Centric Friction Development Lab

by Steve Ruiz of StopTech


Centric and Stoptech recently opened a Friction Development Lab that focuses on in-house research and development of friction materials. Past friction development cycles required long lead times from outside manufacturers, and limited control of the actual friction mixtures and associated components. The Friction Development Lab, coupled with our in-house friction expert Dr. Poh Wah Lee, allows Centric/Stoptech to rapidly produce custom friction blends and immediately test them on our Link Chase Machine or three Link Brake Dynamometers, thereby reducing the friction development cycle time substantially.

A main component of the Friction Development Lab is the Model 600 Link Chase Machine. The Chase
Machine has been designed and engineered to rapidly evaluate friction material characteristics using the SAE J661 test protocol. The Chase Machine can be used to evaluate prototype or development materials, and also perform in-process quality control checks on production samples to ensure conformance. A one inch square of friction material is used as the test sample, and the sample is held at a specific normal force on a rotating brake drum. Throughout the SAE J661 test protocol, test sections with various speeds, temperatures, and normal forces are employed to produce an assessment of the friction material’s properties. Typical test durations range from 3 to 4 hours.

The rotating speed of the Chase drum is controlled by a variable speed drive that can spin to 1000 rpm. The normal force application is controlled by a closed-loop servo system that can apply up to a 600 pound force on the Chase drum. The drum also has two resistance heating coils that can heat the drum up to 540°C (1000°F), as well as a forced-air cooling system to facilitate cooling from elevated temperatures.

Stoptech/Centric Friction Lab and Link Chase Machine:

Restricted Entrance to Stoptech/Centric Friction Lab

Link Model 600 Chase Machine and associated control workstation

Link Model 600 Chase Machine Technical Specifications:

Parameter  Model 600 Chase Machine Range
 Normal Force Control 0 - 600 lbs
 Friction Force 0 - 300 lbs
 Rotating Speed 0 - 1000 rpm
 Temperature 0 - 1000º F
 Sample Size 1" x 1" x 0.25"

Note: The above parameters (excluding Sample Size) are
calibrated by Link on a yearly basis. The last calibration was
performed in July 2015, and the next calibration is scheduled
for July 2016.

Additional Friction Lab Photos:

An electronic locking cage guards the test drum during operation. The
cage can be opened once testing has completed for easy service of
the test sample and drum.

A close-up view of the test drum and normal force applicator.

A close-up view of a test sample after completing the SAE J661 test.
The friction sample is inverted 180 degrees to show the contact surface
(the top surface shown is in contact with the test drum during testing).

A control screen is shown on the Chase Machine control computer.
Various test parameters can be monitored or changed from this screen.

Various pad shape molds for creation of small-batch brake pads. These
molds are filled with a backing plate and friction materials then 
compressed and heated to form the brake pad.

Close-up view of the D1611 brake pad mold. The backing plate is placed
in the bottom of the mold, followed by the friction material mixture, then
the mold insert (part on top of mold). The assembly is then placed into a
hydraulic hot press at a specific temperature and pressure to form the brake pad.

Various components can be seen at the friction material mixing station.
From left to right:
-Isotemp Muffle Furnace
-Hydraulic Hot Press
A ventilation hood can be seen on the back wall, and provides ventilation
when working with various chemicals.

Two separate grinders are used for Chase sample preparations. Each
grinder is installed inside a hood to prevent friction material particles
from entering into the atmosphere during grinding operations.

Vertical grinder used for shaping Chase samples prior to testing.

Rotary grinder used for shaping Chase samples prior to testing.

A 3-in-1 grinder is used to grind slots, pad surfaces, and chamfer pad
edges for variations on standard pad shapes. These variations can then be
evaluated on Centric/Stoptech’s Brake Dynamometers for overall effectiveness.

Friction Lab Testing Initiatives:

The chart below illustrates current Friction Testing Initiatives that the Friction Development Lab is currently undertaking.

Test Description  Test Purpose Data Output Test Requirements
 Low Copper
 Identify new formulas with low
to no copper that outperform current industry standards and product lines.
 New friction formulations
designed to be more
environmentally friendly
and compliant with industry regulations.
 Per Senate Bill 346, all
brake pads sold in
California by 2021 must contain no more than 5% copper. Friction
alternatives must be less
hazardous to public health
and the environment.
 Chase Testing  Pre-screen friction materials on the Chase machine prior to dyno testing in order to
identify potential formulas.
In-process test production
friction formulas for quality control and baselining.
 SAE J661 test report
illustrating the friction
performance in various
conditions like Green, Post-Burnish, Fade, and Recovery.
 Requirements defined by
SAE J661. Friction
samples cut from brake
pads or shoes, and are
ground down to a 1” x 1” x
0.25” thick test sample.