Abstract:
A fluid tank is disclosed. The fluid tank includes at least one joint including an adhesive that is non-tacky at a first temperature, has a flow point temperature at a second temperature that is greater than the first temperature, and a cure and bond temperature at a third temperature.

Description:
TECHNICAL FIELD 
     The present disclosure relates generally to a fluid tank and, more particularly, to a fluid tank having a heat-activated adhesive joint. 
     BACKGROUND 
     Machines such as, for example, track-type tractors, wheel loaders, on and off-highway haul trucks, motor graders, and other heavy equipment are used to perform many tasks. To effectively perform these tasks, an engine provides torque to propel the machine and/or to power various hydraulic systems (e.g., implement systems, steering systems, and braking systems). The machine may include various fluid tanks capable of storing fluids required for operation of the engine and/or hydraulic systems. For example, a fluid tank may store a supply of hydraulic fluid for use with the implement systems or air for a brake system. 
     Typically, the walls of a fluid tank, e.g., a fuel tank, a hydraulic tank, and/or an air brake tank, are welded together using resistance seam welding. Because resistance seam welding creates heat-affected zones that may have a reduced fatigue life, the fluid tank may be designed with extra material in the area of the weld joint or on neighboring surfaces to increase fatigue life. As a result, the fluid tank may be undesirably heavy and/or expensive. 
     One attempt at reducing the effects of welding in a fluid tank is described in U.S. Pat. No. 5,828,033 (the &#39;033 patent) issued to Mitsuyoski et al. In particular, the &#39;033 patent discloses a tank with upper and lower shell members. The upper and lower shell members have respective flanges that overlap each other. The upper and lower flanges are welded to each other by a laser. 
     Although laser welding may be suitable for some applications, high frequency vibration induced from engine or implement system operation and low frequency vibrations associated with the travel of the machine over terrain can be transmitted through the machine to the tank. These vibrations can cause the tank wall joints to fatigue over time, and may lead to failure. Furthermore, known high-strength adhesive materials (e.g. epoxies) generally have low elongation-to-failure and, although could be equally effective in bonding a tank together, could not resist the vibrations and resulting elongation at the adhesive joint. 
     The disclosed fluid tank is directed to overcoming one or more of the shortcomings set forth above and/or other problems in existing technology. 
     SUMMARY OF THE INVENTION 
     In one aspect, the present disclosure is directed to a fluid tank. The fluid tank includes at least one joint including an adhesive that is non-tacky at a first temperature, has a flow point temperature at a second temperature that is greater than the first temperature, and a cure and bond temperature at a third temperature. 
     In another aspect, the present disclosure is directed to a method of assembling a fluid tank. The method includes positioning an adhesive that is non-tacky at first temperature with respect to a first wall and a second wall. The method further includes heating the adhesive above a second temperature at which the adhesive flows, and heating the adhesive to a third temperature to form a structural bond between the first wall and the second wall. 
     In yet another aspect, the present disclosure is directed to a fluid tank. The fluid tank includes a first member, a second member, and a joint. The joint includes an adhesive that is non-tacky at a temperature below a flow point temperature of the adhesive and forms a first bond between the first and second members upon heating to a third temperature. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an isometric pictorial illustration of an exemplary disclosed fluid tank; 
         FIG. 2  is an exploded view of the fluid tank of  FIG. 1 ; 
         FIG. 3  is a cross-sectional illustration of a joint associated with the fluid tank of  FIG. 1 , taken along the line  3 - 3  of  FIG. 1 ; and 
         FIG. 4  is cross-sectional illustration of another joint associated with the fluid tank of  FIG. 1 , taken along the line  4 - 4  of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  illustrates an exemplary fluid tank  10 . The fluid tank  10  may be mounted on a mobile machine (not shown) and supply a liquid or gaseous fluid for fuel, lubrication, cooling, work tool operation, or for any other purpose to one or more systems of the machine. 
