US2087573A - Electrical resistance and electrical heater and method of producing the same - Google Patents

Description

' y 1937- B. H. N. H. HAMILTON 7 ELECTRICAL RESISTANCE AND ELECTRICAL HEATER AND METHOD OF PRODUCING THE SAME Y Filed Oct. 16, 1935 3 Sheets-Sheet l 3 7 2 5 r 7 w 8 h 0 a 2 s t e R e E h T s A E 10 H E M A N I E E 3 mm M AN H 5 d .I Hs

July 20, 1937 y 1937- B. H. N. H. HAMILTON 2,0$7,57Q

ELECTRICAL RESISTANCE AND ELECTRICAL HEATER AND METHOD OF PRODUCING THE SAME Filed Oct. 16, 1935 3 Sheets-Sheet 3 Patented July 20,1937

ELECTRICAL RESISTANCE AND ELECTRICAE HEATER AND METHOD OF PRODUCING Benjamin Henry Noel Hans Hamilton, London,

England, assignor to The Expanded Metal Company, Limited, London, England gAppilcatiorr October 10, 1935, sci-m No. 45,348 Y H In Great Britain November 5, 1934 V 14.0mm. (Cl. 201-73) girder form but consisting of simple lengths or This invention relates to electrical resistances andto electrical heaters and has for one object to provide improved electrical resistances and heaters which may be simply and cheaply made with a minimum of waste material and which shall be compact and have great mechanical strength and high wattage dissipation per unit weight and size.

' Although not limited to its application thereto the invention is. particularly applicable to re- .sistance constructions for usein connection with the electrical control of relatively small electric motors and also to electrical heaters, both high temperature heaters and also low temperature domestic and similar electrical heaters of the type sometimes termed convection heaters.

It is known tomake an electrical resistance or heater from open or meshwork sheet metal by cutting away portions of the sheet so as to cause the current flow thrcugh'the cut away sheet to proceed in a zigzag or tortuous path. Forexample, it is known to take a sheet of metal resistance and tocut away the metal in slots which are parallel to one another and are transverse to the sheet there being two sets of slots, the-slots in one set extending from one side edge of the sheet but not reaching the other side edge and the slots in the other set extending from the said other side edge but not reaching the first mentioned edge, the slot in one set altermating with those of the other so that the current through the slotted metal is constrained to follow a zigzag path. Known resistances and heaters constructed in this manner present the serious disadvantage that the slotting of the metal involves a considerable wastage in manufacture. while, moreover, such zigzag resistances of the simple flat sheet form are not as compact 'as is desirable.

United States Patent No. 1,991,935 describes inter alia expanded metal resistances which do not possess the above disadvantages; for example Figures 12 to 14 of the said specification illustrate constructions which may be made very compact and involve very little wastage of material in manufacture. The resistances which form the subject of Patent No. 1,991,935 are, however, of split tubular girder form, 1. e. in tubular form with the tube not completely closed.

The object of the. present invention is to provide resistances and heaters which shall also have the advantages of great compactness and ability to be manufactured without any substantial waste of material; the'saiti'resistances and 55 heaters, however, not being of the split tubular expanded more or less flat expanded metal.

Another object is to provide an improved meth- 0d for making electrical resistances and heaters from expanded or intermedia expanded metso-called intermediate expanded resistance or heater wherein sheet expanded or intermediate expanded metal is cut to provide a zigzag or tortuous current path. the cuts being as nearly as possible of zero width (that is to say cutting away as little as possible of the metal) and the The present invention provides an expanded or metal on either side of each out being bent out of the general plane of the original sheet, so

that, although the width 01. each cut is almost zero, there is ample space in the finished resistance or heater between neighbouring lengths of the zigzag current path, this space being obtained by virtue of the bending of the metal out of the original plane. Expanded metal per se of course is wellknown, but by intermediate expanded metal is meant the slitted product obtained from slitting a sheet of metal in the well known slitting and stretching method of making expanded metal, but with the stretching operation omitted.

