Rockwell Hardness Test

Summary

This video explains the Rockwell hardness test, specifically using scale C. The test measures the permanent depth of indentation made by a diamond cone indentor under a specific force. Initially, a minor force of 10 kiloponds is applied, followed by a major force of 140 kiloponds, for a total of 150 kiloponds. The depth of indentation is measured after removing the major force, and the Rockwell hardness (HRC) is calculated using this value. The process is demonstrated using a gear wheel, with modern machines automating the test. The gear wheel in this example has a hardness of 55 HRC.

Takeaways

• 🛠️ The Rockwell hardness test measures the permanent depth of indentation caused by a hard indenter under a specific test force.
• 💎 For the Rockwell hardness test scale C, a conical diamond indenter is used to measure hardness.
• 🔧 The test consists of three steps: applying a minor force, increasing the force to a major level, and measuring the permanent depth of indentation after reducing the force.
• 📏 In step one, a minor force of 10 kiloponds is applied, setting the reference depth for measurement.
• ⚙️ In step two, the test force is increased by 140 kiloponds, resulting in a total force of 150 kiloponds on the indenter.
• ⏳ The major force is held for a certain time before being removed, while the minor force remains applied.
• 📐 The permanent increase in the depth of indentation is measured to calculate the Rockwell hardness.
• 📊 The Rockwell hardness (HRC) is calculated as HRC = 0.2 - permanent depth of indentation (e) * 500.
• 🖥️ Modern Rockwell hardness testing machines are often fully automated, making them widely used in automated production lines.
• ⚙️ In the example given, the hardness of a gear wheel was measured at 55 HRC, as shown on the machine's display.

Q & A

What is the basic principle of the Rockwell hardness test?

The basic principle of the Rockwell hardness test is to measure the permanent depth of indentation of a hard indentor, such as a diamond cone, under a test force.

What type of indentor is used in the Rockwell hardness test scale C?

In the Rockwell hardness test scale C (HRC), a diamond cone with a rounded tip is used as the indentor.

What is the minor force applied in the first step of the Rockwell hardness test?

The minor force applied in the first step of the Rockwell hardness test is 10 kiloponds.

How is the reference point established in the Rockwell hardness test?

The reference point is established by pressing the diamond cone onto the surface of the test piece with a minor force of 10 kiloponds, measuring the initial depth of indentation.

What happens in the second step of the Rockwell hardness test?

In the second step, the test force is increased by 140 kiloponds, resulting in a total force of 150 kiloponds acting on the indentor, and this force is held for a certain time.

What happens after the major force is removed in the Rockwell hardness test?

After the major force is removed, the minor force remains in place, and the permanent increase in the depth of indentation is measured.

How is Rockwell hardness (HRC) calculated?

Rockwell hardness HRC is calculated using the formula: HRC = 0.2 - (permanent depth of indentation in millimeters) × 500.

What tool is used to measure the depth of indentation during the test?

A microscope is used to focus on the surface of the test piece and measure the depth of indentation.

Why is the Rockwell hardness test commonly used in automated production lines?

The Rockwell hardness test is often used in automated production lines because modern testing machines can perform the test fully automatically, ensuring efficiency and accuracy.

What was the Rockwell hardness result for the gear wheel tested in the video?

The Rockwell hardness of the gear wheel tested in the video was 55 HRC.