PC injection molding knowledge

1. Related knowledge of PC plastic

PC plastic (polycarbonate)

English name: Polycarbonate

Specific gravity: 1.18- 1.20g/cubic centimeter Molding shrinkage: 0.5-0.8% Molding temperature: 230-320℃ Drying conditions: 110-120℃ Can be used for a long time at -60~120℃ for 8 hours

Material performance impact strength High, good dimensional stability, colorless and transparent, good colorability, good electrical insulation, corrosion resistance, and wear resistance, but poor self-lubrication, prone to stress cracking, easy to hydrolyze at high temperatures, and poor compatibility with other resins. Suitable for making small instrument parts, insulating transparent parts and impact-resistant parts

Molding properties 1. Amorphous material, good thermal stability, wide molding temperature range, poor fluidity. It absorbs little moisture but is sensitive to water and must be dried. The molding shrinkage is small and melt cracking and stress concentration are prone to occur, so the molding conditions should be strictly controlled and the plastic parts must be annealed.

2. For plastic parts with high melting temperature and high viscosity, larger than 200g, a heated extension nozzle should be used.

3. The cooling speed is fast, the mold pouring system should be thick and short, a cold well should be set up, the gate should be large, and the mold should be heated.

4. If the material temperature is too low, it will cause material shortage and the plastic parts will be dull. If the material temperature is too high, it will easily overflow and the plastic parts will blister. When the mold temperature is low, the shrinkage, elongation, and impact strength are high, but the bending resistance, compression resistance, and tensile strength are low. When the mold temperature exceeds 120 degrees, the plastic part cools slowly and is prone to deformation and sticking to the mold

2. How to inject PC material

1 Consider the impact of PC’s high thermal conductivity. The processing temperature is difficult to control and can easily lead to "stratification" during molding. An appropriate temperature control system can improve melt temperature rise.

2 Control the temperature carefully. Use advanced mineral-filled heating rings (belts) and automatic tuning controllers to improve temperature control; pay attention to the temperature control of the barrel screw end to improve defects such as silver streaks and scorch marks.

3 Use a new specialized screw head to improve the shear generation during plasticization and ensure the streamlined transportation of materials.

4. Use PC-specific injection screw. It is recommended to use a medium-length feeding section (7 spirals) and a screw with a longer (8-10 spirals) and shallow groove compression section.

5 Use the special screw head stop valve (NRV) for PC injection molding. The PP stop valve (NRV) will cause excessive shearing of the molten material and must be configured to "suck back" the valve seat.

6 It is best to use chrome-plated threads in the screw feeding section.

7. Thoroughly clean the barrel and screw of the injection molding machine every time it is shut down. Otherwise, the stop valve may break and the screw coating may peel off.

8 Moisture control. When the weather is rainy or humid, materials must be dried for production.

3. What are the molding processes of PC?

(Polycarbonate, PC for short) is a colorless and transparent amorphous thermoplastic material.

Its name comes from the CO3 group inside it. Polycarbonate is colorless and transparent, heat-resistant, impact-resistant, flame-retardant BI grade, and has good mechanical properties within normal operating temperatures.

The same performance is close to PMMA. In comparison, polycarbonate has good impact resistance, high refractive index, and good processing performance. It needs to add a resistor to comply with UL94 V-0 level.

PC can be injection molded, extruded, molded, blow molded, thermoformed, printed, bonded, coated and machined. The most important processing method is injection molding. It must be pre-dried before molding, and the moisture content should be below 0.

02%, trace amounts of moisture will cause the product to produce white turbid color, silver threads and bubbles when processed at high temperature. PC has considerable forced high elastic deformation ability at room temperature. It has high impact toughness, so it can be processed by cold pressing, cold drawing, cold rolling and other cold forming processes.

The molecular weight of PC for extrusion should be greater than 30,000, and a gradual compression screw should be used. The length-to-diameter ratio is 1:18~24, and the compression ratio is 1:2.5. Extrusion blow molding can be used, injection- Blow, injection-draw-blow methods are used to form high-quality, highly transparent bottles.

