Rockwell Hardness Tester for Mold Hardness Testing

Why Mold Hardness Matters

Have you ever wondered why some molds last for years while others wear out much faster, even when used for similar plastic injection processes? In many cases, the answer comes down to one key factor: Mold Hardness.

Mold steel is a core material in the mold-making and plastic injection molding industry, forming the foundation of mold performance and durability. During daily production, molds are exposed to complex stresses. Hot-work molds, for example, face repeated mechanical loads combined with fluctuating temperatures. If the mold steel is too soft, it can deform or wear out quickly. On the other hand, if it is too hard, machining becomes more difficult and dimensional accuracy may be compromised.

This is why hardness plays such a critical role in mold performance. Properly hardened molds are better able to maintain their shape, dimensional accuracy, and consistent performance throughout long production cycles.

What Does Mold Steel Hardness Affect?

1. Wear resistance

Higher hardness generally means better resistance to friction and surface wear. This helps extend mold life, especially in high-volume injection molding.

2. Material strength

Hardness is closely related to strength. In general, higher hardness indicates better load-bearing capability.

3. Machinability

Too much hardness increases machining difficulty, while too little hardness may fail to meet operational requirements.

How Is Mold Hardness Measured?

Mold hardness is commonly expressed using Rockwell hardness values such as HRC or HRB. Rockwell hardness testing is one of the most widely used hardness measurement methods in the mold industry because it is fast, reliable, and easy to apply in production and quality control environments.

What Is a Rockwell Hardness Tester?

A Rockwell hardness tester is a hardness testing machine that measures hardness using the differential depth method. It is widely used for material verification, incoming inspection, and process control to ensure mold steel meets required specifications.

Recommended Product: BENKWELL LHRS-150 Digital Rockwell Hardness Tester

The BENKWELL LHRS-150 is a recommended Rockwell Hardness Tester for reliable mold hardness measurement. It features a clear LCD display, supports 15 Rockwell scales (HRA–HRV), and is equipped with a built-in printer and RS-232 interface for easy data output and quality record management. Ideal for production and quality control applications.

How Does a Rockwell Hardness Tester Work?

A Rockwell hardness tester measures how resistant a material is to permanent indentation. The test begins by pressing a diamond cone or a steel/tungsten carbide ball indenter into the material’s surface.

First, a minor preload is applied to establish a stable reference point and minimize the effects of surface irregularities. After that, a major load is applied, forcing the indenter deeper into the material. Once the major load is removed, the tester measures the difference in indentation depth while the minor load remains in place.

This depth difference, measured in millimeters, represents the material’s permanent deformation. The Rockwell hardness number is then calculated automatically based on this value. Because the system is designed so that shallower indentations produce higher numbers, harder materials always result in higher Rockwell hardness values.

The result is a fast, repeatable, and reliable method for evaluating material hardness without complex measurements or visual interpretation.

Which Rockwell Scale Should You Use?

Not all materials are tested the same way. Rockwell offers multiple scales for different applications.

HRC – For Hard Materials and Mold Steels

The Rockwell C scale (HRC) is the most commonly used scale for mold hardness testing. It uses a diamond cone indenter with a 150 kgf load and is ideal for heat-treated mold steel, tool steel, and stainless steel.

Does Dwell Time Affect Rockwell Test Results?

Yes. Dwell time directly affects accuracy. Rockwell testing includes:

• Minor load dwell time
• Major load dwell time
• Recovery (post-load) time

These stages allow elastic recovery and indentation creep to stabilize. Materials with higher elastic recovery can show significant differences in final readings if dwell times are inconsistent. Proper dwell time control ensures repeatable and reliable hardness results.

Calibration Hardness Test Blocks and Percentage Tolerances

Reference blocks are essential for verifying the accuracy and repeatability of a Rockwell hardness tester. Before use, calibration blocks must be cleaned and meet specific physical requirements, including sufficient thickness, flatness, and surface condition.

During calibration:

• Five indentations are typically performed on the reference block.
• The tester’s repeatability must fall within accepted percentage limits.

Typical acceptable repeatability limits are:

• ≤ ±1.5% for HRC
• ≤ ±3% for HRB
• ≤ ±2% for HRN
• ≤ ±3% for HRT

If the measured hardness values fall outside these percentage tolerances, the tester must be adjusted or recalibrated before further use.

Why Rockwell Hardness Testers Are Popular

Rockwell hardness testers remain popular across industries because they offer:

• Fast and easy operation
• High versatility for metals, plastics, and composites
• Reliable, repeatable results across multiple hardness ranges

Hardness Tester Distributor in Singapore

LFC PTE LTD is the authorized distributor of BENKWELL digital Rockwell hardness testers in Singapore. Contact us to learn more about Rockwell hardness testers and how they support reliable mold hardness testing in injection molding applications.

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