STRUCTURAL DESIGN AND DEVELOPMENT OF
UTIAS
IMPLOSION-
DRIVEN
LAUNCHERS
by
w.
CzerwinskiSubmitted May, 1971 •
•
tunity of Studies. course of
ACKNOWLEDGEMENT
I wish to thank Dr. G.N. Patterson and Dr. I. I. G1ass for the oppor-carrying out this design research at the Institute for Aerospace The constructi ve discussions with Dr. 1. 1. G1ass throughout the this work aJr._e very much appreciated.
The considerab1e effort devoted to the design of the Mark 11 Launcher by Dr. V. C. D. Dawson and his Associates, by Dr. R. F. F1agg as we11 as the assistance of Mr. S. K. Chan and Mr. W. O. Graf in form of he1pfu1 discussions, during the design-deve1opment of the hypervelocity 1aunchers are acknow1edged with thanks.
The assistance obtained from the Machine Shop, and particu1ar1y from Mro Wo H. Kubbinga, Mr. J. L. Bradbury and Mr. R. McKay is appreciated.
The work was financia11y supported by the Aerospace Research Labora-tories of the United States Air Force under Contract No. AF 33(615)-5313 and the Nationa1 Research Çounci1 of Canada.
J
SUMMARY
A condensed account is given of the design effort expended in the structural development of the implosion-driven hypervelocity launchers at the
Institute for Aerospace Studies, over the past few years.
This type of experimental research equipment is subjected to loads
whose modes and magnitude do not occur in any other related mechanical
arrange-ment. Therefore, it should be considered as a highly advanced design problem.
The design of astrong enclosure and barrel assembly presents a very great challenge from the standpoint of safety and economy of operatien, owing to unusually high internal pressures and extreme temperatures.
Some novel techniques had to be developed in order to obtain
satis-factory pressure and vacuum sealing, as well as to provide protection for the
inside surface of the explosion chamber. The inevitable damage to some parts of the launcher system require special design solutions, in order to make the
operation and servicing of the launchers reasonably economical in time and funds.
Based on observations made during the running and testing of several launcher models at UTIAS, some recommendations are made at the end of this report
with respect to the eventual future development of such launchers.
It is hoped that they might be useful in case of a resumptien andjor continuation of this type of hypervelocity research.
1. 2.
3.
5.
6.
7.
8.
9.
10.
1:1.12.
13.
14.
'l'ABLE OF CONTENTS
INTRODUCTION
EVALUATION OF
MARKI HYPERVELOCITY LAUNCHER
SPECIFICATION
ANDFIRST INITIAL PROJECT OF THE 30-in. dia.
CAVITY HYPERVELOCITY LAUNCHER
SPECTRUM QF POSSIBLE DESIGN SOLUTIONS
DESIGN
OF MARK 11HYPERVELOCITY LAUNCHER
DEVELOPMENT OF PRESSURE SEALING SYSTEM FOR THE EXPLOSION
CHAMBER
DEVELOPMENT OF SEGMENTED CONE
ANDTHE
BARRELSYSTEM
MARK
III HYPERVELOCITY LAUNCHER
DEVELOPMENT
OFTHE IGNITION ELECTRODE
DEVELOPMENT OF EXPLOSIVE LlNER
ANDPETN CHARGE
HYDRAULIC PRETENSIONER
AND THE PNEUMATIC WRENCH
REPAIR SCHEMES
ANDTHE CONICAL
~INERSTRENGTH CONSIDERATION
13.1 Dynamic Loading and Rèlated Problems
13.2 Statie Stressing
A PROSPECTIVE LAUNCHER
REFERENCES
FIGURES 1 to
33
PAGE
1 2 34
5
7 912
15
19
20
22 2224
31
33
I
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1. INTRODUCTION
The main topics of this report deal with the design and structural development of the implosion-driven hypervelocity launchers evolved and built at UTIAS. This new approach to launch projectiles at hypervelocities was first proposed by Prof. I. I. Glass at UTIAS in 1959. He suggested te utilize an
operating cycle which exploits the very high pressures and temperatures in the origin of a hemispherical implibsion for the purpose of acceleratieg. In Fig. 1, a schematic diagram illustrating the principle of operation of such a launcher is presented and the theoretica~ and physical principles involve4 are thoroughly discussed in Refs. 1, 2 and 4.
In order to prove and develop the basic idea ef prejectile acceleration by an explosive implosion, the first hypervelocity launcher having an 8-in dia hemi~pherical cavity and 0.22 calibre barrel was built, as shewn on Fig. 2. It consists of a high strength alloy steel enclosure in which an e~~n dia hemis-pherical chamber was machined. The explosion chamber is closed by a circular front plate held in place by a heavy ring- shaped nut. The preper .al.ignment of the explosion chamber and the front plate is obtained by two dowels B (Fig. 2).
The front plate holds the barrel and has two additional smalle~ holes, fer bring-ing into the chamber the ignition electrode, as well as the pressuie and vacuum
connections, which are not shown on the drawing. On the mOUhting surface between the explosion chamber and the front plate, two O-ring groeves, (A) f(i)r pressure and vacuum sealing were machined.
The advantages and weaknesses of the first model (Mar-,k I) i of the
implo-sion driven launcher ever built will be discussed in more detail in the next
chapter . Based on very encouraging initial test runs and experience ebtained from Mark I launcher, a much bigger model having a 24-in dia hemispherical explosion chamber and l-in dia barrel was designed up to the stage of productien drawings. Figure 3 shows the engineering concept of this design. Befere entering the pro-duction stage of such a large and expensive facility, a 1/3-scale Mark 11 model was built and tested in order to obtain more experience with this new type of launcher, as -well as prove its usefulness and structural integrity.
During the operation of the Mark 11 model some new~acts and~roblems
came to light which had a direct impact on the performance ~nd structural efficiency of the tested configuration. As a result, a second 1/3-scale m0~e~was designed and built which is known as the Mark 111 launcher. The history ~tttèst runs done with the Mark 11 and Mark 111 launchers, performance trials, as well as the
experience gained are discussed in Ref. 10. In the following chapters·only the design and structural aspects of Mark 11 and Mark 111 launcher models yill be discussed in detail.
The implosion-driven hypervelocity launcher is a piece of experimental equipment which is subjected to modes and magnitude of loads net 0ccurring in any other known type of research facility. This fact should be kept in mind when judging and appreciating the effort expended at UTIAS by a small group of researchers and designers involved in this project, with respect to time and the limited amount of money spent by them on developing this new type of hyper
-velocity experimental equipment.
