Physical Address
304 North Cardinal St.
Dorchester Center, MA 02124
SAE J379: Gogan Hardness Testing for Brake Linings
Hardness testing is a cornerstone of quality control for brake linings, ensuring consistency in formulation and processing. The Gogan hardness test (SAE J379-2017) is a nondestructive method that measures the compression of the lining material under load. Unlike Rockwell hardness, which measures depth after load, Gogan captures the penetration distance as force increases from the minor to the major load. This article provides a practical overview of the standard, equipment, procedures, and best practices.
How Gogan Hardness Is Defined and Measured
In the Gogan test, a flat cylindrical penetrator is forced into the lining supported by a matching anvil. The Gogan hardness number (GHN) is the distance the penetrator advances into the lining, expressed in units of 0.0064 mm (0.00025 in), while the force increases from the minor load to the major load. The machine applies either a 1500 kg or 3000 kg major load (with corresponding minor loads of 500 or 1500 kg).
The test cycle is automated:
- ET1 (0.75 s): The hardness indicator is disengaged and arrested once the major load is reached.
- ET2 (1.75 s): The cycle terminates, allowing a 1‑second dwell for the operator to read the dial.
The penetrator travel to the lining surface is set at 13 ± 3 mm. The test is valid only if the penetrator is completely supported by the lining, with a minimum of 3 mm clearance from any edge or groove.
Selecting the Right Scale and Equipment
The standard defines four scales based on penetrator diameter and major load:
| Scale Symbol | Major Load [kg (kN)] | Penetrator Diameter | Recommended Gogan Range |
|---|---|---|---|
| A | 1500 (14.71) | 25.4 mm (1 in) | GA10–GA80 |
| B | 3000 (29.42) | 25.4 mm (1 in) | GB10–GB80 |
| C | 1500 (14.71) | 19.05 mm (¾ in) | GC10–GC80 |
| D | 3000 (29.42) | 19.05 mm (¾ in) | GD10–GD80 |
The choice of scale should balance sensitivity with minimal surface damage. Typically, readings within the recommended range provide the best compromise. For grooved linings, a split penetrator (two semicircles spaced apart) is used, and the Gogan number is prefixed with an additional “S” (e.g., GAS, GBS).
Anvils must be matched to the lining contour: curved anvils for curved linings (minimum inside radius, chord length 50.8 mm), and a flat 44.4 mm diameter anvil for flat linings.
Calibration and Best Practices 🎯
To ensure accurate readings, the Gogan hardness tester must be calibrated using a standard Brinell test block. The setup uses a 10 mm ball penetrator and an anvil with a 203.2 mm spherical radius. Calibration readings must fall within the ranges specified in the standard:
| Major Load | Brinell Indentation Diameter | Required Gogan Reading |
|---|---|---|
| 1500 kg (14.71 kN) | 2.50–2.55 mm | 25.1–25.5 |
| 1500 kg (14.71 kN) | 2.55–2.60 mm | 25.5–26.2 |
| 3000 kg (29.42 kN) | 3.20–3.25 mm | 32.0–32.5 |
🛠️ Engineering Design Insight: Gogan hardness values are formulation- and part‑specific. Manufacturers must establish acceptable ranges for each product. Remember: the Gogan method alone does not predict friction coefficient or fade resistance. It is a consistency check, not a performance indicator.
⚠️ Common Mistakes:
- Failing to maintain a 3 mm clearance from edges or grooves (use a split penetrator if necessary).
- Selecting the wrong scale for the lining thickness or curvature.
- Incorrect timer settings (ET1/ET2) or insufficient machine warm‑up.
- Not seating the anvil or eliminating backlash before testing.
Frequently Asked Questions (FAQs)
How do I choose between Gogan and Rockwell hardness testing?
Gogan measures the compression of the lining under load, while Rockwell (per SAE J2654) measures depth after load. For sintered metal friction materials, Rockwell is often specified (ASTM B347). Your choice should align with the properties you need to control. The two methods are complementary.
What does the “S” in GAS or GBS mean?
The “S” prefix indicates that a split penetrator was used for a grooved lining. The standard defines four additional scales: GAS, GBS, GCS, and GDS.
How often should a Gogan hardness tester be calibrated?
Calibration should be performed periodically to maintain accuracy. The standard provides a procedure using standard Brinell test blocks. If the machine drifts, check the major load with a load cell or proving ring, then adjust the minor load pressure switch.
What is the most important rule for valid test results?
The penetrator must be completely supported by the lining, with no less than 3 mm (1/8 in) from any edge or groove. If this clearance cannot be achieved, a split penetrator is mandatory. Always allow a 2‑minute warm‑up and operate the machine a few times before testing to seat the anvil.
For complete details, refer to SAE J379-2017. This standard is stabilized, but users should verify that it meets current application requirements.
