US2333567A - Electrolytic process of forming flame or explosion traps - Google Patents

Description

Nov. 2, 1943. w o 2,333,567

ELECTROLYTIC PROCESS OF FORMING FLAME OR EXPLOSION TRAPS Filed Dec. 28, 1940.

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Patented Noy..2, 1943 ELECTROLYTIC PROCESS OF FORMING FLAME OR EXPLOSION TRAPS William Helmore, Kingston Hill, England v Application December 28, 1940, Serial No. 372,200 In Great Britain March 31, 1939 2 Claims.

This invention relates to flame or explosion traps of the kind in which a flame or explosion in an inflammable fluid mixture passing through a large number of long narrow passages is extinguished by reason of heat losses from the burning mixture to the surfaces of the said passages, which passages are formed between alternate plain and corrugated plates and are preferably arranged parallel to the direction of fluid flow.

In flame or explosion traps of the kind described, the plain and corrugated plates are usually housed in a rectangular or circular casing adapted to be accommodated in a socket or recess in the conduit or manifold of an internal combustion engine. Such flame traps are usually subjected to gas pressure, high temperature and severe vibration in service which maycause sumcient increase in the cross sectional area of one or more of .the passages to render the flame trap inefiective. Furthermore great care has to be exercised in assembling the plates, to ensure even approximate maintenance of their positions relative to-each other in service, and this has the eflect of slowing up production with consequent increase in cost. Furthermore, with present methods of manufacture and with materials at present used in the construction of the flame trap plates the flame resisting properties of the trap are not utilised to the fullest advantage; severe restrictions are also placed upon the range of constructional materials which can be utilised.

It has been proposed to provide the casing of electrical apparatus with a vent plug containing two spirally wound metallic ribbons, one corrugated and the other plain, forming a number of narrow passages longitudinally of the plug. The

plug serves as a protective device since if the electrical apparatus is used in an explosive atmosphere, the plug will preventthe passage of a flame from the apparatus through the vent to the surrounding atmosphere. In this proposal it iii was suggested that the plug should be manufactured by tinning two metallic ribbons, winding them into a spiral, inserting them into the plug the interior of which has also been tinned, and then heating the assembly up to the meltingpoint of tin in order to ensure that the surfacesof the ribbons adhere together and to the sides of the plug.

One object of my invention is to'produce a flame or explosion trap of the kind described of high strength and efliclency which can be manufactured in a simple and economical manner.

According to my inventon, I provide a method of making flame or explosion traps of the kind described in which after the plain and corrugated plates have been assembled they are bonded together by electro-deposition of an adherent layer My invention also includes a flame or explosion trap of the kind described characterised in that the alternateplain and corrugated plates are bonded together by means of a matt metallic adherentdeposit on at least part of that surface of the plates at or immediately adjacent to their contacting positions.

The bonding of the flame trap plates is preferably such as to efie'ct a rigid union between the lines or surfaces of contact of the plates, but the present invention also comprises semi-rigid union in which movement of the crests of the corrugations of the corrugated plates relative to the surfaces of the plain plates is impeded, and the term bonding as used herein is to be regarded as including both these forms of unions.

This invention represents an important advance in the art. As compared with previous proposals in which assembly plate structures have been bonded by tinning or even formed from pretinned sheet and subsequently bonded by heating, my invention provides substantial mechanical strength for a minimum thickness of bonding material, and consequently ensures that the passages through the assembled structure have for a given weight of plate structure the maximum cross-sectional area consistent with mechanical strength. In some plate structures, as for example in devices intended for mixing combustible gases tobe supplied to internal combustion engines, the cross-sectional dimensions of the passages may be relatively large in comparison with the size of the structure as a unit, and in such cases the increase in weight and the reduction in cross-sectional area brought about by a tinning operation may not be a serious disadvantage. In flame or explosion traps, however, in which the passages through the structure must of necessity be of very small -cross-sectional area, suitably less than 0.01. sq. in. and preferably less than 0.005 sq. in., it is of paramount importance to secure a minimum weight and minimum resistance to gas flow consistent with proper functioning of the .device. Ibis also very important in flame traps to obviate the risk that any of the passages may be partially or completely obstruct- 1 ed, as may easily occur in a tinning operation. These requirements are of particular importance in flame or explosion traps intended for aircraft, and my invention enables these requirements to be fulfilled in a simple and economical manner.

It is a matter for surprise that it is possible to obtain by means of an electro-deposition process a sufliciently uniform deposit along the length of the very narrow passages which constitute the flame trap structure. In the more extreme case of the flame traps employed in the induction systems of spark-fired supercharged aircraft engines where the cross-sectional area of the passages is even smaller in relation to the length of the channels than is customary in other types of flame trap, I employ an electro-deposition process and material possessing high throwing propertie in order to obtain a sufficiently uniform deposit.

