Method of DI can surface treatment

Inverted DI cans are fed by a conveyer having partitions in a plurality of rows such that they are spaced apart in each row, and treatment liquid is sprayed against the travelling cans from above and below the center of each row. The liquid is sprayed from above in a uniform and a full-cone pattern greater in area than the top surface of the can and from below also in a full-cone pattern or in a fan-shaped pattern narrow in the widthwise direction of the conveyer and greater in length than the can open end diameter. The liquid is further sprayed against the travelling cans from side nozzles on the opposite sides of and symmetric with respect to the center of each row. The side walls of the cans are thus washed without contact of adjacent cans in the direction of travel of the cans. The washing force is increased in the space between adjacent cans in the direction of travel to prevent washing irregularities and thus permit uniform surface treatment of the inner and outer surfaces of the cans.

FIELD OF THE INVENTION 
This invention relates to a method of surface treatment of drawn and ironed 
can bodies that are manufactured by blanking and drawing a metal strip 
into cups and re-drawing and ironing the cups to form thin walled can 
bodies. More particularly, the invention relates to a method of treating 
surfaces of drawn and ironed can bodies right after they are trimmed to a 
predetermined height, without causing can-to-can contacts. The term 
"surface treatment" used herein means a series of washing and surface 
treatment processes including "pre-wash" for the removal of lubricant used 
in preceding forming operations, "chemical treatment" for treating metal 
surfaces by chemical solutions, and "post-wash" for removing chemical 
solutions and final rinsing. 
BACKGROUND OF THE INVENTION 
In recent years, demands for drawn and ironed cans, or so called DI cans 
have been growing remarkably. Largely because of seam-free and 
aesthetically improved features, DI cans have been extensively used-for 
canning beer, juices and other beverages. 
DI cans are produced commercially on a mass production scale and DI can 
manufacturing processes generally include blanking and drawing metal 
strips into shallow cups, redrawing and ironing the cups to form hollow 
tubular bodies with thin sidewalls, and trimming the open ends of the 
tubular bodies to a predetermined height. Then, the trimmed bodies are 
subjected to surface treatment processes, in which sprays of treatment 
liquid such as degreasing solutions, industrial water, chemical solutions 
and deionized water are directed against the inner and outer surfaces of 
the trimmed bodies. Subsequently, the bodies are dried in a drying oven, 
decorated externally, coated internally with a protective coating and 
finally subjected to necking and flanging and formed into complete can 
bodies. 
A line of production equipment to perform the above processes and 
manufacture DI cans is typically very long and many can manufacturers have 
been experiencing difficulties in accommodating such a long line in their 
available space. Various efforts have so far been made to develop compact 
lines by making component machines of the equipment more compact and, for 
example, a device for the surface treatment, which essentially occupies 
the largest installation space among components of the line equipment, has 
ordinarily been designed to accommodate a drying oven in a piece of 
machinery for continuous processes. 
One of the most extensively adopted systems for the surface treatment in 
the industry uses an endless mesh conveyor belt having large numbers of 
openings that allow passage of sprays of the treatment liquid, and the 
conveyor belt progresses through a pre-wash zone, a treatment zone and a 
post-wash zone accommodated in a long tunnel and partitioned one from 
another, so that trimmed can bodies placed in a mass in an inverted 
position with their bottoms up off the conveyor belt receive sprays of the 
treatment liquid directed from a series of spray nozzles positioned above 
and beneath the upper flight of the conveyor belt (U.S. Pat. No. 
3,952,698). 
Nowadays, DI cans having extremely thin sidewalls or so called lightweight 
DI cans have become available in the industry as the result of efforts of 
various manufacturers for savings of manufacturing costs. Since these cans 
are very light, however, they can be readily tilted or displaced to come 
into contact with another on the conveyor belt or tipped over by 
impingements of sprays during the surface treatment, and such can-to-can 
contacts and tipping over often result in defects such as poor and 
irregular wash and inadequate surface finish. Such defects may adversely 
affect adhesion performance and corrosion resistance of a film of the 
protective coating and extremely deteriorate luster of the coated or 
decorated surfaces to such an extent that commercial values of finished 
cans may be completely destroyed. 