There are many types of PC alloys, which can improve the defects of PC such as high melt viscosity (processability) and easy stress cracking of products. PC forms alloys or mixtures with different polymers to improve material properties. .

4. What is the common sense of using the injection molding machine

1. Preparations before starting the injection molding machine

1. Wear the safety regulations prescribed by the workshop before starting production Protective clothing.

2. Clean the environment around the equipment and do not store any items unrelated to production.

3. Clean the workbench and the debris inside and outside the equipment, and wipe the injection seat guide rail and mold clamping part tie rod with clean cotton yarn.

4. Check whether the control switches, buttons, electrical circuits, operating handles, and handwheels of the equipment are damaged or malfunctioning. Each switch and handle should be in the "off" position.

5. Check whether the safety protection devices of each part of the equipment are intact and work sensitively and reliably. Check whether the "emergency stop" test is effective and reliable, whether the safety door slides flexibly, and whether the limit switch can be triggered when opening and closing.

6. The safety protection devices on the equipment (such as mechanical lock levers, stop plates, safety protection switches, etc.) are not allowed to be moved casually, nor are they modified or intentionally disabled.

7. Check whether the screws in various parts are tightened and whether they are loose. If any abnormality or damage to parts is found, report it to the foreman, who will handle it himself or notify the maintenance personnel to handle it.

8. Check each cooling water pipeline, test the water flow, and check whether the water flow is smooth and whether it is clogged or leaking.

9. Check whether there are foreign objects in the hopper. No items are allowed to be stored above the hopper. The hopper cover should be closed to prevent dust and debris from falling into the hopper.

2. Start up the injection molding machine

1. Turn on the main power switch of the machine tool, check whether the equipment is leaking, and preheat the barrel and mold according to the set process temperature requirements. When the barrel temperature reaches the process temperature, it must be kept warm for more than 20 minutes to ensure uniform temperature in all parts of the barrel.

2. Open the cooling water valve of the oil cooler, cool the oil return and water transport pipes, and start the oil pump. If no abnormality is found, the oil pump can be officially started. Wait until the screen displays "Motor on" "Only after the operation can be carried out, check whether the safety door is functioning normally.

3. Manually start the screw rotation and check whether the screw rotation sound is abnormal or stuck.

4. The operator must use a safety door. If the safety door travel switch fails, the machine is not allowed to be started. It is strictly prohibited to operate without a safety door (cover).

5. The various covers and protective covers of the electrical, hydraulic and rotating parts of the operating equipment must be covered and fixed.

6. Anyone who is not an operator on duty is not allowed to press buttons or handles without permission. Two or more people are not allowed to operate the same injection molding machine at the same time.

7. When placing molds and inserts, they must be stable and reliable. If any abnormalities are found during the mold closing process, the machine should stop immediately and notify relevant personnel to troubleshoot.

8. When the machine is repaired or the mold is cleaned for a long time (more than 10 minutes), the injection seat must be moved back to make the nozzle leave the mold, and the motor is turned off. When the maintenance personnel repair the machine, the operator must not Off duty.

9. No one is allowed to start the motor when someone is handling the machine or mold.

10. When the body enters the machine tool or the mold opening, the power supply must be cut off.

11. Avoid hitting the fixed mold with the injection seat when the mold is open to prevent the fixed mold from falling off.

12. The air injection generally does not exceed 5 seconds each time. When the injection fails twice in a row, please notify nearby personnel to avoid the danger zone. When cleaning the nozzle rubber head, do not clean it directly with your hands. Use iron pliers or other tools to avoid burns.

13. The melt barrel is exposed to high temperature, high voltage and high electricity during operation. It is prohibited to step on, climb or place objects on the melt barrel to prevent injury, electric shock and fire.

14. When the hopper is not loading, it is not allowed to use metal rods or rods to poke the hopper roughly to avoid damaging the split screen, screen shield and magnet frame in the hopper. It is easy to cause serious equipment damage accidents in which metal rods get caught in the barrel.