As a mechanical system, the implosion driven launcher consists of four distinct subsystems, namely;
a) strong enclosure containing the hemispherical explosion chamber
b) the barrel, c) the blast tank,
d) the auxiliary equipment consisting of such secondary subsystems as explosive liner, ignition, driving and initiation gas, injection, vacuum, range instrumentation, service and assembly equipment.
As some of the auxiliary equipment is novel and highly sophisticated and had to be developed from scratch, the strong enclosure system and the barrel assembly present a most difficult design problem from the standpoint of safety and economy of operation, owing to the unusually high internal pressures and shock loads, as well as to the very high temperatures.
2. EVALUATION OF MARK I IMPLOSION-DRIVEN HYPERVELOCITY LAUNCHER AS A RESEARCH FACILITY
As shown on Fig. 2, the Mark I explosion chamber is a flat cylindrical block made of high strength alloy steèl with a machined hemispherical cavity. In order to avoid as much as possible any increased stress arising from holes, the explosion chamber and the covering front plate are held together by a peri-pherally applied force obtained from the coupling nut. This type of joint is very inefficient from the standpoint of rigidity, as it allows relatively large deflections around the lip of the hemispherical cavity. This has been proven by static tests, as well as difficulties experienced during explosive runs with
the pressure sealing of the chamber by means of O-rings. Frequent blow-outs have been experienced and special wedge-shaped metal rings supporting rubber
~-rings were added to provide successful sealing. More about that subject will be said in the chapter on pressure sealing.
Difficulties were experienced during the unscrewing of the coupling-nut af ter runs because of j,amming and galling of material in the threads. As a countermeasure, a system of 24 socketbead setscrews were installed in the flange of the nut which are shown on the front view of the nut on Fig. 2. The addition of setscrews made the servicing of the launcher much easier by tightening or loosening the setscrews af ter the nut was fully screwed on. However, the
installation of 24 setscrews had two adverse effects on the launcher. The first one was, thatthe holes accommodating the setscrews made the flange of the nut much weaker and more flexible, thus increasing the danger of separation of both parts of the strong enclosure at the sealing diameter. The second disadvantage caused by the increased flexibility of the flange was that the uniform tigh ten-ing of sets crews was made almost impossible as tightening of one screw spoiled the setting of al~ the others, thus unnecessarily prolonging the tedious manual work required for screw tightening.
As a result of increased deflections and reduced strength, a.severe limitation on the magnitude of the internal pressure had to be imposed, which had to be reduced to about one-quarter of the pressure for which the Mark I launcher was initially designed and stressed.
Apart from structural problems connected with t he strong enclosure,
2
there were some others, associated with the efficiency of operation and the
serviceability of the launcher. It was found for instance, that af ter each explosive run the inside surface of the front plate especially in the central
region around the inlet to the barrel was badly scorched, deformed, and eroded.
3. SPECIFICATION AND THE FIRST INITIAL PROJECT
In spite of the deficiencies, described in previous chapter the first experiments with Mark I launcher were encouraging and it was decided to start the design of a much larger facility having a 30-in dia hemisphere and al-in
dia barrel, in order to meet the current test requirements for a useful launcher. Using the experience,gained from the Mark I experiments, a specification for a larger launcher was compiled by Dr. R. F. Flagg, Dr. I. I. Glass and Dr.
V. C. Dawson, for the design of a 30-in dia hypervelocity launcher (Ré!. 8). Among
the specifications issued in July, 1966, was the requirement that all surf~ces expOsed to the direct contact of high pressure and temperature caused by an explosion should be replaceable, and that the closing and opening of the hemis-pherical chamber will be done by means of a breech block for the purpose of rapid reloading of the launcher. The specifications also emphasized the need for easy
replacement of the barrel and its entrance nozzle block, as well as to provide
a replaceable insert for at least first
4
feet of the barrel.The first initial project submitted to UTIAS was the launcher shown on
Fig.
4,
and it should be looked upon as a reasonable solution to fulfil the requirements set up by the UTIAS specification. An analysis of this launcher design and its feasibility showed that this first attempt to find a practicalsolu-tion required further modification.
The greatest objection against this specific design solution was the
prohibitive cost and almost nonavailability of forged steel billets of the size
required. The strong enclosure required a billet in form of a cylinder of
72-in dia and 80-in dia in length weighing about 95,000 lbs. Very few steel
mills on this continent would undertake the manufacture of such a billet made
of high-strerygth steel, and would not guarantee a product free of blemishes or
flaws. In case of a faulty billet, the eventual loss of time and momey spent on machini4g might be very high, as flaws are usually only discovered at the final
stages of fabrication. If the breech block design solution would be the only answer to a successful launcher, the only way to make it ~easible would be the
reduction of the overa~l dimensions to such a size to make the procurement of forged billets possible.
Another very undesirable feature of a breech block design is the very sudden change of section
A-A
in the strong enclosure shown on Fig.4
.
whichinduces . very serious stresses at the smaller diameter of this section.
The elongation in the threaded connection between the chamber and the
breech block will be greatest at the explosion chamber end, which in combination
with the contraction of the thread in the breech block caused by the explosion pressure, would induce prohibitive shear stresses in the thread. This fact, augmented by the marginal average strength of thread, might cause undue service
trouble due to jamming that might render the launcher unserviceable.
The breech block proper weighs about 25,000 lbs and the thread has
accomplished rotating the breech block through
45
0 and trans lating it axially into or out of the strong enclosure. Such an operation has to be done very precisely to avoid thread damage, and would require an expensive auxiliary mechanical arrangement.In view of very high explosion pressure, the breech block has to be wrenched with a torque high enough to prevent separation of the liner plate from the hemispherical chamber. In case of any leakage which might occur owing to even slight separation of both parts, very severe damage would result caused by the escaping hot plasma, which would erode and melt away the metal along the escape path. A number of cases of this type were, actually experienced in the Mark I launcher before the right type of sealing was developed.
To avoid such problems a special type of sealing was proposed ).f as
shown in detail on Fig.
4.
It consists of a bronze ring with two O-rings located at the hevelled outer peripheries. Such an arrangement would probably allow some slight separation without the danger of severe damage inflicted by leakage.More discussion on this subject will be presented in the chapter devoted to the development of special type of high-pressure sealing which is a very vital item in this type of equipment.