U.S. Pat. No. 3,291,143 discloses an apparatus for surface treatment of 
lightweight cans as illustrated in FIG. 8 (a side sectional view of the 
apparatus) and FIG. 9 (a sectional view taken along line IX--IX in FIG. 
8). The apparatus comprises a surface treatment housing 15, a lower 
endless conveyor belt 11 which progresses with cans K held thereon through 
the housing, a plurality of lower nozzles 13 disposed beneath the lower 
conveyor belt 11, a plurality of upper nozzles 14 disposed above the cans 
K in the housing and arranged to face the lower nozzles 13, and an upper 
endless mesh conveyor belt 12 surrounding the upper nozzles 13 and 
progressing in the same direction as the lower conveyor belt 11. The 
specification further describes that the lower flight 12a of the upper 
conveyor belt 12 should preferably be spaced upwardly by about 0.3 to 0.6 
cm (i.e., 1/8 to 1/4 inches) from the bottoms of the cans K held in the 
inverted state on the lower mesh conveyor belt 11 and fed continuously in 
the direction of the arrow Z. 
As cans K travel through the housing, they receive sprays of the treatment 
liquid directed from the upper and lower nozzles 13 and 14. The spray 
pressure of the lower nozzles is set so as to overcome that of the upper 
nozzles to urge the cans upwardly against the lower flight of the upper 
conveyor belt 12, and with this arrangement, it is indicated that even 
light weight cans may not be tilted or displaced to come into contact with 
one another or tipped over during the surface treatment. 
From the viewpoint of productivity in a mass production, the apparatus 
disclosed in U.S. Pat. No. 3,952,698 is certainly desirable as the mesh 
conveyor belt of the apparatus for holding cans has no partitioning and 
thus permits a large number of cans to be placed on it. With such 
apparatus, however, cans on the conveyor belt may come into contact with 
one another during the processes so that contacting portions and adjacent 
areas of the cans may not receive adequate sprays. 
Since the upwardly and downwardly directed sprays in the apparatus will not 
prevent contact of cans, occasional occurrence of defects due to 
can-to-can contacts is unavoidable with such apparatus. It should be noted 
that, in such apparatus, sprays of the treatment liquid just flow through 
gaps between adjacent can bodies, so that when a can has just advanced 
past the sprays a negative pressure is created momentarily in the gaps to 
pull an adjacent can, causing can-to-can contacts and resultant defects. 
Further, varied flow of cans into such apparatus may cause additional 
problems. Depending on the flow of cans, they may be pushed by one another 
and forced to slide over the surface of the conveyor belt, so that 
sidewall portions near the bottom rim of a can are rubbed with those of 
another to develop a band of dark scars in the rubbed portions and nicks 
are caused at the edge of the open end due to friction with the conveyor 
belt. Also, if a can is pushed excessively, it may jump out of the way or 
tip over. On the other hand, the apparatus disclosed in the U.S. Pat. No. 
3,291,143 permits efficient washing of the inner and outer surfaces of 
lightweight cans by relatively high fluid pressure of sprays directed 
thereto as the cans are held against the lower flight of the upper 
conveyor by the pressure of the upwardly directed sprays. Since fluid 
pressures created in the lateral directions by the sprays are not 
controlled in such apparatus, however, the cans may be moved in the 
lateral directions due to imbalanced spray pressure and brought into 
contact with one another to cause defects, particularly when the cans are 
closely spaced from one another in an attempt to improve productivity. In 
the above apparatus, lateral forces of upwardly and downwardly directed 
sprays are not balanced as the upper and lower sprays are not aligned with 
each other. 
As discussed above, neither of the aforementioned prior art surface 
treatment apparatus has adequate measures for eliminating can-to-can 
contacts and resultant defects as well as certain incidental damage to 
drawn and ironed lightweight cans. 
