A new methodology for detecting adhesion location in aluminum tube expansion

Abstract

During the expansion forming of aluminum tube, the efficiency of heat exchanger diminishes due to the adhesion of groove and expansion ball inside the tube. Despite its importance, a limited number of researches on the adhesion problems in aluminum tube expansion have been published. This study aims to analyze the adhesion occurring during the expansion forming of aluminum tube for heat exchanger and to identify its location. For this, the method of using the statistical analysis of geometry by image processing and the slope of force measured from expansion forming was suggested. The new method discovers the adhesion location from the standard deviation of groove height measured before and after expansion of tube and the differentiation of force measured from expansion forming. To prove this method, the area with deviation of groove height above average was discovered, and it was confirmed that from the actual expansion of tube cross-sectional images, the height of some grooves was abnormally shorter due to adhesion. Also, from this method, it was confirmed that the changes in differentiation of force occurring from the expansion of the tube also include the information on adhesion location.

The Role of the Process and Design Variables in Improving the Performance of Heat Exchanger Tube Expansion

“…However, the standard deviation of S05H, which had the lowest expansion force, was ~568 N/s (Figure 6b and Table 3). According to our previous study [17], the adhesion of tube's inner grooves can be associated with the standard deviation of the expansion force rate, because the sudden increase in the expansion force has a close relation to the occurrence of adhesion in the tube's inner grooves during the expansion. In the current study, a linear correlation (R 2 = 0.984) was observed between the expansion force and the expansion force rate's standard deviations (Figure 7).…”

“…Our previous study predicted the adhesion locations by comparing the differentiation of expansion force in terms of time (i.e., expansion force rate) with measurements of the tube's inner groove adhesion, because the sudden increase in the expansion force has a close relation to the occurrence of adhesion in the tube's inner grooves during the expansion [17]. In the present study, a custom expansion experimental device was made with a jig to position the tube, a 1-axis current controller (RCS-6000G, Robostar, South Korea), a 100-kgf load cell (CDFS-100, Bongshin, Gyeonggi-do, Korea), a 12-bit A/D converter (VSAD-101, Visol, Gyeonggi-do, Korea), and signal amplifiers.…”

“…ball and tube, and lubricants with higher viscosity could stick to the ball surface for a longer time, resulting in more reduction in the expansion force (Figure 6a). The expansion force rate, which is differentiation of the expansion force with respect to time, can be used to represent the occurrence of adhesion in the tube's inner grooves [17]. The standard deviation of the rate was the highest for S1N (~815 N/s), which also produced the highest expansion force.…”

“…G1N (n = 3) 69.6 713.4 S1N (n = 4) 338.8 815.2 S1A (n = 10) 53.0 613.1 S1H (n = 10) 438.7 600.2 S05H (n = 10) 26.8 567.9 The expansion force rate, which is differentiation of the expansion force with respect to time, can be used to represent the occurrence of adhesion in the tube's inner grooves [17]. The standard deviation of the rate was the highest for S1N (~815 N/s), which also produced the highest expansion force.…”

Effects of Air Conditioner Operating Environments on the Fatigue of Heat Exchanger Aluminum Tubes (Al3003-O)

“…Regarding tube materials, although copper has popularly been used, aluminum has currently been considered copper's replacement due to its cheaper production cost and high anticorrosive property, light weight and high productivity, compared to copper. Aluminum tubes are one-fourth times cheaper and 35% lighter than copper tubes 2,3 . In the operation of air conditioners, aluminum tubes are not subject to high loads or high stresses.…”