DESIGNING AND TESTING INTERTANK AIR BEARING

• Document Type: CREST
• Collection: NGA Records (Formerly NIMA)
• Document Number (FOIA) /ESDN (CREST): CIA-RDP78B04747A002800070001-4
• Release Decision: RIPPUB
• Original Classification: K
• Document Page Count: 16
• Document Creation Date: December 28, 2016
• Document Release Date: May 31, 2001
• Sequence Number: 1
• Publication Date: June 1, 1965
• Content Type: REPORT

STATINTL
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June 1965
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submits this report in compliance with Item 4.2
of the Development Objectives of Contract 974.
Approved Research Manager
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The two objectives of this task were to study the possibility of
designing an improved plenum-type air bearing that is particularly suit-
able for a cleanroom environment and (making a radical departure from
this type of bearing) to design one that incorporates its own blower fan.
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CONTENTS
SECTION PAGE
I INTRODUCTION 1
2 TECHNICAL DISCUSSION 2
2.1 PLENUM-TYPE BEARING 2
2.2 SELF-POWERED AIR BEARING 4
ILLUSTRATIONS
FIGURE
-
PAGE
1
Plenum Type Air Bearing
3
2
Air Bearing Using Transverse-Flow Fan
5
3
Scheme of Air Bearing with Transverse-Flow Fan
7
4
Layout of Air Bearing Test Bed
8
5
Air Bearing Test Bed Showing Fan Installation
9
6
Air Bearing Test Bed Showing Fan Installed
and Wheel
10
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1. INTRODUCTION
The type of air bearing presently in use consists of a tube into
which air is pumped and then released through slots or holes in a segment
of the periphery. Adjustable flanges are provided on each side of the film
to permit the release of air between the bearing and the film at a control-
led rate, thereby maintaining a cushion over which the film is transported.
When the flanges are adjusted to suit the specific film width, the slots or
holes outside of the flanges are closed to prevent loss of air,and collapse
of the air cushion between.
This type of air bearing requires a high flow of air, which, in the
case of the HTA-5 processor, necessitated a blower of 10 horsepower pro-
ducing 1740 cfm at a static pressure of approximately 20 inches of water.
An undesirable result of the high air flow is the release of aero-
sol spray caused by the air impinging on the liquid present on the film.
To overcome this problem, a plenum-type bearing was constructed in which
the film is totally enclosed from tank to tank.
As an alternative to this type of air bearing, one in which the air
pressure and flow would be generated internally was studied.
Where one main blower is supplied for all bearings in a proces-
sor, a high pressure drop must be allowed for in all main and branch feeder
ducts (thus increasing the initial horsepower requirements) or as an alter-
native, minimizing pressure drops by providing all ducts with as large a
cross sectional area as is practical. Supplying each bearing with a blower
coupled directly to it only partially solves the problem of efficiency and
compactness, since with the pressure and flow required, these blowers
are of a significant size. High performance blowers of a smaller envelope
are available but these are custom built and operate at very high speeds.
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2.1 PLENUM-TYPE BEARING
A study made of the requirements for an improved bearing showed
that the following requirements should be considered:
1) Completely enclose the film in its passage between tanks.
2) Reduce the air flow required by enclosing the film in a tun-
nel, the entrance and exit of which would be below the liquid level in the
tanks.
3) Provide air release holes that would center the film in the
tunnel by equalizing the air pressure on both sides of the film; also, by
closing the release holes to control the air pressure, possibly permitting
the passage of all widths of films without the use of adjustable flanges.
4) Reduce the aerosol spray by controlling the release of air.
Figure 1 illustrates the design selected to meet the above require-
ments. It is, in effect, a tunnel which carries the film from one tank to
another. A satisfactory air cushion was obtained with a load of 1 pound
after the air flow on each side of the film had been balanced by increas-
ing the air to the underside of the film and decreasing it against the oppo-
site side of the film.
It was found that the film oscillated at a high frequency at the
entrance and exit slots. Additional air release holes were added in the
film path, which reduced the oscillations but did not eliminate them. When
the air bearing was positioned over a tank of water with the film entrance
and exit slots under the surface, film oscillation was damped. Because
of the favorable result of this test, a method of extending the sides of the
film path further into the solution will be developed and testing will be
resumed.
