GB2153274A

GB2153274A - Process and apparatus for lost foam casting with bonded sand core

Info

Publication number: GB2153274A
Application number: GB08500520A
Authority: GB
Inventors: Rens Russell J Van
Original assignee: Outboard Marine Corp
Current assignee: Outboard Marine Corp
Priority date: 1984-01-30
Filing date: 1985-01-09
Publication date: 1985-08-21
Also published as: FR2558749A1; CA1222862A; JPS60180644A; GB8500520D0; DE3502167A1; IT8547592A0

Abstract

In order to prepare for casting a foam mold pattern 10 having a portion 14 into which loose sand will not readily flow when sand is compacted around the foam mold pattern 10, a bonded sand core 16 is attached e.g. by gluing, to the foam mold pattern 10 so that the bonded sand core 16 will occupy only the portion 14 of the foam mold pattern 10 into which sand will not readily flow. The core 16 may include means e.g. a lug 20, for securing it into the sand compacted around the pattern. <IMAGE>

Description

SPECIFICATION Process and apparatus for lost foam casting with bonded sand core BACKGROUND OF THE INVENTION The invention relates to a lost foam casting process, and more particularly to a process and apparatus for providing a sand core in foam molding pattern portions that cannot be completely filled with loose sand.

In a lost foam casting process, the mold pattern which forms the desired molding cavity in the sand is a foam mold pattern that vaporizes when contacted by molten metal, thus the pattern need not be removed from the sand before casting. Since the foam mold pattern is not removed from the sand before casting, the mold flask need not be separable into two parts, the cope and the drag, and the mold pattern can have a more complicated configuration than with conventional cope and drag flasks.

A lost foam casting process includes the steps of placing the foam mold pattern in the mold flask, compacting sand around the mold pattern, and pouring molten metal into the foam mold pattern. The molten metal causes the foam mold pattern to vaporize, and when the metal cools, the casting is removed from the sand.

Sand is typically compacted around the mold pattern by depositing loose sand into the mold flask to surround the mold pattern, and then by causing vibration of the loose sand to compact it.

Because complicated mold pattern configurations are possible with lost foam casting, it is sometimes difficult to cause loose sand to flow into and to become compacted in portions of the foam mold pattern. For instance, vibrating sand does not readily flow uphill, so it is difficult to cause sand to flow into a portion that extends above the surrounding area, such as a concavity in the upper surface of a passage.

If sand cannot be completely compacted into all portions of the foam mold pattern, the casting formed by the pattern will not have the desired shape.

Prior methods for compacting sand into a portion of a passage into which sand will not readily flow include filling the entire passage with a bonded sand core. Sand can be bonded together by a resin or adhesive.

A prior use of bonded sand cores with foam mold patterns is the use of foam mold patterns to support large sand cores within bonded sand molds. Prior methods for providing a bonded sand core in a foam mold pattern passage include "foaming" patterns around sand cores, and curing air-set cores in the passages of foam patterns. These methods generally result in a relatively large sand core.

A disadvantage of large sand cores is that they generate large amounts of gas when contacted by molten metal, thereby causing porosity of the casting. Another disadvantage of large sand cores is that they release resin and/or adhesive into the surrounding sand, thereby reducing the useful life of the sand, since these contaminants reduce the ability of the sand to flow.

Attention is directed to the following U.S. patents which relate to the field of the invention.

Patentee Patent No. Issued Hayashi 4,077,458 March 7, 1978 4,281,705 4,276,922 309,811 51,366 SUMMARY OF THE INVENTION The invention provides a process for preparing for casting a foam mold pattern including a portion into which loose sand will not readily qpw when sand is compacted around the mold pattern. The process comprises the step of attaching a bonded sand core to the foam mold pattern so that the borided sand core will occupy only the portion of the foam mold pattern into which sand will not readily flow.

In one embodiment, the attaching step is provided by gluing the bonded sand core to the foam mold pattern.

The invention also provides a process for preparing for casting a foam mold pattern including a portion into which loose sand will not readily flow when sand is compacted around the mold pattern, the process comprising the steps of attaching a bonded sand core to the foam mold pattern so that the bonded sand core will occupy only the portion of the foam mold pattern into which sand will not readily flow, positioning the foam mold pattern in a mold flask, surrounding the foam mold pattern with sand, and compacting the sand around the foam mold pattern and the bonded sand core.