In comparison to the Mark I launcher, two novel design features were introduced. First, the liner plate protects the flat surface of the hemis-pherical cavity fr om adverse effects of high pressure and temperature caused by the explosion. Second, a segmented cone encases and holds the barrel, and allows its release a!ter moving the cone far enough to the left af ter separating the breech block from the strong enclosure. The segmented cone and the barrel are held together by a split ring located on the outside of the breech block. The whole assembly consisting of the barrel, front plate, and the split cone are pressed together by six bolts threaded into the split ring.
The segmented-cone arrangement proved to be a very efficient means for removing the barrel aft er firing, and replacing it by a new one. However, the idea of using a segmented cone showed very definite structural weaknesses in servïce which will be discussed in chapter
7.
It was proposed initially to weld the end of the barrel to the liner plate, in order to achieve the proper attachment and sealing. This idea however, was abandoned in the following design solutions to simplify the assembly by
avoiding troublesome machining af ter welding. Instead of welding, other solu-tions were found which allow the assembly of subcomponents sealed with O-rings.
4.
qPECTRUMor
POSSIELE DESIGN SOLUTIONSFrom a feasibility study of the breeeh bloek solution, as well as the experienee gained from the Mark I launcher, it became apparent that the requirements compiled in the UTIAS specification for the design of a 30-in dia implosion-driven launcher were much too specific, and that in order to obtain a satisfactory solution, the designer should not be restricted by too rigid a specifieation and should be given much more freedom in finding his own solutions.
Modern morphological design techniques recommend the eonsideration of as complete a set of various approaches as possible in order to cover the whole field of potential solutions. To do this properly, the designer has to start from the very initial stage of design. Here, the basic design parameters
4
characteristic of a specific design have to be considered together with all their functional as well as regional constraints.
As a starting point; a design stage was chosen at which some very basic possibilities of shaping the launcher's strong enclosure were investigated. On Fig.
5
the first row of arrangements Al' Bl' and Cl show the three possible waysof opening and closing the hemispherical cavity of the launcher by a specific
choice of the division line separating the front and the rear portion of the strong enclosure. It can be easi~y recognized that the arrangement A~ corresponds to a solution similar to Mark I, whereas arrangement a~ represents the schemàtic picture of tqe sol ut ion suggested by Flagg in the UTIAS specification for the 30-in dia hypervelocity launcher.
The second row of design solutions on Fig.
5
indicates suggested means of joining both parts of the strong enclosure. Solution B2 uses a system of bolts located as close as possible to the cavity diameter. This tries to cure the
difficulties already encountered with the Mark I launcher. The third row of solutions shows designs derived from row two, where by combining the salient features of solutions A
2 and B2' so+utionAB~ was obtained. A similar remark applies to solutim BC. Solutions shown 1n the third row combine some of the advantages of previous 3 so1utions by creating the possibility of an easy separa-tion of the parts, in case of jamming the thread in the front or the rear breech block. However, it should be mentioned here that the third row of design solutions would be more expensive than those shown in row two~ as they have a greater number of parts to be machined and fitted together.
The solution ABC
4
embodies most of features of the previoms ones, but it does not bring about any radical improvement. It should be considered as a unique design solution in which all basic parts are made as separate subcom-ponents that are held toge\her by an additional component. This principle could be developed still further to create a more versatile and improved launcher.Additional thoughts along this line will be discussed in chapter
14.
A feasibility study done on all design solutions shown on Fig.
5,
selected solution B as the most promising for the ful~ size 30-in dia cavity hypervelocity launcfter. The B
2-s01ution is a unique solution in which billets for manufacturing of the front and the rear part of the strong enclosure are
about equal in weight. Consequently, it is a solution which requires the smallest sizes of billets to be procured. The rati~ of weights of larger size bil~ets when choosing the design B? instead C
2, is 1:2.1. This means that the saving on the weight of billets in tfie case of so~ution B
2 will be slightly better than
50%,
and the size is such that the presently-available technology could handle the job.5 •
DESIGN OF MARK II HYPERVELOC ITY I:.AUNCHERThe initial project of Mark II launcher, having a 30-in dia hemispherical cavity based on solution B2' was finished and presented for approval to UTIAS
in the fall of 1967. Af ter a number of meetings and modifications, general
agreement on basic design princip+es was reached, and a set of production drawings was prepared which in turn were sent to prospective Canadian and USA
manufac-turers for quotation.
The general arrangement of the Mark II 30-in dia cavity launcher is presented on Fig. 6. As seen from the drawing, the .design combines the best
features of the B configuration with some selected features proposed in the initial project of the breech block solution shown 0n Fig.
4.
The front and rear part of the strong enclosure have well balanced proportions, which ensures the smallest possible si ze and weight of steel billets required for manufacture. Both parts are centered by a double-cone ,flange protruding from the explosion chamber into the front plate, which in addition to centering provides a good shear connection in the plane of contact of both parts. Thirty-twobolts 5-in a.D. made of high tensile steel provide a reliable and safe connection of both parts. To ensure a positive contact during the full cycle of launcher opera-tion, the joining bolts have to be prestrained by a total load greater or equal to the force created by the explosion pressure within the chamber. At a full charge of 25 kg PETN explosive, the amount of preloading required for each bolt is 1.9
x 106
lb.In order to produce such a high load in each bolt, two methods of pre-tensioning were considered feasible:
1) using a hydraulic torque wrench
2) using a commercial stud-pretensioner.
Af ter some deliberation i t was decided that the second method would be used, as it has two distinct advantages over the hydraulic torque wrench. First, it has the cOmPactness and small space required for a pretensioner, as it extends axially in the direction of each bolt. Second, is the absence of high shear stresses in the bolts, which are unavoidable when a hydraulic wrench is used.
Figure
7
shows such a pretensioner arrangement located forward of the front plate. It consists of a carriage moveable on rails and supports a rotatable drum on which two hydraulic pretensioners are ~o~ted. Each pretensioner ismounted at a different distance from the axis of rotation of the drum, that is, equal to the inner and the otuer perimeter of .the bolts.
,
For the purpose of facilitating the servicing, the explosion chamber and tpe front plate are mounted on special carriages, each fitted with four systems of rollers riding on two cylindrical rails. ' In this way a free move-ment of each component of the 'launcher is achieved for the purpose of assembly and disassembly of both parts of the strong enctosure and the pretensioner. A more detailed description of the servicing procedure of the launcher is presented in UTIAS Technical Note No.
147
(Ref.8).
The design of the interior arrangement of the Mark II launcher looks similar to that of the initial project of the breech block solution shown on Fig.
