GB2147531A

GB2147531A - Facilitating the division of a feeder heat from an article cast in a mould

Info

Publication number: GB2147531A
Application number: GB08425206A
Authority: GB
Inventors: Katsuki Harano
Original assignee: Aikoh Co Ltd; Mitsubishi Steel Mfg Co Ltd
Current assignee: Aikoh Co Ltd; Mitsubishi Steel Mfg Co Ltd
Priority date: 1983-10-07
Filing date: 1984-10-05
Publication date: 1985-05-15
Also published as: GB8425206D0; AU3387384A; DE3436808A1; KR850003854A

Abstract

A casting (2) and feeder (1) between which there is formed a portion (20) having a reduced diameter and a height (H) to allow the end portion of a gas cutting torch to be at least partially introduced into the gap thus formed between them, the said portion (20) being formed by mounting a core, made of a heat insulating material, at the boundary of the cavities of a mould for the feeder head and the casting and pouring a molten metal into the mould. As an alternative, the feeder may be impacted to break it off. <IMAGE>

Description

SPECIFICATION A method for gas cutting a hot top and a core for carrying out the method BACKGROUND OF THE INVENTION The present invention relates generally to molding and more particularly to a method for removal of a riser from a casting and a core for carrying out the method. The present invention also pertains to applications of the inventive core to a so-called neck-down core.

It has been well-known in the art that in manufacturing a casting, a riser plays an important role in feeding molten metal to the casting so as to compensate for any shortage of the molten metal in the casting caused by the solidification and shrinkage of the molten metal forming the casting. The riser becomes unnecessary once the casting has been completed, and must be removed from the casting, the casting being subsequently adequately finished.

There are two principal methods for the removal of risers of steel castings.

In the first method, which generally can be used for risers of all dimensions and materials, as shown in Fig. 1 of the attached drawings, a riser 1 is removed from a casting 2 by melting and cutting at the boundary between them by the use of a gas flame such as propane, acetylene, etc. and oxygen. This method is generally referred to as a gas cutting method. In Fig. 1 the wavy line indicated by reference numeral 3 denotes the boundary line between the riser 1 and the casting 2.

In the second method which is mainly adopted for the removal of risers having small diameters and made of materials having low toughness, as shown in Fig. 2 the riser 1 is given a impact so as to remove from the casting 2 at a notch portion 4 having a small diameter which has been previously provided at the base of the riser 1 when the mold 6 is assembled. This method is generally referred to as a neck-down core method.

These methods have been hitherto widely adopted for the removal of risers in steel castings.

These methods will be explained in detail below.

The gas cutting method is, as shown in Fig. 1, a method for removing the riser 1 from the casting 2 and is adapted with every material ranging from carbon steel to alloy steel regardless of the dimensions or shape of the riser. However, as mentioned above, since this method is carried out by cutting the riser 1 from the casting 2 along the boundary line 3 between them with gase flames such as propane, acetylene, etc. and oxygen, this gas cutting operation is performed at a high temperature and is accompanied by the generation of smoke, fume, etc.

Therefore, improvements in this method have been desired from the viewpoints of safety, and operational environment.

In addition, the costs of the fuel necessary for the gas cutting, preheating, as well as postheating of the riser 1 and the casting 2 constitute an important factor in increasing the cost of the steel casting if fuel prices increase. Therefore, an improvement in the efficiency of the operation and a reduction of the fuel costs required for the gas cutting method have been strongly desired.

On the other hand, in the neck-down core method, as shown in Fig. 2, at the time of assembling a mold, a neck-down core 5 made of a sand core (hereinafter referred to simply as a "sand core") is previously mounted to the base of the cavity of the mold for the riser 1, and after the complete solidification of the casting, the riser 1 is impacted so as to be instantly knocked off from the casting 2 at a notch portion 4 formed by the core 5. When compared with the gas cutting method, the neck-down core method is very advantageous in all respects such as the manufacturing process, costs, and operational environment. However, the ease with which the riser 1 can be knocked off by an impact largely depends on the material of which the steel casting, is made the diameter N of the neck or notch portion 4 of the sand core 5 and the sintering of the core 5 to the castings 1, 2.In particular, the smaller the diameter N of the neck portion, the greater is the ease with which the riser 1 can be knocked off. However, when the diameter N is small, since the molten metal at the neck portion 4 of the sand core 5 solidifies faster than the molten metal in the casting 2, the molten metal, i.e. molten steel to supplement the solidification and shrinkage of the casting 2 cannot be fed from the riser 1 to the casting 2, there arise a shrinkage cavity in the casting 2 so that it is often the case that the casting must be discarded.

