Duan C.G., Karelin V.Y. Abrasive Erosion and Corrosion of Hydraulic machinery

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Abrasive Erosion and Corrosion of Hydraulic Machinery

(2) Technology of painting

(a) Preparation of composite nylon powder

Nylon Powder must be dried for 8 hours at the temperature ranging

from 75°C to 80°C and epoxy powder has to be put on dried

conditions.

(b) Clarification on the surface of component

The cleaning measure is the same as that adopted in epoxy emery

coating.

The preheating is necessary also as above-mentioned

(d) Painting

Composite nylon coating materials are made to powder through

grinding, and the flame spraying measure is used to implement the

painting process. When the component is heated to 250°C, the

composite nylon powder is quickly sprayed upon the component, and

making to the formation of coating. The powder spraying duration

should be short as much as possible from the thin position to the thick

one.

To the position where erosion is serious, the thickness of coating

could be larger to certain extent which can be completed through two or

three layers with spraying.

In order to improve the adhesive strength, the coating material in

the bottom sheet should be selected from polymers possessing excellent

adhesion with surface of

metal,

on which copolymers binary nylon with

good tenacity is covered.

(e) Cure and anneal

For the component with large thermal capacity, curing temperature can

be relatively low because it takes time to cool down.

Some of big molecule of the melted high polymer are forced to

deform in the process of painting, and which, however, have the

tendency to recover in aggregation freely at the formation of coating

with the generation of contraction stress, and at this moment the

thermal stress is produced because of non-coincidence of thermal

expansive coefficient between the coating and the metal on the critical

surface of adhesion while annealing treatment is available for internal

stress reducing purpose.

Erosion - Resistant Materials

305

(3) Application in practice

Composite nylon coating was tested in the pumps installed at the Jia Ma Kou

Pumping Station on the Yellow River, and the coating in operation of more

than 4,000 hours without damage. The same achievement have also been

obtained in several other pumping stations.

According to the experience for years, it is quite valid to use composite

nylon coating in pumping stations. But in the case of water turbine with big

components, reparation readily appears at the position of strong cavitaition

because of the affects resulting from the variation of temperature and the

decline of adhesive strength. Powder with low melting point and local thermal

spraying should be further studied.

5.6.3 Rubber Coating of Polyurethane

Many sorts of elastic coating materials exist for the erosion-resisting

protection in hydraulic machinery. Simple introduction of a polyurethane

rubber coating with good achievements in the operation of prototype machines

is herewith given. The physic-mechanical property of Jj polyurethane rubber

is shown in Table 5.24.

Because this sort of Polyurethane rubber is obtained through pouring, the

appropriate mould has to be manufactured, in which certain distance is

required between the inner surface of the mould and the outer surface of the

component, and the value of distance is determined by the thickness of rubber.

Table 5.24 Physical-chemical property of J

polyurethane rubber

Molecular weight

Tensile strength (kgf/cm

)

Percentage elongation (%)

Stable percentage elongation (%)

Hardness

Tearing strength (kgf/cm

)

Permanent deformation (%)

1000

400 ± 40

450-560

90-

170

70-95

50-80

<10

1700

300 ±30

500-580

80-

130

70-90

60-80

<12

2000

280 + 30

450-550

80-130

70-85

50-75

<14

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Abrasive Erosion and Corrosion of Hydraulic Machinery

The surface of blades should be treated carefully through shaping and

manufacturing. And then clarify the surface of component: The solution

containing 1.5 percent of KH-550 anhydrous ethanol with coupling agent is

painted upon the surface of component. The mold-releasing agent of silicone

grease is painted in the region where there is no requirement for rubber

pouring process.

The component that has been clarified is put into the oven where the

component is heated to the rated temperature and keeps this level for one

hour, and then the adhesive of

821

that has been allocated is sprayed upon the

surface of component with powder spraying gun. At this moment, the

component is put into the mould and as the temperature of the mould reaches

80°C or so, the gluing material is poured into the void between the component

and mould to form the composite layer.

