PRODUCTION

The present invention generally relates to spray-deposited production of a product on a moving substrate.

A commercial process for production of 5 spray-deposited, shaped preforms in a wide range of alloys has been developed by Osprey Metals Ltd. of West Glamorgan, United Kingdom. The Osprey process, as it is generally known, is disclosed in detail in U.K. Pat. Nos. 1,379,261

10 and 1,472,939 and U.S. Pat. Nos. 3,826,301 and 3,909,921 and in publications entitled "The Osprey Preform Process" by R.W. Evans et al, Powder Metallurgy. Vol. 28, No. 1 (1985), pages 13-20 and "The Osprey Process for the Production

15 of Spray-Deposited Roll, Disc, Tube and Billet Preforms" by A.G. Leatha et al, Modern Developments in Powder Metallurαry. Vols. 15-17 (1985), pages 157-173.

The Osprey process is essentially a rapid

²⁰ solidification technique for the direct conversion of liquid metal into shaped preforms by means of an integrated gas-atomizing/spray-depositing operation. In the Osprey process, a controlled stream of

25 molten metal is poured into a gas-atomizing device where it is impacted by high-velocity

jets of gas, usually nitrogen or argon. The resulting spray of metal particles is directed onto a "collector" where the hot particles re-coalesce to form a highly dense preform. The collector is fixed to a mechanism which is programmed to perform a sequence of movements within the spray, so that the desired preform shape can be generated. The preform can then be further processed, normally by hot-working, to

10 form a semi-finished or finished product.

The Osprey process has also been proposed for producing strip or plate or spray-coated strip or plate, as disclosed in European Pat. Appln. No. 225,080. For producing these products, a substrate or collector, such as a

15 flat substrate or an endless belt, is moved continuously through the spray to receive a deposit of uniform thickness across its width. Heretofore, extensive porosity typically

20 has been observed in a spray-deposited preform at the bottom thereof being its side in contact with the substrate or collector. This well known phenomenon, normally undesirable, is a particular problem in a thin gauge product, such as strip or tube, since the porous region may

25 comprise a significant percentage of the product thickness. The porosity is thought to occur when the initial deposit layer is cooled too rapidly by the substrate, providing insufficient liquid to feed the inherent interstices between

30 splatted droplets.

Another defect feature often associated with this substrate region is extensive lifting of initial splats which promotes a non-flat surface. The lifting of the splats is a

35

consequence of solidification contraction and distortion arising from the rapid solidification of the splats.

One approach of the prior art for

5 eliminating these problems is preheating the substrate to minimize or reduce the rate of heat transfer from the initial deposit to the substrate so that some fraction liquid is always available to feed voids created during the spray

10 deposition process. However, it is often difficult to effectively preheat a substrate in a commercial spray deposit system because of the cooling effects of the high velocity recirculating atomizing gas. Further,

15 preheating a substrate increases the potential for the deposit sticking to the substrate.

Therefore, a need exists for an alternative approach to elimination of the porosity problem particularly in thin gauge product produced by

2 _Q the above-described Osprey spray-deposition process.

The present invention provides a substrate with a softenable glass surface layer designed

25 to satisfy the aforementioned needs. The unique approach of the present invention is to use, at least as a surface layer of the substrate, a glass which will soften over a broad predetermined temperature range but still retain

30 a viscosity of sufficient strength to prevent it from being blown away by a pressurized atomizing gas flow and thereby maintain its capability to function as a substrate. The transition or initial softening temperature of the glass must

35 be less than the minimum casting temperature of

the metal and the glass must be able to reach an elevated temperature above the maximum temperature of the pressurized gas upon impingement while it still retains a viscosity 5 with sufficient strength to withstand deformation due to the high pressure atomizing gas flow.