4.
The internal surface of the hemispherical cavity is protected by thethick-walled metal liner holding the explosives, which has a lip housed mn a circular groove machined in the liner plate.
The pressure and vacuum seal is arranged at thè lip of the hemispherical liner by means of a rubber a-ring. This is the best locat~on for the pressure seal, as it provides the possibly smallest sealed area over which the explosion pressure acts, thus yielding the smallest separation force.
The front plate assembly consists basically of the front porti9n of the strong enclosure, the liner plate, the segmented cone 'and the barrel. All
6
-.~
. ,ol
-these parts 'are held together by a split ring which threads on the barrel,
in which
6
bolts are installed. The bolts tighten all parts together by pulling the split ring and the barrel in an outward direction. When reversing the tor~ueapplied to the bolts, they push the barrel inward, loosening the segments of
the cone, which enables the removal of barrel and the liner plate for replacemento
During the preparation of the production drawings of the 30-in dia
hypervelocity launcher, an 8-in dia scale model was built and testing was started. The production drawings were sent to suppliers who advised that the availability
of high tensile steel billets of the size specified on drawings was marginal, and that the cost of construction would be much higher than the allocated funds. Consequently, it was then decided, to reduce the 30-in dia cavity to 24-in,
1eaving the diameter of the barrel unchanged. This decision was based on the existing performance calculations" which showed that no really significant reduc-tion of projectile velocity would be caused by this reducreduc-tion. By reducing the cavity to 24-in dia, the weight of,the strong enclosure was cut down by about one half, thus drastically redufzing the first cost to about 65% quoteà for the 30-in dia launcher.
As the design contract between UTIAS and Dro Dawson (Ref. 8) came to an end with the delivery of the set of production drawings for the 30-in dia launcher, the preparation of the production drawings for the 24-in dia Mark 11
launcher was done at UTIAS by the author of this report, using seme outside casual design and drafting help. Figure 3 shows a perspective view of the 24-in dia Mark 11 launcher on which some minor improvements of the internal arrangement are visible. The main i tem which should be mentioned here .is the modified seg-mented cone, which shows an increased bearing area, as well as an increased thick-ness of the first cone to improve the shear strength in the axial direction. Another item worthwhile'mentioning is the improved barrel arrangement with a
strengthened barrel holder.
6.
DEVELOPMENT OF THE PRESSlJRE SEALING SYSTEM FOR THE EXPLOSION CHAMBER Numerous failures of the O-ring sealing system experienced in the early runs of the Mark I hypervelocity launcher, erophasized the great importanceof the proper type of sealing. The extent of damage done to the launcher by the escaping hot plasma in case of a sealing failure was always very severe and difficult to repair.
The improved sealing system used on Mark I launcher shown on Figo Ba was based on the reçoromendation made byOQ-ring manufacturers, which consisted of two rubber O-rings arranged in series and equipped with back-up rings made of brass. The triangularily shaped back-up rings served the purpose of filling up the gap created by the deflecting front plate, thus preventing the extrusion of O-ring material into the opening gap •
This type of pressure sealing was adequate at low-weight explosive charges, but was inadequate for larger amounts of explosives. The reasons for this deficiency was twofold. First, the strong enclosure of Mark I launcher
was not rigi~ enough, owing to the unnecessarily high separation forces caus~Q
by the much larger pressure area than optimal. The mean radius of the double· O-ring sealing system had to be much greater than the radius of the hemispherical cavity, for reasons arising from the chosen design configuration. Second, failure could be attributed to much higher pressures and temperatures typical for this type of sealing, as weIl as to the extremely high rate of increase of the
over-pressure from zero to a maximum. This very high rate of increase of the over-pressure in combination with an easy escape path for the hot plasma create very unfavourable sealing conditions for an O-ring, as it may be easiiy bypassed and damaged by the escaping hot gases before it has time to expand and seal the inc-reasing gap.
A great improvement in comparison with the Mark I launcher was the
solu-tion shown o~Fig. 8b. It ~epresents the sealing system proposed for th~ 30-in dia full scale launcher. It consists of a metal double-tapered, sealing ring, plus a rubber O-ring arranged at the lip of the explosion liner. The main improve-ment consisted in reducing to a minimum the pressurized area by arranging the seal at the smallest possible radius. The secoqd favourable feature of this type of seal is the complex escape path for the hot gases, which have to change direct ion several times before reaching the exterior of the launcher. This specific seal
was never tested in practice as the 30-in dia launcher was never built.
Figure 8c shows the type of seal used and tested on the 1/3 scale (8 -in dia) model of the Mark 11 24--in dia launcher. The combination of a tapered lip pressing the O-ring underneath the explosive liner with a relatively deep g~oove
cut in the liner plate, proyed very successful in service. The only failure of this type of seal which happened during the test runs~ was due to a badly off-focussed implosion which melted away a portion of the exp10sive ~iner right at
the lip. This type of failure is well illustrated on FigJs.
9
and 10, whichshow the damaged explosive liner, as well as the liner plate with a correspondingly
badly distorted lip and O-ring groove.
During this specific mishap, very severe damage also occurred to the
strong enclosure\ owing to the very bad erosion of the steel along the escaping path of the hot plasma. ~ order to safeguard against such a mishap, a second
line of defence was added in shape ofl an additional O-ring outside of the lip of the explosion liner, which is shown on Fig. 8d. A final step in the develop-ment of the sealing of the explosion chamber is show4 on Fig. 8e, which shows the sealing arrangement on the Mark
:nu
launcher.A maj or improvement was achieved through the addi tion of a conica,l flange to the liner plate that protrudes into the explosion chamber on the outside: of the explosive liner. This specific design feature creates a type of self-sealing device, as the portion of the explosive liner located bstween the groove in the
liner plate and the lip of the conical/lange, is being pressed to it by the explosion pressure, thus producing a very efficient barrier for the escaping
gases,.in case of failure of the O-ring located in the groove (Fig. 8e).
The increased thickness of the liner plate caused by the added conical
flange requires more material for manufacture, but the simplified shape and the
reduction in high-tolerance precision machining, counterbalance the increased cost of material.
Another improvement was achieved by placing the second Q-ring in a
~ocation where the escaping gases would have to ~hange their direction along the path of escape. This design feature prevents the gases to bypass the O-ring~
and assures a better seal by a more efficient blocking of the escape route.
All explosive runs made up-to-date with the Mark 111 launcher proved that the sealing system developed for the explosion chamber was solved success-fully.
