DE1195910B - Process for making cast hollow turbine blades - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. CL:

B22d

German class: 31c-5/03

Number:
File number:
Registration date:
Display day:

1195 910
G 28786 VI a / 3 Ic
January 13, 1960
July 1, 1965

The invention relates to a method of making cast hollow turbine blades with webs that are located in the cavity and connect the blade walls by forming a destructible one Core corresponding to the cavity. Coating the core with a melt-out modeling compound for Formation of the blade walls and the webs, embedding of the lost model with the enclosed therein Core in a refractory material, melting out of the model to form the casting space, casting the shape so formed and removal of the core.

For the production of an impeller with solid blades in the sand casting process it is known that Holes in the sand mold, which are used to form the massive blades, through removable elastic ones Keeping plates open. This method cannot be used for the formation of hollow turbine blades. The invention therefore uses the lost wax process, which is particularly advantageous for small components. In this case, however, the formation of the core for the cavity of the blade causes difficulties, since this is tedious and thus the pace of manufacture is limited. Another difficulty is with hollow turbine blades in that only very small openings for the mechanical removal of the core after casting To be available.

The pull-through process is also used for the production of cylindrical sieve cores from sand and water glass Known in one-piece forms to make the openings in the subsequently to be dried To form core.

The invention makes a quick and convenient one Manufacturing process for cast hollow turbine blades with their blade walls joining Bridges created.

The method according to the invention consists in that the core is formed in a core forming device the two mold halves to form a core mold space for a plastic ceramic Molding compound to be produced core and extending through the core mold space and pull-out Metal pins for the formation of openings in the core, which have the webs to be formed the blade are arranged and designed accordingly. In a further embodiment of the invention The method is proposed that the core is formed from ceramic material and after the pouring of the mold is removed by a solvent, making the quick and flawless Removal of the core is guaranteed. With an in

Process for the production of cast
hollow turbine blades

Applicant:

General Motors Corporation, Detroit, Mich.

(V. St. A.)

Representative:

Dipl.-Ing. K. Walther, patent attorney,

Berlin 19, Bolivarallee 9

Named as inventor:

Hamilton Lee McCormick, Carmel, Ind.

(V. St. A.)

Claimed priority:

V. Sf. v. America January 22, 1959 (788 429)

This way guided method for the production of a blade with a double plate, which with a Blade root is connected by shafts to form an opening to the cavity of the blade, Finally, it is proposed that the core marks form the openings for the supply and discharge serve the cooling air.

The invention is described with reference to the drawings. In this is

1 shows a section through a core forming device,

F i g. 2 a section through the core forming device with parts in a different position,

F i g. 3 is a view of a core formed in the core forming device;

Fig. 4 is a cross section along the line 4-4 of Fig. 3,

5 shows a side view of a hollow turbine rotor blade cast with the aid of the core according to FIG. 3;

F i g. 6 shows a cross section through the blade according to the line 6-6 of FIG. 5,

F i g. 7 is a perspective view of the blade in the direction of arrows 7-7 of FIG. 6 seen and F i g. 8 shows a section through the finished blade along line 8-8 in FIG. 6th

The F i g. 1 and 2 show a core molding device for producing a core which is used for casting a hollow turbine blade is used. The facility

509 598/314

device has an upper mold half 10 and a lower one Mold half 12 which rests on a base plate 13. In the closed position, the mold halves form 10 and 12, a core mold cavity 14 having the shape of the one shown in FIGS. 3 and 4 has the core shown. In A sprue 16 through which the core material is injected is formed in the mold halves. It is further a riser opening 18 is provided through which the air can escape from the core mold cavity and which takes up the excess core material as the core mold device is filled.