It is well known that the heat. of explosion of gases passing through a trap is transferred to the surface of the material forming the trap, partly by convection, partly by conduction and partly by radiation, but hitherto no means have been employed to utilise to the best advantage the large proportion of heat which might be transferred by radiation, a quantity which in the case of black body radiation may be approximately proportional to the difference of the fourth powers of the absolute temperatures of the gases and the surface of the plates.

According to a further feature of my invention, therefore, surfaces of the plates of the flame trap, either during or after the bonding operation, are rendered specially absorbent to radiation so that in addition to the best extracted from the gases by conduction and convection, the considerable quantity of heat capable of passing by radiation to the surface is more readily absorbed; In this way the temperature of the gases is more rapidly reduced below that required for flame propagation and a shorter length or a greater cross sectional area of the passages of the explosion trap.

may be employed or the area of the cooling sur faces may be reduced.

The radiation absorbing surfaces may be produced by chemical interaction with the layer of adherent material applied to the surface of the flame or explosion trap plates for the purpose of bonding the said plates. Alternatively the layer of adherent material electro-deposited on the plates may be so selected as to possess radiation absorption properties.

In order that the invention may be clearly understood reference is made to the accompanying drawing, in which:

Figure l is a general view in perspective of a flame trap comprising alternate series of flat and corrugated plates;

Figure 2 is a longitudinal section through the flame trapofFigurel,and 1 Figure 3 is a fragmentary end elevation to an enlarged scale.

1 .b-nl the drawing a flame trap l comprises an assembled pack of corrugated metal plates 2 and alternate flap plates 3 housed within a casing 4.

- I-l'he plates 2 and 3 define a series or substantially triangular passages l for the passage of inflammable fluid mixtures, the apices 6 of the corrugated plates 2 being in contact with the fiat plates Iss shown in Figure 3. The casing 4 is provided with retaining flanges 1 which come into contact with the periphery of the end-faces 8 and 9 of the assembled pack. v 1

After assembly the flame trap plates and the casing are immersed in an electrolytic bath and a layer of metal is deposited on the surface of the plates to bond them together to form a rigid or semi-rigid structure. The process may be so carried out that the layer of metal is electro-deposited on the complete surface of both the flat and corrugated plates or on a portion or portions of thesurfaces of the assembled plates, as for example on those portions of the plates adjacent totheend facesiandl. Itisalsowithin the scope of my invention to deposit the metal layer only on those portions of the plates adjacent to the apices 0 of the corrugated plates 2 (Figure 3). This may be effected by stopping oil" the troughs of-the corrugations so that the electrodeposition of metal occurs only near the apices. Thus for example, before the flame trap is assembled, a lacquer composition may beapplied to the corrugated plates and before it has dried or set the corrugations wiped to remove the lacquer from that part of the surface near to the apices. After the remaining lacquer coat has dried or set the plates are assembled and treated as described herein whereby a layer of material is electrodeposited on the plain plates and on that part of the surface of the corrugated plates from which the lacquer had been removed. After electrodeposition the rest of the lacquer may be removed. for exampl by means of a solvent.

By subjecting the assembled flame trap plates to the electrolytic process after they have been fitted into the casing, those portions of the plates in contact with the interior of th casing may be bonded to the said casing.

In one method of carrying my invention into effect, I construct a flame trap of alternate plain and corrugated plates of German silver, in which the channels formed by the corrugation are 0.75 inch in length, 0.028 inch in height and 0.0008 square inch in cross ectional area. The alternate plain and corrugated plates are assembled in a suitable frame or jig so that all the corrugations are parallel to each other. The assembled flame trap together with the frame or jig are then immersed in a plating bath containing grammes Per litre of sodium stannate and 20 grammes per litre of caustic soda. The bath is maintained at a temperature of about 70 C. and at a current density of 30 amps. per square foot, the flame trap assembly being made the cathode and rolled nickel being used as the anode. I

The electro-deposition process is continued until a layer of tin is deposited on the surface of the plates to bond them together to form a rigid structure. The deposition of the adherent layer not only increases the strength of the flame trap structure but since the plain and corrugated plates are bonded together in metallic union the heat conductivity of the complete flam .trap structure surfaces is materially increased. Owing to the matt-nnish of the electro-deposited layer of tin, the radiation absorption of the flame trap is also increased.

