Electrically heated multi-section hose having electrically heated hose joints

A hot melt hose has multiple electrically heated hose sections physically and electrically interconnected end-to-end between a pressurized hot melt source and hot melt dispenser, such as a hand-held gun having a trigger-controlled valve for regulating the flow of hot melt from the gun. Each of the hose sections includes an inner, fluid impervious, chemically inert tube, preferably fabricated of tetrafuoroethlene; an electrically conductive multi-strand braided resistance heating sheath snugly embracing the exterior surface of the inner tube and in intimate heat transfer contact therewith for supplying strength and heat to the tube; and an outer sheath of thermal insulating material for minimizing heat loss. The hose sections are interconnected by a heated joint which comprises electrically conductive hose end fittings electrically connected to the braided sheath and connected by threaded swivel nuts to an electrical insulating fitting. Internally of the insulating fitting there is an electrical resistance heater spring which extends between and electrically interconnects the hose end fittings. The spring has an electrical resistance such that the flow of current from the braided sheath of one hose section to that of the other produces sufficient heat in the fitting so that the interior of the joint is maintained at approximately the same temperature as the interior of the hose sections.

This invention relates to a hot melt multi-section hose heating system, and 
more particularly to a heating system for a hot melt hose having multiple 
series-connected sections interconnected by a connector joint. 
Hot melt dispensing systems of the type with respect to which this 
invention is applicable typically include a source, or tank, of molten 
adhesive. The adhesive is maintained at a desired temperature in the tank, 
such as 350.degree. F. by a suitable thermostatically controlled tank 
heater. The molten adhesive is supplied under pressure by a pump to a 
dispenser via a hose. The dispenser may be a hand-held gun having a 
trigger-controlled valve for regulating the flow of hot melt adhesive from 
the gun. To avoid undesirable temperature drop in the hot melt adhesive 
between the time it is pumped from the tank and the time it is dispensed 
from the gun, the hose interconnecting the pressurized source of hot melt 
material and the dispenser is usually heated. 
As would be expected, the required length of hose between the pressurized 
source and the dispenser varies from one application to another. While it 
is possible to accommodate these different length hose requirements by 
connecting single hoses of different length between the tank and gun, it 
has been found more convenient to provide hose sections of some arbitrary, 
but fixed, length such as ten feet. Depending upon the length of hose 
required for a particular application, different numbers of these 
fixed-length hoses can be serially connected end-to-end to provide a 
multi-section hose of the desired length. 
A typical heated hot melt hose includes an inner tube through which the hot 
melt adhesive actually flows. This inner tube, which is in contact with 
the adhesive, is fluid impervious and chemically inert relative to the hot 
melt material. The inner tube additionally possesses certain other 
desirable characteristics such as strength, flexibility, electrical 
nonconductivity, and the like. A suitable material for the inner tube, 
exhibiting the foregoing characteristics, has been found to be 
tetrafluoroethylene. The hot melt hose also typically includes a single 
layer of stainless steel wire braid which surrounds the inner tube. The 
wire braid performs the dual function of providing structural 
reinforcement for the tube as well as serving as an electrical resistance 
heater for the tube along its length. For these reasons the single layer 
stainless steel wire braid reinforcement snugly embraces the outer surface 
of the inner tube as well as is in intimate thermal contact therewith. 
Surrounding the metal braid is a sheath of electrically nonconductive 
thermal insulating material for minimizing heat loss to the environment. 
In the past the sections of hose used in a given installation have been 
interconnected by conventional heat and electrically conductive metal 
joints. But, the only heat imparted to those joints was the heat conducted 
through the hose end fittings from the braided section of the hoses with 
the result that those hose joints were at a lower temperature than the 
adjacent braided hose sections. Consequently, the molten adhesive tended 
to cool in the course of passage through the hose joints, thereby creating 
a problem in maintaining the molten adhesive at an even temperature. 
It has therefore been an objective of this invention to provide an improved 
multi-section heater hose for transporting molten adhesive in which the 
adhesive is not cooled in the course of passage through the hose joints 
interconnecting the multiple sections of hose. 