After the pouring, the mould has to be heated to 120°C for vulcanization

of rubber, and core of adhesive, and then the mould can be released. Finally,

the component with the composite layer is heated to 120°C and kept in this

temperature for 2 hours in order to make it vulcanized kept in further.

In order to examine the erosion and cavitation-resisting property of

several metal and non-metal materials developed in recent years, Chinese

Ministry of Water Conservancy and Electric Power has organized an

industrial comparison experiment for erosion-resisting materials in a Hydro-

electric Power Plant in Shanxi Province. Sixteen sorts of metal and non-metal

materials are examined. In the year of 1980, the experiment started to test

until the end of 1985. Three Kaplan water turbines are installed at this power

plant with average sand content being 48.28 kg/m

. The blades of water

turbine that are cast by cast steel 2G30 are seriously damaged in after running

for 1500 hours.

pouring polyurethane rubber composite coating obtained the best

evaluating among all the materials that were tested. After running for 12,320

hours,

the blades with the bottom sheet made up of SE 822 adhesive, was not

damaged at all on the pressure side, and only 5 cm

was found to be damaged

on the suction side, amounting to 0.2 percent of the total area.

It has to be pointed out that the application of this material is limited to

some extent because of its pouring formation, complex technology and high

costs for mould manufacturing aspect.

Erosion

- Resistant Materials

307

5.6.4 Composite Enamel Coating

(1)

Characteristics

and prescription

Composite enamel coating has high hardness, smooth surface and good

property in anti-erosion and anti-cavitation. The enamel coating is hard and

brittle, against that the collision should be avoided. The composite coating

consists of bottom glaze and surfece

glaze,

the prescription of which is shown

in Table 5.25 and Table 5.26.

Table 5.25 Main composition for bottom glaze

Glaze

No.

Percentage of raw material (%)

Si0

42.8

83.2

47.3

4.6

6.9

8.7

10.5

8.0

3.8

10.1

7.4

11.5

20.0

13.4

18.7

CaF

3.9

8.9

6.6

CoO

MnO

5.9

AlF

Table 5.26 Main composition for surface glaze

Raw material Si0

Percentage (%) 68.2 3.5 16.7 3.5

(2)

Operation technology

(a) Treatment on the surface

The measure of treatment upon the surface is the same as that used in

the epoxy emery coating.

(b) Preparation for

glaze

slurry of enamel

All the raw materials with appropriate proportion are put into the

melting pot at the temperature that is higher than

1,350°C

to be melted

into glass-like liquid, and then quenched with water and finally grained

into powder. Lapping materials, i.e. viscous soil, alumna and borax

etc.,

are added to obtain

the

bottom glaze and surface glaze.

308 Abrasive Erosion and Corrosion of Hydraulic Machinery

The surface of component has to be grained with abrasive cloth, on

which the bottom glaze is sprayed, and is sent inside the flame

separation furnace with the burning temperature being 900°C. The

burning temperature for the slurry of surface glaze is about 850° ~

900°C. The multi-burning technology should be adopted for

components with large gradient of thickness, keeping the average

temperature to avoid the phenomenon of over-burning or under-

burning.

(3)

Application in practice

After running for

5,520

hours at a power plant where axial-flow stables blade

water turbines are installed with annual average silt content being 104 kg/m

the composite enamel coating on the runner blades are still perfect, except

having slight damage at the outer rim of trailing edge. The composite enamel

coating has not separated from trailing edge surface until the turbine operates

for 22,515 hours. But the previous blades of cast steel 2G35 are seriously

damaged after only running for

4,871

hours.

The application of composite enamel coating is limited to some extent

because it's processing technology is some complicated for the component

largess and it seems to be impossible to repair the damaged local composite

coating at power plant site.

5.7 Surface Treatment against Erosion Damage

E. Chen

The heat treatment of component surface is one of

the

measures to raise the

resistance to abrasive erosion and cavitation erosion of hydraulic machinery

components. The heat treatment can increase the hardness of the surface of

components in the erosion-resisting purpose.

