Electric Band Heaters

Abstract

Electric band heaters wherein a heater includes resistance wire wound on an insulating strip sandwiched between two other insulating strips, the heater being sandwiched between an open strap and an open band which is engageable with a peripheral surface to be heated. Sheet metal loop brackets are spot-welded to the opposite ends of the strap and a headed screw extends through a rod in one bracket and is threaded into a rod in the other bracket for tensioning the strap. Folded over side and end portions of the band engage outer and inner surface portions of the strap to connect the strap and the band for installation together and to provide a sealed connection while allowing free tensioning movement of the strap independently of the band, to tightly press the strap against the heater and the heater against the band and the band against the surface to be heated.

Description

This invention relates to electric band heaters and more particularly to heaters which are readily installed and which are highly efficient in transferring heat while being very reliable and economically manufacturable.

BACKGROUND OF THE PRIOR ART

Electric band heaters are known in which an electric heater is positioned between inner and outer members with tensioning means being provided for tensioning the outer member, or both the inner and outer members, to press the inner member tightly against a surface to be heated, usually the outer surface of a pipe.

In one type of construction, as exemplified in the Desloge Pat. No. 2,545,653, an outer member is provided having means at the ends thereof adapted to be drawn together and having a jumper plate between the ends thereof which is apertured for receiving terminals projecting from the ends of the heater adjacent the ends of the inner member. This type of construction has been used extensively and has an important advantage in that tensioning of the outer member is effective to press the heater against the inner member which, in turn, is pressed against the surface to be heated, thereby providing good heat transfer. Also, as disclosed in the Desloge patent, the outer member may have a lower coefficient of thermal expansion than the inner member and the pipe which is heated, the result being that as the temperature is increased, the applied pressures and thereby the heat transfers are increased. However, this type of construction presents difficulties with respect to installation. Except in cases in which the heater can be slipped on from the end of a pipe, it is necessary that the ends of the outer member be disconnected while the inner member and the heater are placed in position, after which the outer member is installed and its ends connected and pulled together. This procedure is cumbersome, especially when the pipe and thereby the heater are of large sizes.

In another type of construction, the inner and outer members are held together as by folding side edge portions of the inner member over side edge portions of the outer member. The ends of the two members are effectively joined together and are moved together, tensioning both at the same time. For example, the ends of the outer member are looped back on themselves over rods connected by bolts, while the ends of the inner member are folded back over plates welded to the looped ends of the outer member at the inside thereof. With this type of construction, a unit is provided which can be readily installed but it is not possible to obtain the advantageous pressure engagement obtainable with the construction of the Desloge patent, and it is not possible to effectively use an outer member of a low thermal expansion material and to obtain the advantages thereof, the inner and outer members being effectively connected together at the sides and at the ends.

The prior art constructions are also difficult and expensive to manufacture, especially with regard to providing heaters of various sizes, different diameters being required for different sizes of pipe and different axial lengths being required for different applications.

BRIEF SUMMARY OF THE INVENTION

This invention was evolved with the general object of overcoming the disadvantages of prior art constructions and of providing electric band heaters with which heat is transferred with a high degree of efficiency and which are highly reliable, readily installed and economically manufacturable.

In an electric band heater constructed in accordance with the invention, heater means are provided which preferably include a resistance wire wound on a strip of mica and sandwiched between two additional strips of mica. The heater means are sandwiched between an open band and an open strap on the outside of the band, with tensioning means being provided for pulling the opposite ends of the strap toward each other to effect tensioning movement of the strap and to clamp the heater means against the band and the band against the peripheral surface of an object to be heated, such as a pipe.

According to a very important feature, the openings the the open band and the open strap are aligned, the opposite end portions of the strap being adjacent the opposite end portions of the band, and the strap and the band are connected to permit installation together as a unit, the strap and the band being bendable outwardly together to allow them to be slipped onto a pipe from one side. At the same time, the connection between the strap and the band is such that the end portions of the strap are freely movable toward each other and is such as to permit free tensioning movement of the strap independently of the band. With this combination, the heater can be readily installed and, at the same time, highly efficient heat transfer is obtained, the heater being pressed tightly against the band and the band being pressed tightly against the pipe when the strap is tensioned.

