US 3027044 A
Description (OCR text may contain errors)
March 9 "r. w. WINSTEAD 3,027,044
CONTAINER 0R DRUM LINER Filed March 24, 1959 8 AVERAGE WALL THICKNESS IN VENTOR THOMAS M. WINSTEAD BY M ATTORNEY United States atent 3,027,044 CONTAINER R DRUM LINER Thomas W. Winstead, Baltimore, Md, assignor to Hedwin Corporation, Baltimore, Md., a corporation of Maryland Filed Mar. 24, 1959, Ser. No. 801,510 1 Claim. (Cl. 220-63) This invention relates to a hollow thermoplastic article, such as a container or container liner, which may be manufactured in accordance with the process disclosed in my copending application Serial No. 780,163 filed December 12, 1958, and now Patent No. 2,985,915. More particularly, the invention consists in new and useful improvements in a hollow thermoplastic article of this type having selectively reinforced or thickened wall areas that the fiberboard itself is not resistant to moisture and liquids, most applications thereof to fiber drums have been for use in connection with dry materials.
It has long been recognized that if a fiber drum could be made suitable for the shipment of liquids, it would then begin to find applications which thus far have been primarily delegated to liquid-type metal drums. For this reason, considerable effort has been spent to find ways and means of achieving a satisfactory liquid container in the form of a fiber drum. One of these approaches has been to coat the fiber itself with various synthetic materials, either by coating the inside of the complete package or by laminating thermoplastic films to the paper from which the drum is made, before the paper is wound into the cylindrical side wall. Each of these coating systems has many inherent weaknesses and therefore leaves much to be desired.
Another popular approach to the problem has been to fabricate a separate liner from thermoplastic films, which is then inserted into the completed fiber drum to act as a waterproof liner which prevents the liquid contents from coming in contact with the insides of the fiber drum. Although this approach has been satisfactory in some applications, it has been shown to have many inherent weaknesses also. These weaknesses have resulted in the development of pin holes" and other breaks in the film liner and the ultimate leakage of the contents and spoilage of the fiber drum.
One of the biggest problems with bag liners has been the poor flex resistance of the synthetic films from which these liners have been fabricated. As a result, when these liners have become creased or crinkled because of the fact that they do not fit snugly in and around the various interior contours of the drum, flexing results during the shipment because of vibration incident to transportation, and this flexing of these creased areas ultimately causes failure in the form of a small hole which thereby results in leakage. Furthermore, on impact, these liners have failed because they are too light to absorb the impact forces and pinches which frequently occur at ice the bottom of the drum. These liners have usually been made relatively thin, perhaps .004 inches thick, in the hope of reducing the extreme fiber stress in the area of a bend or fold. It has been found that thicker liners can actually fail more quickly than the thinner liners, because of the fact that folds and creases under flexing vibration are so highly stressed that they fatigue very rapidly. Although heavier liners have more abrasion resistance and resist puncture better than the thinner liners, because of the fact that they inevitably have to be creased or folded in order to conform to the interior contours of a drum when filled with liquid, their performance has been unsatisfactory.
Since neither thin nor heavy fabricated film liners have been entirely satisfactory for the shipment of liquids, a new approach to the problem had to be developed. First, it was determined that if a liner could be made heavy enough to resist flex fatigue by precluding its flexing entirely during shipping vibration, it would have to be contoured and formed to conform to the inner surfaces of the fiber drum in order to prevent folds or creases of any kind.
Second, it was decided that a liner made so heavy throughout its cross-section would undoubtedly be too costly to meet the economical requirements of the application. It was therefore determined that the liner should be designed with sufiicient thickness from its top to slightly below the normal liquid level in a drum, to resist the type of flexing inherent in a bag liner, and with sufficient thickness at its bottom radius and sufl'lciently above this bottom radius, to resist failure caused by impact or pinching during a severe drop of the filled drum on its bottom edge, utilizing thinner wall material between these two thickened portions where the need of heavy material is unnecessary. It was found that by thus designing a drum liner, a considerable reduction in material cost could be effected, rendering such a liner economically practical.