There are various sorts of heat treatment, but few of them is adaptive for

erosion protection in hydraulic machinery, because the requirements of not

only high hardness and low brittleness but also that a certain thickness of

resistant erosion layer on surface is required as well. The heat-treatment

measures should satisfy this requirement for hydraulic machinery.

Erosion - Resistant Materials

309

The adaptive heat treatment measures which can satisfy the above-

mentioned requirements are briefly introduced in this section.

5.7.1 Quenching and Tempering

It is known that quenching makes the metal phase changing and obtains

martensite and residual austenite. The erosion-resisting property of the treated

metal can be increased with the rising of hardness. Main change in the

tempering is the decomposition of martensite and the transform of residual

austenite. Tempering can improve in the brittleness and eliminate the stress

that is caused by quenching. Appropriate controlling on the tempering

temperature can raise the erosion-resisting property for carbon steel,

especially for alloy steel. Although the low temperature of tempering can raise

hardness and anti-abrasiveness, it can also lead to increase of

brittleness.

The

temperature of tempering, therefore, is ranging from 220°C to 600°C.

5.7.2 Diffusion Permeating Plating

The principle of diffusion permeating plating is as follows: high temperature

(800° ~ 1000°C) treatment on the surface makes the metal or non-metal

elements diffusing into the inner layer of component, forming the surface layer

made up of these elements. One can obtain the various sorts of surface layer

with the different elements permeated into the component, improving the

erosion-resisting property. Carbon permeating, nitrogen permeating. Ion-

bombarded heat treatment is used for increasing erosion resistance of

hydraulic machinery.

(1) Carbon-permeating

method.

Carbon-permeating method is a chemical measure that is widely used in the

mechanical manufacture. In this measure, the component is put in the

reducible CO gas, or in the carbonator, and is heated to 910° ~ 980°C, then to

keep this temperature while the active carbon atoms produced on the surface

of component by the permeated carbon medium, which will make carbon

permeated into low carbon steel or low carbon alloy steel through the

absorption and diffusion on the surface. After the permeation, quenching and

tempering are required in order to guarantee high hardness, high abrasiveness

and coordination of tenacity in the center for the permeated component. With

this treatment, the component can reach 720 ~ 900 Hv in hardness and

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Abrasive Erosion and Corrosion of Hydraulic Machinery

abrasiveness can be greatly improved. The depths of carbonized layer is

usually ranging from 0.5 ~ 2.5 mm, and even 4 ~ 10 mm for some special

component.

(2) Co-permeation of carbon and nitrogen

Carbon and nitrogen can be permeated into metal at the same time, which

possesses the following advantages as compared with carbonization: The

surface of co-permeation has high hardness, abrasiveness and fatigue strength

than carbonization, and at the same time nitrogen reduces austenite-forming

temperature. Therefore, copermeation can be proceed with at low temperature

keeping the component will not be overheated and direct quenching is valid

with small deformation.

Now gas of carbon and nitrogen is widely used at co-permeation, in which

ammonia gas is added and the component is heated and quenched in this

medium. The hardness on the surface using this treatment can reach to Hrv

1580 ~ 1590, and with the depth of permeation being

mm.

(3) Ion-bombarded heat treatment

With the development of plasma physics and vacuum technology, the method

of ion-bombarded heat treatment has appeared. This category of measures

includes ion nitrogenation, ion permeation of carbon, ion co-permeation of

carbon and nitrogen, ion copermeation of sulfur and nitrogen, and permeation

of ion into metal, etc.

As compared with chemical heat treatment, ion-bombarded heat treatment

has its own advantages: it shortens the production period and can control the

phase construction on the surface, obtaining excellent properties; the bright

surface, energy-saving purpose and harmlessness can be achieved because of

sputtering phenomenon.

When the Gas of C-H series passes the furnace in which the component is

put in and heated at pressure-reducing atmosphere, at the moment a high

voltage is imposed between the positive polar and the component, glow

discharge will rise with producing plasma. Rapid reduction of voltage around

the component forces the carbon ions accelerated to bombard the surface of

component that is then carbonized. This makes surface of component be clear,

energy saving and harmless. The depth of permeation can reach 1mm.