Accordingly, in order to obtain a sound casting without shrinkage cavity the solidification time of the molten metal at the various points of the mold must satisfy the following inequality: time for casting 2 < time for the neck portion 4 of the sand core 5 < time for the riser 1.

Solidification in this order is generally referred to as directional solidification. Thus, the sand core 5 mounted in the cavity of the mold between the riser 1 and the casting 2 is subjected to strictly limited thermal conditions. In order to meet the thermal conditions, the shape and dimensions of the sand core 5 constitute important factors; precise data concerning these factors have been obtained from tests and many years of experience. For instance, reference can be made to "Directional Solidification of Steel Casting", written by R. Wlodawer and issued in 1977; pages 87 to 91 and the data therein have been widely adopted as the standard for dimensions of a neck-down core made of sand. Figs. 3 and 4 of the attached drawings are reproductions of the pertinent diagrams thereof.

However, these data concern a neck-down core principally made of sand such as quartz sand, zircon sand, chromite sand, magnesia sand, etc. with a bonding agent such as sodium silicate, phenol resin, vegetable oil and the like.

In accordance with the present invention a method for gas cutting a riser from a casting is provided wherein a core made of a heat insulating material is previously set in the cavity of a mold between the cavity for the riser and that for the casting in the course of the mold assembling.

In this case it is generally necessary to determine the thickness of the core such that the gap thus formed between the riser and the casting is as small as possible to allow only the free end portion of a torch for the gas cutting to be introduced into the gap.

The present invention further provides a core to carry out the method in accordance with the present invention which is made of a heat insulating material.

In a preferred embodiment of the core in accordance with the present invention the neck portion of the core is made of an exothermic material.

Although the objects of the present invention can be achieved in several forms as exemplified above the principle of the present invention originally resides in the following knowledge.

It was found that not only the shape and dimensions of the core but also its material properties (its heat conducting and specific heatj are important factors in satisfying the thermal requirements of a core to be used for carrying out the method in accordance with the present invention. As a result of experiments, it was found that it is effective to use heat insulating materials as the material for the core.

When a heat insulating material is used as the material for a core, since the heat conductivity of the core becomes very low the generation of the solidified layer at the neck portion of the core is extremely retarded compared with when a conventional sand core is used. Therefore, a core made of heat insulating material in accordance with the present invention makes it possible to produce a sound casting even if the dirnensions of the core are decreased to the extent exemplified below.

For instance, if the diameter of the neck portion of a core made of heat insulating material in accordance with the present invention (hereinafter referred to as a heat insulating core") is assumed to be the same as the diameter N of the neck portion 6 of a conventional sand core 5 made of sand as shown in Fig. 2, the thickness H of the heat insulating core 5 can be made larger than the thickness T of the sand core as given by the diagram represented in Fig. 4, or, if the thickness H of the heat insulating core is selected to be the same as the thickness T of the sand core given by the diagram shown in Fig. 4, even if the diameter N of the neck portion of the heat insulating core is made less than the diameter N of a sand core as given by the diagram shown in Fig. 3 the feed of the molten metal to the casting is made possible, resulting in sound castings.