15. When abnormal noise, odor, sparks, oil leakage and other abnormal conditions are found during the operation of the machine tool, the machine should be stopped immediately and reported to the relevant personnel immediately, and the fault phenomenon and possible reasons should be explained.

16. Pay attention to safe operation and do not allow any reason or excuse to operate in a manner that may cause personal injury or damage to the equipment.

3. Precautions for shutdown

1. Close the hopper gate and proceed with normal production until there is no material in the barrel or manually operate the empty injection - pre-molding, repeat several times until No molten material is ejected from the nozzle.

2. If corrosive materials (such as PVC) are produced, the barrel and screw must be cleaned with other raw materials when shutting down.

3. Separate the injection seat from the fixed template, and the mold is in the open state.

4. Close the cooling water pipeline, turn each switch to the "off" position, and turn off the main power switch of the machine tool when the last shift is shut down during holidays.

5. Clean the machine tools, workbench and floor debris, oil stains and dust to keep the workplace clean and tidy.

5. Basic knowledge of injection molding

Injection molding is an engineering technology that involves transforming plastic into products that are useful and maintain their original properties. The important process conditions for injection molding are the temperature, pressure and corresponding action time that affect plasticization flow and cooling.

1. Temperature control

1. Barrel temperature: The temperatures that need to be controlled during the injection molding process include barrel temperature, nozzle temperature and mold temperature, etc. The first two temperatures mainly affect the plasticization and flow of plastic, while the latter temperature mainly affects the flow and cooling of plastic. Each plastic has a different flow temperature. The same plastic has different flow temperatures and decomposition temperatures due to different sources or grades. This is due to different average molecular weights and molecular weight distributions. Plastics in different types of injection molding have different flow temperatures and decomposition temperatures. The plasticizing process in the machine is also different, so the temperature of the barrel is also different.

2. Nozzle temperature: The nozzle temperature is usually slightly lower than the maximum temperature of the barrel. This is to prevent the "salivation" that may occur in the straight-through nozzle. The nozzle temperature cannot be too low, otherwise it will cause premature solidification of the melt and block the nozzle, or the premature solidification material will be injected into the mold cavity and affect the performance of the product

3. Mold temperature: Mold temperature has a significant impact on The intrinsic performance and apparent quality of the product have a great influence. The mold temperature depends on the crystallinity of the plastic, the size and structure of the product, performance requirements, and other process conditions (melt temperature, injection speed and pressure, molding cycle, etc.).

2. Pressure control: The pressure during the injection molding process includes plasticizing pressure and injection pressure, and directly affects the plasticization of plastic and product quality.

1. Plasticizing pressure: (back pressure) When using a screw injection machine, the pressure on the melt at the top of the screw when the screw rotates and retreats is called plasticizing pressure, also known as back pressure. The size of this pressure can be adjusted through the relief valve in the hydraulic system. In injection, the size of the plasticizing pressure remains unchanged with the screw speed. Increasing the plasticizing pressure will increase the temperature of the melt, but will reduce the plasticizing speed. In addition, increasing the plasticizing pressure can often make the temperature of the melt uniform, the color materials can be mixed evenly, and the gas in the melt can be discharged. In general operations, the plasticizing pressure should be determined as low as possible while ensuring excellent product quality. The specific value varies with the type of plastic used, but it usually rarely exceeds 20 kg/cm2.

2. Injection pressure: In current production, the injection pressure of almost all injection machines is based on the pressure exerted by the plunger or the top of the screw on the plastic (converted from the oil line pressure) of. The role of injection pressure in injection molding is to overcome the flow resistance of the plastic from the barrel to the cavity, give the molten material a filling rate and compact the molten material.

3. 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 labor productivity and equipment utilization. Therefore, during the production process, the molding cycle should be shortened as much as possible while ensuring quality. Each relevant time. In the entire molding cycle, injection time and cooling time are the most important. They have a decisive impact on the quality of the product. The filling time in the injection time is directly inversely proportional to the filling rate. The filling time in production is generally About 3-5 seconds.

