Coating cracking

Physical condition of the fiber coating (cracks, contamination) GC inlet liner type and volume... 

Figure 3. SEM photomicrograph at 26X of (a) uncoated polycarbonate sample after 3,3 X 10s impacts and (b) polycarbonate sample coated with Mobay9s E-397 friction coating after 4.5 X 10s impact. The same impact conditions were used in both tests. The surface friction was halved after coating. Note the presence of coating cracks.

As a numerical application, we can consider here a shear stress of 800 MPa, estimated from coating cracking stresses. Then the inter-crack distances resulting from perfect adherence can be calculated. This distance can be compared to the experimental values in Table 7. For SiC/Tag 3/steel, there is good agreement between the theory (perfect adhesion) and the experimental observations. On the other hand, for the other systems, the significantly smaller theoretical distances compared with experimental distances is indicative of unsatisfactory interfacial attachment in the vicinity of the transverse cracks of the coating. 

Sugar coatings are particularly susceptible to cracking when they are applied to large batches of tablet cores that are dried rapidly. As most active substances are hydrophobic, copovidone is useful as an additive to prevent the tablet coating cracking away from the tablet core during manufacture. 

Type A plasma polymers have the characteristic internal stress built in the film, and the plasma polymerization coating acts as the tempered ultrathin layer on the substrate. The internal stress is caused by the wedging effect of the deposition process, and the total stress increases linearly with the thickness. As the thickness increases, the internal stress reaches the critical point beyond which the internal stress becomes greater than the cohesive force or the adhesive force of the plasma polymerized coating. Above the critical thickness, therefore, the coating cracks (not necessarily in macroscopic sense) or delaminates (buckles) from the substrate. Consequently, there exists a thickness limit of plasma polymerization coating. The tighter the structure, the smaller is the thickness limit. 

MAJOR PRODUCT APPLICATIONS filtration, ceramics, foams, floor tiles, shoe soles, paints, food, building products, welding electrodes, gaskets, stucco, EIFS, asbestos alternative, sealants, roof coatings, athletic surface coatings, crack fillers and sealers, brake pads, clutches, pavement, artificial leather, electrical components, automotive components, household appliances, mastics, putties, patching compounds, grouts... 

A study by Wuebker et al. (2001) investigated the effect of impact damage on seed vigor with a rotating horizontal cylinder. Each revolution of the cylinder lifted 250 g of seeds with a horizontal paddle and allowed the seeds to drop within the cylinder. Impact damage was assessed visibly by an increase in seed-coat cracks and splits and... 

Several methods exist for determining seed-coat crack percent es, including a soak test where soybeans are immersed in a 0.1% solution of sodium hypochlorite for 5 min. Soybeans with seed-coat cracks or openings quickly absorb the sodium hypochlorite solution and swell to two to three times their original size (Rodda et al., 1973). 

Galvanization protects iron in two ways. As long as the zinc layer is intact, water and oxygen cannot reach the irons surface. Inevitably, the zinc coating cracks. When this happens, zinc protects iron from rapid corrosion by becoming the anode of the voltaic cell set up when water and oxygen contact iron and zinc at the same time. Figure 20.18 illustrates how these two forms of corrosion protection work. 

Figure 11.97. CORRPASSIV without top coat no rust under Figure 11.99. Metal-reactive two-component primer with top cross-hatch cut. coat cracking and considerable undermining by rust.

The temperature should meet film-forming criteria for the coating system without introducing coat cracking, particle agglomeration, or twinning. 

ASTM D2137-11 provides Standard Test Methods for Rubber Property -Brittleness Point of Hexible Polymers and Coated Fabrics. Related Methods for Brittleness Point Test are ISO 812, DIN ISO 812 (Germany), and BS 903-A25 (UK). These test methods cover the determination of the lowest temperature at which rubber vulcanizates and rubber-coated fabrics will not exhibit fi actures or coating cracks when subjected to specified impact conditions (ASTM D2137-11). 

Nickel coated bags may have conductivity discontinuities due to the thin coating cracking after repeated bag handling. These bags should be periodically tested and examined for physical damage. 

Fig. 12-4B. Plastic bottle caps which were coated with a brittle lacquer prior to over-tightening by various degrees. After the coating cracks, a die is allowed to stain the cracked areas. This allows the analysis of direction of principal stresses.

---