Advantageously, a substrate with such a softenable glass surface layer promotes a fully 10 dense and highly flat bottom surface by capturing initial metal splats and preventing them from lifting from the substrate surface. Glass, having a low thermal conductivity, prevents too rapid an extraction of heat by the substrate resulting in the availability of an adequate fraction of liquid in the initial deposit layer to minimize porosity. Another advantage is that glass is a relatively inexpensive material to use. 2o Accordingly,. the present invention is directed to a molten metal gas-atomizing spray-depositing apparatus. The apparatus includes the combination of: (a) means employing a pressurized gas flow for atomizing a stream of 2 molten metal into a spray pattern of metal particles and producing a flow of the particles in the pattern thereof along with the gas flow in a generally downward direction; and (b) a substrate having at least an upper surface layer

30 of glass, thermally softenable over a predetermined temperature range, being disposed below the atomizing means for impingement thereon of the pressurized gas flow and for receiving thereon a deposit of the particles in

35 the spray pattern to form a product.

Further, the metal particles at the instance of deposit on the substrate upper surface layer are at a known minimum casting temperature; thus, the softenable glass to be usable as the substrate upper surface layer must be one that has an initial softening temperature which is below the minimum casting temperature. The pressurized gas flow at the instance of impingement on the substrate upper

10 surface layer, before deposit of the metal particles, is at a known maximum impact temperature; thus, the softenable glass to be usable as the substrate upper surface layer must be one that retains a viscosity of sufficient

15 strength to withstand deformation, due to the impingement by the pressurized gas flow, at a temperature which is above the maximum impact temperature.

In summary, due to the presence on the

20 substrate of a glass being softenable over the above-defined predetermined temperature range, a reduction of porosity and an improvement of flatness of a bottom surface of the deposit located in contact therewith can be realized.

-i "i Another aspect of the present invention provides a substrate composed of a material design to satisfy the aforementioned needs. The unique approach of this aspect is the selection of material for the substrate having a thermal

3 ₀ conductivity correlated with the steady state temperature of the atomizing gas flow in the spray chamber of the apparatus. The steady state temperature is maintained by the atomizing

- 6 -

gas flow which is heated by the molten metal atomized by the gas flow and spray deposited on the substrate in the spray chamber.

Since different metals have different melting temperatures, the particular steady state temperature of the spray chamber and, thus, of the substrate in the chamber primarily depends upon which metal is being processed in the spray chamber. To ensure that the initial deposit on the substrate maintains a sufficient fraction of liquid to provide a wetting interface with subsequent deposits, the material selected for the substrate is one which has a thermal conductivity correlated to the particular steady state temperature so as to limit or minimize heat transfer from the initial deposit to the substrate and thereby prevent complete solidification of the initial deposit. Accordingly, the present invention is directed to a molten metal gas-atomizing spray-depositing apparatus. The apparatus includes the combination of: (a) means employing a pressurized gas flow for atomizing a stream of molten metal into a spray pattern of semi-solid 5 metal particles and producing a flow of the particles in the pattern thereof along with the gas flow in a generally downward direction; and (b) a substrate disposed below the atomizing means for impingement on the substrate of the 0 gas flow at a particular steady state temperature resulting from heat transfer by the metal particles to the gas flow and for receiving thereon a deposit of the particles in the spray pattern to form a product thereon. ,-. The substrate is composed of a material having a

thermal conductivity correlated with the particular steady state temperature of the gas flow so as to limit or minimize heat transfer from the initial deposit to the substrate and thereby prevent complete solidification of the initial deposit. Use of a substrate composed of such material ensures that the initial deposit on the substrate maintains a sufficient fraction of liquid to feed the inherent interstices between the splatted droplets and provide a proper interface with subsequent deposits whereby reduction of porosity and improvment of flatness are achieved in the deposit.

According to another aspect of the present invention a non-preheated low thermal conductivity substrate is provided which is designed to satisfy the aforementioned needs. In the approach of this aspect of the present invention to solving the porosity problem, no preheating of the substrate is required.

Instead, heat extraction to achieve

solidification of the deposit is due solely to the cooling effects of atomizing gas flow over the deposit. Since the substrate does not have to extract heat, the porosity problem can be minimized if the substrate thermal conductivity (TC) is low. Materials having a thermal conductivity in the single digit range, as measured in watts per meter per degree Kelvin (W/M-K) , were found to be ideally suited for use

10 as a non-preheated substrate for spray-deposited production of product, although materials of a thermal conductivity of fifteen or less may be used.

