U.S. patent application number 13/562194 was filed with the patent office on 2014-01-30 for flashback arrestor.
This patent application is currently assigned to Victor Equipment Company. The applicant listed for this patent is Nhyanh Duyet Nguyen, David A. Pryor. Invention is credited to Nhyanh Duyet Nguyen, David A. Pryor.
Application Number | 20140030666 13/562194 |
Document ID | / |
Family ID | 48986220 |
Filed Date | 2014-01-30 |
United States Patent
Application |
20140030666 |
Kind Code |
A1 |
Pryor; David A. ; et
al. |
January 30, 2014 |
FLASHBACK ARRESTOR
Abstract
A flashback arrestor for use in gas cutting or welding equipment
includes a porous body which defines a proximal end portion and a
distal end portion and which has a plurality of pores. Each of the
pores defines a pore size. The pore size is a function of a
detonation cell size such that the pore size is increased to reduce
a size of the sintered body.
Inventors: |
Pryor; David A.; (Denton,
TX) ; Nguyen; Nhyanh Duyet; (Frisco, TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Pryor; David A.
Nguyen; Nhyanh Duyet |
Denton
Frisco |
TX
TX |
US
US |
|
|
Assignee: |
Victor Equipment Company
Denton
TX
|
Family ID: |
48986220 |
Appl. No.: |
13/562194 |
Filed: |
July 30, 2012 |
Current U.S.
Class: |
431/346 ;
239/418; 431/354 |
Current CPC
Class: |
F23D 14/54 20130101;
F23D 14/38 20130101; B23K 7/10 20130101; F23D 14/465 20130101; B23K
5/22 20130101; A62C 4/02 20130101; F23D 14/82 20130101; B23K 37/006
20130101; Y02E 20/344 20130101; Y02E 20/34 20130101 |
Class at
Publication: |
431/346 ;
431/354; 239/418 |
International
Class: |
F23D 14/82 20060101
F23D014/82; F23D 14/54 20060101 F23D014/54 |
Claims
1. A flashback arrestor for use in gas cutting or welding equipment
comprising: a porous body defining a proximal end portion and a
distal end portion and having a plurality of pores, each of the
pores defining a pore size, wherein the pore size is a function of
a detonation cell size such that the pore size is increased to
reduce a size of the sintered body.
2. The flashback arrestor according to claim 1, wherein the pore
size is between approximately 10 and approximately 16 microns.
3. The flashback arrestor according to claim 1 further comprising a
fitting disposed at the proximal end portion, the fitting being
adapted to secure the flashback arrestor to the gas cutting or
welding equipment.
4. The flashback arrestor according to claim 3, wherein the fitting
is sized to fit within a bore of a standard pipe thread.
5. The flashback arrestor according to claim 4, wherein the
standard pipe thread is a 1/4-18 National Pipe Thread (NPT).
6. The flashback arrestor according to claim 3 further comprising a
filter disposed within the fitting.
7. The flashback arrestor according to claim 1, further comprising
an end cap secured to a distal end portion of the porous body.
8. The flashback arrestor according to claim 1, wherein the porous
body is formed with a sintering process.
9. The flashback arrestor according to claim 1, wherein the pores
define passageways through the porous body having irregular
shapes.
10. The flashback arrestor according to 1, wherein the sintered
body defines a cylindrical geometry.
11. A flashback arrestor for use in gas cutting or welding
equipment comprising: a body defining a proximal end portion and a
distal end portion and having a plurality of pores, each of the
pores defining a pore size, wherein the pore size is a function of
a detonation cell size such that the pore size is increased to
reduce a size of the body.
12. The flashback arrestor according to claim 11, wherein the body
is sintered.
13. The flashback arrestor according to claim 11 further comprising
a fitting disposed at the proximal end portion, the fitting being
adapted to secure the flashback arrestor to the gas cutting or
welding equipment.
14. The flashback arrestor according to claim 13, wherein the
fitting is sized to fit within a bore of a standard pipe
thread.
15. The flashback arrestor according to claim 13 further comprising
a filter disposed within the fitting.
16. The flashback arrestor according to claim 11, wherein the pore
size is between approximately 10 and approximately 16 microns.
17. The flashback arrestor according to claim 11, wherein the pore
size is a function of an initial pressure of a gas mixture and an
equivalence ratio of the gas mixture.
18. The flashback arrestor according to claim 17, wherein the pore
size .lamda. is defined by the equation:
.lamda.=1309.2.times.(P).sup.-0.907 wherein P is the initial
pressure of a mixture of oxygen and acetylene having an equivalence
ratio of about 2.5.