The present invention, applying the above principle to a riser having a large diameter which cannot be knocked off by an impact if the core is made of sand in a conventional manner, proposes to utilize a heat insulating core which has low heat conductivity in place of the sand core to allow the riser to be knocked off by an impact. Adopting such a measure, when the diameter N of the neck portion 4 of a heat insulating core 5 in accordance with the present invention is assumed to be the same as for a sand core, even if the thickness T of the core 5 is 1.5 to 4.0 times that of the conventional sand core, the feed of molten metal from the riser 1 to the casting 2 is assured, resulting in a sound casting.Therefore, when the heat insulating core is used in place of the sand core, since the cross sectional area of the neck portion 4 of the core 5 is about 1 5% of that of the riser 1, the gas cutting area can be reduced to as low as 85% compared with the gas cutting area conventionally required. Further, since the thickness T of the heat insulating core 5 is made thick, the forward end of a torch for gas cutting can be introduced into the gap formed between the riser 1 and the casting 2, the productivity of the gas cutting is remarkably increased.

In the case of a riser having a smaller diameter, notwithstanding the utilization of a heat insulating core, since the forward end of a torch for gas cutting cannot be introduced into the gap formed between the riser 1 and the casting 2, it is necessary to increase the thickness T of the core. To this end it is proposed to additionally secure an exothermic material to the neck portion 4 of the heat insulating core. Thanks to the exothermic reaction of the exothermic material with the molten metal at the time of its pouring into the mold, since the formation of a solidified layer at the neck portion 4 is extremely retarded, even if the thickness of the heat insulating core is made thicker than the thickness T of the sand core 5, the feed of the molten metal from the riser 1 to the casting 2 during the solidification of the casting is made possible.

In this case, when the diameter N of the neck portion 4 was selected to be the same as in the sand core, it was confirmed that the thickness of the heat insulating core ould be made as thick as 2.0 to 6.0 times the thickness T of the sand core.

From the foregoing it will be appreciated that the heat insulating core in accordance with the present invention reveals an excellent advantage over the conventional sand core for both the gas cutting method and the neck-down core method for removal of a riser from a casting.

BRIEF DESCRIPTION OF THE DRAWINGS These and other objects of the present invention will become more readily apparent upon reading the following description and upon reference to the attached drawings, in which: Figure 1 is an explanatory view illustrating how to effect a gas cutting procedure to remove a riser from a casting; Figure 2 is a similar view illustrating how to effect a neck-down procedure to remove a riser from a casting; Figures 3 and 4 are diagrams for determinating the principal dimensions of a neck-down core made of sand; Figure 5 is a partial sectional view illustrating how to carry out the method in accordance with the present invention together with an embodiment of cores made of a heat insulating material also in accordance with the present invention; Figure 6 is a view similar to Fig. 5 illustrating a modification of the core shown in Fig. 5;; Figure 7 is a partial sectional view illustrating how to practice the method in accordance with the present invention in a modified manner together with a core made of a heat insulating material adapted to be used in conjunction with the above method and also in accordance with the present invention; Figure 8 is a similar view to Fig. 7, but illustrating a modification of the core shown in Fig. 7; Figure 9 is a partial sectional explanatory view illustrating how to carry out the gas cutting in accordance with the present invention at the neck portion formed between a riser and a casting; Figure 10 is a partial sectional view of a neck-down core as an application of the core for gas cutting in accordance with the present invention; Figure 11 is a partial sectional view of a neck-down core somewhat modified from the neckdown core shown in Fig. 10;; Figure 12 is a partial sectional view of a neck-down core with an exothermic material being bonded to the neck portion of the neck-down core shown in Fig. 10; Figure 13 is a partial sectional view of a neck-down core with an exothermic material being bonded to the neck portion of the neck-down core shown in Fig. 11; and Figure 14 is a longitudinal sectional view of a mold for a casting and a riser with a heat insulating sleeve and core.

