GB2245514A

GB2245514A - Tube fabrication with reusable mandrel

Info

Publication number: GB2245514A
Application number: GB9108807A
Authority: GB
Inventors: Paul Alfred Siemers; Stephen Francis Rutkowski; Joseph Jay Jackson; Joel Alexis Alexa
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1990-06-29
Filing date: 1991-04-24
Publication date: 1992-01-08
Also published as: FR2663872A1; GB9108807D0; ITMI911110A0; DE4112746A1; FR2663872B1; ITMI911110A1; JPH04231449A; CA2038273A1

Abstract

A method for forming a multiplicity of ring structures having essentially the same internal diameter is taught. A first step in the process is the provision of a mandrel (10) of relatively high thermal coefficient of expansion and the deposit of a layer of un-reactive oxide (14) on the surface of the mandrel. Following the oxide coating of the mandrel surface, a layer (22) of a matrix metal of relatively low thermal coefficient of expansion is deposited thereon to form a ring structure on the mandrel. The coefficient of thermal expansion of the mandrel metal and that of the matrix metal are sufficiently different that there is a spontaneous separation of the deposited matrix metal ring structure from the mandrel as the mandrel and deposited layer cool to room temperature. Following the cooling, the matrix metal ring structure can be removed from the mandrel and the mandrel is then re-coated and thus rendered suitable for repetition of the process to deposit yet another matrix ring structure thereon. <IMAGE>

Description

TUBE FA.BRICATION WITE REUSABLE KANDREL The present invention relates

generally to the fabrication of tubes through plasma spray techniques. More particularly, it relates to the plasma spray forming of articles of generally tubular configuration employing a reusable mandrel.

It is known that the plasma spray forming technology can be employed in forming articles of a variety of configurations. A number of patentsconcern the process of plasma. spray forming of articles employing RF plasma as the plasma medium. The preparation of titanium alloy base foils, sheets, and similar articles and of reinforced structures in which silicon carbide fibers are embedded in a titanium base alloy are described in U.S. Patents 4,775,547, 4,782,884, 4,786,566, 4,805,294, 4,805,833, and 4f838,337, all assigned to us. The disclosures in these patents are incorporated herein by reference.

Preparation of composites as described in these patents is the subject of intense study inasmuch as the com- posites have very high strength properties in relation to their weight. one of the properties which is particularly desirable is the high tensile properties imparted to the structures by the high tensile properties of the silicon carbide fibers or filaments. The tensile properties of the structures are related to the rule of mixtures. According to this rule the proportion of the property,'such as tensile property, which is attributed to the filament, as contrasted with the matrix, is determined by the volume percent of the filament present in the structure and by the tensile strength RD-20. 403 of the filament itself. Similarly, the proportion of the same tensile property which is attributed to the matrix is determined by the volume percent of the matrix present in the structure and the tensile strength of the matrix itself.

Prior to the development of the processes described in the abovereferenced patents, such structures were prepared by sandwiching the reinforcing filaments between foils of titanium base alloy and pressing the stacks of alternate layers of alloy and reinforcing filament until a composite structure was formed. However, that prior art practice was found to be less than satisfactory when attempts were made to form ring structures in- which the filament was an internal reinforcement for the entire ring.-

The structures taught in the above-referenced patents and the methods by which they are formed, greatly improved over the earlier practice of forming sandwiches of matrix and reinforcing filament by compression.

Later it was found that while the structures prepared as described in the above-referenced patents have prop- erties which are a great improvement over earlier structures, the attainment of the potentially very high ultimate tensile strength of these structures did not measure up to the values theoretically possible. The testing of composites formed according to the methods taught in the above patents has demonstrated that although modulus values are generally in good agreement with the rule of mixtures predictions, the ultimate tensile strength is usually much lower than predicted by the underlying properties of the individual ingredients to the composite. A number of applications have been filed which are directed toward overcoming the problem of lower than expected tensile properties and a number of these applications are copending. These include US applications RD-20. 403 Serial No. 445,203, Serial No. 459,894 (GB9024189.4) and.Serial Nos. 455, 041 & 455,048 (GB9024187.6 and 9024188.6). The disclosures in these applications are incorporated herein by reference.

One of the structures which has been found to be particularly desirable in the use of the technology of these reference patents is an annular article having a metal matrix and having silicon carbide filament reinforcement extending many times around the entire ring. Such ring structures have very high tensile properties relative to their weight particularly when compared to structures made entirely of metal. However, it has been found difficult, particularly because of the very high temperatures which.must be used in forming such articles to produce a ring structure which is dimensionally very precise in its internal dimensions. Such structures must be precise in their internal dimensions in order for the structures to be used most effectively in enduse applications inasmuch as the structures are often used as Part of a more complex structure and for this Purpose are fitted over one or a number of elements in a circular form in order to serve as a reinforcing ring.

