Steel fastener

11 Appearance of the fastener assembly (30 mm diameter steel cathode) after immersion horizontally in the 5% NaCI solution (20). 

12 Image of corrosion on Mg surface coupled with 10 mm diameter steei insert [20], 

Comparison of the physical appearance of the corrosion, with the area of galvanic corrosion as simulated by the BEM model, showed that the computer model provided good predictions of the effective galvanic corrosion area for each of the three different sizes of steel cathodes in 5% NaCl solution. 

13 Comparison of corrosion current density between the BEM model and the experiments for Mg couple with 10 mm diameter steel insert [20]. 

The experimental measurements indicate that the measured corrosion rate was significantly higher than the galvanic corrosion rate, and this was interpreted as self-corrosion of Mg. This self-corrosion was estimated by subtracting the galvanic corrosion (as predicted by the BEM model) from the total measured corrosiou. The value as estimated was 10mA/cm at the 

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Note that zinc anodes are often used to protect steel and other relatively noble metals cathodically. In this case, the fasteners were acting as unintentional sacrificial anodes, protecting the stainless steel. Simple solutions to the problem would be to insulate the fasteners from the stainless steel electrically or to use stainless steel fasteners. 

Mechanical properties High tensile (HT) fasteners as in ISO 4014 and ISO 898, grade 8.6 Ordinary MS (mild steel) fasteners as in ISO 4016, grade 4.6... 

A point that cannot be overemphasised is that, in the long term, stainless steel fasteners should be used for securing joints of stainless steel. 

Coatings consisting of a mixture of equal parts of cadmium and tin are particularly suitable for the protection of steel fasteners in contact with aluminium in aircraft structures where electrochemical corrosive attack is prone to occur under adverse conditions. The protection afforded is... 

Wood at moisture contents in excess of 20% is liable to decay, and above ca. 22% it is quite corrosive in both the treated and untreated conditions. Wet wood can be found in leaky roofs, in ground contact and in many outdoor locations. Coated steel, stainless steel and, less satisfactorily, galvanised steel fasteners are used. This appears to be largely because of the high cost of more suitable materials. 

Figure 2.26 Replicas prepared from fracture surfaces and viewed in TEM. (a) River patterns of a brittle failure of a steel fastener (b) fine, equiaxed ductile dimples on the surface of a tensile fracture of high-strength steel. The small carbide particles where local rupture and void formation initiated are apparent. (Reprinted with permission from ASM International. All rights reserved www.asminternational.org)...

Failure Investigation. The clamp was nonmagnetic and the stamped identification on the side of the U-shaped shells indicated that they were fabricated from forged 304 austenitic stainless steel. Visual examination of the fracture surfaces revealed they were entirely brittle and exhibited a very coarse fracture morphology. Liquid penetrant inspection revealed the presence of additional cracks in the fractured half of the clamp. There was no cracking present in the high-strength steel fasteners. 

From the viewpoint of the easiness of demolition and recycling, not ordinary steel reinforced concrete (RC) cast-in place completely in a body, but hybrid structural systems composed of steel reinforced precast RC columns and new continuous fiber reinforced plastics (FRP) reinforced lightweight precast concrete (FRPRC) beams connected with steel fasteners are recommended. 

Water-based preservatives are often used where cleanliness and paintability of the treated wood are required. Typically, wood treated with a water-based preservative has little or no odour when compared to oil-based preservatives. However, unless supplemented with a water repellent, the water-based systems do not confer any dimensional stability to the treated wood. In addition, water-based preservatives that utilize copper as a fungicide may not adequately protect hardwood species under conditions that favour soft rot attack. Some water-based preservatives can increase the rate of corrosion of mild steel fasteners. 

J1199—Mechanical and Material Requirements for Metric Externally Threaded Steel Fasteners... 

Bronze Liquid End - All parts of the pump coming in direct contact with the liquid pump are to be made of bronze, with stainless steel fastenings. 

Cadmium Cadmium plating is used to increase the corrosion resistance of steel fasteners and electrical connectors. However, the Cd plate is itself subject to oxidation and tarnishing in humid and tropical environments to such an extent that electrical and mechanical functionality may be adversely affected. CCCs may are applied to Cd to resist oxidation, or to increase paintability [81]. Cd plating can be successfully conversion coated using chemistries applicable to other metals. 

The fracture surfaces were brittle and exhibited a very coarse morphology. Additional cracks in the fractured half of the clamp were observed and the high-strength steel fasteners were free from cracks. 

This carbon steel fastener shall not be used above 400°F or below - 20°F. See also Note (4). Bolts with drilled or undersized heads shall not be used. 

The potential difference established when two metals (alloys) are electrically connected in a conducting medium produces electron flow and causes the metal (alloy) with more negative potential to preferentially corrode. The more positive metal (alloy) becomes a cathode and is protected by the negative metal (alloy), which becomes an anode (Fig. 1.5). Because the driving force for corrosion is the potential difference between the metals (alloys), this form of corrosion is called galvanic corrosion. Steel fasteners in an aluminum foil, the solder on a copper pipe, and stainless steel in contact with... 

Figure 12.5. Types of nut (a) wing (b) dome or acorn (c) rivet bush or nut(d) blind (e) flat spring steel fastener and (f) J type fastener...

Spring-steel fasteners are available which as well as holding also provide a locking action. If access is available from both sides, a flat nut can be used. Fig. 12.5(e), or from one side a J-type nut can be used, Fig. 12.5(f). In their natural state these nuts are arched, but they are pulled flat when the screw is tightened. 

The normal thickness of coating is 5-25 jjim and has low frictional properties, making it an ideal surface on fasteners which reduces the tightening torque and prevents jamming. It also provides an effective barrier to prevent bimetallic reaction between steel fasteners and aluminium, e.g. where parts are fixed to an aluminium framework. Cadmium-plated surfaces can be easily soldered without the use of corrosive fluids. 

D. L. Hawke and T. Ruden, Galvanic compatibility of coated steel fasteners with magnesium, paper no. 950429, International Congress and Exposition, Detroit, Michigan, SAE International, Warrendale, PA, 1995. 

Other Mechanical Fasteners. Push-on spring steel fasteners can be used for holding Ught loads. They are used when low-cost, rapid mechanical assembly is required. Spring steel fasteners are also often referred to as speed nuts and speed clips. 

Spring steel fasteners are simply pushed over a molded stud with hand pressure. A simple push-on spring steel fastener is illustrated in Figure 7.10. The stud should have a minimum 0.38 mm (0.015 in) radius at its base. Too large a radius could create a thick section, resulting in sinks or voids in the plastic molding. 

Galvanic corrosion may occur in carbon fiber composites if aluminum fasteners are used, due to the chemical reaction of the aluminum with the carbon. Coating the fastener guards may prevent corrosion but adds cost and time to the assembly process. As a result, aluminum fasteners are often replaced by more expensive titanium and stainless steel fasteners in carbon fiber composite joints. 

Zinc, unlike most paints, can be left in place on the faying surfaces of a bolted joint. This property, together with the use of zinc-coated steel fasteners, ensures that the Joint is fully protected. The initial lubricity of the coating is... 

Certain proprietary zinc and aluminum filled polymers and some ion vapor deposited aluminum coatings, applied to steel fasteners may actually produce more damage than the untreated steel fastener itself. This was attributed to two possible causes either the high surface area involved with each of the particulate coatings or the contamination of the particulate surface with active cathodic contaminants such as iron, nickel, or graphite ... 

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