SUMMARY OF THE INVENTION 
An object of the present invention is to overcome the aforementioned 
difficulties encountered in the conventional surface treatment by 
providing an improved method of surface treatment and a novel apparatus 
therefor that enables complete elimination of tipping over and can-to-can 
contacts without using any special can holding mechanism and ensures 
efficient and thorough surface treatment of drawn and ironed lightweight 
can bodies without causing defects such as partly unclean or inadequately 
treated spots. 
According to the invention, there is provided a method of treating surfaces 
of drawn and ironed can bodies right after they are trimmed to a common 
height, by feeding them in an inverted state onto an endless conveyor belt 
having rods in the form of an open framework which travels through a 
tunnel, and by continuously directing sprays of treatment liquid in fully 
conical, pyramid or thin fan-shaped patterns against respective inner and 
outer surfaces of the can bodies from beneath and above an upper flight of 
the endless conveyor belt. The trimmed can bodies are arranged on an upper 
flight of the conveyor belt in a plurality of partitioned rows, each row 
extending in the direction of travel of the conveyor belt and in spaced 
relationships with another, and adjacent cans in each of the rows being 
spaced apart from each other by a distance of at least 2 mm. 
The continuous sprays of surface treatment liquid are directed downwardly 
from above and upwardly from beneath the upper flight of the conveyor 
belt, such that each trimmed can body, as it travels in the inverted 
state, simultaneously receives, at its outer surface, a downwardly 
directed fully conical or pyramidal spray wherein the treatment liquid is 
uniformly dispersed over a square or circular area on a plane containing 
an annular rim of the outer bottom surface of the trimmed can body, and 
which area is larger than a circular area defined by the annular sidewall 
of the trimmed can body, and at its inner surface, and an upwardly 
directed fully conical, pyramidal or transversely disposed fan-shaped 
spray wherein the treatment liquid is either uniformly dispersed over a 
square or circular area on a plane containing the annular edge of the open 
end of the trimmed can body, which area is larger than a circular area 
defined by the annular sidewall of the trimmed can body, or is dispersed 
transversely with respect to the direction of travel of the conveyor belt 
over a narrow elongate area longer than the diameter of the can body on a 
plane containing the annular edge of the open end of the can body. The 
pressure of the sprays directed downwardly is high enough to prevent the 
can body from being forced to float off of the conveyor belt by the sprays 
directed upwardly through the upper flight of the conveyor belt. 
Concurrently with the downwardly and upwardly directed sprays, other 
continuous sprays of surface treatment liquid are directed at equal 
pressures towards the center of a path along which the can bodies travel 
from locations at both sides of and transversely symmetrical with respect 
to the path. Thus, each can body, as it travels in the inverted state, 
receives a continuous fan-shaped spray wherein the treatment liquid 
covers, at each side of the path, a narrow and vertically elongate area 
extending over a distance greater than the height of the can body. 
According to the invention, adjacent can bodies are spaced apart from each 
other by at least 2 mm in each of the partitioned rows. If the spacing 
were less than 2 mm, the sprays of treatment liquid directed from the side 
spray nozzles would not flow down smoothly along the sidewalls of the can 
bodies but would be retained in the form of a film in the space between 
the can bodies due to the surface tension. Also, the can bodies could 
contact each other by being tiled back and forth slightly as they travel 
to or away from each upper nozzle due to slight fluctuations of forces of 
the downwardly directed sprays they receive at their bottom surfaces, 
resulting in an inadequate surface treatment of the can bodies. 
For the above reasons, adjacent can bodies to be treated must be spaced 
apart from each other by at least 2 mm but, on the contrary, too large of 
a spacing between can bodies adversely affects productivity and economy of 
operations and therefore it is preferable from a practical point of view 
to set the spacing at a maximum of 5 mm. 
Also, it is preferable that the fan-shaped sprays directed from the side 
spray nozzles cover, at both sides of the can feeding section, a narrow 
and vertically elongate area having a width in the range of 2 to 10 mm. If 
the width is less than 2 mm, sufficient surface treatment cannot be 
obtained and if the width exceeds 10 mm, on the other hand, the sprays 
could excessively impact the can bodies and cause them to tip over. 
