RU2083327C1 - Mold for manufacture of products from (self-inflammable) mistress - Google Patents

Abstract

FIELD: manufacture of products from (self-inflammable) mixture. SUBSTANCE: the offered mold has thin pressing disk between punch and heat insulator. Expansion during heating of thin disk do not cause its wedging in die. Conjugation of cold pressing disk with die is accomplished with minimal, particular, zero clearance. This excludes or reduces to minimum the phenomenon of back pressing of heat insulator out of die at the stage of application of pressing force. As a result, dimensional accuracy of product is increased as well as product yield. Thickness of pressing disk is calculated by formula offered by the invention description. EFFECT: higher efficiency. 1 dwg

Description

 The invention relates to powder metallurgy, in particular to devices for producing products from refractory compounds and alloys.

 A known mold for the manufacture of products from SHS mixtures containing a punch and a closed matrix, which are made of graphite. To reduce heat loss during combustion of the billet charge, the matrix walls are heated by induction heating.

 A disadvantage of the known mold is that, due to the low strength of graphite, the compression pressure of the combustion products is negligible and is only 5 6 MPa. This pressure is not enough to obtain products with a high density of material. The maximum relative density of the compressed products is 0.75 0.83. The disadvantage is that the tool made of graphite is disposable.

 The noted drawbacks are not present in a metal, in particular steel, mold, in which a heat-insulating shell is provided between the hot combustion products and the inner surface of the matrix.

где δ величина радиального зазора между матрицей и пуансоном;
p давление прессования;
[τ]_c допускаемое напряжение среза материала пресс-шайбы.A mold for manufacturing products from SHS mixtures is proposed, containing a punch, a closed matrix filled with a loose heat insulator and consisting of a base, a housing and a ring placed between them with a device for initiating a combustion reaction, and a press washer, the press washer being made in the form of a plate with a thickness calculated by the formula:

where δ is the value of the radial clearance between the matrix and the punch;
p pressing pressure;
[τ] _c permissible shear stress of the material of the press washer.

 As a first approximation, we can take h 0.01d, d the diameter of the matrix.

 A significant difference of the proposed device is that between the punch and the heat insulator placed a press washer of small thickness. The expansion during heating of a thin press washer does not cause it to jam in the matrix, since friction against the matrix walls and the radial stiffness of the press washer will be insignificant due to the small thickness. Therefore, the pairing of the cold press washer with the matrix is performed with a minimum, in particular with zero clearance. This eliminates or minimizes the phenomenon of reverse extrusion of the heat insulator from the matrix at the stage of application of the pressing force. The field of axial deformations in the heat insulator and combustion products will be uniform, and the distortion of the product shape will be minimal. As a result, dimensional accuracy of the product and yield increase.

 The drawing shows a General view of the proposed mold.

 The mold contains a closed matrix, which consists of a base 1, a ring 2 with an initiating device and a housing 3. A spiral 4 of the initiating device is connected to a DC or AC power source. The cavity of the matrix is filled with a loose heat insulator 5, inside which a billet 6 is placed. A die 7 is installed in the matrix with a guaranteed gap and a press washer 8 with zero clearance.

 The operation of the device is as follows.

 The cavity of the base 1 is filled with a loose heat insulator, for example river sand. On the sand in the center of the base 1 is placed a blank 6, which is a compressed briquette from an exothermic mixture of powders. A ring 2 with a spiral 4 is installed on the base 1. Then, the cavity of the ring 2 is filled with sand and a press washer 8 is installed on top. Assembly of the mold is completed by installing the housing 3 and the punch 7. The assembled mold is placed under the press, an electrical impulse is applied to the spiral 4 and carry out the ignition of the billet 6. The combustion of the exothermic mixture proceeds in the mode of self-propagating high-temperature synthesis. After the passage of the combustion wave over the entire volume of the workpiece 6, the hot combustion products are pressed together with the heat insulator. Then carry out the exposure for a predetermined period of time, relieve the pressing pressure, disassemble the mold and remove the finished product. Press washer 8 is installed in ring 2 with zero clearance. The absence of a gap eliminates the reverse extrusion of the heat insulator 5 from the matrix at the pressing stage. The seal of the heat insulator and the combustion products occurs uniformly throughout the cross section of the matrix and the shape of the product is not distorted. At the stage of exposure under pressure, the press washer 8 and the punch 7 are heated and expanded. To avoid jamming, the gap between the cold punch and the die is larger than the radial expansion of the punch when it is heated in a single pressing cycle. Therefore, when disassembling the mold, the punch 7 is easily removed from the die. The press washer 8 installed in the matrix with zero clearance is pressed into the ring 2 during heating at the holding stage. However, due to the low radial stiffness, removing the press washer from the ring does not require much effort. In addition, due to the low mass and heat content, the press washer cools quickly and decreases in size. This facilitates the process of disassembling the mold.

 The thickness h of the press washer is calculated from the shear strength of the annular belt.

где δ величина радиального зазора между матрицей и пуансоном;
p давление прессования;
[τ]_c допускаемое напряжение среза материала пресс-шайбы.

where δ is the value of the radial clearance between the matrix and the punch;
p pressing pressure;
[τ] _c permissible shear stress of the material of the press washer.

The SHS-pressing process is carried out at pressures p 150 200 MPa. The clearance for molds with a diameter of d 100 115 mm is δ 0.25 0.4 mm. The allowable shear stress for carbon steels is [τ] _c = 60 MPa. Then, for the considered tool size, the thickness of the press washer is h 0.8 1.0 mm or, to a first approximation, h 0.01d.

 Example. A square plate with a nominal size of 70 x 70 x 7 mm is made from a SHS mixture corresponding to the production of a STIM-5 grade alloy. Synthesis and pressing are carried out in a mold with a diameter of 125 mm on a D-1932 press with a nominal force of 1600 kN.

Option 1. Pressing the combustion products together with the heat insulator is carried out directly by the punch. To avoid jamming, the coupling of the punch 7 with the ring 2 is made with a radial clearance of 0.25 mm The thickness of the synthesized workpiece in the middle part is 7.2 mm, in the corner zones
9.5 mm, i.e. the thickness difference is 2.3 mm.

 Option 2. Pressing of the combustion products and heat insulator is carried out through a press washer 8 with a thickness of 1.2 mm, which is cold mounted in ring 2 with zero clearance. The synthesized preform in the middle part has a thickness of 7.2 mm, in the corner zones of 8.0 mm. The thickness difference is 0.8 mm or decreased by 3 times compared to option 1.

 Thus, the proposed mold, equipped with a press washer of small thickness, allows the manufacture of products from SHS mixtures with minimal distortion of the shape specified by the original charge billet.

Claims (1)

Mold for the manufacture of products from SHS mixtures, containing a punch and a closed matrix consisting of a body and a base, characterized in that it is equipped with a press washer, a ring placed between the base and the body, and a device for initiating combustion reactions, the matrix is filled loose heat insulator, and the press washer is made in the form of a metal plate with a thickness

where δ is the value of the radial clearance between the matrix and the punch;
P pressing pressure;
[τ] _c permissible shear stress of the material of the press washer.