accelerated thermal upshock rates in the exhaust cycle of a crt envelope are attained for crts , and especially a tension mask crt having a shadow mask - supporting rail frame affixed to a flat , skirtless front panel . the corner walls of the crt funnel are made with thinner walls to provide an increased compliance of the normally very rigid corners of the funnel - to - panel seal area . panel - fracturing stresses generated in the funnel - to - panel seal area corners during upshock are thus alleviated allowing for faster crt throughput during manufacture .