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EXPLOSIVES RESEARCH & DEVELOPMEWESTABLISHMENT

TECHNICAL MEMORANDUM: No. 6/M/60A

CCU.r)F5F*OAq MML0 UTOWAT. 10 DOJES IC RArWD DiR 20 PPNOrA

(DAn Investigation of the Explosivt Hazards ofAmmonium Perchlorate/Polyurethane Rubber G)

Propellants in the Uncured and CuredConditions

ftAnRw "SEWTMHNICAL INFORMA"ON nff'Av J. K%.. Clark

A -y

s'4 P. D Vericioyle

TAW

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UNCLASSIFIEDE. R.D.E. 6/M/6o WAC/117/06

-/1 MINISTRY OF AVIATION

(EXPLOSIVES RESEARCH AND DEVELOPMENT ESTABLISHMENT. ,KJ .

TECHNICAL MEMORANDUM NO. 6/m/60 >

An Investigation of the Explosive Hazardcs of

Ammonium Perchlorate/Polyurethane Rublier

Propellants in the Uncured and Cured Conditions

by

J.K. Clark and P.D. Verschoyle

Approved:$yC (-AG.K. ADAMSS.P.R.II

Approved forCirculation: I+

C.H. JOHNSONDIRECTOR

WALTHAM ABBEY 28th June 1960

ESSEX

DISTRIBUTION STATEMENT A

Approved for Public ReleaseDistribution Unlimited

UNCLASSIFIED

UNCLASSIFIED

CONTENTS

Page No.

1. Summary 1

2. Introduction 1

3. Test Methods and Results 2

3.1 Tests in 3-inch Diameter Thick-walled Steel Tubes 2

3.2 Tests on 100 lb of Uncured Materials in 12-inchDiameter Containers 2

3.3 Tests on 1000 lb of Uncured Propellant in "Mock-up"Incorporators 5

3.4 Tests on Fully Cured Propellants in 12-inchDiameter Containers 6

4. Conclusions 7

Figures 1 to 10

U NC TAFTMIE

. UWCLASSIFIED

UNCLASSIFIED

Reference: IAC/117/06

1. SUM viARY

Trials have been carried out to determine what precautions and safetydistances would be appropriate to the risks involved in the mixing, curing

and storage of two polyurethane/ammonium perchlorate propellants.

Uncured propellant was tested in three types of vessel,

(a) 3 inches I.D. with ) inch wall, containing 1700 g. of propellant.

(b) 12 inches I.D. with 9/32 inch wall thickness (calcula-ed bursting

strength 3160 p.s.i.) containing 100 lb of pro.pellant.

(c) in two mock-up incorporators, 3 ft diameter, Y : Ich wall thickness,each containing 1000 lb of propellant.

The propellant was ignited either by heating the cont2irers externally or byfiring a 7 g. SR 371C igniter inside the container.

Cured propellants were tested in 12-inch diameter containers by heatingover fires only.

In these conditions the propellant showed no sign of detonation, andvery little blast was produced. It was concluded that the propellants tes3tecould be treated as a "Y" risk, the operatives being protected from frag:nents,and that for future trials, the 12-inch diameter vessel containing 10O lb ofpropellant could suitably be used to simulate a larger diameter, but weaker,vessel containing a greater weight of propellant.

2. INTRODUCTION

The investigation was made to determine what prucautions were nocussryduring the mixing, filling, curing and storage of polyurothane/ammonium

perchlorate propellants.

At E.R.D.Z. it had been decided as standard practice, when manufacturingpropellants containing aluminium, to mix the aluminium with the polyesterbefore the ammonium perchlorate was added, since "dry" mixtures of aluminiumand perchlorate were known to be dangerous. It was thought that, althoughthis particular danger had been avoided, there might still be a dangerousphase during the mixing process, since early work (1) had shown ammoniumperchlorate by itself to be capable of sustaining detonation, and it se3!edprobable that, when mixed with organic material in certain proportions,its sensitiveness might be increased. The early series of tests weretherefore designed to simulate different stages in the mixing process,after the addition of perchlorate to the aluminium/polyester mixture.

