1. Dissolution method
(1) acetic acid immersion
The acetic acid (CH3COOH) used must be more than 95% acetic acid, and the repeated use times shall not exceed 10 tests.
① Surface stress test: Pour acetic acid (glacial acetic acid) into glassware, and immerse the product completely in acetic acid for 30 seconds. After 30 seconds, take out the sample with a clamp and immediately wash it with clean water (tap water is enough) to see if the surface of the sample is white or cracked. It is concluded that there shall be no cracking phenomenon and slight whitening of the surface is allowed.
② Internal stress test: Dry the sample that passed the surface stress test and soak it in acetic acid completely for 2 minutes. After 2 minutes, take out the sample and immediately rinse it with clear water (tap water is enough), and inspect whether the sample is white or cracked. Judgment: No fracture is allowed, and slight cracks and surface whitening are allowed at the insert.
⑵ Methyl ethyl ketone+acetone addiction method: Immerse the whole machine into the mixed solution of methyl ethyl ketone+acetone at 1: 1 at 21℃, immediately spin it dry after taking it out, and review it according to the above method.
Principle: According to the phenomenon of medium stress rupture, that is, after the solvent molecules penetrate into the macromolecules of the resin, the interaction force between the molecules is reduced. Where the internal stress is large, the force between the molecules before immersion is weakened, and after immersion, these weakened places are further weakened, causing cracking, while the places with small internal stress will not crack in a short time. Therefore, the magnitude and location of the internal stress in the plated parts can be determined from the time and degree of surface cracking. So as to judge whether the plastic parts are electroplated or not.
2. Instrument method
Illuminate plastic partswith polarized light, analyze the strength of internal stress according to the number of color bands, and it is only applicable to transparent parts. The instruments required by polarized light method are expensive, complicated to operate and low in accuracy, because the changes before and after processing are not significant, and the light bands emerging in the spectral bands are not necessarily affected by internal stress, for example, the ripples on the surface of the parts will also affect the inspection results. In addition, this method has no influence on the function of the parts. For nondestructive testing, the tested parts can be electroplated and used.
3. Temperature sudden change method
In this method, plastic parts to be plated are repeatedly cooled and heated, and the internal stress is evaluated according to the time when cracks appear. It is applicable to all kinds of plastic forming parts. The equipment required by sudden temperature change method is simple, but the test time is longer. The repaired plastic parts have been damaged and cannot be used continuously.
