Patent Application
20060213632
The present invention relates to a glass-forming metallic die and method providing improved cooling of the glass-forming surface of the die.
Current glass bottle molding processes consist of three main steps. First, a small portion of glass, called a ‘gob’, drops in a pre-measured amount from a liquid glass holding tank above a high speed glass bottle forming machine. This gob falls into a die called a ‘blank’ mold, which is typically made of cast iron. The blank mold includes a cavity to receive the glass gob and configured to form an intermediate bottle shape known as a parison. The parison is then removed from the blank mold and moved to a final or finish die having a cavity with the final bottle shape and markings to be imparted to the bottle. In the final or finish die, the parison is blown using compressed air into the final bottle shape. The final or finish die is typically made of an alloy such as nickel-bronze.
The entire bottle molding process from the parison stage to the final bottle stage takes approximately 8-10 seconds. Of this time, each molding process takes approximately 4 seconds and the balance is transfer time between the initial die (i.e. blank mold) and final or finish die. Removal of heat from the surface of the glass gob in the blank die is critical. If too much heat is removed, the parison will not be plastic enough to be formed to final shape in the final or finish die, resulting in formation of a defective bottle. If too little heat is removed, the parison may be too plastic during transfer to the final or finish die. For example, the temperature of the parison typically is maintained within a range of about 25-40 degrees F. of a nominal parison temperature value in some bottle making processes.
The current state-of-the-art cast iron blank molds for glass making are cast into shape or machined from preforms into the required desired die shape. The blank mold is provided with a plurality of straight cooling air passages which are gun drilled into the mold body along its length from one end to the other. During operation of the bottle forming machine, the cooling air holes of the blank mold receive cooling air which is blown onto the blank mold.
The gun drill process only allows for straight cooling air passages. Consequently, the distance from the cooling holes or passages to the blank mold cavity surface (and therefore the molten glass) varies considerably along the length of the blank mold and the ability to change that distance is extremely limited. Cooling adjustments of the blank mold are made as needed by plugging certain cooling holes or passages, or machining sections of the blank mold.
Another integral part of the glass bottle manufacturing process is the application of a carbonaceous lubricant to the dies in intervals of approximately 20 minutes. The application of the lubricant is a manual process which requires the operator to be in close proximity to moving components of the glass bottle forming machine and molten glass and results in some scrap bottles as the excess lubricant ‘burns off’. Non-uniform cooling of the initial die (blank mold) can cause mold ‘hot spots’, which in turn allow the molten glass to stick to the blank mold cavity. Eventually (over approximately 3-4 months), the dies can no longer be successfully lubricated and are replaced. The reasons for this phenomenon is not completely understood but may be related to oxidation of secondary phases in the cast iron or thermal mechanical fatigue cracking. Both mechanisms lead to void or crack formation which can capture bits of molten glass.
There thus is a need for improved dies for use in the manufacture of glass bottles as described above as well as for a method of making such dies.
The present invention provides a glass-forming die having features for improving control of heat removal from the die to thereby provide a desired temperature profile, uniform or non-uniform, of glass material molded in the die body.
Pursuant to an embodiment of the invention, the glass-forming die comprises a die body having a molding surface with a curved contour to form at least a portion of a glass article to be made. The die body includes one or more cooling passages through which a cooling fluid passes inside the body to remove heat. In one embodiment, the cooling passage(s) is/are non-linear (non-straight) along at least a portion of its/their length in a manner to improve uniformity of heat removal from the die body when the cooling fluid passes therethrough. Alternately, the cooling passage(s) can be non-linear (non-straight) along at least a portion of its/their length in a manner to provide a desired temperature profile, uniform or non-uniform, at the molding surface. The die can comprise a blank mold (parison-forming die) and/or a finish die (bottle-forming die) for use in a bottle forming machine.
Pursuant to another embodiment of the invention, the glass-forming die comprises a die body having a molding surface with a curved contour to form at least a portion of a glass article to be made. The die body includes one or more heat radiating elements such as projections including, but not limited to, cooling fins, posts, pins, and/or ribs, extending from the exterior of the die body in a manner to improve removal of heat from that region. The die body preferably includes a substantially constant cast wall thickness such that the back (outer) side of the die body has the same contour as the molding surface in that region of the die body.
The glass-forming dies pursuant to certain embodiments of the invention are investment cast, or otherwise cast, using refractory molds having fugitive refractory cores therein when the dies include the cooling fluid passage(s) in the cast die pursuant to a particular method embodiment of the invention. The glass-forming dies pursuant to other embodiments of the invention are investment cast, or otherwise cast, using tubular insert members about which the die body is cast so that the tubular insert members become permanently incorporated in the die body and form cooling passages therein through cooling fluid can flow. The glass-forming dies pursuant to still other embodiments of the invention are made by consolidating metallic powder material about cores or tubular insert members.