Preferably the expanded or intermediate expanded metal when it has been cut, as above described, is bent so that adiacent lengths of the final zigzag or tortuous path are made up of strips which are at right angles or substantially at right-angles to the original plane of the sheet. Again preferably the cuts are at right angles to the selvedge edges. The preferred forms of heater or resistance in accordance-with this indiate expanded metal (the slitt'ed product obtained from the slitting operation in the well known slitting and stretching method of making expanded metal). This however, is not preferred and its application is rather limited since its heat dissipating properties are obviously inferior to those of expanded metal.

The invention is illustrated in and further explained in connection with the accompanying drawings. I

Figs. 1-3 show a multi-unit resistor constructed in accordance with this invention.

Fig. 4 shows a sheet of expanded metal before being bent. The strips being half a mesh. wide.

Fig. 5 shows a side elevation ofthe resistor of Fig. 4 after being formed.

Fig. 6 shows the zigzag current path obtained.

This is a view looking down on the resistor of Fig. 5.

Fig. 7 is a view at right angles to Fig. 5.

Figs. 8-11 correspond to Figs. 4-? except that the strips are a full mesh wide.

Figs. 12 and 13 show different views of the clip used to mount the element.

Fig. 14 shows the resistor fixed in place by means of the clip.

In one way of carrying out this invention a sheet S of expanded metal the material of which will depened upon design requirements-for ex ampie it may be of any known resistance composition -is cut as shown in Figure 4 with a plurality of parallel transverse cuts K1 & each of as nearly as possible zero width. There are two sets of cuts, the alternate cuts (K1) in one sheet commencing at one side of the sheet and extending through the expanded metal body portion, but not extending to the other side of the whole sheet, while the intervening cuts (K2) in the second sheet commence at the other side edge and do not extend to the first-mentioned side edge. The sheet of expanded metal is left with unexpanded side edges E (which may be stamped to the shape shown) which form selvedges and the cuts are of such length that each extends from the side in which it commences to the selvedge at the other side without actually extending into the said selvedge. After the sheet has been cut as just described, it is bent in such manner that the material between adjacent cuts K1 K2 lies at right angles to the original plane of the sheet, the direction of bending alternating from end to end of the'sheet. Each uncut portion PS of the selvedge which connects the length of material on the front side of any one cut to the length on the rear side thereof is bent through two right angles at Q and B so that the said lengths L of material lie at right angles to the original plane of the sheet each length lying immediately behind and parallel to the next. Each portion PS constitutes an unexpanded mounting portion including a central section included between the bending lines Q and R and two flank sections. The central sections of the severalv mounting portions lie substantially in a common plane whereas the flank sections are bent at angles to this plane, the flank section at one end of each strip L being bent relatively upwardly and the flank section at the opposite end of the strip being bent relatively downwardly. The result of the bending is to provide a succession of lengths or substantially planar strips L of expanded metal any two adjacent lengths being connected together at one end by a piece of selvedge but being not connected at the other end, the connecting piece of selvedge appearing, when viewed endwise oi. the lengths of expanded metal, as approximately of U form.

The same process of bending is continued throughout the sheet for 'any desired length so that the final resistance product consists of a 'plurality of straight flat lengths or substantially planar strips L of expanded metal, the lengths being parallel to and behind one another and at right angles to the original plane of the sheet. The current path through the whole resistance or heater, as the case may be, is a zigzag path through all the lengths in series, the connections between adjacent lengths being constituted by the U shaped portions of selvedge. Because of the cutting of the slits Kr and K2 of nearly zero width as shown in Figure 4 the sum of the widths of each two strip L will be nearly equal to the distance between centers of the central sections of adjacent unexpanded mounting portions when the strips have been arranged in substantial parallelism as shown in Figures 5, 6 and 7.

