Spray cooling of steel dies in a hot forging process

by Endres, Matthew J.

Spray cooling has been important to control die temperature in forging processes for years. One area that has had little research is how thermal stresses in a metal are related to flow characteristics of the spray. Wyman-Gordon Corporation at its North Grafton MA facility uses spray cooling to cool their die after a forging process. It is believed that the current system used causes cracking along the surface of the impression in the die. The purpose of this work is to compare the nozzle system used by Wyman-Gordon to selected commercially available spray nozzles, and determine if there is a better spray cooling system than the one currently used. First, the Sauter mean diameter, particle velocity, and volumetric spray flux were experimentally found using a laser PDA system for four water driven nozzles, including the Wyman-Gordon nozzle, and one air-atomizing nozzle. The water atomizing nozzles were tested using pressures from 30 psi to 150 psi. For the air-atomizing nozzle, the water pressure was set at 60 psi and the air pressure was varied from 30 to 150 psi. Three nozzles were chosen: the Wyman-Gordon nozzle, a smaller orifice water atomizing nozzle, an airatomizing nozzle, and an air stream, to conduct an heat conduction experiment. Using the temperature gradients created by the cooling effects of each nozzle, the heat flux and induced thermal stresses were determined. The results showed the Wyman-Gordon nozzle was causing higher thermal stresses than the air/water and water nozzles. However, the airatomizing nozzle and air stream, due to the high temperatures that the dies are subjected to, did not cool the die quick enough to be practical. The smaller orifice water atomizing nozzle proved to be the nozzle that would cool the surface of the dies within a practical time, and induce allowable thermal stresses, sufficiently enough below the yield strength of the die material. These results, although collected specifically to study the cooling of dies at Wyman-Gordon, could be generalized to include the cooling of any test piece with a high surface temperature. ii Spray Cooling of Steel Dies in a Hot Forging Process by Matthew Jason Endres A Thesis Submitted to the Faculty of the