There has been a need for an inexpensive and practical procedure for providing seamless, one-piece gas dispensing metal bottles that may be used and reused for receiving and dispensing gas under pressure, such as oxygen, hydrogen, nitrogen, etc. Gas bottles are not only used in industry but also in medical facilities. The need is for a metal bottle of improved strength which is seamless, and is of substantially uniform thickness and strength throughout.
Heretofore, it has been customary to make bottles of two-piece, girth welded-together construction to reduce the expense involved from the standpoint of manufacture. However, such bottles do not have the strength required for reuse which is thus prohibited by industrial regulations. The expense involved in endeavoring to produce an elongated or deep seamless one-piece vessel or bottle as an end product has heretofore been prohibitive. It has not been practical to employ an impact-extruded or spun shell in endeavoring to provide an elongated or so-called deep bottle.
In endeavoring to find a solution to the problem, I found that certain factors had to be met, such as avoiding attempting to after-shape work-hardened areas, and avoiding shell wrinkling during the forming of a suitable nose. At the same time, a final product should be provided having a substantially uniform wall thickness throughout, and in an economical and practical manner.
I have been able to meet all the important factors involved, primarily by a two main step procedure in which a flat metal blank is progressively formed into an elongated cylindrical shell-like shape having an elongated cylindrical side wall of uniform diameter which at one end has an open mouth end portion and at its other end has a closed bottom end wall of substantially the same uniform thickness as the side wall. In a second main step, a portion of the side wall of the shape is reduced in thickness or tapered towards its open end and thereafter, the tapered area is turned-inwardly or swaged into a nose portion having an open mouth end of reduced size and whose wall thickness is substantially uniform therealong and with respect to the wall thickness of the remaining side wall and the bottom end wall. In an intermediate step, the shell-like shape as formed by the first main step may be further elongated, a dimple or depression simultaneously formed in its bottom end wall and a flange formed about its open end by employing a draw punch and die and a pilot punch. The worked flange portion of the shape is then severed before the tapering operation is effected. The dimpling provides the bottom end wall with curvilinear shape that tends to give it stability when a gas-filled bottle is placed in an upright position on a floor.
The necking-in, nose-forming operation is important in that no internal support is needed in forming the nose. This is an essential factor in enabling a one-piece construction. The shaping of the tapered nose area produces a substantially uniform thickness throughout that corresponds in thickness to the uniform thickness of the side and bottom end wall portions of the completed bottle. In this manner, a strong, seamless, lightweight bottle can be formed with a substantially uniform thickness and consistent wall strength. The dies used in swaging the nose first apply force in a circular, restricted engagement and progressively advance and widen such engagement from the side wall of the shape towards its open mouth in the direction of the reduced thickness of the wall taper, and in such a manner as to avoid wrinkling or crushing of the nose wall while working-thickening the tapered area towards the open mouth end. At the finish or end of the die movement, progressive full area contact has been made along the extent of the nose being formed.
The concept is unique, particularly from the standpoint of the second main steps thereof, with a nose being formed without the need for the employment of internal supporting or controlling structure for the wall of the shell-like shape being formed. In addition, the process is relatively inexpensive, such that the resultant product is cost-wise competitive with a two-part welded-together bottle that has the disadvantage of only being allowable for one filled usage before it has to be discarded. The process also avoids the expense and complications involved in attempting to form a bottle by spinning operations.
I have found that the weakest point in a shape is represented by the tangent at its closed end. By tapering the open end portion, I have been able to avoid wrinkling which tends to occur if the open mouth portion has a thickness greater than the cylindrical side wall. It is also important to start the forming of the nose as a circular line contact about the side wall and to advance it towards the edge of the open mouth end of the shell-like shape. A bottle made in accordance with the invention of deep drawing steel (such as SAE No. 30905, 30915) easily meets conventional requirements for withstanding gas pressures up to about 6100/sq. inch.
By way of example, I have started with a sheet steel having about 0.110 to 0.115 of an inch in thickness and finish with a bottle having a minimum wall thickness of about 0.095 of an inch. The total length of the finished bottle may be about 1/4 of an inch shorter than the shell (see FIG. 8A) from which the finished nose portion is made. Although it is possible to provide a spun-formed shell for use in the initial bottle forming operations of my process, I find that a less expensive and better product is produced by a series of deep drawing preliminary forming operations.