RU2585604C1 - Mould for centrifugal end shaped castings from refractory and chemically active alloys - Google Patents

Abstract

FIELD: technological processes.

SUBSTANCE: invention can be used in producing large-size cast parts of aircrafts and nuclear equipment operated at high loads. Mold comprises metal tray with centering device, graphite inserts and forming metal inserts installed in tray. Metal jacket made in form of truncated cone is attached to tray by means of screw connections. On jacket there is detachable crucible with gating system including runners. Tray is equipped with fasteners, connecting and retaining graphite inserts and metal inserts. Crucible is made from titanium and runners are made from steel, cast iron or titanium and have shape of trapezoid in cross-section.

EFFECT: higher precision of fabrication of parts.

1 cl, 15 dwg, 2 ex

Description

The invention relates to the field of metallurgy, specifically to titanium-based alloys, and can be used to obtain large-sized cast parts of aircraft, helicopter and rocket engines, as well as other cast parts of aircraft operating under high loads, for example cast parts of the "separation body" aircraft engine, hull power parts of aircraft, etc., as well as for parts of nuclear energy.

The details of aircraft engines differ in complex shape and small wall thickness (minimum 2.5 mm), so they are usually made of titanium alloys of the type VT20L, VT5L (TU 1-92-148-91), etc. mainly by centrifugal casting: in shell molds made by the technology of investment casting. In world practice, investment casting methods usually produce castings having overall dimensions up to 600 mm. The manufacture of large castings is associated with difficulties in achieving the required dimensional accuracy. This is due to so many factors: the inconsistency of the temperature regime during the production and storage of models and refractory shells, the inconstancy of the composition and properties of materials of model masses, binders and ceramics, warpage of models and blocks during the formation of shells, removal of the model composition, heat treatment of molds and their storage . It is very difficult to determine at what stage of the technological chain the deviation of the mold dimensions from the set occurs, therefore, the development of this technology requires a long time and high material costs associated with the repeated manufacture (correction) of foundry equipment.

Molds made using model-less technology are also used in the manufacture of large castings and provide their accuracy far exceeding the accuracy achieved by casting in shell molds.

The essence of the model-free technology of large-sized titanium casting is the manufacture of a mold from graphite blanks by processing them on milling 3-5-coordinate machines with numerical control (CNC). In domestic practice, there are examples of the manufacture of castings using this technology, but it is still not used in the aircraft industry. In world practice, such a method of manufacturing casting molds for castings (not from titanium alloys) up to 2500 mm in size from sand blocks for gravity casting is also known.

The closest analogue of the claimed invention is a casting mold for centrifugal casting of large-sized castings of complex shape from heat-resistant and chemically active alloys, containing a metal pallet with a centering device, a metal jacket attached to the pallet, graphite embedded elements installed in the pallet, a metal receiver with a gating system, including the gating system moves (Sosnenko MN Modern foundry molds, Moscow: Mashinostroenie, 1967, 141-146, fig. 54, p. 120).

This invention does not provide for the manufacture in the proposed casting molds of titanium castings and castings from other heat-resistant chemically active alloys.

The technical result is the creation of a new design of casting molds for large-sized shaped titanium castings of complex shape and large size (over 600 mm) by centrifugal casting for aircraft and nuclear power.

The technical result is achieved by the fact that a mold has been developed for centrifugal casting of large-sized castings of complex shape from heat-resistant and chemically active alloys, containing a metal tray with a centering device, graphite embedded elements and forming metal inserts installed in the tray, a metal jacket made in the form of a truncated cone and detachable metal receptacle attached to the pallet using screw connections, with a gating system including gating passages, Oddone provided with fastening elements connecting and retaining elements embedded graphite and metal parts, made of titanium metal reservoir, a runner moves from steel, iron or titanium and have a sectional shape of a trapezoid.

The invention is illustrated by drawings, where in FIG. 1 shows the construction of a metal tray with which the assembled mold is mounted on a centrifugal table of a melting and casting plant, FIG. 2 shows a diagram of the installation of a jacket on a pallet; FIG. 3 shows the installation diagram of a metal detachable metal receiver with gate runs, FIG. 4 shows a pairing circuit for a detachable metal receiver with gateways, FIG. 5 shows a diagram of a centering device onto which a detachable metal receiver is mounted; FIG. 6 shows a diagram of the simultaneous pouring of several castings into combined molds installed symmetrically with respect to the axis of rotation of the centrifugal table; FIG. 7 and 8 show a computer model of the “Bushing” casting with an outer diameter of 920 mm and a height of 370 mm, which was made by casting in a combined mold with the original design of the gate system, FIG. 9 shows a computer model of the mold assembly; FIG. 10 shows fragments of the form; FIG. 11 shows the finished form on a pallet, in FIG. 12 shows the obtained casting with the remains of a graphite rod; FIG. 13 shows the microstructure of a cast alloy VT20L (sample from a casting body), FIG. 14 shows a computer model of the “Rack” casting with a sprue system for centrifugal casting, FIG. 15 shows the “Stand” casting.

