EP0730922A1 - Method for producing castings which are later connected to concrete - Google Patents

Abstract

The method is carried out into a sand mould formed by a permanent pattern (1). There is at least one internal projection (5) at the edge of the space later to be filled with concrete, thus forming a recoil base for the concrete. The pattern for the internal wall (2) of the space has a ring (6) at the point at which the edge projection is made. Before the pattern is removed, the ring is widened to the final dia. of the recoil. The ring is hollow and can be inflated. It may be a double-wedge spreading ring.

Description

The invention relates to castings that are later connected to concrete. Such castings are, in particular, manhole covers which have an open cavity for filling with concrete and which are designed as a shell with an outer support edge. The concrete filling is used to save cast iron. The concrete lies above the neutral bending moment line and is therefore only subjected to pressure when loaded. Nevertheless, it is important that there is an intimate, inseparable connection between cast iron and concrete.

Dynamic traffic loads (jumping tires) can lead to micro-movements on the connection surface, which can destroy the connection. As a measure for better connection of the concrete with the cast iron, the enlargement of the contact area is already being practiced. The area enlargement can take the form of nubs, waves, ribs (DE-U-78 31 227) or edge waves (DE-U-92 06 734). Another proposal to improve the connection is aimed at hook-shaped concrete anchors which are cast onto the cover shell (DE-U-81 28 885). Because of the high workload for inserting the cores or anchors, it has recently been proposed to design the shape for the curved concrete anchors as flexible pins on the cover model (DE-C-41 42 259). When the molding sand is introduced and solidified, the pins bend to the side and can be pulled out while stretching.

Such concrete anchors can only be placed in the bottom of the lid shell. This does not improve the connection of the concrete with the cast iron in the edge area of the cover shell. To solve this problem, it is now proposed to cast an inward projection on the edge of the cover shell, so that there is a recess underneath, which is filled with concrete. The concrete filling would also be covered on the top in such a lid and could no longer come loose. However, the casting of such an edge projection fails because the permanent model for the top side of the lid can then no longer be removed from the mold. The process of inserting a core for the recess in the lid cavity is very complex.

The task of casting the edge projection without a core is achieved according to the invention in that the permanent model for the inner wall of the cavity in the cover shell has a ring at the point at which the inward edge projection is cast on, which before the demolding of the Permanent model is expanded to the clear diameter of the recess underneath. Another possibility for solving this problem is the method of removing shaped sand for casting the edge projection on the sand mold after the demoldable permanent model has been removed from the mold, in particular using a turning tool or a milling cutter. The processed molding sand either falls down automatically from the molding box on top or is thrown off when turning. Both process variants do not require cores and can easily be practiced in continuous operation.

Fig. 1

eine erste Ausführungsmöglichkeit mit zusammenziehbarem hohlen Formring;

Fig. 2

eine zweite Form der Verfahrensdurchführung mit einem durch Keilwirkung aufweitbaren Metallring;

Fig. 3

eine dritte Variante mit einem als verlorenes Modellteil wirkenden Ring aus Hartschaumkunststoff, und

Fig. 4

das Verfahren zum Formen des Randvorsprungs mittels Abtrag des Formsands.

In addition to the ones just described, the figures also show further process variants and configurations. The pictures show:

Fig. 1

a first embodiment with a contractible hollow form ring;

Fig. 2

a second form of carrying out the process with a widenable metal ring;

Fig. 3

a third variant with a ring made of rigid foam plastic acting as a lost model part, and

Fig. 4

the method for forming the edge projection by removing the molding sand.

In the molding process according to FIG. 1, the permanent model 1 for the inner wall 2 of the cover shell is at the bottom and the molding box 3 is placed on and already filled with sand 4. At the edge where the projection 5 is later cast, the permanent model has an annular tube 6, which has the shape of the projection as an outer profile. It is attached to the model and connected to a suction air line 7, through which the ring hose is emptied before the molding box is lifted off and then assumes the shrunk (dashed line) state. Now the molding box can be lifted off the model without resistance. The ring hose is inflated again to form the next bale of sand.

In the embodiment of the permanent model according to FIG. 2, the expandable and shrinkable form ring is designed as a double wedge ring 16. The lower wedge 17 has the inclined surface on the inside and can be pressed upwards by means of a plunger 18, so that the upper wedge ring 19, which has the counter inclined surface on the outside and is open at least at one point on the circumference, is spread under contact with the counter-holder 20 and thereby withdrawing from the molding sand.

A lost molded ring 22 made of rigid foam plastic is placed on the permanent model 21 according to FIG. 3 where the projection is later to be cast on. The ring is enclosed by the molding sand and remains in the sand mold when the mold bale is lifted off. It is gasified without residue when the liquid cast iron penetrates; the cast iron occupies its space.

Finally, there is also the possibility not to provide a model part for the edge protrusion on the permanent model, but to form the lid shell without this protrusion and then to remove the molding sand at the edge by means of a form cutter 23 after the permanent model has been removed. The rotating milling cutter only needs to make one revolution, being carried by a swiveling device, e.g. is placed on the guide bolts of the molding box (Fig. 4). The milled molding sand falls into a collecting trough, which is attached under this station.

The embodiment according to FIG. 2 is also suitable for an edge projection that is interrupted several times on the circumference. Instead of a completely closed edge protrusion, the short wedge ring sections result in several short protrusions, which are also ideally suited for clamping the filling concrete.

Claims (7)

Process for casting castings which are later connected with concrete in a sand mold shaped by permanent models, characterized in that at least one inner projection is cast on the edge of the cavity which later receives the concrete, which forms a recess for the concrete underneath. Method according to Claim 1, characterized in that the permanent model for the inner wall of the cavity has a ring at the point at which the inwardly directed edge projection is cast on, which ring is expanded to the clear diameter of the recess before the permanent model is removed from the mold. A method according to claim 2, characterized in that it is an inflatable hollow ring. Method according to claim 2, characterized in that an open double wedge expansion ring is used. A method according to claim 1, characterized in that after the permanent model has been removed from the mold, molding sand for the inner edge projection is removed, in particular worked out with a turning tool or milling cutter. A method according to claim 5, characterized in that the sand mold is stationary and the turning tool or milling cutter executes a full revolution. Method according to Claim 1, characterized in that the model part which forms the edge projection is designed as a lost model which is plugged onto the permanent model.

Images