J
.'
7.
DEVELOPMENT OF SEGMENTED CONE AND BARREL SYSTEM 7.1 Segmented ConeIt is a very difficult task for a designer to solve successfully the assembly of the barrel with the front portion of the strong enclosure in such a manner as to satisfy the extremely severe strength requirements as well as easy servicing.
The most highly stressed area in the implosion-driven hypervelGcity launcher is the vicinity of the origin of the hemispherical cavity, and particu-larly the entrance to the
6
barrel. The peak pressure at the origin of the cavity is of the order of5
x 10 psi. Upon reflection of the implosion, the pressure profile decreases rap~dly in the radial direction along the liner plate from the above maximum, down to about 3,000 psi.The range of the maximum peak pressure at the orlgln and its vicinity is of such a magnitude that it puts the entire problem of the structural integrity of this region outside of the existing designs state of the art. Knowing that the damage to the critical area is inevitable, the designer's effort should be directed towards finding of the suitable materials, as weil as the best design arrangement that would a~low an easy replacement of
amy
damaged parts. At the same time, the cost of replacements must be kept at the lowest possible level. Another very im-portant objective, which should be kept in mind during design, is that whatever arrangement will be conceived it will not affect adversely the strength of the front portion of the strong enclosure.In order to achieve the best structural-design solution for the area sub-jected to extremely high implosion pressures, the designer should provide the largest possible volume of continuous, uninterrupted high-strength material around the origin. In view of the above requirement, the best solution seems to be the one shown on Fig. 2, and Fig. lla, which represents the area of interest in the front plate of Mark I launcher. Unfortunately, this particular arrangement had to be abandoned because of the lack of protection of the internal surface of the front plate from the effects of the implosicn, as wel~ as the impossibility of replacing the badly expanded and eroded barrel without expensive instrumentation. All these shortcomingsWOuQarne~fltolerable in the case of a larger facility and a new solution satisfying all the basic requirements of adequate strength and good serviceability had to be found.
In order to make possible the easy removal of the used barrel, the idea of a segmented cone was proposed initially by Dr. Dawson (Ref.8) for the breech block design solution (Fig.
4),
which was finally accepted as a working scheme for th§ 30-in dia Mark II hypervelocity launcher. It consists of a body of revo-lution having a two-step, conical shape, which surrounds and holds the barrel. It is split into4
segments by two perpendicular cuts passing through the axis of the launcher. Such an arrangement was tested on the 8-in dia Mark II launcher model and proved to be a very efficient device for easy serviceability ~f thelauncher. Even in cases of very badly expanded and damaged barrels and liner plates, the dismantling procedure of the front plate assembly was very simple and straight-forward.
However, it became evident af ter first few runs, that good serviceability was achieved by sacrificing the other very critical property, that is, the strength of the front plate and barrel assemb~y. It was soon discovered that within the
critical area subjected to the extreme implosion pressures, the whole central portion of liner plate together with the segmented cone and the barrel was sinking and distorting prohibitively, rendering the liner plate and the segmented cone unserviceable prematurily.
Figure 12 shows the Mark 11 segmented cone, as well as the mode of the experienced distortion, shown in an exaggerated scale by a dotted line. A closer analysis of the case showed two basic deficiencies of the Mark 11 segmented cone arrangement. The first one was caused by a low efficiency in bearing strength of the conical surfaces of the split cone in axial loading. When applying the principle of the virtual displacement to all bearing surfaces 1, 2 and 3 (Fig. 12) it was found that both surfaces 1 and 3 have a bearing efficiency equal to sin2~, which when reduced to the frontal areas Al and A3 becomes siq;~. Hence, the total reaction force of the split cone in axial direction before distortion is equal to:
R=R =R +R 1 2 3
As the reaction R has to be equal to the total force acting on the frontal face of the split cone, it is obvious, that because of the very low efficiency of the areas A3 and the zero efficiency of area
A4,
there exists a very high shear load in the cylindrical section S-S shown on Fig. 12, which is causing failure.The second deficiency should be attributed to the lack of continua-tion of the cone material caused by peripheral cuts. Because of this tangential discontinuity the cone material cannot support the barre!h against the radial expansion caused by extremely high implosion pressures. This deficiency becomes more pronounced in cases where the projectile is placed initially further down the barrel, in order to save it from disintegration caused by the excessive base pressure, which attains its highest values at the origin of the hemis-phere (see be~ow).
The barrel and the barrel holder are not strong enough to withstand the extremely high pressures at the origin, without a very efficiency support from the outside. The pressure at the origin is usually many times higher than the yield stress of the barrel material and the expanding barrel induces very high compressive stresses in areas of the cone-segments adjacent to the barrel. As the induced compression stresses are much higher than the yield stress of the cone material, they create high residual stresses, which in turn cause permanent distortions and swelling in the affected areas of cone-segments. This phenomenon spoils the high-tolerance fit of the segmented cone-cum barrel assembly, and creates the necessity of frequent remachining or replac-ing of the distorted parts.
Af ter starting the explosive runs it soon becomes evident, that the projectile has to be placed at a certain minimum distance from the origin in order to prevent it from destruction by the collapsing hemispherical implosion wave. The magnitudg of this pressure in case of the 8-in dia launcher is of the order of
5
x 10 psi. In order to make this shock wave more planar and thereby reduce the sharp peak pressure it was found necessary to recess the projectile from the origin as far as 3 inches. This distance was found to be the minimum to achieve a satisfactory base pressure for preventing projectile failure, and all the following runs were done at the 3-in recess distance.Locating the projectile down the barrel was a reasonably effective remedy to save its integrity, but from the standpoint ofothe strength of the front plate of the launcher it was very poor. All parts located around the
barrel, as well as the barrel proper, were never expected to be loaded by such a high pressure, and a completely new design approach might be needed to develàp an adequate solution that would be able to cope successfully with such high pressures. Figure l3b shows a section through a badly distorted barrel af ter a run, in which the projectile was recessed 3 inches.
It became evident that, the split-cone configuration as used in the Mark 11 launcher is far from an acceptable solution. I t proved to be quite work-able in view of the servicing requirements, but it fell very short with respect to the required strength.
It
was also very difficult and expensive to manufacture, and it would have been much too costly to have it considered as an expendable part.In order to keep the tests going without changing radically the design of the front plate assembly, which would have caused a serious delay, it was decided to redesign the segmented cone in such a manner as to minimize its main shortcomings, as well as to reduce as much as possible the cost of manufacture.
