Optical Dispersion Testing is one of the fastest ways to determine mix quality. However, sample preparation is the most important factor of the test.
Dispersion Tester’s, like the DisperTester 3000 provide a fast and convenient optical method for objectively testing dispersion of reactive and inert fillers in a rubber mix. With any optical test method, it is crucial to ensure the surface of the sample under test has good optical properties: flatness, cleanliness, and alignment.
Sample preparation is a critical part of the dispersion testing process. The following tips and considerations for preparing test samples will ensure optimally repeatable results.
Sample Preparation Tips:
Make sure the sample testing area of the instrument is clean and free of dust and debris. Only use clean sharp blades, made from hardened steel that will not bend when cutting stiff materials.
With the sample secured, the cut is made using a single, consistent and quick stroke to cleave the sample cleanly. This is especially important, therefore MonTech offers the DisperCut to safely make perfect cuts every time.
When handling the sample, avoid touching the surface. Any contaminants can greatly affect the results of the test. Following this, place the sample parallel to the viewing window in front of the instrument. There should be no light escaping the aperture when the test specimen is secured by the clamping device.
Considerations for Uncured Compounds:
Air Pockets:
Samples straight from the mill typically have pockets of air in them due to the mixing process. These pockets will appear as dark black patches in the image which do not properly reflect agglomerates. This can affect consistency of the results. It is recommended to press the compound (preferably under heat) to eliminate these air pockets before cutting a test sample.
Soft / Oily Compounds:
Some soft or oily compounds may not be stiff enough to cleave a flat surface. This can cause the surface of the sample image to appear distorted or smeared. For a good flat cleave of a soft or oily sample, cool the sample to a temperature where its hardness will allow a proper cut – preferably close to the glass transition temperature. Instrument’s like the DisperCool rapidly chill materials down to proper cleaving temperatures.
Cured vs Uncured:
In most cases, dispersion results will be different for a compound depending on whether it is cured or uncured. Therefore, the MonDispersion software allows the user to designate whether the compound being tested is cured or uncured. Reports from the software will indicate the state of the material tested for future reference.
Common Troubleshooting Tips:
Striations in the Sample Image:
Worn blades will produce striations on the surface of the sample. These stripes, typically brighter than the filler matrix, are parallel with the stroke of the cut and can affect test results. It is recommended to replace the blade at this time.
Inconsistent Image Brightness:
After initial setting the exposure level for a compound does not typically need to be readjusted before every test image is taken. Image brightness variation of a compound can affect test results and is usually caused by the following:
- Sample cross-section size:
Escaping light can affect the amount of illumination available to the sample surface – requiring unnecessary exposure adjustments. Make sure the cross-section of the sample is large enough to completely cover the sample viewing window.
- Alignment of the sample:
If the sample cross-section surface is not parallel to the viewing window, it will reflect more or less light to the optical sensor depending on the angle of incidence. Ensure the sample surface is flush with the viewing window or cut a new cross-section
- Gradient in the Sample Image:
A gradient from light to dark in the sample image is caused by the sample surface not receiving equal light coverage and can affect test results. The sample is either not placed flush with the viewing window or the surface is concave/convex due to distortion of the material during cutting. Common causes:
Blades that are not stiff enough may bend while cutting and might not produce an optically flat c
The sample distorted while cutting, creating a concave/convex surface.
The sample is not flush with the viewing window.
- Large / Irregularly Shaped Particles:
These particles are unusually bright with defined shadows and are often slightly blurry. This is typically caused by contamination of the surface with dust and debris. The cross-section should not be touched and it is recommended to test the cut sample immediately to prevent airborne particles from collecting on the surface.
By following these tips and considerations to optimize sample preparation, you can significantly improve your dispersion test repeatability. For additional information please contact us any time. We are committed to providing our customers with premier support and service.
Have questions about Dispersion Testing? Contact us and one of our experts will provide the answers you need!