The holding time in the injection time is the pressure time on the plastic in the cavity. It accounts for a large proportion of the entire injection time, generally about 20-120 seconds. (Extra thick parts can take up to 5~10 minutes). The holding time before the melt is frozen at the gate will have an impact on the dimensional accuracy of the product. If it is later, it will have no effect. The holding time also has the most favorable effect. value, it is known that it depends on the material temperature, mold temperature and the size of the main channel and gate. If the size of the main channel and gate and the process conditions are normal, the pressure with the smallest fluctuation range of the product shrinkage is usually obtained. The cooling time is mainly determined by the thickness of the product, the plastic's plastic properties and crystallization properties, and the mold temperature. The end of the cooling time should be based on the principle of ensuring that no changes are caused when the product is demoulded, and the cooling time is Generally, it is between 30 and 120 seconds. It is not necessary for the cooling time to be too long. It will not only reduce the production efficiency, but also cause difficulty in demoulding complex parts. When forced demoulding, demoulding stress will even occur. Other steps in the molding cycle The time is related to whether the production process is continuous and automated, as well as the degree of industrialization.

6. Does anyone have a detailed introduction to injection molded PC

1. PC polycarbonate is a mechanical property Very good engineering plastic with excellent heat resistance.

1) Characteristics:

? PC is a non-toxic, highly transparent amorphous engineering plastic. Shrinkage rate "0.5~0.7%";

? A hard plastic with good mechanical properties and high impact resistance. Resistant to thermal energy radiation, and has good light stability and weather resistance.

? Good electrical properties, insulation and corona resistance. Resistant to oil, low temperature and high heat distortion temperature. "The product can be used at temperatures of +130°C and -80°C.

? The melt viscosity is high, not resistant to strong alkali, not resistant to ultraviolet rays, and easy to hydrolyze and crack.

2) Processing performance:

PC molding performance is average, suitable for injection, extrusion, molding, thermoforming, printing, metal cutting and bonding, etc.

Injection molding: < /p>

? PC amorphous plastic has good thermal stability and a wide molding temperature range. It will decompose seriously when it exceeds 300°C. It is non-toxic and non-corrosive gas when it decomposes.

? Water sensitive. It has strong resistance and is easy to be hydrolyzed at high temperatures. The water content should be controlled below 0.02% during molding, otherwise silver filaments, bubbles and hydrolysis will easily occur.

? PC has poor fluidity and overflows when the gap is 0.06mm during molding. It is sensitive to temperature and has a fast cooling rate.

It has small shrinkage and is easy to process products with high precision, but the internal stress of the product is large, so it is best to post-process to remove the internal stress. ? High viscosity, insensitive to shear, and cools quickly. The runner and gate of the mold should be thick and short. The mold temperature should be 70~120°C.

The mold temperature is low, the shrinkage, elongation, and impact resistance are high, but the bending and compressive strength are low.

3) Main uses:

In the electronics industry, "connectors, coil bobbins", instrument lampshades, 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. Molding properties 1. Amorphous material, good thermal stability , wide molding temperature range and poor fluidity.

It has low hygroscopicity but is sensitive to water and must be dried. The molding shrinkage is small and melt cracking and stress concentration are prone to occur, so the molding conditions should be strictly controlled and the plastic parts must be annealed.

2. For plastic parts with high melting temperature and high viscosity, larger than 200g, a heated extension nozzle should be used. 3. The cooling speed is fast, the mold pouring system should be thick and short, a cold well should be set up, the gate should be large, and the mold should be heated.

4. If the material temperature is too low, it will cause material shortage and the plastic parts will be dull. If the material temperature is too high, it will easily overflow and the plastic parts will blister. When the mold temperature is low, the shrinkage, elongation, and impact strength are high, but the bending resistance, compression resistance, and tensile strength are low.

When the mold temperature exceeds 120 degrees, the plastic parts cool slowly and are prone to deformation and sticking to the mold.