Adhesion is then rated by comparing lm removed against an established rating scale. Because of the variability in adhesion strength from batch-to-batch and with time, it is essential that tape from the same batch be used when tests are to be run in different laboratories. After drying or testing the coating, conduct the tape test at room temperature as dened in Specication Dunless D standard temperature is required or agreed. Users shall not use intermediate values for ranking adhesion tests within this method.
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First published in , it is widely used in a variety of industries and applications. It can be performed in the laboratory, shop, or field on both newly applied and aged protective coating systems. It is relatively easy to perform and does not require specialized equipment. Yet there are many potential issues and challenges with successfully performing such a basic test. This article includes an overview of the testing procedures and presents some common pitfalls associated with performing these tests.
Test Description The Test Description information in the following section was extracted from an article written by Raymond Tombaugh, Sr. Either method can be performed in the shop, field or laboratory. The test was developed for assessing the adhesion of coating to steel but can be used on other hard substrates.
The test has also been used successfully on softer substrates e. Both tests are performed by scribing the coating to the substrate with a sharp knife blade in a specific pattern, applying a pressure sensitive tape and then rapidly pulling the tape from the surface. When the coating is greater than 5-mils thick, an X-cut with each leg approximately 1. When the coating is less than 5-mils thick, a cross-cut lattice pattern is created with either six or eleven cuts in each direction.
For coatings up to 2 mils thick, eleven incisions are made that are spaced 1 mm apart. For coatings between 2 mils and 5 mils thick, six incisions are spaced 2 mm apart. Once the incisions are made, a pressure sensitive tape with adhesive properties conforming to the requirements of the standard; Figure 1 is applied over the incisions and pressed in place using a pencil eraser.
After removal of the tape, the amount of coating removed from the substrate or underlying coating is rated. It is important to evaluate the coated surface and not the back of the tape, since coating debris from the incisions is often removed by the tape.
Table 1 provides the evaluation criteria for Method A; Table 2 provides the evaluation criteria for Method B. The standard also contains a pictorial guide to aid in the rating of the cross-cut Method B. When appropriate, the nature and location of the separation is documented. A cohesive separation is one that occurs within a coating layer; an adhesive separation is one that occurs between coating layers or between the coating and the substrate.
Generally, adhesion ratings of 4 and 5 are considered good, adhesion values of 2 and 3 are considered marginal and adhesion values of 0 and 1 are considered poor. Issues and Challenges Following are ten issues and challenges when performing tape adhesion testing on coating systems. The list is not exhaustive but addresses some of the more common pitfalls to avoid. Those listed below are in the order in which they would be performed during actual testing.
The method selected is based on the total thickness of the coating system to be evaluated. Method B is used for coating systems up to 5 mils thick and Method A is used for coating systems in excess of 5 mils.
The spacing between incisions for Method B is generally 1mm to 2mm apart depending on the thickness of the coating. An X-cut intersection that is too wide or too narrow may affect the adhesion rating.
A special template Figure 2 is available to help ensure the X-cut is made correctly. Figure 2 Creating the Correct Spacing Between Parallel Incisions for Method B: According to the standard, the spacing between parallel incisions is 1mm for coatings up to 2 mils thick and 2mm for coatings greater than 2 mils thick up to 5 mils thick. Incisions made too close together, too far apart, or that do not remain parallel can produce misleading ratings. A special template Figure 3 is available to help ensure the spacing is correct.
Alternatively, a multi-blade cutter can be used to generate the cross-cut pattern Figure 4. Figure 3 Figure 4 Blade Sharpness: Section 5. Section It also notes the importance that the cutting edge or edges be in good condition. It is common to use a utility knife to make the incisions. Since use of a knife blade in this manner making an incision down to the base metal or other hard substrate tends to dull the blade quickly, it may be necessary to replace the blade frequently.