Ionic carbonization is superior to traditional carbonization in mechanical

performance if carbon density is constant throughout the depth of permeation.

After experiencing 90 minutes of ionic carbonization, the surface hardness of

Erosion - Resistant Materials

311

steel containing 0.3% of

carbon,

0.69% of

manganese,

1.15% of chrome and

0.24% of molybdenum can reach 900 Hv, which is 50 Hv higher than

traditional gas co-permeation of carbon and nitrogen.

This new technology of ionic carbonization is at its primary stage in

resisting erosion and cavitation of hydraulic machinery.

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Abrasive Erosion and Corrosion of Hydraulic Machinery

References

5.1 Boldy A.P.and Duan C.G., (1990). 'The Current State of Technology

in Hydraulic Machinery', Gower Technical.

5.2 Duan, C.G., (1998). 'Approach to the Demand on Anti Abrasive

Erosion from Hyduaulic Machinery Project', Proceedings of19

IAHR

Symposium on Hydraulic Machinery and Cavitation, World Scientific,

Singapore, Volume 1, pp. 59 ~ 69.

3 Duan, C.G., Tanaka, H., Zhao K., Han S.H., and Zhao, X.L., (1987).

'Multipositon and multimetering scheme for silt erosion test of

hydraulic machinery', Proceedings of the 2nd China-Japan Joint

Conference on Fluid Machinery.

4 Duan, C.G., (1982). 'Sand Particles Erosion of Water Turbine', Press

of Tsinghua Univ., (in Chinese)

5 Ebata, M., (1988). 'Amorphous Alloys Coating', Maintenance, No.92,

January, pp. 19 ~ 25.

5.6 Hojo, H., Tsuda, K. and Cao M.T., (1980). 'Erosion Damage of

Polymethy 1 Methacrylate', Journal of the Society of Materials

Science, Japan, 1980, No.332, July, pp. 731 ~ 735.

7 Matsumura, M., Oka, Y., Ebara, R., Kobayashi, T. Odohira, T.,

Wada, T. and Hatano, M., (1989). Submitted to ASTM.

8 Mitsui SRC Development Co., LTD, Toyo Engineering Corporation

and Yamatake Honeywell Co., LTD, (1988). Report on Coal

Liquefaction Technology, Tokyo.

9 Oka, y., Ogasahara, T., Yamawaki, M. and Matsumura, M., (1986).

'Slurry Erosion-Corrosion on Commercially Pure Iron in Vibratory

Testing Facility', Boshoku Gijutsu, vol. 35, No.4, April, pp.223 ~ 229.

5.10 Oka, Y., Matsumura, M., Yamawaki, M. and Sakai, M., (1987). 'Jet-

in- Slit and Vibratory Methods for Slurry Erosion-Corrosion Tests of

Materials', Slurry Erosion: Uses, Applications and Test Methods,

ASTM STP 946, J. E. Miller and F. E. Schmidt, Jr., Eds., American

Society for Testing and Materials, Philadelphia, pp. 141 ~ 154.

Erosion - Resistant Materials 313

5.11 Owada, S., Nakai, Y., Ikeda, Y., Nakarai, T. and Kobayashi, T.,

(1986).

'Manufacture and Property of Room-Temperature Curing

Type of Polyurethane Lined Steel Pipe for Abrasive Slurry

Transportation', Proceedings of the Eleventh International

Conference on Slurry Technology, Hilton Head, South Carolina, USA,

pp.

293 ~ 302.

5.12 Sheldon, G.L. and Finnie, I., (1966). 'On the Ductile Behavior of

Nominally Brittle Material during Erosive Cutting', Journal of

Engineering for Industry. Trans. ASME, Series B, vol. 88, No. 4,

November, pp. 387 ~ 392.

5.13 Shetty, D.K., Wright, I.G. and Claver, A.H., (1983). 'Wear of

Ceramics by Erosive Slurry', Proc. 6th Int. Conf on Erosion by

Liquid and Solid Impact, Cambridge, England, pp. 621 ~ 629.