In a further example of carrying my invention into effect I treat the surfaces of the flame trap plates after bonding to render them specially absorbent to radiation. The flame trap assembly is first subjected to an electro-deposition process as described in the previous example, whereb a layer of tin is deposited on the surface of the plates. This deposit, being matt, is itself radiation absorbent, but the radiation absorbent properties are then increased'by immersing the flame trap as the anode in a bath containing grammes per litre of disodium hydrogen phosphate and 20 cos. per litre of phophoric acid of specific gravity 1.75. A copper cathode is used and the bath is maintained at a temperature of about 90 C. and at a current density of between 30 and 40 amps. per square root. This anodic process results in the formation of a film of black tin oxide on the surface of the predeposited layer and in order to prevent the tin coating being completely converted to oxide the basic layer of tin is-preferably about 0.0002" thick. The resulting film of oxide is of black matt appearance and is highly absorbent to heat radiation.

While I prefer to form an adherent layer in such a manner as to provide a rigid bond at or adjacent to the contacting surfaces of the plates it will be understood that the layer of adherent material may be so formed or applied that movement of the crests of the corrugations relative to the surfaces of the plain plates is not entirely prevented but is impeded. Thus the electrodeposition process may be so regulated as to form a layer of sufflcient thickness to impede movement of the plates but the layer may be of insufficient thickness as to form a completely rigid bond between the crests of the corrugated plates and the surfaces of the plain plates. I

By means of this invention the strength and resistance to vibration fatigue of flame traps constructed of plain and corrugated plates may be increased. and in the case of plates which are treated in a jig or frame, insertion in the casing and mounting are facilitated since the assembled flame trap is a rigid unit by virtue of the bonding of the plates. The trap, after bonding in a jig, may be subsequently bonded to the casing. On the other hand where the adherent material is applied to the flame trap plates and to the surrounding casing simultaneously, improved heat conductivity throughout the whole struc-- ture and casing results.

Further thinner materials may be employed in the construction of such flame traps than hitherto witha resultant reduction in resistance to fluid flow through the flame trap, and in particular the invention enables thin cooling surfaces of mechanically weaker materials possess ing high heat conductivity to be employed in cases where mechanically strong materials of low conductivity have hitherto been necessary since each triangular channel is made to form a rigid truss unit and flexibility is thereby eliminated. Materials subject to corrosion, which have hitherto been unsuitable for use, may be em loyed in accordance with my invention, by treating the surface of the said material with a corrosion resistant layer. For example, copper plates may be treated with electro-deposited tin as described above.

A further benefit is obtained where this invention is employed in circumstances where explosions of high pressure have to be resisted, for example, in flame traps in highly supercharged spark flred engines, where owing to the high maximum flame temperature of the gases, the resultant increased proportion of heat transmitted by radiation is'more readily absorbed at the surfaces of the flame trap. Moreover in flame traps in accordance with this invention, it

is possible forthis heat to be more rapidly conducted through the flame traps structure by virtue of the metallic union between the component parts of the flame trap.

In internal combustion engines the surfaces of the flame trap may locally reach very high temperatures but nevertheless I have found by experiment that in the case of flame traps con structed in accordance with this invention and having a metallic bond.the union between the plates is maintained in spite of repeated heating which may exceed the melting point of the adherent material used.

As example of constructional materials for the plates of the flame traps of this invention there may be mentioned German silver, copper, cupro-nickel, iron, steel and brass. As examples of the metals which may be deposited electrolytically for the purpose of bonding the flame trap plates together, there may be mentioned tin, copper, cobalt, zinc, nickel and chromium. For the purpose of increasing the radiation absorbent properties of the electrolytically deposited metal, the said metal may, for example in the case of tin, copper, cobalt or nickel, be converted into the form of the black oxide by anodic oxidation. Altern'atively,for example in the case of copper, the metal may be converted to the form of the black sulphide.

The term flame trap as used in the appended claims denotes a device adapted for the purpose of suppressing either flame or explosion in an inflammable fluid mixture passing therethrough.

As many widely different embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that I do not limit myself to any of the embodiments set forth.

I claim:

1. The method of manufacturing flame traps which comprises assembling in contact a plurality of alternate plain and corrugated thin sheet metal plates to define a plurality of elongated passages the area of each of which is less than 0.01 square inch, and electrodepositing an adherent matt coating of tin on the surfaces of the plates of said assemblage at regions adjacent the lines of contact of said plates to bond said plates together as a unit.

2. The method of manufacturing flame traps which comprises assembling in contact a plurality of alternate plain and corrugated thin metal plates to define a plurality of elongated passages the area of each of which is less than 0.01 square inch, electrodepositing an adherent matt coating of tin on the surfaces of the plates of said assemblage at regions adjacent the lines of contact of said plates to bond said plates together as a unit, and subjecting said assemblage to anodic oxidation of the tin to produce a dark fllm of tin oxide thereon.

WILLIAM HELMORE.

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