GB1181552A - Improvements in or relating to Articles made of High-Chromium, High-Carbon Iron Alloys, Hydraulic Valve Tappets made from these Alloys, and to Processes for making said Articles and Tappets. - Google Patents

Abstract

1,181,552. Casting processes; moulds; cores; casting composite valve tappets. E. A. THOMPSON. 22 Feb., 1967 [24 Feb., 1966], No. 8573/67. Headings B3A and B3F. [Also in Division C7] Hydraulic valve tappet 10 for an I.C. engine comprises cast plunger 28 slidable in cast cupshaped body having tubular portion 20, at least one of these members being composed of an alloy consisting by weight of C 1À3-3À1%, Cr 15-35%, Mn and/or Si up to 3À25% in total, Fe and impurities-balance, the alloy having a minimum hardness of 61 R c and large and small chromium carbide particles distributed in a martensite matrix. One half of a symmetrical section of a mould for casting simultaneously a number of tappet bodies is shown in Fig. 2. It comprises central casting passage 50, lower runner passages 52 for pouring the metal of the feet 22 (Fig. 1) when this metal is different from that of the tubular portions (see below), upper passages 54 for pouring the metal of the tubular portions 20, and a plurality of cavities 56 in which the bodies are formed between mould sections 58 and core sections 60. Central openings 62 help the casting cool quickly from pouring temperatures of, e.g., 2750‹ F. Rapid cooling may also be effected by moulding thicker sections in zircon sand, by using chills or by using a water-cooled permanent mould. After rapid cooling, the casting is heated slowly (to, e.g. 1600‹ F) and then cooled slowly. Machining may next be effected, e.g. the groove for snapring 34 (Fig. 1) may be machined in member 20, oil passage 39 may be bored, the inner and outer diameter of the body ground to nearly exact finished size, oil passage 40 may be bored in plunger 28, the passage for check valve 44 may be bored, if not already cast, the valve seat may be coined and the outer surface of the plunger ground to nearly exact finished size. Finally, hardening may be effected by heating and quenching, and a finish grinding operation performed. Tappets may be cast having zones of different hardness as disclosed in Specification 991,513, i.e. in shell moulds on a rotating table or in a chain and into which the metal is forced by inert gas. Thus, foot 22 is cast first using an alloy containing high C and Cr, and tubular portion 20 then cast using an alloy containing lower proportions of these elements.