Manufacturing method for thermoplastic container with integral lifting ring

A plastic container with an integral handling ring is formed in a mold having a pair of side sections movable toward each other and a pair of co-planar end sections movable toward each other and toward said side sections, by placing molten extrudate in a mold between the side and end sections, so that a handling ring can be formed and compression joined to the container at the same time the container is being formed by blow-molding.

BACKGROUND OF THE INVENTION 
Field of the Invention 
The present invention is directed to a container and to a method for 
manufacturing from thermoplastic material a hollow container having an 
integral lifting handle. 
In fabricating large hollow bodies, such as, for example, 55 gallon drums, 
from thermoplastic materials, it is common practice to blow-mold such 
bodies from an extruded, hollow, tubular shaped preform or parison. The 
parison is placed within an open blow-mold apparatus, the apparatus is 
closed and air blown into the parison to force it to expand outward 
against walls of the mold apparatus. Generally, it is desirable to provide 
lifting handles or roller chimes about the formed body for ease of 
handling. The lifting handles may comprise rings encircling the body which 
also serve as roller chimes. 
Various method have been utilized to attach lifting surfaces or handles to 
thermoplastic blow-molded hollow bodies. For large bodies such as drums, 
it is known to place prefabricated roller hoops into a blow-mold so that 
the hoops are welded to the drum when the parison is inflated. Such 
construction has resulted in separation of the hoops from the drums during 
handling. In order to avoid such separation problems, some processes 
employ channels formed in the mold cavity into which a portion of the 
thermoplastic material of the parison is forced. The channels are defined 
by moveable components of the mold. After the plastic material has been 
forced into the channel, the moveable components compress the material 
into a desired shape of a chime or handle. The latter method is disclosed, 
for example, in U.S. Pat. Nos. 4,228,911 and 4,529,570. It is believed 
that a disadvantage of this type of construction is a weakened area at the 
point at which the chime joins the drum. Although it has been proposed to 
increase the volume of material and therefore the wall thickness in the 
area of the protrusion, such extra material also has a tendency to 
undesirably increase wall thickness over a broad area. Accordingly, the 
thickness and location of rings are limited in this type process. 
Furthermore, in order to minimize stress cracks, these compression molded 
rings are formed of very low melt index materials (approximately 2 HLMI) 
resulting in processing difficulties requiring non-conventional extrusion 
equipment. 
An example of a process for welding or bonding roller chimes to a plastic 
drum is set forth in U.S. Pat. No. 3,960,474. In that patent, the 
pre-formed chimes or hoops are placed in a blow-mold and a parison 
inflated such that the soft thermoplastic material of the parison adheres 
to the preformed chimes. The bond between the chimes and drum thus depends 
on the ability of the plastic material to adhere to the chime material, 
and such bonds have been known to separate under stress, such as by 
lifting of a filled drum by the chime. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to overcome the above mentioned 
disadvantages of the prior art processes of forming a drum with a chime or 
lifting handle. In the present invention, a drum is formed by blow-molding 
of a parison in a mold of a desired configuration. Within the mold there 
is provided an area defined by moveable components which, in their final 
closed position, will create a shape corresponding to a desired 
configuration of a roller chime or handle. A suitable thermoplastic 
material is placed into the defined area prior to blow-molding the drum. 
As the drum is molded, the moveable components compress the thermoplastic 
material causing it to attain the desired shape. Since the defined area is 
open to the mold cavity, in one form of the invention a portion of the 
compressed material is forced into the cavity and into contact with the 
expanded and pressurized parison. The pressure existing at the point of 
contact is sufficient to cause the compressed material to infuse into the 
material of the expanded parison to create an integral joining of the 
formed chime to the molded drum.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to the drawings, and particularly to FIGS. 6 and 7, it will 
be seen that a drum, indicated generally at 8, is shown as having a 
generally cylindrical side wall 10 and top and bottom end walls 12 and 
12a, respectively, (only top end wall 12 being shown in FIG. 6). Top end 
wall 12 may be provided with one or more dispensing or venting openings 
11. 
Container 8 has at its upper corner an integral solid handling ring, 
indicated generally at 14, which includes a main section 16 with a narrow 
flange section 18 joined to the body of drum 8. The ring 14 is sometimes 
referred to as a roller chime. Ring 14 may be used either for lifting the 
drum or for supporting the drum for rolling. Although the ring 14 is shown 
at a top surface of drum 8, it will be appreciated that ring 14 could be 
placed at other positions and that multiple rings could be employed. 
Referring to FIG. 7, there is shown a partial cross-sectional view of a 
joint between ring 14 and drum 8 formed by the practice of the present 
invention. The ring 14 and flange section 18 are compression molded into 
the shape illustrated. During the compression molding process, the section 
18 extrudes from the closing portion of the mold, as will be described 
with respect to FIGS. 1-5, and infuses into the thermoplastic material of 
the drum 8. By selecting the material of both the ring 14 and drum 8 from 
a common family of thermoplastics, the resulting joint will be essentially 
a molecular bond or joint, i.e., the joint will be indistinguishable from 
the surrounding material and will have the strength of the material. In 
one form, for example, the ring 14 and drum 8 may be formed from the same 
type of thermoplastic material. 