19. A device for arresting a flame comprising: a body having a
plurality of pores, each of the pores defining a pore size, wherein
the pore size is a function of a detonation cell size such that the
pore size is increased to reduce a size of the body.
20. The device according to claim 19, wherein the body is
sintered.
21. A flashback arrestor for use in gas cutting or welding
equipment comprising: a sintered body defining a proximal end
portion and a distal end portion and having a plurality of pores,
each of the pores defining a pore size; a fitting disposed at the
proximal end portion, the fitting being sized to fit within a bore
of a standard pipe thread, wherein the pore size is a function of a
detonation cell size such that the pore size is increased to reduce
a size of the sintered body.
22. The flashback arrestor according to claim 21 further comprising
a filter disposed within the fitting.
23. The flashback arrestor according to claim 21, wherein the pore
size is between approximately 10 and approximately 16 microns.
24. An oxy-fuel cutting/welding torch comprising: a torch body
defining a proximal end portion and a distal end portion; an oxygen
passageway having an inlet at the proximal end portion; a fuel
passageway having an inlet at the proximal end portion; a first
flashback arrestor disposed within the oxygen passageway at the
proximal end portion; and a second flashback arrestor disposed
within the fuel passageway at the proximal end portion, wherein
each of the first and second flashback arrestors define a body
having a proximal end portion and a distal end portion and comprise
a plurality of pores, each of the pores defining a pore size,
wherein the pore size is a function of a detonation cell size such
that the pore size is increased to reduce a size of the body.
25. The oxy-fuel cutting/welding torch according to claim 24,
wherein the bodies of the flashback arrestors are sintered.
26. The oxy-fuel cutting/welding torch according to claim 24
further comprising: a first fitting disposed at the proximal end
portion of the first flashback arrestor; and a second fitting
disposed at the proximal end portion of the second flashback
arrestor, the fittings being adapted to secure the flashback
arrestors within the passageways of the oxy-fuel cutting/welding
torch.
27. The oxy-fuel cutting/welding torch according to claim 26,
wherein the fittings are sized to fit within a bore of a standard
pipe thread
28. The oxy-fuel cutting/welding torch according to claim 28
further comprising: a first filter disposed within the first
fitting; and a second filter disposed within the second
fitting.
29. The flashback arrestor according to claim 24, wherein the pore
size is between approximately 10 and approximately 16 microns.
30. A device for arresting a flame comprising: a body having a
plurality of pores, each of the pores defining a target pore size,
wherein the pore size is a function of an initial pressure of a gas
mixture and an equivalence ratio of the gas mixture such that the
pore size is increased to reduce a size of the body.
31. The device according to claim 30, wherein the target pore size
.lamda. is defined by the equation:
.lamda.=1309.2.times.(P).sup.-0.907 wherein P is the initial
pressure of a mixture of oxygen and acetylene having an equivalence
ratio of about 2.5.
Description
FIELD
[0001] The present disclosure relates to oxy-fuel cutting or
welding equipment and more specifically to flashback arrestors for
the oxy-fuel cutting or welding equipment.
BACKGROUND
[0002] The statements in this section merely provide background
information related to the present disclosure and may not
constitute prior art.
[0003] Oxy-fuel cutting or welding torches generally employ oxygen
and a fuel gas, such as acetylene or propane, by way of example, to
cut or weld a workpiece. The oxy-fuel torch is generally connected
to an oxygen hose that supplies preheat and cutting oxygen, and a
fuel gas hose that supplies fuel, to the cutting or welding torch.
Preheat oxygen and the fuel gas are mixed in the cutting or welding
torch and ignited to provide heat to the workpiece. Cutting oxygen
may be added to react with the heated workpiece to initiate a
cutting process.
[0004] While the oxy-fuel cutting or welding torches have proven to
be relatively safe if operated properly, an inherent hazard, known
as "flashback", is present in the process. Flashback can occur when
oxygen enters the fuel side of the system or vice versa due to a
reverse flow. The mixed gases, if ignited, can cause a flame to
retreat into the torch handle or even the gas hoses and can cause
an explosion at any point in the system.
[0005] One solution to this problem is to install a check valve in
each of the oxygen and fuel passageways to allow the oxygen and the
fuel to flow in one direction to prevent the reverse flow. Check
valves, however, are mechanical devices and may become unreliable
when contaminated with dirt or debris, which can cause the check
valve to leak. Moreover, the check valves cannot prevent flashback
flame from propagating upstream once flashback occurs.
