Composite electrical connector is a new type of electrical connector developed by foreign countries in the mid-1980s. This kind of electrical connector made of non-metallic materials is welcomed by the air force and Navy for its excellent corrosion resistance, small weight, excellent performance and good durability. According to reports, the US Air Force and navy have used a large number of composite electrical connectors on various types of aircraft, which is known as a major reform of electrical connector technology. In 1989, military specification for high density small circular electrical connectors made of environment resistant quick connect composite materials, MIL-C-29600, was issued by the United States. Lm123 series electrical connector of Deutsch is a kind of fully instrumented and standardized composite electrical connector. In the early 1990s, Deutsch has been able to produce composite electrical connectors with 17 shell sizes and 92 hole group insulators. Many famous foreign connector manufacturers produce this new type of electrical connector such as Amphenol(US) and Souriar (France). At present, the shell parts of MIL-C-38999 Ⅲ series electrical connectors widely used in the world, have been made of composite materials, in particular, composite materials have been used in the shell parts and tail accessories of the most advanced optoelectronic hybrid electrical connector of the world. This indicates that the application of composite connectors in military electrical equipment and electronic systems is expanding.
Polyether ether ketone (PEEK) is an aromatic semi crystalline thermoplastic polymer material with good stiffness and flexibility, and its mechanical properties are little affected by temperature, can be used for a long time up to 250 ℃ and can maintain good mechanical properties even at 300 ℃. Its chemical solvent resistance is only second to fluoroplastics, insoluble in all solvents except concentrated sulfuric acid, not subject to the chemical erosion of water and steam. Its products can still maintain excellent performance after long time soaking in high temperature and high pressure hot water and steam. Peek has become the preferred material for electrical connector manufacturers to develop composite electrical connectors due to its unique good performance.
Fig. 1 molecular structure of PEEK
In the composite electrical connector products, peek is not only used to make insulating parts, but also used to make external shell parts which play the role of connection and support. In the composite electrical connector products, peek is not only used to make insulating parts, but also used to make external shell parts which play the role of connection and support. Therefore, in the application process of PEEK, not only the problem of forming, but also the problem of surface treatment should be solved, so as to achieve the shielding performance.
PEEK is a super heat-resistant resin with high thermal deformation temperature and decomposition temperature, good fluidity at high temperature (350 ~ 400 ℃) and high thermal decomposition temperature (560 ℃). Therefore, it can be processed by injection molding, extrusion molding, powder spraying and other methods.
PEEK can be processed by injection molding machine with common screw or plunger, and the injection molding machine should meet the following basic conditions:
1) The barrel temperature can rise to 400 ℃. Generally, the approximate temperature of each part of the barrel is shown in Figure 2;
2) There is no dead space in the barrel;
3) Because the melt viscosity is high, it will not flow automatically, so the nozzle does not need to add a stop valve.
Figure 2 approximate temperature of each part of the barrel during peek injection molding
When the mold temperature is controlled above 160 ℃, the semi crystalline peek can be fully crystallized. Forming at high temperature can not only produce parts with good comprehensive performance, but also improve the appearance quality of parts.
The water absorption of PEEK is very low, and its saturated water absorption is only 0.5%. However, in order to have good molding quality at high temperature, the material needs to be dried at 150 ℃ for more than 3 hours before injection molding.