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Systematization of material consumption norms in spray-coating

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Page 1: Systematization of material consumption norms in spray-coating

Powder Metallurgy and Metal Ceramics, Vol. 33, Nos. 9-10, 1994

S Y S T E M A T I Z A T I O N O F M A T E R I A L C O N S U M P T I O N N O R M S

IN S P R A Y - C O A T I N G

I. M. Lelyukh UDC 621.762

Regulating the consumption of materials is particularly important in the economics and organization of spray-coating

operations. Three main factors are taken into account when establishing norms for the consumption of the materials of the coating: the physicomechanical and chemical properties of the particles; the shape of the substrate; the dimensions of the

substrate. The most important parameters of the spraying regime are the velocity and temperature of the particles. Given the

same velocity, the optimum particle kinetic energy for producing a strong bond with the substrate depends on particle shape and size and the density of the materials being spray-coated. These parameters determine the heating of the particles in the plasma jet or, in the case of the use of a detonation gun, during collision with the surface of the part.

Powders of fragmented or drop shape, 20-100/~m in size, are used to obtain coatings by spraying. The density of the deposited materials 3' -> 2.7-18.0 g/cm 3. Here, the porosity of the coatings P = 0.1-20.0% [1].

As a quantitative criterion of the amount of material lost during spraying (with allowance for the physicomechanical

properties of the particles), we can use a coefficient Knf that expresses the roughness (nonuniformity) of the surface of the

coating [2]. The value of this coefficient depends in turn on the porosity of the surface layer [2]. The coefficient is deter- mined by differentiating the total thickness of the coating 80 as the thickness of the layer that determines the service proper-

ties and the thickness of the top (surface) layer forming the relief. The porosity of the top layer is different than the porosity of the main layer of the coating. The values of Knf for the top layer of the coating are determined with and without allowance

for the cavities that are formed. The roughness coefficient is greater than 100%, since allowance is made for the fraction of residual porosity calculated from formulas introduced in [2]. The residual porosity of the top layer II, in the form of cavkies and depressions, approaches the porosity of the coating P for the optimum spraying regime. Then the roughness coefficient

can be nominally represented as Knf = 100 + P (where II = P). A substantial amount of material is lost during spray-coating. The magnitude of these losses depends mainly on the

shape and perimeter of the substrate and the angle (convex polygon, circle) or arc (cylinder, sphere) of its surface. In connection with this, we introduced geometric coefficients Kg to account for utilization of the materials. These coefficients are theoretically equal to the ratio of the volumes of deposited material with and without allowance for the formation of the coating beyond the limits of the surface being treated. Formulas for calculating these coefficients were presented in [3, 4]. For example, with a spraying distance H = 8 cm, particle dispersion angle/3 = 14 °, radius of deposition spot r = 1 cm, limiting angle of incidence of the particles and the substrate c~ = 45 °, total coating thickness 80 = 0.1 cm, and critical radius

Rcr = 1.7 cm (solids of revolution are divided into two groups in relation to Rcr: with a radius smaller (R < Rcr) or larger

(R > Rcr ) than the critical value; loss of the materials being deposited takes place along the arc of the substrate in the first case but not in the second case), Kg = 1.6-98.9% in the treatment of a surface in the form of a cylinder and Kg = 8.2-

94.6% in the treatment of flat (rectangular, circular, etc.) surfaces (Table 1). The processing coefficient Kp, characterizing

the ratio of the mass of material consumed to the mass of material in the coating, fluctuates within the range 40-60% in detonation spraying and 65-85 % in plasma spraying (the values are more stable in the latter case).

In light of the foregoing, we can use the form of the surface being treated (Fig. 1) and its geometric parameters as the basis for systematizing norms on the consumption of coating materials for the given method of coating. For flat surfaces, the geometric parameters determining the norms are length and width L × B (in the case of a rectangle) or radius R (in the

case of a circle). As regards solids of revolution of small diameter (R < Rcr), the determining parameters are radius and height H for cylinders and radius R for spheres (Table 2). Thus, the norms can be systematized in matrix form in relation to the shape and the corresponding geometric parameters of the part (substrate).

Institute of Problems of Materials Science, National Academy of Sciences of the Ukraine, Kiev. Translated from oroshkovaya Metallurgiya, Nos. 9/10, pp. 99-102, September-October, 1994. Original article submitted March 19, 1992.

1068-1302/94/0910-0535512.50 ©1995 Plenum Publishing Corporation 535

Page 2: Systematization of material consumption norms in spray-coating

TABLE 1. Change in Material-Use Coefficients in Relation to the Shape and Di-

mensions of the Substrate

S, cm 2 I

Rectangular surfaces ] Circular surthces

1 n, e . I Kg, % R, eM l Kg, %

Cylindrical solids of revolu- tion with R = 1.8-10.0 cm

H, cu [ Kg, %

I 20,2--4,0 8,2--24,7 0,56 26,0 0,088--0,,016 8,0--1,6 I0 200,2--12,6 9,0--57,5 1,78 60,0 0,88--0,16 46,7--13,8

100 '2000,2--40,0 9,08----82,6 5,64 84,2 8,85--1,59 89,9---61,4 1000 20000,2--126,67 9,1--93,9 1Z,85 94,6 88,46---15,92 98,9--94,1

Note. S and II represent the area and perimeter of the part being treated.

