Fitting for formation of a fluid-conducting connection

[0001] The present invention relates to a fitting for forming of a fluid-conducting connection on an opening in the wall of a container of plastic, in particular a tank for receiving a fluid, a hydraulic fluid in particular.

[0002] Plastic tanks are widely used in hydraulic systems to contain hydraulic fluids. Because of the possibility of relatively simple configuration, low weight, and corrosion resistance, plastic tanks are extensively used especially in hydraulic systems of machines such as excavators, wheel loaders, and the like.

[0003] Such tanks are usually produced by well-known rotomolding or blow molding processes. Polyethylene or polyamide plastics, for example, are used for larger containers such as tanks for hydraulic fluids.

[0004] The advantages of corrosion resistance, low weight, and ease of molding are offset in the case of plastic tanks, however, by the disadvantage that production of fluid-conducting connections on openings in the plastic wall of the container or tank has certain difficulties. Because of the physical properties of the plastic material, the danger exists that deformations may occur in the area of the opening as a result of sealing forces and temperature effects. Such deformations can lead to leaking between plastic tanks and add-on elements, even if costly sealing elements are employed.

[0005] An object of the present invention is to provide a fitting permitting an operationally reliable long-term leak-free connection to an opening in a plastic container.

[0006] According to the present invention, this object is attained by a fitting having a connecting element enclosing the opening in the container and embedded in the plastic of the wall of the container. A reinforcing element is provided with fastening means for mounting of the connecting element. The loads acting on the connection, such as fastening force, sealing force, dynamic (vibration) and thermal effects, do not act directly on the plastic material of the container wall. Rather, such loads act on the connecting element forming a reinforcing element. Embedding of a connecting element, which is made of an appropriately selected material with the operating loads taken into account, preferably metal or a duroplastic of high fatigue strength and thermal stability, affords reliable protection from deformation of the plastic material of the container wall, so that a connection reliable in operation and free of leaks is ensured.

[0007] The connecting element may be advantageously in the form of an inserted element molded into the wall of the container in the molding process in rotomolding of the plastic container.

[0008] When the opening in the container is round, the connecting element preferably is configured as a metal annular element. The annular opening of the annular element encloses and is aligned with the opening in the container. The annular element may be of an aluminum alloy produced by injection molding, extrusion, or the like, and preferably is configured so that it has a level annular surface on its side associated with the outside of the container. It may be flush with the exterior of the wall of the container surrounding the opening. As an alternative, the annular element may be molded into the wall of the container so that the annular element is slightly recessed in the container wall.

[0009] An especially close connection of annular element and the plastic wall of the container is obtained if the side of the annular element facing the inside of the container has a plurality of pouch-like recesses. If the annular element is molded as an inserted element in rotomolding of the container, the plastic material entering the pouch-like recesses forms a serration of the annular element with the container wall and provides correspondingly good securing of the annular element against loads.

[0010] The annular element may have bores for retaining screws as fastening means for mounting, for example, a flange for fastening the respective closing element.

[0011] Preferably, the bores are configured as blind-end bores with interior threading and are provided at regular angular distances on the circumferential edge of the annular element.

[0012] Other objects, advantages and salient features of the present invention will become apparent from the following detailed description, which, taken in conjunction with the annexed drawings, discloses a preferred embodiment of the present invention.

[0020] FIG. 1 illustrates a part of the upper side of a container in the form of a plastic tank 1 made of a plastic material suitable for larger containers by the known rotomolding process (cf. Schaab/Stoeckhert, AKunststoff Maschinenführer@ [Plastic Machine Operator]), pages 561–564). A tank opening is formed on the upper side in the rotomolding process. In the opening in the plastic wall 3, a fitting 5 is provided for a fluid-conducting, leak-free connection to a connecting element represented in the embodiment illustrated by the connecting head 7 of a tank-top filter the filter element 9 projecting through the opening to the interior of the tank 1. The connecting head 7 has a fastening flange 11 mounted on the tank 1 by two retaining screws 13, only one of which is visible in FIG. 1.

[0021] The retaining screws 13 extend through the fastening flange 11, and are screwed into internally threaded blind-end bores 15 provided on a connecting element configured as an annular element 17, additional details of which are illustrated in FIGS. 2 to 6. The annular element 17, in the present exemplary embodiment, is made of an aluminum alloy, and is molded as an inserted element in rotomolding of the tank 1 so that the round annular opening 19 forms the opening in the tank.

[0022] In FIGS. 2 to 6, the annular element 17 has on its upper side, which is flush with the exterior of the plastic wall 3 of the tank 1, a level annular surface 21 interrupted only by four cylindrical pins 23 spaced at angular distances of 90°. These pins project a short distance axially above the annular surface 21, and are positioned on the circumferential edge so that they also project a certain distance radially beyond the circumferential edge of the annular element 17. As shown in FIG. 1, only two of the four blind-end bores 15 on the annular element 17 are used for engagement of retaining screws 13.

[0023] In FIGS. 4 to 6, pouch-like recesses 25 are made in the lower side of the annular element 17, all of which are not identified by number in FIGS. 5 and 6. Each recess 25 has a level bottom 27 (see FIG. 4) and is of a depth which, as is shown the most clearly in FIG. 4, amounts to more than three-fourths of the axially measured thickness of the annular element 17. As seen in FIG. 5, the recesses 25 are positioned in sequence approximately in the center between the unrecessed outer edge of the annular element and the unrecessed inner edge of the annular element. Except in the area of the recesses positioned in the area of the pins 23 of the blind-end bores 15, the recesses 25 are more or less triangular in outline and are arranged in succession so that unrecessed areas of the annular element 17 in the form of ribs 29 remain between adjacent recesses 25. The ribs 29 extend between the annular opening 19 and the circumferential edge of the annular element 17. Consecutive ribs 29 extend diagonally in an opposite direction relative to each other.

[0024] To effect sealing between annular element 17 and connecting element, the level annular surface 21 in the area between annular opening 19 and the pins 23 on the annular element 17 may be provided as a sealing surface adjoining an axial seal, for example. In the example illustrated in FIG. 1, sealing between annular element 17 and fastening flange 11 of the connecting head 7 is effected by a radial seal (not shown) between fastening flange 11 and the inside of the annular opening 19 in the annular element 17.

[0025] As is shown by FIG. 7, the annular element 17 need not be molded into the tank wall 3 so that the annular surface 21 is flush with the outside of the wall 3. The annular element 17 may be embedded in the wall 3. As illustrated by FIG. 7, the upper side of the pins 23 with the blind-end bores 15 may be flush with the outside of the wall 3. As FIG. 7 also shows, the outside of the annular element 17 is enclosed in its entirety in the plastic material of the wall 3, this material also penetrating the recesses 25.

[0026] While various one embodiment has been chosen to illustrate the invention, it will be understood by those skilled in the art that various changes and modifications can be made therein without departing from the scope of the invention as defined in the appended claims.