There are holes 20 in the upper mold half 10 and the same in the lower mold half 12 A number of corresponding holes 22 are present, which are aligned in a direction perpendicular to the holes 20 lie. In the closed position of the mold halves 10 and 12, metal pins 24 extend through the Holes 22, the core mold cavity 14 and the holes 20. Each of the metal pins 24 is in one vertically adjustable block 26 fixed in a chamber 28 of the base plate-16 under the lower Mold half 12 is provided. The block 26 can be secured by rods 30 between the positions shown in FIGS. 1 and 2 positions shown are moved. Are the mold halves 10 and 12 in the closed and the block 26 in the upper layer, as shown in FIG. 1 is shown, the metal pins 24 protrude through the Core mold cavity 14. If the block 26 is in the lower position according to FIG. 2, so are the metal pins 24 pulled out of the core mold cavity 14.

As already mentioned, the core mold cavity 14 in FIG. 1 the shape of the core to be formed according to Fi g. 3. This core has a part 32 for the formation of the cavities in the blade profile and a Foot part 34 for forming a channel in the blade root which forms the access to the hollow blade profile. The part 32 has perforations 36 that are spaced apart from one another, as shown in FIG. 3 and 4 shown is.

The core is produced in the following way: A plastic ceramic molding compound is prepared, which is injectable into the core mold and not excessively in the subsequent firing shrinks or warps and the temperature shock when it comes into contact with molten metal endures. In addition, the ceramic molding compound must be suitable for after the metal casting process leached or otherwise removed.

A suitable ceramic molding compound contains oxides of aluminum and silicon, a plasticizer and a binder such as polystyrene. Such ceramic ones suitable for these purposes Molding compounds are commercially available. As a particular example of a suitable ceramic molding compound indicated a mixture of the following composition: 84 parts by weight of clay, 5 parts by weight Shellac, 5 parts by weight Ethocel, 0.2 parts by weight stearic acid, 2 parts by weight kerosene, 2 parts by weight butyl phthalate, 0.5 parts by weight oleic acid and 2 parts by weight of n-butyl stearate.

A preformed and preheated cake of the plastic ceramic is used to manufacture the core Molding compound inserted into a cavity, not shown, of the core molding device, whereupon it is pressurized to be brought through the gate 16 into the core cavity 14 to will. Thereafter, the metal pins 24 are withdrawn from the core cavity 14 by the block 26 is moved to its lower position. The mold halves 10 and 12 are then opened as shown in FIG. 2 is shown. The core is then dried and fired.

After the core has been manufactured, it is covered with a meltable model mass and that formed lost model embedded in refractory material.

ίο The meltable model mass is advantageous made of a material that melts at a low temperature, such as wax, or thermoplastic Materials. Satisfactory results have been obtained with polystyrene, albeit other thermoplastic ones Materials are suitable, such as resinous polymerized derivatives of acrylic acid or methacrylic acid.

The lost model can be formed in that the core, as shown in FIG is inserted into an injection device, not shown, which is one of the shovels to be cast corresponding cavity, the core through the ends of the part 32 and the foot part 34, which as Core supports act, is supported. The model compound is injected around the core so that a lost model is formed which corresponds to the blade to be cast later. In Fig. 5 is that formed lost model indicated by the dashed lines.

The surface of the lost model is then first coated with a ceramic material, to achieve a smooth casting surface in the refractory mold to be formed. This coating material consists of an aqueous dispersion of finely divided refractory material, a binder, such as z. B. an air-drying silicate cement, defoaming agents and wetting agents.

The cast-out model is coated by immersing it in the solution. The solution will be kept in constant motion by stirring with the exception of the actual immersion time. The stirring process but should not be such that air is unnecessarily introduced into the mixture. as well When immersing the lost model, care should be taken to ensure that the lost model do not form any air pockets. Usually the solution is immersing the lost cast Maintained at room temperature because too high a temperature will destroy the lost metal model could. Excess coating material is allowed to drain off before further processing and wrapping of the lost model takes place.

After the lost model is completely coated, the surface of the coating material z. B. by sanding od. Like. Roughened to better adhesion between the coating and to secure the main part of the refractory mold. After all cast surfaces of the lost model are well covered with sand, the lost model and the core enclosed by it are air-dried.