One of the structures which is formed has the reinforcing filament wound many times and in many layers around the circumference is a reinforced ring structure. The rein- forced ring can be used for example as a reinforcing ring for te compressor blades of a compreszor disk of a jet engine. In order to serve to hold the blades in a compressor stage of a jet engine a large number of layers of reinforcing filaments are required. It has been found that it is very diffi- cult to continue to add mbre and more layers of filament reinforcement to a ring structure because of differences in thermal expansion coefficient and other factors. One way in which-this problem has been solved is described in copending Ejj-20, 403 US application Serial No. 546961 filed 2 July 1990, the disclosure in which is incorporated herein by reference. The method described in the copending application is carried out by forming a series of concentric rings which are then assembled together to provide a reinforced ring structure having more than 100 layers of reinforcement. Such ring structures may be of quite large diameter of the order of a foot or several feet and must nevertheless be nested together within very close tolerances of only a few thousands of an inch.

In order to form a nest of reinforced ring structures, it is desirable to have a set-of standard internal diameters of the rings to be nested so that some standardization of the ring structure dimensions can be employed to facilitate these manufacturing processes and achieve some economy in the ring manufacture. For example, if an overall structure is to have an internal diameter of about one foot (05inm), a number of rings having different starting diameters can be employed to build a set of reinforced_ structures, each of which has a thickness of about 0.2 inch (5mm). For example, if an overall ring structure is to have an internal diameter of 12 inches (305mm) and a total of over 100 plies, it may be desirable to fabricate the structure using 5 nesting hoops, each having 20 individual plies.. Since each ply is about 0.009-0.010 (0.23-0.25mm) inches thick, each hoop would be 0.2 inch (5mm) thick. Hence, the initial ring structures to be nested would have inside diameters of 12, 12.4, 12. 8, 13.2 and 13.6 inches (305, 315, 325, 335, 345mm). Each of these rings can be employed as the starting ring for the deposit of reinforcement and matrix material in layers having an overall thickness of about 0.200 inch (305mm).

What is needed, therefore, is a convenient and ecostarting rings having nomical method for producing sets o.

closely reproducible internal diameters.

Rn-20.4nR There is described herein, as an embodiment of the present invention, a method of making such ring structure using a mandrel having a relatively high coefficient of thermal expansion and having external dimensions slightly smaller than the internal dimensions of the ring structure to be formed. The mandrel is heated in a plasma flame and is then plasma sprayed with a protective oxide surface layer such as a layer of aluminum oxide. Following the deposit of protective oxide on the mandrel surface, a sprayed deposit of a matrix metal having a coefficient of thermal coexpansion substantially smaller than that of the mandrel is applied to the oxide coated mandrel surface. The oxide coated mandrel and deposited tube of matrix metal is then allowed to cool to room temperature.

During the cooling, the mandrel shrinks away from the tube of matrix metal because of the relatively large difference in thermal coefficients of their respective materials. The RD-20. 403 oxide coated mandrel surface separates from the ring so that the ring may be removed from the mandrel. It is observed that the separation of the ring from the mandrel occurs in the oxide layer so that the initial oxide layer must be pars tially replenished before a second matrix layer is deposited. Following the removal of the ring of matrix metal, the mandrel is again heated to a temperature at which a plasma spray deposit of a protective oxide coating and of a matrix metal layer can be formed on the mandrel. The second ring of matrix metal is formed on the oxide coated mandrel and this ring and the contained mandrel are permitted to cool to room temperature to cause -a separation, of the ring from the oxide coated surface.

The process of depositing ring structures on the oxide coated surface is repeated whereby a plurality of plasma sprayed ring structures having essentially the same internal diameter is reliably and economically produced.

By providing a set of mandrels of different diameters sets of rings of matrix metal having reproducible diame- ters may be fabricated.

In the following description of an embodiment of the invention reference is made to the accompanying drawings in which:

FIGURE 1 is a semischematic isometric illustration of a mandrel to which a surface coating of a protective oxide has been applied; FIGURE 2 is a semischematic isometric illustration of the deposit on the oxide coated mandrel of Figure 1 of a plasma spray deposit of a matrix metal; and 30 FIGURE 3 is a semischematic isometric illustration of the oxide coated mandrel of Figure 1 being removed from the 7 1 RD-20.40-- plasma spray deposited ring structure after the structures have been permitted to cool.

It is known that RF plasma spray deposit of titanium base matrix metal material on a substrate can be employed to form a foil of the matrix material. Such a process is disclosed in U.S. Patent No. 4,838,337. Numerous other structures have been formed by the plasma spray deposit of a metal on a substrate and there is extensive patent and technical literature on such processes. However, where the substrate is a mandrel, the conventional process for removal of the mandrel is either the machining of the mandrel out from within the plasma spray deposit or the chemical dissolution of the mandrel from within the plasma spray deposit.

is The subject process is one by which the mandrel and the deposited ring structure spontaneously and automatically separate from each other so that the ring structure can be removed from the mandrel on which it is deposi ted without recourse to chemical dissolution agents or machining or other metal working techniques.

