Method and apparatus for supplying conditioned air to a blow-molding oven

A method and apparatus which allows blow-molded plastic containers to be manufactured at high rates of production independent of ambient environmental conditions. The method and apparatus eliminate the need to make adjustments to blow-molding oven operating parameters when environmental conditions change and reduce defects such as caused by water spots. The method includes the steps of flowing ambient air over cooling coils to remove moisture, heating the air to a constant pre-determined temperature and delivering the conditioned air to the blow-molding oven. The apparatus includes a variable speed blower which forces ambient air at a predetermined volumetric flow rate over cooling coils and an electric heater to provide the blow molding oven with a constant volumetric flow rate of constant temperature and low humidity air.

FIELD OF THE INVENTION 
The present invention relates to the efficient and high speed manufacture 
of plastic blow-molded containers, and more particularly to a method and 
apparatus for supplying conditioned air to a blow-molding oven such that 
the air is supplied at a desirable volume, a constant temperature and a 
low humidity to enable consistent processing. 
BACKGROUND OF THE INVENTION 
Blow-molded plastic containers are commonly used as packaging for a variety 
of products, such as juices. The process for their manufacture inherently 
requires the intake of ambient air by the blow-molding oven and machinery. 
The ambient air is applied to either a preform, a semi-blown container, or 
both, in a step, or steps, in the manufacturing process. An example of 
such a process is disclosed in U.S. Pat. No. 5,322,651 issued to Emmer. 
Preforms are initially heated in a blow-molding oven, and are then indexed 
into blow-molding machinery where they may be stretched and/or blown. Such 
a process may produce up to 250 bottles per minute when operating at full 
speed, depending on the type and size of blow-molding machinery. 
A problem with known processes utilizing blow-molding ovens is that under 
certain environmental conditions, the ambient air conditions can cause a 
slowdown of the process and a reduction in the quality of the goods 
produced for a variety of reasons. 
Blow molding ovens are designed to permit adjustment to effect efficient 
usage. For instance, as ambient temperature and humidity levels of the air 
change throughout the day, adjustments can be made to the heating elements 
in the ovens to maintain efficient processing. However, when the ambient 
temperature rises above a certain level, for instance, 85.degree. F. at 
50% relative humidity, the ovens cannot provide the required thermal 
environment for the preforms at full speed production. Such conditions are 
commonly experienced in plants having hot and humid ambient air 
environments. Therefore, the only recourse at these plants when 
experiencing these ambient conditions is to slow the pace of production. 
Another problem is that adjustments to blow-molding ovens must be made 
frequently throughout the course of the day. This requires constant 
monitoring of the machinery and environmental conditions by a worker, 
since temperature and humidity may frequently rise and fall during a given 
day. In addition, the adjustments are largely accomplished by trial and 
error methods which sometimes result in defective products being produced 
for a period of time until proper adjustments are made. 
A further problem relates to wind drafts which are experienced within the 
confines of the manufacturing plant. Such drafts can be created by the 
opening of doors or windows within the plant. The drafts affect the 
temperature, rate and direction of air drawn into the blow molding oven 
and can have an effect on the process parameters to cause the production 
of defective containers. Often, at such plants, doors are required to be 
maintained in a closed position during blow-molding to prevent such 
problems. However, such precautions are not always effective in completely 
eliminating the problems caused by drafts. 
A still further problem relates to the moisture contained in the ambient 
air. While blow-molding ovens heat the body portion of a preform, the 
finish of the preform must not be subjected to heat; otherwise, the finish 
would become deformed. For this reason, the finish of a preform is 
insulated from the heat by a cooling device. However, moist ambient air 
flowing past the finish cooling device produces condensation. As the 
condensation collects under and adjacent to the path of the preforms 
within the blow-molding oven, drops of water are often lifted by swirling 
air and deposited onto the preforms. The water drops create spots on the 
preforms, resulting in the production of defective, non-useable 
containers. 