It is the object of the present invention to provide a liner or the like formed of a thermoplastic material such as polyethylene, with a thickness distribution of the material designed to resist the particular areas of physical abuse inherent in an application of this type, and to simultaneously minimize material in the large cylindrical body area of the liner, thereby meeting the performance requirements at a minimum of cost. By developing the special technique disclosed in my said copending application Serial No. 780,163, it has been possible to produce a liner or insert for a fiber or steel drum, fulfilling these basic requirements. This insert is formed so as to fit very closely the contours of an open head drum at its top, beginning outside the lip and rolling over the lip and around the internal radii of the drum, down the side wall to a point perhaps an inch below the liquid level. The specific thickness of this top section depends upon the drum dimensions, its capacity and other shipping requirements. However, for purposes of illustration, it might be assumed that this thickness is on the average, two to four times thicker than the large cylindrical area below it.
This large cylindrical area is made in such a thickness as to assure the elimination of pin holes and prevent leakage in the normal use of the drum. At a point perhaps /s of the total heighth measured from the bottom of the drum, the material thickness is again increased substantially and preferably increases even more gradually toward and through the bottom radius of the insert, to an amount where the thickness is perhaps two to five times thicker than the large cylindrical area in the body of the liner. Beyond this radius across the bottom of the insert, the material is gradually decreased in thickness to the single area of the bottom which need be no thicker than the large cylindrical area of the side wall, above referred to.
In practicing the method disclosed in my said copending application, the controlled thickness distribution in thermoplastic liners and the like is effected by chilling selected circumferential areas of the liner wall so as to preclude stretching of the chilled areas in the forming operation, and then stretching the thermoplastic material lying between the thickened areas, thus producing a liner having alternate thick and thin areas, so proportioned and distributed as to achieve maximum liner performance. It is therefore another object of the invention to make full utilization of the reinforcing qualities of the annular thickened areas resulting from the process of manufacture, so as to provide a drum liner having selectively spaced, integral reinforcing bands.
Although the insert or liner thus far described is an integrally formed structure without welds or joints, the invention is not to be considered as limited to such an integral structure, as in some instances, it may be desirable and practical to employ other means of fabrication with the same basic objectives in mind.
With the above and other objects in view which will appear as the description proceeds, the invention consists in the novel features herein set forth, illustrated in the accompanying drawings and more particularly pointed out in the appended claim.
Referring to the drawings in which numerals of like character designate similar parts throughout the several views:
FIGURE 1 is a view in side elevation showing one form of drum liner manufactured in accordance with this invention;
FIGURE 2 is a top plan view of the liner shown in FIGURE 1; and
FIGURE 3 is an enlarged sectional view taken on line 3-3- of FIGURE 2, illustrating the thickness distribu tion in one form of liner.
In the drawings, referring first to FIGURE 1, 5 generally represents a polyethylene or other suitable thermoplastic liner or insert made in accordance with the present invention, for use in connection with a conventional fiber shipping drum. When the liner is to be employed in a fiber shipping drum of the type usually provided with an internal radius of smaller diameter near its top, the liner is shaped to conform to the internal surface contours of the drum and provided with a complementary reduced radius 6, near its top, terminating in an outwardly directed lip 7 for engaging the upper edge of the fiber drum (not shown). A complementary top or cover 8 also of thermoplastic material may be provided and is preferably designed to embrace the outwardly directed lip 7 with a sealing engagement.