[0006] Another solution to this problem is to use a flashback
arrestor (FBA). FBAs do not prevent flashback from occurring, but
can stop the flashback flame from further propagating beyond the
FBA and into the oxygen/fuel hoses or other components in the
oxy-fuel cutting or welding system. The FBA generally includes a
stainless steel filter that removes heat and free radicals from a
flame at a rate that is fast enough to quench the flame and to
prevent re-ignition of the hot gas.
[0007] The FBAs, however, have the disadvantage of being easily
clogged with debris. The stainless steel filter used in a typical
FBA is a porous body generally having a pore size of approximately
7 .mu.m (0.000276 inches in diameter), which is about 1/14 the size
of a human hair (0.004 inches in diameter). Due to such fine pore
size of the filter, FBAs can be easily clogged with debris.
Moreover, the FBAs are installed in the oxygen and fuel gas
passageways in the torch and can restrict flow of the oxygen and
fuel gases due to the fine pore size. Therefore, the torch
performance is adversely affected.
SUMMARY
[0008] In one form of the present disclosure, a flashback arrestor
for use in gas cutting or welding equipment includes a porous body
defining a proximal end portion and a distal end portion and having
a plurality of pores. Each of the pores defines a pore size. The
pore size is a function of a detonation cell size such that the
pore size is increased to reduce a size of the sintered body.
[0009] In another form of the present disclosure, a flashback
arrestor for use in gas cutting or welding equipment includes a
body defining a proximal end portion and a distal end portion and
having a plurality of pores. Each of the pores defines a pore size.
The pore size is a function of a detonation cell size such that the
pore size is increased to reduce a size of the body.
[0010] In still another form of the present disclosure, a device
for arresting a flame includes a body having a plurality of pores.
Each of the pores defines a pore size. The pore size is a function
of a detonation cell size such that the pore size is increased to
reduce a size of the body.
[0011] In still another form of the present disclosure, a flashback
arrestor for use in gas cutting or welding equipment includes a
sintered body and a fitting. The sintered body defines a proximal
end portion and a distal end portion and having a plurality of
pores. Each of the pores defines a pore size. The fitting is
disposed at the proximal end portion. The fitting is sized to fit
within a bore of a standard pipe thread. The pore size is a
function of a detonation cell size such that the pore size is
increased to reduce a size of the sintered body.
[0012] In still another form of the present disclosure, an oxy-fuel
cutting/welding torch includes a torch body defining a proximal end
portion and a distal end portion, an oxygen passageway having an
inlet at the proximal end portion, a fuel passageway having an
inlet at the proximal end portion, a first flashback arrestor
disposed within the oxygen passageway at the proximal end portion,
and a second flashback arrestor disposed within the fuel passageway
at the proximal end portion. Each of the first and second flashback
arrestors defines a body having a proximal end portion and a distal
end portion and includes a plurality of pores. Each of the pores
defines a pore size. The pore size is a function of a detonation
cell size such that the pore size is increased to reduce a size of
the body.
[0013] In another form, a device for arresting a flame is provided
that comprises a body having a plurality of pores, each of the
pores defining a target pore size, wherein the pore size is a
function of an initial pressure of a gas mixture and an equivalence
ratio of the gas mixture such that the pore size is increased to
reduce a size of the body.
[0014] Further areas of applicability will become apparent from the
description provided herein. It should be understood that the
description and specific examples are intended for purposes of
illustration only and are not intended to limit the scope of the
present disclosure.
DRAWINGS
[0015] The drawings described herein are for illustration purposes
only and are not intended to limit the scope of the present
disclosure in any way.
[0016] FIG. 1 is a cross-sectional view of a prior art flashback
arrestor mounted internally within a torch body;
[0017] FIG. 2 is an exploded view of a prior art flashback
arrestor;
[0018] FIG. 3 is a cross-sectional view of another prior art
flashback arrestor contained in a safety device external to a
cutting torch;
[0019] FIG. 4 is a top view of an oxy-fuel cutting/welding torch
including flashback arresters constructed in accordance with the
teachings of the present disclosure;
[0020] FIG. 5 is a cross-sectional view of the oxy-fuel
cutting/welding torch, taken along line 5-5 of FIG. 4;
[0021] FIG. 6 is a cross-sectional view of a flashback arrestor
mounted internally within a torch body and constructed in
accordance with the teachings of the present disclosure;
[0022] FIG. 7 is an exploded view of the flashback arrestor of FIG.