An enveloping form (not shown) made of a relatively coarse refractory material is used then formed around the lost model. On the lost model, sprues are made from the same Material like the lost model that extends through the wall of the refractory mold. When melting out the melted-out

model the escape of the material of the lost model and at the same time form inlets for the molten cast metal. The refractory mold can be used around the lost model in any suitable manner are formed, so that a more detailed description appears dispensable. Of the possible procedures however, in order to form the main part of the refractory mold, the following is preferable. The refractory mixture is mixed with a certain amount of a liquid binder and then into a suitable one Poured in the form that is shaken when pouring. Then the mixture is allowed to set. Of the The main part of the refractory mold can be made of a silicone with an ethyl silicate binder or else any other suitable covering material. An example of a dry mix, which can be used is indicated. It contains large proportions of finely ground chamotte and Silica powder and small amounts of magnesium oxide and borax glass. The binder for this mixture can be an aqueous solution of condensed ethyl silicate, ethyl alcohol and hydrochloric acid. In education the shape are the core marks of the core, which, as shown in FIG. 5 indicated, about the lost model protrude, embedded in the refractory material, so that the core is supported in the mold is.

If the refractory material has set or solidified to a sufficient extent, heat is generated supplied to melt out the lost model, its material through the sprues of the mold drains.

After the material of the lost model has flowed off, the Cast metal cast that fills the cavity created. After the cast metal has solidified the casting is exposed by breaking the mold. At this point the casting has essentially the form of the in F i g. 5, but there is the core shown in dashed lines still in the shovel. The casting is then immersed in a solvent which dissolves the core or leached out. A suitable solvent for this purpose is a molten reducing agent Salt that does not have a harmful effect on the cast metal. Such salts are known to be commercially available.

As FIGS. 5 to 8 show, the blade 38 formed has a hollow blade profile part 40 with Web 42, which are transversely between the concave blade surface 44 and the convex blade surface 46 extend. The webs 42 stiffen the hollow blade so that the blade walls 44 and 46 are continuous can be poured thinly. These walls can therefore expand evenly, whereby the possibility of heat cracks due to uneven expansion is reduced.

The webs 42 also serve to dissipate the heat from the outer surfaces of the blade in the latter Interior space where the heat is given off to the coolant flow that is conducted through the blade. As FIGS. 6 and 8 show, the webs 42 are thin and uniform over the greater part of the airfoil part distributed.

As shown in FIG. 7, the finished blade has, in addition to the blade profile part 40, a base plate 48, a Shank 50 and a foot 52. The foot portion 34 of the core (FIG. 3) forms an opening 54 in the shank of the ίο Shovel through which air can enter the shovel.

Claims (3)

Patent claims: 1. Process for the production of cast hollow turbine blades with lying in the cavity, the webs connecting the blade walls by forming a destructible core accordingly the cavity, coating the core with a fusible mass of fashion to form the blade walls and the webs, embedding the lost model with the enclosed therein Core in a refractory material, melting out the model to form the casting space, Pouring off the mold thus formed and removing the core, characterized in that that the core (32) is formed in a core mold, the two mold halves (10, 12) to form a core mold space (14) for the one made of a plastic ceramic Molding compound to be produced core and through the core molding space extending and pull-out metal pins (24) for formation of perforations (36) in the core, which correspond to the webs (42) to be formed of the blade are arranged and designed. 2. The method according to claim 1, characterized in that the core made of ceramic Material is formed and removed by a solvent after the mold has been poured. 3. The method according to claim 1 for producing a blade with a base plate with a blade root connected by shafts to form an opening to the cavity of the blade is, characterized in that the core marks (32,34) to form the openings serve for the supply and discharge of the cooling air. Considered publications:
German Patent Nos. 737479, 860438, 904610; German Auslegeschrift No. 1032 898;
British Patent Nos. 731292, 742476, 781492; U.S. Patent No. 2,801073;
"Metall", 1957, pp. 1066 to 1069;
"Journal of the Association of German Engineers", issue January 1956, p. 97. 1 sheet of drawings 509 598/314 6.65 © Bundesdruckerei Berlin