At the time of this report, further tests are scheduled to plot
air pressure and flow against the load lifting capability of the bearing.
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Fi c-ure 1, Plenum lye air Be arinc
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2.2 SELF-POWERED AIR BEARING
As an extension of the work being carried out on the plenum-
type bearing, a design study was made for a self-powered air bearing in
which a fan would be incorporated to generate the air pressure and flow
necessary to provide a transport cushion.
The use of a standard centrifugal blower, squirrel-cage wheel
as a built-in power source presents difficulty because, to obtain optimum
efficiency at the given design speed, the width of the wheel should not
generally exceed 0.6 of the diameter. Various methods of avoiding this
restriction can be employed, such as the use of two wheels, but achieving
even flow becomes a serious problem over the length of the 9-1/2-inch
bearing required. A mockup model of a bearing for a single film width of
70mm was constructed and provided a reasonable cushion after suitable
flow restrictors had been provided to even the flow over the upper 180 de-
gree half of the model. On the basis of the encouraging results obtained
from the crude model an intensive study was made of all available types
of blowers. (See Monthly Progress Report No. 6)
. A new type of fan developed in Europe, the transverse-flow fan,
showed promise for this application. A conventional centrifugal blower
draws in air axially and discharges it radially. The transverse-flow fan
draws air inward radially and discharges it outward radially through a
different section of the fan periphery.
The advantage of incorporating this type of fan in an air bearing
is that higher static pressures are obtainable for the same rotor diameter
(a pressure coefficient of 1.8 to 5.5 as against 0.60 to 1.10) over a length
restricted only by structural considerations, such as housing strength. A
second mockup bearing, using an available wheel 1.8 inches wide, con-
firmed the feasibility of this concept (see Figure 2). The main problem
appeared to be the air flow distribution over the required 9-1/2-inch
length, which was hoped to be solved by using the transverse-flow fan.
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Figure 2. Air Bearing Using Transverse-Flow Fan
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The transverse-flow type fan selected was the Coester type in
which two vortex generators cause a flow of air radially through the fan
when the wheel is rotated. This type was selected since the drawing of
air in through the lower half of the bearing and expelling it through the
upper half best suited an air bearing configuration. The licensee of this
design in the U.S.A. cooperated to
develop this concept, but unfortunately problems arose in this companys'
development program. It was found that a sudden transient obstruction in
the output air flow could cause a reversal of flow in the vortex generators
and therefore in the fan itself. In terms of an air bearing, this would
cause the film to be drawn into the bearing. ,
STATINTL A further design concept was proposed by the in
which a Datwyler type of transverse-flow fan was integrated. However,
this investigation was not pursued because of the air intake section being
adjacent to one side of the film loop (see Figure 3).
As an alternative to utilizing the transverse-fan concept, an
experimental test stand is now under construction (see Figure 4) to deter-
mine whether a combination of propellers and fans can be utilized. Parts
required at the time of this report are all in manufacture. (See Figures
5and6.)
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Figure 3. Scheme of Air Bearing with Transverse-Flow Fan
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NOTES: I
1. FOR USE WITH VARIOUS FAN AND
WHEEL SET UPS AS IDENTIFIED
IN LEGEND SUCH AS:
2OR4FANS '/1
2 TO 4 WHEELS
2 OR MORE FANS WITH IMPELLER
ALONE, ETC.
2. FOR SPEEDS UP TO 6000 RPM FILM
WIDTHS TO 9-1/2 INCHES.
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LEGEND:
A-FAN HOUSING AND SHAFT
BRG. SUPPORT
B-PLASTIC SPACER
C-BLOWER WHEEL
D- VANE TYPE IMPELLER
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Figure 4. Layout of Air Bearing Teat
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i Be Grin g ''e st Sec S o"?'i g, F' to Inst:II :i 7
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i. '1 2 ? vim: B?'.L, v}: J'L:1_ is In .., n
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 STATINTL
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