NASA CASE NO. LAR-13r996-1SB 

PRINT FIG. 8 1 

The invention disclosed in this document resulted from 2P 

research in aeronautical and space activities performed under 

programs of the National Aeronautics and Space Administration. 

The invention is owned by NASA and is, therefore, available for 

licensing in accordance with the NASA Patent Licensing 

Regulation (14 Code of Federal Regulations 1245.2). 

To encourage commercial utilization of NASA-owned inventions, 

it is NASA policy to grant licenses to commercial concerns. 

Although NASA encourages nonexclusive licensing to promote 

competition and achieve the widest possible utilization, NASA 

will consider the granting of a limited exclusive license, 

pursuant to the NASA Patent Licensing Regulations, when such a 

license will provide the necessary incentive to the licensee to 

achieve early practical application of the invention. 

Address inquiries and all applications for license for this 

invention to NASA Patent Counsel, Langley Research Center, Mail 

Code 279, Langley Station, Hampton, VA 23665. Approved NASA 

forms for application for nonexclusive or exclusive license are , 

available from the above address. 

Serial No: 07/426,345 

Filed: 10/25/39 

LaRC 

(NASA-L?S~-~AP-~~Q~G-~-~LI) ISNITa>TLTTY N9O-iclhl 

TFST MkTfsZt: AN3 APPARbTIl-2 Pat-ot: Agpi i int i 3n 

(NAtA) 25n t+CL ? LP 

Uncl cts 

G3/25 025bb.33 
AWARDS ABSTRACT 

IGNlTABlLlTY TEST METHOD AND APPARATUS 

NASA CASE NO. LAR-13996-1 -SB 

This invention relates generally to measuring and testing, and more 

particularly, to a method and apparatus for testing ignitability. 

As illustrated in the drawings, an ignition material holder 30 has a 

hemispherical cavity 34 which receives ignition material to be ignited by an 

initiator. Pressure generated by ignition is sensed by a transducer 64 and 

a pressure trace is generated which reveals the ignitability characteristics 

of the initiator. 

The invention is useful for testing percussion primers and other initiators 

for their ability to ignite ignition materials. 

Inventor: Laurence J. Bement 

Home Address: 46 Ramshaw Lane 

Newport News, VA 23602 

Employer: 

SS #. 

NASA-Langley Research Center 

Inventor: James W. Bailey. 

Home Address: 504 Tidemill Road 

Tabb, VA 23602 

SS itEmployer: PRC Kentron 

Inventor: Morry L. Schimmel 

Home Address: 8127 Amherst Avenue 

St. Louis, MO 63130 

SS #- 

Employer: Schimmel Company, St. Louis, MO 

Initial Evaluator: William W. Fernald 

Serial No.: 071426,345 

Filed: October 25, 1989 
FIG. I 

36 

I 

FIG. 3 

FIG. 4 
FIG. 6 

FIG. 7 

FIG. 5 
FIG. 8 

FIG. 9 

PRIMER I 

PRIMER 11 

5 10 

TIME- MILLISECONDS 

PRIMER I 

TIME- MILLISECONDS 
FIG. I0 PRIMER I, FFC BLACK POWDER / ,,r PRIMER II, FFC BLACK POWDER 

PRIMER I, A CANNON BLACK POWDER 

PRIMER II, A CANNON BLACK POWDER 

PRIMER TYPE I BKNOj 

oy 

r 

I I I 1 I I 

0 5 10 15 20 25 30 35 

TIME - MILLISECONDS 

FIG. II 

5O0FL TIME TO 50% OF PEAK PRESSURE 

\PRESSURE AT 1 Y ILLISECOND 

2 000 - 

1500- 

1000- 

TO PE 

'SURE 

PEAK PRESSURE 7 

-TIME 

/50% OF PEAK PRESSURE PRES 

0 I I I 1 

0 5 10 15 

TIME - MILLISECONDS 
LAR 13996-1 -1 - PATENT APPLICATION 

IGNlTABlLlTY TEST METHOD AND APPARATUS 

Origin of the lnvention 

The invention described herein was made in the performance of 

work under a NASA contract and is subject to the provisions of Section 

305 of the National Aeronautics and Space Act of 1958, as amended, 

5 Public Law 85-568 (72 Stat. 435; 42 USC 2457). 

Background ofhe lnvention 

Field of the lnvention 

The present invention relates generally to the field of measuring 

and testing, and more specifically, to a test apparatus and method for 

10 determining the ignition performance of ignition devices, i.e., devices that 

produce flame. 

