This article describes a thermal stress boundary element analysis which was carried out to select a mechanical device that would innovate the frit salvage of cathode ray tubes (CRT). The panel and funnel of a CRT are fritted at the seal edge. To reuse a CRT, the panel and funnel are separated by etching and then applied a thermal shock. This procedure is known as frit salvage. Current yield of the frit salvage success rate is about 61 %, which means that 39% of the components are lost and cannot be reused. The financial burden can be reduced if the salvage rate is improved through a better understanding of the thermal shock mechanism.
During thermal shock, a crack was observed to initiate at the end of the axes and traverses towards the corner along the seal end. A CRT is lost when the crack travels along the diagonal corner. A thermal stress analysis was carried out using the boundary element method. The analysis determined that maximum stresses are located near the blend radius on the panel skirt at approximately 1–2 inches on either side of the diagonal. Also it was found that the stresses along the frit seal edge are uniform from the end of the major and minor axes towards the diagonal. The stresses at the diagonal location were reduced by approximately 29%. The direction and location of the crack obtained by the boundary element anlysis were consistent with those observed in the frit salvage procedure.
The crack's promoter along the seal edge is used to protect thermal shock on the outer face panel near the heel radius in order to prevent thermal failure on the diagonal corner. The resultant stresses' directions through the crack's promoter have two holds. The directions of the dominant high stresses at the seal edge through the crack's promoter were changed perpendicular to the seal edge. Therefore, it induces the crack to follow along the seal edge. Secondly, the stresses' directions on a diagonal corner have also been changed to be perpendicular to the seal edge. Consequently, this will prevent the crack along the seal edge from propagating to the diagonal corner, as the crack will advance normally to the maximum principal stress. The crack continues to traverse along the dominant high stress lines at the seal edge as required for a successful frit salvage process. This application is an excellent example of the advantages of using the boundary element method in an industrial setting. 相似文献
Arteriovenous fistula (AVF) dysfunction is a common problem in hemodialysis patients. After surgical revision for malfunction, we used AVFs early to avoid complications associated with central venous catheters. In this study, we report experience with surgical revisions of native AVFs with suspected arterial dysfunction as the cause of inadequate arterial inflow for dialysis. Exclusion criteria were presence of a central venous catheter as a hemodialysis access, and clinical or radiologic evidence of stenosis or thrombosis of the distal venous segment of the AVF. We prospectively studied 50 patients (mean age 60.2 ± 10.5 years, 25 men and 25 women) with 59 revisions. The patients were followed until change in the modality of dialysis, transplant, or death. The types of AVFs revised were left wrist radiocephalic in 27 patients (54%), left forearm radiocephalic in 10 (20%), right wrist radiocephalic in 6 (12%), left antecubital brachiocephalic in 3 (6%), right antecubital brachiocephalic in 2 (4%), and right forearm radiocephalic in 2 (4%). The causes of inadequate arterial flow were juxta‐anastomotic thrombosis in 20 patients (40%), inadequate arterial anastomotic flow in 16 (32%), inadequate anastomosis in 7 (14%), and juxta‐anastomotic venous stenosis in 7 (14%). The primary surgical revision techniques were proximal neo‐anastomosis using the semiarterialized vein in 43 patients (86%), thrombectomy and re‐anastomosis in 5 (10%), and resection and repair in 2 (4%). Technical success, defined as successful cannulation of the revised AVF for hemodialysis and avoidance of central venous catheter, was achieved in 44 of 50 patients (88%). Technical failure occurred 6 cases, the causes being inadequate arterial flow in 3 patients, failure to cannulate the veins in 2 patients, and steal syndrome in 1 patient. After primary revisions failed, 9 re‐revisions were done in 6 patients. The 1‐year, 2‐year, and 3‐year primary and overall patency rates were 76.2%, 67.6%, 65.0%, and 85.7%, 75.7%, 65.0%, respectively. In conclusion, surgical salvage of the AVF with inadequate arterial flow is an effective approach that can be performed as an outpatient procedure and allows early cannulation of the semi‐arterialized veins, thus avoiding the use of central venous catheters. 相似文献