DESCRIPTION OF PREFERRED EMBODIMENTS Reference will now be made to Fig. 5 of the attached drawings, wherein is shown a manner of carrying out the method for gas cutting a riser from a casting in accordance with the present invention by the use of one embodiment of a heat insulating core also in accordance with the present invention. In this case the thickness T, of the heat insulating core 10 is so selected that a gap sufficient to allow the introduction of the top end of a torch for gas cutting is formed between the riser 1 and the casting 2.For instance, even if the thickness T1 is selected to be 1.5 to 4.0 times the thickness T of a sand core as defined by the diagram shown in Fig. 4, when the diameter N of the neck portion 11 of the core 10 is selected to be the same as for a sand core as defined by the diagram shown in Fig. 3 the feed of molten metal from the riser 1 to the casting 2 is sufficiently assured, resulting in a sound casting. In this case, in order to prevent the core 10 from being burned on with the molten metal, it is coated with an appropriate facing.However, if the drying of the facing is insufficient, since the surface of the casting deteriorates, it is preferable to bond a thin sand core 1 2 to the surface contacting the casting 2 as shown in Fig. 6, and in this case, the facing is applied also to the thin sand core 1 2. The surface of the casting 2 is then improved.

Fig. 7 shows the case where the diameter of the riser 1 is small so that the introduction of the top end of a torch for gas cutting into the gap formed between the riser 1 and the casting 2 is not possible. To remedy this, in order to further broaden the gap between the riser 1 and the casting 2 an exothermic material 1 7 having a given thickness is secured to the heat insulating core 15 at its neck portion 16.

In this case, if the diameter N of the neck portion 1 6 of the core 1 5 is selected to be identical to the diameter N of a sand core as given by the diagram shown in Fig. 3, the thickness T2 of the heat insulating core 1 5 can be made thick enough to allow the top end of the torch for gascutting to be introduced between the riser 1 and the casting 2. For example, even if the thickness T1 of the core 1 5 is made to be 2.0 to 6.0 times the thickness T of a sand core as given by the diagram shown in Fig. 4 it was confirmed that a sufficient feed of the molten metal from the riser 1 to casting 2 was assured, resulting in a sound casting.

Similar to the case of the heat insulating core 10, 1 5 shown in Fig. 6, in Fig. 8 a thin sand core 12, 18 are secured to the core 10, 1 5 at the surface contacting the casting 2 as a precaution against deterioration of the surface of the casting in case of insufficient drying of the facing applied to the core 10, 1 5.

Fig. 9 shows diagrammatically a casting produced by the use of the method according to the present invention. As can be seen from Fig. 9, although the riser 1 and the casting 2 are connected together by a neck 20 having a height H and a diameter N which has been formed by the use of a heat insulating core, since the height H is sufficient to allow the introduction of the top end of the torch for gas cutting, the riser 1 can be removed from the casting 2 by the gas cutting procedure. In the drawing, the wavy line 21 indicates the cut line along the neck 20 by the gas flame. In this case it will be appreciated that the diameter of the neck 20 is remarkably reduced, and consequently the consumption of fuel gases for the gas cutting is greatly decreased.

Thus, as is apparent from the above description, the method for gas cutting of a hot top from a casting according to the present invention can be carried out by the use of the insulating core 10 or 15. Now, a detailed explanation as to the materials constituting such a heat insulating core 10, 1 5 will be given below.

The heat insulating core in accordance with the present invention is mounted within the cavity of a mold at the base of the cavity for the riser when the mold is assembled. The core itself is made using partly or entirely commonly marketed heat insulating materials. The heat insulating materials on the market are generally so manufactured that the raw materials such as refractory materials, inorganic fibers, organic fibers, binding agents, etc. are dispersed in water to form a slurry-like substance, and after it is dehydrated and molded to a desired shape and dimensions, it is dried. In this case, the refractory materials are quartz sand, zircon sand, chromite sand, magnesia sand, etc., the inorganic fibers being glass wool, asbestos, aluminum silicate, etc., and the organic materials are pulp, old paper subjected to beating, synthetic resin fibers, cotton, etc.The binding agents are synthetic resins such as phenol resins, furan resins, etc. and starch, dextrin, etc. One or more of these various components are used singularly or in combination.

Since the heat insulating material comprising these various materials has very low heat conductivity, it has high heat insulating properties and also has high pressure resistant, a low melting loss, and an excellent stripping property from the castings.