In one embodiment, the bonded sand core includes means attached thereto for securing the bonded sand core to the sand which is compacted around the foam mold pattern and the bonded sand core, and the process further includes the step of compacting the sand around the securing means.

The invention also provides a pattern assembly for use in casting molten metal in sand. the assembly comprising a foam mold pattern including a portion into which loose sand will not readily flow when sand is compacted around the mold pattern, and a bonded sand core attached to the foam mold pattern so that the bonded sand core will occupy only the portion of the foam mold pattern into which sand will not readily flow.

In one embodiment, the bonded sand core is glued to the foam mold pattern.

In one embodiment, the bonded sand core includes means attached thereto for securing the bonded sand core to the sand which is compacted around the foam mold pattern and the bonded sand core.

In one embodiment, the means for securing the bonded sand core include a lug integrally attached to the bonded sand core and adapted to extend into the sand compacted around the core.

A principal feature of the invention is that it minimizes the size of a bonded sand core used with a foam mold pattern. This minimizes the amount of gas generated by the bonded sand core when it contacts hot metal, thereby reducing the porosity of the casting.

Another principal feature of the invention is that in minimizing the size of the bonded sand core, it reduces the amount of resin and/or adhesive released into the surrounding sand, thereby prolonging the useful life of the sand.

Another principal feature of the invention is that in minimizing the size of the bonded sand core, it reduces the amount of time and material necessary for preparing the bonded sand core, thereby saving time and money.

Another principal feature of the invention is that it provides for the bonded sand core to be glued to a foam mold pattern.

Another principal feature of the invention is that it provides a means for preventing the bonded sand core from moving once the foam mold pattern around it has vaporized.

Other features and advantage of the invention will become apparent to those skilled in the art upon review of the following detailed description, claims, and drawings.

DESCRIPTION OF THE DRAWINGS Figure 1 is a cross-sectional view of a foam mold pattern positioned in a mold flask and surrounded by sand, the foam mold pattern including a portion into which sand will not readily flow.

Figure 2 is a top view of the mold pattern of Fig. 1.

Figure 3 is a cross-sectional view of the foam mold pattern having attached thereto a bonded sand core, the bonded sand core being attached to the portion into which sand will not readily flow and including an integrally attached lug.

Figure 4 is an enlarged view of the bonded sand core of Fig. 3 Figure 5 is a bottom view of the bonded sand core of Fig. 4.

Figure 6 is a cross-sectional view of the foam mold pattern and the attached bonded sand core surrounded by sand.

Before explaining one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangements of components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting.

DESCRIPTION OF THE PREFERRED EMBODIMENT Illustrated in Fig. 1 is a foam mold pattern 10 positioned in a mold flask 1 2 and surrounded by sand, the foam mold pattern 10 having a portion 14 into which vibrating sand will not readily flow. As best shown in Figs. 1 and 2, this portion 1 4 is a concavity in the upper surface of a passage in the foam mold pattern 10. Sand will flow horizontally into the passage to fill the majority of the passage, but because sand will not readily flow uphill, it will not flow into the concave portion 14 of the passage.

The invention provides a process for attaching a bonded sand core to a foam mold pattern to fill a portion of the foam mold pattern into which sand will not readily flow. illustrated in Fig. 3 is a bonded sand core 16 attached to the concave portion 14 of the foam mold pattern 10. In the preferred embodiment, the bonded sand core 1 6 is glued to the foam mold pattern 10, although the bonded sand core 16 could be attached to the foam mold pattern 10 by conventional means such as, for example, a press fit, dovetail lock, or locking taper.

By attaching the bonded sand core 1 6 to the foam mold pattern 10 only in the portion 14 into which sand will not flow, the size of the bonded sand core 1 6 is minimized. This is beneficial because bonded sand cores tend to give off gas when contacted by molten metal, and this gas causes porosity in the casting. Minimizing the size of the bonded sand core minimizes gas generation and the resultant porosity in the casting.

The bonded sand core 1 6 can be held together, for example, by a resin of adhesive. Methods for forming bonded sand cores are well known in the art, and will not be further described herein.

When the foam mold pattern 10 and the attached bonded sand core 16 are surrounded by compacted sand, and when molten metal is poured into the foam mold pattern 10, the foam mold pattern 10 vaporizes, and the sand and the bonded sand core 1 6 form the desired casting.

