Abstract: An aromatic polyimide laminate sheet having a relatively large thickness of 50 .mu.m or more comprises (1) at least one first film layer comprising a polymerization-imidization product of an acid component containing 80 to 100 molar % of at least one biphenyltetracarboxylic acid with an amine component containing 80 to 100 molar % of at least one aromatic diamine having two or more benzene rings, and having a glass transition point of 250.degree. C. to 350.degree. C.; and (2) at least one second film layer comprising an aromatic imide polymer, the first and second film layers being alternately laminated on and directly bonded to each other without using bonding material.

Abstract: A spark plug having a center electrode comprises a ceramic insulator whose leg portion is shaped at the tip in a bag form so as to close the insulator bore. A firing tip is provided at the bag-shaped tip in a face-to-face relation with a side electrode by fixing an electrode element made of a sinter of a ceramic powder containing particles of a size between 10 and 200 .mu.m which are coated with a noble metal to a thickness of 0.1-20 .mu.m. An electrode axis extends from the top end of the plug and is inserted through the insulator bore.

Abstract: A method and apparatus for monitoring the operation of a reciprocating liquid injection unit wherein charges of an injection liquid, such as molten metal, are injected one-by-one to a point of consumption, such as an injection molding die, by an injection plunger reciprocating in a sleeve and driven by a double acting hydraulic cylinder and fluctuations in the oil pressure on the return side of the hydraulic cylinder are monitored to detect abnormal increases in such pressure which indicate the occurrence of dragging between the injection sleeve and the plunger head.