The propellant chosen for these tests was "P2", which had thefollowing composition:

/Ammonium .....

UNCLASS'FIEr"'

CONFIDENTIAL

Ammonium perchlorate 61.5

Polyester 20.64

Tolylene di-isocyanate 1.86

lonol 1.0

,luminium 15

For trials intended to simulate the mixing process the tolylene di-isocyanate(.I.I.) cross-linking agent was omitted, to ensure theft the material was inthe uncured condition when tested some time after mixing.

3. TEST METHODS AND RESUTTS

3.1 Tests in 3-inch Diameter Thick-walled Steel Tubr,

Preliminary trials were made in vessels fabricated <Y m mild steel tubinof %-inch wall thickness and 3 inches internal diameter I i. IL). 'ievessels were approximately half-filled with propellant ' ipredients.

In some tests the vessels were heated until a bursLt occurrea, by meansof electrical resistance windings round the outside. This hcated s ailhad been developed at L.I.B.L. as a possible replacement for t'ie .5-inchshell for use in trials for the categorisation of propellarts. Ocio: todifficulties with temperature recording equipm,. nt thu ratc of p .ru rin the present experiments was not well controlled.

In other trials in these containers the means of ignition was a 7--ramigniter of SR 371C either immersed to about half the depth of the 1.ropellat.or placed above the propellant surface. The first of these igniter positionswas intended to represent an ignition which might Ie iproCuced below the wiA wcof the propellant in the mixer if the stirrer became deformed, or wasobstructed by a foreign body. The second represented an it.nition of duet orvapour in the space above the propellant in the mixer. In the tests ia;igniters the propellant was preheated to 800 to 900C., the temperature atwhich mixing might be done.

The materials tested were:

1. Ammonium perchlorate alone,

2. Aluminium, polyester, Ionol mixture, with ammonium perchlorateadded in the proper proportion in the thick-walled vessel butnot stirred in,

3. As in 2, except that the perchlorate was mixed with the otheringredients for different lengths of time, in a Beken mixer,before transfer to the thick-walled tube.

4. As in 2 and 3, but constituents fully mixed.

Particulars of the tests and of the results obtained are Ziven in Table IThe uamage to these containers is showm in Figs. 2 and 5.

3.2 Tests on 100 lb of Uncured Materials in 12-inch Dia.eter Contuir _r

The containers (Fig. 4) were intended to simulate, on a reduced scale,the incorporator used for mixing the propellant. In order to compensate

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CONFIDENTIAL

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CONFIDENTIAL

T_"22L I ±00 1 1' I ....... N.. IN 12-IC1 DIVIETER CONTAINERS

TABLE 3

Series B, Trials with Igniters

Shot No.' Material Type of Burst Explosive Equivalent,and Remarks lb of P.E., Determined

from Blastmeters

Bl Ammonium Perchlorate Small amount of white 4.8alone smoke from igniter lead

hole, followed byexplosion after2 - 3 s. Someperchlorate left on baseplate

B2 Polyester + Ionol + Explosion after a fraction 4.2Aluminium perchlorateof a second. Polyester

added but unmixed but no perchlorate left on)ase plate

B3 Polyester + Ionol + imilar to B2 4.9

aluminium. B

Perchlorate addedand crudely mixedin

B4 P2 propellant less ;mmediate explosion, end 4.6T.D.I., fully mixed plate blown off,

at E.R.D.-]. propellant burnedfiercely

No craters were formed in either the A or the B trials.

It was suspected that the blast registered, which showed only rather

slight variations from shot to shot, might correspond to the bursting pressure

of the vessels, and not to any explosive effect from the propellant. One

of the containers was therefore burst by nitrogen pressure (at a pressure

of 2500 p.s.i.), but the blast meters failed to registet any appreciable

deflection. It is considered possible, however, that the vessel might have

burst at a higher pressure if it had been possible to apply nitrogen pressure

as quickly as the pressure generated by the propellant. The result of the

trial with nitrogen is therefore inconclusive.

Typical views of two of the containers are shown in Figs. 5 and 6.