Description of the Related Art 

Ignition of propellant materials used in rocket motors, or munitions, 

or even automobile air bags, all start with an igniter or initiator which can 

15 be fired either electrically or mechanically. Percussion primers are one 

type of munitions application. Percussion primers are small brass cups, 

loaded with friction-sensitive pyrotechnic compositions and an internal 

anvil. An impact on the cup's bottom ignites these compositions by 

compression between the cup and anvil to produce an output of heat, 

20 light, gas and burning particles. 

Percussion primers have been in use for over one hundred years. 

Over this time, test methods and apparatuses have been devised to 

measure different aspects of an ignition output, such as heat, light, 

pressure, and burning particles. Heat output has been measured with 

25 calorimeters and light output has been measured with photocalls and 

photographs of an ignition output's light and burning particles in a 

darkened room and with the aid of vented test volumes. Pressure 
LAR 13996-1 -2- PATENT APPLICATION 

measurements have been made by simply having an operator listen to 

relative sound of the output in vented test fixtures, and by measuring the 

pressure in closed test volumes. 

Tests of the effect of burning particles are made in a vented 

5 volume and by a "standoff" method. In the latter, a primer is fired into a 

large, deep volume with a test propellant at the base. The depth is 

varied until ignition fails to occur. 

One of the disadvantages common to the above-mentioned test 

methods and apparatuses is that virtually all system-level tests have been 

10 performed on a golno-go basis. That is, a system or sub-system is 

assembled and then initiated. The results will show that the tested 

initiator, such as a percussion primer, either did or did not work properly. 

Thus, the tests do not provide sufficient information on actual ignition 

interfaces used in ignition system designs. Consequently, little technical 

15 understanding has been achieved in determining the relative importance of 

system variables and functional margins. Individual measurements of 

heat, light, pressure, and burning particles cannot be adequately 

extrapolated to a system-level performance. For example, the large 

volumes in all of the above-mentioned test apparatuses are not 

20 representative of actual applications. The volumes reduce the available 

pressure and allow heat to dissipate, even to the point of quenching the 

burning particles. 

Generally, the known methods and apparatuses discussed above 

only provide relative comparisons, which often depend on operator 

25 judgment. These tests are incapable of measuring ignition within the first 

millisecond. 

lgnitability has particular significance to aerospace applications 

where there is a need to measure how well an initiating element can 

ignite other materials. Specifications require that igniters fire when 

30 supplied with sufficient electrical or mechanical input energy. For some 

devices, such as the NASA standard initiator, (NSI), output is controlled by 

specifying pressure performance limits when fired into a closed volume 
LAR 13996-1 -3- PATENT APPLICATION 

(known as a "bomb") with no requirement for ignition by its output. 

However, no military specification or other generally accepted tests exist 

for measuring primer output, which is used only for ignition. 

Percussion primers are generally about 0.2 inch or less in diameter 

5 and consist of thin wall brass cups containing blended pyrotechnic 

compositions and an internal anvil. Impacting and deflecting the bottom of 

the cup compresses the friction-sensitive pyrotechnic composition against 

the anvil to achieve ignition, thereby outputting a quantity of heat, light, 

gas and burning particles. 

10 One specific test method and apparatus was developed for 

measuring energy output for many different kinds of explosive devices, 

including percussioned primers. The apparatus included a pistontcylinder 

energy sensor containing a strength-calibrated, crushable honeycomb 

element. The output of a percussion primer was measured as the work 

15 done in stroking the piston to crush the honeycomb. Output was equated 

to the distance crushed multiplied by the crush strength of the 

honeycomb, and was expressed in units of inch-pounds. 

Significantly, the most important percussion primer output parameter 

is not energy output to stroke a piston, but is instead the ignitability 

20 performance. A need exists to develop a test method and apparatus 

which will determine whether the primer will ignite the next item in the 

train, and with what margin. The apparatus, however, was not capable of 

providing information with regard to ignition efficiency or time delay for 

achieving initiation. 