A still further problem is created by the presence of dust and like 
airborne material which float in the ambient air. Such material is drawn 
into the blow-molding oven and can coat the preforms and internal 
components of the blow-molding oven. 
Manufacturers of blow-molding machinery have made attempts to address the 
above referenced problems with their ovens, but none has satisfactorily 
solved the problem. For instance, the aforementioned patent to Emmer 
utilizes a system which automatically controls the temperature of air 
drawn into a blow-molding oven by mixing ambient air with recycled air. 
However, if the process demands a circulation of air at, for instance, 
80.degree. F. and the temperature of the ambient air rises near or above 
80.degree. F., then the process will not be able to produce satisfactory 
containers since the temperature of the circulating air will not be able 
to be maintained at the required 80.degree. F. Therefore, the heating 
elements must be adjusted to a lower temperature, and the pace at which 
the preform travels through the blow-molding oven must be slowed. In 
addition, the system disclosed in Emmer does not address the problems 
created by moisture and dust in the air, or the problems created by wind 
drafts within the manufacturing facility. 
Although the referenced Emmer system provides a blow-molding oven which can 
be used effectively in some ambient plant environments at high speeds, 
there is a need for an improved method and apparatus which allows 
blow-molding operation independent of ambient environmental conditions. 
The improvement should be useable with existing ovens, should be capable 
of ready installation, and should be easy to operate. 
OBJECTS OF THE INVENTION 
With the foregoing in mind, a primary object of the present invention is to 
provide a method of manufacturing blow-molded, plastic containers at high 
rates of speed independent of ambient environmental conditions. 
Another object of the present invention is to provide a method of 
manufacture which eliminates the need to continually monitor and adjust 
control parameters of blow-molding ovens during the course of the day due 
to changing environmental conditions. 
A further object of the present invention is to provide an apparatus to 
deliver a desirable volume of constant temperature and low humidity air in 
a closed system to a blow-molding oven. 
A still further object of the present invention is to provide a method and 
apparatus for supplying air to existing blow-molding ovens located in 
plants subject to hot and humid ambient air conditions, which prevents the 
collection of condensation and dust within the oven and which is 
unaffected by wind drafts in the plants. 
SUMMARY OF THE INVENTION 
More specifically, in one aspect, the present invention provides a method 
of manufacturing blow-molded plastic containers at high rates of 
production independent of ambient environmental conditions. The first step 
of the method comprises forcing air at a pre-determined flow-rate into a 
chamber which is connected and feeds into a blow-molding oven where 
preforms are heated. A preferred predetermined flow-rate is in a range of 
about 2,250 to 11,500 cubic feet per minute (c.f.m.) depending on oven 
type and size. Another step includes cooling the air to between about 
42.degree. to 48.degree. F. as it flows through the chamber. The cooling 
causes moisture to be removed from the air so that the relative humidity 
in the air is reduced to between about 40 to 50 percent. The next step is 
to heat the air after the cooling step to increase the temperature of the 
air to between about 83.degree. to 88.degree. F. which is then fed into 
the blow-molding oven. The method provides a desirable volume of constant 
temperature and low humidity air to the blow-molding oven. 
In another aspect, the present invention provides an apparatus for 
supplying air to a blow-molding oven which is used in the manufacture of 
blow-molded plastic containers. The apparatus comprises a variable-speed 
blower, or damper, for forcing a pre-determined volume of air into the 
blow-molding oven. Before the air enters the blow-molding oven, it is 
first cooled and dehumidified by a cooling unit and then heated to a 
constant pre-determined temperature by a heating unit located downstream 
from the cooling unit. A controller is used to regulate the constant 
pre-determined temperature of the air with a temperature measuring device 
located downstream from the heating unit. The apparatus provides a 
constant volume of constant temperature and low humidity air to the 
blow-molding oven.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 4 illustrates schematically a blow-molding oven 10 used to manufacture 
plastic containers. Inside the blow-molding oven 10, preforms 52, or 
parisons, are heated, and then transferred to blow-molding machines where 
they are stretched and/or blown into finished containers. Known 
manufacturing processes utilize any number of steps, or stations, to 
accomplish the above identified steps. For instance, a preform, a parison, 
a semi-blown container, or an over-blown container, may be indexed through 
an oven chamber for heat treatment. 