Still another objective of this invention has been to provide a 
multi-section hose having an improved system for heating the hose 
throughout its length without the occurrence of any cold or cool spots 
throughout the length of the hose. These objectives are achieved and this 
invention is predicated upon the concept of heating the multiple sections 
of a multi-section hose via an electrical resistance braiding wrapped 
about the hose sections and heating the hose joint via an electrical 
resistance spring located internally of the joint to which electrical 
current is supplied via the hose braiding through electrically conductive 
hose end fittings in the end of the hose sections. The electrical 
resistance of the spring is chosen so that it imparts sufficient heat to 
the hose joint to maintain the adhesive at a fixed temperature or to melt 
solidified adhesive within the joint as a consequence of the same current 
flow through the spring as occurs through the hose braiding. Consequently, 
the construction results in a hose having a heated hose joint wherein 
there is no need for auxiliary electrical leads or power supplies to the 
heater of the hose joint. 
The primary advantage of this invention is that it provides a multi-section 
heated hose wherein the joints of the system are heated without the 
requirement for any additional electrical leads or auxiliary power 
supplied to the joint heater. This invention also has the advantage of 
utilizing hose swivel joints which are conventional except for the choice 
of materials of which this joint is manufactured. Consequently, no special 
tools, electrical wiring or other special arrangements are to be made when 
substituting the multi-section heater hose having heated hose joints of 
this invention for conventional heated hoses now in use in adhesive 
dispensing systems. 
In one particular application of this invention wherein the hose was 
maintained at a temperature of 350.degree. F., 28 amperes of current was 
passed from a constant current power source through the braided sheaths of 
the series-connected hose. This particular hose consumed a total power 
input of 48.6 watts per foot of hose to maintain the hose at 350.degree. 
F. The joints of this hose required a power imput of approximately 10 
watts to maintain an operating temperature of 350.degree. F. Therefore, a 
heater for the joint having a resistance of 0.013 ohms was required if the 
28 amperes power supply of the braided hose was to be used to heat the 
joint. A spring having this resistance and capable of operation at 
425.degree. F. without losing its resiliency was made by coiling 18-8 type 
302 stainless steel spring stock having a cross section 0.031 inches thick 
by 0.250 inches wide into a helical configuration approximately 0.290 
inches in outside diameter by 1.375 inches in length and at a pitch of 
approximately 3/8 inch. 
With the foregoing hose and joint configuration, the joint of the 
multi-section hose is heated from the same constant current power supply 
as is the braided hose. Therefore, there is no need for auxiliary 
electrical leads to the joint heater or for an auxiliary power supply 
different from that used to heat the hose sections.

With reference to the drawings, the system of this invention is seen to 
include a pressurized source 10 of hot melt adhesive which is equipped 
with a suitable thermostatically controlled heater (not shown) for 
maintaining molten adhesive at a desired temperature, such as 350.degree. 
F. Of course, by suitable adjustment of the heater the temperature of the 
molten adhesive in the tank 10 can be adjusted to any desired temperature 
compatible with the particular chemical composition of the adhesive. 
Also included in the system is a molten adhesive dispenser 12. The 
dispenser 12 can be of the hand-held variety, such as a gun, having a 
manually operated trigger 12a which controls a flow valve (not shown) in 
the gun for selectively regulating the flow of pressurized molten adhesive 
from the gun dispenser. Alternatively, the dispenser 12 may be of the type 
typically found in an automatic installation in which the dispenser is 
either stationarily mounted, such as in operative relation to a conveyor 
line on which articles move therepast for receiving shots of molten 
adhesive, or alternatively, movably mounted on a suitable motorized 
reciprocator under automatic control for applying molten adhesive to an 
article in a predetermined pattern. 