While the illustrated embodiment indicates an infusion of the extrudate 
from the ring 14 into the material of the container 8, it will be 
appreciated that there may be occasions when it is desirable for the 
material of the container 8 to fuse to the ring 14 without material of one 
component being forced into material of the other. Furthermore, it is 
possible to force the material of container 8 to infuse into the ring 14. 
A more significant advantage of applicant's invention is that by using two 
separate material components for the container and ring, the ring 14 may 
be colored by addition of an additive. Coloring of ring 14 may permit 
identification of containers by ring color which could advantageously be 
used for quick identification of contents of a container, if such color 
coding scheme is used. 
Since the extrudate from which the ring 14 is formed is separately 
provided, the ring 14 may be made as thick as is necessary for heavy 
lading. Additionally, the ring 14 may be placed in any position on the 
container 8. Having the ring 14 on top provides protection for the vent 
openings 11. For a better understanding of the forming method of the 
present invention, reference is now made to FIGS. 1-5 which illustrated a 
blow-molding apparatus 20 of a conventional type, except for portions of 
the structure described hereinafter which are used for an insert 
compression molding type operation in addition to the blow molding 
operation. 
Mold apparatus 20 includes a pair of side sections 22, which are movable 
toward and away from each other, and a pair of end sections 28, which are 
movable toward and away from related mold side sections 22. Each of the 
side sections 22 includes a generally semi-cylindrical side wall 24 and an 
integral generally semi-circular end wall 26. It will be noted that the 
end walls 26 are at the top of the drawing, but they actually form the 
bottom of the container, because the container is formed in an upside down 
position. 
Side section end walls 26 are provided with aligned annular recesses 25 
which form an annular boss or flange 17 at the bottom of the container 8. 
Each of the side section side walls 24 presents at the opposite end 
thereof, or lower end as shown in the drawings, an annular recess 27 which 
cooperates with annular recesses 29 in end sections 28 to form a common 
annular groove, the purpose of which is described hereinafter. End 
sections 28 of the mold apparatus are generally semi-circular in shape and 
correspond to and are aligned with end walls 26 of side sections 22. 
Each of the end sections 28, as previously mentioned, presents at its outer 
periphery an axially inward facing recess 29 which cooperates with related 
recess 27 in the side wall 24 of side section 22 to provide a common 
annular groove the purpose of which is to receive material necessary to 
provide the container handling ring 14 in a manner hereinafter described. 
It will be understood that the shape and dimensions of the recesses 27 and 
29 may be varied as desired. 
Positioned above the mold is a conventional extruding apparatus, indicated 
generally at X, from which is extruded a generally cylindrical tube or 
parison P of plastic material. Positioned at the lower end of the molding 
apparatus is a blowing mechanism including a blow pipe indicated generally 
at B. The details of the extruder and the blow pipe mechanism are not 
shown in detail since their structures may be of the type found in 
conventional blow molding equipment. 
In the practice of the present invention, the mold apparatus 20 is first 
placed in the open position shown in FIGS. 1-2. A molten plastic 
extrudate, indicated generally at E, is inserted into the related recesses 
27 and 29 of the mold 20. 
At approximately the time the extrudate E has been placed in the mold, the 
parison P is extruded from the extruder X, as shown in FIG. 2, with the 
lower end of the parison being disposed to extend over the blow pipe B. 
The side sections 22 are then moved toward each other to pinch off the 
ends of the parison. Air under pressure is introduced into the center of 
the parison through the blow pipe B to start formation of the container 
body by a conventional blow molding process, as illustrated in FIG. 3. 
As the container body is being formed, the end sections 28 of the mold are 
moved toward each other and toward the related side sections 22, so that 
the molten plastic extrudate E is compressed between the end sections 28 
and the side sections 22 of the mold to form handling ring 14, as shown in 
FIG. 4, while air is continued to be introduced to complete formation of 
the container body. 
Thus, it will be understood that, at the same time the container body is 
being formed by a blow molding process, the handling ring 14 is not only 
being formed by the compression molding process, but also ring 14 is being 
joined to the adjacent portion of the body of drum 8. Ring 14 therefore 
becomes an integral portion of drum 8. Thus, it will be seen that the 
present invention contemplates a novel method for forming a hollow body 
container which represents an improvement over and eliminates many of the 
disadvantages of the prior processes in forming a hollow container with an 
attached drum handling ring. The final stage of the operation is the 
opening of the mold sections to remove a completed container as best seen 
in FIG. 5. 
Although, the container described above is provided with only one ring 
which is located at the upper corner of the container body, it should be 
understood that, if desired, the same process can be employed to form a 
pair of rings, with one ring at each end of the container. Also, if 
desired the process may be used to join a ring to a container body at a 
location other than at a corner. In addition, while the ring 14 has been 
shown as continuous, it will be appreciated that for some applications it 
may be desirable to provide a discontinuous handle arrangement. By 
limiting the extent of recesses 27 and 29 in a circumferential direction, 
the drum 8 may be formed with spaced handles for lifting. Furthermore, 
while the method of the present invention has been disclosed in 
conjunction with an illustrative shaped lifting surface or roller chime, 
other shapes of chimes or lifting surfaces may be achieved by variation of 
the configuration, position and size of the components defining the 
recesses 27 and 29.