Nowadays many car appearance adopt decorative electroplating technology, by this not only could add automotive fashion sense, but also can make the whole car full of advanced feeling. However, due to the plating parts on car are usually exposed to outdoor, as well as to experience a variety of environments testing, so car exterior plating process requires very strict technology and evaluation criteria. General automotive Lights will choose electro plating methods based on using conditions, which divided into 4 kinds:
Class U: using condition as rigid, suitable for external decoration;
Class S: using condition as strict, suitable for external decoration;
Class A: using condition as normal, which is suitable for external decoration;
Class B: using condition as relaxation for cases of interior parts.
We will elaborate one of car decorative chromium electroplating processes and test methods as follows.
1, Car decoration plastic electro plating types:
Decorative lights electroplating grade S, which is strict condition for cases of exterior parts, material types as plastic.
2, Car decoration plastic electro plating quality:
2.1, Electroplating method:
On base material through electrolytic copper, nickel, chromium and other elements attached to the surface, makes it has a metallic luster. In addition, the nickel layer is also diveded into several plating method, while this light plating method is double or triple nickel + despersive stress, tiny holes chromium. In double and triple nickel, half lustre nickel layer thickness not less than 1/2 of the total nickel layer thickness.
2.2, Minimum coating thickness:
Thickness measurement method based on microscope, can also use electrolytic film thickness meter. Further, if only for chromium, with a fluorescent X-ray thickness meter is ok. Plating layer thickness measurement site principle should be at a minimum thickness. But if workpiece shape cause coating layer uneven thickness, can change the measurement site after consultation between the parties concerned. Other base material copper electro plating can be instead of nickel plating. Copper thickness should be able to ensure the appearance and thermal cycling resistance. Although the basic material such as different shapes, sizes, forming conditions and other, the copper layer thickness measuring points should be at least 1 times more than thickness of the nickel layer. The minimum thickness requirements of nickel plating and chrome plating shall according to different service environments.
In room light, 500mm away from test surface for visual. Electroplating surface should be smooth and shiny, and there is no blemish, bulging , injuries, cuts, exposed material, trachoma, not smooth and other anomalies. But this, does not apply to the invisually portion of the vehicle. Determined by the parties concerned to determain limits of the sample, the limit shall for the vehicle spacing at 50cm visual status in the sunlight, the extent of appearance defect is not obvious.
Salt spray test (SST): or according to JISZ2371 ASTMB117 continuously conduct. To S-class, A-class, not proceed flying stone test does not rust as qualified. For plastic material, no need conduct salt spray test (SST).
Accelerating weather resistance test (Corrodkote):
Or based on ASTMB380 or JISH8502 to conduct. Can be selected Corrodkote bonding solution as follows: 2.5g copper nitrate (Cu (NO3) 2_3H2O), dissolved in volumetric flask and precisely diluted with distilled water to 500ml, then weigh 2.50g of iron chloride (FeCl3_6H2O), dissolved in a second volumetric flask and accurately diluted to 500ml with distilled water (when not in use, ferric chloride solution should be stored in a dark place stoppered with a rubber or a glass stopper ) ( ferric chloride solution storage time shall not more than 2 weeks, because if storage time too long will cause instability ). Weigh 50.0g ammonium chloride (NH4Cl) then dissolved and diluted to 500ml with distilled water precisely in the volumetric flask. Then accurate measurement 7.0ml copper nitrate solution, 33.0ml ferric chloride solution and 10.0ml ammonium chloride liquor, put these above solution into pour mouth beaker and add 30.0g china clay, the stir with a glass rod. Corrodkote bonding liquid shall be how much used then how much made. Visal can’t see rust and discoloration. However, except for U class, the local corrosion rate at least not more than 10%. For an area less than 25cm2, all corrosion rate shall not exceed 10 %. For S class plating process, accelerating weather resistance test as more than 48 hours.
Coating corrosion resistance test (CASS):
According JISH8502 or ASTMB368 to proceed. Intervals 50cm can not see rusty ( surface rust ), discoloration and so on. For the S class plating process, CASS should be more than 60h or more.
2.5, Hot and cold circulating:
Regarding to S class, basic material as plastic, conduct hot and cold circulating according to following test method, hot and cold circulating cycle is 4 or more, after testing, effective surface not occur expansion, peeling and isolating phenomenon as qualified.
Hot and cold test methods:
Condition as 1 time cycle, principle as after electroplating, place more than 48 hours, conduct this circulation.
The adhesion of the plastic substrate according to the following test method, then distance between substrate and the coating layer does not peel off easily. However, criterions are different according to tesing motheds, so shall be determined by the parties concerned. Shall be based on JISH8630 affiliated with 6 or ASTMB533 as a reference. In principle, 48 hours placement after plating, test should according to following steps :
⑴, On coating surface crossed with a sharp blade, blade should be approached basic material.
⑵, In acute angle open the plating layer on cross point.
⑶, In vertical direction of plating surface to pull the opened coating layer. Plastic basic material coating layer adhesion force as, peel amplitude 10mm, with a peeling speed of 30mm/min to test, usually above 9.8N/cm.
Brightness nickel plating layer scalability, according to ASTMB490 to proceed, should be required above 0.1. Semi brightness nickel electr plating ductility, according to ASTMB490 to conduct, shall be required above 0.4.
3, Technological conditions:
3.1, Double nickel:
⑴, Implement double nickel electroplating: lower layer as semi brightness nickel electroplating, while upper layer as brightness nickel plating.
⑵, Sulfur content on electroplating layer, semi brightness nickel plating of 0～0.005%, while brightness nickel plating as 0.05%～0.07%.
3.2, Triple nickel:
⑴, Based on same as double nickel pating, in the middle of semi brightness and brightness plating layer, to conduct more than 0.6μm middle Ni plating.
⑵, Sulfur content of the intermediate nickel layer at least more than 0.1%.
3.3, Tiny pores chrome plating ( ordinary chrome ):
⑴, The nickel plating layer under the chrome plating layer, to proceed non-electrically conductive fine particles of nickel eutectoid plating, the chrome layer will produce many fine pores.
⑵, Tiny pores over 2000/cm2.