Case Study

Statistical Process Control of temperature Uniformity for Batch Furnaces (PDF 533kb)

Hayes Heat Treating utilizes SPC to analyze the data created during a temperature uniformity survey. Hayes Heat Treating, who is accredited by NADCAP (National Aerospace and Defense Contractors Accreditation Program) for heat treating, follows the requirements of AMS 2750 when performing temperature uniformity testing. The requirements stated in AMS 2750, for performing temperature uniformity of batch atmosphere and vacuum furnaces, gives you the guidelines needed to set up a SPC capability study on a furnace. It states the frequency of testing, load configuration, required tolerance sample size and frequency of sampling. Instead of looking at a particular run of parts or series of runs, this technique looks more at capability of the furnace to perform a given function such as tempering or hardening. It offers the consistency and repetitiveness that is needed to develop useful statistical data that may be lacking in production batch runs.

Through-Carburized Tacks (PDF 275kb)

About two years ago, Hayes Heat Treating (HHT) was given an opportunity to work on a project with one of furnace builder C.I. Hayes' customers. The East Providence, R.I., manufacturer makes very small metal tacks that are used to attach signs and labels to machines (Fig. 1). Tacks are driven into steel plate as hard as 100 HRB using special pneumatic hammers.

Tacks were turned from wire coil of AISI 41L40, a leaded low-alloy steel, and heat treated in a shakertype furnace with muffle (a C.I. Hayes Model CST). Parts were run in nitrogen atmosphere and oil quenched, and then oven-tempered in air. The CST furnace gave very good results with minimal lot variation in hardness. Properly hardened and tempered 41L40 tacks have the hardness and toughness required for this high-impact application.