1、 The concept and hazards of material degradation

In the injection molding process in Dalian, material degradation refers to the phenomenon of molecular chain breakage, cross-linking, or chemical structural changes that occur in polymers under thermal, mechanical, and chemical reactions. This degradation can lead to a decrease in material properties, manifested as:

Reduced mechanical strength

Deterioration in appearance quality (such as discoloration, silver lines)

Changes in rheological properties

Decreased product size stability

Shortened service life

Material degradation not only affects product quality, but also increases waste rate and production costs. Therefore, effectively preventing material degradation is a key step in optimizing injection molding processes.

2、 Temperature control strategy

1. Accurate control of barrel temperature

The temperature of the material barrel is one of the important factors affecting material degradation. Reasonable temperature gradients should be set according to the characteristics of different materials:

For heat sensitive materials such as PVC and POM, the temperature of the barrel should be strictly controlled below their decomposition temperature

Adopting a temperature distribution of "high in the front and low in the back" to avoid the material staying in the barrel for too long

Using high-precision temperature control system and responsive heating elements to ensure temperature fluctuations within ± 2 ℃

2. Optimization of nozzle temperature

The nozzle is the post heating area in contact with the mold, and improper temperature setting can easily lead to material degradation:

The nozzle temperature is usually 5-10 ℃ lower than the temperature at the front end of the barrel

For hot runner systems, it is necessary to ensure that the temperature in each heating zone is uniform

Regularly check the working status of the nozzle heating ring to prevent local overheating

3. Mold temperature management

Appropriate mold temperature can not only improve product appearance, but also reduce material degradation:

Excessive mold temperature will prolong the cooling time and increase the material's thermal history

If the mold temperature is too low, it may cause difficulty in filling, and it is necessary to increase the melt temperature compensation

Using a mold temperature machine to accurately control the mold temperature within the recommended material range

3、 Optimization of process parameters

1. Injection speed and pressure control

Although high-speed and high-pressure injection can improve filling, it will generate excessive shear heat:

For thermosensitive materials, medium low speed injection should be used

Reduce shear rate while ensuring filling through multi-stage injection control

The back pressure setting should be moderate (usually 10-20% of the injection pressure), as excessive back pressure can increase melt shear and residence time

2. Optimization of screw speed

The screw speed directly affects the shear history and temperature rise of the material:

The screw speed of thermosensitive materials should be controlled within a lower range (30-60rpm)

Ensure that the plasticizing time is slightly longer than the cooling time to avoid repeated heating of the material in the barrel

Adopting a progressive screw design to reduce local shear overheating

3. Cycle time management

Excessive cycle time can lead to an increase in the residence time of materials in the barrel:

Optimize cooling system design to shorten cooling time

Balance the hot runner of the mold to reduce material retention inside the hot runner

For multi cavity molds, ensure balanced filling of each cavity

4、 Equipment and mold maintenance

1. Inspection of injection molding machine status

Poor equipment condition is a common cause of material degradation:

Regularly check the wear of screws and barrels, as excessive wear can increase shear and retention

Ensure that the thermocouple is working properly and avoid temperature measurement distortion

Check the sealing of the check valve to prevent melt reflux and repeated heating

2. Key points for mold maintenance

The mold state affects material flow and heat exchange:

Regularly clean the exhaust groove of the mold to avoid local high temperatures caused by trapped gas

Check the size of the gate. A gate that is too small will produce high shear

Ensure smooth cooling water channels and improve cooling efficiency

3. Selection of auxiliary equipment

Choosing appropriate auxiliary equipment can effectively prevent degradation:

Adopting a dehumidification dryer to avoid hydrolysis and degradation caused by moisture

For easily oxidizable materials, consider using a nitrogen protection system

Install a melt filter to remove local overheating caused by impurities

5、 Material processing and formula optimization

1. Raw material pretreatment

Proper material handling is the first step in preventing degradation:

Strictly follow the drying conditions recommended by the material supplier for processing

Avoid mixing materials from different batches

For recycled materials, control the addition ratio and mix thoroughly

2. Application of stabilizer system

Improving material heat resistance through additive formula:

Select appropriate antioxidants and heat stabilizers based on material types

For materials such as PVC, sufficient heat stabilizers must be added

Consider using lubricants to reduce shear heat generation

3. Material selection strategy

Reduce degradation risk from the source:

For high-temperature applications, priority should be given to selecting heat-resistant materials

Consider using material grades with wide processing windows

Evaluate the thermal history sensitivity of materials and select materials suitable for multiple processing

6、 Production management and monitoring

1. Process monitoring system

Establish a comprehensive monitoring system to promptly detect signs of degradation:

Install online viscosity monitoring equipment

Regular sampling for melt finger testing

Establish product appearance inspection standards

2. Process stability control

Maintaining process stability is the key to long-term prevention of degradation:

Establish Standard Operating Procedures (SOP)

SPC control of key process parameters

Regularly conduct process validation

3. Employee training and awareness

Enhance operators' awareness of material degradation:

Train employees to identify signs of degradation

Establish an exception handling process

Encourage employees to provide improvement suggestions

Preventing material degradation during injection molding requires comprehensive consideration from multiple aspects such as materials, equipment, processes, and management. Through accurate temperature control, optimized process parameters, good equipment condition, appropriate material formulation, and strict production management, the risk of material degradation can be reduced, and product quality and production efficiency can be improved. Each material and product has its own characteristics, and targeted optimization should be carried out according to the actual situation, and a continuous improvement mechanism should be established to achieve long-term stable high-quality production.