Accordingly, the present invention is

15 directed to a molten metal gas-atomizing spray-depositing apparatus. The apparatus includes the combination of: (a) means employing a pressurized gas flow for atomizing a stream of molten metal into a spray pattern of semi-solid

20 metal particles and producing a flow of the particles in the pattern thereof along with the gas flow in a generally downward direction; and (b) a non-preheated substrate composed of a material having a thermal conductivity of about fifteen or less (W/M-K) , and preferably one or

25 less (W/M-K) , disposed below the atomizing means for receiving thereon a deposit of the particles in the spray pattern and for impinging thereon of the pressurized gas flow for cooling the deposit on said substrate to form a product

30 thereon. The predetermined thermal conductivity of the substrate of about one or less precludes too rapid an extraction of heat by the substrate from, and thus solidification of, the deposit upon initial contact with the substrate whereby

35

- 9 -

a reduction of porosity is achieved in the deposit.

Many glass types of materials, such as

Vycor, glasses, Pyrex, glass-ceramics, etc., have thermal conductivities in a single digit range that meets the requirement of the present invention. An added advantage with these glass type materials is that they do not react chemically with copper and have significantly

10 different thermal coefficients of expansion

(TCE) as compared to copper. Due to these properties the deposits can readily be stripped from the substrate as a uniform flat product on cooling to low temperatures. 1 ₅ The present invention provides a substrate deposit-receiving region orientation designed to satisfy the aforementioned needs. The configuration or orientation of the deposit-receiving area of the moving substrate

20 i _s specifically arranged relative to the axis of the spray cone to improve the resulting distribution of temperature through the cross-section of the product produced on the moving substrate.

₂ 5 Accordingly, the present invention is directed to a molten metal gas-atomizing

spray-depositing apparatus. The apparatus includes the combination of: (a) means for atomizing a stream of molten metal into metal particles in a divergent spray pattern being of 5 higher temperature at a center region of the spray pattern than at an outer peripheral region thereof; and (b) means in the form of a substrate movable along an endless path and having an area thereon being disposed below the 10 atomizing means for receiving a deposit of the particles in the spray pattern to form a product. Furthermore, the deposit-receiving substrate area has sequentially arranged upstream, intermediate, and downstream portions 15 upon which respective bottom, intermediate, and upper cross-sectional portions of the deposit are layered one upon the next to form the product. The bottom deposit portion is disposed closest to, and the upper deposit portion is 20 disposed farthest from, the substrate and the intermediate deposit portion is disposed in between.

In accordance with the principles of the present invention, the deposit-receiving 2 substrate area is oriented relative to, and displaced from, the atomizing means such that particles of the spray pattern travel through at least as great a distance (and preferably a greater distance) to reach the intermediate

30 portion of the deposit-receiving area as particles of the spray pattern travel to reach the upstream leading portion thereof. With such orientation and displaced relation of the deposit-receiving substrate area with respect to

35 the spray pattern, a more uniform temperature

distribution is achieved through the inner and intermediate portions of the deposit and a reduction of porosity is achieved in the inner portion of the deposit. More particularly, the deposit-receiving area of the substrate has in one orientation an inclined configuration relative to a central axis of the spray pattern, whereas in another orientation it has a generally concave configuration relative thereto.

A potential problem associated with employment of the Osprey process for strip production using a horizontal substrate system is entrainment of overspray particles in the product. These solidified droplets and/or splats are undesirable since they can produce voids, oxide inclusions, etc., resulting in unacceptable product quality. Entrainment of overspray is a consequence of secondary gas flows in the spray chamber which can recirculate overspray particles upwardly back into the atomizer region.

Ideally, gas flow should allow overspray particles to fall directly to the bottom of the spray chamber where they cannot be recirculated. However, in strip production using the horizontal substrate system, gas flow is such that secondary vortices above the strip are difficult to avoid and so incorporation can readily occur.