Figure 4 shows an arrangement in which the successive cuts K1 K2 are spaced apart by a distance of half a mesh of the expanded metal with the result that the adjacent lengths L are each half a mesh acrossi that is to say each such length appears as shown in Figure 5 as a zigzag conductor. Figure 6 is a schematic view taken at right angles to Figure 5 showing the way in which a zigzag current path is obtained throng. the successive lengths which appear edgewise in Figure 6 (they are represented in this figure by broken lines) and are joined together by the U shaped selvedge pieces which are integral therei with. Figure 7 is a view at right angles to Figure 5. Figures 8, 9, 10 and 11 are views corresponding to Figures 4, 5, 6 and'l respectively the diflference being that in the construction shown in Figures 8, 9, 10 and 11 the cuts K1 K1 are spaced apart by a full mesh of the expanded metal and each of the lengths L is accordingly one mesh, instead of half a mesh, wide.

The lengths of resistance material comprised in the zigzag path may be maintained in their desired mutual relationship by anchoring the U shaped selvedge portions to suitable parallel carrier members which may form part of a suit able carrier frame, the said U shaped portions tinuous or in short lengths and is threaded upon steel or other carrier Ix bars CR. In this way a whole series of elements integral with one another niay be carried from and insulated from a pair of parallel carrier bars, one passing through the holes A in one selvedge edge, the other passing through the holes A' in the other. Preferably the lengths L of resistance material are mounted under slight tension .50 as to reduce liability to distortion as a result of overheating. It has been found that by leaving the lengths of resistance material under slight tension when cold any tendency to bowing out of the lengths of material is avoided or at any rate reduced to unimportant minor proportions.

A multi-unit resistance in accordance with this invention is illustrated in Figures 1, 2 and 3 which show in three mutually perpendicular views a four unit construction.

Referring to Figures 1 to 3 the units are gen erally indicated by the references I, 2, 3 and 4 each unit consisting of a plurality of lengths or strips L of expanded metal resistance material chorage are made to carrier bars B which may.

be of steel and have insulation strips W laid thereon, the points of anchorage being further insulated in any convenient manner. For example, anchorage may be made at each point by means of a nut and bolt, the bolt passing through the bar B and being insulated therefrom by a surrounding insulating sleeve (not shown) insulating washers W beingalso provided so as to insulate the nut from the steel bar. Alternatively the points of anchorage between the Ushaped portions and the carrier bars B may be, and preferably are made by rivets with similar provision for insulation. The bolt type of anchorage is exemplified at A13 and the rivet type at AR. Stamped interconnecters I of U form connect each unit to its neighbour and the whole multi-unit structure is carried by end carrier rods GR in association with strip or bar members SM as clearly shown in Figure 3. It will be noted that in Figure 3 the members SM are shown bolted together at X and riveted together at Y. In practice, of course, either bolts or rivets can be used throughout, rivets being preferred. The drawings of Figure 3, however,

show both methods of construction in order to indicate that either may be used. As will be seen these bolts or rivets, as the case may be, mechanically connect the appropriate members 'SM by clamping them with the appropriate carrier bars B. The lead-in to the whole resistance unit is shown at LI and the lead-out at L0, and it will be apparent that all, four units are in series with one another.

When mounting and constructing the device the length Z (see Figure 2) is made somewhat longer than the normal unstretched length 0! a portion L-between the points of anchorage and thus the said portions are put under slight tension. 1

It will be appreciated that the cooling of a resistance or heater as shown and described will be extremely eflicient since there is great free- .dom for air flow. Furthermore, owing to the from the point of view of economy of construction, residing in the fact that since the cuts expanded metal in each portion L is either one mesh (that is to say one "diamond) or one half mesh wide, the invention is, of course, not limited to this, and the portion L may be more than one mesh wide, if desired; e. g. it might be one and a half meshes wide or two meshes wide and bent back on itself as described. Again, the invention may be embodied in multi-unit constructions wherein the individual units are not simply in series (as they are in the construction of Figures 1 to 3) for obviously parallel connection or series-parallel connection may be resorted to where-desired.

