Patent Application
20080069992
The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way.
The invention now will be described merely by way of example with reference to the accompanying drawings, wherein:
The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features.
For the purposes of the following discussion it will be assumed that the elastomeric bag of the present invention is used within an oil-filled electric motor protector of the type used with submergible electric motors to be suspended within wellbores. However, it should be understood that the present invention can be used within any other type of downhole or surface motor, pump, turbine or other industrial machine that requires the use of an elastomeric body to contain it or to contain oil supplied to it.
As has been briefly described above the present invention is a reinforced elastomeric bag for use within an oil-filled electric motor protector. Electric motor protectors are well known to those skilled in the art, and they provide the capability for thermal expansion of the electric motor's cooling oil, they provide isolation of the cooling oil from wellbore fluids, and they usually contain thrust bearings to absorb the axial loading of the pump that is connected thereto.
The interior of the motor protector 10 contains one or more generally cylindrical elastomeric bags 22, which are clamped on each end by annular brackets or rings 24 across spaced inner housings 26. The interior 28 of each bag 22 is filled with cooling oil that is conveyed to and from the electric motor 14 through internal passages (not shown) in the protector 10 and the motor 14, as is well known to those skilled in the art. The elastomeric bag 22 is preferably formed as a single continuous body, without a seam or weld, and has a thickened portion or bead 30 adjacent each mouth or end opening 32.
The bag body is preferably formed primarily from an elastomeric material that provides desired elasticity at temperatures above 300° F. (150° C.). Suitable elastomeric materials include tetrafluoroethylene-propylene copolymers, vinylidene fluoride hexafluoropropylene copolymers, virtually saturated acrylonitrile-butadiene copolymers, vinylidene fluoride-perfluoromethylvinylethertetrafluoroethylene terpolymers, vinylidene fluoride hexafluoropropylene tetrafluoroethylene terpolymers, ethylene propylene diene monomer-based polymers, and combinations thereof. One or more bonded layers of such material(s) can be used as desired.
To increase the tear resistance of the elastomeric material one or more reinforcing materials is added. For example tetrafluroethylene, aromatic p-polyamides, aromatic o, m-polyamides, fibreglass, ferrous metal, nonferrous metal, and combinations thereof of the particles, threads and/or weave, are dispersed within, bonded to or layered within the elastomeric material in manners to improve the tear resistance of the bag 22 at elevated temperatures, such as at temperatures of greater than about 300° F. (150° C.).
In U.S. Pat. No. 6,537,628 (from which the above description is largely taken), it is suggested that the elastomeric material be reinforced with woven material which is wrapped around a form mandrel before the bag is moulded around it. Alternatively it is applied by hand after the bag has been moulded and vulcanized, and is bonded or glued to it. We consider that neither of these techniques is satisfactory. The woven material is in sheet form and, where its edges overlap, the integrity of the bag depends in that region entirely on the strength of the bond between the elastomeric material and the woven sheet material. Furthermore when the sheet material is glued to the surface of the bag, the integrity of the whole structure depends on the strength of the adhesive bond.
In the present invention, the reinforcing material is provided in the form of a tube, preferably a knitted tube or sock, preferably seamless. Referring to
The tube or sock 40 is shown in
The resulting product is shown in
A suitable fibre material from which to weave the sock is PBO, ie. poly (p-phenylene-2, 6-benzobisoxazole). This is available for example under the trade name ZYLON from the Toyobo Co Limited.
To assist the integration of the sock with the bag material, the sock material can be surface-treated eg. by Chemosil® 5150, applied by dipping or brushing, and carried in a suitable solvent such as industrial methyl alcohol, for example at a concentration of 50% by volume. The sock material alternatively can be plasma-treated to alter the surface chemistry of the fibres or remove unwanted process aids, lubricants etc or other contaminants from the surface of the fibres to promote adhesion so that they bond directly to the bag material. The sock material then chemically bonds to the bag material rather than being dependent solely on mechanical adhesion. This is particularly advantageous when the sock is embedded in the inner or outer surface of the bag.
The plasma treatment typically comprises placing the sock in a treatment chamber and exposing it at chamber ambient temperature to a plasma formed by exciting a gas (for example ammonia, argon, water vapour, air, oxygen or nitrogen or a mixture thereof) in an electric field at low pressure (for example in the range 10−1 to 10−3 Pa). The excited gas forms ions, free radicals or other reactive species which react with (particularly organic) impurities from the sock material surface to form oxides or other volatile compounds which are then pumped out of the chamber. The plasma treatment can also increase the surface area of the material and modify its surface chemistry by ablation (micro-etching) and thereby improve its chemical and physical adhesive interaction with the elastomeric bag material.
