DE1608774B1 - Mold made of cast iron with Gugelgraphite or cast steel - Google Patents

Description

The heat transfer from a block into a mold takes place in such a way that from the Block dissipating heat initially through direct contact, later after the formation of an air gap released indirectly through convection and radiation to the inner surface of the mold wall and from there to the wall parts lying behind in cross-section. There are, however xlie volume fractions of the wall assigned to a unit area of the inner wall side with all around about the same wall thickness very different.

In an essentially flat area of the mold wall, the wall volume Q _F available for heat absorption per unit area of the inner wall side is equal to the wall thickness α

Qp (mm ³ / mm ³ ) -a.

In the area of a wall corner, on the other hand, under the simplifying assumption according to FIG. 1 that the outer edge and the inner edge with a larger radius J? or a smaller radius r are rounded concentrically to one another, the relationships;

25th

corresponding section of the inner wall side

This results in the wall volume per unit area of the inner wall side, i.e. based on one certain height,

2 '^ = T-

If one now uses the usual values for the wall thickness α and the inner radius r and thus also obtains the value for the outer radius R = r + a , the ratio of Q _x to Qe is ^roughly between 2 and 2.5. If the wall thickness of a mold is essentially the same all around, a comparatively much larger wall volume is available at the corners than at the other points. As a result, the mold is heated less at the corners than in the area of the flat wall surfaces. According to measurements by Butler and Glaisher as well as Fowler and Savage, published in the Journal of the Iron and Steel Institute, July 1951, p. 287/301 and July 1952, p. 277/288, the temperature differences at the points concerned are 8- t-molds in the predominant period of time during which the mold is heated to around 100 ° C. The resulting thermal stresses are, among other things, the cause of the resulting distortion.

Another factor in the different heating up of the mold is due to that the edges of the block contain the least amount of heat in relation to their surface area and therefore also cool down the fastest, while those in the middle of the area of the block The amount of heat contained and thus also the heat flow to the outside increase.

While the last-mentioned factor is due to the block format, the ratio Q _K to Q _t can be favorably influenced by an appropriate change in the external shape of the mold. The idea of reducing the wall thickness at the edges compared to the flat surfaces in this sense, however, is practically impossible in the case of hematite molds because of the comparatively low strength and elongation of cast iron with lamellar graphite, because otherwise there is a risk of cracking. Literature references in which such a reduction in wall thickness at the edges of hematoid molds is dealt with at all are limited to only minor differences; in one case a ratio of 0.95 and in another case a lower limit of 0.83 is mentioned.

However, it has not yet been thought of from the fact that the requirements for the The applicability of such a measure to molds made of spheroidal graphite cast iron is different, to draw appropriate conclusions. The invention is based on this consideration, namely has It has been shown on the basis of test results that with such a material, which is a comparatively has greater plastic deformation and therefore warping of the mold without cracking, to achieve a more uniform "temperature distribution and thus reducing the thermal stresses leading to warpage with regard to the wall thickness ratio It is advisable to only begin between edges and the center of the surface where in the other case after the information that has become known is already the lower limit.

In the drawing, for example, is shown in

F i g. 1 shows a cross section through a mold in the usual shape and in

F i g. 2 shows a cross section through a mold in the new form according to the invention.

In Fig. 1, the approximately constant wall thickness all around with a, the outer radius and the inner radius at the edges with R and r and the "double hatched wall cross-section belonging to an edge in the area of a quarter-circle arc of the two radii" with I _K In contrast, the wall thicknesses in the center of each mold side are designated with O ₁ and at each edge with O _2. In this case, the relation a ₂ to U ₁ < 0.8 applies.

In the case of molds made of spheroidal graphite cast iron, it is known that the mold volume falls within a range of Bring less than 0.79 of the block volume, with the wall thickness evenly over the mold cross-section is distributed.

It is also known that molds made of spheroidal graphite cast iron achieve greater numbers of casts as such made of cast hematite, especially in the case of small block formats, large tapering of the inner shape and a high volume ratio.

It is accordingly the object of the present invention to provide a permanent mold made of spheroidal graphite cast iron or to create cast steel that is free from warpage. '

The invention consists in that the wall thickness ratio αϊ to O ₁ in molds made of spheroidal cast iron or cast steel is between 0.4 and 0.8, the wall thicknesses steadily decreasing from the center of the side wall to the edges.

Claims (1)

Claim: Chill made of an iron-carbon casting alloy for casting blocks or the like made of steel and other iron alloys whose wall thickness is in The area of the edges is smaller than that of the middle of the side wall, characterized in that in a mold made of spheroidal graphite cast iron or cast steel, the ratio between the wall thicknesses of the edges on the one hand and the side wall centers on the other (a ₂ to O ₁ ) is between 0.4 and 0 , 8 and that the wall thicknesses steadily decrease from the side wall centers towards the edges. 1 sheet of drawings