Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22C—FOUNDRY MOULDING
  • B22C9/00—Moulds or cores; Moulding processes
  • B22C9/06—Permanent moulds for shaped castings
  • B22C9/061—Materials which make up the mould
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22C—FOUNDRY MOULDING
  • B22C23/00—Tools; Devices not mentioned before for moulding
  • B22C23/02—Devices for coating moulds or cores
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22C—FOUNDRY MOULDING
  • B22C3/00—Selection of compositions for coating the surfaces of moulds, cores, or patterns
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D17/00—Pressure die casting or injection die casting, i.e. casting in which the metal is forced into a mould under high pressure
  • B22D17/20—Accessories: Details
  • B22D17/22—Dies; Die plates; Die supports; Cooling equipment for dies; Accessories for loosening and ejecting castings from dies
  • B22D17/2209—Selection of die materials
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D25/00—Special casting characterised by the nature of the product
  • B22D25/02—Special casting characterised by the nature of the product by its peculiarity of shape; of works of art
  • B22D25/04—Casting metal electric battery plates or the like

Definitions

• the present invention relates to a mold for the casting of thin objects of metal or alloy with a low melting point, a method of covering the active surface of this mold, as well as the use of such a mold.
• Objects of small thickness, made of metal or of an alloy with a low melting point, such as for example the grids for electrodes of electrochemical accumulators, are generally cast in metal molds whose surface intended to come into contact with the molten metal must have well-defined properties. This surface must, in fact, be thermally insulating in order to prevent, by rapid trep cooling, the molten metal introduced into the mold at approximately 480 ° C. from obstructing the pouring channels, thus preventing the complete filling of the mold.
• the interior surface of the mold must have a thermally resistant bucket due to the high production rate (12 to 15 castings per minute) keeping the temperature of the mold at around 150 to 180 ° C.
• the grids are also necessary to prevent the grids from adhering to the interior surface of the mold.
• This adhesion can be avoided by suitably adapting the roughness of the mold surface and by reducing the wettability of this surface by the molten metal.
• the coating must, moreover, give the grids a surface condition capable of allowing good electrical contact between the grid and the active material of the finished electrodes.
• the interior surface of the mold is coated with a layer of cork particles fixed by a binder. This type of coating has sufficient insulating qualities; it has, however, the failure to wear out very quickly. Indeed, cork does not tolerate high temperatures very well and the insulating layer is gradually oxidized, thus losing its insulating properties.
• the molten metal causes an erosion of this cork layer, which results in a progressive reduction in the thickness of said layer.
• the coating must be renewed after approximately 2000 castings so that, in an eight-hour working day, production must be interrupted at least twice to carry out this renewal.
• German patent application published before examination No. 3 040 960 proposes to remedy this state of affairs by depositing on the internal surface of the mold a ceramic layer of variable thickness.
• the main disadvantage of such a solution is that it is difficult to implement and, moreover, this ceramic layer does not have sufficient insulating qualities.
• US Patent 3,684,004 proposes to coat the interior surface of a graphite mold with refractory particles deposited by spraying and fixed by a binder. If this process allows the casting of parts whose thickness is relatively large, the thermal insulation which it makes it possible to obtain is insufficient for casting grids for electrodes of electrochemical accumulators.
• Patent FR 1 495 568 describes a mold with low thermal conductivity, made up of sintered metal particles.
• the quality of the thermal insulation linked to the porosity of this mold is dependent on the sintering pressure and, incidentally, on the impregnation with sodium silicate or ethyl silicate.
• the object of the present invention is precisely to remedy the drawbacks mentioned. It relates to a mold for the casting of thin objects, of metal or of alloy with low melting point, the active surface of which intended to be brought into contact with the metal or the alloy in fusion is covered with a layer of thermal insulator, this mold being characterized in that this insulator is composed of a plurality of hollow particles of ceramic material, fixed to said surface by a binder.
