Bolts, nuts, screws and other metal parts generally need a surface treatment before delivery.
The common surface treatment types are electric plating, mechanical galvanizing, black oxide, phosphated, hot dip galvanizing, powder coating, spray painting, Dacromate and Ruspert.
6X60 Timber Structural Screw – Royal Decking
Ruspert coating is a new processing of metal surface treatment. It provide high performance of corrosion resistance. The coating includes 3 layers. First layer is base coating (metallic zinc), the second layer chemical conversion film and the third layer is baked ceramic surface coating. Due to the material and process differences, the final coated bolts, screws, other fasteners and metal parts could be in various anti-corrosion grades. 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 suggestion, however by adding the time and thickness of a coating, an extra protection could be achieved, for example 1500 hours and 2000 hours salt spray test pass results. The Ruspert coating method are suggested with use of tapping screws and drilling screws which need a high anti-corrosion performance after drilling into the object, for example wood and metals. Another important reason to choose Ruspert coating is that it can be coated in various colors, for example, blue, brown, dark, grey, silver, red, etc. Almost all common colors could be achieved. Ruspert coating can also combine with other coatings to achieve more customized requirements.
Dacromate is basically a kind of coating material. It’s a mixing of fine scale like Zinc & Aluminium powder, chromate and organic dissolvent with sticky material. It has good performance of anti-corrosion after coating on metal parts and baked under 300°C temperature. The generally so-called Dacromate for bolts, fasteners including this coating mixture and the coating workmanship and process. There are various coating mixtures including Chinese local producers and imported Dacromate, Geomet, Zintek and Delta. The different coating mixture varies in corrosion-resistance from 500 hours to 1200 hours free from rust and defectiveness under neutral salt spray tests. The usual coating thickness is from 5 mic. – 8 mic. There is the misunderstanding on the Dacromate environment-friendly performance. It’s not one question. We must divide it into 2 steps. Firstly the Dacromate coating workmanship and process is environment-friendly. It’s not like the traditional electric galvanizing or hot dipper galvanizing. The whole Dacromate process does not create waste water, air and waste acid. In this way, it’s replacing workmanship to traditional electric galvanizing. Secondly, the Dacromate mixture itself, the normal mixture with added
Chromate. This is the economic way while keeping high performance in the chemical reactions in the coating mixture. But at the same time, Chromate creates some poisonous factor (Cr+6) to humans and the environment after the fastener’s coating surface are being destructed. There are the non-poisonous coating mixtures like Geomet, Zintek and Delta.
Dacromate has the excellent anti-rust performance, almost 7 times to the electric galvanizing. Furthermore it has high osmosis characteristics that can coat on metal parts, between small gaps and holes while the traditional electric galvanizing or hot dipper galvanizing cannot reach. The Dacromated bolts or nuts can also keep its stability under high temperature (even 250C), salty and humid condition. While there are its cons. For example, it cannot resist acid corrosion, only white-grey and silver-grey colors, easy to scratch when facing hardened object. In this case, an extra coating or combined coating can follow. For example Ruspert, Zinc-Aluminium coating and other coatings to get a further protection from acid corrosion and various colors.
ELECTRIC GALVANISING, HOT DIPPER GALVANISING
& Mechanical Galvanizing, JS500, DT2000
Electric galvanizing is a traditional coating method. The most often way is zinc plating, nickel 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 fasteners surface, creating a protection film. This coating generally has a 24 hour or 48 hour protection under neutral salt spray tests. Hot dipper galvanizing is to heat the coating material, like zinc, to a melting liquid then coating it to the fastener’s surface to get a protection layer. This coating process has a better anti-rust performance than the above said electric plating. Mechanical galvanizing is a combination of chemical reactions and mechanical reinforcement. The screws or other fasteners and the coating material, for example, zinc powder (dispersant, accelerant and other materials to be added) are loaded into a running-barrel, through the mixing between the screws and the glass beads, the zinc powder is coated on the screws surface. This coating method also gets a better corrosion-resistance performance than electric plating.
OXIDE AND PHOSPHATE
Oxidation is a chemical reaction, using Alkaline or acidic oxidation method to create a corrosion-resistance layer on the fastener’s surface. Phosphate is to dip the fasteners into a phosphate solution, there will be a layer created on the fastener’s surface which has a medium protection.
E-COATING AND POWDER COATING
E-Coating is the coating material’s electrically charged ions which move to the cathode under the voltage affection, creating an insoluble material deposited on the work piece surface.
Powder Coating is to spray the coating powder onto the work piece then heating to fix onto the surface. This method provides various colors and more options of painting material for different anti-corrosion requirements.
The above mentioned Dacromate, Geomet, Zintek and Delta are brands/ producers of the related coating materials.