In Fig. 5 it will be seen that one end of the vessel came off prematurely,

before the full bursting pressure of the tube was reached.

3.3 Tests on 1000 lb of Uncured Propelant in "Mock-up" Incorporators

From the 100 lb trials reported above, it appeared that the materials

tested were capable of producing an explosive effect equivalent to about

5 per cent of their weight, but it was impossible to predict whether

1000 lb of propellant would behave similarly, Two mock-up incorporators,

3 ft diameter and 3 ft 6 inches high over the dished ends, made from

) -inch mild steel plate (Fig.7) were therefore half-filled with 1000 lb

of uncured P2 propellant (less T.D.I. cross-linking agent). One was

/heated

-5-

CONFIDENTIAL

C0NFID:NTIAL

heated over an Avtag fire until it burst, and the other was exploded by meansof a 7-gram SR 371C igniter buried in the propellant, after heating for threedays in a water tank at about 180 0F (820C) to simulate the mixing temperature.The temperature reached at the centre of the propellant was 600C. Thefirst vessel gave a very mild explosion with no measureable blast, while thesecond produced blast equivalent to only about 3 lb of P.E.

Since, in the earlier, small-scale, trials, no marked differenceshas b-en found between partially mixed and full.- mixed propellants, the testson the 1000 lb scale were done only on uncured propellant which had been fullymixed at E.R.D.E.

Tne remains or one of these incorporators after testing are shown inFir .

3.4 Tests on Fully Cured Propellants in 12-inch Diameter Containers

Further trials were carried out, by agreement with the Director ofSafety Services, to determine the behaviour of the propellants after fillinginto rocket motors, during curing and in subsequent storage.

Since it appea-ed from the results of previous trials that the LO lbcontainers, 12 inches in diameter, produced conditions at least as stringent(as judged by the amount of blast produced) as the weaker 1000 lb containers,diameter 36 inches, it was agreed to use the 100 lb type, thus effecting aconsiderable economy in materials, In order to improve the consistency ofthe pressure at which the containers burst, the design was modified to preventthe ends blowing off (Fig.9), thus allowing the bursting pressure of theseamless tubing to be reached.

As well as the P2 propellant used for previous trials, propellant U 322 wasincluded. This had a higher perchlorate content than P2 propellant, itscomposition being:

Ammonium perchlorate 74

Polyurethane rubber(Polyester + T.D.I.) 20

Aluminium 5

Ionol 1

A set of four containers was half-filled with each of the two propellants,and, for comparison, two containers were tested with ammonium perchloratealone.

Since it was not appropriate to use an igniter within the charg.s,because in practice there would be no probable internal source of ignitioncorresponding to the stirrer during mixing, the containers were allheated over Avtag fires to simulate an accidental fire in a store or processbuilding.

To simulate the temperature during curing, the containers andpropellant were preheated to 600C. This had not been done in the previoustrials in which the containers were heated over Avtag fires, but it wasthought to be desirable, because the heating time over a fire was usuallyso short that the temperature at the centre of the propellant when notpreheated might not have risen appreciably above the air temperature.

/The .....

-6-

CONFIDENTIAL

CONFIDENTIAL

The results, with P.E. equivalents derived from the blastmeter readings,are given in Table 4. On this occasion the blastmeters were calibratedspecially by firing a 5-lb P.E. charge at each of the two firing stationswith the blast meters occupying the same positions as during the trials, sothat these results may be regarded as somewhat more accurate than thosepreviously quoted, which were based on calibrations made during an earlierstudy (2).

TABLE 4

Tests on 100 lb. of Propellant in 12-inch Diameter Containers of

Stronger Design

Material Quantity, lb P.E. Equivalent; Remarks

lb of P.E. No. 3Aj

Ammonium Perchlorate 81.5 0.8 Pressure burst

" " 68 0.8 It

Propellant P2 100 1.4 Very mildexplosion

1.6 I

1.2 I

1.0

Propellant U.322 10 1.7

0.8

" 3.1 ,

3.0 "

The strengthened containers all failed; as intended, in the seamless tubes,the ends remaining in position. The bursting strength had been calculated as3160 p.s.i., the tensile strength of the tube material having been determinedas 68,300 p.s.i. Flame was seen coming from a split in the side of severalof the containers some considerable time before they blew up. Fig. 10shows a typical view of one of these containers after test.