25 SummaIyof the Invention 

An object of the present invention is to provide a test method and 

apparatus capable of providing quantitative measurements of the efficiency 

of all types of initiators, one type thereof being percussion primers. 
LAR 13996-1 -4- PATENT APPLICATION 

Another object of the invention is to provide a relatively simple 

method of comparing output performance of percussion primers and other 

initiators in terms of ability to ignite typical propellant materials. 

In a preferred embodiment, an apparatus for testing ignitability of an 

5 initiator includes a body having a central cavity, an initiator holder for 

holding the initiator over the central cavity of the body, an ignition material 

holder disposed in the central cavity of the body and having a cavity 

facing the initiator holder which receives a measured quantity of ignition 

material to be ignited by the initiator and a chamber in communication 

10 with the cavity of the ignition material holder and the central cavity of the 

body, and means in communication with the central cavity of the body for 

measuring, recording and analyzing pressure characteristics generated by 

ignition of the ignition material by the initiator. Firing the initiator into the 

ignition material causes the ignition material to ignite, and the pressure 

15 generated in the closed chamber is measured as a function of time to 

generate a pressure trace. Preferably, the method includes measuring 

pressure at one millisecond, time to reach 50 percent peak pressure, and 

time to reach peak pressure. "lgnitability" is then expressed as the ratio 

of one millisecond pressure to peak pressure. This ratio can be 

20 compared to ratios similarly devised using other materials to provide 

comparative results. 

These objects, together with other objects and advantages which 

will be subsequently apparent reside in the details of construction and 

operation of the apparatus and method steps as more fully hereinafter 

25 described and claimed, reference being had to the accompanying drawings 

forming a part hereof, wherein like reference numerals refer to like parts 

throughout. 

Brief Description of the Drawlnas 

Fig. 1 is a cross-sectional view of an apparatus for testing 

30 ignitability of an initiator according to the present invention; 
LAR 13996-1 -5- PATENT APPLICATION 

Fig. 2 is a cross-sectional view of a portion of the apparatus 

illustrated in Fig. 1 ; 

Fig. 3 is a view similar to Fig. 2, turned 90 degrees; 

Fig. 4 is a top plan view of the portion illustrated in Fig. 2; 

5 Fig. 5 is an enlarged, cross-sectional view of another portion of the 

apparatus of Fig. 1 ; 

Fig. 6 is a top plan view of the portion illustrated in Fig. 5; 

Fig. 7 is an exploded view of a sub-assembly of the apparatus of 

Fig. 1; 

10 Fig. 8 is a graph illustrating a pressure trace of two different primer 

types (Primer I = M42C1 and Primer II = M42C2), both using the same 

type of ignition material (FFG black powder); 

Fig. 9 is a graph showing a comparison of pressure traces 

produced by Primer I and Primer II percussion primers using A-Cannon 

15 black powder ignition material; 

Fig. 10 is a graph showing typical pressure traces produced by the 

Type I and Type II percussion primers, using 200 mg each of three 

different ignition materials; and 

Fig. 1 1 is a graph illustrating a pressure trace, and data point 

20 selected for numerical description and analysis of ignitability according to 

the method of the present invention. 

Detailed Description of the Preferred Embodiments 

The aforementioned drawings will be discussed with reference to 

examples of test materials, such as percussion primers and ignition 

25 materials. In conducting tests using the apparatus and method of the 

present invention, the following percussion primers were used: 
LAR 13996-1 -6- PATENT APPLICATION 

Percussion Primer I 

Diameter - 0.1748 to 0.1756 inch; Height - 0.1 11 to 0.1 19 inch 

Composition 

lnaredients Percentage bv Weiaht 

Lead Styphnate 53 

Barium Nitrate 22 

Antimony Sulfate 10 

Aluminum (powdered) 10 

Tetracene 5 

Percussion Primer II 

Diameter - 0.1748 to 0.1756 inch; Height - 0.11 1 to 0.1 19 inch 

Composition 

Ingredients Percentage bv Weight 

Lead Thiocyanate 25 

Potassium Chlorate 33 

Antimony Trisulfide 25 

TNT 3 

Calcium Silicide 14 

The two primers I and II, are available as percussion primers 

20 M42C1 -PA1 01 and M42C2-793, respectively, and were selected for their 

markedly different output performances. The output of Primer I is 

considerably more brisant than Primer II, due to Primer 1's lead styphnate 

content. 