Important specific features of the invention relate to a construction such that a sealed connection is provided, protecting the heater, while at the same time permitting ready installation and allowing the advantageous free tensioning movement of the strap. In accordance with these features, side edge portions of the band extend outwardly and thence toward each other over side edge portions of the strap and end edge portions, at the opposite ends of the band, extend outwardly and thence away from each other in engagement with inside surface portions of the strap.

Additional important features relate to the provision of tensioning means such that tensioning of the strap to the degree required is facilitated while, at the same time, the heater is readily and economically manufacturable. In accordance with these features, a pair of brackets are provided each in the form of a loop of sheet metal including a C-shaped intermediate portion and end portions converging from the ends of the C-shaped portion into flush engagement, the end portions being spot-welded to each other and at least one of the end portions being spot-welded to ths strap. Rods are disposed in the transverse openings defined by such brackets and a screw has a shank portion extending through an opening in one of the rods and threaded into an opening in the other of the rods. Tensioning is facilitated, it being only necessary to turn the head of the screw, as contrasted with turning the head of a bolt while holding a nut stationary, or vice versa. Manufacture of the heater is facilitated because the strap can be cut to any length and width required for a particular application after which the brackets, which can be separately fabricated and of uniform size, can be spot welded to the strap. In the case of wide straps, required in some applications, a plurality of brackets can be spot-welded to each strap end in side-by-side relation and a plurality of screws can be so tightened as to obtain uniform tensioning of the wide strap.

This invention contemplates other objects features and advantages which will become more fully apparent from the following detailed description taken in conjunction with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a side elevational view of an electric band heater according to the invention, shown installed on a pipe which is shown in cross-section;

FIG. 2 is a top plan view, on an enlarged scale, of a portion of the heater of FIG. 1;

FIG. 3a is a cross-sectional view taken substantially along line III--III of FIG. 2;

FIG. 3b is a partial enlarged cross-sectional view of the electric hand heater taken substantially along line III--III of FIG. 2; and

FIG. 4 illustrates a modified arrangement.

DESCRIPTION OF A PREFERRED EMBODIMENT

Reference numeral 10 generally designates an electric band heater constructed in accordance with the principles of the invention. In general, the heater 10 comprises an open band 11, an open strap 12 and electric heater means, hereinafter described, connected to terminals 13 and 14 for connection to an electric power source. Opposite ends of the open strap 12 are detachably connected by tensioning means 15, the arrangement being such that the heater 10 can be installed on a pipe 16 as illustrated in FIG. 1. The heater 10 can be slipped on the end of the pipe 16 or, in some cases, can be installed from the side with the heater 10 being opened to a position as shown in dotted lines in FIG. 1. For installation from the side, however, a modified construction shown in FIG. 4 is preferred, as discussed hereinafter. After disposition on the pipe 16, the ends of the strap 12 are connected through the tensioning means 15, then operated to securely clamp the heater 10 to the pipe 16.

Reference numeral 18 generally designates the heater means which comprises a resistance wire 19 wound on a strip of insulating material 20 and sandwiched between an outer strip of insulating material 21 and an inner strip of insulating material 22. The strips 20-22 are preferably of mica but other insulating materials could be used.

The heater means 18 are sandwiched between the band 11 and the strap 12 which is provided with openings through which the terminals 13 and 14 extend, such openings being large enough to allow movement of the strap 12 relative to the terminals 13 and 14. Terminals 13 and 14 are connected to the ends of the resistance wire 19 in conventional fashion.

