1. Reference Injection Times:
Instrument Console: 4-6s; Bumper/Door Inner Panel: 3-5s; Console/Grill: 2-4s; Spoiler/License Plate: 2-4s; Bright Trim/Fender Bumper/Wheel Cover: 1.5-3s; Pillar Trim/Door Inner Panel Trim/Instrument Console Trim: 1.5-3s; Side Panel Trim/Glove Box/Lid: 1-2s; Other Small Parts: 1-2s.
2. Reference Holding Time:
Instrument Console: 15-20s; Panel: 8-12s; Bright Trim/Fender Bumper/Wheel Cover: 6-10s; Pillar Trim/Door Inner Panel Trim/Instrument Console Trim: 5-8s; Side Panel Trim/Glove Box/Lid: 4-6s; Other Small Items: 3-5s

1. Reference Injection Time:
LCD TV Case: 4-6s; Standard Color TV Case: 3-5s; Air Conditioner Case/Panel: 2-4s; Refrigerator Door: 2-4s; Washing Machine Cover: 1.5-3s; Vacuum Cleaner Case: 1.5-3s; Small Appliance Case: 1-2s; Water Dispenser Case: 1.5-3s; Knobs: 0.5-1.5s
2. Reference Holding Time:
LCD TV Case: 10-15s; Standard Color TV Case: 8-12s; Air Conditioner Case/Panel: 6-10s, Refrigerator Door 6-10s, Washing Machine Cover 5-8s, Vacuum Cleaner Housing 5-8s, Small Appliance Housing 4-6s, Water Dispenser Housing 5-8s, Knobs 2-4s

 

1. Reference Injection Time:
Copier Housing 3-5s, Paper Feed Tray 3-5s, Drive Frame 2-4s, Printer Housing 1.5-3s, Paper Feed Tray 1.5-3s, Other Small Items 1-2s
2. Reference Holding Pressure Time:
Copier Housing 10-15s, Paper Feed Tray 8-12s, Drive Frame 6-10s, Printer Housing 5-8s, Paper Feed Tray 4-6s, Other Small Items 3-5s

 

1. Reference Injection Time:
Ultrasound Machine Housing 3-5s, Ultrasound Machine Keyboard Cover 3-5s, Monitor Housing 2-45s, Biochemistry Analyzer Housing 4-6s, Blood Pressure Monitor Housing 1.5-3s, Massager Housing 1.5-3s
2. Reference Holding Time:
Ultrasound Machine Housing 10-15s, Ultrasound Machine Keyboard Cover 8-12s, Monitor Housing 6-10s, Biochemistry Analyzer Housing 10-15s, Blood Pressure Monitor Housing 4-6s, Massager Housing 5-8s

1. Reference Injection Time:
Mobile Phone Housing 1-2s, Telephone Housing 1.5-3s, Intercom Housing 1-2s, PDA Housing 1-2s, Antenna Cover 0.5-1.5s
2. Reference Holding Time:
Mobile Phone Housing 2-4s, Telephone Housing 3-5s, Intercom Housing 2-4s, PDA Housing 2-4s, Antenna Cover 1-3 seconds

1. Reference Injection Time:
Laptop Case 2-4 seconds, Keyboard Case 2-4 seconds, Mouse Case 1-2 seconds, Computer Case Panel 2-4 seconds, Server Panel 2-4 seconds, Server Case 3-5 seconds, Router Case 1.5-3 seconds, Keyboards 0.5-1.5 seconds
2. Reference Holding Time:
Laptop Case 6-10 seconds, Keyboard Case 5-8 seconds, Mouse Case 3-5 seconds, Computer Case Panel 5-8 seconds, Server Panel 5-8 seconds, Server Case 6-10 seconds, Router Case 3-5 seconds, Keyboards 1-3 seconds

 

Polycarbonate (PC) is an excellent engineering plastic. It boasts high transparency and excellent impact toughness, as well as creep resistance, non-toxicity, a wide operating temperature range, excellent dimensional stability, superior electrical insulation, and excellent weather resistance. Therefore, it is widely used in industries such as instrumentation, lighting, electronic and electrical equipment, household appliances, and packaging. Furthermore, with rapid advancement of polymer materials technology, new modified varieties have emerged, greatly expanding its application areas. Simultaneously, its processing technology is gaining increasing attention.
PC is a linear polymer containing benzene rings, isopropyl groups, and ester bonds in its molecular backbone. This structure imparts both rigidity and a certain degree of flexibility, as well as good high-temperature resistance. However, PC also suffers from limitations such as high melt viscosity and moisture sensitivity, making injection molding challenging.
Its processing characteristics are that it has no distinct melting point. Within normal processing temperature range of 230-320℃, melt viscosity is high. Its viscosity is less sensitive to shear rate and more sensitive to temperature, similar to Newtonian fluid behavior. It is also sensitive to moisture, with resin prone to hydrolysis at high temperatures. Finished product is prone to internal stress. Therefore, PC is a relatively difficult plastic to process. Consequently, we encounter numerous problems during actual production. Here we analyze and discuss several common product defects.

