Patent Application
20090114497
The present invention relates to flexible inflatable tubes that are inflatable under pressure to operate or engage a coupling component used in a mechanism such as an industrial clutch or a brake.
Clutches and brakes used in industrial machinery and equipment may include a coupling component having an inflatable annular tube that is mounted on a rigid annular rim. Friction shoe assemblies are connected with the tube in an annular array. When pressurized, the tube is expanded to press the friction shoe assemblies against another coupling component to interconnect the two coupling components or retard relative motion therebetween.
Coupling components having this, construction have previously been made by a method that includes hand-building an inflatable annular tube, placing the inflatable annular tube in a mold, inflating the tube, and heating the mold to vulcanize the elastomeric material of the tube. This process is labor intensive and, accordingly, significantly increases the cost to manufacture the tube and the clutch or brake.
Referring now to the drawings, which are not intended to limit the invention,
The friction shoe assemblies 14 are moved into engagement with the drum by radial expansion of the inflatable tube 12. Thus, when fluid pressure, such as air pressure, is conducted through a conduit 16 into the annular tube 12, the tube expands radially inwardly. This causes the tube 12 to press the friction shoe assemblies 14 against the drum. The friction between the shoe assemblies 14 and drum interconnect the drum and the coupling component 10.
In the illustrated coupling component 10, a rigid annular metal rim 18 is connected with the inflatable tube 12. The rim 18 has an annular mounting flange 20 which is used to connect the coupling component 10 with an associated apparatus or support structure (not shown). The rim 18 has a cylindrical web 22 with a radially inner side surface which is bonded to a radially outer side wall portion of the tube 12. Upon inflation of the tube 12 to press the friction shoes 14 against a drum or other coupling component, torque is transmitted between the friction shoe assemblies and the rim 18. To enable the tube 12 to withstand relatively large torque forces, one or more reinforced and non-reinforced layers 24 are provided in the tube 12 as will be described in further detail below.
Referring to
In an embodiment, tube 12 includes at least one reinforced layer 32 sandwiched between an inner, unreinforced layer 34 and an outer, unreinforced layer 36. However, it will be appreciated that tube 12 may have any number of layers, including for example, multiple reinforced layers 32 as shown in
The tube 12 is constructed by building the elongated, generally tubular-shaped structure 24, cutting the tubular-shaped structure 24 into predetermined lengths and joining the ends 26a, 26b of each length at the joint 28 to form the toroidal-shaped tube 12. While a range of elastomers may be used in the unreinforced layers 32 to facilitate this construction, including uncured thermoset and thermoplastic elastomers, thermoplastic elastomers provide the best blend of efficiency and integrity when joining the two ends. Thermoplastic polyurethane is particularly suited for tubes used in clutches given its good overall balance of mechanical, thermal, chemical and aging performance. Similarly, while a variety of organic and inorganic fibers may be used in the reinforced layers, organic fibers such as polyester, nylon, and rayon are particularly suited for use in tube 12 given their relatively low cost, low stiffness and generally acceptable thermal performance. Polyester fiber including multiple twisted fiber bundles similar to bundles used in the vehicle tire and industrial hose, industries—commonly referred to as “tire cord”—is particularly, but not exclusively suited for use in tube 12; however, if is recommended that traditional resorcinol formaldehyde latex fiber sizing used with thermoset elastomers be replaced with isocyanate, blocked isocyanate, or epoxy sizing to provide more robust adhesion to the thermoset elastomer.
With reference to
A chemical cross-linking agent may be added to the thermoplastic elastomer during extrusion coating of the fiber reinforcement (e.g., dosed into the barrel of an extruder), When so employed, partial cross-linking between the reinforced layer materials occurs while the thermoplastic elastomer is at a relatively high temperature, promoting cross-linking of polymer chains between the fiber and the resin and within the body of the thermoplastic elastomer itself. The type and amount of chemical cross-linking agent may be selected to facilitate a relatively low level of cross-linking, sufficient to improve elevated temperature stability of the reinforced layer, but low enough so that additional flow and bonding may occur during subsequent high temperature processing operations.