By using a tube of reinforcing material rather than wrapped sheet material the overlapping join of U.S. Pat. No. 6,537,628 is avoided. Preferably the tube is formed seamlessly by knitting it as a sock, but a tube can be made from sheet material by joining its edges eg. by sewing. However, the knitted construction can provide an inherently more resilient reinforcing structure then material woven as a sheet. This better enables the reinforcement to expand and contract with the bag material during use. The limitations on the choice of reinforcing material which were seen as a problem in U.S. Pat. No. 6,537,628 can thus be avoided to some extent, and reinforcing fibres having little inherent resiliency can be used, for example carbon fibre, glass fibre or aramids or some of the other conventional materials dismissed in U.S. Pat. No. 6,537,628 as unsuitable.
Alternatively or in addition, temporary elasticity can be provided in the sock or tube by including elastic material in the thread from which it is woven, and then destroying that elasticity during subsequent processing. For example natural rubber (latex) threads can be included amongst the threads; this material will survive during the moulding and initial curing step but not the post cure (which can be as much a 12 hrs @ 230° C.) due to the elevated temperature. The temperatures encountered in use also are likely to be beyond the capability of latex.
If permanent elasticity is required in the sock a heat resistant material can be included in the thread from which the sock is woven. For example a fine extruded cord of soft fluorocarbon elastomer, preferably of about 60 IHRD may be used, although the resulting sock would be harder to stretch over the mandrel then a comparable one containing latex.
One of the strips is wound helically around a pre-heated mandrel or core (stage 58) to cover its circumferential surface as required for the finished shape of the bag. Advantageously the mandrel can be rotated eg. in the headstock of a lathe to facilitate this. The PBO sock or tube, having first been cut to length, is pulled over the first layer of rubber (stage 60). A second strip of rubber is then wound helically over the sock (stage 62); it may be found advantageous for this layer to be wound to the opposite hand to the first layer so that the strip edges in the two layers are not parallel. The assembly then is placed in a compression mould for 20 minutes at 160° C. wherein the two layers of rubber are compressed together and merge through the interstices of the sock, and abutting surfaces (both between the layers and between the edges of the strip forming each layer) fuse together and the completed make-up is subjected to compression moulding at elevated temperature. The resulting product consists of a single homogeneous layer of elastomeric material in which the sock is embedded.
Full cure may or may not be completed in the moulding process. A post moulding process whereby the bag is placed in an autoclave or oven and subjected to a ‘ramped’ heated and cooling process may be employed. This process may take place whilst the bag is still on the mandrel or after it has been removed. The latter is preferred because otherwise the release of the mandrel or core for the manufacture of another bag is delayed. A suitable post-moulding even cure cycle is as follows (ramp up to 100° C. @ 50° C. per hour, dwell for 1 hour @ 100° C., ramp up to 180° C. @ 20° C. per hour, dwell for 1 hour @ 180° C., ramp down to room temperature @ 40° C. per hour).
The finished bag is blown off the mandrel by means of compressed air supplied via a collar eg. of PEEK (polyetheretherketone) material inserted between the bag and the mandrel. Alternatively if a collapsible mandrel is used, the bag is removed by disassembling the mandrel and removing it from within the bag.
The laminates are fitted under the end of the sock so as to contact the end of the rubber tube previously fitted to the mandrel. They are temporarily held in place by one turn of the narrower strip material (stage 76); some solvent may be applied to the rubber to assist temporary adhesion. Then the lay-up is completed by helically winding an outer layer of wider strip (stage 62). The subsequent stages 64, 66 and 68 then proceed as previously described.
In this and the other embodiments the rubber overlaps the free end or ends of the sock by a small amount. If preferred, the edges of the strip can in each embodiment overlap each other slightly.
Compression moulding of the bag has the advantage that the tube or sock 40 is less likely to be displaced during the moulding operation because it is already held in position by the uncured rubber material when it is put in the mould. Excessive displacement of the tube 40, in addition to resulting in a less repeatable product, may otherwise tear the tube fabric unless particular care is taken. Partial pre-curing (eg. to between 20% and 50% of full cure) of the inner layer of rubber in
Each feature disclosed in this specification (which term includes the claims) and/or shown in the drawings may be incorporated in the invention independently of other disclosed and/or illustrated features. A feature of one embodiment can be incorporated in another embodiment.
Statements in this specification of the “objects of the invention” relate to preferred embodiments of the invention, but not necessarily to all embodiments of the invention falling within the claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 0618231.5 | Sep 2006 | GB | national |
