Process for reducing backmixing

Claim 1

In a process for preventing the backmixing of gases into a metal heat treating furnace having two ends, one or both of said ends having openings; each of said openings being defined by its dimensions of width and height and having a gas jet positioned in said opening in such a manner that at least part of the gases is prevented from backmixing into the furnace, the improvement comprising preventing substantially all of said gases from backmixing into the furnace by carrying out the following steps: (a) constructing the gas jet by providing a row of uniformly distributed holes in the wall of a straight tube, said row of holes being about parallel to the hypothetical axis running through the center of the tube from one end of the tube to the other end, the ratio of the distance between any two adjacent holes to the height of the opening being no greater than about 1:6; (b) positioning the gas jet at about the top, and across the width of each opening, the holes being pointed into the furnace in such a direction that a hypothetical line drawn through the center of each hole from, and perpendicular to, the axis of the gas jet would be at an angle in the range of about 0 degree to about 110 degrees as measured from a hypothetical line corresponding to the height dimension of the opening; and (c) inserting a plate above the gas jet at about the top, and across the width, of at least one opening at about a ninety degree angle to the hypothetical line corresponding to the height dimension of the opening, said plate extending into the furnace a distance at least about equal to the height of the opening; and (d) introducing a gas through each gas jet at a flow rate through said gas jet, which is (i) about equal to or greater than the value determined by the following formula when the furnace has one opening and (ii) about equal to the value determined by the following formula when the furnace has two openings: ##EQU4## wherein: A=density of ambient air B=density of furnace gases at the opening for said gas jet C=density of jet gas g=acceleration of gravity D=total area of holes in said gas jet E=width of said opening F=height of said opening G=about 1 to about 5 H=the pressure in number of atmospheres inside the gas jet J=the temperature in degrees Kelvin inside the gas jet.