Abstract:
A gear box or the like adapted for prolonged effective use in a harsh and/or corrosive environment such as found in the chemical industry and are in which salt water is prevalent. Components of the gear box are provided with protective polymer coatings which are low friction and impervious to attack from the environment and materials used therein. Exterior surfaces of the housing are coated with a polymer that also withstands impact from foreign objects as exemplified by polyamides, epoxies and fluorocarbons with nylon being preferred. Other components such as the input shaft, bushings and the like are preferably coated with one or more layers of fluorocarbon polymers, with layers in contact with the component including a thermosettable binder component such as a phenolic. Certain coating thicknesses are most preferred.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to gear boxes and, particularly, to gear box structures which are coated with corrosion resistant material for permitting use of the gear box within a corrosive environment, particularly a salt water environment. 
     Conventional gear boxes are generally devised as a heavy duty tool, particularly constructed to withstand long-time usage under extreme power requirements and under adverse conditions. However, it has been found that the life span for a gear box in a salt water or other harsh environment is reduced considerably from many years to only a few weeks before corrosion deteriorates the gear box beyond further useful service. The materials utilized in conventional gear boxes are generally cast iron and/or steel and, in special applications, stainless steel in order to ensure long life usage. Since cast iron and steel offer little or no protection, eventually stainless was introduced to obviate this problem. However, even stainless steel is not able to survive a salt water environment, and at best, may only prolong the life of the gear box very slightly. 
     Therefore, it is a principal object of the present invention to enhance the life span of gear boxes under adverse corrosive environments such as those involving salt water, fertilizers, concrete, sewage disposal, and chemical processes. 
     Another object of the present invention is to improve the art of gear boxes by permitting the use of standard materials susceptible to corrosion in the construction of the same and yet extend the life span for these devices. 
     These and other objects of the present invention are achieved by the present invention which is directed to a gear box or the like which has a corrosion resistant material coating thereon, preferably a fluorocarbon polymer which is impervious to oxidation, chemical attack and the like. In a most preferred arrangement, two different coatings of fluorocarbon polymers may be applied in particular thickness ranges. The coating thicknesses are devised in accordance with acceptable tolerances associated with each of the details of the gear box assembly in order to avoid any binding in the movement of the parts and the prevention of inadvertent wear of the material from the parts while also affording the desired protection in harsh environments. 
     In a most preferred embodiment, the outer housing of the gear box or the like is coated with a polymeric material which not only will resist corrosion and chemical attack, but which also has adequate resilience and/or toughness to withstand blows from hammers, wrenches and other foreign objects and which will not chip off the structure. Polyamides such as nylon are most preferred for coating of the outer housing though epoxies and fluorocarbons may also be applied thereto. Other elements which are normally received within the exterior housing and/or otherwise located where damage from foreign objects is not likely are preferably covered with fluorocarbon coatings. Practically speaking, the polytetrafluoroethylenes are most often employed and, when in direct contact with the metal, include a thermoset binder component such as a phenolic for proper adherence to the prepared metal surface. Further, a top coating of polytetrafluoroethylene polymer composition may then be applied atop the base coating for crosslinking therewith. 
    
    
     These and other objects of the present invention will become apparent when reading the following specification taken in conjunction with the accompanying wherein: 
     FIG. 1 is an elevational view of a speed reduction device showing the device combined with a torque arm assembly; 
     FIG. 2 is a side view of the device illustrated in FIG. 1; 
     FIG. 3 is a cross-sectional view of a bushing element used in the reduction device of FIG. 1; and 
     FIG. 4 is an end view of the bushing applied to the output hub for the device. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     As shown in FIGS. 1 and 2, a typical gear reduction device, for example, a reducer, is indicated generally by the reference numeral 10 as including a housing 12, an input shaft 14 and an output hub 16. 
     The input shaft 14 is formed with a pinion 18 integral therewith within the housing 12 and being in operative engagement with a output gear 20 enmeshed therewith. Suitable sealing devices 22, such as double-lipped rings, or the like, surround the shaft 14 within the housing 12 for sealing against the influx of outside material into the housing. 
     The output hub 16 is formed with a tapered inner surface 23 at each end and having fitted thereto tapered bushing 24, 26 positioned on both sides of the housing 12, the details of each bushing being illustrated in FIGS. 3 and 4. Each of the bushings includes a cylindrical element or barrel 28 having its outer circumferential surface 30 tapered for engagement with the corresponding tapered surface 23. Interior circumferential surface 32 formed on the element 28 is arranged to receive an output shaft (not shown) useful with the reduction box 10. The bushings 24, 26 are the subject matter of a companion application filed concurrently herewith to the same inventors which is incorporated herein by reference. 
     Each of the bushings 24, 26 is formed with a flange 34 to which a hub back-up plate 35 may be attached as well as coupling devices (not shown) for connecting the hub 16 to a driven mechanism. While the hub 16 and the bushings 24, 26 are described and illustrated as having cooperating tapered surfaces, which is the preferred structural arrangement for effecting a driving connection to a driven mechanism, it will be understood that other forms of surfaces may be utilized, such as a key and groove or splines, as well as straight walled bushings. 