     The fluid tank  10  may have any shape suitable for storage of fluid. For example, as shown in  FIG. 1 , the fluid tank  10  may be generally cubic. The fluid tank  10  may include a generally planar top member  20  and a generally planar bottom member  21 . The top member  20  and bottom member  21  may be substantially parallel and separated by side members  22 ,  24  and two additional side members (not shown), substantially parallel to the side members  22 ,  24 , respectively. The side members  22 ,  24  may each be substantially perpendicular to each other, to the top member  20 , and to the bottom member  21 . In an exemplary embodiment, the members may be formed from steel, aluminum, or any other material known in the art suitable for storing a fluid material and may be, for example, about 1.2 mm thick. 
     Referring to  FIG. 2 , the top member  20  may include curved mating features  32  and  34 . Side member  22  may include curved mating features  36  and  38 . Side member  24  may include curved mating features  40  and  42 . Each curved mating features in a pair (e.g.  32  and  34 ) may be adjoining and generally non-planer to the other. The curved mating features  32 ,  34 ,  36 ,  38 ,  40 ,  42 , the top member  20  and side members  22 ,  24  may each include two additional mating features. The additional mating features may be similar to those shown in  FIG. 2 , for example, the additional mating features of the top member  20  may be generally configured as mirror images of the mating features  32  and  34 , respectively. The curved mating features  32 ,  34 ,  36 ,  38 ,  42 , may be formed by a process such as, bending on a hydraulic press or deep drawing. It is further contemplated that the members  20 ,  21 ,  22 ,  24  may be formed by forging or by die casting of aluminum, magnesium, or zinc. 
       FIGS. 3 and 4  illustrate cross-sectional views of the fluid tank  10 , taken along the lines  3 - 3  and  4 - 4 , respectively. The curved mating features  32  and  34  may be configured so that when assembled, the curved mating features  32  and  34  generally overlap and engage the curved mating features  36  and  40 , respectively. For example, an inner surface  44  of the curved feature  34  may be generally parallel to an outer surface  46  of the mating feature  40  of the side member  24  and form a lap joint  48  (referring to  FIG. 3 ). An inner surface  50  of the curved mating feature  32  may be generally parallel to an outer surface  52  of the curved mating feature  36  to form a lap joint  54  (referring to  FIG. 4 ). In addition, the curved mating feature  38  may be configured to generally overlap the curved mating feature  42  so that when assembled, an inner surface  60  of the curved mating feature  38  and an outer surface  62  of the curved mating feature  42  are generally parallel and form a lap joint  64  (referring to  FIG. 4 ). Although only three lap joints are described in detail here, the remaining joints may be configured in a manner similar to that described above. It is further considered that the fluid tank  10  may include additional features  66  for receiving and providing a fluid flow and that the members forming the fluid tank  10  may have any other configuration that enables the formation of lap joints. 
     Flexible strips of a heat-activated adhesive  70  may be positioned between the overlapping surfaces of the top member  20  and side members  22 ,  24  to form a bonded joint between adjacent members. The strips of adhesive  70  may have substantially the same size and shape as the area of the surfaces to be joined (e.g.,  44 ,  46 ,  50 ,  52 ,  60 ,  62 ). The heat-activated adhesive  70  may be a rubber material that is non-tacky at a temperature below its flow point temperature. That is, the adhesive  70  may not adhere to itself or other substrates without the application of heat and pressure. The adhesive  70  may have a flow point at a temperature between about 250-275° F., and cure and bond at about 300-325° F. to form a structural bond. Once the structural bond is formed, it may be maintained when the adhesive  70  is returned to a temperature below the flow point temperature and may be maintained when exposed to temperatures at or above the bonding temperature. 
