Flexible tubing with annular corrugations to provide crush resistance has been made in the past using the basic methods and apparatus shown and described in U.S. Pat. Nos. 3,669,586; 3,705,780 and 3,809,522. These patents are referred to below and are incorporated by reference herein.
In general, the apparatus shown and described in the above patents includes a mandrel adapted to receive a sleeve of uncured rubber thereon and an external forming member adapted to be positioned around the mandrel and sleeve. The external forming member includes a plurality of axially spaced annular discs of uniform size and shape and which have circular openings coaxial with one another.
The discs are supported by various means, such as those shown and described in the above patents, to keep the discs in uniformly spaced relation and to permit the external forming member to be axially extended and axially collapsed to vary the spacing between the discs.
The apparatus also includes means for applying fluid pressure between the outer surface of the mandrel and the inner surface of the sleeve to radially expand portions of the sleeve into the annular spaces between the discs. The mandrel is preferably tubular and has a number of small openings in its tubular wall to for this purpose.
With the sleeve in its radially expanded condition, the external form may be axially collapsed with the annular wall portions of the sleeve still within the constricted annular spaces between the discs. This causes the radially expanded wall portions of the sleeve to be squeezed in accordion fashion between the discs to form preliminary annular impressions in the uncured rubber sleeve.
More specifically, the apparatus to which the present invention relates is a variation of the general type of apparatus described above. In this variation, the apparatus has an external forming member that uses a flexible tubular support for positioning the discs in equally spaced relation and in approximate axial alignment. The tubular support is preferably formed of cured elastomeric material and has a generally uniform wall thickness. The support also has annular corrugations with alternating internal and external ridges and grooves. The internal ridges have a diameter slightly greater than the outer diameter of the sleeve. The discs are positioned in the external annular grooves of the tubular support.
Thus, when the sleeve is radially expanded, the outer surface of the sleeve is forced into engagement with the inner surface of the tubular support to form annular bulges between the internal ridges. Then, when the external forming member is axially collapsed, the radially expanded annular bulges of the sleeve are squeezed in accordion fashion within the internal grooves of the tubular support to form preliminary annular impressions.
Then the external forming member is axially extended together with the sleeve to permit the sleeve to be removed from the mandrel and external forming member. After this, the sleeve is placed on a curing mandrel where it is axially foreshortened into annularly corrugated form with the desired spacing between adjacent annular corrugations. Finally, the sleeve and the curing mandrel are placed in an oven to cure the sleeve and set the corrugations.
The tubular product resulting from the use of the apparatus described above is both flexible and resilient, but also has sufficient crush resistance to satisfy most applications. In addition, the tubular product has a wall that defines both internal and external annular ridges and grooves along at least a portion of the tube length. In other words, the wall portions that define the annular external ridges, also define on their opposite side the annular internal grooves. Typical applications for the resulting product include farm machinery, particularly seeding equipment.
One problem with the type of external forming member that uses a flexible tubular support for positioning the discs is that the discs are not tightly retained in the external grooves of the support but rather are somewhat loosely carried. As a result, when the underlying uncured rubber sleeve is radially expanded by fluid pressure, the discs may not be accurately positioned in axial alignment with one another. This results in irregularities in the annular bulges of the sleeve and thus, corresponding irregularities in the preliminary annular impressions produced when the external forming member is axially collapsed.
The end result is that in some instances, there are visible irregularities in the annular corrugations of the resulting tubular product. While these visible irregularities do not affect the performance of the tubing, it would be desirable from an aesthetic point of view to produce a product with more uniform annular corrugations.
The device of the present invention, when used in association with the external forming member described above, reduces the visible irregularities referred to and affords other features and advantages heretofore not obtainable.