Baking-free injection molding machine is a kind of equipment that can realize direct injection molding of raw materials without pre-drying through technological innovation. Its core principle is to remove moisture and volatiles in raw materials simultaneously during injection molding process through special structural design and process optimization. Following is a detailed analysis from two aspects of working principle, advantages and disadvantages:

 

1. Exhaust screw design
Core of baking-free injection molding machine lies in its unique screw structure. Screw is divided into two stages:
- First stage: complete initial plasticization and compression of plastic to form a molten state;
- Decompression section: set a decompression zone at the end of first stage, and reduce melt pressure by suddenly increasing screw groove volume, so that volatiles such as moisture and gas expand and separate from melt;
- Second stage: melt enters second stage and is plasticized again, and melt quality is ensured by shear homogenization, and gas is discharged through exhaust port.
2. Vacuum or negative pressure exhaust system
An exhaust port is set on barrel of decompression section, usually connected to a vacuum pump or atmosphere, and negative pressure is used to accelerate exhaust of gas. This process can remove up to 0.2% of moisture and volatile substances in raw materials, avoiding defects such as bubbles and silver wire.
3. Raw material modification technology
Some equipment reduces hygroscopicity of material by adding additives (such as low hygroscopic additives) or using specially formulated plastic raw materials, further reducing need for drying.
4. Intelligent temperature control and pressure regulation
Equipped with a closed-loop control system, real-time monitoring of parameters such as barrel temperature and injection pressure to ensure balance between melt fluidity and exhaust efficiency, improve injection molding stability.

1. Significantly improve production efficiency
- Eliminate traditional drying process (usually takes 2-6 hours), shorten production cycle, and is especially suitable for rapid processing of high-humidity raw materials (such as recycled materials and biodegradable plastics).
2. Energy saving and consumption reduction
- No need to operate drying equipment, reduce electricity consumption (traditional drying equipment energy consumption accounts for 15%-30% of total production energy consumption), reduce plant space occupation and equipment maintenance costs.
3. Improve product quality
- Effectively remove bubbles and volatiles in melt, reduce surface defects of products (such as silver threads and black spots), improve transparency and mechanical properties. For example, moisture content of PA66 products can be reduced from 0.17% to 0.07%, and appearance is more uniform.
4. Strong adaptability
- Suitable for engineering plastics with strong hygroscopicity (such as PA, PC, ABS), biodegradable materials (PLA/PBAT) and high-proportion recycled materials, solving problems of easy degradation and unstable processing in traditional processes.
5. Environmental protection and cost optimization
- Reduce exhaust gas emissions caused by drying, in line with trend of green manufacturing; at the same time, reduce raw material storage requirements (such as avoiding moisture resurgence) and reduce waste.

 

1. High initial investment in equipment
- Core components of exhaust injection molding machine, such as screw and barrel, require special design and precision processing, resulting in higher equipment costs than traditional models. Price of drying-free injection molding machine is 20%-30% higher than that of ordinary models.
2. Complex process control
- Temperature, pressure and screw speed need to be precisely controlled, otherwise it may lead to incomplete exhaust or overheating and degradation of melt, which requires high technical requirements for operators.
3. Limitations of applicable materials
- Although it covers 90% of common plastics, some extremely high-humidity or high-volatile raw materials still require a small amount of pretreatment.
4. Increased maintenance difficulty
- Exhaust port is easily blocked by residues and needs to be cleaned regularly; wear rate of screw and barrel may also increase due to frequent shearing.

- High humidity/recycled material processing: such as recycled PET, high proportion of recycled PP, etc.;
- Precision transparent parts production: such as optical lenses, medical equipment, need to avoid bubble defects;
- Biodegradable materials: PLA and other materials are sensitive to humidity, and traditional drying can easily cause thermal degradation.
Drying-free injection molding machine significantly improves production efficiency and environmental protection through innovative exhaust structure and intelligent control technology, especially for high humidity raw materials and green manufacturing needs. However, its high equipment cost and process complexity may limit application of small and medium-sized enterprises.