US1667642A - Method for prevention of cracking of castings - Google Patents

Description

Patented Apr. 24,1928;

UNITED STATES canne vANzar'rL METHOD Foa I BEvaN'rIoN Application med september 22, 192s, serial Itis known that in almost all metals the dimensions of the castings obtained by casting the molten metal are less than the `corresponding dimensions of the mold. In

general, for cast iron, a contraction of 1% generally occurs, while for steel this contraction can vary from 1 to 3%. The molds in which metal is cast generally comprise earth or sand, and are filled with the melted 19 metal in a liquid state. AVhen the mold is filled, the'metal commences to pass into a solid state and it is then that the contrac.- tion takes place. During 'this period of contraction it is natural that the mold must folylow the successively decreasing-dimensions of the casting, and this is particularly true in the case of the core or in the parts of the mold which remain under compression on account of the contraction. However, the

20 mold of earth or sand is always slightly deformable either on account of its own composition or because, by means of suitable devices, empty spaces are left at the proper v points which fill up before fusion wlth the 4more yielding and more iiexible material.

But it is also certain-that at the moment of fusion, while all the metal is still liquid, the latter exerts a hydrostatic pressure on the surfaces of the mold which must be ve resistant at thattime. v

Theoretically the mold for casting metal of high contraction must, therefore, be very resistant from the start in order to resist the hydrostatic pressure of the metal, and must be readily deformable in the subsequent stage to permit the metal to contract as it cools. If the mold is so strong as not to be deformable under theaction of stresses pro- 40 duced by contraction, the casting would crack and crevices would be produced over its entire section, or else small fissures would be produced. The crevices or fissures would occur at the point of least resistance of the casting at the moment of rupture. For example it may happen that a steel lcasting breaks at its point of smallest section or, on the contrary, at its largest section, since at the momentof rupture the smallest section has already cooled considerably and can ofi'er a resistance greater than` that of larger sections which are still liquid or almost liquid. And it can also happen that the casting breaks at its smallest sectinas -at the moment of rupture the largest vsections have, for example, their external, surface PATENT. OFFICE.

already sufciently cooled to enable the resistance of'that section to be greater than the resistance of the smallest section.

It is also generally known that large castings, particularly if produced by metals having great contracting coeilicients as for instance steel, can suffer great internal stresses during cooling down, if the molds do not move or adjust themselves in such mannertha-t the contraction during cooling down can proceed regularly. This drawback is very imporant, if. castings of such form are considered in which a part of the casting in one or two of the three ldimensions 1s not equal topor proportional with the dimensions of the other parts, since in ysuch case cracks or even total fractures take place. This particularly takes place quite often in quadrangular frame castings, tubes of greater diameter, etc.

This invention relates to a method, which enables the attainment of a general movement and contraction of the sand during the period of cooling down of the casting, and the examination and promotion of the contraction of the casting. v

This contraction is obtained by any mechanical arrangement that `can exert and regulate a suicient pressure in all directions where an irregular contraction may cause a fracture or other flaw'ofiaws. This is accomplished by means of strong plates applied on the exterior part of the mold, and the pressure is applied on the plates by mechanical, hydraulic or other means. In this way the pressure can be re ulated according to the time required, and the sand can completely move to accommodate the gradual 'contraction Iof the casting and even to precede it.,

At the instantv when .the shrinking begins, a uniform pressure is applied on the mold. After the main contractlon has taken place, the moment ofthe formation of cracks is present. These cracks arise in the parts of the casting which cannot resist with suflicient strength.

By careful examination of the shape of the'casting and the location of risers one can determine beforehand the sections where cracks vare most likely to occur. After sev-- eral experlments one can follow accurately with the help of pyrometerslocated at lpredetermined places, the way in which the pressure and the sand motion should be ad- Justed. v

rIlhe apparatus for carrying out this method depends upon the nature of the castings but for purposes of illustration several preferred forms of molds are shown on the accompanying drawing in which:

Figure 1 is a cross-sectional view of a mold for casting a car frame, v

Fig. 2 is a top view of the mold,

Fig. 3 is a sectional view of a mold for casting a pipe, and I Fig. 4 .is a sectional view of a modified form of mold shown in Fig. 3.

In the drawing there' are indicated several dimensions which are merely for the purpose of showing the large dimensions of the casting compared with the thickness.

The contraction or movement of the sand is accom lished by means of a pair of plates 1 and 1 and 2 and 2 disposed in the interior of the frame 3 and respectively on op- A positc sides of the mold. The contraction orv movement is accomplished by forcing screws 4 which are provided on a cross beam .5 and which move the plates. Nuts 6 (see Flg. 4),

can also -be used, which are provided on the.

extremities of tie rods 6'. In each case these contracting plates produce a contraction and a movement of the sand following the contraction of the casting G, thus relieving it of stresses. Thus the successful contraction of the casting is accomplished by meansl of the violent contraction and movement of the sand after having finished the step of i actual casting. n I claim as m v1. A mold or large castings, comprising' a frame; and means 1n said frame for exertinvention I In testimony whereof I ing a pressure on the molding sand in the frame to thus force the sand to contract and move with the cooling of the casting.

2. A mold for large castings, comprising a frame; a plurality of plates provided in said frame; and means in said frame for actuating sald plates in orde'r to exert a prcs sure on the molding sand in the frame to thus force the "sand to contract and move with the cooliifg of the casting.

3. A mold for large castings, comprising a frame; a plate provided on each side of said frame; and means in said frame for actuating said plates in order toexert a pressure on the molding sand in the frame to thus force the sand to contract and move with the cooling of the casting. l

4. A mold for'largc castings, comprising avframe; a plurality vof plates iovided advjacent the sides of the frame; and screws threaded insaid frame for actuating said i plates in order toexert a pressure on the molding sand in the frame to thus force the sand to contract and move with the cooling of the'casting. v y 5. A mold for large castings, comprising a frame; a plurality of lates `provided adjacent the sides of t ey frame; screws threaded in` said frame for actuating said plates in order to exert a pressure on thev molding sand in the frame to thus force the sand to contract and move with the cooling vof the casting; and. cross beams for said screws. 1

aiiix my signature.

l CARLO v'ANzE'r'rI.

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