The technique by which the accomplishment of the production of a plurality of plasma spray deposited ring structures with essentially the same internal dimensions is achieved is dependent on a combination of actions. One such action is the coating of the mandrel surface with an oxide surface coating to serve as a release agent for the separation of a plasma spray deposited material from the substrate on which it is deposited.

The second action on which the process depends is the provision of a mandrel which as a sufficiently large RD-20. 403 thermal coefficient of expansion relative to that of the matrix material which is plasma spray deposited thereon that the mandrel tends to shrink away from the internal surface of the plasma spray deposited ring structure formed thereon. It is this combination of elements of the applicant's process which makes possible the repeated production of ring structures having essentially the same internal diameter from a single starting mandrel structure.

Some of the advantages of the present invention can be best understood if considered in relation to a production process with which the instant invention may advantageously be used.

The illustration is given above of the need for production of a set of rings which may be nested together in concentric fashion to produce a single ring having a relatively large number of filament reinforcement layers in excess of one hundred such layers. For this purpose a set of five concentric rings each having about twenty layers of filament reinforcement may be used, as previously discussed.

Each of the five rings has a different internal diameter and differs by about 0.4 inch (10mm) from the internal diameter of the adjacent ring, whether it is larger or smaller.

What is desired in order to produce such a set of filament reinforced rings, and what is made possible by the present invention, is the production of starting matrix structures which have initial diameters which are reliably reproducible within close tolerance of a predetermined initial diametric dimension.. In other wordsif a ring structure having a 12 inch (305mm) ID (internal diameter) is sought. the method of the present invention provides for production 'Of a ring structure - having an internal diameter of 12 inches (305mm within a t RD-20. 403 very close tolerance. And the same production capability exists for rings of 12.4, 12.8, 13.2 and 13.6 inches (315, 325, 335, 345mm) The production of a single such ring structure is described now with reference to the figures. Referring first now to Figure 1 mandrel 10 is provided having an external diameter slightly smaller than the diameter of the ring to be produced. The mandrel 10 is preferably thick walled or solid as illustrated in Figure 1. This wall thickness is preferred in order to avoid distortion of the mandrel shape to out-ofround due to the sequence of heating and cooling steps as the mandrel is used over and over again. The mandrel is first plasma sprayed with a protective oxide layer using a conventional plasma gun 12 and using an-oxide powder such as alumi- num oxide, magnesium oxide or some similar oxide. To form an oxide surface deposit 14 on mandrel 10 with the aid of a conventional plasma flame 16. We have demonstrated such oxide coatings to be adherent and to form a persistent coating on a metal surface such as the surface of mandrel 10.

The oxide coated mandrel is next introduced into a low pressure RF plasma deposition chamber (not shown) where the mandrel 10 is mounted for rotary movement under a plasma flame 20 emanating from an RE plasma gun 18. Such an RF gun may be one as described in the patents, such as the U.S.

Patent 4,782,884, discussed above. Preferably it is one such as is described in our co-filed application No.

Docket RD-17,823) entitled. "Low Frequency Radio Frequency Plasma Spray Deposition".

The RF plasma gun 18 is used to deposit a layer 22 of a titanium base metal such as Ti-6242 (titanium 6 aluminum-2 tin-4 zirconium-2 cobalt) onto the oxide coated surface 14 of mandrel 10. the layer formed may be for example about 1. /8 inch thick.. The preferred thickness of the layer 1 RD 20.403 is dependent on a few factors. one factor is that the ring formed must be self supporting and the thickness of the layer must be sufficient so that it provides a ring with a wall thickness sufficient to be supporting. Another factor is the planned use of the ring. If the outer surface of the ring is to be machined, an additional thickness to allow for the metal to be removed by machining should be included.

For reasons explained more fully in co-pending US application Serial No. 546961, the inner position of a deposited ring of matrix metal is a sacrificial portion of a reinforced ring structupe to serve as one member of a set of rings to be nested concentrically and to be HIP consolidated into a ring of over 100 layers of filament reinforcement. It is a sacrificial portion in that it is machined out of the interior of a 20 layer component ring of the set after the 20 layers of reinforcement have been added but before the five component rings are assembled in concentric array and consolidated into a super ring or a single ring over 100 layers.

0 The innermost layer of the matrix metal of each o the rings to be assembled is sacrificed, i.e., machined and discarded, in order to increase the volume fraction of filament of each component ring of the set.

