Method of chromizing large size articles

A method particularly suited for applying a chromium coating to one or more of the surfaces of large size articles comprising the steps of:

• a. providing a stationary foundation and a plurality of supports positioned in spaced relation one to another on the stationary foundation;
• b. mounting on the plurality of supports positioned on the stationary foundation a retort having a removable cover and sufficient internal size to accommodate therewithin a layer of large size articles;
• c. spreading evenly over the bottom of the retort a one-half inch thick layer of a powder containing as a source of chromium 3% ammonium chloride and 42% ferrochromium, the balance consisting of alumina;
• d. positioning on the layer of powder in the retort a layer of large size articles to which a chromium coating is to be applied to one or more surfaces thereof;
• e. covering the large size articles positioned in the retort in accordance with step d. with an additional four inch thick layer of the chromium source powder;
• f. placing the cover on the retort;
• g. sealing the cover in place;
• h. positioning in surrounding relation to the retort a furnace embodying electrical heating elements capable of providing a uniform amount of heat over a given area;
• i. sealing off the furnace and thereby also the retort from the environment surrounding the furnace;
• j. heating the retort and the large size articles emplaced in the retort to a uniform temperature of 2100.degree. F.;
• k. supplying concurrent with the commencement of the heating in accordance with step j. an inert gas to the interior of the retort;
• l. conveying out of the retort by means of the inert gas flowing through the retort the fumes generated in the retort as the retort and the large size articles emplaced within the retort are each being uniformly heated;
• m. discharging from the retort the inert gas and the fumes;
• n. igniting the fumes conveyed out of the retort;
• o. supplying concurrent with the commencement of the heating in accordance with step j. an inert gas within the furnace in surrounding relation to the retort;
• p. conveying and discharging the fumes generated within the furnace during heating out of the furnace by means of the inert gas flowing within the furnace in surrounding relation to the retort;
• q. igniting the fumes discharged from the furnace;
• r. continuing heating the retort at 2100.degree. F. for 10 hours;
• s. shutting off both the flow of the inert gas to the retort and the flow of inert gas to the furnace upon terminating the heating;
• t. cooling the retort and the large size articles emplaced within the retort uniformly throughout to a temperature of 400.degree. F.;
• u. removing the furnace from its surrounding relation to the retort upon completion of the cooling in step t.;
• v. removing the cover from the retort;
• and
• w. removing the coated large size articles therefrom.