Therefore, a need exists for an approach for reducing the overspray recirculation problem in order to improve the quality of strip product produced by the above-described Osprey spray-deposition process.

The present invention provides a substrate orientation designed to satisfy the aforementioned needs. The moving substrate disposed in vertical orientation or 5 configuration can significantly minimize the potential for entraining overspray by permitting more efficient gas flow. In this orientation of the substrate, overspray particles are directed by a streamlined gas flow toward an exhaust port 10 at the bottom of the spray chamber instead of being recirculated upwardly toward the atomizer region at the top of the chamber.

Accordingly, the present invention is directed to a molten metal gas-atomizing 15 spray-depositing apparatus. The apparatus includes the combination of: (a) means employing a pressurized gas flow for atomizing a stream of molten metal into a spray pattern of metal particles and producing a flow of the particles 20 in the pattern thereof along with the gas flow in a generally downward direction; and (b) means movable continuously along an endless path and having an area thereon disposed below the atomizing means for receiving a deposit of the 25 particles flowing in the spray pattern to form a product thereon. The endless path of the movable means being generally elongated in the downward direction and thus extends parallel to the general downward direction of gas flow such 30 that any particle overspray past the deposit-receiving area is carried by the gas flow downward past the movable means, substantially avoiding entrainment of the particle overspray in the product being formed 35 thereon.

More particularly, the movable means is an endless substrate having a pair of parallel runs movable about the elongated endless path and thereby extending in the downward direction 5 parallel to the direction of gas flow. The spray pattern has a central vertical axis and the pair of parallel runs are displaced below and on opposite sides of the vertical axis of spray pattern and extend generally parallel 10 thereto.

In the course of the following detailed description, reference will be made to the attached drawings in which:

Fig. 1 is a schematic view, partly in 15 section, of a prior art spray-deposition apparatus for producing a product on a moving substrate, such as in thin gauge strip form.

Fig. 2 is a graph of the correlation between a range of steady state temperatures 20 produced by atomizing gas when spray depositing different metals and a range of materials of different thermal conductivities which are respectively appropriate and inappropriate for use at such steady state temperatures in 25 accordance with the principles of the present invention.

Fig. 3 is a fragmentary schematic sectional view of one modified form of the 30 spray-deposition apparatus in accordance with the present invention.

Fig. ⁴ i _{s a} fragmentary schematic sectional view of another modified form of the apparatus.

Fig. 5 is a schematic sectional view of the spray-deposition apparatus substrate modified to a vertical orientation in accordance with the principles of the present invention. Referring now to the drawings, and particularly to Fig. 1, there is schematically illustrated a prior art spray-deposition apparatus, generally designated by the numeral 10, being adapted for continuous formation of products'. An example of a product A is a thin gauge metal strip. One example of a suitable metal B is a copper alloy.

The spray-deposition apparatus 10 employs a tundish 12 in which the metal B is held in molten form. The tundish 12 receives the molten metal B from a tiltable melt furnace 14, via a transfer launder 16, and has a bottom nozzle 18 through which the molten metal B issues in a stream c downwardly from the tundish 12. Also, a gas atomizer 20 employed by the apparatus 10 is positioned below the tundish bottom nozzle 18 within a spray chamber 22 of the apparatus 10. The atomizer 20 is supplied with a gas, such as nitrogen, under pressure from any suitable source. The atomizer 20 which surrounds the molten metal stream C impinges the gas on the stream C so as to convert the stream into a spray D of atomized molten metal particles, broadcasting downwardly from the atomizer 20 in the form of a divergent conical pattern. If desired, more than one atomizer 20 can be used. Also, the atomizer(s) can be moved

transversely in side-to-side fashion for more uniformly distributing the molten metal particles.

