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Mechanism and Description

Discussion on countermeasures

Material particle aspect

There are certain requirements for the physical and mechanical properties and chemical resistance of the material.

The physical and mechanical properties must meet the standards of the OEM, and the materials with safety margins and post-painting processing should have chemical-resistant design plans.

Item

Mechanism and Description

Discussion on countermeasures

Forming process

The selection of injection process parameters should make the internal stress of the part as small as possible, and overcome the appearance defects such as flow marks and ripples.

It should appropriately increase the mold temperature (70℃ - 80℃); reduce the injection pressure, shorten the pressure holding time, and appropriately reduce the injection speed, etc., will reduce the internal stress of the parts to varying degrees, and the "Flame treatment method" can be used for the plastic parts to evaluate the apparent quality of plastic parts.

Item

Mechanism and Description

Discussion on countermeasures

Post-processing of plastic parts

There is internal stress concentration in the BOSS column and the buckle part of the plastic parts. Experiments show that heat treatment annealing can reduce internal stress. After heat treatment, the internal molecules of the plastic parts are rearranged, so that the molecular arrangement is uniform, the stress is released, and the internal stress is significantly reduced.

If necessary, it is recommended to bake at 70℃- 80℃ for more than 2 hours, and appropriately prolong the heat treatment time, so that the internal stress can be reduced to a minimum.

Item

Mechanism and Description

Discussion on countermeasures

Mould 

The multi-point pouring design of the hot runner of the mold, the heating of the gate hot plate and the hot nozzle at different positions are controlled by the temperature control components respectively. The sensitivity of the temperature control components affects the temperature control heating effect, and there is a risk of a small amount of local melt degradation when the high temperature is abnormal; The influence of the service life of temperature control components on the sensitivity; The sealant of the hot nozzle is not tight, resulting in the residual coating of the overflowing melt, which interferes with the detection of the temperature by the thermocouple temperature sensor;

The temperature control components of the hot channel should be dismantled regularly for maintenance;

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Mechanism and Description

Discussion on countermeasures

Post-processing painting

There are differences in the concentration blending of paint primers. If the corrosion is too strong, the substrate will be etched too much, and micro-notches will be formed on the surface of the substrate, resulting in a notch effect and deteriorating the mechanical properties of the substrate.

The corrosion strength of the paint primer should be appropriately reduced.

Item

Mechanism and Description

Discussion on countermeasures

Assembly fatigue stress

Excessive assembly force causes long-term fatigue stress cracking. Fatigue cracking refers to the fracture caused by the first crack in the local stress concentration or lower strength part, and the subsequent expansion of the crack; Fatigue failure is a damage accumulation process, so its mechanical characteristics are different from static failure. The main difference is that failure may occur when the cyclic stress is much smaller than the static strength limit, but not immediately, but after a period of time or even a long time.

The main ways to improve the fatigue limit are: 1. Try to avoid sharp corners, notches and sudden changes in section in the structural design of parts, so as to avoid stress concentration and resulting fatigue cracks; 2. The BOSS column locking screw should not be over-stressed, otherwise the parts will be deformed by local stress; 3. Improve the surface quality of parts and reduce fatigue sources.