6;
[0023] FIG. 8 is a cross-sectional view of another form of a
flashback arrestor contained in a safety device external to a
cutting torch and constructed in accordance with the teachings of
the present disclosure;
[0024] FIGS. 9A and 9B are perspective views of another form of the
flashback arrestors having end caps and constructed in accordance
with the teachings of the present disclosure;
[0025] FIG. 10 is a schematic view of detonation cells and shock
wave during detonation;
[0026] FIG. 11 are graphs of relationships among oxy-acetylene cell
width, critical tube diameter and initial pressure;
[0027] FIG. 12 is a graph of the relationship between the
detonation cell width and the initial pressure when the
oxy-acetylene (C.sub.2H.sub.2-O.sub.2) mixture is under
stoichiometric condition;
[0028] FIG. 13 is a graph of the relationship between the
detonation cell width and the initial pressure when the equivalence
ratio of the C.sub.2H.sub.2--O.sub.2 mixture is 2.5;
[0029] FIG. 14 is a graph of the relationship between the
detonation cell width and the equivalence ratio of the
C.sub.2H.sub.2--O.sub.2 mixture;
[0030] FIG. 15 is a graph of the relationship between the
detonation velocity and the fuel volume % of the
C.sub.2H.sub.2--O.sub.2 mixture; and
[0031] FIG. 16 is graph of the relationship between the detonation
velocity and the tube diameter for different oxy-acetylene
mixtures.
DETAILED DESCRIPTION
[0032] The following description is merely exemplary in nature and
is not intended to limit the present disclosure, application, or
uses. It should be understood that throughout the drawings,
corresponding reference numerals indicate like or corresponding
parts and features. It should also be understood that various
cross-hatching patterns used in the drawings are not intended to
limit the specific materials that may be employed with the present
disclosure. The cross-hatching patterns are merely exemplary of
preferable materials or are used to distinguish between adjacent or
mating components illustrated within the drawings for purposes of
clarity.
[0033] Referring to FIGS. 1 and 2, a pair of typical flashback
arrestors 10 are installed in a torch body 12 of a cutting or
welding torch (not shown). The torch body 12 defines an oxygen
passageway 14 and a fuel gas passageway 16. The pair of flashback
arrestors 10 each includes a porous metal portion 18, a fitting 20,
and a check valve 22. The fitting 20 includes a bore 24 in fluid
communication with the oxygen passageway 14 or the fuel gas
passageway 16. The fitting 20 includes a proximal threaded portion
26 and a distal threaded portion 28. The check valve 22 is disposed
in the bore 24 proximate the proximal threaded portion 26. The
proximal threaded portion 26 has an outside diameter D1 and
functions as a hose connector for connecting to an oxygen or fuel
gas hose (not shown). The distal threaded portion 28 engages an
inner surface of the torch body 12 to secure the flashback arrestor
10 to the torch body 12 via a threaded connection. The distal
threaded portion 28 has an outside diameter D2 which is greater
than the outside diameter D1 of the proximal threaded portion 26.
An insertion portion 29 is provided proximate the distal threaded
portion 28 and inserted into the porous body 18.
[0034] An O-ring 31 is disposed in an annular groove 32 (shown in
FIG. 2) of the fitting 20. When the fitting 20 is installed in the
torch body 12, the O-ring 31 prevents leakage of gas from the
oxygen passageway 14 and the fuel gas passageway 16 to outside the
flashback arrestors 10. A mounting assembly 36, which includes a
mounting plate 38, a washer 40, and a screw 42, is used to secure
the flashback arrestors 10 to the torch body 12.
[0035] Referring to FIG. 3, another form of typical flashback
arrestors 50 are mounted to a pair of add-on devices, i.e., safety
devices 52 separate from the cutting/welding torch. The safety
devices 52 each include a housing 54 and a bore 56. The flashback
arrestor 50 is inserted into the bore 56 of the housing 54 and
includes a porous body 58, a bushing 60, and a check valve 62. The
housing 54 includes a proximal threaded portion 64, which functions
as a hose connector for engaging an oxygen or fuel gas hose. The
bushing 60 includes a distal threaded portion 66 for engaging an
inner surface of the housing 54 of the safety device 52. An O-ring
68 is provided between the housing 54 and the bushing 60 to prevent
leakage of gas to outside the flashback arrestor 50. An adaptor 72,
in the form of a hose nipple, has one end inserted into a hose
fitting nut 70 and the other end inserted into the bushing 60 to
mount the safety device 52 to the hose fitting nut 70. The distal
threaded portion 66 of the bushing 60 has an outside diameter D4
greater than the outside diameter D3 of the proximal threaded
portion 64 of the add-on device 52.