Furthermore, the sprays directed from the paired side spray nozzles meet 
with each other to cause turbulent flows at spaces between adjacent can 
bodies in a row and ensure sufficient distributions of the treatment 
liquid to the sidewalls of the can bodies. Also, a relatively high 
pressure created in the spaces between the adjacent can bodies due to the 
sprays serves to force them away from each other. Thus, desired can-to-can 
spaces in the direction of travel of the can bodies are maintained at all 
times and since the can bodies are prevented from moving sideways by the 
partitions, they are completely free from coming into contact with one 
another. 
Still further, the can bodies are urged downwardly and prevented from 
floating off of the conveyor belt by the downwardly directed sprays having 
a fluid pressure higher than that of the upwardly directed sprays, so that 
the can bodies can travel stably through the zones without the use of any 
can holding mechanism. It is to be noted that obliquely downwardly 
directed sprays issuing from the side spray nozzles at an equal pressure 
should further enhance effect of holding the can bodies in position.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Now, an embodiment of a method and apparatus according to the invention 
will be described in detail with reference to the drawings. 
Referring to FIG. 1, reference numeral 21 designates is an apparatus 
according to the invention, comprising a tunnel in which a series of 
surface treatment processes take place continuously and the tunnel 
accommodates a pre-wash zone 21A comprising a de-oiling station 30 and a 
first wash station 31, a treatment zone 21B a chemical treatment station 
32, and a post-wash zone 21C comprising a second wash station 33 and pure 
water (or deionized water) rinse station 34. 
As is seen from FIGS. 1 and 2, an endless conveyor belt 23 comprising rod 
forming an open framework supports drawn and ironed can bodies 2 in the 
inverted states with their bottoms up and travels through the individual 
zones. The can bodies 2 have been trimmed to a predetermined height. 
As the can bodies 2 held inverted on the conveyor belt 23 advance in the 
direction as shown by the arrow Y, from the upstream side 24 to the 
downstream side 25, they are subjected to de-oiling and first washing in 
the pre-wash zone 21A, chemical treatment in the treatment zone 21B and 
second washing and pure water (or deionized water) rinsing in the 
post-wash zone 21C. Thereafter, the can bodies are dried in a hot air 
drying oven (not shown). 
A plurality of upper and lower nozzles are provided above and beneath the 
upper flight of the conveyor belt 23 for directing sprays of treatment 
liquid against the can bodies 2. 
More specifically, reference numeral 35 designates lower nozzle headers 
disposed beneath the upper flight 23a of the conveyor belt 23 such that 
each header 35 extends across the belt substantially over its full width. 
Reference numeral 36 designates nozzle headers disposed above the can 
bodies 2 on the conveyor belt such that each header 36 extends across the 
belt substantially over its full width. Each upper nozzle header 36 faces 
one of the lower nozzle headers 35 via the upper flight 23a of the 
conveyor belt and both cooperate as a pair. Pluralities of pairs of the 
upper and lower nozzle headers 35 and 36 are provided in the respective 
stations of zones 21A, 21B and 21C as spaced in the direction of travel of 
the conveyor belt. These headers 35 and 36 are respectively closed at one 
end 35a and 36a and connected by piping at the other ends 35b and 36b to 
liquid tanks 37 provided at each station beneath the conveyor belt 
(different treatment liquid tanks are provided for the respective stages). 
Treatment liquid is pumped from the respective liquid tanks and let 
through the connected nozzle headers 35 and 36, so that sprays of liquid 
are directed from lower and upper nozzles 38 and 39 mounted thereon 
against the can bodies and are returned to the respective tanks 37 in a 
well-known manner. 
The upper nozzles may be well-known full-cone type spray nozzles to form a 
circular spray pattern or pyramid type spray nozzles to form a rectangular 
spray pattern and the lower nozzles may be well-known full-cone type spray 
nozzles, pyramid type spray nozzles or thin fan-shaped flat type spray 
nozzles to form a thin fan-shaped spray pattern. The lower nozzles 38 are 
provided on the top wall portions of the lower nozzle headers 35 such that 
each nozzle 38 is disposed right underneath the center line of a row of 
can bodies 2 received in one of can feeding sections as will be described 
later. The upper nozzles 39 are provided on the bottom wall portions of 
the upper nozzle headers 36 such that each nozzle 39 is disposed in 
alignment with one of the lower nozzles 38 via the upper flight 23a of the 
conveyor belt. Fluid pressure of the treatment liquid in each individual 
header can be independently controlled by means of flow control valves 
provided on connecting pipe lines. When fan-shaped flat type spray nozzles 
are used as the lower nozzles, they are arranged to direct sprays of a 
thin fan-shaped spray pattern transversely across the conveyor belt in 
such a manner that the pressure of the sprays will not force the can 
bodies into contact with one another. 
