Drum with bungs

The invention is directed to a molded drum of thermoplastic material, in which the bungs are arranged in troughs on the drum-head and in which the troughs are open toward an adjacent L-shaped roller chime formed directly from the drum-body at some distance below the top end of the drum.

BACKGROUND OF THE INVENTION 
The invention relates to molded drums of thermoplastic material having 
bungs arranged in trough-shaped indentations in the head end of the drum 
and roller chimes of an L-shaped section formed directly from the drum 
shell at some distance away from the head and bottom ends of the drum. 
The blowing mold for the manufacture of drums with bungs consists of two 
mold halves which are separable along a vertical plane, that is, the plane 
extending in the axial direction of the drum. The upper and lower region 
of each mold half is horizontally divided to provide mold parts which 
slide one into the other. 
The extrusion head of the blowing machine delivers a parison of extruded 
plastic between the mold halves which are in the separated position so 
that the parison can enter therebetween. At this time, the mold parts in 
each mold half which slide relative to one another are opened. After the 
parison is lowered in the axial direction of the drum into the mold, the 
two mold halves are closed. In the closed position the mold halves clamp 
the previously extruded parison at what will be the head and bottom ends 
of the drum creating a seam across both clamped portions of the parison. 
The blowing process is then commenced. Molding apparatus of this type is 
conventional. See, for example, U.S. Pat. No. 3,985,257 for "Blow Molded 
Industrial Drum" and U.S. Pat. No. 3,050,773 for "Process and Apparatus 
for Manufacturing Blown Articles". In this type of molding apparatus air 
blown into the mandrel expands the parison so that it is pressed outwardly 
against the inner wall of the closed mold and, as a result, assumes the 
predetermined shape of the drum. With the upper and lower mold parts of 
each mold half disposed in an open position, the material of the parison 
enters into the recesses formed by the open mold parts. With such a mold 
construction, radially outwardly extending channels are formed on the 
container during the blow molding operation. These channels open toward 
the inside of the container. 
Subsequently, the mold parts are moved relative to one another into a 
closed position. The mold parts which can be moved relative to one another 
are shaped to provide the roller chime configuration and the material of 
the channels pressed into the recesses provided by the mold parts forms 
the roller chimes when the mold parts are moved relative to one another. 
The roller chimes have an L-shaped cross section each with an outwardly 
extending horizontal web or leg and with a vertical leg extending from the 
outer end of the horizontal leg in either the upward or downward direction 
depending upon the location of the chimes. 
The shape of the roller chime is of special significance. The gripping 
device for lifting and carrying the drum grasps with its tong arms under 
the horizontally outwardly projecting roller chime leg and behind the 
vertically extending leg. Accordingly, the vertical leg of the upper 
roller chime, that is, the chime adjacent the drum head, extends upwardly 
from the horizontal leg while the vertical leg of the lower chime, that 
is, the chime adjacent the bottom end of the drum, is directed downwardly 
from the horizontal leg. 
Due to the varying material distribution in the drum body, difficulties 
occur in the formation of the roller chimes. In the region of the dividing 
seams in the mold, the material of the extruded parison is doubled when 
the mold halves are moved to the closed position and the material has been 
squeezed into a clamped seam extending diametrically across the closed 
mold at both the top and bottom of the mold. During the blowing process, 
the parison is stretched and those regions which move in a direction 
perpendicularly away from the squeezed seam become significantly thinner. 
In the formation of the roller chimes in the upper and lower displaceable 
parts of each mold half, different volumes of material are available. As a 
result, due to the larger amount of the material in the region of the mold 
dividing seams, the displaceable mold parts cannot close completely and, 
thus, a satisfactory formation of the roller chimes in the region of the 
thinner areas becomes impossible. Because of the gripping devices used in 
lifting and transporting the drums, a satisfactory formation of the roller 
chimes is required. 
For this reason, dimensioning of the mold (and thus of the roller chimes) 
has been effected in such a manner whereby the same depth of the grooves 
of the roller chimes is maintained about the entire circumference of the 
drum. This is effected by forming the horizontal legs of the chimes with a 
thickness that decreases from the dividing seams in the mold for an 
angular extent of 90.degree. until the thickness reaches a minimum 
corresponding to the thickness of the drum body and then increases 
steadily to the region of the next mold dividing seam. The horizontal leg 
of the roller chime adjacent the head end of the drum where the region of 
largest material accumulation occurs is widenend, that is, in the radial 
direction from the drum, by providing indentations in the head end 
directed toward the interior of the drum. 