As an exothermic material to be used, if desired, at the neck portion of the core, publicly known exothermic materials mainly consisting thermit are suitable. For example, the exothermic components are those comprising easily oxidizable metals such as aluminium, magnesium, calcium, and silicon, oxidizing agents such as iron oxide, magnesium oxide, and nitrates, auxiliary combustion agents such as fluorite, refractory materials such as alumina, guartz sand, and aluminium residul ash, organic substances such as paper, pulp, and wood flour, organic or inorganic binding agents, and the like.

Next the manner of making the heat insulating core and the conventional sand core as well as the results of tests which were carried out to compare their properties will be explained with reference to Table I.

In Table I, "conventional method" indicates a core made in accordance with a conventional method as comparative example, and the mold was prepared, as shown in Fig. 1, without a core and was molded from self-hardening furan sand in the same manner as for the other molds.

As the metal to be cast, the steel designated as SC 46 by the Japanese Industrial Standards was poured at 1,565 C. This comparative example had good stripping properties from the sand and a sound interior structure, but it took 48 seconds to cut off the riser, which had a diameter of 1 20mm, by a gas-cutting method.

Table I

Donventional Example No. 1 Example No. 2 Example No. 3 Example No. 4 Method Type of Molding Fig. 1 Fig. 2 Fig. 2 Fig. 2 Fig. 2 Riser Diameter (mm) 120 120 120 120 120 Casting Diameter (mm) 120 120 120 120 120 Mold Material Furan Sand furan Sand Furan Sand Furan Sand Furan Sand Core Heat Insulating Heat Insulating Heat Insulating Heat Insulating Material --- Material Material + Sand Material + Sand Material + Exo Molding Molding thermic Material +Sand Molding Core Shape --- Fig. 5 Fig. 6 Fig. 7 Fig. 8 Neck Diameter (mm) --- 47 47 47 47 Core Thickness (mm) --- 25 25 30 30 Casting Material SC 46 SC 46 SC 46 SC 46 SC 46 Pouring Temperature ( C) 1,565 1,565 1,565 1,565 1,565 Strippability and Somewhat Somewhat Casting Surface Good Good Good Good Good Riser Cutting Time (sec) 48 15 15 12 12 Soundness of Casting Interior Good Good Good Good Good In contract in Table I, Example No. 1 and Example No. 2 indicating the present invention were cast with the use of the heat insulating cores 10 in accordance with the present invention as shown in Figs. 5 and 6, respectively, and the diameter N of the neck portion was adopted to be 47 mm which is the recommended value of the nech portion for a riser having a diameter of 1 20 mm determined from Fig. 3. However, the thickness T, for the heat insulating core 10 was adopted to be 25 mm, which was two times the standard thickness given in Fig. 4 for a sand core for use with a 120 mm diameter riser. Further, in Example No. 2, the core had its surface contacting the casting secured by a thin sand core formed of chromite sand by a CO process.

Both corps pre dried at a low temperature of 1 20 C for 2 hours after they had been covered with a water soluble facing The cores could be stripped off from the castings smoothly, but Example No. 2 revealed a finer surface than Example No. 1. The soundness of the interior of the castings was good in both, no shrinkage cavity being recognized. The time required for gas cutting the riser was only 1 5 seconds, considerably below the gas-cutting time for the conventional casting, but since the diameter of the top end of the torch for the gas cutting was 23 mm, the top of the torch was barely introduced into the gap formed between the riser and the the casting 2.

Example No. 4 and Example No. 5 utilized the heat insulating cores 1 5 shown in Figs. 7 and 8. respectively, with exothermic materials 1 7 secured to the neck portion 1 6 of the cores 1 5.

The thickness T2 of the heat insulating cores 1 5 was selected to be 30mm, three times the thickness of the standard sand core. Further, in Example No. 4 a thin sand core 18 formed of chromite sand by a CO2 process was bonded to the core 1 5 at the surface contacting the casting 2. Both of them were coated with a water soluble facing and dried at a low temperature of 1 20 C for 2 hours.

Although both examples exhibited sintering at the neck portion of the core owing to the use of the exothermic material as well as uneveness due to the generation of gases from the exothermic material, these phenomena were less noted in Example No. 3 than in Example No.