4. CONCLUSIONS

4.1 From a limited number of trials, it does not appear that there isa critical stage, during the mixing of the ammonium perchlorate with theother ingredients, when the polyurethane propellant is particularlysusceptible to detonation. This aspect is being investigated further, inlaboratory studies.

4.2 No marked difference in behaviour was found between uncured andcured propellant.

4.3 When ignited by external heating or by means of an igniter withinthe charges, the propellant showed no signs of detonating, and producedonly a small amount of blast.

4.4 As a result of these trials, D.S.S. agreed that the propellantstested could be regarded as a "Y" risk when filled into rocket motors, and

/that .....

-7-

CONFIDENTIAL

CONFIDENTIAL

that "Y" safety distances could be used during processing, but with protection

for the operatives against fragments.

4.5 The 12-inch diameter vessels containing 100 lb of propellant appeared

to be quite suitable for use in future trials to simulate an incorporator

containing 1000 lb of propellant, or a large-diameter rocket motor rendered

non-propulsive by leaving the ends open.

M.233/60s.699/ss

-8 -

CONFIDNTIAL

CONFIDENTIAL

2 2INCHES

im;cH 1. D. THICK -WALLED VESSEL. FIG. 1.

CONFIDENTIAL

COW~.FIDENTIAL,

SHOT No. I. AMMONIUM SHOT No. 2. AMMONIUJMPERCHLORATE ALONE. PERCHLORATE UNMIXED WITH

OTHER CONSTITUENTS.

SHOT No. 3. AMMONIUM SHOT No. 4.PERCHLORATE MIXED FOR 5 FULLY MIXED PROPELLANTMINUTES WITH OTHEQ CON-

STITUENTS.

SHOTS 0 ,213 AwD 4, CONTAINER EXTERNALLY HEATEDELECTRICALLY. FIG. 2.

CONFIDENTIAL

CONFIDENTIAL

SHOT No. 5. AMMONIUM SHOT No.6.

PERCHLORATE MIXED FOR I FULLY MIXED PROPELLANT

MINUTE WITH OTHER COKWTUENTS

SHOTS 5 AND 6. SR. 371 C. IGNITER AT CENTRE OF PREHEATED

PROPELLANT.

SV4OT No. 8. SHOT W1.7. SHOT No. 9. SHOT 9,

SHOTS 7 AND 8. SR.3 71. C. INITER S.R. 371 C AT CENTRE OF

ABOVE SURFACE OF PREHEATED PREHEATED PROPELLAW4T.

PROPELLANTFIG. 3.

CONFIDENTIAL

COW4FIDENTIAL

IGNITSP

HOUSING Ii

0 01 2 3456I INCHES

VESSEL USED FOR TRIALS ON 100 lb. OF UNCURED PROPELLANT.

CONFIDENTIAL FIG. 4.*

COW%FIDENTI AL

TYPICAL VIEW OF 'vIO0 lb'6 VESSEL,o THE END OF WHICH BLEW OFF:BEFORE THE BURSTING STRENGTH OF THE TrUBE WAS REACHED.CONSTRUCTION OF VESSEL AS SHOWN IN FIG. 4. USED WITH

UNCLOtElD PROPELLANT. FIC7.5.

TYPICAL VIEW OF VESSEL AS IN FIGS. 4 AND 5, WHERE THEBURSTIWG PRESSURE OF THE TUBE WAS REACHED.FI.G

CONFIDENTI AL

CONFIDENTIAL

0I

rjI

0I

INHE

.........

MOCK -UP INCOPPOPATOP USED FOR TPIALS ON

1000 lb. OF UJNCUPED PPOPELLANT. FIG.7.

CONFIDEW~.TIAL

CONFIDENIAL

MOCK-UP INCORPORATOR AFTER FIQING FIG. S.