In an exemplary implementation of the present invention, a medium durometer TPU made by BASF having material number 1185A10, was mixed with either of two experimental chemical cross linking agents (e.g., 7 w % Link 1.0 or 5 w % Link 2.0. A T-Peel test was then performed yielding a bond strength between the layers as high as 80% of the unmodified thermoplastic at bonding temperatures only slightly higher (e.g., 10-20° C.) than required for the unmodified, fully thermoplastic polymer. These results indicate that the polymer chains retain sufficient mobility for adequate thermal bonding and still allow thermal consolidation of the layers after wrapping.
Alternatively, the fiber or fabric may be coated with a chemical cross-linking agent prior to extrusion coating. During extrusion coating, the relatively hot thermoplastic elastomer contacts the coated fiber or fabric, activating the chemical cross-linking agent and causing localized cross-linking of the polymer chains between the fiber or fabric and the thermoplastic elastomer. This process improves fiber or fabric adhesion to the elastomer and long-term creep performance since the fiber is mechanically and chemically secured to the elastomer. A majority of the elastomer remains uncross-linked to preserve the thermoplastic behavior of the reinforced layer.
Similarly, each unreinforced elastomer layer 32 may be constructed by producing a semi-continuous sheet of unreinforced elastomer, such as by sheet or blown film extrusion. The reinforced and unreinforced sheets may then be slit or cut into individual strips of “tape,” each having a predetermined width.
In an embodiment, the tubular-shaped structure 24 is constructed by spiral wrapping individual strips of unreinforced elastomer “tape” onto a mandrel 38. The width of each tape strip may be selected to match the minor diameter, amount of overlap and fiber helix angle desired in a given wrap layer. To facilitate removal of the mandrel from the tubular-shaped structure, the mandrel may be coated with a release agent, such as zinc state or polyethylene film. While the mandrel shown in
Referring to
Prior to thermal consolidation of the layers, a nylon fabric tape or other suitable material (not shown in FIG.) may be spiral wrapped around the outer unreinforced elastomer 36 layer to apply a radially inwardly directed pressure onto the layers and to protect the tubular-shaped structure 24 during thermal consolidation. Thermal consolidation of the tubular-shaped structure 24 may be accomplished using a variety of methods, including, without limitation, heating the mandrel (electrical resistance, induction or heated fluid within the mandrel) or by inserting the entire tubular-shaped structure info a heated atmosphere, such as a steam autoclave or oven. In a steam autoclave, for example, temperature and pressure promote molecular mobility and bonding between the layers. It was determined that subjecting the tubular-shaped structure to saturated steam at approximately 293° F. for about 35 minutes was sufficient to bond and consolidate the tube structure described above using a relatively low hardness polyester thermoplastic urethane, such as Seaman 1940 PTFF
Following consolidation, the nylon tape is removed and the mandrel 38 may be extracted from the tubular-shaped structure 24, such as by using fluid pressure (e.g., high pressure wafer) to eject the mandrel. The continuous and still relatively straight tubular-shaped structure 24 may be permanently deformed using additional heat and pressure to obtain the generally fiat shape shown in
In the embodiment shown in
The ends 26a, 26b of the straight tubular-shaped structure may be joined using a thermoset or thermoplastic adhesive. For thermoplastic tubes, a solvent bond or thermal weld may also be used to join the ends. Heat to effect a thermal weld may be generated using various sources, including, without limitation, a heated tool, hot gas, vibration, ultrasonic, induction, radio frequency, resistance, infrared and laser energy.
The invention has been described in great detail in the foregoing specification, and it is believed that various alterations and modifications of the invention will become apparent to those skilled in the art from a reading and understanding of the specification. If is intended that all such alterations and modifications are included in the invention, insofar as they come within the scope of the appended claims.