[0036] In the typical flashback arrestors 10 and 50, the porous
bodies 18 and 58 have a pore size of approximately 7 .mu.m. This
pore size is based on the indicated pores size from ISO 4003 bubble
point testing. Bubble point testing indicates the pore size is
based on "capillary theory" and cylindrical capillary tube data.
The indicated pore size is related to the bubble point pressure
based on Poiseuille's law which incorporates an empirical constant
that is a function of the filter material, form, etc. This constant
is essentially a capillary shape factor. Therefore, the bubble
point testing is typically only a relative comparison for a given
element or medium. In various forms, the true pore size is likely 2
to 5 times smaller than that indicated by bubble point test
results.
[0037] Referring to FIGS. 4 and 5, an oxy-fuel cutting/welding
torch that includes flashback arrestors constructed in accordance
with the teachings of the present disclosure is generally indicated
by reference numeral 100. The cutting or welding torch 100 includes
a torch head 102 and a handle portion 104. The handle portion 104
includes a torch body 106 and a barrel 108. The oxy-fuel
cutting/welding torch 100 further includes a preheat fuel tube 112,
a preheat oxygen tube 114, and a cutting oxygen tube 116 extending
from the torch head 102 to the barrel 108 for supplying fuel gas
and preheat/cutting oxygen to the torch head 102. A lever 118 is
connected to the torch body 106 for controlling a gas valve 146. A
pair of flashback arrestors 130 (only one is shown in FIG. 4) are
removably mounted to the torch body 106.
[0038] Referring to FIG. 5, the torch head 102 includes a
cutting/welding tip 132. The torch body 106 defines a fuel gas bore
134, an oxygen bore 136, a fuel gas passageway 138, and an oxygen
passageway 140. The fuel gas passageway 138 is provided between the
fuel gas bore 134 in the torch body 106 and the fuel gas tube 112
in the barrel 108 to provide fluid communication therebetween. The
oxygen passageway 140 is disposed between the oxygen bore 136 in
the torch body 106 and the preheat oxygen tube 114 (shown in FIG.
4) in the barrel 108 to provide fluid communication therebetween.
The oxygen passageway 140 also provides fluid communication between
the oxygen bore 136 and the cutting oxygen tube 116. A fuel gas
hose 142 (which has left-hand threads) and an oxygen hose 144 are
connected to the flashback arresters 130 to supply fuel gas and
oxygen, respectively, to the fuel gas bore 134 and the oxygen bore
136. Fuel and oxygen valves 146 are provided at the torch body 106
to control flow of fuel or oxygen from the fuel gas bore 134 or the
oxygen bore 136 to the fuel gas and oxygen passageways 138 and
140.
[0039] Referring to FIG. 6, the flashback arrestors 130 constructed
in accordance with the teachings of the present disclosure each
include a porous body 150, a fitting 152, and a check valve 154.
The flashback arrestors 130 are inserted into the fuel gas bore 134
and the oxygen bore 136 in the torch body 106 for arresting and
quenching flames when a flashback occurs.
[0040] The fittings 152 each include a proximal threaded portion
156, a distal threaded portion 158 and an enlarged portion 160
therebetween. The proximal threaded portion 156 has outer threads
for engaging the fuel hose 142 or the oxygen hose 144 (shown in
FIG. 5). The distal threaded portion 158 has outer threads for
engaging inner threads of the torch body 106 such that the
flashback arrestors 130 are secured to the torch body 106 via
threaded connection. The proximal threaded portion 156 has an
outside diameter D5 and in one form is sized to fit within a bore
of a standard pipe thread, which is a 1/4-18 National Pipe Thread
(NPT).
[0041] The check valve 154 is press-fitted inside the bore 168 of
the fitting 152 proximate the proximal threaded portion 156 and
allows oxygen or fuel gas to flow in one direction, i.e., from the
oxygen/fuel gas hoses, through the fittings 152 to the porous
bodies 150.
[0042] The porous body 150 of the flashback arrestor 130 is, in one
form, a cylindrical body and is formed by a sintering process. In
one form, the material for the porous body 150 is a stainless steel
grade 316. However, it should be understood that a variety of
materials having a high thermal conductivity may be employed,
including other metallic materials such as nickel, brass, bronze,
and alloys thereof, among others.
[0043] The porous body 150 defines a proximal end portion 162 and a
distal end portion 164 and a bore 166 extending therebetween. The
bore 166 of the porous body 150 is in fluid communication with the
bore 168 of the fitting 152. The porous body 150, in one form, is
press-fit into the distal threaded portion 158 of the fitting
152.