Ignition Materials used for testing are identified as follows: 
LAR 13996-1 -7- PATENT APPLICATION 

Nomenclatu re Material 

FFFG 

5 FFG 

Physical 

Descri~tion 

Black Powder 0.020 to 0.030 in. 

granules 

Black Powder 0.020 to 0.060 in. 

granules 

A-Cannon Black Powder 0.125 to 0.250 in. 

platelets (0.60 in 

thickness) 

10 20140 Boron-Potassium Salt to flour 

Nitrate (BKNO,) consistency 

Type 2R (BKNO3) 

15 Pellets 

0.60 to 0.130 

granules 

0.125 DIA x 0.100 

height, domed ends 

The ignition materials were selected to provide a wide range of 

initiation sensitivities and burning rates. That is, the finer powders and 

granules would be expected to ignite more easily and burn more rapidly 

than the larger granules and pellets. Black powder and boron-potassium 

20 nitrate are the most extensively used ignition materials. 

The test apparatus of the present invention is generally referred to 

in Fig. 1 by the numeral 20. 

A percussion primer is pressed into a primer holder 22 which is 

placed into an upper cavity of a body 24. An adapter 26 threads down 

25 onto the primer holder 22 in order to firmly hold the primer holder in the 

upper cavity of the body 24 and over a central cavity. An O-ring 28 

provides a pressure seal between the adapter 26 and the primer holder 

22. 

An ignition material holder 30 is disposed in a central cavity of the 

30 body between the primer holder 22 and a plug 32 threaded into a lower 

cavity provided in the body 24. The material holder 30 has a 

hemispherical cavity 34 facing the primer holder 22 which, when 
LAR 13996-1 PATENT APPLICATION 

performing a test, is designed to receive a quantity of ignition material (in 

Gne en-ibodiment about 200 mg). The ignition material is weighsd out 

and inserted into the hemisph9riczl cizvity 34 prior to assembly of the 

apparatus. In the embodiment of tha invention which uses about 200 mg 

5 of material, the hemispherical cavity 34 has a diameter of 0.435. 

The body 24 is illustrated in Figs. 2-4 prior to assembly with the 

other parts. These figures illustrate the upper cavity 36, tho central 

cavity 38, and the lower cavity 40. The three cavities collectively form a 

l~ngitudinal passageway thrcugh the body 24 which, upon assembly, 

10 receives the adapter 26, the material holder 30, and the plug 32, all of 

which are in end-to-encl contact at opposite ends of the csntral cavity 38. 

The body 24 is s~tbstantially cy!indrical in shape, except for parallel 

flattened surfaces 42 and 44. 

A pair of sockets 46 and 48 extend transversely through the body 

15 24 from diametrically opposite sid~s of the central cavity 38. Tho 

sockets 46 and 48 have bores 50 and 52, respectively, which extend into 

communication with the csntril cavity 38. 

Ref~rring to Figs. 5 and 6, the material holder 30 is shown in 

greater detail by enlargeme~t. The rnat~rizl holder 30 has an upper 

20 portion 54 in which the hemisphericnl cavity 34 is formed. Six axialiy 

oriented hcles 56 extend from an outor region of the hemispherical 

surface of the hemispherical cavity to an axiatly disposed cylindrical 

chamber 58 formed in the material holder 30 below the upper portion 54. 

Four lateral holos 60, which are subst?r!tially horizonta!ly coplanar, extend 

25 from the cylir?driczl chclrnb?r 51! to an annt~lar recess 62 formed 

externally aro~ind the of~tor cylindricd si~rlase of the material holder 30. 

Ex?andir,g hot gas ?.nd burning partlclzs bhich pass through the six 

vertical hcl!es 56 enter thc: cy!'ndrical chsmber 58 arid exit therefrom 

through the lateral holos 60. Whcn assembled into the body 24 of the 

30 test apparatus, the latsrsl holt.: 63 are disposed in a horizontal plane 

bon~ath the bores 59 and 52 so 2s to protect the transducers 64 and 66 

(Fig. 1) which 2.re fitted In13 the sockets 46 and 48, respectively. The 
LAR 13996-1 PATENT APPLICATION 

annular recess 62 allows the hot gas and thus the pressure generated by 

ignition, to be communicated to the transducers. 

When assembled, the hemispherical cavity 34 and the cylindrical 

chamber 58, which are in communication with each other by virtue of the 

5 vertical holes 56, are sealed at opposite ends by the primer holder 22 

and the plug 32. 