Figure 14 shows the 24-in dia Mark 111 hypervelocity launcher with the new type of segmented cone and barrel arrangements. The main features of the new cone are readily recognizable. The high-efficiency bearing-area, which is normal to the axis of the launcher was greatly increased, and the embarrassing complexity of the double-cone arrangement was completely abandoned. The size of the cone was reduced to a minimum and the shape was made as simple as possible with the smallest number of matching surfaces to be machined.
The diameter of the barrel holder was substantially increased, in order to strengthen the structure in the imediate vicinity of the highest pressure, thus trying to reduce the adverse affect of segmenting the cone.
7.2 Barrel and Barrel Holder
The Mark I launcher, as wel~ as the early test runs of the Mark 11-1/3-scale launcher model, used as a barrel a commercial-type,ustainless-steel, high-pressure tubing 5/l6-in dia and 1/8-in thick wall.
Figure l~a presents the method of utilizing this type of tubing as a barrel in case of the Mark I launcher. A3-ft to 5-ft long piece of tubing was provided with a retaining collar produced by a direct build-up of steel material by welding, which had to be machined afterwards to proper dimensions from the
outside, as well as reamed and polished fr om the inside, especially in the vicinity of the collar where-; the initial finish and internal dimensions were spoiled by welding. The retaining screw threads directly into the front plate, thus holding the barrel securely in position. The vacuum and the pressure seal was obtained from a single O-ring located on the pressurized side of the collar.
The inlet to the barrel was shaped in a block of copper and was held in position by epoxy resine Copper was used as its physical property of high thermal conductivity was considered important for high-temperature flows.
Figure llb shows the same type of tubular barrel fitted into the 8-in dia Mark II launcher. The main improvement with respect to Mark I was the introduction of a separate new subcomponent, the barrel holder, to which the tubular barrel was mechanically attached by means of threads and special nuts. The elimination of the welded collar greatly reduced the amount of work involved
in manufacture of a tubular barrel.
The idea of using the commercially available 5/16 in dia stainless steel tubing did not work too well because of the impossibility of obtaining very
straight barrels. The experiments carried out at UTIAS as well as other hyper-velocity laboratories proved that an ideally straight barrel is needed to assure projectile integrity in this range of velocities.
Figure 15a represents a barrel arrangement for thé 30-in dia Mark 11 hypervelocity launcher. The main design idea was to use a sturdy barrel fitted
with a commercial grade smooth bore tubular liner, to be replaced af ter each run.
The tubular liner is welded to the barrel proper at the origin, which seemed to
be a most practical arrangement at that time. This type of barrel design has
to-day only a historical significance, it would never have worked as imagined. The
integra~ flange arranged at the origin would have been much too weak to withstand
the implosion pressure at the or~gin, and the inevitable damage to the barrel inlet,
would have required a complete overhaul or replacement of the barrel af ter each
run.
When it became obvious that a commercially available high pressure steel
tube could not be considered as a satisfactory design solution, a solid barrel
made of high-strength steel bar 1-1/4 in od was chosen as standard equipment
for all test runs done with 8-in dia Mark 11 and Mark 111 launcher models. This
type of barrel was supplied by Canadian Arsenals Ltd., Toronto, and the quality
and price were quite satisfactory. The projectile recessed location, as weIl as
the shape of the inlet geometry could be changed easily to suit the test program by additional local machining and the constant outside diameter assured alowest possible cost. A new item was added a barrel holder, and the whole arrangement for Mark 11 8-in dia launcher is shown on Fig. 15b.
To the shortcomings already described in the discussion of the Mark 11 segmented cone, one more can be added here, that is, the excessively high bearing
pressure acting on the shoulder of the barrel ho~der. It was causing failure
in bearing at the common contact area. To counteract this very undesirable effect, an impnoved barrel holder having much larger shoulder area was designed, and used
together with the improved segmented cone for the ~rk 111 launcher. It is shown
on Fig. 15c.
In conclusion, it can be stated here that the Mark 111 segmented cone and the barrel arrangement has reduced considerably the deficiencies discovered during test runs with the Mark 11 launcher. Some supplementary improvements were contemplated, but the lack of funds for continuation of testing and development of this type of hypervelocity launcher has ceased all further design work.
8.
THE MARK III HYPERVELOCITY LAUNCHERDuring the explosive test runs done with the Mark 11 launcher several
weak spots and design deficiencies were discovered. In an attempt to correct
them a new improved model was built which is known as the Mark 111 hypervelocity
launcher. The main effort of the author of this report was directed toward the'
improvement of the strength of the Mark 11 launcher, as well as lowering the cost by eliminating expensive machining and simplifying some unnecessarily· complicated design details.
Figure 14 shows the general arrangement of the Mark 111 launcher, on
.
,
which all major improvements are visible. The front portion of the strong enclosure is much more rigid, as much less material was removed in order to
accommodate the new segmented cone. In case of the front plate, the material located in close vicinity to the longitudinal axis of the launcher is very valuable from the standpoint of strength, as it improves greatly it's stiffness and reduces the stress level. This specific point will be discussed in more detail in the chapter on stressing. The mating surface between the explosive chamber and the front plate was greatly simplified, thus requiring much less of expensive high-tolerance machining. The number of conical flanges was reduced
from two to one, and was arranged at alocation where it is structurally most
useful. The bearing area of the remaining conical flange was made làrger by
increasing its depth.
The height ~ of the segmented cone was reduced radically to a"dimension
required to support the barrel efficiently against the excessive swelling caused
by recessing the projectile from the origine As it was proved experimentally,
the expansion of the external diameter of the barrel becomes negligible at a
station 4 to 5 inches from the origin, which indicates that the barrel does not
require any elaborate support outside of this region. Therefore, a very generous
clearance was left between the barrel and the front plate, which is shown on
Fig. 14.
A greatly simplified and improved pressure sealing system for the Mark
111 launcher was already discussed in chapter 6, together with the modifications
to the segmented cone and barrel, which create a much more efficient front plate
assembly. Figure 16 presents an exploded view of the Mark 111, 24-in dia cavity launcher. I~ shows and explains the basic design principle of this launcher as compared to the Mark I configuration. The whole design concept is based on two
disyinct subsystems, each of them performing its prescribed function.