Further, a continuous substrate system 24 employed by the apparatus 10 extends into the spray chamber 22 in generally horizontal fashion and in spaced relation below the gas atomizer 20. The substrate system 24 includes drive means in the form of a pair of spaced rolls 26,

10 an endless substrate 28 in the form of a flexible belt entrained about and extending between the spaced rolls 26, and a series of rollers 30 which underlie and support an upper run 32 of the endless substrate 28. The

15 substrate 28 is composed of a suitable material, such as stainless steel. An area 32A of the substrate upper run 32 directly underlies the divergent pattern of spray D for receiving thereon a deposit E of the atomized metal

2 particles to form the metal strip product A.

The atomizing gas flowing from the atomizer 20 is much cooler than the molten metal B in the stream C. Thus, the impingement of atomizing gas on the spray particles during flight and

25 subsequently upon receipt on the substrate 28 extracts heat therefrom, resulting in lowering of the temperature of the metal deposit E below the solidus temperature of the metal B to form the. solid strip F which is carried from the

30 spray chamber 22 by the substrate 28 from which it is removed by a suitable mechanism (not shown) . A fraction of the particles overspray the substrate 28 and fall to the bottom of the spray chamber 22 where they along with the atomizing gas flow from the chamber via an

35 exhaust port 22A.

In the prior art apparatus 10, the solid strip F formed on the substrate 28 typically exhibits extensive porosity in its bottom side adjacent the substrate. The cause of this porosity problem is believed to be due to contact with the cool substrate 28 which together with the impingement of the cooler atomizing gas extracts too much heat and thereby

10 lowers the temperature of the spray deposit E too rapidly, starving it of a sufficient fraction of liquid to feed the interstices between splatted droplets.

One unique solution of the present

15 invention is to employ, at least as an upper surface layer of the substrate, a glass which will soften over a broad predetermined temperature range but still retain a viscosity of sufficient strength to prevent it from being

20 blown away by the pressurized atomizing gas flow and thereby maintain its capability to function as a substrate. The transition or initial softening temperature of the glass must be less than the minimum casting temperature of the

25 metal particles and the glass must be able to reach an elevated temperature above the maximum impact temperature of the pressurized gas and still retain a viscosity with sufficient strength to withstand deformation due to the

30 high pressure atomizing gas flow. Preferably, the glass should have a viscosity of 10 ⁷ poise or less at the minimum casting temperature, and a viscosity of 10 ⁴ poise or greater at the maximum temperature of the gas flow upon impingement with the glass.

35

A substrate with such a softenable glass surface layer promotes a fully dense and highly flat bottom surface by capturing initial metal splats and preventing them from lifting from the substrate surface. Also, the extremely low thermal conductivity of glass would clearly limit the heat tranfer from the initial deposit layer E to the substrate and help ensure an adequate fraction of liquid in the initial 0 deposit layer E to feed the interstices between the droplets and thereby minimize porosity. An additional benefit is that glass is a relatively inexpensive material to use.

The substrate may include a flexible 5 material such as stainless steel or the like which has an upper layer of the glass.

The following example presents a range of glasses which would be appropriate for use as the substrate surface layer for spray-depositing 0 copper alloy thereon.

Exampl

Assume that copper alloy will be spray cast at approximately 1200 degrees C. In accordance with the concept of the present invention, the 5 glass selected for use as the substrate must be soft at the instance of spray casting thereon. Since glasses start softening at their respective glass transition temperatures where they have viscosities of 10 ⁷ poise, glasses 0 appropriate for use as the substrate for receiving copper alloys must have a transition temperature below the minimum casting temperature of 1200 degrees C.

Also, in accordance with the concept of the

_... present invention, glasses selected for use as

3D

the substrate when in the softened state must not be capable of being blown away by the high pressure atomizing gas flow impinging upon them just before the molten spray of metal particles are deposited on them. Assume a temperature of 600 degrees C at impact for the pressurized gas flow. Glasses at that temperature with a viscosity of 10 ⁴ poise would have sufficient strength to withstand the deformation due to the

10 gas flow. Thus, glasses appropriate for use as the substrate receiving copper alloy must have a viscosity of at least 10 ⁴ poise at a temperature above the maximum impact temperature of 600 degrees C.