The dies preferably comprise metal alloys having resistance to degradation in air and to molten glass at the elevated temperatures employed in the glass forming operation. The dies can be cast or otherwise formed in a manner to provide a die microstructure having a coarse grain size or a fine grain size, which can be a beneficial very small and/or cellular grain size of ASTM 2 or less.
Glass-forming dies pursuant to the invention are advantageous to improve uniformity of heat removal from the die body and thereby maintain a more uniform temperature of glass material molded in the die body, such as a parison used in manufacture of a glass bottle wherein, for example, parison temperature must be maintained within a range of 25 to 40 degree F. of a nominal parison temperature value. Alternately, glass-forming dies pursuant to the invention are advantageous to provide a controlled temperature profile, uniform or non-uniform, of glass material (for example, a parison) molded in the die body. Moreover, the invention can be practiced to improve die life via selection of materials which are resistant to degradation, such as oxidation and thermal fatigue, and which require less lubrication over time. A benefit of the invention may be the ability to run glass-forming machines at higher speed, thus allowing more production volume without increasing capital investment.
Other advantages, features, and embodiments of the present invention will become apparent from the following description.
Referring to
The die bodies include respective mold cavity regions 10c, 12c that form a complete molding cavity having the three dimensional shape of the parison when the dies 10, 12 are closed or pressed together in the bottle making machine. The mold cavity regions are defined by respective molding surfaces 10s, 12s on the die bodies 10a, 12a. As is shown in
The mold cavity formed by the mold cavity regions 10c, 12c is open at the top when the dies 10, 12 are closed or pressed together. The dies bodies include partial top openings 10o, 12o to collectively form the top opening when the dies are closed. After the gob of molten glass has been introduced into the mold cavity, the top opening is closed by a so-called baffle (not shown) of the bottle making machine. The baffle of the bottle making machine closing the top opening forms no part of the invention.
The mold cavity formed by the mold cavity regions 10c, 12c also has an opening at the bottom. The dies bodies include partial bottom openings 10p, 12p to collectively form the bottom opening when the dies are closed. The bottom opening is closed by a ring and plunger assembly (not shown) of the bottle making machine. The plunger is movable into the mold cavity to force the glass gob introduced into the mold cavity to take the shape of the mold cavity in order to form the parison therein. The ring and plunger assembly of the bottle making machine closing the bottom opening forms no part of the invention.
Pursuant to an embodiment of the invention, each die 10, 12 comprises a plurality of cooling passages 20,
The non-linear (non-straight) portion of each cooling passage 20 preferably is curved in a manner to generally follow the curved contour of the respective molding surfaces 10s, 12s along at least a portion of their length, preferably along much of their length as illustrated in
In
The passages 20 can also be turbulated in that alternating large and small diameter passage sections are provided along the length of the cooling passages 20. The turbulator(s) cause(s) fluid turbulence in the cooling fluid passage to increase heat transfer between the fluid and the die to improve cooling. The turbulation can be in local regions of the passages 20 or along the entire length of the passages 20, as necessary. In addition, one or more ribs, ridges, fins, bumps, posts or other projecting heat absorbing elements extending from the die body into the cooling passages can be provided for improving heat transfer from the die body to the cooling fluid; see
In
Moreover, referring to
Each die body 10a, 12a described above and shown in
The pattern 45 having the core tubes or rods 50, 51 therein is invested in ceramic material pursuant to the well known lost wax investment process wherein the pattern is repeatedly dipped in ceramic slurry, drained of excess slurry, and then stuccoed with coarse ceramic stucco to build up a ceramic shell mold on the pattern. The pattern then is selectively removed from the shell mold by melting the pattern or using other pattern removal processes, leaving a ceramic shell mold having the ceramic cores 50, 51 in the mold cavity thereof. Then, the ceramic shell mold is fired to develop mold strength for casting.
To cast the die body 10 or 12, the shell mold is preheated to an appropriate casting temperature and molten metallic material is poured into the mold and solidified to form the die body 10 or 12. The shell mold is removed from the investment cast die body 10 by a conventional knock-out operation, and the ceramic core, tubes, or rods 50, 51 then are removed by chemical leaching in a caustic medium or otherwise, leaving the investment cast die body 10 or 12 having the cooling fluid passages 20, 21 where the core, tubes, or rods 50, 51 formerly resided.
The dies 10, 12 preferably are investment cast of metal alloys having resistance to degradation in air and to molten glass at the elevated temperatures employed in the glass forming operation. For example, the dies can comprise an iron base alloy having a nominal composition, in weight %, consisting essentially of 19.75% Co, 20.0% Ni, 0.20% C, 1.5% Mn, 1.0% Si, 21.25% Cr, 2.5% W, 3.0% Mo, 1.0% Nb and 0.15% N with the balance Fe. This alloy corresponds to Multimet iron base N155 alloy (N155 is a trademark) having a published composition of, in weight %, 0.08% to 0.16% C, 20% to 22.5% Cr, 18.5% to 21% Co, 1% to 2% Mn, 2.5% to 3.5% Mo, 19% to 21% Ni, Nb and Ta wherein Nb+Ta is 0.75% to 1.25%, 0.1% to 0.2% N, 2% to 3% W, and balance Fe.