4. The soundness of the interiors of the castings was good for both, no shrinkage cavity being recognized.

The time required for cutting off the riser through the gas-cutting method was 1 2 seconds, remarkably less than with the conventional method. Further the top end of the torch for gascutting was easily introduced into the gap formed between the riser 1 and the casting 2, considerably facilitating the gas-cutting operation.

A neck-down core as an application of the heat insulating core in accordance with the present invention is based on the same principle as that of the method for gas cutting a riser from a casting in accordance with the present invention as described above.

The principle behind the neck-down core according to the present invention resides in the knowledge that not only the shape and dimensions but also the material properties (the heat conductivity and specific heat) of the core are important factors in satisfying the thermal requirements for a neck-down core. The present invention achieves its objects by giving the neck-down core better cutting off properties for the riser than a conventional neck-down core made of a sand mold through the selection of specific materials for the core.

For the above reason the heat insulating core for gas cutting a riser as described above can be in general utilized also as a neck-down core with a small modification being made at the neck portion. That is, as shown in Fig. 10 the neck portion 11 of the heat insulating core 10 has to be formed to exhibit a circumferentially protruded neck portion at substantially half the thickness T of the core 10.

The following is a somewhat concrete description of the neck-down cores in accordance with the present invention as applications of the heat insulating cores for cutting off a riser from a casting according to the present invention fully described above.

Firstly, Fig. 10 shows an embodiment of a core 10 solely made of a heat insulating material to be processed and shaped. In this case, if the thickness T of the heat insulating core 10 is assumed to be the same as that of a sand core as determined in Fig. 4, even if the diameter N, of the neck portion 11 of the heat insulating core 10 is made to be 30 to 55% of the diameter determined N from Fig. 3 with the area of the neck portion being 10 to 30% of the area of the neck portion 6 of the sand core 5 shown in Fig. 2 it was confirmed that the supply of molten metal from the riser 1 to the casting 2 was well assured, enabling a sound casting 2 to be obtained. In this case, the heat insulating core 10 is used either as it is or with a facing being applied thereon, but the surface of the casting is not good when the drying of the facing is insufficient. However, if a thin sand core 12 is, as shown in Fig. 11, bonded to the surface contacting the casting 2 and a facing is applied, the surface of the casting can be improved.

Fig. 1 2 shows another embodiment of a heat insulating core 1 5 in which in order to further improve the knocking off property of the riser 1, an exothermic material 1 7 is bonded to the neck portion 1 6 of the heat insulating core 15.In this case, if the thickness T of the heat insulating core 1 5 is adopted to be the same as the thickness T of a sand core 5 as determined in Fig. 4, even if the diameter N1 or the area of the neck portion 16 of the core 1 5 is made to be 22.3 to 55% or 5 to 30%, respectively, of the diameter N or the area of the neck portion 4, respectively, of the sand core 5 shown in Fig. 2, it was confirmed that the feed of molten metal from the riser to the casting 2 was well assured, enabling a sound casting to be obtained.

Fig. 1 3 shows a core 1 5 which is a modification of the core 1 5 shown in Fig. 1 2 wherein, similarly to the heat insulating core 10 shown in Fig. 11, in order to prevent the surface of the casting from deteriorating due to insufficient drying of a facing applied to the core 1 5, a thin sand core 1 8 is bonded to the core 1 5 contacting the casting 2.

From the foregoing, it will be appreciated that even if the dimension of a riser made of a conventional neck-down sand core does not allow the riser to be knocked off by subjection to an impact, if a heat insulating core in accordance with the present invention is adopted in place of the sand core, when the thickness T of the heat insulating core 10 or 1 5 is selected to be the same as the thickness T of a sand core 5 given in Fig. 4, even if the diameter N, and N2 or the areas of the neck portion of the heat insulating core 10 or 1 5 are 30 to 55% or 10 to 30%, respectively of the diameter N or the area of the neck portion 4, respectively, of the sand core 5, it is possible to feed the molten metal from the riser 1 to the casting 2, giving a casting having a sound interior, and the breaking off property of the riser 1 by the impact can be remarkably improved.

