~ 120 seconds between the cooling time is unnecessary, not only reduce production efficiency, for complex parts will also cause demolding difficulties, and forcible demolding will even produce demolding stress. Other time in the molding cycle with the production process is continuous and automated and the degree of dualization and so on.
6. Who has a specific introduction to injection molding PC
1. PC polycarbonate, is a mechanical properties of the engineering plastics, excellent heat resistance.
1) Characteristics:
? PC is non-toxic, highly transparent non-crystalline engineering plastics. Shrinkage rate "0.5 ~ 0.7%";
? Good mechanical properties, high impact strength of the hard plastic. Resistant to heat energy radiation, and light stabilization and good weather resistance.
? Good electrical properties, insulation and corona resistance. Resistant to oil, low temperature and heat deformation temperature is high. "The products can be used at temperatures of +130°C and -80°C.
? Melt viscosity, not resistant to strong alkali, not resistant to ultraviolet rays, easy to hydrolyze and crack.
2) Processing performance:
PC molding performance in general, suitable for injection, extrusion, molding, thermoforming, printing, gold cutting and bonding and other types of processing.
Injection molding:
? PC non-crystalline plastic, good thermal stability, molding temperature range, more than 300 ℃ was a serious decomposition, decomposition of non-toxic and non-corrosive gases.
? Water-sensitive, easy to hydrolyze at high temperatures, molding water content control at 0.02% or less, otherwise easy to silver wire, bubbles and hydrolysis.
? PC mobility is poor, molding gap in 0.06mm when overflow edge. The fluidity is sensitive to temperature, and the cooling speed is fast.
? Shrinkage is small, easy to process high-precision products, but products with high internal stress, it is best to post-processing, to remove internal stress.
? High viscosity, insensitive to shear action, fast cooling. Molding mold sprue and gate is best coarse and short. Mold temperature take 70 ~ 120 ℃. Low mold temperature, shrinkage, elongation, impact strength, but low flexural and compressive strength.
3) Main applications:
Electronic industry "connectors, coil skeleton" instrument lampshade, medical and surgical instruments and other fields.
7. pc plastic is what, what is the main products
Suitable for the production of instrumentation small parts, insulation and transparent parts and impact parts Molding properties 1. amorphous material, good thermal stability, molding temperature range is wide, poor fluidity.
Small moisture absorption, but sensitive to water, must be dried. Molding shrinkage is small, easy to melt cracking and stress concentration, so the molding conditions should be strictly controlled, the plastic parts must be annealed.
2. High melt temperature, high viscosity, greater than 200g of plastic parts, it is appropriate to use heated extension of the nozzle. 3. Cooling speed, mold pouring system to coarse, short for the principle, it is appropriate to set up a cold material well, the gate should be taken as large, the mold should be heated.
4. Material temperature is too low will cause the lack of material, molded parts without luster, material temperature is too high easy to overflow edge, molded parts blistering. When the mold temperature is low, the shrinkage, elongation, impact strength is high, bending, compression, tensile strength is low.
When the mold temperature exceeds 120 degrees, the cooling of the plastic parts is slow, and it is easy to deform and stick to the mold.