Following the deposit of the layer 22 of matrix metal the ring and mandrel are allowed to cool. The ring 22 separates spontaneously from the mandrel and slides off the mandrel as illustrated in Figure 3.

The subject method and the way it may be carried into effect is illustrated by the following example:

EXAMPLF 1..

t RD-20. 40-1 A hollow ring of mild steel having a length and a diameter each of 411 (101mm) was provided. The steel had a coefficient of thermal expansion of approximately 14 - 6 a _1 x 10 C The hollow ring was mounted for air plasma spray depositing of a 0.00311-0.00511 (0.08-0.13mm) thick surface coating of aluminum oxide thereon. The plasma gun employed was a Metco 3MB using the spray conditions suggested by Metco. The mandrel was first heated with the plasma flame and then the layer of aluminum oxide was spray deposited thereon.

Following the air deposition of the aluminum oxide, the mandrel was introduced into a low pressure RF plasma deposition chamber similar to those described in the U.S. Patents and applications referred to in the background state- ment above. The oxide coated hollow ring was again heated by the plasma torch to a suitably high temperature for deposit thereon of a matrix metal. The matrix.metal applied was a titanium base alloy and specifically Ti6242 (Ti-6Al-2Sn-4Zr 2Mo). The thermal coefficient of expansion of the deposited titanium base alloy matrix metal was approximately 11 x 10-6 C-1.

Following deposit of approximately 0.125 inches (3.17mm) thickness of the titanium base alloy matrix, the mandrel and its coatings of oxide and metal were allowed to cool to room temperature and were removed from the low pressure plasma deposition-chamber.

On removal from the chamber, it was found that the collar of matrix metal had separated spontaneously and automatically from the oxide coated mandrel so that it was possi- ble to slide the collar off the mandrel without the employment of chemical agents or machining or other destructive inasive steps.

RD-20. 403 It will be appreciated that the operation of the present method is dependent both on the coating of the mandrel with a nonreactive oxide coating and on the existence of a significant difference in thermal coefficient of expansion between the metal of the mandrel and the matrix metal deposited on the oxide coated portion thereof. Significant differences of thermal coefficient of expansion of are required for satisfactory operation of the present invention and preferably the differences in thermal coefficient of expansion should be as high as feasible.

Following the deposit of the titanium base metal collar and its removal from the ox ide coated mandrel, the mandrel was again re-sprayed with additional A1203 to make up for the amount which was incorporated in the matrix ring when it separated from the oxide coated mandrel. The mandrel with its fresh coating of oxide was introduced into the low pressure plasma deposition chamber and heated in preparation for -deposit of a second collar of matrix metal thereon. The matrix metal of the same titanium alloy was formed on the surface of the mandrel and again the mandrel and collar were permitted to cool to room temperature and then removed from the low pressure plasma deposition chamber. Again, the collar separated spontaneously from the oxide coated mandrel and was removed from the mandrel without the aid of mechanical or chemical agents.

The internal diameter of the two collars formed as described in the example were measured and were found to be the same within 0.003-0.005 inch (0.02-0.13mm).

There has thus been described a method by which a plasma spray deposited ring structure can be ploduced economically qnd_reliably while permitting repetitive production of plasma spray deposited ring structures having well defined internal diameters.

z k RD-20403 The foregoing demonstrates that it is possible to introduce a multiplicity of ring structures having essentially the same internal diameter by the process of the subject invention.

14 -

Claims

CLAIMS:

1. The method of forming a plurality of ring structures having essentially the same diameter which comprises:

providing a mandrel having a high thermal coefficient of expansion, coating the mandrel with an oxide of low reactivity, RF plasma spray depositing a collar of matrix metal of low thermal coefficient of expansion on the oxide coated sur10 face of the mandrel, allowing the-mandrel and collar to cool to cause spontaneous separation of the_collar from the-mandrel, and repeating the spray depositing and cooling a plurality of times to form a plurality of collars having essentially is the same internal diameters.

RD-20. 403

2. The method of claim 1, in which the deposited oxide is aluminum oxide.

3. The method of claim 1, in which coating of the mandrel with oxide is by plasma spraying.

4. The method of claim 1, in which the matrix metal is a titanium base metal.

5. The method of claim 1, in which the matrix metal is Ti-6242.

6. The method of claim 1, in which the matrix col- lar has a thickness of about 1/8 inch (3.17MM).

7. A method of forming ring structures substantially as hereinbefore described with refeience to the accompanying drawings.

"ewpur NT9 I RI-i copis may bc onained frorn Published 1991 at The Patent Office. Concept House. cidjff Road - N. E, Gwen'. Further. - vs. N ques lid. 5, Marv Cray. Kent- Sales Branch. Unit 6. Nine Mile Point. Cwinfelinfach. Cross Ke.ewport. NPI 7HZ. Printed by Multiplex techni 1\