Circular abrasion

Circular abrasion is based on the same concept as linear abrasion and it uses the same experimental apparatus with the only difference being the type of movement that the abradant material performs. In this case the abradant material has the shape of a disk and it performs a rotational motion. The only disadvantage in this case, compared to the linear abrasion, is that different parts of the abradant material move with different speeds. Even if in most of the cases this is not very crucial, we cannot exclude the possibility that this technique can produce diverse surface characteristics in the abraded surfaces. The Martindale method is a common circular abrasion test that is used mainly for evaluating textiles (see also Section 9.5.1). 

Raimimdo et al. fabricated aliuninum alloy surfaces with omniphobic behavior [48]. Fimctional, hybrid organic-inorganic coatings were obtained by a classic sol-gel route, followed by a controlled dip coating of the substrate in order to achieve surface nanostructures. The surfaces 

Rubbing between two solid surfaces is a common case that can occur in everyday use of liquid repellent materials. However, there are also occasions when surfaces could come into contact with sharper objects (e.g. knives, pens, forks, etc.) that induce much more severe damage. Driven by this problem, a few studies have been published where liquid repellent surfaces undergo blade tests, which are practically linear abrasion tests but instead of a flat abradant material the rubbing is performed by a sharp blade. 

Wang et al. [49] used both blade and circular abrasion tests and plotted the wetting characteristics of their samples against the number of abrasion cycles. Superomniphobic, surface-treated polyester fabrics were fabricated 

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Figure 9.6 SEM images of various superhydrophobic surfaces before and after performing the wear tests with forces given in figure (a) nanograss surface (NS), (b,c,d) microcone and nanograss combinations. Scale bar 5 pm (a), 20 pm (b-d). On the right there is a sketch depicting the circular abrasion configuration. Reproduced with permission from [47], Copyright 2014 American Chemical Society.

The superomniphobic polyester fabrics tested with the blade test by the same group (Zhou et al.) were also tested under laimdry and circular abrasion [49]. In the machine laundry process, the coated fabric did not show changes in the APCAs of water, hexadecane or ethanol after 200 cycles of washing. However, the SA values increased to 4.5°, 36.7°, and 47.5° for water, hexadecane, and ethanol respectively. After 20000 abrasion cycles nearly no nanoparticles could be observed on the top surface. However, the damaged surface after the abrasion test was healable when the coated fabric was heated at 140° C for 30 min. The APCAs of water and hexadecane recovered to 171° and 152°, respectively. However, the heat treatment could increase the APCA of ethanol only to 127°. 

One advantage of sintering is the close control of si2e and shape of the abrasive particle. Extmded, cylindricaHy shaped, sintered abrasives of circular cross section were produced from bauxite (24) and from calcined alumina (25). The Uelt2 sintered bauxite was also later produced in extmded cylinder form and designated as 76A. Extmded sintered abrasives of a wide variety of cross-sectional configurations, eg, square and triangular, were later patented (26). 

To reduce the amount of dust produced, water can be added to the abrasive from a circular water sprayer around the no22le. Chemical corrosion inhibitors must be dissolved in the water to prevent flash msting of the steel. Newer methods to reduce dust include the use of ice, soHd carbon dioxide (dry ice), or plastic beads as abrasives. Blasting with dry ice is inexpensive and effective, but the accumulation of carbon dioxide must be avoided in enclosures. Plastic beads are inexpensive, but the cutting efficiency is low and paint removal is slow the beads can be cleaned of paint particles and reused. 

There is usually more than one test method to determine a performance because each test has its own behavior and meaning. As an example there are different tests used to determine the abrasion resistance of materials. There is the popular Taber abrasion test. It determines the weight loss of a plastic or other material after it is subjected to abrasion for a prescribed number of the abrader disk rotations (usually 1000). The abrader consists of an idling abrasive speed controlled rotating wheel with the load applied to the wheel. The abrasive action on the circular specimen is subjected to a rotary motion. 

For the above polyol blend viscosity (Brookfield, ASTM D-2196) = 1500 mPa-S at 23° C. For the reaction mixture working (pot) life 20 min Gardner circular dry times [72°F, 54% relative humidity (RH)] surface dry = 1.0 h, hard dry = 2.0 h, mar free = 3.5 h. For the finished coating gloss (ASTM D-523) = 90+ at 60° impact (ASTM D-2794) = 60 in.-lb direct, 10 in.-lb reverse Tabor abrasion (ASTMD-4060,1000 g load, 1000cycles, CS-17 wheel) = 95.6 mg pendulum hardness = 180 s MEK double rubs (ASTM D4752-95, 50 double rubs) = softened. 

Whether the GC is mounted or not, the most common polishing procedure involves a series of abrasives used as slurries on a commercial fabric polishing cloth. The as-received electrode or GC piece is first sanded on 600 grit emery paper to remove gross surface defects and impurities. In most cases, each polishing step involves a circular motion for a few minutes, with the objective being uniform roughness over the electrode surface. The sandpaper is followed by... 

Studies using a rotating abrasive surface on a hand-held electric drill [Figure 5(a)] to achieve superficial dermabrasion of established small, circular mustard vapour burns in our porcine model have shown that the healing time of such injuries can be reduced from 12 to 3 1 weeks (Rice et al., 2000) [Figure 5(b)]. 

The rotary abradcr applies two abrasive wheels under controlled pressure to a circular sample mounted on a rotating table or platform. The wheels arc free to rotate under the friction exerted by the moving specimen, and being mounted at an acute angle they induce wear. The weight loss of the coating can be determined after a fixed number of cycles... 

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