BACKGROUND OF THE INVENTION
The present invention is directed to techniques for manufacturing open ended tubular structures of multilayer form such as seals, bushings and bearings and other wear components from a fiber-resin material, in particular from continuous-carbon-fiber-reinforced thermoplastic materials.
The use of continuous-carbon-fiber-reinforced thermoplastics for seals, bushings, and bearings is gaining excitement. These materials have distinct advantages in a wide variety of industries, including aerospace, oilfield, and chemical/fluid handling. The benefits include:
1) Excellent corrosion and chemical resistance,
2) Superior wear properties, due to low coefficient of friction and self-lubrication,
3) High mechanical strength and stability,
4) Extreme temperature capabilities,
5) high dimensional stability at different temperatures due to low coefficient of thermal expansion in fiber direction,
6) Finished parts are easily machinable.
- SUMMARY OF THE INVENTION
It would be desirable if improvements could be made to known methods for manufacturing tubular structures such as seals and wear components made from fiber-resin material such as continuous-carbon-fiber-reinforced thermoplastic materials. It would be desirable if such improvements could enhance the end product while reducing costs.
An object of this invention is to provide improvements in the manufacturing techniques for such multilayer tubular components.
A further object of this invention is to provide such manufacturing techniques which result in improved product quality while reducing costs.
In accordance with this invention a tubular multilayer structure open at both axial ends is manufactured by winding a continuous fiber pre-impregnated with a thermoplastic resin around a rotating heated mandrel. The manufacturing method is improved by feeding the material from a supply station to a shaping station before the material is wound around the mandrel. The material is then heated over a shaped hot plate while in the shaping station to lightly melt the material without heating the entire wound structure. The material is tensioned to at least 15,000 psi before the material is wound around the mandrel to ensure good bonding of the wound layers.
In a preferred practice of this invention the material is a continuous fiber such as carbon-graphite pre-impregnated with a thermoplastic resin. The material is tensioned by a tensioning structure located between the material supply station and the shaping station. Preferably the material is tensioned from 15,000 to 25,000 psi.
FIG. 1 is a top plan view of an assembly for manufacturing a tubular multilayer structure in accordance with this invention;
FIG. 2 is a side elevational view of the assembly shown in FIG. 1; and
FIG. 3 is an end elevational view of the formed tubular structure.
The present invention relates to a process or method for manufacturing standard tubular shapes such as rings which are open at both axial ends. Such tubular structures could have various known uses including seals, bushings, bearings and other wear components. The invention is directed to improvements in known processes wherein a thermoplastic winding process uses continuous fiber such as carbon-graphite that is impregnated with a thermoplastic resin such as PEEK, PEKK or TPI. Reference is made to U.S. Pat. No. 5,198,281 and U.S. Pat. No. 5,094,883, all of the details of which are incorporated herein by reference thereto and which disclose the types of materials that may be used in the practice of this invention.
Although the invention is preferably practiced where continuous carbon fiber composites are used for forming the structure, it is to be understood that other materials may be used within the practice of this invention.
In order to assure good wet-out of fibers by resin, which is critical for the applications of this invention, the fiber volume fraction of the fiber-resin mixture is less than 65%, typically 60%.
In prior techniques the material is heated before it is laid down in order to obtain fiber orientation. The tubular structure is formed by wrapping the material around a hot rotating mandrel until sufficient layers are created for the intended final structure. When the mandrel has cooled the tubular structure can then slide off the mandrel and can then be machined or otherwise finished. In the conventional practices pressure is applied to the material through nip rolls. Among the objections to conventional practices are that residual stresses cause delaminations which impairs the quality of the tubular structure.
In accordance with this invention the tubular structure is formed by winding the fiber-resin material directly onto a mandrel and then later extracting the thus formed structure from the mandrel so that the resulting structure can be machined or otherwise treated particularly with regard to the exposed interior surface of the tubular structure.