As shown in FIG. 4, the oven 10 has a fan 54 for drawing in a volume of air 
at a pre-determined rate. The air is circulated past preforms 52 having a 
body portion 52a and a finish portion 52b. The body portions 52a are 
heated by a set of heating elements 58 as the preforms 52 travel through 
the oven 10 on a traveling support 60. The finish portion 52b is insulated 
from the heat by a set of cooling elements 62. 
The predetermined path of the air through the oven 10 is illustrated in 
FIG. 4. The air is first directed at the open end of the finish portion 
52b. The air then flows past the finish portion 52b and through a gap 
between the cooling elements 62 and the preform 52. The air then flows 
along the sides of the body portion 52a toward the closed end of the 
preform, and then, out of the blow molding oven. This flow path is 
particularly advantageous, since the flow of air prevents the heat, which 
emanates from the heating elements, from transferring through the gap and 
heating the finish portion 52b. Thus, the finish portion 52b is protected 
from heat induced damage. 
Upon a call for air, the conventional blow-molding oven will cause a 
desirable volume of ambient air to be drawn into the blow-molding oven 10. 
However, depending on the temperature and humidity level of the ambient 
air at the manufacturing facility, the blow-molding oven 10 may not be 
able to provide, or maintain, the required thermal treatment within the 
prescribed time period. This results in defective containers which may not 
have the rigidity to maintain their required integrity during hot fill, 
transportation and handling. Since this result is not satisfactory, the 
rate of production is intentionally decreased to allow extra time for the 
blow-molding machines to compensate for the adverse effects of ambient 
environmental operational conditions. 
As an example, a process not utilizing the present invention may produce 
250 bottles per minute at maximum production speed. The process requires 
the heating elements 58 to radiate heat at 392.degree. F., and for ambient 
air to circulate around the preforms 52. Best results are achieved if the 
ambient air is at a temperature of 85.degree. F. However, the temperature 
of the ambient air may fluctuate throughout the day and frequent 
adjustments may be required to the temperature set point of the heating 
elements 58 and to the pace at which the preforms 52 pass through the oven 
10. In addition, depending on the amount of moisture in the air, 
condensation will develop on cooling elements 62. The condensation may 
collect in the oven 10 and the circulating air may lift drops of water 
into contact with the preforms 52 and create water spots. Finally, dust 
and wind drafts are not prevented from entering the oven 10, both of which 
can cause further problems. 
The present invention solves the above problems by initially conditioning 
the supply of ambient air outside of the blow-molding oven 10 before 
directing the air supply into the blow-molding oven 10. As illustrated in 
FIG. 4, a conditioning unit 12 is connected to the blow-molding oven 10 by 
a duct 14. The conditioning unit 12 intakes air at ambient temperatures 
and humidities and feeds the air to the blow-molding oven 10. The 
conditioning unit 12 conditions an appropriate volume of ambient air so 
that by the time the conditioned air is received by the blow-molding oven 
10, the conditioned air is at a pre-determined constant temperature and 
humidity at which the blow-molding oven 10 operates most efficiently. 
The conditioning unit 12 allows the blow-molding oven 10 to operate at its 
maximum rate of production. The use of the conditioning unit 12 eliminates 
the need to decrease the rate of production by as much as about 25 to 35% 
during hot and humid ambient air conditions, as was previously required. 
The conditioning unit 12 also eliminates the need to make operating 
parameter adjustments to the blow-molding oven due to changing 
temperatures, as was previously required. Thus, the conditioning unit 12 
functions to maintain design blow-molding oven production rates under 
adverse temperature and humidity conditions. 