In this case, the form may consist entirely of rods made on 3-5-coordinate CNC milling machines. However, this mold design should only be used for the manufacture of test or piece castings. To implement serial technology, it is proposed to use combined forms, which are a metal chill mold, used repeatedly with graphite embedded elements (rods) of graphite made on 3-5 coordinate CNC milling machines. In this case, the form must meet the following requirements:

- all mold elements must be technologically advanced for their manufacture from graphite on 3-5 coordinate machines;

- the design of the mold must be technologically advanced for its assembly and disassembly;

- the form must guarantee the receipt of castings in accordance with the requirements of the design documentation for the geometry and surface roughness;

- the mold must withstand the pressure from the side of the metal poured into it during centrifugal pouring with the required rotation speed;

- the overall and landing geometrical dimensions of the mold must be consistent with the dimensions of the pouring container of the smelter.

The invention consists in the following.

The mold for centrifugal casting of titanium alloys is a combined design consisting of a chill mold made of cast iron, steel, titanium alloys and graphite embedded elements (rods) that perform complex profiles. High accuracy (depending on the equipment used, from ± 0.2 mm and more precisely) of the manufacture of mold elements allows castings to be obtained that are superior in accuracy to similar castings manufactured by investment casting.

The manufacturing process of castings in combined form consists of the following steps.

Based on the classical design techniques for titanium castings and gating systems, a computer model of the casting and gating system is being developed. At the same time, the minimum wall thickness of the casting is 3.5 mm, which allows to obtain the wall thickness of the part 2.5 mm with a casting dimension of 600 mm or more, after sandblasting without additional mechanical or chemical attack. After modeling the process of centrifugal casting and solidification of the casting in the field of centrifugal forces, the design of the mold is carried out in compliance with the following conditions:

- all mold elements must be technologically advanced for their manufacture from graphite on 3-5-coordinate CNC machines;

- the design of the mold must be technologically advanced for its assembly and disassembly;

- mold elements made of metal (steel, cast iron) should be easily removed from the casting, not have undercuts and structural elements that prevent disassembling and assembling the mold after pouring it;

- mold elements made of metal must be covered with a layer of soot with a torch of a gas burner before pouring;

- the mold should guarantee the casting in accordance with the requirements of the design documentation for the geometry and surface roughness;

- the mold must withstand the pressure from the side of the metal poured into it during centrifugal pouring with the required rotation speed;

- the overall and landing geometrical dimensions of the mold must be consistent with the dimensions of the pouring container of the smelter.

Graphite mold elements are made using CNC machines designed for processing graphite.

Metal mold inserts are manufactured using conventional metalworking equipment.

The mold is assembled using locking mechanisms based on wedge cone mounts.

Before pouring, the assembled form is dried in a heating furnace without using a protective atmosphere at a temperature of 150-300 ° C. Drying time is selected based on the dimensions and mass of the mold in such a way as to ensure the heating of all elements of the mold to the temperature of the furnace.

The dried form is removed from the furnace and mounted on a centrifugal table of the smelter. After that, pouring is carried out similarly to casting into shell molds. Dismantling of the mold is carried out after opening the casting chamber of the smelter. After removing the casting from the mold with graphite inserts, it can be reused with new graphite inserts. Thus, multiple use of one set of molds during a work shift can be ensured.

The proposed form provides the manufacture of large-size castings, including thin-walled castings (wall thickness from 3.5 mm). The maximum size of the casting is limited only by the size of the casting chamber of the foundry.

A schematic of a combined mold for centrifugal casting device is shown in FIG. 1-6. On the pallet 1 (Fig. 1, Fig. 9), mounted on a rotating casting table of the melting and casting plant, an assembled form is fastened, the shaping surface of which is assembled from mold-forming reusable metal inserts 4 (Fig. 3) and disposable graphite embedded elements 5 ( rods) (Fig. 3), performing undercuts in the casting. The form is attached to the pallet with a metal jacket 2 (Fig. 2, Fig 9), having the shape of a truncated cone with an opening angle of 7-13 °, which ensures its integrity during the pouring process and preservation of the given geometric dimensions of the casting. A metal detachable metal receiver is installed on top (Fig. 3 (3-1), Fig. 4 (6)) with gating paths having a trapezoidal cross-section to enable removal of the mold (Fig. 3 (3), (Fig. 4 (7)) so that the elements forming the horizontal gateways (Fig. 4 (8)) coincide with the vertical wells (Fig. 3 (3-2)) that feed the casting. It is also possible to fill several castings in combined forms at the same time, setting them symmetrically relative to the axis of rotation of the centrifugal table (Fig. 6 (10)). In this case, the metal receiver (Fig. 4 (6)) mounted on a special centering device (Fig. 5 (9)). The gateways can be led to the casting both from above and from below (see examples).