An important feature relates to a connection between the band 11 and the strap 12 such that they can be installed together as a unit while at the same time, the strap can be moved freely relative to the band during tensioning of the strap. The band 11 has side edge portions 23 and 24 which are folded to extend outwardly and thence inwardly toward each other over side edge portions of the strap 12. During tensioning movement of the strap 12, the edge portions thereof may slide relative to the edge portions 23 and 24 of the band, engaged therewith. In addition, the band 11 has end edge portions 25 and 26 at its opposite ends which are folded to extend outwardly and thence away from each other, such end edge portions of the band 11 being engaged with inward surface portions of the strap 12, adjacent the ends thereof. As the strap is tensioned, the ends thereof slide relative to the end portions 25 and 26 of the band 11 and as the tension increases, pressure is applied from the strap 12 to the outer strip 21, from the outer strip 21 to the strip 20 and wire 19, from the strip 20 and wire 19 to the inner strip 22, from the inner strip 22 to the band 11 and from the band 11 to the pipe 16. Also, the pressure between the strap and the portions 25 and 26 increases and as a result of such pressure engagement and the engagement between the side edge portions 23 and 24 and the strap, a sealing engagement is obtained which is effective to protect the heater means 18 from contaminants which might short-circuit turns of the resistance wire 19 or otherwise interfere with the proper operation of the heater means.

Additional important features relate to the construction of the tensioning means 15. A pair of brackets 27 and 28 are provided which are in the form of loops, including intermediate generally C-shaped portions 29 and 30, inside end portions 31 and 32 and outside end portions 33 and 34, the inside end portions 31, and 32 and the outside end portions 33 and 34 being converged from the ends of the C-shaped intermediate portions 29 and 30 into flush engagement. Spot welds 35 and 36 secure the outer end portions 33 and 34 to the inner end portions 31 and 32 and additional spot welds 37 and 38 are provided to secure the inner end portions 31 and 32 to the strap 12 at points spaced from the terminal ends of the strap 12. Preferably, the inner end portions 31 and 32 are longer than the outer end portions 33 and 34, as illustrated.

The brackets 27 and 28 define transverse openings in which a pair of rods 39 and 40 are disposed, each having a central opening therethrough, the opening through rod 39 being indicated by reference numeral 41 and the opening through rod 40 being indicated by reference numeral 42. A screw 44 is provided having a shank portion 45 extending through the opening 41 which is not threaded and threaded into the opening 42 which is threaded internally for this purpose. A head portion 46 of the screw 44 engages the rod 39 adjacent the opening 41 thereof, rod 39 being preferably provided with a planar surface for engagement by the head portion 46. Brackets 27 and 28 are provided with clearance openings 47 and 48 for projection of the head and shank portions of the screw 44 therethrough.

With this arrangement, the tensioning of the strap 12 can be accomplished simply by turning the head 46 of the screw 44. The illustrated bracket construction greatly facilitates manufacture in that the strap 12 can be cut to the length and width required for a particular application and the brackets can be separately made with a uniform size to be spot-welded in place after the strap is cut to the proper size. It is noted that in some applications, the heater and hence the strap must be of a width substantially greater than the width of the illustrated heater which has only one pair of brackets. In such cases, a plurality of brackets can be spot-welded to each strap end in side-by-side relation, for connection by a plurality of screws in a manner such that uniform tensioning of the strap can be accomplished.

As above described, the heater 10 can be installed on the pipe 16 from one side with the heater being opened to a position as shown in dotted lines in FIG. 1. When the heater is so opened, there is a possibility of damage from undue distortions of the parts and a binding action therebetween, so that it is preferable to slip the heater onto the end of the pipe. In many cases, however, it is inconvenient or impossible to slip the heater on from the end, as where the heater is to be positioned a considerable distance from an accessible end of the pipe or where the pipe is already installed with the ends thereof being inaccessible. In such cases, to insure against the possibility of damage, a modified construction of FIG. 4 may be used in which the band 11 and the strap 12 are, in effect, cut at a point diametrically opposite the tensioning means 15 and connected by an assemply 50 having a construction substantially identical to that of the tensioning means 15, the heater means being also effectively cut into two sections, one being connected to terminals 13 and 14 and the other being connected to a second pair of terminals 51 and 52. In installation, the assembly 50 provides a hinged connection permitting the heater to be readily opened to be slipped onto the side of the pipe, after which the parts of the tensioning means 15 are joined by the screw 44 which is then turned to apply tension.