The first subsystem is the strong enclosure. It. consists of the
explo-sion chamber, the front plate and the joining bolts, which provides a positive
and safe containment for the gun or launcher proper, and is strong enough to
withstand the internal loads caused by the very high implosion pressures,
includ-ing all associated types of loading such as severe shock waves and their
frequen-cies. It provides also for easy closing and opening the launcher for the
re-loading of the explosive charge as well as easy replacing of all expendable parts.
The chosen design of the Mark 111 strong enclosure fulfils satisfactorily the
specified functions. The second subsystem, which should be called the launcher
proper, comprises all such typical parts as the barrel, the projectile, the explosive cartridge, protective lining, including the pressure sealing, and the means for the easy replacing of expendable parts. This subsystem is shown on Fig. 16, below the strong enclosure, as a separate assembly.
The lowest row of separate parts on the same figure shows explicitly the simplicity of the Mark 111 design, which makes it possible and relatively easy to modify these parts in case it was desirable or necessary.
The Mark I design did not have such clearly separatable functional
subcomponents. The function of the strong enclosure and the launcher proper
were intermingled thereby making it more difficult to operate, repair, or
modify.
As mentioned in the previous chapter, the Mark 111 segmented cone
pre-sents a significant improvement over the Mark 11 model. However, it did not
cure completely all the experienced weaknesses. The deficiency that was mentioned before caused by the lack of the material continuity in the direction of hoop-stresses was not corrected, as this would require a complete redesign of the involved region.
The experience obtained from the test-runs of the Mark 111 launcher indicates explicitly that some further improvements to the Mark 111 model are still desirable, especially to cope successfully with the newly-adopted test-procedure of recessing the projectile 3-in down the barrel. This specific pro-cedure imposes on the launcher structure a new and much more severe type of load-ing, which was not considered nor specified in the original UTIAS design specifi-cation. It could change significantly the design approach for a new and better
~auncher.
9.
DEVELOPMENT OF IGNITION ELECTRODEIn order to detonate the explosive-gas mixture compressed inside the explosion chamber, a positive electrode inlet was inserted on the flat surface of the liner plate. The electrode was introduced into the explosion chamber through a hole drilled in the front plate; and it was insulated all along this passage. It was proved experimentally that a 1/16-in thick wall teflon tubing will provide suffi'cient insulation for the 8-in dia launcher models.
Figure 17 shows three distinct stages of development of the ignition electrodes for Mark I, 11 and 111 launchers. Figure 17a represents the design of the electrode for the Mark I launcher, which was also used in the Mark 11 launcher during its few early test runs. It consists of a steel rod 1/8-in thick having a larger diameter cylindrical head arranged at the explosion-chamber end. The electrode was machined from a thicker steel rod of 3/8-in dia.
The electrical insulation was obtained by using a teflon tubing 1/4-in O.D. hav1/4-ing an 1/4-integral flange at the explosion chamber end. The 1/4-installation of the electrode in the front plate, as well as pressure and vacuum sealing was achieved by using epoxy resin, which filled the cylindrical gap at the
high-pressure end, as well as all contact surfaces between the steel electrode, teflon tubing and the front plate.
The exploding wire was then soldered to the steel nipple sticking out into the explosion charnber. This type of electrode served satisfactorily in all runs done with the Mark I launcher. A weakness of this type of electrode was its high cost of manufacture, as both the electrode and the insulation oad to be pro-duced by machining from much thicker stock. As the electrode was an expendable item which was discarded af ter each test run, the cost of manufacture became important.
Another drawback of this electrode could be traced to the fact, that the achievement of the proper pressure and vacuum sealing depended heavily on the degree of accuracy and care with which the epoxy resin was used during the
assemb~y and installation of the electrode. There were cases, where the appli-cation of the epoxy resin had to be repeated because of faulty sealing.
The Mark I electrode did not perform very well during the first test runs of the Mark 11 launcher. Severe blow-outs occurred, during which the whole electrode was pushed out through the inlet hole in the front plate. Under the effect of the implosion temperature and pressure, the teflon flange was crushed
in compression and the escaping hot plasma melted away the head of the electrode, pushing the whole unit out.
Figure 17b shows an improved electrode design for the Mark 11 launcher.
The electrode proper consists of a steel rod 1/8-in od with a much.larger
cylindrical head screwed and silver soldered to the rad. The cylin4rical head
is housed in a sturdy cup made of steel. Instead of teflon, a much stronger
Bakelite was used as a base supporting the head. The whole unit was assembled on the bench with the epoxy resin, and as a completed subassembly was installed
in the front plate. The steel cup was sealed by an O-ring which is shown on
Fig. 17c. The way in which the entireelectrode unit was assernbled .also appears on the sketch. The Mark 11 electrode which was much easier to manufacture and
install than Mark I, performed reasonably well, until it was discovered that the distance between the electrode he ad and the massive plate was too small, and was
causing an electric discharge during ignition cycle.
Figure 17c shows the final improved design of the electrode for the
Mark 111 launcher. The only difference between solutionsl'B and C ;is the increased diameter of the electrode head made to improve its resistance against the extreme
implosion pressure, as well as bevelling the head around the electrode nipple in purpose to increase the distance between the electrode and the mass. The shallow
ditch created by the bevelled head was filled with epoxy resin to improve the insulation and keep the inside surface of the explosion charnber perfectly flat.
10. DEVELGPMENT OF EXPLOSlVE LlNER AND THE PETN CHARGE
A well-focussed implosion is a primary condition for the successful launching cycle of an implosion-driven hypervelocity launcher. If an off-focussed implosion releases its very high energy at the wrong spot, it creates a great potential danger to the integrity of the launcher. Depending upon the magnitude of the off-focus distance, the worst case wouid take place if the faulty implo-sion would focus at the edge of the hemisphere. In this case it is possible for the implosion to cut through to the sealing rings and it could render the
launcher unserviceable. A very significant decrease in performance was found in these cases where the centre of implosion was shifted away from the entrance to
the barrel. The problem of obtaining a perfectly focussed implosion consis-tently is a very complex one. However, it has been found (Ref.~) that the im-plosion following a gaseous detonation can be made to focus about 100% of the time. Whereas, explosive-liner implosions can be made to focus about
50%
of the time, owing mainly to a lack of very consistent density and geometry of the PETN shells.Figure 18 shows a survey of parameters prepared by the author, which may have an impact upon the occurrence and quality of a well focussed hemis-pherical implosion. The parameters shown in the table have a varied degree of importance. Some of these may bevvepyi Ji.~portant and even critical·, while ethers
may be less influential. The nurnber of generated implosions at various
labora-tory conditions at UTIAS was probably much too small to evaluate the very large range of parameters or their combinat.ions. In this chapter only two basic para-meters, the explosive liner and the PETN charge will be discussed. Two other parameters, the initiation and the chamber geometry are discussed in Ref.~. In chapter 12, the conical liner plate is discussed as a possible safeguard against detrimental effects of a badly defocussed implos~on.
design and the sort of material to be used for the explosion liner upon the
well-focused implosion. The Mark I launcher used an explosive liner made of lead
3j16-in thick. It was believed at that time, that by choosing a highly plastic material and proper wall thickness for the explosive liner, the very strong elasticjplastic shock wave produced by exploding PETN at the explosivejmetal interface, will be partially absorbed by the plastic lead material and only the
elastic wave will propagate furtller into the steel body of the strong enclosure
without harming it.
