Reusable disc filter with spacing bosses for high temperature gasses

A reusable filter to remove contaminants from high temperature gases, in excess of 4500.degree. F., developed by burning propellants and used to do work such as actuation of pistonpowered devices in aircraft store ejector racks. Contaminants are removed to prevent fouling of the device being acted upon, to increase reliability and to decrease maintenance of the device. The filter has stacked metal discs spaced from one another to permit side entry of the gas between the disc edges, and the discs are made of molybdenum, columbium or tantalum. A plurality of studs pass through the discs to align and hold the filter together, with raised bosses at the stud holes in each disc establishing the filter gaps between the discs. Each disc has a plurality of flow openings communicating with the filter gaps and aligned with the openings of the other discs to allow axial gas flow along the filter for end exit. The discs are sufficient in size and number to provide adequate filtering capability and absorb heat to prevent melting, but are not so large as to remove excess heat from the gas upstream from where the gas does its work. Filtering gaps in an axial direction between adjacent discs may be of the order of a few microns to a few hundred microns.

BACKGROUND OF THE INVENTION 
The invention relates to a filter that may be reused many times without 
damage to remove dirt and other contaminants from high temperature gases 
generated by burning propellants, and thus prevent the contaminants from 
fouling movable members exposed to the gas. 
Present day military aircraft of high performance capability require 
external stores to be displaced from the aircraft at high velocity in 
order for the stores to properly leave the aircraft flow field without 
damage. This is generally accomplished by ejector racks, missile launchers 
and the like, using explosive cartridges that create high temperature 
gases as an energy source. The high temperature gases act on piston 
actuated devices that in turn eject the stores at the desired high 
velocity. The propellants burnt in conventional cartridges generate gases 
of a temperature in excess of 4500.degree. F. Unburnt propellant, residue 
from igniters, oxides from the cartridge cases, and erosion of the breech 
all create particles which act to ultimately foul the ejector rack piping 
and the ejector guns or the like. 
In the past, the residue of these particles has been removed by periodic 
disassembly and cleaning of the rack and the like, which is costly and 
affects operational availability of the rack. On the other hand, the 
failure to carry out periodic cleaning affects reliability, since the 
residue buildup can cause the rack to fail to operate properly. Various 
solutions to this problem have been sought, including attempts to arrive 
at a clean burning cartridge that does not provide contaminants, and 
attempts to design a filter to remove the contaminants from the high 
temperature gas path before the gas acts on the piston actuated devices. A 
sufficiently clean burning cartridge is yet to be developed, and filters 
that may be reused through a large number of operational cycles have not 
been satisfactorily obtained because of the destructive effects of the 
high gas temperature on the filter. 
SUMMARY OF THE INVENTION 
The present invention consists of a reusable filter for high temperature 
gases which will collect the residue from the gas and thereby provide 
cleaner gas to a piston actuated device such as found in an ejector rack, 
missile launcher or the like. The device operation will then be more 
reliable, and will result in a need for less maintenance than present 
systems. The filter is constructed with particular materials and a 
particular design configuration so as to withstand, without ablation or 
erosion, gas temperatures of over 4500.degree. F. A hot gas filter thereby 
may be obtained which will be reusable in bomb racks, guns and the like 
through many firings, without jamming or fouling of the piston actuated 
devices and without the need for maintenance. The present invention 
utilizes filter components made from either molybdenum, columbium or 
tantalum, which have sufficiently high melting points in relation to the 
hot gas generated. The filter also is designed with sufficiently large 
mechanical disc components to provide adequate heat sinks to prevent 
melting, which disc components are mechanically spaced to provide fine 
slots to capture the contaminants. The components, however, must not be so 
large as to cool the gas too much and dissipate its energy before the gas 
reaches the point where it is to act as an energy source; the components 
must also be sufficiently small to fit within the intended working 
environment of an aircraft or missile. The design must also be of 
sufficient size to provide maximum filtering capacity without excessive 
pressure drop in the gas. 
The invention may also have applicability where the hot gases from burning 
propellants are used to actuate devices or drive mechanisms such as in 
gyroscopes in a missile, or to provide thrust in a missile to change its 
path, it being desired in the former instance that contaminants in the gas 
not foul the gyroscope and in the latter instance that contaminants in the 
gas not foul control valves through which the gas passes.