Provided adjacent the downstream end of each stage are an air jet nozzle 41 
for blowing off treatment liquid trapped in the recessed portions of the 
outer bottom surfaces of the can bodies 2 and a suction nozzle 41' for 
sucking sprays of treatment liquid flowing along the sidewalls 2c and 
remaining at the open ends of the can bodies as well as treatment liquid 
picked up by the conveyer belt. The air jet nozzle 41 and the suction 
nozzle 41' are disposed to extend across the conveyor belt and face each 
other on the opposite sides of the upper flight 23a thereof, as shown in 
FIG. 2. 
The conveyor belt 23 comprises an endless belt of rods leaving a plurality 
of openings 26 which allow sprays of treatment liquid directed from the 
upper and lower nozzles to pass therethrough and a plurality of partitions 
27 partitioning a plurality of rows of can bodies from one another and 
extending in the direction as shown by the arrow Y in FIG. 4. In this 
embodiment, the partitions 27 are formed by linkages of a plurality of 
U-shaped members. The partitions slightly project outwardly from the outer 
surface of the conveyor belt and define feeding sections 23b of the 
conveyor belt. Each can feeding section 23b has a width W a little greater 
than the diameter of the can bodies and receives the can bodies in a row. 
(In this embodiment, the width W is greater by 4 mm than the diameter of 
the can bodies.) Thus, the can bodies are held in a row in each feeding 
section 23b and the partitions 27 restrict their sideway displacement so 
that they may not come into contact with the can bodies in adjacent rows. 
The conveyor belt 23 is driven by an engagement of the links of the 
partition members with teeth of a plurality of associated sprockets 29 
mounted on a drive shaft 28. 
FIG. 3 shows the can bodies 2 placed in a plurality of feeding sections 23b 
defined by adjacent partitions 27. 
The bottom wall of each upper nozzle header 36 is further provided with a 
plurality of side spray nozzles 40 and 40'. On the header 36, the side 
spray nozzles 40 and 40' are lined up with a plurality of the upper 
nozzles 39 and are mounted symmetrically to each side of each upper 
nozzle. A pair of the opposed spray nozzles 40 and 40' are spaced apart 
from each other by a distance not less than the diameter of the can 
bodies. (In this embodiment, the distance has been set to 100 mm for 
treating can bodies having diameter of 66 mm.) 
The side spray nozzles 40 and 40' are well-known flat type spray nozzles 
producing a thin fan-shaped spray pattern and are disposed in this 
embodiment above upper side portions of the can bodies being conveyed. 
These side spray nozzles receive treatment liquid from the upper nozzle 
header 36. 
Now, the surface treatment operation carried out by the aforementioned 
apparatus will be described. 
Can bodies 2 are distributed in rows on the can feeding sections 23b of the 
conveyor belt 23 in an inverted state with their bottoms facing up. In 
each can feeding section 23b, adjacent can bodies are spaced apart from 
each other by a distance of 5 mm (the distance is designated by d in FIG. 
1.) 
FIGS. 4 and 5 illustrate a manner of directing sprays of the treatment 
liquid from a set of nozzles 38, 39, 40 and 40'. In FIG. 4, an inverted 
can body Q in a can feeding section 23b is right underneath the upper 
nozzle and FIG. 5 shows the can body Q just advanced by a half of the 
center-to-center distance between adjacent can bodies in the direction Y 
and the space between the can body Q and the next can body R is right 
underneath the upper nozzle. At this moment, the sprays of treatment 
liquid directed from the side spray nozzles 40 and 40' collide with each 
other and scatter in the space to create turbulent flows. 
