These manufacturers primarily used the Brinell, Rockwell and Vickers methods to test hardness. Brinell is used to test large parts such as castings and forgings of low to medium hardness. With the Brinell, a known load is applied for a given length of time to the surface of the specimen with a hardened steel or carbide ball. The diameter is measured and compared to known conversion scales.

Rockwell and Vickers tests are used on smaller parts and those of low, medium or high hardness. With a Vickers hardness test, a known load is applied for a specified time to the surface with a square-based pyramid diamond. The Rockwell and Rockwell Superficial hardness tests measure the depth of penetration made on the test block by a steel ball. The Rockwell Superficial test is designed for measuring the hardness of thin material or case-hardened metals.

Testing made easy

The Starrett 3817 System Bench Hardness tester is an automated, one-touch testing device that can display hardness values from 1 to 1/100th point on a digital control panel.

It features closed-loop load cell technology that improves repeatability and efficiency. The load cell eliminates the conventional weights, which may lead to some measurement uncertainty, says Scott Robinson, tech services/quality control representative for Starrett. Commonly used dead-weight testers are designed with a number of pivot and slide points that cause friction and can result in errors.

The system has built-in electronic conversion charts that allow cross referencing of hardness scales and approximating tensile strength, eliminating the need for mechanical or electronic adjustments. The system also has upper and lower limit alarms and RS232C output for documenting readings.

The 3817 System meets or exceeds American Society for Testing and Materials (ASTM) and ISO requirements and meets direct NIST-traceability requirements. In addition, preset dwell times and automatic cylindrical correction for hardness value comply with ASTM E 18 tolerances.

A self-contained head assembly is adaptable for special applications and the base is a rigid, modular assembly. Other features include a detachable clamping device for oversized or irregular parts and a fitted tray for indentors and anvils.

The system, which costs approximately $12,000, is furnished with an indentor, three calibration blocks, a penetrator and a table specific to each user’s Rockwell applications. An operator’s manual and AC power cable are also provided.

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TECH TIPS

• The tester can measure hardness in all Rockwell, Rockwell Superficial, Vickers and Brinell scales.
• One-touch, automated testing displays hardness values from 1 to 1/100th point on a digital control panel.
• A closed-loop load cell replaces the conventional weights method for more reliable results.
• The system has upper and lower limit alarms and RS232C output for documenting readings.

QUALITY SPECS

• The minor load limit is 10 kilograms for Rockwell and 3 kilograms for Rockwell Superficial.
• The major load is 60/100/150 kilograms for Rockwell (A/B/C), and the major load for Rockwell Superficial is 15/30/45 kilograms.
• The throat depth is 5 1/2 inches and maximum test height is 10 inches.