[0044] As further shown, the proximal end portion 162 of the porous
body 150 has an open end, whereas the distal end portion 164 of the
porous body 150 has a closed end with a distal face 168. The porous
body 150 defines a plurality of pores. The bore 166 of the porous
body 150 is in fluid communication with the fuel gas passageway 138
(shown in FIG. 5) or the oxygen passageway 140 (shown in FIG. 5)
through the pores of the porous body 150. The pores have irregular
shapes and define passageways through the porous body 150. The
pores define a pore size, which is a function of a detonation cell
size .lamda. such that the pore size is increased to reduce a size
of the sintered porous body. As an example, the pore size is
between approximately 10 .mu.m and approximately 16 .mu.m. Because
the pore size of the present disclosure is greater than the pore
size (7 .mu.m) in a typical flashback arrestor, the outside
diameter of the porous body 150 can be made smaller than that of
the porous body in a typical flashback arrester for a predetermined
flow capacity. As such, the distal threaded portion 158 of the
fitting 130 proximate the porous body 150 can also be made smaller
than that of a fitting in a typical flashback arrestor. In the
embodiment of FIG. 6, the distal threaded portion 158 has an
outside diameter equal to or smaller than the outside diameter D5
of the proximal threaded portion 156. The porous body 150 of the
present disclosure has a reduced outside diameter and an increased
pore size.
[0045] The flashback arrestor 130 may further include a check valve
170 disposed within the fitting 152. The fitting 152 is used to
secure the check valve 154 to the torch body 106. Therefore, no
O-ring or additional mounting assembly is needed to mount the
flashback arrestors 130 to the torch body 106.
[0046] Referring to FIG. 7, the flashback arrestors 130 constructed
in accordance with the teachings of the present disclosure have
fewer components than the typical flashback arrestors 10 of FIG. 2.
As shown in FIG. 2, the typical flashback arrestors 10 require a
pair of O-rings 31 and a mounting assembly 36, which includes a
mounting plate 38, a washer 40 and a screw 42, to mount the
flashback arrestors to the torch body 12. In contrast, as shown in
FIG. 7, the flashback arrestors 130 of the present disclosure can
be mounted to the torch body 12 without using O-rings and the
mounting assembly.
[0047] Referring to FIG. 8, another form of a flashback arrester
200 is provided in an add-on device, i.e., a safety device 202
external to the hose fitting 206. The safety devices 202 are
mounted to the hose fitting 206 by adapters 215 in the form of a
hose nipple. The flashback arrestors 200 include a porous body 204,
a fitting 207 and a check valve 208. The safety device 202 has a
proximal portion 210, a distal portion 212 and a bore 205
therebetween. The adaptor 215 has one end inserted into the hose
fitting nut 206 of the oxy-fuel cutting/welding torch and another
end inserted into the bore 214 proximate the distal portion 212 of
the add-on device 202 to mount the safety device 202 to the hose
fitting nut 206. The fitting 207 includes a proximal threaded
portion 214, a distal threaded portion 216, and an enlarged portion
218 therebetween. The proximal threaded portion 214 has an outside
diameter D6. The distal threaded portion 216 may have an outside
diameter equal to or smaller than the outside diameter D6 of the
proximal threaded portion 214. The distal threaded portion 216
engages an inner threaded portion 220 of the safety device 202 via
threaded connection such that the flashback arresters 200 are
secured to the safety device 202. The flashback arrestors 200 are
disposed outside the safety device 202 except the distal threaded
portion 216. The porous body 204 includes a proximal end portion
230 and a distal end portion 232. The proximal end portion 230 is
inserted into the bore 236 of the fitting 207 proximate the distal
threaded portion 216. The distal end portion 232 is a closed end
including a distal face 234. The check valve 208 is press-fitted
into the bore 236 of the fittings 207.
[0048] Referring now to FIGS. 9A and 9B, the flashback arrestors
130 in another form may also be provided with end caps 172, which
are secured to a distal end portion of the porous bodies 150 as
shown. In this form, the porous bodies 150 have open end portions
rather than closed ends as previously set forth, which allows for
improved manufacturability. More specifically, the porous bodies
150 can be formed in a continuous length and subsequently cut to
size according to the specific torch application. The end caps 172
are a similar or the same material as the porous bodies, namely, a
sintered metal material in one form. The end caps 172 may be press
fit into the porous bodies 150, or they may be bonded in another
form of the present disclosure.