The lower nozzle 38 is a well-known pyramid type spray nozzle provided to 
direct sprays of the treatment liquid upwardly through the upper flight 
23a of the conveyor belt. On a plane coincident with the open end 2a of 
the can body Q, sprays from the lower nozzle 38 are uniformly disposed in 
a square spray pattern 38a over an area slightly greater than the circular 
area defined by the annular edge of the open end 2a of the can body. 
The upper nozzle 39, which is vertically aligned face to face with the 
lower nozzle 38, is again a pyramid type spray nozzle provided to direct 
sprays of the treatment liquid downwardly against the outer bottom surface 
2b of the inverted can body. On the plane coincident with the top rim 
portion of the outer bottom surface 2b of the inverted can body, sprays 
from the upper nozzle are uniformly disposed in a square spray pattern 39a 
over an area slightly greater than the circular area defined by the 
periphery of the sidewall of the can body. 
The pair of the side spray nozzles 40 and 40' are well-known flat type 
spray nozzles and sprays of the treatment liquid are directed obliquely 
downwardly against the outer bottom surface 2b of the can body. Sprays of 
the treatment liquid from both side spray nozzles are directed under a 
uniform spray pressure (4 kg/cm.sup.2 in this embodiment) in a 
transversely symmetrical thin fan-shaped spray pattern with respect to the 
center line X--X of a row of the can bodies in the can feeding section. 
The sprays of treatment liquid directed from the two nozzles 40 and 40' 
meet with each other and thus form spray patterns 40a and 40'a having an 
overlapped portion 40"a on the plane coincident with the top rim portion 
of the outer bottom surface 2b of the can body. Since the two nozzles 40 
and 40' are spaced apart from each other by a distance greater than the 
diameter of the can body, the sprays of the treatment liquid directed from 
them are disposed over areas, at both sides of the can body, extending 
beyond the sidewall 2c. In this embodiment, the width of the sprays 40a 
and 40'a is set by 8 mm. (The width is designated at D in FIG. 4.) 
Further, the spray pressures from the upper and lower nozzles 39 and 38 are 
set at 5 and 4 kg/cm.sup.2 respectively, for preventing the can body from 
floating off of the conveyor belt. 
FIG. 7 shows the state in which sprays of the treatment liquid directed 
from the side spray nozzles 40 and 40' are colliding with each other to 
form turbulent flows in the space between adjacent cans (Q and R, for 
instance). 
As a consequence of the aforementioned arrangements, those portions of 
sidewalls 2c of adjacent can bodies that face one another, which have 
heretofore been difficult portions to treat efficiently, can receive 
sufficient turbulent flows of sprays of the treatment liquid, so that the 
sidewalls are treated uniformly and efficiently. In addition, relatively 
high pressure created in the space d due to an accumulation of sprays of 
the treatment liquid serves to force adjacent can bodies in the can feed 
section away from one another and thus prevent can-to-can contacts and the 
occurrence of defects that may result therefrom while, in the prior art 
methods, sprays of surface treatment liquid just flow through gaps between 
adjacent can bodies, so that when a can body has just advanced past the 
sprays, a negative pressure is created momentarily in the gaps to pull the 
adjacent can bodies, causing can-to-can contacts and resultant defects. 
As such, the embodiment of a method and apparatus according to the present 
invention successfully eliminates can-to-can contacts by controlled forces 
of spray pressures and ensures adequate surface treatment of drawn and 
ironed lightweight can bodies that can be readily displaced by 
impingements of even slightly imbalanced sprays. 
Specific experiments using an apparatus according to the invention are 
described below together with comparative examples. 