Many glasses which will meet these

15 requirements are given in Table I. The properties of these glasses are also summarized in the same table. Specifically, it will be noted that the intial softening temperature (at

20 10 ⁷ poise) of each glass, the lower limit of its softened temperature range, is below the minimum casting temperature of 1200 degrees C. Also, it will be noted that the elevated temperature at which each glass is of a viscosity of 10 ⁴ , the upper limit of its softened temperature range,

25 is above the maximum impact temperature of the gas flow of 600 degrees C.

Table I Temperature <Decrees Cϊ At Which

M . Glass IP ⁴ oise

1 Potash Soda Glass

2 Soda Lime Glass

3 Alumino Silicate Glass 5 4 Soda Zinc Glass

5 Boro Silicate Glass

6 96% Silica

7 Fused Silica

8 Titanium Silicate Glass ₁₀ Another solution of the present invention is to select a material for the substrate 28 havin a thermal conductivity correlated with the steady state temperature of the atomizing gas flow in the spray chamber 22 of the apparatus 10. The

15 steady state temperature of the chamber 22 surrounding the substrate 28 is produced and maintained by the atomizing gas flow which is heated by the atomized molten metal particles being spray deposited on the substrate in the

₂ o spray chamber.

Since different metals have different melting temperatures, the steady state temperature of the spray chamber 22 and, thus, of the substrate 28 in the chamber depends primarily upon which metal is being processed in

25 the spray chamber. To ensure that the initial deposit E of particles on the substrate 28 maintains a sufficient fraction of liquid to feed the inherent interstices between the

30 splatted droplets and provide a proper interface

- 20 -

for subsequent deposits of particles, the material selected for the substrate 28 is one having a thermal conductivity which minimizes heat transfer from the initial deposit E to the substrate 28 at the particular steady state temperature. In such a way, the thermal conductivity of the selected substrate material is correlated to the particular steady state temperature and to the particular metal being spray deposited for preventing total solidification of the initial deposit E. The result is a reduction of porosity and improvement of flatness of the deposit E. Fig. 2 is a graph of the correlation between a range of steady state temperatures produced by atomizing gas when spray depositing different metals and a range of materials of different thermal conductivities which are respectively acceptable and unacceptable for use at such steady state temperatures. The points on the graph represent substrate material/spray deposited metal combinations, with the type of substrate material indicated by the shape of the data point and the spray deposited metal or melt indicated in parentheses. For example, *(Sn) means the substrate material is aluminum and the spray deposited metal or melt is tin. The X-axis represents the temperature difference between the melting temperature of the metal being spray deposited and the steady state temperature (which is also generally the substrate temperature) . The Y-axis represents the thermal conductivity of the substrate material.

The line on the graph is the boundary between satisfactory and unsatisfactory deposits produced by different substrate material and deposit metal combinations at different temperature differences. At the opposite extreaes of the boundary line, asymptotic relationships are defined between the temperature difference and the thermal conductivity of the substrate material. Specifically, when the temperature difference approaches zero, materials of an almost infinite range of thermal conductivities can be used because, in effect, the substrate has been preheated up to the melting temperature of the spray deposited metal and thus no heat will be transferred to the substrate regardless of its thermal conductivity. Conversely, as the thermal conductivity approaches zero, the choice of substrate material narrows down to materials, such as glass, whose thermal conductivities are very small. Below the line on the graph the condition of the deposit is good, meaning that a sufficient fraction of liquid was present in the initial deposit to feed the inherent interstices between the splatted droplets and to provide a good interface for subsequent deposits and minimal porosity. On the other hand, above the line on the graph the condition of the deposit is not good, meaning that an inadequate fraction of liquid was provided and unacceptable porosity is present in the deposit.

It has been found that it is possible to produce alloy preforms with excellent surface quality and which are capable of being stripped

- 22 -

from the substrate (i.e., non-consumable) for the unique conditions set forth in Fig. 2. In the spray chamber 22, the recirculation of the atomizing gas flow will produce a steady state 5 temperature expected to be approximately 500 degrees C for Cu base alloys. At this temperature, experiments indicate that substrates with thermal conductivities of 25 w/m ² -sec degrees K or less will result in high 10 quality strippable deposits. Examples of such materials include glasses, Si ₃ N ₄ , AI2O3 and A42 (Fe-42 Ni).

