January 2018 Archives

[Table] shows the types and characteristics of electric spraying method using electric power as the heat source.

[Table] Types and characteristics of electric spraying method

[Table] shows the types and characteristics of oxygen fuel spraying using gas as the heat source.

Flame spraying Detonation flame spraying Wire flame Rod flame Powder flame Detonation flame High velocity flame FARE GUN process Oxyacetylene, oxyhydrogen flame, oxypropane Oxyacetylene Oxyacetylene, oxyhydrogen flame, oxypropane Explosion energy of oxyacetylene Explosion energy of oxygen propane MAPP (C2H3) Explosion energy of air MAPP (C2H3) Steel materials such as carbon steel and stainless steel, non-ferrous metals including nickel/ molybdenum and their alloy metals Oxides such as AL2O3, Cr2O3, ZrO3, and ZrSiO4 Most of the metals, nylon and epoxy resin, oxides including AL2O3・TiO2 Most of the metals, oxides including AL2O3 and Cr2O3, carbides including WC-Co and CrC, and cermet Most of the metals, carbides including WC-Co and CrC-Ni-Cr, some of the oxides, and cermet Most of the metals, carbides including WC-Co and CrC-Ni-Cr, some of the oxides, and cermet Wire Rod Powder Powder Powder Packed powder Most of the metals; glass, ceramics and two to three organic materials with some limitations Most of the metals and graphite, etc. Most of the metals; glass, ceramics and two to three organic materials with some limitations Most of the metals Most of the metals Most of the metals Can be controlled under 200 ℃ 5-15% 5-18% 10-20% No more than 3% No more than 3% No more than 3% Simple equipment allows for spraying materials on site. Oxide thermal spray can be applied with gas flame. Oxide thermal spray can be applied. Suitable for plastic spraying. Dimensions and shapes of the substrates are limited. High film density. Fuel is economical. Equipment is small. Suitable for carbides. High film density. Suitable for spraying tiny areas. Difficult to spray oxides. High film density.

（1）What is thermal spraying?

When building heavy, thick, long, and large structures as Seto-ohashi Bridge, adopting anti-corrosion measures is particularly important.Under the painted exterior, the interface between the based paint film and the steel substrate is treated with "metallic spraying" using metals such as zinc.This treatment improves the anti-corrosion properties and reduces the maintenance cost.
In Japan, metallic spraying is called "metallikon". This is one of the surface treatment methods to form metal films on the surfaces of steel products by melting metal wires made of zinc or copper using frame's heat and spraying with compressed air. The products treated with this processing can withstand severe corrosion conditions.In addition to enhancing the corrosion resistance, thermal spraying to metal surfaces using ceramics is also common when it is necessary to improve the abrasion and heat resistance.
In recent years, these surface treatment technologies are widely adopted not only in the industrial equipment for increasing resistance to corrosion, rust, abrasion and heat, as well as for the build up, it is also adopted in dental implants and artificial bones in order to improve biocompatibility.
JIS defines thermal spraying as follows:

（2）Classification of thermal spraying methods

Thermal spraying methods can be classified by the heat source used for melting spraying materials, types of spraying materials, purposes of the application, and so on.Thermal spraying can be classified by the spraying heat source as shown in [Table 1].Thermal spraying can be classified by the spraying materials as shown in [Table 2].

[Table 1] Classification of thermal spraying methods by heat source

[Table 2] Classification of thermal spraying methods by spraying materials

Thermal spraying is also classified by the following purposes of application: spraying for prevention of corrosion, rust and abrasion, heat-resistant spraying, thermal barrier spraying, build up spraying, spray forming, and so on.

Galvanizing can considerably improve the anti-corrosion properties of steel. Furthermore, applying coating over it can significantly increase the corrosion resistance, while improving the appearance.
The coated steel sheets are also referred to as pre-coated steel sheets. ("Pre-coated" means coating applied prior to molding as opposed to "post-coating" that refers to coating applied after molding.) Pre-coated steel sheets used to be made of hot-dip galvanized steel sheets, but recently, they are made of various materials including electro-galvanized and alloyed zinc-coated steel sheets as well.
[Table 1] shows the surface-coated steel sheets.

[Table 1] Surface-coated steel sheets

The organic films used for the paint film applied on the steel sheets listed in the table are made of polyester, acrylic resin, vinyl chloride, silicone polyester, urethane, and fluorine-based resins.
Zinc-rich paint film is a high molecular epoxy polymer-based organic film in which fine zinc particles are dispersed. It is known to have excellent corrosion resistance. However, due to the drawbacks of workability and weldability, organic composite plated steel sheets were developed.
Organic composite plated films are made by applying a composite of acrylic resin, epoxy resin, and silica sol to form an approx. 1 µm film thickness onto electroplated Zn-Ni alloyed steel sheets through a chromate layer. They are known to have enhanced formability and weldability.