What I claim is:- e V 1. Method for making an electrical resistance or heater from a sheet of expanded metal having two oppositely disposed longitudinal unexpanded selvedges and a body portion of expanded metal therebetween, said method comprising cutting said expanded metal body portion to form a plurality of spaced substantially transverse slits of nearly zero width, adjacent slits bounding on two sides a substantially planar unit strip of ex- Again the whole conpanded metal, alternate slits extending through one and the same selvedge only and intervening slits extending through the other selvedge; then positioning said unit strips in a plurality of planes disposed respectively at an angle to the plane of the original sheet by bending the selvedge portion to which one end of each unit strip is connected upwardly relative to the plane of the original sheet, and bending the selvedge portion to which the other end oi. the strip is connected downwardly relative to the plane of the original sheet.

2. Method for making an electrical resistance or heater from a sheet of intermediate expanded metal having two oppositely disposed longitudinal unexpanded selvedges and a body portion of expanded metal therebetween, said method comprising cutting said intermediate expanded metal body portion to form a plurality of spaced substantially transverse slits or nearly zero width, adjacent slits bounding on two sides a substantially planar unit strip of expanded metal, alternate slits extending though one and the same selvedge only and intervening slits extending through the other selvedge; then positioning said relative to the plane of the original sheet, and

bending the selvedge portion to which the other end of the strip is connected downwardly relative to the plane of the original sheet.

'3. Method for making an electrical resistanceor heater from a sheet of expanded metal having two oppositely disposed longitudinal unexpanded selvedges and a body portion ofexpanded metal therebetween, said method comprising cutting said expanded metal body portion to form a plurality of spaced transverse slits of nearly zero width and being disposed at right angles to said selvedges, adjacent slits bounding on two sides a. substantially planar unit strip of expanded metal, alternate slits extending through one and the same selvedge only and intervening slits extending through the other selvedge; then positioning said unit strips in a plurality of planes disposed respectively at an angle to the plane of the original sheet by bending the selvedge portion to which one end of each unit strip is connected upwardly relative to the plane of the original sheet, and bending the selvedge portion to which the other end of the strip is connected downwardly relative to the plane of the original sheet.

4. Method for making an electrical resistance or heater from a sheet of expanded metal having two oppositely disposed longitudinal unexpanded selvedges and a body portion of expanded metal therebetween, said method comprising cutting said expanded metal body portion to form a plurality of spaced substantially transverse slits of nearly zero width, adjacent slits bounding on two sides a substantially planar unit strip of expanded metal, alternate slits extending through one and the same selvedge only and intervening slits extending through the other selvedge; then positioning said unit strips in a plurality of planes disposed respectively at an angle to the plane of the original sheet by bending the selvedge portion to which one end of each unit strip is connected upwardly through ninety degrees and bending the selvedge portion to which the other end of the strip is connected relatively downwardly through ninety degrees.

5. In a method as deflned in claim 1, spacing the substantially transverse slits so as to include between adjacent slits unit strips of expanded metal one-half mesh wide.

6. In a method as deflned in claim 1, spacing the substantially transverse slits so as to include between adjacent slits unit strips or expanded metal a plurality of half meshes wide.

7. Method for making an electrical resistance or heater from a sheet of expanded metal having two oppositely disposed longitudinal'unex'panded selvedges and a body portion oi expanded metal therebetween, said method comprising cutting said expanded metal body portion to form a pinrality oi spaced substantially transverse slits oi nearlyv zero width, adjacent slits bounding on two sides a substantially planar unit strip of expanded metal, alternate slits extending through one and the same selvedge only and intervening slits extending through the other selvedge; then positioning said unit strips in a plurality of planes disposed respectively at an angle to the plane of the original sheet by bending the selvedge portion to which one end of each unit strip is connected upwardly relative to the plane of the original sheet, bending the selvedge portion to which the other end of the strip is connected downwardly relative to the plane of the original sheet; and attaching unexpanded selvedge portions to insulated supporting means with said strips of,

expanded metal tensioned while cold.