Additionally, the conditioning unit 12 removes a significant amount of 
moisture from the ambient air so that condensation does not collect on or 
near the cooling elements 62 in the blow-molding oven 10. Thus, the 
conditioning unit 12 also functions to prevent container defects due to 
water spots created by drops of water lifted onto the preforms 52 in the 
oven 10 by the circulating air. The adverse effects of wind drafts and 
dust are also eliminated by use of the conditioning unit 12. 
According to the method of the present invention, the first step is to 
initiate a pre-determined volumetric flow of ambient air into an intake 
opening 24 of the conditioning unit 12. The flow rate of the air should 
closely match that which is normally drawn into the blow-molding oven 10 
by the fan 54 when it operates independent of the conditioning unit 12. 
This can be accomplished, for instance, with the use of a variable speed 
blower, or damper, which is located in the conditioning unit 12 and which 
is set automatically to mimic the fan 54 located in the blow-molding 
machine 10. Although various blow-molding machines require various 
volumetric flow rates, it has been determined through testing that 
creating a volumetric flow rate between about 2,250 to 11,500 c.f.m. is 
sufficient depending on the type and size of oven. 
Once a flow of air has been established through the conditioning unit 12, 
into the duct 14, and then into the blow-molding oven 10, the next step 
according to the method of the present invention is to cool the air as it 
flows through the conditioning unit 12. This can be accomplished, for 
instance, by passing the air across chilled water coils located adjacent 
the ambient air intake 24. The extent of cooling may vary depending on 
ambient air temperatures and humidities; however, it was determined 
through testing that the temperature of the air should be decreased to 
about between 42.degree. to 48.degree. F. 
Cooling the air results in lowering the moisture content of the air. Since 
warm air can retain higher levels of water vapor than cooler air, when hot 
air of high humidity is cooled, water vapor retained by the air is 
reduced. The cooler air, not being able to retain as much water vapor, 
releases the water vapor as condensation. Thus, the moisture content of 
the conditioned air as compared with the ambient air is reduced. It has 
been determined through testing that conventional blow-molding ovens 
operate most efficiently when the humidity level of the air is between 40 
to 50% relative humidity. 
After the ambient air is cooled and dehumidified, it continues to flow 
through the conditioning unit 12 and is heated. Heating of the 
dehumidified conditioned air to a constant pre-determined temperature 
allows the blow-molding oven 10 to receive a supply of air which it can 
readily use at maximum production speed in providing the thermal 
treatments required in preform, or parison, heating. The heating step in 
the conditioning unit 12 can be accomplished, for instance, by an electric 
heater, steam heat, hot water heat, or any heat source located downstream 
from the cooling apparatus. It has been found through testing that best 
results are achieved by heating the conditioned air to between about 
83.degree. to 88.degree. F. before allowing the air to flow into the 
blow-molding machine 10. 
The method according to the present invention can include other steps to 
aid in automation of the process. For example, the temperature of the 
conditioned air as it is discharged from the conditioning unit 12 can be 
measured to ensure precise control of air temperature. The temperature 
measurement information can be fed back to the heater controls to increase 
or decrease the amount of heating automatically so that the temperature is 
within a desired pre-set range. The volumetric flow rate and the relative 
humidity of the conditioned air can likewise be monitored to provide 
feedback to control operation of the conditioning unit 12. 
In view of the foregoing, it should be apparent that the present invention 
now provides a method for allowing blow-molded plastic containers to be 
manufactured at high rates of production independent of ambient 
environmental conditions and without the need to constantly monitor and 
adjust blow-molding oven operating parameters in response to changing 
environmental conditions. In addition, production of containers having 
water spots is eliminated. 
Turning to another aspect of the present invention, an apparatus is 
provided which is particularly useful in performing the steps of the above 
described method. As illustrated in FIGS. 1-3, the conditioning unit 12 
has a housing 20 defining a chamber 22 through which the air flows. The 
chamber 22 has an ambient air intake opening 24 and a conditioned air 
discharge port 26. The intake opening 24 has a series of louvers 50. The 
discharge port 26 connects to the duct 14 which defines a path for the air 
to flow to the blow-molding oven 10. 