Referring to Fig. 7, the adapter 26 has a central bore 68 slidably 

receiving a firing pin mechanism 70 having a pin 72 at a proximal end 

thereof. Upon actuation of the firing pin mechanism, the pin 72 passes 

10 through an opening 74 to strike a primer held in the primer holder 22 

which is received in a space 76. 

The primer holder 22 has a cavity 78 which receives a percussion 

primer 80. When the firing pin mechanism is thrust downwardly to the 

full extent, the pin 72 will strike the upper portion of the percussion 

15 primer thus firing the same. The percussion primer acts as a seal to 

prevent venting of pressure created during the burning of the ignition 

material. 

In operation, the percussion primer 80 is initiated by impacting the 

firing pin with about 100 inch-ounces of striking energy. Primer ruptures, 

20 caused by excessively deep penetration of the firing pin into the primer, 

are prevented by restricting the firing pin penetration to about 0.030 inch. 

The output of the percussion primer transfers through a spit hole 84 of 

the primer holder 22 onto the ignition material received in the 

hemispherical cavity 34. The high pressure gases, generated by the 

25 combu5tion of the ignition material vent through the six vertical holes 56 

in the holder 30 into the cylindrical chamber 58 and subsequently to the 

pressure transducers 64 and 66. The transducer outputs are measured 

with an oscillograph 65 and recorded on magnetic tape and permanent 

records are created. 

30 After testing, the apparatus is easily disassembled for cleaning to 

assure the same initial conditions exist for each firing. 
LAR 13996-1 -1 0- PATENT APPLICATION 

The pressure transducers 64 and 66 are preferably piezoelectric 

type transducers, which are well known and commercially available. One 

such transducer is the KISTLER MODEL 601A. An associated 

measurement system measures pressure sensed by the transducers, and 

5 can include known components such as charge amplifiers, voltage 

amplifiers, a tape recorder and oscillograph, which has a frequency 

response that is preferably flat to 40 kHz. 

The system will facilitate the creation of a "pressure trace" which is 

a graphical illustration of a pressure wave plotted on X and Y axes, with 

10 pressure on the Y-axis and time on the X-axis. These pressure traces 

are illustrated in Figs. 8-1 1. 

Tests performed with the ignition materials in the bottom of the 

central cavity 38 (thus resting on the upper surface of the plug 32 in the 

absence of the material holder 30) produced very little performance 

15 differences. To evaluate the ignition and burning rate extremes afforded 

by very fine to very coarse ignition materials, the 20140 and 2R BKNO, 

materials were tested. Quantities were doubled to exaggerate potential 

differences of burning rate and peak pressures achieved. The pressure 

traces generated by either primer indicated poor ignition characteristics, 

20 that is, very slow (100 millisecond time frame) non-reproducible build-up 

of pressure. The material holder of the present invention was found to 

facilitate a better presentation of the ignition material to the output of the 

percussion primer, and provide a more controlled burning of the ignition 

material. 

25 In using the ignition material holder 30 in the central cavity 38, the 

initiation and combustion characteristics improved immediately. Pressures 

rose quickly and the powdered ignition material was consumed in less 

than 10 milliseconds. The 20140 BKNO, and FFFG black powder ignited 

very quickly, so that little differentiation could be made between the 

30 ignition performance of these two primers. Conversely, the 2R BKNO, 

pellets ignited so slowly that, again, differentiation could not be 

recognized between primers. 
LAR 13996-1 -1 1- PATENT APPLICATION 

The first successful differentiation was achieved in using the FFG 

black powder, as shown in the graph of Fig. 8. The pressure produced 

by primer I rose immediately, and primer II produced an initial gradual 

increase, followed by a rapid rise in comparison to primer I. 

5 Fig. 9 shows the pressure traces produced when using the Acannon ignition material. As before, the differences are significant. 

Two percussion primers, Primer I and Primer II were used in five 

tests, with each of the FFG and A-Cannon black powder and the Type I 

BKNO,. Typical pressure traces generated by the parametric 

10 investigation were plotted on the same coordinate system and then 

analyzed to determine a statistical compilation and comparison of the 

performances achieved. A compilation of typical pressure traces 

produced by primer I and primer II percussion primers, using 200 mg 

each of the three different ignition materials is shown in Fig. 10 (which 

15 has a reduced time scale, compared to the preceding graphs). 