[0049] The pores of the porous body of the flashback arrestors 130
and 200 constructed in accordance with the teachings of the present
disclosure can be used to arrest both deflagrations and
detonations. The pore size of the pores is a function of a
detonation cell size .lamda..
[0050] Flashback in an oxy-fuel system is the propagation of
combustion that travels in a reverse direction of the normal gas
flow. The propagation of combustion undergoes two phases: a
deflagration phase and a detonation phase. During the deflagration
phase, the flame first enters the torch and progressively increases
in velocity. The velocity of the flame during the deflagration
phase is at a rate below mach 1 (i.e., subsonic velocity); however,
the velocity of the flame continues to increase until it reaches
mach 1 (sonic velocity). Once the velocity reaches sonic speed, a
deflagration-to-detonation transition (DDT) can occur with
associated abnormally high velocities and pressures.
[0051] The detonation phase ensues and continues to increase in
velocity beyond mach 1 (supersonic velocity). The distance the
flame travels during the phase change from deflagration to
detonation is known as the induction length. Testing reveals that
the induction length is very short and occurs approximately 0.5''
to 0.7'' from the tip end of the torch.
[0052] When a detonation phase is reached, a large amount of energy
is released and the propagation rate of the combustion process
becomes supersonic. Testing reveals that the propagation rate of a
detonation can reach 3,000 meters/second.
[0053] Referring to FIG. 10, as the combustion propagates during
the detonation phase, detonation cells are created and continue to
generate and re-establish themselves. Detonation cells represent
the 3-D structure of the detonation wave, which has a detonation
cell size or width .lamda.. The detonation cell size .lamda. is a
function of the composition of the mixture, initial temperature and
pressure, and the types of the fuel (such as propane, propylene,
natural gas) and the oxidizer (such as oxygen). For example, the
detonation cell size .lamda. increases as the initial pressure
decreases. The pore size of the porous body also depends on the
oxy-fuel mixture. When the mixture of fuel and oxygen is more
susceptible to detonation, the detonation cell size is relatively
smaller. Therefore, the pore size should be smaller for effective
arrestment of detonation for more volatile mixture.
[0054] The pore size of the porous body 150 in accordance with the
teachings of the present disclosure is determined based on the
detonation cell width .lamda., which is a function of the
composition of the mixture, initial temperature and pressure, and
the types of the fuel and the oxidizer. The pore size of the porous
body 150 can effectively disrupt regeneration of detonation cells
to thereby extinguish the flame propagation.
[0055] Referring to FIG. 11, the pore size is determined based on
the critical diameter. The critical diameter is the minimum pipe
diameter below which a detonation of a specific fuel/oxidizer
combination will not propagate because the detonation cell
structure cannot exist. When a flame travels to a flashback
arrestor having a pore size smaller than the detonation cell size
of the detonation wave, the flame will be quenched and stop
propagating because the detonation cell does not exist when the
detonation wave travels through the pores.
[0056] Therefore, the target pore size in accordance with the
teachings of the present disclosure is based on critical tube
diameter data, which is calculated from cell width data for
oxy-acetylene worst case initial pressure and stoichiometry
conditions. Acetylene (C.sub.2H.sub.2) is used as the fuel gas in
determining the desired pore size of the flashback arrestors
because acetylene is the most volatile and has the highest burning
velocity. As long as the determined pore size of the flashback
arrestors can stop generation of the oxy-acetylene detonation cell,
the determined pore size can also stop generation of the detonation
cell by a mixture of oxygen and other fuel gases.
[0057] FIG. 11 shows the critical tube diameter (cell width/Pi) for
a range of available initial pressure data when the oxy-fuel
mixture has an equivalence ratio (ER) of 2.5 (.about.47.5% fuel by
volume). The equivalence ratio is the ratio of the fuel-to-oxidizer
ratio to the stoichiometric fuel-to-oxidizer ratio (.about.28.5%
fuel by volume). The stoichiometric ratio is the xoy-fuel ratio
necessary for complete combustion. The acetylene pressure of 22.5
psig (37.2 psia) is considered worst case based on operating
pressures in Europe. Therefore, from the curve fit equation, the
cell width for oxy-acetylene detonations at this initial pressure
would be approximately 49 .mu.m (0.0019 in). The critical tube
diameter associated with this cell size is approximately 16 .mu.m
(0.0006 in).