The assembled form (Fig. 9, 11) is placed on a rotating casting table of the melting and casting plant and fixed on it (the form fixing scheme depends on the design of the melting and casting plant). Before draining the metal, the form is untwisted up to a certain angular velocity. The resulting centrifugal force provides the necessary pressure in the liquid metal to fill the mold. After the metal is drained, the mold continues to rotate until the liquid metal solidifies.

EXAMPLE 1

The staff of the LTM Information Center and the TLP Department of NUST “MISiS” (Moscow) developed a computer model of the “Casting” casting with an outer diameter of 920 mm and a height of 370 mm, where a gate system with an annular “sectoroidal” metal supply to the casting cavity was used . (Application for RF patent No. 2014126233 dated 06/27/2014). FIG. 7.8 (Computer model of the "Bushing" casting with gating system).

This casting is part of the casting part “Central Bushing” of the separation body of the PD-14 aircraft engine and was designed for manufacturing using model-free technology at the UMPO site taking into account the material equipment of the NIAT 833D melting and casting plant. During the design, the minimum casting wall thickness of 3.5 mm was laid, which allows to obtain a part wall thickness of 2.5 mm, according to LT5 (OST 1 41154-86), after sandblasting without additional mechanical or chemical exposure. The casting was made of VT20L titanium alloy (TU 1-92-148-91), electrode diameter 280 mm, casting table rotation speed 250 rpm. The mass of the drain was approximately 150 kg.

Fragments of the mold and a computer model of the assembled assembly are shown in FIG. 9.10. Finished form on a pallet - in FIG. 11. To ensure fixation of the mold on the casting table, it was assembled on a steel base having a central sleeve coinciding with the axis of rotation of the casting table, and was fixed with a metal jacket that ensured the integrity of the mold during casting and prevent breakthrough of metal through the mold connectors.

The obtained casting with the remains of a graphite rod is presented in figure 12 (Casting obtained by molding in a combined form).

The casting did not have an alpha layer. The structure of the cast metal is typical for the VT 20L alloy, shown in Figure 13 (Microstructure of the VT20L cast alloy (sample from the casting body)).

EXAMPLE 2

The staff of IC LTM and the department of TLP NITU "MISiS" developed a computer model of the "Stoyka" casting, having overall dimensions of 450 × 260 × 200 mm, where the gate system was used by traditional supply of metal into the mold cavity. Figure 14 (Computer model of the casting "Rack" with gating system for centrifugal casting).

This casting is part of the separation housing of the PD-14 aircraft engine and was developed for manufacturing using model-free technology in the NIAT 833D vacuum installation at the site of UMPO OJSC. During the design, the minimum casting wall thickness of 3.5 mm was laid, which allows to obtain a part wall thickness of 2.5 mm, according to LT5 (OST 1 41154-86), after sandblasting without additional mechanical or chemical exposure. The casting was made of VT20L titanium alloy (TU 1-92-148-91), electrode diameter 280 mm, casting table rotation speed 250 rpm. The mass of the drain was 70 kg.

To ensure the fixation of the mold on the casting table, the mold was collected in a standard casting container of the unit and fixed by backfill with a support filler according to the technology of UMPO OJSC, which ensures the integrity of the mold during the pouring process and prevents mold displacement due to centrifugal force. For one discharge, two castings were obtained.

The obtained castings are presented in figure 15 (Castings "Rack" obtained in combined forms).

The castings did not have an alpha layer and corresponded to the requirements of technical documentation.

Claims (1)

A casting mold for centrifugal casting of large-sized castings of complex shape from heat-resistant and chemically active alloys, containing a metal pallet with a centering device, graphite embedded elements and forming metal inserts installed in the pallet, a metal jacket made in the form of a truncated cone and attached to the pallet with screw connections, a detachable metal receiver with a sprue system, including sprue strokes, while the pallet is equipped with fasteners that connect and rzhivayuschimi fitting pieces graphite and metal parts, made of titanium metal reservoir, a runner moves - from steel, iron or titanium and have a sectional shape of a trapezoid.

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