     The gear reduction box 10 also includes a torque arm assembly generally indicated by the reference numeral 36 having a turnbuckle 38 secured at one end by a fulcrum device 39 to a suitable rigid structure 40 and at its other end to an adapter plate 42 secured to the lower section of the reduction box 12. The assembly 36 maintains the box 10 against rotation during operation, and the turnbuckle provides adjustability as to positioning of the fulcrum 39, and to permit tightening of belts, etc. 
     The gear box 10 also includes a sealed expansion chamber 44 for permitting the introduction of a lubricant into the box and provide a relief spacer for expansion of lubricants and/or air during the normal operation of the box. The chamber 44 replaces the conventional standard vented breather normally associated with gear boxes. 
     As stated in the foregoing, the gear box 10 is arranged to be corrosion resistant and impervious to most environments, in particular, with respect to extremely corrosive environments, such as salt water, fertilizers, concrete, sewage disposal and chemical processes, for preventing premature rusting and deterioration of the internal parts as well as the external parts of the box. In accomplishing this goal, the gear box housing 12 is coated with a protective coating such as epoxy coatings, or polyamides exemplified by nylon, the latter being preferred due to its unique characteristic of being most durable of the known materials for this purpose. The coating of the nylon has a thickness approximately 0.008&#34; to 0.020&#34;. The input shaft 14 is coated with a base coat of a polytetrafluoroethylene polymer having a thermoset binding material, such as a phenolic binder included therein for adherence to these parts, the coating having a thickness of 0.0004&#34; to 0.0006&#34; and being applied from the end of the shaft and extending into the housing 12 under the adjacent input seals 22. Such coating thus effectively covers all exposed portions of the input shaft. The hub 16 is preferably made from stainless steel but may also be made of steel coated with a base coating of a polytetrafluoroethylene with a binding material. 
     The bushings, 24, 26, including the tapered surface 30, the interior surface or bore 32, and the flange 34 are also base coated with a base coating of a fluorocarbon polymer such as a polytetrafluoroethylene polymer having a thermoset binding material included therein. Similarly, the torque arm assembly and the fulcrum 39 has applied thereto a base coating of the polymer with binding material. A coating of a nylon is applied to the adapter plates 42 to a thickness of 0.008&#34; to 0.020&#34;. In addition to the base polymer composition, further a top coating may be applied to the bushings 24, 26, the torque arm assembly 36, the fulcrum 39, and other like coated parts of another or same fluorocarbon, though without a thermoset binder, and thus is thermoplastic in character. The fluorocarbon polymer of the top coat is thus in a more pure form to greatly enhance the protective nature of these materials against corrosive environments. The top fluorocarbon polymer binds with the base coat under proper temperature-time conditions. The combined coatings applied to the bushings 24, 26, including the flange 34, the surface 30 and bore surface 28, have a thickness of 0.0015&#34; to 0.002&#34; and the combined coatings on the torque arm assembly 36 and fulcrum 39 is 0.0015&#34; to 0.002&#34;. 
     From the foregoing, it will be appreciated that the present invention provides the use of a gear box for use in extreme environments without causing rusting or deterioration of the internal and exterior parts of the box. In accomplishing this goal, various coatings have been applied to critical elements of structure and to thicknesses which will prevent or minimize wear of the applied coating during operation of the gear box as well as protect the elements from the harsh environment. With the specified coating being applied to the outer surfaces of the barrel of the bushing, considerably less friction is present between the surfaces and the hub 16, thereby enabling easy removal of the bushing. In actual operation, the bushings pop out even against the stainless steel of the hub, or against the base coating of the polymer applied to steel if such coating is utilized. In effect, then, the coatings on the tapered surfaces also provide a substantial mechanical advantage as well as to minimize deterioration. In the event that other than tapered surfaces are utilized between the bushings and the hub, the coatings of polytetrafluoroethylene polymer with and without binder enables ease of assembly and disassembly of these parts, even in corrosive environments. The thicknesses of the specified coatings for the different structural elements provide optimum operating conditions which will not only protect the gear box and its structural elements from undue rusting and deterioration, but also to prevent the stripping or wearing of the material comprising the coatings during operation. 
     While other fluorocarbon polymers may be employed in accordance with the present invention, a preferred base polymer is a polytetrafluoroethylene with a phenolic binder, such as Teflon S, a fluorocarbon coating material produced by E. I. duPont, Wilmington, Del., which is quite suitable and may be applied to the prepared metal surface by spraying or the like. Preparation of the metal part includes cleaning of the part to remove oils, greases, and the like, roughening of the part by grit blasting or the like and preheating of the part to a suitable metal temperature, e.g., about 400° F. to about 425° F. Top coatings may thereafter be suitably applied as by electrostatic spray techniques followed by heating at temperatures of about 725° F. for about 20 minutes, or the like. 
     Products coated according to the present invention thus not only resist corrosion and other deterioration in harsh environs, but also have been found to facilitate cleaning such as by high pressure washes and facilitate better seating of the inter-related elements, while at the same time facilitating ease of removal for repair, replacement and the like. It has, in fact, been unexpectedly found that bushings coated according to the present invention transmitted adequate torque without keys or splines. While it was anticipated that a significant drop in torque would be experienced, such was not the case. In fact, only very slightly less torque is realized. 
     While preferred embodiments of the various aspects of the invention have been described using specific terms and arrangements, such descriptions are for illustrative purposes only, and it is to be understood that changes and variations may be made without departing from the scope of the following claims.