As will be seen from FIGURE 3 of the drawings, which is purely illustrative of a particular thickness distribution which may be employed, it will be seen that the annular top portion 9 of the liner and its bottom portion 10 are relatively thick walled and that the intervening wall portion is provided with a series of vertically spaced, integral, thickened rings or hands 11 which, as previously stated, have been formed by chilling these particular areas during the forming operation to prevent the stretching thereof. The thin or stretched areas, a between the respective thickened bands 11, vary in number and thickness, depending upon the dimensions of the drum with which the liner is to be used. For example, in the particular liner illustrated, the thickness of the top portion 9 of the drum, including the reduced radius 6, is .039 inch and mately an inch below the liquid level to be maintained in the filled drum. The thin or stretched area a between the band 11 defining the lower limits of the upper portion 9 and the next succeeding band 11, is .010 inch thick and reading down, the succeeding three thin areas, b, c, and d, are .011 inch thick. The middle thin area e is .010 inch thick, areas 1 and g are .011 inch thick and as the bottom of the liner is approached, the thinned areas become thicker. In other words, area It is .012 inch, area i.014 inch, area j.019 inch and the bottom portion 10 is .028 inch. Preferably, the radius at the bottom edge of the liner is .071 inch to afford adequate resistance in the handling of the filled drum and beyond this radius across the bottom of the insert, the material is gradually decreased in thickness to the center area of the bottom, from .037 inch to a thickness no greater than that of the large cylindrical area of the side wall above referred to.
Thus, a liner is provided, wherein all of the points of stress in handling are adequately reinforced both by the selected thickness distribution of the wall itself and the provision of the annular thickened bands 11 which afford circumferential strength at the points needed, much in the manner of the hoops of a barrel.
It is to be clearly understood that the specific thicknesses above described are in' no way critical and may be varied to meet the requirements of, liners for containers of different sizes and for different uses. When the insert or liner is used as an open-head container, a top such as 8 above referred to, is provided which generally conforms to the drum lid and is sufficiently thick to protect the drum lid from the liquid contents. This lid or disc may be omitted if the drum lid itself is protected satisfactorily by coatings or other means. The drum lid may also be heat sealed to the insert itself at the top, to provide in effect, a closed-head insert. Outlets also may be provided for content dispensing by conventional fittings which communicate through both the drum lid and the liner top 8. Of course, if the product to be shipped is corrosive, these fittings should be made of plastic or other materials to resist attack.
While the foregoing description has emphasized the use of this insert or liner with fiber drums, it is to be noted that this device may also be used with equal effect with steel drums, although its contour and shape, particularly at its top, would be such as to conform generally to the shape of a steel drum which normally has no internal radius of smaller diameter such as 6, near the top-which is usually provided with fiber drums. The use of this type of insert with a steel drum of much thinner construction would materially reduce the costs of the combined container. It is also contemplated that this type of insert will be used with reconditioned steel drums which might not otherwise be suitable for the shipments of many liquids. It is further contemplated that if a thickened area in the liner wall proves to be desirable in the area of the rolling hoops which are usually a part of steel drum construction, such a thickened area should be and can be provided at these points, thereby permitting the side wall to span these grooves rather than conform to them. Of course, conformity in these areas might also be provided, should this prove desirable from a performance standpoint, although insertion of the liner then becomes more difficult.
From the foregoing, it is believed that my invention may be readily understood by those skilled in the art without further description, it being borne in mind that numerous changes may be made in the details disclosed without departing from the spirit of the invention as set forth in the following claim.
A drum liner comprising a cylindrical body of substantially thin thermoplastic material, open at its upper end and closed at its lower end by a relatively thickened bottom, circumferentially thickened wall areas integrally extends downwardly on the side wall to a point approxibounding said upper end and bottom, the wall portion of said body between said upper and lower thickened areas being relatively thinner than the latter areas and substantially flexible, said thinner area being separated vertically by relatively narrow, integral, eircumferentially thickened reinforcing bands, spaced to provide a series of vertically broadened wall areas, and the broadened wall areas of the lower portion of said body being respectively of progressively increased thickness from an intermediate point in said body to the bottom thereof.
References Cited in the file of this patent UNITED STATES PATENTS Whitman Sept. 13, 1955 Colombo June 19, 1956 Kruszynski July 30, 1957 locelyn Nov. 24, 1959