Alternately, the dies 10, 12 can be made of heat and corrosion resistant nickel alloys such as a nickel base superalloy including, but not limited to, commercially available IN-718, IN-713LC, and MM-247, to this end. The dies 10, 12 alternately can be made of heat and corrosion resistant cobalt alloys such as a cobalt base superalloy including, but not limited to, commercially available cobalt superalloys to this end. The dies 10, 12 still further can alternately be made of heat and corrosion resistant refractory metals such as W, Nb, Mo, Ta, Zr, or Hf, or alloys thereof one with another or with other metal(s). Moreover, the dies 10, 12 alternately can be made of conventional cast iron, bronze, aluminum-bronze alloy, and aluminum-nickel bronze alloy.
The dies can be cast in conventional manner to provide a die microstructure having a coarse grain size or a fine grain size. Pursuant to one embodiment, the dies 10, 12 are cast by the lost wax investment casting process to provide a coarse or fine equiaxed grain microstructure, or by the so-called MX casting process described in U.S. Pat. No. 4,832,112 to produce a very fine (small) and/or cellular equiaxed grain microstructure, such as an ASTM 2 or less grain size in the die bodies 10a, 12a, as described in the patent, which is incorporated herein by reference. The dies can be cast by any suitable casting process including, but not limited to, countergravity casting, permanent mold casting, plaster mold casting, die casting, sand casting, and others. The molding surfaces 10s, 12s as well as other surfaces/features of the die body optionally can be machined and/or coated after casting of the die body.
Pursuant to another illustrative embodiment of the invention, the glass-forming die 10, 12 can be made by forming a fugitive pattern having a shape of the die to be made as shown in
The tubular metallic insert members 50′, 51′ are disposed in the pattern 45. Some tubular metallic members 50′ are non-linear along at least a portion of their length, while other tubular metallic insert members 51′ are straight or linear as described for the cores 50, 51 of
The pattern 45 with the tubular metallic insert members 50′, 51′ therein is invested in a refractory material to form a refractory mold on the pattern as described above. The pattern is removed as described above, leaving the tubular members 50′, 51′ in the mold cavity of the refractory mold. Molten metallic material then is introduced in the mold cavity of refractory mold about the tubular metallic insert members 50′, 51′ for solidification therein to form the die having the tubular metallic members 50′, 51′ permanently disposed therein to form cooling passages inside the tubular metallic insert members 50′, 51′ for receiving the cooling fluid. The die of this illustrative embodiment thus differs from the die 10 shown in
The tubes 50′, 51′ can be made of the same or different metallic material depending upon the temperature profile, uniform or non-uniform, desired for the parison. For example, in one embodiment, tubes 50′ and 51′ both can be made of copper or stainless steel. In another embodiment, tubes 50′ can be made of a metallic material different from that of tubes 51′. Alternately, each tubes 50′ and/or 51′ can be made of two or more different metallic materials having different thermal conductivities. For example, tube 50′ and/or 51′ can comprise a copper tube section and another tube section comprising stainless steel wherein the tube sections are joined together end-to-end by welding or other joining technique.
Pursuant to another illustrative embodiment of the invention, the glass-forming die 10, 12 can be made by powder metallurgy processes where metallic powder material is placed in a deformable metal container (not shown) having the shape of the die and having cores 50, 51 or tubular metallic insert members 50′,51′ disposed in the container. The container is sealed and cold and/or hot isotatically pressed in conventional manner to consolidate the metallic powder material about the cores 50, 51 or about the tubular metallic insert members 50′,51′. When cores are employed, the container and cores then are removed to leave the die having the cooling passages therein corresponding to locations where the cores formerly resided. Alternately, when the tubular metallic insert members are employed, the can then is removed, leaving the die with the tubular metallic insert members 50′, 51′ therein. The consolidated powder metal die body optionally can be heat treated as desired to develop desired mechanical properties.
Pursuant to another embodiment of the invention shown in
In particular, the back wall 100w of the die body 100 conforms to the same contour as the mold cavity region (not shown) on the opposite side of the die body (corresponding to mold cavity region 10c or 12c of
The projections, such as cooling fins 110a and/or ribs 110b, extending from an exterior region 110e of the die body 100a can be cast integrally with the die body, can be machined on the cast die body, and/or can be formed separately of the same or different material as the die body and then attached to the die body 100a.
The die body 100 of
It should be understood that the invention is not limited to the specific embodiments or constructions described above but that various changes may be made therein without departing from the spirit and scope of the invention as set forth in the appended claims.
This application claims benefits and priority of provisional application Ser. No. 60/660,919 filed Mar. 11, 2005.
| Number | Date | Country | |
|---|---|---|---|
| 60660919 | Mar 2005 | US |