Parts

Flat Solids of revolution <. / -., . / Small Large

Rectangular Circular diameter diameter

L Cylindrical

Spherical

Fig. 1. Classification of parts according to the shape of the

coating.

Matrix of Material Consumption Norms for Spraying

Flat rectangular surfaces

Parameter, m ... Lx X Bt Lx X B2 Lt X B 8 ... Lx X B n

Norm, kg/m2 X l . . .

Parameter, m ... L2 X B~ ... L2 X Bn+ 1 Ln X B n L n X Bn+ 1 Norm, kg/m 2 X42 2 n n . . . . . . .Xnq_ 1 X n Xn..]- I

Flat circular surfaces Parameter, m R1 R t R8 ... R n

Norm, kg/m 2 X 1 X s X s . . . X n

L~XB2 L2XBa.

Ln X B n + 2 ... Ln X B n + ~ x~+~ . . x ~ + ~

A formula for calculating norms X was presented in [2]. In changing over from calculations performed for a unit of

volume to calculations performed for a unit of area, the formula acquires the following form:

104y (100 - - P) 6 o (1) my ~- K p K m f K g

The first multiplier (1027(100 - P)~io)/(KpKnf) establishes a relatively constant quantity mp that depends on the deposition

regime and the physicomechanical properties of the particles. The second multiplier 100/Kg characterizes a quantity that

changes in relation to the shape and geometric parameters of the part, i.e., the geometric material-use coefficients. If we

assume that rap, the process norm for consumption of the coating materials, is a constant which is independent of the shape

or dimensions of the part, then the formula for calculating the overall consumption norm will have the form

X----- 100rap (2) Kg '

where X, kg/m 2, is the coating-material consumption norm calculated for each 1 m 2 of substrate surface when the thickness

of the deposited layer is 100 ~m; nap, kg/cm 2 is the relatively constant process norm for coating-material consumption for

each 1 m 2 of surface with a coating thickness of 100/zm. The value of nap is determined by the first multiplier in Eq. (1).

In the formation of plasma coatings using a wire of steel 40Kh13 (3, = 7.8 g/cm 3, 50 = 100/xm, P = I0%, Kp =

80%, Knf = 110%) and in the formation of detonation coatings with the use Of iron powder (3' = 7.9 g/cm 3, 6 o = 100 tzm, P = 1%, Kp = 50%, Knf --- 101%), the following nominally constant (process) norms were obtained for the consumption of the coating materials per 1 m 2 of surface: mpP = 0.79 kg/m 2, mp d = 1.55 kg/m 2. With allowance for the geometry of the

536

Page 3: Systematization of material consumption norms in spray-coating

TABLE 2. Matrix of Material Consumption Norms (kg/m 2) in the

Spraying of Coatings on Solids of Revolution of Large and Small Diam-

eters

Parameter, m R < Rcr

Rt / R~ R, ... R n R > Rcr

H1 x] H2 XI 2 Hs XI 3 :

H. X~ t

Xx

Cylindrical surfaces

x~' x~'.. , xL x, x~ x ~ . . . x~ x~ x~ x~...X~n X' : .- : :

x~ x~' . . x~. X" Spherical surfaces

X ~ X s . . X n X

surface of the parts, the consumption norms were 0.80-49.0 kg/m 2 (flat surfaces) and 0.84-9.6 kg/m 2 (solids of revolution)

for plasma-arc spraying and 1.57-96.9 kg/m 2 and 1.66-18.9 kg/m 2, respectively, for detonation spraying.

Thus, the above norms for material consumption in spray-coating (allowing for the shape and geometric parameters

of the surfaces of the parts) can serve as a starting point for estimating material, labor, and financial resources for spray-

coating operations and improving the technology and equipment currently in use. Practical use of the tables of norms will

allow more efficient use of the materials available as coatings.

REFERENCES

.

2.

3.

4.

V. A. Kakuevitskii, Use of Sprayed Coatings in Machine Manufacture and Repair [in Russian], Tekhnika, Kiev

(1989).

I. M. Lelyukh, "Determination of norms for material consumption in spray-coating," Tekhnol. Organ. Proizvod.,

No. 1, 43-46 (1991).

I. M. Lelyukh, "Effect of the shape of the surface of the substrate on material consumption in spray-coating"

Poroshk. Metall., No. 1, 49-53 (1987).

I. M. Lelyukh, "Determination of coating material consumption in the spray-coating of small-diameter solids of

revolution," Ibid., No. 4, 68-71 (1987).

537