The data points selected to provide a numerical description and 

analysis of the pressure traces for the ignitability test method are shown 

in Fig. 11. Logical descriptives are the time to reach peak pressure, the 

time to reach 50% of peak pressure, and the peak pressure achieved. 

20 Another significant measurement is the pressure achieved at one 

millisecond. Since the major portion of both primers I and I1 heat 

contribution is achieved within the first millisecond, this time interval is 

significant for measuring primer initiation capability. According to the 

present invention, the ratio of the pressure at one millisecond to the peak 

25 pressure defines ignitability. 

The following tables I-VI summarize test data obtained using the 

aforementioned descriptives. The initial comparison for each ignition 

material reveals that primer I achieved ignition sooner and more rapidly 

than did primer 11. Secondly, the FFG black powder, using either primer 

30 (according to Tables I and II) produced the highest ignitability values (the 

ratio of pressure achieved at one millisecond over the peak pressure). 
LAR 13996-1 -1 2- PATENT APPLICATION 

The A-cannon black powder (Tables Ill and IV) was second, and the 

Type I BKNO,, Tables V and VI, was third. 

TABLE I.- FUNCTIONAL DATA ON THE M42C1 PERCUSSION 

PRIMER USING 200 MG FFG BLACK POWDER 

IGNITION MATERIAL 

5 

AVE 

STD DEV 

3.2 

3.0 

.15 

.7 

.78 

.08 

1955 

2046 

53.7 

1200 

1271 

53.5 

61 

61.8 

1.6 
LAR 13996-1 PATENT APPLICATION 

TABLE 11.- FUNCTIONAL DATA ON THE M42C2 PERCUSSION 

PRIMER USING 200 MG FFG BLACK POWDER 

IGNITION MATERIAL 

TEST 

NUMBER 

AVE 

STD DEV 

TIME TO 

PEAK 

PRESSURE 

(ms 

TIME TO 

50% PEAK 

(ms 

PEAK 

PRESSURE 

(psi) 

PRESSURE 

@ lms 

(psi) 

P @ lms 

P PEAK 

(%) 
LAR 13996-1 PATENT APPLICATION 

TABLE 111.- FUNCTIONAL DATA ON THE M42C1 

PERCUSSION PRIMER USING 200 MG OF 

A-CANNON BLACK POWDER IGNITION 

MATERIAL 

TIME TO 

PEAK 

PRESSURE 

(ms) 

TIME TO 

50% PEAK 

(ms 

PEAK 

PRESSURE 

(psi) 

PRESSURE 

@ lms 

(psi 1 

P (a lms 

P PEAK 

(%I 

TEST 

NUMBER 

AVE 

STD DEV 
lAR 13996-1 -1 5- PATENT APPLICATION 

TABLE 1V.- FUNCTIONAL DATA ON THE M42C2 

PERCUSSION PRIMER USING 200 MG OF 

A-CANNON BLACK POWDER IGNITION 

MATERIAL 

5 

AVE 

STD DEV 

16.8 

16.4 

1.9 

5.3 

5.1 

1.1 

1250 

1311 

89.1 

180 

170 

60 

14.4 

12.8 

3.9 
LAR 13996-1 PATENT APPLICATION 

TABLE V.- FUNCTIONAL DATA ON THE M42C2 PERCUSSION 

PRIMER USING 200 MG OF TYPE T BORONPOTASSIUM NITRATE IGNITION MATERIAL 
LAR 13996-1 -1 7- PATENT APPLICATION 

TABLE VI.4 FUNCTIONAL DATA ON THE M42C2 PERCUSSION 

PRIMER USING 200 MG OF TYPE I BORON 

POTASSIUM NITRATE IGNITION MATERIAL 

Finally, and most importantly, ratioing the ignitability of the two 

primers for each ignition material, the FFG black powder indicated the 

P B lms 

P PEAK 

(% 

3.1 

2.1 

8.8 

7.5 

9.8 

6.6 

3.4 

most differentiation in performance. The FFG black powder ignitability for 

PRESSURE 

@ lms 

(psi) 

25 

16 

66 

56 

74 

47.4 

25.5 

primer I was 61.8 (Table I) and for primer 11, 8.7 (Table II) producing a 

5 ratio of 7.1. For the A-cannon black powder, the ratio was 3.5, and for 

the Type I BKNO,, the ratio was 3.0. 