Further, if the heat insulating core 1 5 according to the present invention has an exothermic material 1 7 bonded to its neck portion 16, the formation of the solidification layer at the neck portion 1 6 is more retarded than with a simple heat insulating core 10, even if the cross sectional area of the neck portion 1 6 of the heat insulating core 1 5 is 5 to 30% of that of the neck portion 4 of a conventional sand core 5 the feed of molten metal from the riser 1 to the casting 2 is made possible, providing a sound casting and resulting in further improvements in the knocking off property of the riser.

At this point, results of tests carried out for proving the superiority of the neck-down core in accordance with the present invention over a conventional sand neck-down core are listed in Table II, which is similar to Table I.

In Table II, "Conventional" refers to a neck-down core manufactured along the lines of Fig. 2 as a core for comparison, the core being prepared from self-hardening furan sands. The diameter N and the thickness T determined in Fig. 3 and Fig. 4. The material for the core, chromite sand was shaped into a desired shape by a CO2 process.

Although the casting tested had good separation from sand and also soundness in the interior of the casting, the riser could not be knocked off by the impact.

Table II

Convention Method Example No. 1 Example No. 2 Example No. 3 Example No. 4 Example No. 5 Type of Molding Fig. 2 Fig. 2 Fig. 2 Fig. 2 Fig. 2 Fig. 2 Riser Diameter (mm) 110 110 110 110 110 110 Casting Diameter (mm) 110 110 110 110 110 110 Mold Material Furan Sand Furan Sand Furan Sand Furan Sand Furan Sand Furan Sand Core Shape Fig. 2 Fig. 10 Fig. 11 Fig. 12 Fig. 13 Fig. 14 Neck Portion Diameter 42.3 21.2 21.2 13.4 13.4 17.2 (N,N1,N2) (mm) Core Thickness (T) (mm) 10 10 10 10 10 9.5 (Ht. Insulating -- 10 8 10 8 9.5 Material (mm) (Sand Mold) (mm) 10 -- 2 -- 2 -- Casting Material SC 46 SC 46 SC 46 SC 46 SC 46 SC 46 Pouring Temperature ( C) 1,565 1,565 1,565 1,565 1,565 1,565 Strippability and Somewhat Somewhat Somewhat Somewhat Casting Surface Good Good Good Good Good Good Knocking Off by Hammer Impossible Possible Possible Possible Possible Possible Soundness of Casting Interior Good Good Good Good Good Good In contrast, Example No. 1 and Example No. 2 in accordance with the present invention and cast using the heat insulating cores 10 shown in Figs. 10 and 11, respectively, had the same thickness T as that of the sand core 5, but the diameter N1 of the neck portion 11 was 21.2mm, 50% less than the diameter N of the neck portion 4 of the sand core. As the materials of the cores 10, in Example No. 1 a heat insulating material was used whereas in Example No.

2 a heat insulating material was used with a thin sand core 1 2 being bonded to the surface contacting the casting 2, the thin sand core 1 2 being shaped from chromite sands by a CO2 process. Both cores 10 were coated with a water soluble facing and thereafter they were dried at a low temperature of 1 20 C for 2 hours.

Example No. 1 and 2 after casting had good separability from sand, but Example No. 2 had a better surface than Example No. 1. The knocking off of the riser 1 by the impact of a hammer was possible for both, and the soundness of the interior of the casting was good in both, revealing no shrinkage or blow holes.

The heat insulating cores 1 5 of Example No. 3 and Example No. 4, prepared along the lines of Figs. 12 and 13, respectively, had exothermic materials 1 7 bonded to their neck portions 16.

The diameter N2 of the neck portion 1 6 was 1 3.4 mm, 68% less than the neck portion of the sand core 5. Further, in Example No. 4 a thin sand core 1 8 was bonded to the surface contacting the casting 2 the thin sand core 1 8 being formed of chromite sands through a CO2 process. Both cores 1 5 were coated with a water soluble facing and dried at a low temperature of 1 20 C for 2 hours.

