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Surface Treatments Generally, a tap properly designed and used under ideal conditions will produce satisfactory results without the use of special surface treatments. However, in certain conditions and in specific types of materials, the use of surface treatments can result in improved tap life, better surface finish and improved gaging. The treatments applied can be divided into two groups—those which penetrate the surface and those which are applied to the external surface itself. The first group generally includes the additional hardness type of treatments—“Nitriding” being the main type. The second group covers a wider range of choices including external treatments such as steam oxide, titanium nitride (TiN), hard chrome, and titanium aluminum nitride (TiAlN).
Oxide This treatment is applied to finished tools and produces a thin black iron oxide surface coating. It also provides additional tempering and stress relieving. This coating reduces galling and chip welding and also increases the ability of the tool to retain lubricants. Recommended in iron and steel drilling applications. It should not be used in non-ferrous metals such as aluminum because it increases the loading tendencies of the tool. Nitride This treatment produces a hard case which is highly resistant to abrasion. It also retards the tendency of softer materials to cling or load on tools. Generally recommended for tools that are used for ferrous, non-ferrous, and non-metallic materials which are abrasive and have loading characteristics. Traditionally the surface treatment is only located on the drill’s margins with the inception of performance coatings. Nitriding is not as often recognized for any future benefit. Nitride and Oxide Combines the advantages of the lubricity of oxide with the abrasion resistance of nitriding. Recommended for abrasive ferrous applications. Not recommended for soft materials such as aluminum, magnesium or similar non-ferrous applications. Chromium Carbide (CrC) A super hard coating (>80Rc) applied to the surface utilizing PVD coating technology. Same hardness as TiN coating but with an oxidation resistance that is 20–30% higher. Highly recommended for machining titanium and aluminum alloys.		Chromium Nitride (CrN) A superior alternative to conventional chrome plating, applied using the PVD process which, unlike regular chrome plate, has no negative environmental side effects. This chromium-based coating has higher hardness, approx. Rc78, offering improved edge sharpness. Particularly effective in the tapping and drilling of titanium, nickel and copper alloys. The thin nature of the coating (approx. .0001") will not alter dimensional tolerances. TiN-Titanium Nitride An excellent general purpose coating for protecting a wide variety of cutting tools from wear generated from heat dissipation. TiN is a good Iron- based materials. Tin coated tools are easily recognizable by their bright gold color. TiCN-Titanium Carbonitride TiCN has a higher hardness value than TiN which provides excellent heat resistance for more abrasive materials. The lower oxidation temperature limits the use of TiCN to workpiece materials where moderate temperatures are generated at the cutting edge. Tools coated with TiCN have a platinum/blue sheen. TiAlN-Titanium Aluminum Nitride TiAlN performs very satisfactorily in materials that generate high cutting temperatures during machining. The key to its success is the addition of Aluminum to TiN, which increases its hot hardness capability and oxidation stability. When this coating is exposed to high cutting temperatures, TiAlN forms a hard aluminum oxide layer that has low thermal conductivity. This layer acts as an insulator to the heat and rejects more heat into the chip. Tools coated with TiAlN have a purple sheen.