In accordance with this invention the conventional practices are modified by managing or controlling the tension and heating in such a manner as to produce good interlaminate bond strength while limiting residual stresses, thus reducing the occurrence of delaminations. This is accomplished without the need for complicated expensive techniques. The tensioning aspect of invention involves applying a tension of at least 15,000 psi to the material before the fiber-resin material is applied to the mandrel. This ensures good bonding. The range of tension could theoretically have an upper limit approximating the yield strength of the material. For practical purposes, however, it would not be desirable to apply too much tension since this would make it difficult to extract the structure from the mandrel. In the preferred practice of the invention the tension could be in a range of 15,000-100,000 psi. A more preferred range would be 15,000-25,000 psi and the most preferred range would be 20,000-25,000 psi. The tension creates good bonding and consolidation of the layers in the structure.
In accordance with the heating aspect of this invention before the fiber-resin material is applied to the mandrel the material is heated over a shaped hot plate such that the incoming material is lightly melted without heating the entire wound part. If desired, supplemental heat from an external source can be added to the wound part at specific locations such as wear surfaces and highly machined areas. The supplemental heat may come from any suitable external source such as a torch which could be manually operated or automated. The heating would take place for a short period of time at a location away from the mandrel where the part or structure is actually made.
FIGS. 1-2 illustrate an assembly 10 which may be used in the practice of this invention. As shown therein, the assembly 10 includes a supply station 12 which may take any suitable form such as being a supply roll or creel from which the fiber-resin material 28 is removed. Various components of the assembly as later described including the supply station 12 are mounted on a transversing table or carriage 14 which moves back and forth in the direction of the arrow shown in FIG. 2 parallel to mandrel 38. From the supply station 12 the material 28 passes through a tensioning station 16 which may take any suitable form. For example, the tensioning station 16 may include a support 18 having a pivotable arm 20 at the end of which is a tensiometer 22 which operates in conjunction with brake 24 and roller 26 to control the tension of the material 28. The material 28 then passes through guide rollers 30,32 and then into shaping station 34. Shaping station 34 includes a shaped hot plate arrangement 36 which may be of the type disclosed in U.S. Pat. No. 5,160,561, all of the details of which are incorporated herein by reference thereto. The material 28 is heated over the shaped hot plate 36 so that the incoming material is only lightly melted at a location upstream from the mandrel 38 so that the heating can be done without heating the entire wound part.
In the shaping station 34 the material 28 is shaped into a generally ribbon form which facilitates the application of the material 28 to the mandrel 38. The plate 36 in the shaping station 34 gives intimate contact with the melted resin to create the desired shape for application of the material 28 to the mandrel 38.
When the fiber-resin material passes through the shaping station the material is heated to a temperature slightly above the resin melting point and remains in the station over its path of travel for a sufficient residence time to accomplish the light melting. For example, with a plate 36 which is about 6 to 8 inches long, the material would be fed at a rate of about 20 feet per minute. The material entering the station 34 cold would then gradually heat as it passes over the plate 36 until it leaves station 34 slightly melted.
From the shaping station 34 the material 28 is wound directly on the mandrel 38. Except for mandrel 38 and its associated structure all of the components of the system 10 are mounted on the table 14 in such a manner that the table 14 reciprocates back and forth parallel to the mandrel thereby permitting the material to be wound around the mandrel and create a plurality of layers. Any suitable drive mechanism may be used for moving table 14 back and forth. FIG. 2 schematically illustrates a reversable motor 42 rotating a lead screw 44 on which a drive nut 46 is mounted. The drive mechanism includes a guide rod 48 at the opposite end of table 14. In this manner, depending on the direction of rotation of lead screw 44 the table 14 would move toward or away from the motor 42 in accordance with the back and forth movement of nut 46.
Mandrel 38 may take any suitable construction such as being driven by motor 50 with the mandrel 38 supported by bearing supports 52. Mandrel 38 would be heated and rotated as is known in the art. Thus, during the rotation of mandrel 38 the material 28 is applied or wound on the mandrel 38 to create the desired number of layers in accordance with the intended end product.
FIG. 3 illustrates a tubular structure 54 which is open at both axial ends and is formed from a plurality of layers. Tubular structure 54 could then be used in any conventional manner such as seals, bushings and bearings, wear rings, driveshafts, collars, and sleeves that match desired properties and anti-extrusion rings, drilling tool components, bearings, drill collars, logging sleeves, supports, subsea bearings, drive shafts, pump wear rings and bushings, non-conductive collars, valve seats, tractor systems, single trip perforators, tool bodies, abrasion resistant cylinders, drillable seals and cementing drillable plugs.