PURPOSE: To improve durability, reliability and assembling property by providing such holes at the center of the second heating board and the third and fourth insulating materials that are larger than the holes provided at the center of the first heating board, the first and second insulating materials, and a heat diffusing plate, and providing two pressing faces corresponding to respective holes on the first back plate.
CONSTITUTION: Holes a15-d18 are provided at the center of the first insulating material 9, the first heating board 7, the second insulating material 10 and a heat diffusing plate 4, holes e19-g21 larger than holes a15-d18 are provided at the center of the third insulating material 13, the second heating board 11 and the fourth insulating material 14, and they are fitted by the good-heat conductivity first back material 22 such as a surface-processed steel plate protruded upward at the center and having an outer periphery side section 22c, a through hole at the center, and two pressing faces 22a and 22b corresponding to holes a15-d18 and holes e19-g21 while a pressing margin is provided on the lower face of a heat transfer plate 1. Assembling property, safety and reliability can be improved.
MAEKAWA KAORU
OKABE YOSHIYUKI