Example No. 3 and Example No. 4 revealed the sintering of the sands and uneveness of the surface due to gas generated from the exothermic material, but Example No. 4 exhibited better results than Example No. 3 in the above two points.

The knocking off of the riser by the impact of a hammer was possible for both, and the soundness of the interior of the casting was good in both, no shrinkage cavity being found.

Finally, Example No. 5 was made, as shown in Fig. 14, using a heat insulating sleeve 20 for a riser 1 according to the conventional practice and a heat insulating core 10 in accordance with the present invention similar to the previous examples, but the diameter of the riser 1 was 10 mm, and the thickness T of the core 10 and the diameter N1 of the neck portion thereof were 9.5 mm and 1 7.2 mm, respectively. The material of the heat insulating core 10 was an alumina-silicate base.

Example No. 5 revealed good results similar to the previous examples as is apparent from Table II.

Finally, two typical examples of the heat insulating materials suitable for both the gas cutting and neck-down processes are given in Table Ill together with their chemical compositions and some physical and chemical properties.

Table III

Alumina-Silicate Silicate Base Base Bulk Specific sleight 0.59 1.00 Apparent Porosity (%) 78.1 63.00 MgO ~ 1.4 z 0 SiO rl L É 2 3 55.0 1.6 OLC5 CJ dP ~ Fe203 0.8 0.7 U w CaO 0.5 U Me.AQ 11.6 Ignition loss (t) 8.0 9.1 1 Total Carbon (t) 5.0 6.4 2000C 0.060 0.195 > 1 6000C 0.108 0.224 8000C 0.121 0.238 oo D s 1,0000C 0.140 0.264 U X z 1,200 C 0.160 0.300 ("b' = ~ l,4000C - 0.186 0.350 It is to be understood that although certain forms of this invention have been illustrated and described, it is not to be limited thereto except insofar as such limitations are included in the following claims.

Claims

1. A casting and riser wherein between the casting and the riser there is formed a portion having a reduced diameter and a height to allow the top end portion of a gas cutting torch to be at least partially introduced into the gap thus formed between them, the said portion being formed by mounting a core, made of a heat insulating material, within the cavities of a mold for the riser and the casting at their boundary and pouring a molten metal into the mold.

2. A method for removal of a riser from a casting comprising the steps of assembling a mold for said riser and said casting, mounting at the base of the cavity for said riser a core which has generally a board-like shape with a hole being formed therein and which has a thickness to allow the top end of a torch for gas cutting to be introduced at least partly into the gap to be formed between said riser and said casting, pouring a molten metal into said mold so as to allow said molten metal to feed from said riser through said hole to said casting during the cooling and solidification of said molten metal, removing said riser from said casting either by gas cutting said riser at the portion corresponding to said hole or by applying an impact to said riser so as to knock it off at the portion corresponding to said hole.

3. A core to be mounted at the boundary of a cavity of a mold for a riser and a cavity for a casting, comprising a body having generally a board-like shape with a hole being formed therein and having a thickness to allow the top end of a torch for gas cutting to be at least partially introduced into a gap formed between said riser and said casting after pouring, wherein said hole has a cross-sectional area which is large enough to allow a molten metal to flow therethrough from said riser into said casting during the solidification of said casting, and wherein said core comprises principally heat insulating materials.

4. A core as claimed in claim 3 wherein said core has a core made of sand secured to its side confronting said body of said casting.

5. A core as claimed in claim 2 or 3 wherein said core has said hole covered with an exothermic material.

6. A core as claimed in claim 3, 4 or 5, wherein said core is a neck-down core provided with a circumferentially protruded neck portion around said hole at substantially the midpoint of said thickness.

7. A casting and riser as in claim 1, or a method as in claim 2, making use of a core as in any of claims 3 to 6.

8. A casting and riser as in claim 1, or a method as in claim 2, or a core as in claim 3, substantially as herein described with reference to the drawings.

9. A casting made from or by use of a casting and riser, a method, or a core, as the case may be, as claimed in any preceding claim.