Solving the Requirement for Precise Control of Air Circulation in a Vacuum Deposition Process

A new manufacturer of solar panels has developed a proprietary process for high volume vacuum deposition that will allow them to cost effectively compete in the high-stakes solar industry.

Problem Statement

The high volume manufacturing process alternates the use of air and vacuum, along with heat, to deposit the various gas materials onto a glass sub-strait.  To evenly distribute the heating and cooling air, the air must be moved over the glass at a fairly high flow and a relatively low pressure.  Since the pressures can vary due to normal pressure drops, monitoring of the pressure is required to maintain the required flow of air.  A very precise method of pressure-biased flow control was needed with pressures no more than 30 psig (pounds per square inch, gauge) and air flow as high as 100 scfm (standard cubic feet per minute).

Previous Options

Air flow controls are typically designed to control the flow of air at a set pressure.  A signal can be applied to adjust the flow to a required amount for a given pressure.  If the pressure were to vary, the air flow could vary accordingly.

Solution

E&M Sales, together with Proportion-Air, Inc. of McCordsville, Indiana, developed a compressed gas flow control assembly. The assembly consists of an FQB2 series proportional control valve, a PSR volume booster, and an F series high-speed flow monitor. The FQB2 control valve consists of two normally closed solenoid valves, a control circuit board, and a protective canister. The FQB2 operates by comparing the user’s electronic command input signal to the signal being returned to the FQB2 from the F Series flow monitor. The on-board control circuit examines any differences between these signals and actuates the solenoid valves in response. Opening one solenoid valve removes compressed gas from the pilot operated R-Series regulator’s dome while opening the other solenoid valve adds compressed gas from the supply. The volume of compressed gas on the dome of the R-Series regulator sets the output flow rate. The FQB2 continuously monitors the user command and F-Series feedback signals to keep the assemblies flow rate at the desired point.

The Proportion-Air, Inc. F-Series is a transducer that measures compressed gas-flow rates. This measurement is made with a differential pressure transducer with P1 measuring the input pressure of a venturi and P2 measuring the pressure in the throat of the venturi. Utilizing differential pressure measurement results in an extremely fast flow detection of less than 10mS in most instances. This high speed also allows the F-Series products to be used in conjunction with Proportion-Air’s proportional regulators for compressed gas-flow control. To ensure high speeds, the F-Series products use analog electronics.

The customer is then able to apply a 4-20 mA (milli-amp) signal to the control unit to proportionally set the flow rate from 10 to 100 scfm as needed in the high volume process.

Implementation

A test flow control was provided to the customer to use on a small scale process machine to see if the air flow could be achieved and controlled.  The initial tests showed that the originally selected pressure range was too high, and the units were adjusted by the factory accordingly.  27 units were then incorporated into the process.

Summary

With the introduction of the precision, electronic flow controls, the customer was able to achieve the production rates required for their proprietary solar panel manufacturing process to be successful.  This breakthrough technology, along with the custom flow capabilities of Proportion-Air, Inc. has given the customer the ability to not only prove the process, but expand the production capabilities, further increasing their manufacturing capacity.

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