In an experiment of the inventors, 10,000 drawn and ironed lightweight 350 
ml aluminum cans (each weighing about 12 g) were surface treated by a 
method and an apparatus according to the present invention. The speed of 
the endless conveyor belt was set at 15 m/min. so as to treat the surface 
of the cans for about 30 seconds. The apparatus was equipped with "Model 
1/8 GGSS 3.6SQ" upper nozzles and "Model H 1/8 U-3.6SQ" lower nozzles 
(both manufactured by Spraying System Japan, Inc.) and the respective 
spray pressures and flow rates were set at 5 kg/cm.sup.2 and 3.4 l/min. 
for the upper nozzles and 4 kg/cm.sup.2 and 3.0 l/min. for the lower 
nozzles, respectively. The side spray nozzles used with the apparatus were 
"Model 1/4 KSH0440" nozzles (manufactured by Eveloy Inc.) to produce 8 mm 
thick fan-shaped sprays and the respective spray pressure and flow rate 
from the side spray nozzles were set at 4 kg/cm.sup.2 and 6.6 l/min. (It 
should be noted that, in the treatment and post-wash zones, the spray 
pressures from the respective nozzles may be reduced as required.) 
In the above experiment, the cans were distributed onto each can feeding 
section of the apparatus with a can-to-can spacing of 5 mm in their 
direction of travel, and surface treated. 
These cans were visually checked at the exit of the apparatus and found to 
be completely free from tipping over or can-to-can contacts. 
Moreover, a band of dark scars around lower sidewall portions near the rim 
of, or nicks at the edge of the open end of, a can that may often develop 
in the conventional surface treatment were not found at all in the cans in 
this experiment. Also, these cans were completely free from undesired 
frosted surfaces that might be found in their internal surfaces if they 
had not been adequately washed. As such, the inventors have identified 
that the cans which were surface treated by the apparatus in the 
experiment have a greatly improved and superior surface finish. 
Further experiments were carried out by varying the conditions of the side 
sprays and it has been found that similarily satisfactory results are 
obtained so long as the side spray pressure, flow rate and spray width D 
meet the following conditions. 
Pressure: 2 to 5 kg/cm.sup.2 
Flow rate: 6 to 10 l/min. 
Spray width D: 2 to 10 mm. 
Likewise, an experimental use of flat spray nozzles ("Model HI/SU-8010" 
manufactured by Spraying System Japan Inc.) as the lower nozzles in lieu 
of the pyramid type spray nozzles also showed satisfactory results similar 
to those obtained by the latter. 
The above surface treated cans were subsequently coated and printed and no 
noticeable problem was identified in terms of quality of the finish, 
adhesion performance of the coating, etc. 
For comparison, another experiment was carried out using a prior art 
apparatus of the type disclosed in U.S. Pat. No. 3,952,698 which does not 
have a can holding mechanism. The conveyor speed of the prior art 
apparatus was set at 15 meters/min. and lightweight 350 ml aluminum cans 
were surface treated and inspected. The results of the experiment are 
shown as Comparative Example 1 in Table 1 which indicates that the prior 
art apparatus could not perform satisfactorily at a high production speed 
due to frequent occasions of tipping over of cans and can-to-can contacts 
which result in unsatisfactory surface treatment. For further comparisons, 
results of inappropriate side spray conditions in the aforementioned 
experiments using the method and apparatus according to the present 
invention are also shown in Table 1 as Comparative Example 2 (in which the 
spray pressure and the flow rate were too low and the spray width D was 
too narrow), Comparative Example 3 (in which the spray pressure and the 
flow rate were too high) and Comparative Example 4 (in which the spray 
pressure was too high and the spray width D was too wide). Comparative 
Example 5 in the Table shows results obtained when the spray pressure, the 
flow rate and the spray width D were within the desired ranges but the 
flat spray nozzles were used as the lower nozzles and positioned such that 
the elongate sides of the spray pattern produced by such nozzles extended 
in the direction of travel of the conveyor belt. 
TABLE 1 
______________________________________ 
Results of Surface Treatment of 10,000 350-ml aluminum cans 
Conveyor speed: 15 m/min. 
Surface treatment time: about 30 seconds 
C.E. 1 C.E. 2 C.E. 3 C.E. 4 
C.E. 5 
______________________________________ 
Upper nozzle 
Pressure 4 5 5 5 5 
(kg/cm.sup.2) 
Flow rate 3.0 3.4 3.4 3.4 3.4 
(l/min.) 