Depth of Incisions: The incisions made with the cutting tool for Method A or B must penetrate through all coating layers to the metal substrate using one steady motion. This should be verified visually and with the aid of a magnifier if necessary. This is particularly important when using the multi-blade cutter.
It is important not to attempt to re-cut a previous incision as it may result in a false rating. Any chalking from deteriorated paint, dirt, oils, moisture, or other surface contaminants will interfere with the adhesion of the tape and could yield false adhesion ratings.
It is permissible to clean the surface prior to testing if these surface conditions are present. Also, after the incisions are made, any debris should be removed with a soft bristle brush prior to attaching the adhesive tape. It also cautions that there may be variability in adhesion strength of the tape from batch-to-batch and with time.
The ASTM standard does not require a specific type or manufacturer of tape to use. Currently two companies SEMicro and Elcometer manufacture a tape CHT and P99, respectively specifically for this test method that possess the same backing and adhesive strength as the tape referenced by earlier versions of the standard Permacel 99 , which is no longer available.
Since there is no specific tape to use, it is important to agree on the type to be used in advance of any testing. Further, Sections 7. This practice helps ensure fresh adhesive is on the tape used to conduct testing.
Most of these tapes have a shelf life and should not be used once expired. Shelf life can be determined from the Lot No. While the location of the eraser end of a pencil is likely moot a separate eraser can be used , the end of the utility knife, thumb pressure or other means of ensuring positive contact are not as effective and may yield different results.
An eraser is pliable and can conform to slight surface irregularities, making it an ideal tool for ensuring good contact between the tape and the test area. Tape Direction of Pull: Sections 7. It is important to peel back the tape and not pull upwards since the purpose of the tape is to remove poorly adhered coating so that the X-cut or cross-cut area can be correctly evaluated; it is not intended to remove intact coatings. Since incisions are made into the coating system, the tape will almost always have coating on it; therefore, it is important to base the rating on the test area only.
Evaluation Criteria: Method B cross-cut provides words Table 2 above to describe the ratings of the amount of coating that might be removed for each rating. Method A X-cut does not have a corresponding figure illustrating the different amounts of detachment; only a description of each rating from 5A to 0A Table 1 above.
Therefore, there can be more subjectivity to evaluating the X-cut even though the description of each rating value is relatively straightforward. In some cases, it may be necessary to report a range e. About Bill Corbett.
ASTM D3359 Measuring Adhesion by Tape Test
Brad Kelechava Leave a comment Adhesion is a strongly desired quality between a coating and a substrate, as it allows the coating to fulfill its function of protecting or decorating the substrate. Unfortunately, at the present time, no test exists that can precisely assess the actual physical strength of an adhesive bond. This standard details procedures for assessing the adhesion of coating films applied to metallic substrates through the placement and removal of pressure-sensitive tape over cuts made in the film. Under Test Method A, an X-cut is made through the film to the substrate, and pressure-sensitive tape is applied over the cut and then removed.
ASTM D3359-09 PDF
After drying or testing the coating, conduct the report the results with the adhesion rating s. ASTM D — 09 Standard Test Methods for Measuring Adhesion by Tape Test However, with the tape test, failures within the substrate or coating layers are rare because the tape adhesive is not usually strong enough to exceed the cohesive strengths of normal substrates and organic coatings. This standard has been approved for use by agencies of the Department of Defense. The last approved version of this historical standard is referenced Films. The color under the tape is a useful indication of when good contact has been made. Criticism of these tests arises when they are used to quantify the strength of adhesive bonding. Your comments will receive careful consideration at a meeting of the d technical committee, which you may attend.
ASTM D3359-08 PDF
First published in , it is widely used in a variety of industries and applications. It can be performed in the laboratory, shop, or field on both newly applied and aged protective coating systems. It is relatively easy to perform and does not require specialized equipment. Yet there are many potential issues and challenges with successfully performing such a basic test.
ASTM D3359-17 – Standard Test Methods for Rating Adhesion by Tape Test