[0058] Curve fits of these data allow specifying a target cell
width or critical tube diameter for a given pressure. The curve fit
equation for cell width (A) for oxy-acetylene mixtures with an ER
of 2.5 is:
.lamda.=1309.2.times.(P).sup.-0.907
[0059] where: .lamda.=cell width (microns) [0060] P=initial mixture
pressure (psia)
[0061] The geometry of sintered metal pores is not circular and
thus application of the critical tube diameter for a given
stoichiometry and initial pressure would not necessarily directly
apply. The critical dimension would likely be between the values of
cell width (typically applicable to square or rectangular
geometries) and cell width divided by Pi (typically applicable to
circular geometries). Based on this logic, the critical dimensions
(true pore size) for arresting an oxy-acetylene detonation
(Equivalence Ratio=2.5) is estimated to be between 16 .mu.m to 49
.mu.m.
[0062] The maximum acetylene pressure that is recommended for use
in North America is 29.7 psia, whereas Europe and other parts of
the world allow acetylene pressure to be used at 37.2 psia. With
these parameters, the research and testing result in a determined
detonation cell width size of 0.0019''. By dividing the detonation
cell width by pi, the critical diameter of 0.0006047'' (or 15.4
.mu.m) is achieved.
[0063] As shown in FIG. 12, the detonation cell size is increased
as the initial pressure is decreased. The oxy-acetylene mixture is
at a stoichiometric ratio (28.5 volume % fuel). The
C.sub.2H.sub.2--O.sub.2 detonation indicates that the detonation
cell width ranges from .about.0.003 to .about.0.006 inches at 15-30
psia at the stoichiometric ratio (28.5 v % fuel). For example, when
the pressures are 14.9 psia, 30.4 psia, and 44.3 psia, the cell
widths are 0.169 mm (0.0067 in), 0.081 mm (0.0032 in) and 0.059 mm
(0.0024 in), respectively.
[0064] As shown in FIG. 13, the oxy-acetylene mixture has an
equivalence ratio of 2.5 (i.e., 47.5% fuel by volume). When the
pressure is 14.6 psia, 30.0 psia, and 60 psia, the detonation cell
width is 0.109 mm (0.0043 in), 0.059 mm (0.0029 in), and 0.031 mm
(0.0012 in), respectively. It is clear from FIGS. 11 and 12 that
the cell width is decreased when a richer fuel-to-oxidizer mixture
is used.
[0065] FIG. 14 shows the stoichiometry effect on the determination
of the detonation cell size. When the fuel-to-oxidizer is below the
stoichiometric ratio, the detonation cell size increases abruptly.
When the fuel-to-oxidizer is higher than the stoichiometric ratio,
the detonation cell width is approximately the same when the
equivalence ratio is between 1 and 2.5 and then gradually increases
when the equivalence ratio is above 2.5.
[0066] FIG. 15 shows the detonation velocity increases when the
oxy-fuel mixture has a higher percentage of fuel up to
approximately 55% of the fuel. The detonation velocity then
decreases as the ratio of fuel to oxygen is increased until the
ratio of fuel to oxygen is 70%.
[0067] FIG. 16 is graph of the relationship between the detonation
velocity and the tube diameter for different oxy-acetylene
mixtures. A richer oxy-acetylene mixture has smaller tube diameter
and thus smaller detonation width.
[0068] To provide a degree of safety and allow for variances in the
manufacture of sintered filters, a pore size in the range of 10-14
.mu.m can be viably used. The lower limit of this range is greater
than the pore size of 7 .mu.m in a typical flashback arrestor. The
increased pore size of the flashback arrestors of the present
disclosure increases flow capacity of the sintered porous body. Due
to the increased flow capacity, the physical size of the porous
body can be reduced. The reduced size of the porous body allows the
distal threaded portion of the fittings, which is used to secure
the flashback arrester to the torch body or an add-on safety
device, to have a size adapted for a bore of a 1/4-18 NPT pipe
thread, which is a standard thread in most oxy-fuel torches as a
means to join a hose connection to the torch body. As such, the
flashback arrestor of the present disclosure can be relatively
easily mounted to the bores of most oxy-fuel torches.
[0069] Moreover, by installing the filter directly into the bore of
the fitting proximate to the proximal threaded portion, the
flashback arrestors of the present disclosure can achieve the
advantage of material reduction. In addition, the flashback
arrestors of the present disclosure are smaller than the typical
flashback arrestors and have a simpler design with fewer
components. Therefore, the flashback arrestors can reduce
manufacturing costs.
[0070] The description of the disclosure is merely exemplary in
nature and, thus, variations that do not depart from the substance
of the disclosure are intended to be within the scope of the
disclosure. Such variations are not to be regarded as a departure
from the spirit and scope of the disclosure.
* * * * *