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Fig. I. Diagram of feed of thermal casting assemblies: i) common head; 2) process channel; 3) core; 4) casting body.

This technology can be used in the manufacture of castings for fittings, cocks, petroleum equipment, and other similar shapes. In the foundries of our branch alone, it is possible to obtain several million rubles of profit with small expenditures. It can and should find wide use in other branches of industry.

PLASMA SPRAY-COATING FOR MANUFACTURING NOZZLES

OF STEAM-EJECTOR PUMPS

R. A. Ibragimov, R. M. Galimzyanov, R. A. Shagiakhmetov, V. A. Popov, and E. E. Aver'yanov UDC 621.793:621.526.2

The most important part in a steam-ejector pump is the nozzle for discharge of vapors and gases. The design and quality of the nozzle determine the techno-economic parameters of the pump. Nozzles are currently machined from blanks of 12KhlSNIOT steel. This manu- facturing method requires excessive time and entails large consumption of metal. Moreover, it is difficult to machine nozzles with small inlet and outlet diameters on lathes and to achieve the required finish on the internal surfaces.

In view of the above, it is of interest to manufacture such nozzles by plasma spray- coating of core molds. The basics of this method are as follows. A core mold and appro- priate fixtures are made initially. Therefore, the core mold is spray-coated with power materials in an inert gas plasma. The core mold is then removed to produce the required part with the desired shape and surface finish.

Fig. i. Assembled core mold for a steam- ejector pump nozzle.

Translated from Khimicheskoe i Neftyanoe Mashinostroenie, No. i0, pp. 36-37, October,

1989.

602 0009-2355/89/0910-0602512.50 �9 1990 Plenum Publishing Corporation

Fig. 2. External view of the nozzle blank after removing the mold.

There is practically no published literature regarding manufacture of parts of plasma spray-coating of molds. The technology for producing a few parts and parameters for coating with specific powder compositions are mentioned in [i, 2]. The Vakuummash Prototype plant has developed the technology for steam-ejector pump nozzles: the nozzle core mold material has been selected after considering the coefficient of thermal expansion; materials have been selected for the working and backing layers; various fixtures for different sizes of nozzles have been made; the optimum parameters for plasma spray-coating of the working and backing layers have been selected; and technology has been developed for separating the core molds from the finished products.

The experimental work was carried out on a UMP-6 plasma spray-coating machine using a GNP-0.05/23 plasma generator. The coatings were deposited on core molds consisting of two truncated cones with the parting plane along the smaller diameter. The external surface of the core mold was designe d to correspond to the internal surface of the nozzle.

The nozzle molds were made of 20, 40KhA, and 45 steel. The good finish on the working surface of~the nozzle was achieved by applying chromium plating on the polished surface of the mold. An assembled nozzle mold is shown in Fig. i.

The working surfaces of the molds should have high wear resistance and corrosion resis- tance and should meet the operating requirements. One of the main factors determining the quality and cost of the nozzles is the choice of raw materials used for coating~ The raw materials can be divided into two groups depending on whether they are used for the working layer or for the backing layer. There are different specifications for these two groups of materials.

The materials used for the working layer should have higher hardness, wear and corrosion resistance, ability to fuse in the plasma jet, and permit formation of dense coatings. The materials for the substrates should be more ductile and easy to machine.

The material used for depositing the working layer was PT-19N-01 powder having the following composition (in percentages by weight): 8-14% chromium, 1.7-2.8% boron, 1.2-3~2% silicon, 2-5% iron, 0.3-0.6% carbon, 0.8-1.3% aluminum. The material used for the backing layer was PZh-4 iron powder.

Fig. 3. Mold and machined nozzle.

603

The technological process for manufacturing nozzles of steam-ejector pumps includes the following steps: preparation of the mold; deposition of the working and backing layers; annealing to relieve internal stresses; disassembly of the mold and machining of the blank. The process is carried out as follows.

The chrome-plated and polished mold and mandrel are clamped in a lathe, or other suit- able rotating fixture. The plasma spray-coating device is then prepared for operation. The mold is rotated and heated to about 700~ and the working layer of 1-2 mm thickness is deposited using PT-19N-01 powder. The operating parameters are as follows: rotation speed 315 rpm, current 280 A, voltage 80 V, argon pressure 300 kPa, distance between the mold and plasma generator 120 mm. The backing layer is then deposited using PZh-4 powder, current 260 A, voltage 70 V. The other operating parameters are the same as those used for the working layer.

Internal stresses are relieved after plasma spray-coating by holding the blank in a muffle furnace for 2-3 h at 600~ The blank is then removed from the mold with the help of special screws which are inserted into the threaded holes in the mold. The blank is finally machined to the required external dimensions.

The external view of the blank after removing the mold is shown in Fig. 2 and the mold and machined nozzle are shown in Fig. 3. It can be seen that the new method makes it possible to produce nozzles with much better surface finish on the working surface compared to con- ventional machining. Moreover, the method ensures high productivity and low wastage.

The plasma spray-coating method (with powder materials) was used to produce several sizes of nozzles for steam-ejector pumps, e.g., nozzles of 52 and 63 mm length with 3 mm diameter in the cylindrical part. These nozzles were tested and found to be acceptable.

The time required to produce each of these nozzles was I h compared to 2.5 h by machin- ing which involves 50% metal wastage. Moreover, the plasma spray-coating method helps to reduce labor consumption by a factor of 3 and conserve costly corrosion-resistant steel.

The annual savings accruing from introduction of the new method of manufacturing steam- ejector pump nozzles amount to 33,000 rubles.

LITERATURE CITED

i. A.A. Koval'skii, G. Yu. Poplavskii, and Ya. A. Greiman, Technology for Manufacturing Press Dies by Plasma Spray-Coating [in Russian], LatlNTI, Riga (1971).

2. A.A. Koval'skii, Manufacture of Fixtures by the Plasma Spray-Coating Method [in Russian], LatlNTI, Riga (1977).

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