Comparatively speaking, PC has good heat resistance. When processing standard PC materials, melt temperature can typically be set between 240-300℃, and even prolonged exposure generally prevents decomposition. Why, however, is discoloration common in production of some electrical appliances? This is because market competition is fierce. To reduce production costs, most manufacturers use modified or recycled PC materials for low- and mid-range electrical appliances. Some even use custom blends containing flame retardants, fillers, and other additives. Since these materials are of various types and plasticization requirements are high, process control is more difficult, resulting in various problems. In response to above phenomenon, it is necessary to consider and find solutions from following aspects:

(1) In terms of process conditions, melting temperature is mainly considered. Generally, barrel temperature should be reduced step by step, especially temperature of the first two sections, and different temperatures should be used for different materials. For example, when using polyethylene (PE) to modify PC to produce large electrical products, barrel temperature should generally be controlled at around 230℃; For example, when using ABS or PS to modify PC to produce small electrical components such as switches and sockets, barrel temperature should generally be controlled at around 250℃; and when using PBT to modify PC to produce lighting products, barrel temperature should generally be controlled at around 280℃. Of course, final selection of molding temperature must also comprehensively consider product shape, size, mold structure, product performance requirements and other aspects. Secondly, raw materials should be fully dried to reduce possibility of trace moisture catalyzing cracking of hot melt. In addition, if screw speed is too fast, back pressure is too high, injection rate is too fast, nozzle aperture, runner, and gate size are too small, melt will generate high shear heat, causing PC to fracture. It is also easy for gas in mold cavity to not be discharged in time, causing local burns and blackening of product.

(2) Equipment: Since PC melt has high viscosity and poor fluidity, it requires high injection pressure, strong metallographic bonding, and decomposition products are highly corrosive to metals. Therefore, when selecting processing equipment, it is required to use small or specially designed, chrome-plated screws, and plasticizing system is not allowed to have dead corners, dead materials, gaps, cracks, etc. Generally speaking, if process conditions are fine, but melt is found to change color during air injection, this indicates that there is a problem with plasticizing system. Plasticizing system needs to be checked one by one, starting from nozzle, to nozzle flange, three small parts, screw, and barrel. Sometimes, product will periodically show large areas of discoloration in two or three molds. This is mostly related to presence of dead material in plasticizing system. When amount of PC decomposition products exceeds a certain level, they have a self-catalytic effect, causing a large area of melt decomposition, especially for plastics with flame retardants added. To solve this problem, it is necessary to find dead material points, such as screw sticking, material accumulation, barrel sticking, etc., and solve them through cleaning, repairing, and polishing.
(3) Materials and operating methods
If black spots are found as soon as machine is turned on, it is mostly related to barrel material accumulation. Therefore, it is important to pay attention to operating procedures. If barrel is loaded with PC material before starting machine, it should be cleaned three to four times with new material at molding temperature (injecting into air). If loaded material is other materials, especially those with poor thermal stability such as PVC or POM, temperature must not be raised during startup, and barrel should not be cleaned with PC material. Instead, it should be cleaned with thermally stable materials such as PS or PE at a lower temperature. After cleaning, barrel temperature should be raised to normal PC processing temperature and then cleaned with PC material before processing can continue.
If production needs to be temporarily suspended during processing, barrel temperature should be lowered to below 160℃ (due to glass transition temperature of PC being 160℃) to prevent material decomposition and discoloration over time. Upon completion of production, barrel can be cleaned with thermally stable materials such as PS or PE, and machine can be shut down after cleaning is complete.
If discoloration persists during production, first check materials for possible problems, such as adulteration with other materials or foreign matter, quality issues with new material, quality of gate material, and correct mixing method. After eliminating these issues, investigate other possible causes. Another factor could be severe environmental pollution, such as excessive airborne dust, mold contamination, or an ineffective drying hopper filter that draws in excessive dust particles. This requires maintaining a clean and tidy workspace at all times. It is best to cover hopper air inlet and outlet with fine gauze, which is essential when processing transparent products.