Figure 2 and Fig. 8a show the explosive,liner made of lead, and installed into the Mark I launcher. As can be seen from these drawings, the
explosive liner did not take any part in the pressure sealing of the explosive
chamber, thus creating some shortcomings already discussed in chapter 6. There
was still another drawback not mentioned before, which is the possiblity of
initiating the explosive gas mixture between the liner and the chamber body,
which may have cuased the specific mode of failure depicted on Fig. 19a.
Using lead as a material for manufacturing explosive liners was
later discarded as impractical. Further theoretical work done by Garg (Ref. 7)
showed that the plastic shock wave cannot be entirely eliminated by using a 'liner
and that some cumulative damage to the strong enclosure by high-intensity plasticj elastic waves is inevitable. Also, liners made of lead for the 30-in or 24-in
dia launcher would be prohibitive, as the excessive weight and poor mechanical properties of such liners would not permit the pressure seal to be at its best
location.
A second choice as the best material for explosive liners was cast
or spun aluminum. A number of explosive liners made of aluminum in various
thick-nesses were manufactured and tested during first runs of Mark 11 launcher. They were very light, easy to manufacture to high tolerances, and rigid enough to
provide a reliable pressure seal arranged at the lip-perphery of the liner.
They also withs~ood very well all initial test-runs made with the detonating
gas only, but started to suffer occasional failures during test runs with the
explosive charges. A most common failure for this type of liner is shown on
Fig. 19 and 20a. It shows a liner with a completely burnt out or melted portion due to the exploding PETN.
·This peculiar type of failure with only a portion of the surface
burnt away was never fully understood or explained. It seems, as if the tempera-ture at the explosivejmetal interface was nat evenly distributed, and the aluminum material failed at spots which reached higher temperatures than critical. Another possibility considered was that the aluminum was reacting chemically with products of explosion, thus causing the disappearance of a portion of the explosive liner in an unpredictable way.
In order to find a remedy ,to this type of failure but at the same
time to retain the light weight characteristics, a number of linear models lami-nated of two materials; steel on the inside and aluminum on the outside, were
produced and tested with reasonable success. The relatively high cost of manu-facture as well as the difficulty experienced in obtaining a flawless bond between
the two laminates, necessitated further search for a satisfactory material.
A very successful liner design was found, by spinning a bj4-in
fUlly annealed copper sheat, which was machined afterwards on the outside to
proper tolerances by using a special turning fixture and vacuum chuck.
In the final test runs done with the Mark II launcher, as well as in all the test runs done wi th the Mark III launcher, copper explos~v:e:!ld,.ners were
used successfully without any serious mishaps or damage. For the " " '8"':;i..n 'f' " . .dia
launcher copper proved to be the best choice. However, in case· ~:na, full-scale
24-in dia ~auncher, it might prove to be too heavy and too expensive, and some
future experiments with other materials or laminates might be necessar~.
The second group of parameters on Fig. 18, affecting the proper
focus-sing of implosion, pertains to the manner in which the PETN charge has been
pre-pared. The following parameters such as the thickness of the explosive layer and
its distribution, the density of the layer and its distributien, as well as the surface texture and the type of shape (square or mitred) of the· free edge in the
vicinity of the front plate, depend solely upon the technique of manufaçturing
of the PETN charge. As a result of initial experiments made at UTIAS with various types of explosives for the purpose of finding the most suitable one which could
be initiated by a detonation wave in a mixture of oxygen and hydrogen, the
secon-dary PETN was chosen as one which is safe to handle and has a explos'ive good energy
yield.
The PETN charge could be prepared in a reasonably wide range of densities
from 0.6 to 1.0 gm/cc, but the l.ower densities obtained fr om a "superfine" grade
of PETN were found to be most sensitive to initiation. As the. PETN .crystals do
not adhere to each other without using a proper binding medium, two'ways of
preparation of PETN charge was proposed and tested. The first qne which was
suggested and tried by
Mr.
D. M. Welsh, Canadian Safety Fuse Lt~., Brewnsburg,Quebec., used a water soluble binding additive called Cellosize. A number of
methods of preparation of the PETN charge were tried by Mr. Welsh wlth negative
results. His concept was to prepare a suitably proportioned slurry·of PETN and
Cellosize and then put it into the explosive liner and let it dry te 0btain a
solid bulk or layer, ~hich could be machined later to proper thicknessan~ toler-anee.
Unfortun~tely, the drying öf the PETN slurry to produce a·uniferm and
strong bulk or layer did not prove to be possible, and the final product was always
found to be deficient. The shrinkage of the PETN bulk during drying was suf-ficiently severe to cause cracks and separations, and the pulling aw.f!ty ef the
PETN layer from the liner wall. The failure to obtain a unif0rm layer of PETN
was attributed by Mr. Welsh to the nonuniform distribution of binder in the drying
layer, caused by the evacuation of the Cellosize from the inside of the layer to
the outer surface, thereby leaving a higher concentration of the binder which is
more susceptible to shrinkage. The other method tried~JMr. Welsh which was the
building up of the re~uired thickness of PETN by the gradual assembly of a number of layers with drying periods inbetween this did not work either because ofthe
very poor cohesion between layerso
To solve this problem, a new propo~al was made by Prof. Co Fo Wright, Department of Chemistry, University of Toronto, to substitute the Cellosize binder with cotton linters, which would create some sort of a three-dimensional
lattice providing a mechanical support to the PETN crystals. According to
Prof. Wright this kind of mechanical support would be superior to the Cellosize
binder, as it leaves the very fine crystals of PETN completely clean and uncoated by the nonactive addition of organic matter. The experiments that followed
proved the correctness of these expectations. No difficulties were experienced
