Coating of screw taps: What you should know
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The foundation material of a tap plays a crucial role in determining its quality and longevity. However, it’s not just the raw material that matters; the processes surrounding its production also significantly affect the tool’s performance and durability. After all, the surface of a tap is the part most exposed to wear and tear and corrosion. As a result, most taps go through a surface treatment or receive a protective coating before they reach the market.
These surface treatments and coatings offer several advantages. They enhance the tool's resilience against wear and environmental factors, extending its lifespan. Additionally, they improve the surface finish and allow for higher cutting speeds. Some coatings even provide specific benefits tailored to particular materials, expanding the tap's versatility.
Currently, there are various types of coatings available for taps, and many custom coatings can be requested from manufacturers like BAER. We aim to shed light on the diverse world of tap coatings.
Let’s start with some of the most common surface treatments:
### Nitriding
Nitriding involves exposing the tap to a nitrogen-rich environment under high temperatures. This process creates a hardened outer layer on the tap, improving its surface hardness, wear resistance, and sliding properties. This treatment is particularly effective for materials that cause significant wear, such as cast iron, high-perlite steels, titanium alloys, certain aluminum-silicon alloys, Bakelite, and other thermoset plastics.
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Below is an image illustrating the nitriding process:
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### Vaporizing
Vaporizing is a steam treatment that triggers a chemical reaction on the tap’s surface, creating a crystalline iron oxide layer. This layer reduces friction and improves the adhesion of lubricants, preventing the formation of build-up edges and cold welding. However, this treatment is only suitable for iron-based materials.
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Here’s an image showing the effect of vaporizing:
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### Calduring
Calduring combines nitriding and vaporizing techniques, offering dual benefits. This treatment is ideal for materials that are both tough and wear-inducing.
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An illustration of calduring:
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### Hard Chromium Plating
Hard chromium plating deposits a hard chrome layer onto the tap via electrolysis. This improves the sliding properties and reduces surface roughness. This method is commonly used for machining low-strength materials like copper and copper alloys, but the machining temperature must remain below 250°C to maximize its benefits.
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A visual representation of hard chromium plating:
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### Common Tap Coatings
For taps and cutting dies, coatings often represent the most efficient and eco-friendly way to enhance surface properties. While there are many coating methods, the PVD (Physical Vapor Deposition) method is predominantly used for taps and cutting dies. Let’s explore this method further before diving into the primary coatings.
#### The PVD Process for Surface Coating
PVD stands for “physical vapour deposition,†a vacuum-based process where the coating material transitions into a gaseous state and condenses onto the tap, forming the desired coating.
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Image of the PVD process:
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#### TiN (Titanium Nitride)
A tap coated with titanium nitride is easily recognizable by its golden-yellow hue. This coating boasts a micro-hardness of 2,200 HV and can withstand temperatures up to 600°C. TiN is a general-purpose coating, suitable for soft to tough-hard steels, cast iron, and non-ferrous metals. Tools with TiN coating can be recoated up to five times.
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Visual example of TiN coating:
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#### TiCN (Titanium Carbonitride)
The titanium carbonitride layer is extremely hard and durable, excelling under high mechanical stress. With a micro-hardness of 3,000 HV and temperature resistance up to 400°C, a TiCN-coated tap appears gray-violet. This coating is ideal for high-strength steels and abrasive materials. It also offers excellent resistance to impact stress, making it perfect for interrupted cuts. However, it has limited heat resistance, so proper cooling is essential.
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Illustration of TiCN coating:
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#### TiAIN (Titanium Aluminum Nitride)
The TiAIN coating is black-violet with a micro-hardness of 3,300 HV and temperature resistance up to 800°C. Its exceptional chemical stability and heat resistance make it ideal for high-temperature applications with limited cooling options. This coating is perfect for high-speed cutting over 60 m/min and for machining abrasive or difficult-to-cut materials. TiAIN-coated taps can also be recoated up to five times.
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Example of TiAIN coating:
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#### Other Coatings
Besides these standard coatings, there are numerous variations designed for specific applications. For instance, the X.TREME tap coating combines the properties of TiN, TiCN, and TiAIN in a multilayer red-violet design. The combination of TiAIN with a soft-material glide layer is perfect for dry machining. The silver-gray CrN (chromium nitride) coating offers high thermal stability and corrosion resistance.
If you’re unsure about the right coating or treatment for your project, feel free to reach out! Our BAER customer service team is ready to help bring your ideas to life. All mentioned coatings are available in our online store, or we can quickly produce custom-coated taps from BaerCoil based on your specifications.
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**Note:** Images provided are illustrative and may not exactly match the described processes or products.