TYPICAL VIEW OF STRENGTHENED "100 lb." VESSEL USED FOPTRIALS ON CURED PPOPELLANTS. ALL BURPSTS OCCURRED INTHE TUBES,, NOT AT THE ENDS. RIG. 10.

CONFIDENTIAL

COI~JFIDENTIAL

00

00

*

I II I

I II II II II II II II II II II II II II II II II II II II II II II II II I

I II I

I II II I

I II II II UJJLJI I 01234I I

I INCHES

I II I

* STRENGThENED "100 lb~ VESSEL USED FOP TRIALSON CURED PROPELLANT. FIG.9.

CONFIDENTIAL

A

For Indexing

UNCLASSIFIED

E.R.D.L. Technical An Investigation of the Explosive HazardsMemorandum No. 6/M/60 of Ammonium Perchlorate/Polyurethane Rubber

Propellants in the Cured and Uncured Conditions

J.K. Clark and P.D. Verschoyle Sept. 1960

Trials have been carried out to determine what precautions andsafety distances would be appropriate to the risks involved in themixing, curing and storage of two polyurethane/ammonium perchloratepropellants.

Uncured propellant was tested in three types of vessel,

(a) 3 inclies I.D. with a-ihch wall, contairing 1700 g. ofpropellant.

(b) 12 inches I.D. with 9/32-inch wall thickness (calculatedbursting strength 3160 p.s.i.) containing 100 lb ofpropellant.

(c) in two mock-up incorporators, 3 ft diameter, Y8-inch wallthickness, each containing 1000 lb of propellant.

8 pp., 10 fig., 4 tables ___...._-

L.R.D.E. Technical An Investigation of the Explosive HazardsMemorandum No. 6/M/60 of Ammonium Perchlorate/Polyurethane Rubber

Propellants in the Cured and Uncured Conditions

J.k. Clark and P.D. Verschoyle Sept. 1960

Trials have been carried out to determine what precautions andsafety distances would be appropriate to the risks involved in themixing, curing and storage of two polyurethane/ammonium perchloratepropellants.

Uncured propellant was tested in three types of vessel,

(a) 3 inches I.D. with Y-inch wall, containing 1700 g. ofpropellant.

(b) 12 inches I.D. with 9/32-inch wall thickness (calculatedbursting strength 3lE p.s.i.) containing 100 lb ofpropellant.

(c) in two mock-up incorporators, 3 ft diameter, %-inch wallthickness, each containing 1000 lb of propellant.

8 pp., 10 fig., 4 tablesuT"'TTV'7\I'T AT-

UNCLASSIFIED

,-,I- I S IFIED

The propellant was ignited either by heating the containers externallyor by firing a 7 g. SR 371C igniter inside the container.

Cured propellants were tested in 12-inch diameter containers byheating over fires only.

In these conditions the propellant showed no sign of detonation,and very little blast was produced. It was concluded that thepropellants tested could be treated as a "Y" risk, the operativesbeing protected from fragments, and that for future trials, the 12-inchdiameter vessel containing 100 lb of propellant could suitably beused to simulate a larger diameter, but weaker, vessel containing agreater weight of propellant.

The propellant was ignited either by heating the containers exturnallyor by firing a 7 g. SR 371C igniter inside the container.

Cured propellants were tested in 12-inch diameter containers byheating over fires only.

In these conditions the propellant showed no sign of detonation,and very little blast was produced. It was concluded that thepropellants tested could be treated as a "Y" risk, the operativesbeing protected from fragments, and that for future trials, the 12-inchdiameter vessel containing 100 lb of propellant could suitably beused to simulate a larger diameter, but weaker, vessel containing agreater weight of propellant.

LWW*O"MA"

DETACHABLE ABSTRACT CAR~DS

The Abstract Cards detached from this document are located -as follows:

8' x 5"

1. Section ....... .... Signature .................. Date

2. Section ....................... Signature Date

5' x3'

1. Section ......... Signature ....................Date

2. Section ...... Signature ..... ....... Date

3. Section .................... Signature .......... Date

4. Section ............ ........ Signature ........ Date

F. IED

A I~