8. An electrical resistance element comprising a one-piece unit of expanded metal material, said unit including a plurality of transversely extending substantially planar strips oi expanded metal and unexpanded mounting portions at the oppositeends of said strips, each unexpanded lying respectively in planes disposed at an angle to the plane containing the central sections of the mounting portions, and adjacent strips being connected togetherat one end bythe same mounting portion but being respectively connected at their other ends to diflerent mounting portions.

9. An electrical resistance element comprising a one-piece unit of intermediate expanded metal material, said unit including a plurality of transversely extending substantially planar strips of intermediate expanded metal and unexpanded mounting portions at the opposite ends of said strips, each unexpanded mounting portion including a central section and two flank sections on opposite sides thereof, the central sections of said mounting portions lying substantially in a common plane, each flank section oi each mounting portion having integrallyconnected thereto an end of one oi said strips of intermediate expanded metal, the flank sections at opposite ends of each strip extending respectively relatively above and below the plane containing the central sections, said strips of expanded metal lying respectively in planes disposed at an angle to the plane containing the central sections 01' the mounting portions, and adjacent strips being connected together at one end by the same moun ng connected thereto an end 01' one of said strips of expanded metal, the flank sections at opposite ends of each strip extendingrespectively relatively above and below the plane containing the central sections, said strips ofexpanded metal lying respectively in planes disposed at an angle to the plane containing the central sections of the mounting portions, and adjacent strips being connected together at one end by the same mounting portion but being respectively connected at their other ends to different mounting portions, the sum of the widths of each two strips of expanded metal being nearly equal to the distance between centers of the central sections of adjacent unexpanded mounting portions when said strips are arranged in substantial parallelism. i i

11. An electrical resistance element compris ing a one-piece unit of expanded metal material,

said unit including a plurality of transversely extending substantially planar strips oi expanded metal and unexpanded mounting portions at the opposite ends of said strips, each unexpanded mounting portion including a central section and two flank sections on opposite sides thereof the central sections of said mounting portions lying substantially in a common plane, each flank section of each mounting portion having integrally connected thereto an end 0! one of said strips of expanded metal, the flank sections at opposite ends of each strip extending respectively relatively above and belowand at right angles to the plane containing the central sections, said strips of expanded metal lying respectively in planes disposed at an angle to the plane containing the central sections of the mounting portions, and adjacent strips being connected together at one end by the same mounting portion but being respectively connected at their other ends to diil'erent mounting portions.

12. An electrical resistance element as defined in claim 8 in which the substantially planar strips of expanded metal are one-half mesh wide.

13. An electrical resistance element as defined in claim 8 in which the substantially planar strips I of expanded metal are a plurality of half meshes wide.

14. An electrical resistance element comprising a one-piece unit of expanded metal material, said unit including a plurality of transversely extending substantially planar strips 01' expanded metal and unexpanded mounting portions at the opposite ends 01 said strips, each unexpanded mounting portion including a central section and two flank sections on opposite sides thereof, the central sections of said mounting portions lying substantially in a common plane, each flank section 01 each mounting portion having integrally connected thereto an end of one of said strips of expanded metal, the flank sections at opposite ends 01 each strip extending respectively relatively above and below the plane containing the central sections, said strips of expanded metal lying respectively in planes disposed at an angle to the plane containing the central sections of the mounting portions, and adjacent strips being connected together at one end by the same mounting portion but being respectively connected at their other ends to different mounting p'ortions; and an insulated support connected to said unexpanded mounting portions and mounting said strips of expanded metal under tension when cold.

BENJAMIN HENRY NOEL HANS HAMILTON.

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