Fasteners Surface Treatment

Bolts, nuts, screws and other metal parts generally need a surface treatment before delivery. The common surface treatment types are electric plating, mechnical galvanizing, black oxide, phosphated, hot dipper galvanizing, powder coating, spray painting, dacromate and ruspert.

RUSPERT

Ruspert coating is a new processing of metal surface treatment. It provide high performance of corrosion resistance. The coating including 3 layers. Base coating is metallic zinc layer, then the second chemical conversion film layer, finally a baked ceramic surface coating. Due to the material and process differs, the final coated bolts, screws, other fasteners and metal parts could be in various anti-corrosion grade. Usually a 500 to 1000 hours salt spray test pass result can be guaranteed (according to ASTM B117-03, type 1 and type 2 ) and a pass result on 12-15 periods of acid rain test could be reached (according to DIN 50018)

This is a standard suggestions, however, by adding the time and thickness of coating, an extra protection could be achieved, for example 1500 hours and 2000 hours salt spray test pass result. The RUSPERT coating method are suggested to using for tapping screws, drilling screws which need a high anti-corrosion performance after drilling into the object, for example wood and metals. The another important reason to choose RUSPERT coating is it can be coated in various colors, for example, blue, brown, dark, grey, silver, red, etc, almost all the common colors could be achieved. Ruspert coating can also combined with other coatings to achieve more customized requirements.

DACROMATE

Dacromate is basically a kind of coating material. Its a mixing of fine scalelike Zinc & Aluminium powder, chromate and organic dissolvant with sticky material. Its has good performance of anti-corrosion after coating on metal parts and baked under 300C temperature. The generally so-called dacromate for bolts, fasteners including this coating mixture and the coating workmanship, process. There are various coating mixture including Chinese local producer's and imported Dacromate, Geomet, Zintek, Delta.

The different coating mixture various the corrosion-resistance from 500 hours to 1200 hours free from rust and defective under neutral salt spray test. The usual coating thickness is from 5 mic. to 8 mic.

There is the misunderstanding on the DACROMATE's enviroment-friendly performance. It's not in one question. We must devide its into 2 steps. Firstly the dacromate coating workmanship and process is enviroment-friendly. It's not like the traditional electric galvanizing or hot dipper galvanizing. The whole dacromate process do not create waste water, air and waste acid. In this way, its the replacing workmanship to traditional electric galvanizing. Secondly, the dacromate mixture itself, the normal mixture added the chromate. This content is the economic way while high performance in the chemical reactions in the coating mixture. But at the same time, chromate create some poisonous factor (Cr+6) to human and enviroment after the fastener's coating surface being destructed. There comes the non-poisonous coating mixture, like Geomet, Zintek, Delta.

Dacromate has the excellent anti-rust performance, almost 7 times to the electric galvanizing. Further more it has high osmosis characteristic that can coating on the metal parts small gaps and holes while the traditional electic galvanizing or hot dipper galvanizing can not reach. The dacromated bolts or nuts can also keep its stability under high temperature (even 250C), salty and humid condition. While there are its shortages, for example, it can not resist acid corrosion, only white-grey and silver-grey color, easy scratch when facing hardend object. In this case, an extra coating or combined coating always followed, for example ruspert, zinc-aluminium coating and other coatings to get a further protection from acid corrosion and various colors outlooking.

Electric Galvanizing, Hot Dipper Galvanizing and Mechanical Galvanizing, JS500, DT2000

Electric galvanizing is a traditional coating method. The most often way is zinc plating, nickle plating and also brass, chrome, copper plating. The coating material (for example zinc plating), using the electricity transmission, the positive ion from the zinc liquid comes to the fastener's surface, creating a protection film. This coating generally have a 24 hours or 48 hours protection under neutral salt spray test.

Hot dipper galvanizing is to heating the coating material, like zinc, to a melting liquid then coating to the fastener's surface to get a protection layer. This coating process have a better anti-rust performance than the above said electric plating.

Mechnical galvanizing is a combination of chemical reaction and mechnical reinforcement. The screws or other fasteners and the coating material, for example, zinc powder (dispersant, accelerant and other media to be added) are loaded into a running-barrel, through the collision between the screws and the glass beads, the zinc powder to be coated on the screws surface. This coating method also get a better corrosion-resistance performance than the electric plating.

Oxide and Phosphate

Oxidation is a chemical reaction, using Alkaline or acidic oxidation method to creat a corrosion-resistance layer on the fastener's surface.

Phosphate is to dipper the fasteners into the phosphate solution, there will be a layer created on the fastener's surface which has a medimium protection.

E-Coating and Powder Coating

E-Coating is the coating material's electrically charged ions move to the cathode under the voltage effection, creating an insoluble material deposited on the workpiece surface.

Powder Coating is to spray the coating powder onto the workpiece then heating to fixing on the surface. This method provide various colors and more options of painting material for different anti-corrosion requirements.