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Highly-flexible Spray System Significantly Reduces
Scrap for a Door Manufacturer
Application: “Sandwich-panels”—
used as doors and partitions in the construction industry —
are made of two metal sheets glued to either side of an insulation
sheet in a continual process.
The glue must be applied evenly across the bottom steel sheet to
ensure proper adhesion, and a precise amount of water is required
to act as a catalyst for the glue.
After the insulation sheet is placed on the bottom
sheet, another application of glue and water is required before
the top steel sheet is added and the assembly is sent to the oven
for curing.
The amount of water applied is critical and depends
on the type of glue, the materials of construction and the speed
of the production line.
Problem: A European manufacturer of metal doors
wanted an automated system that would apply the correct volume of
water to sandwich-panels for any line speed using a single set of
spray nozzles for all products.
Depending on the glue and insulation material used,
the flow rate of the water to be applied varied from 6 gr/m2
to 40 gr/m2. In addition, the customer needed to adjust for line
speeds varying from 0.1 m/min to 15 m/min.
 Solution:
Using speed sensors to determine line speed and proximity sensors
to detect the presence of doors for spraying, the AutoJet Spray
System applies the precise volume of water catalyst required for
each product no matter what speed the production line is running.
Using patented SprayLogic® software,
AutoJet Technologies engineers programmed the Model
2250 AutoJet Spray Controller with an advanced Pulse Width Modulation
(PWM) algorithm to control the duty cycle of the spray guns. PWM
flow control requires switching a spray gun
on and off several times per second at a controlled rate. Spraying
Systems Co. PulsaJet® spray guns were chosen because of their
ability to cycle at high speeds – up to 10,000 times per minute.
The flow rate of the system at any given time is clearly
visible on the display panel of the AutoJet Spray Controller.
Because of the large variations in line speed and
flow requirements, a flow rate turndown ratio of 1000:1 was required
to ensure that only one spray nozzle set-up would be required for
the system.
Results: The fully-automated spray system designed
and installed by AutoJet Technologies met all of the customer’s
control requirements. Before installing the AutoJet Technologies
system, quality problems were only detected after doors emerged
from the oven, resulting
in significant scrap.
Precise and reliable spray
control has resulted in higher product quality with a payback
period of three months calculated by the customer.
How Pulse Width Modulation
(PWM) works:
- The time that a spray gun is “on” during Pulse Width
Modulation divided by the total cycle time gives a percentage
called the duty cycle.
- At an 80% duty cycle, the flow rate will be 80% of the maximum
flow rate at a given pressure for the nozzle.
- In addition to providing extremely high flow rate turndown ratio,
PWM can also significantly reduce airborne mists and overspray.
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