Method of Inserting Cores in a Sand Mold

This invention relates to a method of inserting in a sand mould one or more cores provided with one or more prints for engagement in corresponding cavities in the mould.

When casting in moulds with horizontal joint faces the cores are inserted in the lower half of the mould, whereupon the upper half is fitted. In this case there is no risk of the core or cores dropping out during the positioning of the upper mould section on the lower section, but in the joining procedure the cores may be pushed or shaken slightly out of the proper position.

When casting in moulds with a vertical joint face the core or cores are inserted in the mould cavity of a vertical surface, frequently in a manner so that the point of gravity of a core is located in or outside the joint face. In that case the core is but feebly retained during the joining of the mould sections and there is a considerable risk of its falling out or being displaced in the joining procedure.

It is the object of the present invention to provide a method of the aforesaid type in which the said risk has been eliminated or at any rate highly reduced by the core or cores being retained effectively in one of the mould sections.

This object has been accomplished by a method which comprises a compression of the sand in one mould section in one or more regions adjacent to, preferably around at least one of the said cavities by means of one or more elements which are pressed into and produce recesses in the sand mould during the insertion of the core. The compression of the sand by the element adjacent to or around a cavity adapted to receive a core print causes the sand to be squeezed together against or around the said core print so as to increase the frictional force by which the core is retained in the mould section, and the risk of drop out or displacement during the positioning of the second mould section has been substantially reduced.

The said method is of course particularly advantageous where the employed moulds have vertical joint faces, but it is also useful where the joint face is inclined and even where the joint face is horizontal, for irrespective of the position of the joint face this method involves an improved fixation of the core or cores in the mould section.

Where a core mask is employed for positioning the core or cores in one of the mould sections the automatic production of the recess or recesses may expediently be carried out by means of one or more projections on the core mask disposed adjacent to, preferably around at least one print on the core inserted in the core mask or on at least one of the cores inserted in the core mask.

It is known to improve the retention of the cores in a mould section by providing the core prints with specific retaining projections and the mould section with cavities for receiving those projections. Where at least one core print is provided with one or more retaining projections for engagement in corresponding cavities in one or in both mould sections one or more sand-compressing recesses can be produced automatically adjacent to or around such retaining projection by providing at least one of the core prints having retaining projections with one or more further projections adjacent to, preferably around at least one retaining projection for producing the recess or recesses. Thus the said retaining projection and thereby the core will be retained still more effectively in the mould section.

By using projections with an inclined surface facing the said cavity it will be further ensured that the compression of the sand in the mould section effected by the introduction of the projection therein will be directed towards the said cavity and thus increase the contact pressure between the sand mould and the core print or its retaining projection.

The invention will be described in greater detail below with reference to the drawing, in which

FIG. 1 presents a vertical section through a core retained in a core mask during insertion in the sand mould in an embodiment of the method according to the invention, and

FIG. 2 is a perspective view of a core with holding projections on the prints for carrying out another embodiment of the method according to the invention.

FIG. 1 shows a sand core 1 formed as a cylindrical stud with tapered end section. This core is to be inserted in a sand mould 2 provided with a cavity 3 for receiving the core print 10, which also has a tapered end section, whereby the risk of damage to the edges during insertion is reduced. The transition between the core 1 and its print 10 is indicated by a dotted line. For the insertion is used a core mask 4 in which the core is placed in a cavity of shape and dimensions corresponding to those of the core and which during the insertion procedure is moved in the direction indicated by the arrow 5. A channel 6 opening in the bottom of the cavity of the core mask enables the supply of vacuum to the cavity during the transport of the core to retain the core by suction and the supply of compressed air to the cavity when the core has been positioned in the mould 2 to detach the core from the core mask.

The core mask is further provided with an annular projection 7 which encloses the cavity and the core 1 positioned therein and which projects from the mask front facing the sand mould 2.

In the embodiment shown in the drawing the said projection 7 is of triangular cross section and has an inwardly inclined surface 8 which on the penetration of the projection into the mould causes the sand to be compressed in the directions indicated by the arrows 9, viz. around the core 1 which is being positioned in the space 3. This compression of the sand results in an increase of the contact pressure between the print of the core 1 and the walls of the cavity 3, whereby also the frictional force by which the core is retained in the mould is increased. The outwardly facing surface of the projection 7 need not be inclined as indicated but may, if desired, be substantially perpendicular to the front face of the core mask.

FIG. 2 shows a cylindrical sand core 11 provided at both ends with a cylindrical print 12 which form extensions of the core. The transitions between the core and the prints are indicated by dotted lines. On each print 12 is provided a conical retaining pin 13 adapted to be engaged in a corresponding recess in the sand mould to contribute to retaining the core in the mould, which is particularly advantageous where the partition surface of the sand mould is vertical.

Each print is further provided with four arcuate projections 14 arranged in a ring around the retaining pin 13. Like the annular projection 7 of the core mask shown in FIG. 1 these projections are adapted to compress the sand in the mould arond the retaining pin 13 during the insertion of the core in the mould. In the illustrated embodiment the projections are of substantially triangular cross-section, though, on account of the character of the material, with rounded ridge. The inner surfaces facing the pin should be inclined relatively to the pin axis.

The compression of the mould sand aimed at by the invention may be attained by means of many other types of projections than those shown in the drawing and described above. A core like that of FIG. 2 may have retaining projections in the form of peripheral collars instead of the pins shown in the drawing, and the compression projections may then be formed as banks extending along and spaced from the retaining collar on both sides thereof. The banks may form continuous rings or collars or they may be divided into a plurality of banks spaced in extension of each other in the same manner as the projections 14 shown in FIG. 2.