For iron and nickel base alloys where the steady state temperature can be expected to be 15 700 degrees C, the substrate thermal conductivity should be below 15 w/m ² -sec degrees K. Here glasses again would be acceptable while A1 ₂ 0 ₃ and Si ₃ N ₄ would not work. For aluminum alloys the steady state temperature can be 20 expected to be 200 degrees C and substrates with thermal conductivities up to approximately 40 w/m ² -sec degrees K can be used.

Another solution of the present invention to the problem of deposit porosity is to provide a low thermal conductivity substrate. There is no additional requirement for preheating the substrate. Instead, heat extraction to achieve solidification of the deposit is due solely to the cooling effects of atomizing gas flow over the deposit.

Experimentation was conducted to determine the substrate thermal conductivity range over which a flat continuous deposit can be achieved. Molten copper was sprayed onto substrates with a range of different thermal conductivities. The results of this experimentation is given in Table I below.

The data indicates that a flat continuous deposit could be achieved only with low thermal conducting glass type materials such as Vycor, glasses, Pyrex, glass-ceramics, etc. Those materials having thermal conductivities (TC) in the one-tenth to one (W/M-K) range were ideally suited for use as a non-preheated substrate for spray-deposited production of product. However materials with a thermal conductivity of fifteen or less (W/M-K) may also be used. The experiments were repeated for spray casting of iron and the same trend was noted.

An added advantage with these glass type materials is that they do not react chemically with copper and have significantly different thermal coefficients of expansion (TCE) as compared to copper. Due to these properties the

deposits can readily be stripped from the substrate as a uniform flat product on cooling to low temperatures.

Table I

Deposit

Hs su stra Material TCW/M-K condition

10 Copper Block 400 Not Good

Aluminum Block 230 Not Good

Steel Block

15 Alumina

Silicon Nitride

20 Glass (Soda-lime)

Vycor ¹ Glass

8 Pyrex ² Glass

25 Corning Visions ³

1. A 96% silica glass produced by Corning Glass

30 Works, Corning, N.Y., U.S.A.

2. A borosilicate glass produced by Corning Glass, Corning, N.Y., U.S.A.

3. A glass ceramic material produced by Corning Glass Works, Corning, N.Y., U.S.A.

35 The mass density and temperature of the gas-atomized metal of the divergent pattern of spray D is not uniform across the pattern.

Typically, the center region of the divergent spray pattern D is of higher mass density than the periphery or outer fringe regions of the spray pattern. Because of the divergent configuration of the spray pattern D, the particles or droplets in the outer fringe regions thereof have to move through a greater distance to reach the horizontal substrate than droplets in the center region thereof. As a

10 result, the center region is of a higher average temperature than the periphery or outer fringe region when it reaches the substrate.

The porosity problem observed in the bottom surface of the strip F derives from the cooler,

15 low mass density outer fringe regions of the spray pattern D. In effect, this low mass density fringe region supplies insufficient atomized particles or droplets to maintain sufficient liquid to fill voids even when the

20 center region of the spray pattern D is optimized and is producing high density interior structure in the deposit E. The overall result is a generally non-uniform temperature distribution through the cross-section of the deposit E. The bottom portion of the deposit E

25 adjacent to the cool substrate 28 is cooler and lower in density than the intermediate portion which, being protected from gas impingement, is hotter and more liquid tending to trap bubbles of gas, whereas the upper portion of the deposit

30 E subject to gas impingement is cooler and also is lower in density than the intermediate portion.

The solution of the present invention is to modify the orientation of the upper run 32 of

35

the substrate 28 relative to the spray pattern D as depicted in Figs. 3 and 4. Broadly, in accordance with the principles of the present invention, the orientation of the deposit-receiving substrate area 32A is changed relative to a central axis G of the divergent spray pattern D such that the metal particles of the spray pattern travel through at least as great a distance, and preferably a greater distance, to reach an intermediate portion 34 of the deposit-receiving area 32A as particles of - the spray pattern travel to reach the upstream portion 36, and preferably also the downstream portion 38, of the area 32A. With such modified orientation of the deposit-receiving substrate area 32A with respect to the divergent spray pattern D, a more uniform temperature distribution is achieved through inner, intermediate and outer cross-sectional portions H, I and J of the deposit E and a reduction of porosity is achieved in the inner portion H of the deposit E.