DESCRIPTION OF EMBODIMENT 
Referring now to the drawings, hot gas filter 10 of the present invention 
has a generally cylindrical outer shape. Filter 10 is formed by a large 
number, in the order of over a hundred for example, stacked discs 11 which 
are aligned and secured together by four studs 12 which pass through the 
discs 11 and are secured to end flange 13 and closed cap 14 of filter 10 
as by nuts 15. Filter gaps 16 (see FIG. 3) are established between 
adjacent stacked discs 11 by raised bosses 17 integral with each disc 11 
and created by coining at the position of each stud hole 18 in each disc 
11 through which a stud 12 passes. Discs 11 are otherwise flat. 
Each disc 11 has four flow openings 19 which are aligned with the four 
corresponding openings in the other discs 11. The provision of the 
plurality of raised bosses 17 at the plurality of spaced stud holes 18 
around the circumference of each disc 11 provides rigidity to the filter 
and accurately establishes the axial spacing between adjacent discs 11 
from one end to the other of filer 10. 
As diagramatically illustrated in FIG. 1, the hot gas from burning 
cartridge 20 flows to movable member 30 by passing through filter 10. The 
gas enters the sides of filter 10 through the gas flow slots 16 defined by 
the axial spacing between adjacent discs 11 established by raised bosses 
17 at the disc stud holes 18. The high temperature gas passes radially 
inwardly of the filter through the gas flow slots 16 along the filter, and 
then into the four disc flow openings 19 in commmunication with the slots 
16 to in turn move axially along the filter toward the exit end at flange 
13, cap 14 generally being a closed surface. 
Referring to FIG. 4, flange 13 has a discharge port 21, from which the hot 
filtered gas exits to thereafter actuate movable member 30, such as a 
piston powered device, or drive some other mechanical device such as in a 
gyroscope or to pass through a control valve. Discharge port 21 overlaps a 
portion of each of the four flow openings 19 through which the high 
temperature gas is flowing, in order to allow stud placement on the 
flange, but the degree of overlap is not such as to significantly impede 
the gas flow. 
By virtue of passing through the filter, contaminant particles are 
eliminated from the high temperature gas by being captured at the gas flow 
slots 16 by virtue of the narrow axial distance between adjacent discs 11. 
This axial distance, defined by the thickness of raised bosses 17, may 
vary from a few microns to a few hundred microns, by way of example, 
depending on the filtering action desired. 
The studs 12, flange 13, cap 14 and nuts 15 may be constructed of corrosion 
resistant steel, since they are not excessively exposed to hot gas flow. 
Discs 11, however, must be constructed of a material with a sufficiently 
high melting point so that the hot gas of a temperature in excess of 
4500.degree. F. will not cause melting as it passes over the discs. 
Molybdenum, columbium, or tantalum may be used for the discs 11 in a 
filter according to the design of the present invention. 
The size of the discs 11 of the filter must be such as to absorb sufficient 
heat to prevent melting, but not excessive so as to overly cool the gas 
before it reaches the point beyond the filter where the gas is to serve as 
an energy source to do work. The filter should have sufficient filtering 
capacity so that the gas is not subjected to a large pressure drop in 
passing through the filter. The aircraft or missile environment in which 
the filter has application also dictates a small size and weight of 
filter. The discs 11 generally will be several times thicker than the 
thickness of the raised bosses 17 on the discs at the stud holes 18, and a 
large number of discs 11 will be utilized to obtain sufficient filtering 
action. Openings 19 must be sufficient in number and size to avoid 
obstructing the flow of gas inside the filter toward the discharge port 
21. A filter 10 which meets these conditions and is designed for an 
ejector rack might for example be approximately three inches long, with 
over a hundred molybdenum discs 11 of one inch in diameter and of 
approximately 500 microns in thickness, and with filter slots between 
adjacent discs of 50 microns in axial length by virtue of bosses 17 being 
raised 50 microns from the otherwise flat surface of discs 11. Coarser or 
finer filter gaps may be established by varying the thickness of raised 
bosses 17. 
It should be understood that modifications of the present invention may be 
made without departing from the spirit and scope of the invention as 
hereinafter claimed.