     The adhesive  70  may be formulated with hydrogenated nitrile butadiene rubber (HNBR), hydrogenated carboxylated nitrile butadiene rubber (HXNBR), nitrile butadiene rubber (NBR), or carboxylated nitrile butadiene rubber (XNBR) compounded with metal acrylates or metal methacrylates such as zinc-diacrylate to provide adhesion. The compound may include a coagent that may react primarily through a radical addition mechanism that generates substantially no gaseous by-products. The coagent may prevent pore formation during curing, which, if formed, may result in decreased material strength. For example, the strength of the adhesive  70  formed by the above materials may exceed 15 MPa, whereas the strength of the adhesive using a foaming coagent would be reduced by an amount proportional to the increase in material porosity caused by the foaming coagent. Examples of non-foaming coagents include N,N′-m-phenylene dimaleimide (HVA-2), trimethylolpropane triacrylate (TMPTA, Sartomer SR351) and Sartomer SR522D. The adhesive  70  may include a peroxide curative selected to disassociate to form reactive radicals. Examples of applicable peroxides include 1,1-bis(t-butylperoxy)3,3,5-trimethylcyclohexane (R.T. Vanderbilt Varox 231), dicumyl peroxide (R.T. Vanderbilt Varox DCP), or n-butyl-4,4-bis(t-butyl-peroxy)valerate and (R.T. Vanderbilt Varox 230 XL). The adhesive  70  may be capable of elongations greater than 100%, thus the adhesive  70  may allow for relative movement between the members forming the joint. 
     Industrial Applicability 
     The disclosed fluid tank may be suitable for any mobile machine. Specifically, because the disclosed fluid tank may include joints capable of elongation, the integrity of the tank may be maintained, even when the machine is subject to excessive terrain-induced vibrations. In addition, because the disclosed fluid tank does not include welded joints, the weight and cost of the fuel tank may be reduced. Furthermore, because the adhesive used to form the disclosed fluid tank may be non-tacky at temperatures below about 250° F., it may be relatively easy to work with in a manufacturing environment. 
     The fluid tank  10  may be assembled by positioning one or more pieces of the adhesive  70  between the curved mating surfaces to be bonded. For example, referring to  FIG. 3 , the adhesive  70  may be positioned between the curved mating features  34  and  40  of the members  20  and  24 , respectively. The adhesive  70  may have substantially the same shape and area as the overlapping areas of the curved mating features  34  and  40 . Because the adhesive  70  may be neither liquid nor tacky at temperatures below its flow point temperature of about 250-275° F., it may be easy to handle in a manufacturing environment (e.g., the adhesive  70  may not inadvertently stick to a user or component). After the adhesive  70  is placed between the curved mating features  34  and  40 , it may be heated to its flow point temperature. The heating may be achieved via an induction heating method or oven, or any other method known in the art. Because the adhesive has a high viscosity elastomer as a primary constituent it may not exhibit undesirably high flow rates typical of conventional structural adhesives (that rely on fillers to build viscosity). 
     The adhesive  70  may then be heated to a temperature above its flow point temperature so that it may cure and bond to form a structural bond between the curved mating features  34  and  40 . For example, the adhesive  70  may be heated to about 300-325° F. At this elevated temperature, the adhesive  70  may chemically bond with the adjacent surfaces (i.e. the inner surface  44  and the outer surface  46 ) to form a structural bond that may be maintained when the adhesive  70  is returned to a temperature below the its flow point temperature and is not lost when exposed to temperatures at or above the bonding temperature. Because the adhesive  70  may have substantially the same area as the overlapping surfaces, the lap joint formed by this method may have a relatively large bond area compared to a joint formed by conventional welding methods. The increased bond area may result in a total adhesive bond strength that is substantially equivalent to, or greater than, the strength of the sides of the fluid tank  10 , thereby reducing the likelihood of structural failure at the joint. 
     The fluid tank  10  of the present disclosure may be assembled with a lightweight adhesive  70  that is neither liquid nor tacky in a manufacturing environment and therefore easy to work with. In addition, because the adhesive  70  may be capable of elongations greater than 100%, it may allow for relative movement between the members forming the joint due to vibration, thermal mismatch, and alignment issues that a rigid attachment, such as welding, may not. Furthermore, the fluid tank  10  may have a bond area greater than may be achieved with conventional welding methods, thereby increasing the bond strength between the walls of the fluid tank  10 .