APPARATUS METHOD FOR LOCATING, CONTROLLING GEOMETRY, AND MANAGING STRESS OF HOT TOPS FOR METAL CASTING

Abstract

A method and apparatus used to achieve alignment during mold assembly and accommodate thermal expansion comprising employing a compressible region and a modified interface dimension.

Claims

1. A hot top mold assembly system, comprising: a hot top and a mold, said hot top including a dimension creating a locational clearance fit between the hot top and the mold, the hot top including a collar configured to mate with an end of the mold and a depending edge configured to interface with an internal wall of the mold, wherein the edge includes a deformable feature to improve alignment during assembly of the hot top with the mold and accommodate thermal expansion.

2. The hot top of claim 1 wherein the locational clearance fit of the hot top dimension at ambient temperature (S.sub.o) is expressed as: $M_O\le S_O\le \frac{I_O}{1+0.833\mathrm{\alpha \Delta }T}$ wherein M.sub.O is a mold dimension at ambient temperature; I.sub.O is a mold interface dimension at ambient temperature; α is a coefficient of thermal expansion of bulk hot top material; and ΔT is temperature change between ambient temperature and casting temperature.

3. (canceled)

4. The hot top of claim 1 wherein the deformable feature includes elements intended to fracture from the hot top or is a compressible component to allow for thermal expansion.

5. (canceled)

6. The hot top of claim 4 wherein the feature is an O-ring disposed in a gland, shoulder, or a groove.

7. The hot top of claim 4 wherein the compressible component comprises materials with either small bulk moduli or high elasticity.

8. The hot top of claim 4 wherein the compressible component is at least one of ceramic, rubber, and polymer.

9. The hot top of claim 4 wherein the compressible component deflects at a pressure below 65 kPa

10. The hot top of claim 4 wherein the compressible component deflects at a pressure below 50 kPa.

11. The hot top of claim 4 wherein the compressible component deflects at a pressure below 35 kPa.

12. A hot top for use in a hot top mold assembly system, the hot top comprising: a hot top configured to create a locational clearance fit between the hot top and a mold, the hot top including a annular wall configured to penetrate an opening of the mold assembly, a collar extending radially from an intersection with the annular wall, the collar configured to engage an end surface of the opening of the mold, wherein the annular wall further comprises a feature to restrain or locate a compressible component of the hot top.

13. The hot top of claim 12 wherein the locational clearance fit of the hot top dimension at ambient temperature (S.sub.o) is expressed as: $M_O\le S_O\le \frac{I_O}{1+0.833\alpha \Delta T}$ wherein M.sub.O is a mold dimension at ambient temperature; I.sub.O is a mold interface dimension at ambient temperature; α is a coefficient of thermal expansion of bulk hot top material; and ΔT is temperature change between ambient temperature and casting temperature.

14. The hot op of claim 12 wherein the feature is a gland, shoulder, or a groove.

15. The hot top of claims 12 wherein the compressible component comprises materials with either small bulk moduli or high elasticity.

16. The hot top of claim 12 wherein the compressible component is at least one of ceramic, rubber, and polymer.

17. The hot top of claim 12 wherein the compressible component deflects at a pressure below 65 kPa.

18. The hot top of claim 12 wherein the compressible component deflects at a pressure below 50 kPa.

19. The hot top of claim 12 wherein the compressible component deflects at a pressure below 35 kPa.

20. The hot top of claim 12 wherein the compressible component provides centering of the hot top and accommodates thermal expansion.

21. The hot top of claim 12 wherein the compressible component includes elements intended to fracture from the hot top to allow for thermal expansion.

22. A method to reduce thermal stress of a hot top comprising providing a locational clearance fit between the hot top and a mold, wherein the locational clearance fit of the hot top dimension at ambient temperature (So) is expressed as: M.sub.O≤S.sub.O≤I.sub.O/1+0.833αΔT wherein M.sub.O is a mold dimension at ambient temperature; I.sub.O is a mold interface dimension at ambient temperature; α is a coefficient of thermal expansion of bulk hot top material; and ΔT is temperature change between ambient temperature and casting temperature.

23. (canceled)

24. (canceled)

25. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The following is a brief description of the drawings, which are presented for the purposes of illustrating the exemplary embodiments disclosed herein and not for the purposes of limiting the same.

[0022] FIG. 1 shows a steady state third principal stress [MPa] stress plot of an improved method VDC hot top showing low stress magnitudes and downward distortion of the component.

[0023] FIG. 2 shows a side view of a prior art hot top mold assembly device.

[0024] FIG. 3 shows a side view of a hot top mold assembly device.

[0025] FIG. 4 shows a side view of a hot top mold assembly device.

DETAILED DESCRIPTION

[0026] A more complete understanding of the components, processes and apparatuses disclosed herein can be obtained by reference to the accompanying drawing. The figure is merely a schematic representation based on convenience and the ease of demonstrating the present disclosure, and is, therefore, not intended to indicate relative size and dimensions of the devices or components thereof and/or to define or limit the scope of the exemplary embodiments.

[0027] Although specific terms are used in the following description for the sake of clarity, these terms are intended to refer only to the particular structure of the embodiments selected for illustration in the drawings, and are not intended to define or limit the scope of the disclosure.

[0028] The singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise.

[0029] As used herein, the terms about, generally and substantially are intended to encompass structural or numerical modifications which do not significantly affect the purpose of the element or number modified by such term.

[0030] As used in the specification and in the claims, the term “comprising” may include the embodiments “consisting of” and “consisting essentially of.” The terms “comprise(s),” “include(s),” “having,” “has,” “can,” “contain(s),” and variants thereof, as used herein, are intended to be open-ended transitional phrases, terms, or words that require the presence of the named ingredients/steps and permit the presence of other ingredients/steps. However, such description should be construed as also describing compositions or processes as “consisting of” and “consisting essentially of” the enumerated ingredients/steps, which allows the presence of only the named ingredients/steps, along with any impurities that might result therefrom, and excludes other ingredients/steps.