A blower 28 creates a flow of air into the intake opening 26 and out of the 
discharge port 26. As illustrated in the drawings, the blower 28 is 
located adjacent the discharge port 26 and is powered by a motor 30. The 
blower 28 and motor 30 can provide a range of volumetric flow rates so as 
to match the supply of air required by the blow-molding oven 10. 
A filter 32 is located within the chamber 22 adjacent the intake opening 24 
to prevent dust and the like from further passing through the conditioning 
unit 12 and into the blow-molding oven 10. The removal of dust further 
aids in reducing the production of defective containers, and thus, 
increases production rates. 
A cooling unit 34 is located within the chamber 22 to cool and remove water 
vapor via condensation from the ambient air drawn into the chamber 22. As 
illustrated in the drawings, the cooling unit comprises a set of water 
chilled coils 36. A water chilled supply pipe 38a provides chilled water 
to the coils 36, while a chilled water return pipe 38b provides a path for 
the water out of the coils 36. A condensate collector plate 40 is located 
directly below coils 36 to provide a basin for the condensate dripping 
from the coils 36. 
A heating unit 42 is located within the chamber 22 downstream from the 
cooling unit 34. After the ambient air is filtered, cooled and 
dehumidified, it is funneled through the heating unit 42 and heated to a 
pre-determined temperature. As illustrated in the drawings, the heating 
unit 42 is an electric heater 46 encased in a perforated heater shield 48; 
however, other types of heating apparatus can be utilized. 
After the ambient air is filtered, cooled, dehumidified and heated within 
the chamber 22 it exists the chamber through the discharge port 26 into 
the duct 14 and then into the blow-molding oven 10. This closed system 
isolates the air circulating in the blow-molding oven 10 from wind drafts 
created in the manufacturing facility as by opening of doors and the like. 
The manufacturing process continues unaffected by the drafts or any 
temperature or humidity change created by the drafts. Thus, production is 
increased by the elimination of defects which would otherwise result from 
such drafts. 
Parameters such as volumetric flow rate, maximum cooling temperature, 
minimum cooling temperature, relative humidity, maximum heating 
temperature and minimum heating temperature can be controlled by control 
box 44 located on the outside of the housing 20 of the conditioning unit 
12. For instance, temperature measuring devices (not shown) such as 
thermocouples can be located at strategic locations within the chamber 22 
to feedback information to the control box 44 which can then act to 
automatically adjust the blower 28, cooling unit 34 or heating unit 42 as 
required. 
In view of the foregoing, it should be apparent that the present invention 
now provides a method and apparatus for allowing blow-molded plastic 
containers to be manufactured at high rates of production independent of 
ambient environmental conditions. Adjustments to blow-molding oven 
operating parameters in response to changing ambient air conditions are 
entirely eliminated along with the associated defects which such 
adjustments can cause. Other defects, such as those caused by water spots, 
dust or wind drafts are also eliminated. According to the present 
invention, existing blow-molding ovens can accommodate high rates of 
production, even in plants that normally experience extremely hot and 
humid ambient conditions. 
Prior to the present invention, when a blow-molding oven having a design 
capacity of 10,000 bottles/hour was operated in a plant having ambient air 
at a temperature above 80.degree. F. and relative humidity above 70%, it 
was necessary to reduce the blow molding speed by about 30%. After 
installation of the aforementioned apparatus operating in accordance with 
the method of the present invention, it became no longer necessary to 
reduce production speeds under the same air conditions, or to constantly 
monitor and adjust oven operating parameters. Accordingly, the present 
invention has solved perplexing problems and enabled as designed 
production rates to be maintained despite adverse ambient air conditions. 
While a preferred embodiment of the present invention has been described in 
detail, various modifications, alterations, and changes may be made 
without departing from the spirit and the scope of the present invention 
as defined in the appended claims.