Factors Affecting the Injection Molding Process of Water Meter

Abstract: The production speed is fast, the efficiency is high, the operation can be automated, the shape can be from simple to complex, and the size can be from large to small... Injection molding technology has been widely promoted and applied in today's society, but the injection molding process involves The equipment, molds, environment and raw materials are all complicated, which has many factors affecting the injection molding process. The existence of these factors has a considerable impact on the production of plastic parts of the water meter movement, in order to ensure the water meter. The quality requirements of the movement plastic parts must be analyzed and solved in all aspects of the factors affecting the injection molding process. This paper combines the current status of injection molding production of water meter injection molding technology, expounds many factors affecting the injection molding process, and helps to continuously improve the water meter injection molding. Forming quality.

 

Key words: movement, injection molding process, influencing factor, analysis, control

 

If the CPU is regarded as the core of the computer, then the water meter movement is equivalent to the "CPU" of the water meter. The quality of the water meter movement is directly related to whether the water meter flow is up to standard, which is related to the service life of the water meter, and directly determines the quality of the water meter. Bad and customer's reputation, in the water meter industry contending, the competition is fierce today, the customer's requirements for water meters are getting higher and higher, which puts higher requirements on the quality of the water meter movement.

 

As we all know, the water meter movement consists of two core components of the counting mechanism and the metering mechanism, and more than 95% of the movement parts are from injection molding, so the success or failure of the injection molding process is closely related to the advantages and disadvantages of the water meter movement.

The selection of injection molding materials is of great significance for injection molding, and different materials must correspond to different process conditions. In order to better improve the consistency of injection molding products, we need to further understand the injection molding process conditions and the correlation and influence of various factors, analyze various factors affecting the injection molding process, and propose control solutions.

 

1.1 Types of plastic

ABS, PP, PC and other thermoplastics with heat softening and cooling hardening characteristics will change their own volume during the injection molding process, and the internal stress will be enhanced, and the molecular orientation between plastic molecules will become stronger and more intense. Molecular motion will lead to a stronger shrinkage of thermoplastics than thermoset plastics. The direct result is that plastic products will exhibit significant shrinkage. Therefore, the shrinkage prevention holes should be reasonably designed according to the structure of plastic parts. For plastic precision parts, The shrinkage deformation requirements are more demanding, and the part structure should be modified in time to meet the requirements.

 

1.2 Plastic parts characteristics

Compared with metal parts, the thermal conductivity of plastics is relatively poor. During the injection molding pressure-preserving cooling process, the plastics in contact with the surface of the mold cavity will be cooled relatively quickly, while the internal cooling of the plastic parts will be slower. A high-density solid layer is formed inside the plastic part, which is one of the root causes of shrinkage deformation of the plastic part. Therefore, the temperature difference between the inside and the outside of the plastic part is reduced during the cooling process, and the time for the complete cooling of the plastic part is shortened, and the shrinkage deformation can be effectively suppressed. For example, the molded plastic parts are placed in water for rapid cooling.

 

1.3 Molding conditions

Factors such as equipment performance, mold temperature, melt characteristics, pressure, speed and other factors will affect the shrinkage rate of the injection molding process materials. The factors of the shrinkage rate are different, for example, when the mold temperature is high, the melt material The cooling process will be quite long, which will eventually lead to a large change in shrinkage and volume of plastic products. In the hot summer, turning on the ice water machine to cool the mold is a way to reduce the shrinkage rate of the material.

 

2, liquidity

In general, the greater the molecular weight of the material, the better the fluidity, and the plastic composition and properties must be fully understood before injection molding. The main factors affecting the fluidity of plastics are the following:

The first temperature, in general, the fluidity of the material is proportional to the temperature, the higher the temperature, the better the fluidity. However, there are exceptions. For example, the fluidity of PE and POM materials is not so obvious due to temperature, so for most materials, the fluidity of the material can be controlled by controlling the temperature of each section of the barrel.

At the second point of pressure, as the injection pressure increases, the shear force experienced by the material in the barrel increases, which increases the fluidity of the material.

The third point of the mold structure is the ordinary mold or the hot runner mold. In addition, the mold casting form and the size of the pouring port have a relatively large influence on the fluidity of the material.

 

3. Crystallinity

Whether the thermoplastic material crystallizes under condensation state, the thermoplastic material can be divided into two categories: crystalline material and amorphous material. These two types of materials can be differentiated by visual appearance. Generally, crystallization The material is opaque or translucent, and the amorphous material is transparent, with some exceptions. Generally speaking, crystallization causes the brittleness of the material to become high and the ductility to deteriorate. The main factors affecting the crystallization of the material are temperature and pressure. The increase of temperature and pressure can increase the activity of the material molecules, thereby accelerating the formation of crystals.

Special attention should be paid to the temperature control of crystalline materials and amorphous materials during the injection molding process, otherwise injection molding defects are likely to occur.

 

4, screw characteristics

 Screws with different plastics should have different requirements. Generally, transparent products (such as PC materials) must use chrome-plated screws. If a nitride screw is used, the surface of the product is prone to black spots and yellowing; The product must be chrome-plated screw, chrome-plated screw should not be produced containing glass fiber products, because chrome plating is not wear-resistant; nitride screw should not produce flame-retardant products, because nitriding is not resistant to corrosion.

 

5, material thermal performance and cooling rate

Different materials have different heat transfer properties, and plastics with high thermal conductivity require less cooling time in the final cooling. Such materials generally have a relatively early demolding, based on the material properties of thermal expansion and contraction, and need to be done after demolding. It is necessary to prevent the material from undergoing relatively obvious cooling deformation. At this time, the cooling speed should be controlled within a suitable range. In addition, the cooling rate of each plastic itself is also very different, so the cooling rate should be treated differently. .

 

Conclusion:

There are many factors affecting the water meter process. The inspection, injection molding, assembly, packaging, and shipping inspection are all involved. The water meter movement is the core component of the water meter. The components are almost all from injection molding, so mature. A reasonable water meter injection molding process is especially important. In this paper, the main factors affecting the water injection molding process are analyzed, and the control solution is proposed. It can be used as reference for the improvement of water meter injection molding process.

 

References:

[1] Wang Zhiqiang, Experimental optimization method and application research of injection molding process [D]. Zhejiang University of Technology, 2009.

[2] Liu Wei, Chen Limin. Optimization design of thermoplastic injection molding process parameters [J]. Engineering Plastics Application, 2005.

[3] Wu Junchao. Optimization and research on warpage deformation and injection molding process parameters of complex thin-walled injection molded parts [D]. Nanchang University, 2012.

[4] Jin Xiulian. On the influencing factors of injection molding process [J]. Commodity and Quality · Frontier Observation, 2010.