PEAK 

PRESSURE 

(psi) 

785 

756 

742 

744 

748 

755 

17.6 

Although ignition is a major requirement for systems such as 

TIMETO 

50% PEAK 

(ms) 

____1_1-- 

10.9 

14.2 

13.2 

9.5 

12.3 

12.02 

1.8 

TEST 

NUMBER 

1 

2 

3 

4 

5 

AVE 

STD DEV 

aerospace rocket motors, munitions and even automobile air bags, no 

- .- .- 

method currently exists, other than the present invention, to measure 

TIME TO 

PEAK 

PRESSURE 

(ms> 

33.4 

42.2 

37.3 

31.4 

39.2 

36.7 

4.3 

10 relative ignition efficiency, or "ignitability." Consequently; no 'specification , '. , + 

. - t -9. r ... 
LAR 13996-1 PATENT APPLICATION 

exists on ignitability, and surprisingly, there are no output test 

requirements in any military specification for percussion primers which are 

used only for initiation. 

The key parameters for achieving a successful test methodology 

5 and bomb configuration and acceptable pressure performance 

differentiation between primers were determining the proper ignition 

material and its confinement. The fine ignition materials, which were 

easily initiated and exhibited very high burn rates, produced similar 

pressure traces with either primer. Conversely, the large pellet ignition 

10 materials initiated and burned so slowly that the pressure traces were 

again similar with either primer. The ignition material had to be confined 

in a holder at the top of the test bomb cavity, facing the percussion 

primer, rather than in the bottom of the cavity to achieve reproducible 

pressure performances. This confinement provided highly reproducible 

15 initial conditions and allowed primer output to penetrate and mix with the 

igniter material to achieve ignition. Furthermore, the small initial volume 

sustained the initial primer output pressure, supporting the conditions 

needed for stable combustion. This configuration has the added benefit 

of providing a good simulation of actual design interfaces. 

20 The present method clearly differentiates the ignition performances 

of two different percussion primers. The pressure traces produced by 

each primer, test-fired with FFG black powder, A-cannon black powder 

and Type I boron-potassium nit rate (BKNO,), were markedly different in 

any combination. Recorded for statistical comparisons were the times to 

25 peak and 50 percent of peak pressure, the peak pressure, and a term 

defined herein as "ignitability." lgnitability is defined as the ratio of the 

pressure achieved within the first millisecond over the peak pressure. 

The first millisecond is when the major portion of primer output is 

produced to initiate the ignition materials. 

30 The FFG black powder proved to be the best ignition material in 

the test, followed by A-cannon black powder and Type I BKNO, , to 

evaluate the differences in output performance of the two percussion 
LAR 13996-1 -1 9- PATENT APPLICATION 

primers. The most dramatic single data point comparator was ignitability. 

The ignitability of primer I, using the FFG black powder, was 7.1 times 

greater than that produced by the primer II. 

The many features and advantages of the present invention are 

5 apparent from the detailed specification, and thus, it is intended by the 

appended claims to cover all such features and advantages of the 

ignitability test method and apparatus which fall within the true spirit and 

scope of the invention. Further, since numerous modifications and 

changes will readily occur to those skilled in the art based upon the 

10 disclosure herein, it is not desired to limit the invention to the exact 

construction and operation illustrated and described. Accordingly, all 

suitable modifications and equivalents may be resorted to falling within 

the scope and the spirit of the invention. 

What is claimed is: 
LAR 13996-1 

fl 

25 PATENT APPLICATION 

IGNlTABlLlTY TEST METHOD AND APPARATUS 

Abstract of the Disclosure 

An apparatus for testing ignitability of an initiator includes a body 

having a central cavity, initiator holder for holding the initiator over the 

5 central cavity of the body, an ignition material holder disposed in the 

central cavity of the body and having a cavity facing the initiator holder 

which receives a measured quantity of ignition material to be ignited by 

the initiator and a chamber in communication with the cavity of the 

ignition material holder and the central cavity of the body, and a 

10 measuring system for analyzing pressure characteristics generated by 

ignition of the ignition material by the initiator. The measuring system 

includes at least one transducer coupled to an oscillograph for recording 

pressure traces generated by ignition.