[0031] Disclosed herein is a method to achieve alignment during mold assembly and accommodate thermal expansion employing a compressible or deformable region and a modified interface dimension. Upon installation, some of the compressibility or deformability range of the compressible or deformable region is consumed by a locational interference fit. The small magnitude of pressure induced on the hot top is negligible due to the high compressibility or deformability of the material deployed. During casting, the compressibility or deformability range is further consumed as the hot top and other components of influence expand. However, by design, the range is not fully consumed and consequently, only minor pressures on the hot top are realized. This method eliminates interference of the hot top and mold assembly or mold during casting and results in significant reduction of thermal stress that develops. In addition, by eliminating the interference, the positive z direction of distortion is eliminated and slightly reversed to increase the joint allowance between the hot top and the nozzle that accommodates expansion of the nozzle and closely maintaining the overhang of the nozzle to reduce the risk of lapping defects on the casting.

[0032] FIG. 1 shows a steady state third principal stress [MPa] stress plot of an improved method VDC hot top showing low stress magnitudes and downward distortion of the component, a result of the use of an embodiment of the current invention.

[0033] In one embodiment of the invention, the apparatus utilizes an assembly comprised of a modified hot top dimension and a deformable feature that is a compressible component fitted to the hot top or includes elements intended to fracture from the hot top to allow for thermal expansion. The hot top dimension is altered to create a significant locational clearance fit between the hot top and the mold or mold assembly.

[0034] In another embodiment, the apparatus contains a deformable feature and a modified hot top dimension to create a significant locational clearance fit between the hot top and the mold or mold assembly.

[0035] In another embodiment, a hot top dimension at ambient temperature to eliminate thermal stress during casting at casting temperature (S.sub.O) is expressed as:

[00001]$M_O\le S_O\le \frac{I_O}{1+0.833\mathrm{\alpha \Delta }T}$ [0036] where M.sub.O is the mold dimension at ambient temperature, I.sub.O is the mold interface dimension at ambient temperature, a is a coefficient of thermal expansion of bulk hot top material, and ΔT is temperature change between ambient temperature and casting temperature. [0037] where β is the mold interface dimension, a is the coefficient of thermal expansion of the bulk hot top material, and ΔmT is temperature change between ambient and casting temperature.

[0038] Further modifications may include a feature (e.g. gland, groove) to restrain and locate the compressible component of the assembly. The compressible component is made from materials with either small bulk moduli or high elasticity including, but not limited to, ceramic, ceramic paper, ceramic braided rope, rubber, or polymer. To prevent development of undesirable localized pressure, or contact stress, the compressible component must deflect under pressure below 65 kPa.

[0039] FIG. 2 shows a side view of a typical hot top assembly device 100 which shows a hot top 101 and mold 102 configuration as utilized in the prior art in a VDC system. As can be seen, the hot top 101 diameter is not reduced and there is no feature to restrain and locate a compressible component nor a deformable feature to accommodate thermal expansion at elevated temperatures.

[0040] FIG. 3 shows a side view of an embodiment of the current invention wherein the hot top assembly device 200 includes an improved hot top 201 that includes a reduced hot top diameter at the interface of interest with the mold 202 and a gland feature 203 as a part of the hot top 201 wherein the gland feature 203 includes a compressible O-Ring 204. In one embodiment, the hot top 201 comprises a feature to restrain and locate a compressible component of the hot top 201. As shown in FIG. 3, the feature is a gland feature 203, however, a groove feature, or similar feature would also be acceptable. The compressible component can comprise any of a number of appropriate materials with small bulk moduli or high elasticity such as ceramic paper, ceramic braided rope, rubber, and polymer. As shown in FIG. 3, the compressible feature is an O-Ring 204 that can be made of any appropriate material.

[0041] FIG. 4 shows a side view of an embodiment of the current invention wherein the hot top assembly device 300 includes an improved hot top 301 that includes a reduced hot top diameter at the interface of interest with the mold 302 and a deformable feature 303 of the improved hot top 301 body that deforms when the improved hot top 301 expands or is displaced at elevated temperatures experienced during casting. The deformable feature 303 is compressible or includes elements intended to fracture from the hot top 301 body to allow for thermal expansion.

[0042] In one embodiment, to prevent development of undesirable localized pressure, or contact stress, the compressible component deflects under pressure below 65 kPa. In another embodiment, the compressible component deflects pressure below 50 kPa. In yet another embodiment, the compressible component deflects pressure below 35 kPa.

[0043] The current invention will drastically improve hot top performance by simplifying the installation process and increasing confidence in proper hot top location. Further, it reduces or eliminates thermal stress to extend service life and reduce the risk of catastrophic failure. Lastly, it increases the likelihood of quality casting by preventing unwanted distortion in large format hot top geometries.

[0044] The exemplary embodiments described and claimed herein is not to be limited in scope by the specific embodiments herein disclosed since these embodiments are intended as illustrations. Any equivalent embodiments are intended to be within the scope of this application. Indeed, various modifications in addition to those shown and described herein will become apparent to those skilled in the art from the foregoing description. Such modifications are also intended to fall within the scope of the appended claims. All publications cited herein are incorporated by reference in their entirety.

[0045] To aid the Patent Office and any readers of this application and any resulting patent in interpreting the claims appended hereto, applicants do not intend any of the appended claims or claim elements to invoke 35 U.S.C. 112(f) unless the words “means for” or “step for” are explicitly used in the particular claim.