Interconnecting the dispenser 12 and the tank 10 is a multi-section hose 14 
consisting of individual sections 14-1, 14-2, . . . 14-n. The hose 
sections 14-1, 14-2, . . . 14-n are provided with suitable coupling 
elements 15 at their respective ends to facilitate serial interconnection 
between an outlet lOa of the tank 10 and an inlet 12b of the dispenser 12. 
The heating elements to be described, of the hose sections 14-1, 14-2, . . 
. 14n of the hose assembly 14 are connected in electrical series 
relationship with the output 16a of a regulated constant current power 
supply 16 via an electrical conductive connector 16b. The power supply 16 
is provided with a suitable control (not shown) which facilitates 
selectively varying the amperage output therefrom on line 16a to the 
heaters of the hose assembly 14 to, in turn, facilitate selectively 
varying the temperature at which the hose sections 14-1, 14-2, . . . 14-n 
of the hose assembly 14 are commonly maintained. 
In accordance with the preferred embodiment of the invention, at least one 
of the hose sections, such as section 14-1, includes an inner tube 18 
which is chemically inert and fluid impervious relative to the hot melt 
material passing therethrough from the pressurized hot melt tank 10 to the 
dispenser 12. A suitable inner tube 18 can be fabricated of 
tetrafluoroethylene resin extruded to form a smooth seamless tube having 
an inner tube diameter of approximately 0.313 inches with a wall thickness 
of 0.040 inches. Surrounding the inner tube 18 is a braided sheath 20 of 
electrically conductive resistance heating material. In a preferred form, 
the sheath 20 consists of 120 strands of braided wire having a one inch 
pitch. By reason of the pitch and braid diameter, the strands are 18.49 
inches per foot of braid. The wire strands are fabricated of 0.009 inch 
diameter 303 stainless steel, providing a resistance per strand per foot 
of braid of 7.44 ohms. With a braided sheath of the type described, the 
total resistance of the sheath per foot is 0.062 ohms. When input with a 
constant current of 28 amperes, a power consumption of 48.6 watts per foot 
results. 
The braided sheath 20 provides the dual function of supplying heat to the 
tube 18 for maintaining the temperature therein at some preset desired 
value, such as 350.degree. F. as well as providing the tube 18 with added 
structural strength against bursting. To maximize the strength and heat 
transfer provided to the inner tube 18 by the braided sheath 20, the 
braided sheath snuggly embraces the outer surface of the tube 18 with 
respect to which it is in intimate thermal contact. 
Surrounding the braided electrically conducting sheath 20 is a sheath 22 of 
thermal insulating material, such as silicone rubber sponge plastic 
material having a wall thickness of 0.500 inches. If desired, the thermal 
insulation sheath 22 can be provided with a polyester web outer jacket to 
enhance the abrasion resistance of the hose assembly. 
With reference to FIG. 2, there is illustrated the coupling or joint 15 for 
connecting the ends of two sections 14-1, 14-2 of hose 14. The joint 
comprises a pair of hose end fittings 26, an electrical insulating fitting 
27, and a pair of hose swivel nuts 28. Internally of the electrical 
insulating fitting there is an electrical resistance heating spring 30 
which, as explained more fully hereinafter, electrically interconnects the 
ends of the hose fittings 26 and heats the joint 15. 
Each of the hose end fittings 26 is generally tubular in configuration and 
has a pair of flanges 31a, 31b extending outwardly from its periphery so 
as to define an annular channel or groove 32 therebetween. One flange 31a 
is preferably hexagonal in configuration to facilitate grasping of the 
flange with a tool, such as an open end wrench. Each fitting 26 has an 
axial bore or flow passage 33 extending therethrough which is in fluid 
communication with the inner tube 18 of the hose section to which the 
fitting is secured. This bore 33 terminates in an outwardly flaring or 
tapered mouth 34 at the outer end of the fitting. 
Each fitting 26 is made of an electrically conductive material, as for 
example stainless steel, and is swaged or crimped onto the end of the 
braided hose so that the fitting is in physical and electrical contact 
with the end of the braided sheath 20 of the hose. 