For producing the desired horizontal leg thickness, the part of the mold 
which forms the outer surface of the horizontal leg has a wave-like 
contour with the wave troughs arranged in the region of a larger 
accumulation of the material and the wave crests located in the region of 
the lesser material accumulation. Accordingly, the movable mold parts of 
each mold half can be closed completely without pressing the larger 
material volume into the interior of the drum. Furthermore, the shape of 
the mold part forming the outer horizontal leg surface guarantees the 
uniform or constant height of the vertical leg of each roller chime around 
its circumference. Drums of the above construction are disclosed in U.S. 
Pat. No. 4,228,911, assigned to the same assignee as the present 
application. 
To prevent the roller chimes from being damaged during rolling of the drum, 
that is, when the drum is rolled on the ground at a slant, or when a 
filled drum is accidentally dropped, a so-called crasher zone is provided 
by locating the roller chimes at a distance spaced from the top and bottom 
ends of the drum. Also, in order to prevent the bungs from being damaged, 
they are located in recessed areas or troughs in the head end of the drum. 
Conventionally, the bungs are located on diametrically opposite sides of 
the top end of the drum in the region of the mold dividing seams. 
With the drum construction as described above, the closer the roller chime 
comes to the top end of the drum, the larger become the accumulations of 
material at the mold dividing seams and in the adjacent bung trough areas. 
If a favorable distribution of material in the roller chime is achieved in 
the manner described above, unfavorable stress conditions result in the 
transitional zone of the horizontal leg of the chime into the bottom of 
the bung troughs. This is so because the bottom of the troughs are, by 
virtue of their proximity to the mold dividing seams, located where nearly 
no stretching of material occurs during the expansion of the parison in 
the mold, and thus the largest quantity of material remains after blowing 
of the drum. In order to control this supply of material during the 
closing of the mold, it has been the practice to form a raised bead of 
material in the base of the trough between the bung and the roller chime, 
thus precluding a smooth transition between the base of the trough and the 
horizontal leg of the roller chime. The formation of the bead has the 
effect of reinforcing the base of the trough. 
Such a measure can prove somewhat disadvantageous inasmuch as during impact 
stress, in particular during the sidewise impact of a filled drum, during 
a so-called body throw, cracks can occur in the area between the roller 
chime and the outside edge of the bead of material rising above the base 
of the trough. Due to the reinforcing of the trough base by the bead of 
material and because of the shearing stress resulting therefrom in the 
transition between the non-rigid drum shell, the roller chime, and the 
reinforced and therefore rigid base of the trough, the drum can burst in 
the direction of its circumference when under impact stress. 
SUMMARY OF THE INVENTION 
It is a primary object of the present invention to reduce the stress peaks 
between the roller chime and the drum head end by means of evening out the 
material in the area of the base of the troughs. This, in turn, will 
reduce the danger of partial cracking. 
This task is solved according to the invention in that the bases of the 
troughs are open towards the corresponding roller chime and run smoothly 
into the horizontal leg of the roller chime. Also, the upper surface of 
the bottom of each trough forms, with its front part, a smooth plane with 
the surface of the horizontal leg of the roller chime. 
Through this measure, stiffening in the outer dividing seam area is 
neutralized. The trough bottom can therefore evade impact stress. Impact 
force is eliminated through elastic deformation of the material. The 
possibility of the drum cracking at the transition between the trough 
bottom and the roller chime in the area of the dividing seams is thus 
eliminated.

The body of the drum is marked 1. The roller chime 10 is formed radially 
outwards by of the drum body 1 and includes a vertical leg 2 and a 
horizontal leg 3. The roller chime shown in the drawing is located 
adjacent the head end of the drum. A similar chime will be formed adjacent 
the bottom end of the drum. In this regard, see the above-mentioned U.S. 
Pat. No. 4,228,911 and also U.S. Pat. No. 4,228,122, assigned to the same 
assignee as the present application. 
As shown in FIG. 2, the drum head 11 extends above the roller chime 10. The 
same applies to the drum bottom not shown in the drawing. This is done so 
that the roller chimes will be protected when mishandled or several drums 
are stacked one on top of the other. The bungs 6 are arranged in the 
troughs 5 of the drum head 11. The troughs 5 and the bungs 6 are disposed 
on diametrically opposite sides of the drum in the region of the mold 
dividing seam 12. 
The troughs 5 are opened towards the roller chime 10 with the trough bottom 
4 running level, (that is, having an even thickness or distribution of the 
material) into the horizontal leg 3 of the roller chime 10. Also, as best 
shown in FIG. 2, the upper surface 8 of the trough bottom 4 forms a smooth 
plane with the upper surface 9 of the horizontal leg 3 of the roller chime 
.