• the subject of the invention is also a method of covering the active surface of the mold, according to which the active surface is heated to a temperature of approximately 120 ° C. and a suspension of approximately 10% is projected onto this surface. by volume of silicate of soda, approximately 10% by volume of hollow glass beads, with a diameter between 10 and 150 ⁇ m, and approximately 80% by volume of water.
• a third object of the invention is the use of the above mold for the casting of lead or lead alloy grids intended to be used as part of electrodes for an electrochemical accumulator.
• Fig. 1 is a sectional view on a large scale of a portion of the active surface of the mold.
• Fig. 2 is a section through a coated counterweight according to the invention.
• Fig. 3 is an explanatory diagram.
• Fig. 1 shows a portion of a foundry mold 4, where 1 d sign glass beads, whose cavities 2 occupy about 90% of the volume of each ball, and 3 a binder, for example sodium silicate, by which these beads feel attached to the active surface of the mold.
• the beads have a diameter between 10 and 150 ⁇ m, and can be made of a ceramic material other than glass.
• This coating is obtained by spraying a suspension composed of 10% by volume of sodium silicate, 10% by volume of glass beads, and 80% by volume of water, at room temperature (22 ° C). The coating is deposited in successive layers, tooth the thickness is approximately 30 ⁇ m, until a total thickness of 300 ⁇ m is obtained, on the surface of the pre-heated mold (120 ° C.), to allow the practically immediate evaporation of water.
• Fig. 2 is a sectional view showing one of these weights 10, in the shape of a rectangular parallelepiped (length 70 mm, width 50 mm, height 14 mm).
• Each counterweight has a cylindrical cavity 11 whose longitudinal axis 12 is parallel to one of the largest faces 13 of the counterweight, and is located at a distance of 1.75 mm from this face.
• This cavity 11 has a diameter of about 1.5 mm and extends to the center of the counterweight.
• thermocouple 16 intended to be connected to a voltmeter (not shown) by son 15a, 15b, is inserted into the cavity so as to allow the measurement of the temperature prevailing in the central part of the counterweight.
• One of the two weights is covered, on its face 13, with a coating R as described above with reference to FIG. 1.
• the face 13 of the second counterweight carries a coating of the traditional type, that is to say constituted by a layer, 250 to 300 ⁇ m thick, of cork particles fixed to the counterweight by sodium silicate.
• FIG. 3 shows the evolution of the thermal insulation properties of the two types of coating above, when these are repeatedly subjected to a cyclic stress of a thermal nature.
• the tests were carried out by heating the weights beforehand at a temperature of 200 ° C., and then subjecting sixteen times the traditional coating, respectively fourteen times the coating of the mold according to the invention, to a cyclic stress of defined thermal nature.
• Curves A are characteristic of the behavior of the coating according to the invention (first counterweight), and curves B that of a coating of the traditional type (second counterweight).
• the time required for the second counterweight, traditionally coated (cork layer), to reach the different temperatures (230, 240 and 265 ° C) is significantly shorter than that taken by the first counterweight , coated according to the invention (mineral layer), to reach these same temperatures.
• the ratio is in fact about 1 to 3. This means that the coating according to the invention constitutes better thermal insulation than the traditional coating.
• the layer of glass beads can be covered with an additional layer of graphite.
• This layer the thickness of which is less than 5 ⁇ m can, for example, be deposited by projection.
• the coating according to the invention can be obtained by spraying a suspension composed of 80% by volume of water, 10% by volume of sodium silicate and 10% by volume of glass beads containing particles of cork, at a rate of less than 2% of the total mass of the suspension.
• the projection can be carried out as described above.

Landscapes

• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Chemical & Material Sciences (AREA)
• Materials Engineering (AREA)
• Mold Materials And Core Materials (AREA)
• Other Surface Treatments For Metallic Materials (AREA)

Priority Applications (1)

Applications Claiming Priority (2)

Publications (1)

Family

ID=4214251

Family Applications (1)

Country Status (5)

Cited By (4)

Families Citing this family (1)

Citations (4)

• 1983
  • 1983-03-11 WO PCT/CH1983/000029 patent/WO1983003212A1/en active Application Filing
  • 1983-03-11 IT IT20048/83A patent/IT1160804B/it active
  • 1983-03-11 FR FR8304076A patent/FR2523003A1/fr not_active Withdrawn
  • 1983-03-11 DE DE19833337011 patent/DE3337011T1/de active Granted
  • 1983-03-14 BE BE0/210311A patent/BE896148A/fr not_active IP Right Cessation

Patent Citations (4)

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