More particularly, in Fig. 3 the deposit-receiving area 32A of the substrate 5 upper run 32 is oriented in a linear, inclined configuration relative to the central vertical axis G of the divergent spray pattern D. In this orientation of the substrate 28, only the upstream portion 36 of the substrate area 32A is 0 closer to the atomizer 20 than the intermediate portion 34, the downstream portion 38 being farther away. On the other hand, in Fig. the deposit-receiving substrate area 32A is oriented in a concave configuration relative to the , _ι - vertical axis G of the divergent spray pattern

wherein both the upstream and downstream portions 36, 38 are closer to the atomizer 20 than the intermediate portion 34.

The objective is to smooth out the

5 temperature distribution through the cross-section of the deposit E and reduce porosity in the inner portion H of the deposit E. Other configurations can be devised within the purview of the present invention to

10 accomplish that objective. With such configurations of the consecutively arranged upstream, intermediate and downstream portions 36, 34, 38 of the substrate area 32A upon which respective inner, intermediate and outer

15 cross-sectional portions H, I, J of the deposit E are layered one upon the next to form the strip F, a more uniform temperature distribution is achieved through cross-section of the deposit E. The shortened distance of travel to the

2 upstream portion 36 of the area 32A makes higher temperature particles or droplets available, providing a higher fraction liquid in the inner portion H of the deposit E thus promoting minimal porosity.

A fraction of the particles overspray the 25 substrate 28 but ideally will fall to the bottom of the spray chamber 22 where they along with the atomizing gas flow from the chamber via an

exhaust port 22A. However, the horizontal orientation of the moving substrate 28 tends to obstruct the natural pattern of gas flow from the atomizer 20 so as to create secondary gas 5 flow vortices above the strip which promote entrainment of overspray particles in the strip product A being formed on the substrate.

The solution of the present invention to the overspray particle entrainment problem is to 10 modify the orientation of the continuous substrate system 24 of the apparatus 10, as depicted in Fig. 5. After modification of the substrate system 24 in accordance with the principles of the present invention, the drive 15 rolls 26 are spaced vertically one above the other and the endless substrate 28 extends between and about them in a vertical orientation .or configuration in which spaced parallel runs 44A, 44B of the substrate extend generally 20 parallel to a central vertical axis G of the divergent spray pattern D. The metal particles in the spray D now form the deposit E on the substrate 28 at the area thereof passing over the upper one of the rolls 26. A wedge 46 _na y 25 be positioned between the upper roller and the inside surface of the substrate 28 to straighten the substrate and strip as it leaves the upper roller 26.

Such substrate orientation can 30 significantly minimize the potential for entrainment of particle overspray by permitting more efficient gas flow. In the vertical orientation of the substrate 28, overspray particles are now directed by the natural 35 streamlined flow of gas, as represented by

arrows K, past the substrate runs 44A, 44B and toward the bottom of the spray chamber 22 instead of being recirculated upwardly toward the atomizer 20 at the top of the chamber. The overspray particles are then immediately extracted from the chamber 22' at the bottom exhaust port 22A* by operation of an exhaust mechanism (not shown) .

More particularly, as seen in Fig. 5, the

10 pair of parallel runs 44A, 44B of the substrate 28 which move along an elongated endless path extend in the downward direction parallel to direction of gas flow. The parallel substrate runs 44A, 44B are displaced below and on

15 opposite sides of the vertical axis G of spray pattern D and extend generally parallel thereto. The downward direction of gas flow carries any particle overspray past the substrate 28, substantially avoiding entrainment of the

20 particle overspray in the product being formed on the substrate.