US2057892A - Heat treatment of alloy glass machine castings - Google Patents

Description

HEAT TREATMENT OF ALLOY GLASS MACHINE CASTINGS No Drawing. Application July 31, 1933, Serial No. 682,954

2 (Claims. (Cl. 148-215) This invention relates to the manufacture of an improved chromium alloy especially adapted for use in the formation of metallic appliances employed in glass working machines for moulding glass into useful articles, and a principal obiect of the invention resides in the manufacture of metallic parts, used in the glass industry for pressed were, by employing a novel alloy composition and subjecting it to an improved heat treatment, which are conjointly necessary to increase the life or usefulness of any machine part subjected to the severe corrosive and erosive action encountered in the operation of high speed automatic glass article forming machines.

Although it is to be understood that a large number of different parts used on glass making machinery can be made from the alloy formed as a result of the present invention, the following description is confined to plungers for use in the manufacture of pressed glass ware. Heretofore these plungers have been made of cast iron or certain alloy compositions whose efiective period of usefulness or,life under the severe service involved in automatic glass pressing operations varies from one to six hours, whereas plungers made in accordance with the present invention have been maintained in corresponding service in excess of one hundred and twenty-five hours, including sustained use over twenty-four hour periods ,without removal for polishing and with no appreciable wear from the rubbing action of an associated stripping ring, which action rapidly wears and scores a cast iron plunger, rendering it unfit for use in producing the necessary quality of commercial pressed glass ware.

Our prior application, Serial No. 667,632, of which this application is a continuation-in-part, describes our improved alloy and a glass machine plunger made therefrom, while the present invention is more particularly directed to the method of forming and casting articles possessing the improved alloy composition, which we have found to be particularly suitable in the manufacture of glass machine plungers as aforesaid.

A preferred specific composition of our improved alloy is carbon 0.90%, molybdenum 1.00%, nickel 3.50%, silicon 1.00%, chromium 12.00%, titanium 0.50%, the balance being iron except for incidentals, subject to manufacture.

A second typical analysis of our improved formula is as follows: Carbon 0.82%, chromium 11.65%, nickel 3.43%, molybdenum 1.12%, silicon 1.21%, titanium 0.43%, the balance being iron except for incidental impurities.

While we appreciate the fact that our improved metal chromium alloy can be made many of the approved furnaces of today, such as crucible, open hearth, converter, direct or indirect arc and all forms of induction furnaces, yet we prefer electric melting furnaces due to the fact that the alloy requires close temperature control and considerable refinement. It is essential that the alloy be free from all large slag or nonmetallic inclusions, which, if appearing on the surface, would render the casting unfit for use, During casting, large risers are employed in order to compensate for the excessive shrinkage encountered in the casting of this alloy and it has been found to be good practice to cover the top of the riserwith some form of carbonaceous pipe eliminator.

The structure of the alloy in the cast condition is austenitic, showing a Brinell hardness of about 250, and is machinable. When in this condition, the plungers are rough turned to approximate dimensions, allowing only a grind finish on the surfaces exposed to the molten glass, while the other parts or surfaces are finished to size. The

casting is then subjected to anaccelerated age hardening heat treatment, which is accom= plished by heating to 1750 F. and holding the plungers from 1 to 4 hours at this temperature, followed by cooling slowly in the furnace. This heat treatment increases the Brinell hardness to the order of 500 to 550, which hardness is essential for long service under the severe conditions to which these plungers are subjected. The heat treatment also acts as a homogenizing agent which prevents any measurable changes in dimensions which may accrue from the repeated heating and cooling cycles through which the plungers pass in their operation. The alloy is -not susceptible to oxidation at glass molding temperatures, and therefore, alleviating the necessity, as, in cast iron plungers, of repeated removals for repolishing. The addition of .10% to 6.00% titanium has been ,found not only to increase the ease of machinability, but also to prevent excessive shrinkage and cooling cracks, but without detrimentally affecting the usefulness of the alloy under service conditions.

Cast iron plungers in general use today give the resulting glassware a frosty appearance due to the heterogeneity of the material used. Cast iron is a mixture ,of metallic crystals, interspersed with soft particles of graphite, and these softer particleswill wear or tear out first, leaving the surface in a roughenedcondition and which is imprinted uponthe resulting glassware giving it an undesired appearance. Hand or machine blown glassware is made without the use of plungers and is bright in appearance. This is a much more expensive operation and blown glassware commands a higher price on the market. Bythe use of the alloy made in accordance with the present invention, glassware can be made by the pressed or pressed blown process, that is, clear, has no frosty appearance and is comparable with hand blown ware.

Our improved alloy made in accordance with the above mentioned steps, is austenitic and machinable in the cast condition and martensitic and substantially non-machinable in its final heat treated condition. It is highly resistant to oxidation under temperatures employed in the working of molten glass. Similarly, it has a high resistance to abrasion, and shows no measurable growth after being subjected to the homogenizing treatment. While we have described the alloy as particularly suitable for the manufacture of glass machine plungers, nevertheless we do not limit ourselves to the use of the alloy in this connection, since it may be employed in the manufacture of molds, or other machine parts --ducing an alloy casting having substantially the following composition: carbon .80% to 1.0%, chromium 11.50% to 12.00%, nickel 3.40% to 3.75%, molybdenum .90% to 1.25%, silicon .90% to 1.35%, titanium .40% to the balance being substantially iron, said casting having a Brinell hardness of the order of 250 and being in austenitic condition as cast, machining the said casting to desired shape, then subjecting the casting to an annealing heat cycle in which the casting is maintained at temperatures of the order of 1700 to 1750 F. for a period of time varying between 1 to 4 hours, and then slowly cooling the casting while it is retained in the furnace zone whereby to increase the Brinell hardness thereof to the order of 500 to 550 and to homogenize the same against subsequen heating cycles.

2. The method of producing a cast metallic body for use in the manufacture of pressed articles of glassware, which comprises casting said body from a composition composed of substantially the following ingredients in the proportions set forth: carbon 0.80% to 1.0%, chromium 11.50% to 12.0%, nickel 3.40% to 3.75%, molybdenum .90% to 1.25%, silicon .90% to 1.35%, titanium .40% to .55%, the balance being iron except for incidental impurities, subjecting such a body which is as cast of machinable form in austenitic condition and having a Brinell hardness of 250 to a machining operation to reduce it substantially to a desired form, then subjecting said body to an additional heating cycle in a furnace zone wherein said body is heated to a temperature of the order of 1700 to 1750 F. for a period of time ranging from 1 to 4 hours, then slowly cooling said body while it is retained in the furnace zone, the final heat treated body possessing a martensitic non-machinable structure and having a Brinell hardness of 500 to 550 and being homogenized against subsequent heating cycles.

7 ALFRED W. GREGG.

RAYMOND H. FRANK.