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ASTM D785 Standard Test Method for Rockwell Hardness of Plastics and Electrical Insulating Materials
Category:
Mechanical
ASTM D785 Standard Description
ASTM D785 Standard Test Method for Rockwell Hardness of Plastics and Electrical Insulating Materials
ASTM D785 Standard Introduction
ASTM D785 specifies the method for determining the indentation hardness of plastics and plastic electrical insulating materials using a Rockwell hardness tester. It helps evaluate material properties and supports quality control in various applications. Rockwell hardness is an important indicator for evaluating the hardness of plastic and polymer materials used in industries such as automotive, aerospace, electronics and consumer products. Through Rockwell hardness evaluation, the suitability of materials for high-strength applications or specific uses in coatings and plastic components can be determined.
ASTM D785 Scope of Application
ASTM D785 applies to the hardness measurement of plastics and polymer materials.
ASTM D785 Ruler
|
Hardness scale |
Minor Load (kg) |
Major Load (kg) |
Indenter Diameter |
|
R |
10 |
60 |
0.5000±0.0001in(12.700±0.0025mm) |
|
L |
10 |
60 |
0.2500±0.0001in(6.350±0.0025mm) |
|
M |
10 |
100 |
0.2500±0.0001in(6.350±0.0025mm) |
|
E |
10 |
100 |
0.1250±0.0001in(3.175±0.0025mm) |
|
K |
10 |
150 |
0.1250±0.0001in(3.175±0.0025mm) |
ASTM D785 Test program A
Selection of Hardness Scale: Select the appropriate Rockwell hardness scale according to the material properties. When replacing the indenter, ignore the initial reading and directly apply the major load to ensure proper seating of the indenter shoulder.
Specimen Placement and Minor Load Application: Place the specimen on the anvil. Adjust the large pointer to the "set" position on the red scale and set the small pointer to zero. Apply a 10 kg minor load and fine-tune using the adjustment wheel to avoid overshooting.
Application and Removal of Major Load: Apply the major load within 10 seconds after releasing the minor load and remove it after 15 seconds. After removing the major load, maintain the condition for another 15 seconds, then read the nearest value on the red scale.
Reading and Correction Rules: During loading, record the reading when the pointer passes zero. After unloading, correct the value according to the difference:
◎Difference = 0 → Record as 0
◎Difference = 1 → Record as +1
◎Difference = 2 → Record as +2
◎Out of range → Record as -100
Note: The reading must be completed within 15 seconds. If excessive indentation occurs, use a lighter scale. Maintain a minimum distance of 6 mm from the specimen edge to avoid damage. Avoid repeated testing on both sides of the same specimen.
ASTM D785 Test program B
Equipment and Scale Setup: Use the R scale with a 12.7 mm diameter indenter and apply a 60 kg major load. Place a flat copper block on the anvil, raise the indenter to 12.7 mm, align the small pointer with the starting point, and set the large pointer to zero on the black scale to determine the instrument spring constant.
Correction of Instrument Elastic Effects: The operator activates the load release lever to apply the major load. Due to elastic deformation of the indenter spindle and frame spring effects, the dial displays the total penetration displacement. Repeat light loading until the displacement becomes stable, representing only the instrument spring effect, then reset the dial to zero.
Specimen Placement and Minor Load Application: Place the specimen on the anvil, apply a 10 kg minor load and maintain it for 10 seconds before zero adjustment.
Application of Major Load and Reading: After zero adjustment, immediately apply the major load and maintain it for 15 seconds. During this period, record the number of scale divisions passed by the pointer as the material indentation value.
Note: Ignore the numerical values on the traditional dial indicator and use the black scale readings. The recorded value is the number of scale divisions, not the numerical dial reading.
ASTM D785 Test program A with the test program B Difference
|
Comparison Item |
Procedure A |
Procedure B |
Comparison Item |
|
Measurement Principle |
Calculates hardness by measuring the difference in indentation depth under different loads |
Calculates hardness based on total indentation depth indicated by the dial reading |
Measurement Principle |
|
Focus |
Focuses on indentation behavior under different loads |
Focuses on instrument spring effects and total indentation depth |
Focus |
|
Load Holding Time |
Apply and maintain the major load for 10 seconds before reading |
Apply and maintain the major load for 15 seconds and record scale divisions |
Load Holding Time |
|
Result Reading Method |
Read the final result on the red scale after unloading |
Determine the result based on the number of scale divisions passed by the pointer during indentation |
Result Reading Method |
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