Lower nozzle 
Pressure 4 4 4 4 4 
(kg/cm.sup.2) 
Flow rate 3.0 3.0 3.0 3.0 3.0 
(l/min.) 
Side spray 
Pressure None 1 6 8 4 
(kg/cm.sup.2) 
Flow rate None 4.5 11 6.6 6.6 
(l/min.) 
Width None 1 10 12 5 
(mm) 
Can-to-can 
Nil Nil 5 5 5 
spacing d (mm) 
(distributed 
(lined up 
in a mass) 
in close 
contact) 
Tipped-over 
0.01 1.0 50 80 30 
(%) 
Can-to-can 
100 100 20 30 10 
contacts (%) 
______________________________________ 
(Note) "C.E." refers to Comparative Example. 
In the above embodiment, the lower and upper nozzles 38 and 39 are pyramid 
type spray nozzles, and the spray patterns 38a and 39b are thus square. 
Although full-cone type spray nozzles providing circular spray patterns 
can be used as the upper and lower nozzles, the pyramid type spray nozzles 
are more preferable from the standpoint of the stability of cans. Sprays 
of the square pattern can be arranged to form continuous bands of 
uniformly distributed sprays extending in the direction of travel of can 
bodies 2 as shown in FIG. 6, so that all can bodies regardless of their 
positions in can feeding sections may be subjected to a uniform spray 
pressure and held stably. 
Further, in the above embodiment the side spray nozzles 40 and 40' on each 
header are lined up with the upper nozzles mounted thereon and paired 
nozzles 40 and 40' are spaced apart from each other by a distance greater 
than the diameter of the can bodies and disposed above the can bodies in 
one of the can feeding sections at positions transversely symmetrical 
positions to each other with respect to the center line of the can feeding 
section, so that sprays of the treatment liquid are directed obliquely 
downwardly towards central portions of the can feed section to cover the 
sidewall and outer bottom surfaces of the can bodies. 
Of course, each can feeding section may be sufficently spaced from another 
to accommodate the side spray nozzles at an elevation below the outer 
bottom surface of the can bodies in the can feeding sections, and in this 
case sprays of the treatment liquid cover the sidewalls of the can bodies. 
It is to be noted that, in any case, the side spray nozzles should be 
arranged to create turbulent flows of sprays of the treatment liquid at 
spaces between adjacent can bodies in the can feeding section. 
While the side spray nozzles and the upper nozzles are in a linear 
arrangement in this embodiment, these nozzles do not necessarily have to 
be lined up but either of them may be positioned upstream or downstream of 
the other so long as any pair of such side spray nozzles 40 and 40' are 
arranged at transversely symmetrical positions with respect to the center 
line of one of the can feeding section and sprays directed from both of 
the paired nozzles meet each other and cause turbulent flows at spaces 
between adjacent cans in the can feeding section. 
As has been described in the foregoing, surface treatment according to the 
invention prevents adjacent cans in each of a plurality of partitioned 
rows from getting into contact with each other with sprays directed at 
central portions of the respective rows from symmetrically disposed 
opposite side spray nozzles, so that the sidewall portions of adjacent 
cans, which portions have hitherto been difficult to handle, can be 
surface treated sufficiently to eliminate defects such as those caused 
irregular wash patterns and thus improve quality of can bodies in terms, 
for example, of affinity to coatings to be applied. 
Further, can bodies to be treated are urged downwardly and prevented from 
floating off of the conveyor belt by the downwardly directed sprays having 
a higher fluid pressure relative to the upwardly directed sprays, so that 
the can bodies are free from coming into contact with one another during 
their travel and held stably on the conveyor belt without the use of any 
can holding mechanism such as an upper belt conveyor or an upper guide 
which has heretofore been necessary. The aforementioned arrangements, in 
conjunction with the obliquely downwardly directed sprays of treatment 
liquid from the side spray nozzles, ensure highly reliable and efficient 
surface treatment of drawn and ironed lightweight can bodies. Since there 
is no can-to-can contact during surface treatment by a method according to 
the invention, sprays of treatment liquid picked up by the sidewalls of 
can bodies are drained quickly so that the surface treatment time can be 
reduced.