Hard Chrome Plating Explained: Process, Properties, and Industrial Applications
Hard chrome plating, also known as chromium plating, is a highly effective electroplating technique used to enhance the wear resistance, corrosion protection, and overall durability of metal components. By applying a hard chromium layer through the use of chromic acid, this process significantly improves the surface hardness and extends the lifespan of parts subjected to harsh operating conditions. It is widely used in industries such as automotive, printing, mechanical engineering, and more.
Key Benefits of Hard Chrome Plating
This plating process offers a variety of advantages, making it the preferred solution for many industrial applications:
- Improved Wear Resistance: Enhances the durability of components exposed to friction, extending their service life.
- High Hardness: Achieves surface hardness levels of 900 to 1200 HV, maintaining component integrity without distortion.
- Excellent Corrosion Protection: Provides resistance to moisture, chemicals, and aggressive environmental conditions.
- Reduced Friction: Lowers the coefficient of friction, improving efficiency and reducing wear between moving parts.
The Hard Chrome Plating Process
Surface Pre-Treatment
To ensure a strong bond between the workpiece and the coating, proper surface preparation is critical. The surface must have a roughness depth of Rz 2 – 3 μm, as the layer will not cover any structural defects. The workpiece is typically ground or belt-polished to achieve a smooth, clean surface. Additionally, the material must be metallically bright to guarantee proper adhesion.
Step-by-Step Process of Electroplating
The plating process involves the following key steps:
- Electroplating: The workpiece is immersed in an electroplating bath containing chromium ions from chromic acid. A rectifier is used to reduce these ions to metallic chromium, which is deposited onto the workpiece.
- Temperature and Electrical Parameters: The plating bath is maintained at a temperature between 50°C and 60°C, while the current is carefully adjusted to control the plating process.
- Layer Formation: Chromium is deposited evenly across the workpiece surface, although edges may accumulate more plating due to the electric field. Special racks are used to minimize this effect.
Layer Thickness for Different Applications
The required thickness of the chromium layer varies depending on the specific application and wear conditions of the component:
- 5 to 15 μm: Light wear and friction reduction.
- 15 to 30 μm: Moderate wear protection.
- 30 to 60 μm: Adhesive wear resistance.
- 60 to 150 μm: Heavy wear protection.
- 150 to 350 μm: Protection against abrasion and erosion or for repair purposes.
Properties of Hard Chrome Coated Surfaces
Once the plating process is complete, the workpiece exhibits several enhanced properties:
- High Hardness: Achieves 900 – 1200 HV without distortion.
- Wear and Abrasion Resistance: Extends the lifespan of components exposed to friction and harsh conditions.
- Low Coefficient of Friction: Reduces wear and improves efficiency in moving parts.
- Corrosion Resistance: Offers protection against moisture, chemicals, and other corrosive elements.
- Improved Tribological Properties: Enhances the performance of machinery and equipment by minimizing friction and wear.
Decorative Plating and Other Applications
In addition to its functional uses, chromium plating is also widely employed for decorative chrome finishes. This process is used to create attractive, shiny surfaces on automotive parts, household items, and other components where aesthetics are important. Decorative plating provides a bright, appealing look while also offering some level of corrosion protection.
Industrial Applications of Hard Chrome
This process is used in a wide range of industries to improve the performance and durability of various components. Some of the most common applications include:
Printing Industry
In the printing industry, hard chromium layers are crucial for parts such as cylinders, duct rollers, and metering rollers. These components require a flawless surface finish, precise dimensional accuracy, and strong corrosion resistance due to exposure to aggressive inks and cleaning agents.
Paper Industry
In the paper industry, components like screen baskets, creeping cylinders, applicator rollers, and ink metering rollers benefit from plating. These parts need to withstand high wear and require reliable, repairable coatings for long-term use.
Mechanical Engineering
Hard coatings are widely used in mechanical engineering for components such as piston rings, piston grooves, shafts, tools, and measuring rollers. These parts require excellent wear resistance and durability, which plating delivers.
Automotive and Food Industries
The automotive and food industries also rely on this process for various parts, ensuring they can withstand tough environments, high wear, and corrosion.
Alternatives to Hard Chrome Plating
While hard chrome plating remains popular for its excellent wear and corrosion resistance, alternatives such as boronizing and nickel plating offer additional benefits. Bortec’s patented processes, like the BORINOX® method for stainless steel hardening and BOROCOAT® boronizing, provide high wear resistance and durability without the environmental concerns associated with traditional chrome plating.
These alternative methods also offer more uniform coatings, reducing the risk of cracks and improving overall performance. For example, the NICKELCOAT® process for nickel plating offers superior protection against wear and corrosion, particularly for parts that require a smooth, durable finish.
