A change of material helps clean up the environment

A material that seemed ideal for the job was causing problems. Would an improved version meet, or exceed expectations?

AAA Industries was mass producing valve seats from Type 416 stainless steel for Siemens to incorporate in the emission controls it was making for a major automotive manufacturer. There were no problems machining the valve seats, but AAA struggled to meet the surface finish requirements. In addition, Siemens had major concerns staking the valve seats into its cast iron exhaust gas recirculating (EGR) valve base in a new assembly line gearing up for full production.

The stainless steel would not flow as required during the critical staking operation. When press pressure was increased to facilitate the severe cold forming, either one of two pins supporting the ERG base would break after about every 100 parts produced. Each breakdown was costing time in press downtime, and in some instances the EGR bases virtually exploded from the pressure applied.

Technical assistance was sort from Carpenter Technology who supplied the 416 bar stock, and the metallurgist recommended that a change should be made to Carpenter stainless steel No 5-F.

Type 416 stainless steel had originally been specified because of its expected machinability, wear resistance, good behaviour under impact loading and corrosion resistance. Stainless No 5-F – a modification of Type 416 – is a ferritic stainless steel, with a specially balanced composition, that is designed for optimum machinability with corrosion resistance. It is essentially non-hardenable, normally furnished in the annealed and cold finished condition at a hardness of approximately 200 Brinell. After production trials the print specifications were changed to the alternative alloy.

In the current production sequence, the valve seats are produced at the rate of 750,000 per year. The valve seats are a nominally 1/2in long by 1/2in diameter, with a tapered inside diameter which, at the narrow bottom, provides seating for the valve head.

The change in material has resulted in improved surface finish in the lower seal area from 60 micro finish with the Type 416, to 30 micro finish with the No 5-F, resulting in a tighter seal between the base of the valve seat and the face of the valve head.

Since the switch to a more suitable alloy the assembly line, now in full production, has been staking up to 10,000 parts daily, at the rate of one every 5s.

Carpenter Technology Tel: +1 610 208 2576