THIS paper describes production methods of pistons characterized by an elliptical skirt having a slot or slots that affect the form of the piston under operating conditions, as practiced at the Plymouth Motor Corp. Design changes that have affected production technique and changes in production practice itself are important recent developments in aluminum-alloy pistons.
Foundry data include a description of the small open-hearth furnaces and the permanent molds with collapsing cores employed. Other foundry operations - heat-treating, sprue cropping, hardness testing, and rough machining - are dealt with fully. In this foundry an output of 18,000 pistons per 24-hr. day can be maintained in an area of 1,200 sq. ft.
This type of piston fits the cylinder bore with about a 0.001-in. clearance in a cold motor, the expansion at operating temperatures being compensated for in the slotted skirt. This skirt is in the form of an ellipse whose minor axis is 0.011 in. less than its major axis. The skirt also is tapered, as indicated in the paper along with other design details.
Included in the description of the fourteen machining operations are equipment specifications, feeds, speeds, tooling, and production rates. Operation No. 13 is anodizing in which the piston increases its growth uniformly about 0.0003 in. as it is carried by conveyor through an electrolytic bath of sulphuric-acid solution.