It will be appreciated that when the screw 44 is tightened, the strap 12 is tensioned to press against the heater 18 which is pressed against the band 11, the band 11, in turn, being pressed against the pipe 16. Thus highly effecient heat transfer can be obtained. The construction permits use of a low expansion alloy material, i.e., a material having a low coefficient of thermal expansion, for the strap 12, which is preferably of such a material while the band 11 may be of ordinary sheet steel having a coefficient of thermal expansion similar to that of conventional steel pipe. As the temperature of the pipe and heater increases, the pipe and the band expand to a greater degree than the strap 12 of low expansion material, thereby increasing the pressure and the efficiency of heat transfer.

This invention thus provides electric band heaters which are comparatively simple in construction and economically manufacturable while being readily installed and highly efficient and reliable in operation.

It will be appreciated that modifications and variations may be effected without departing from the spirit and scope of the novel concepts of this invention.

Claims

I claim as my invention:

1. In an electric band heater, an open band of flexible metal for disposition around a peripheral surface to be heated with opposite end portions of said band adjacent each other, an open strap of flexible metal outside said band and having opposite end portions spaced from each other and adjacent said opposite end portions of said band, electric heater means sandwiched between said band and said strap, said heater means comprising first and second thin strips of insulating material respectively engaged with the inside surface of said strap and the outside surface of said band, a third thin strip of insulating material, resistance wire wound on said third strip, said resistance wire together with said third strip being sandwiched between said first and second strips, electrical terminal means connected to opposite ends of said wire, tensioning means for pulling said opposite ends of said strap toward each other to effect tensioning movement fo said strap and to apply pressure from the inner surface of said strap to the outer surface of said first strip, from the inner surface of said first strip to said wire and the outer surface of said third strip, from said wire and the inner surface of said third strip to the outer surface of said second strip, from the inner surface of said second strip to the outer surface of said band and from the inner surface of said band to said peripheral surface, and connecting means connecting said strap to said band for installation together as a unit, said connecting means being arranged to allow substantially free movement of said end portions of said strap toward each other independently of said end portions of said band and substantially free tensioning movement of said strap independently of said band, said connecting means comprising side edge portions of said band extending outwardly and thence toward each other outside and against said edge portions of said strap, said side edge portions of said strap being slidable relative to said side edge portions of said band during tensioning movement of said strap, said tensioning means comprising a pair of sheet metal loop means on said opposite end portions of said strap, each of said loop means including an intermediate C-shaped portion defining a transverse opening and end portions converging from ends of said C-shaped portion into flush engagement with each other, weld means securing said end portions together, a pair of rods in said transverse openings, and screw means interconnecting said rods for drawing said rods together and tensioning said strap.

2. In a heater as defined in claim 1, said opposite end portions of said band being formed to extend outwardly and thence away from each other in engagement with inner surfaces of said opposite end portions of said strap for relative slidable movement during tensioning movement of said strap.

3. In a heater as defined in claim 2, said side edge and opposite end portions of said band being in sealing engagement with said strap to protect said heater means while allowing said free tensioning movement of said strap.

4. In a heater as defined in claim 1, said band being of sheet steel and said strap being of a low expansion alloy material.

5. In a heater as defined in claim 1, said loop means being defined by a pair of brackets separate from said strap, and spot weld means securing said brackets to outer surfaces of said opposite end portions of said strap at points spaced from the terminal ends thereof.

6. In a heater as defined in claim 1, each of said rods having an opening therethrough, and said screw means comprising a screw having a shank portion extending through the opening in one of said rods and threaded into the opening in the other of said rods and having a head portion engageable with said one of said rods.