A problem with using a bonded sand core in a portion of a foam mold pattern is that the bonded sand core may tend to be dispiaced once the surrounding foam mold pattern vaporizes.

To deal with this problem, the invention provides means 1 8 attached to the bonded sand core 1 6 for securing the bonded sand core 1 6 to the sand which is compacted around the foam mold pattern 10 and the bonded sand core 16. While various suitable means 18 could be employed for this purpose, in the construction illustrated in Figs. 3 through 6, such means 1 8 comprises a lug 20 integrally attached to the bonded sand core 1 6 and adapted to extend into the sand compacted around the core 1 6.

In the illustrated construction, the lug 20 is an integral part of the bonded sand core 16, although the lug 20 could be a separate piece attached to the bonded sand core 16. As best shown in Figs. 4 and 5, the lug 20 extends outwardly from the bottom of the bonded sand core 1 6 and has undercuts so that the sand compacted around the lug 20 will secure it in place.

Referring now to the process of the invention, in the preferred embodiment, the process comprises attaching the bonded sand core 1 6 to the foam mold pattern 10 so that the bonded sand core 1 6 will occupy only the portion 1 4 of the foam mold pattern 10 into which sand will not readily flow. The bonded sand core 1 6 attached to the foam mold pattern 10 is illustrated in Fig. 3.

In the preferred embodiment, the process also comprises the steps of positioning the foam mold pattern 10 in the mold flask 12, surrounding the foam mold pattern 10 with sand, and compacting the sand around the foam mold pattern 10 and the bonded sand core 1 6. The positioning, surrounding, and compacting steps are already known in the art and will not be further described herein.

When these steps have been completed, the foam mold pattern 10 is ready for casting. When molten metal is poured into the foam mold pattern 10, the foam mold pattern 10 vaporizes and the compacted sand and the bonded sand core 1 6 form the desired casting. Because of the small size of the bonded sand core 16, very little gas is generated as the molten metal contacts the bonded sand core 16, and the porosity of the casting caused by gas generation is minimized. The bonded sand core 16 will not move when the foam mold pattern 10 vaporizes because the lug 20 secures the bonded sand core 1 6 to the surrounding compacted sand.

Various of the features of the invention are set forth in the following claims.

Claims

1. A process for preparing for casting a foam mold pattern including a portion into which loose sand will not readily flow when sand is compacted around the mold pattern, the process comprising the step of attaching a bonded sand core to the foam mold pattern so that the bonded sand core will occupy only the portion of the foam mold pattern into which sand will not readily flow.

2. A process as set forth in claim 1 wherein said attaching step is provided by gluing the bonded sand core to the foam mold pattern.

3. A process for preparing for casting a foam mold pattern including a portion into which loose sand will not readily flow when sand is compacted around the mold pattern, the process comprising the steps of attaching a bonded sand core to the foam mold pattern so that the bonded sand core will occupy only the portion of the foam mold pattern into which sand will not readily flow, positioning the foam mold pattern in a mold flask, surrounding the foam mold pattern with sand, and compacting the sand around the foam mold pattern and the bonded sand core.

4. A process as set forth in claim 3 wherein the bonded sand core includes means attached thereto for securing the bonded sand core to the sand which is compacted around the foam mold pattern and the bonded sand core, and wherein the process further includes the step of compacting the sand around the securing means.

5. A pattern assembly for use in casting molten metal in sand, said assembly comprising a foam mold pattern including a portion into which loose sand will not readily flow when sand is compacted around said mold pattern, and a bonded sand core attached to said foam mold pattern so that said bonded sand core will occupy only the portion of said foam mold pattern into which sand will not readily flow.

6. An assembly as set forth in claim 5 wherein said bonded sand core is glued to said foam mold pattern.

7. An assembly as set forth in claim 6 wherein said bonded sand core includes means attached thereto for securing said bonded sand core to the sand which is compacted around said foam mold pattern and said bonded sand core.

8. An assembly as set forth in claim 7 wherein said means for securing said bonded sand core include a lug integrally attached to said bonded sand core and adapted to extend into the sand compacted around said core.

9. A process for preparing for casting a foam mold pattern, the process being substantially as hereinbefore described with reference to the accompanying drawing.

10. A pattern assembly for use in casting molten metal in sand, the assembly being substantially as hereinbefore described with reference to the accompanying drawing.