The electrical insulating fitting 27 is also generally tubular in 
configuration and provided with an axial bore or flow passage 36 extending 
therethrough. Medially of its length, the fitting 27 has outwardly 
extending flange 37, which is preferably hexagonal in shape, to facilitate 
grasping of the fitting with a conventional tool such as an open end 
wrench. The fitting 27 is tapered at each end as indicated at 38, so as to 
facilitate interfitting with the inward taper 34 of the fitting 26. 
At each end, the insulating fitting 27 is peripherally threaded at 39 for 
the reception of the hose swivel nuts 28. These nuts each are made from 
steel or brass and have internally threaded sections 29 engageable with 
the threads 39 of the insulating fitting 27. The nuts also have inwardly 
extending flanges 40 engageable with the outwardly extending flange 31b of 
the hose end fittings 26. When the nuts 28 are threaded onto the threads 
39 of the insulating fitting 27, the nuts cause the mating tapered 
surfaces 38, 34 of the hose end fittings 26 and the insulating fitting 27 
to be moved into sealing engagement. 
The electrical insulating fitting 27 is preferably manufactured from 
aluminum, the complete interior and exterior surface of which is coated 
with a hard anodized surface coating. This coating acts as an electrical 
insulator to prevent the passage of electrical current through the 
fitting. 
Electrical current flows between the hose end fittings 26 of the two 
sections of hose 14-1, 14-2 interconnected by the joint 15 through the 
electrically conductive spring 30. This spring is made from a material 
which has an electrical resistance characteristic such that the flow of 
electrical current through the spring causes the spring to heat to a 
temperature sufficient to maintain the joint 15 at a preset temperature. 
In one particular embodiment of the invention wherein the constant power 
supply 16 supplies an electrical current of approximately 28 amperes 
through the braided sheath 20 and through the electrical resistance spring 
30, the spring material was chosen such that the spring 30 had a 
resistance of 0.013 ohms. At this resistance and current flow, the spring 
30 had a power consumption of 10 watts, the power necessary to maintain 
joint 15 at approximately 350.degree. F. operating temperature. The 
particular spring 30 which had this resistance and which was capable of 
operating at a temperature of 425.degree. F. without losing its 
resiliency, was made from an 18-8 type 302 stainless steel strip stock. A 
flat stainless steel strip stock approximately 0.013" thick by 0.250" wide 
was configured into a helical shape approximately 0.290" in outside 
diameter by 1.375" in length and having a pitch of approximately 3/8". 
This particular spring had the necessary power consumption to maintain the 
joint 25 at the desired 350.degree. F. temperature. 
In use, electrical current is supplied from the constant current power 
supply 16 to the multi-section hose 14 through electrical conductive 
connector 16b. This power supply is chosen to have a particular current 
output which, when supplied to the electrically conductive braided sheath 
20 of the hose, will cause that braided sheath to heat the hose to a 
preset temperature, as for example a temperature on the order of 
350.degree. F. That same current is caused to flow from the braided sheath 
through the hose fittings 26 through the electrically conductive spring 30 
to the next adjacent hose end fitting 26 and the braided sheath 20 of that 
next adjacent hose section 14-2, 14-n. In the course of passage through 
the electrical resistance material of which the spring 30 is made, the 
electrical current causes the spring to heat the electrical insulative 
fitting 27 to approximately the same temperature as the braided sheath 20 
heats the hose sections 14-1 through 14-n. As a consequence of this 
construction of the hose and the joint, the joint 15 is maintained at 
approximately the same temperature as the heated sections of hose with the 
result that there are no cool spots or cold joints located along the 
length of the hose 14. Consequently, material flowing through the hose is 
maintained at an even temperature and if the hose is allowed to cool, as 
for example between shifts or overnight, the multi-section hose may be 
more quickly reheated and brought up to temperature because of the 
presence of the spring heater 30 in joint 15. 
While I have described only a single preferred embodiment of my invention, 
persons skilled in this art will readily appreciate changes and 
modifications which may be made without departing from the spirit of my 
invention. For example, such persons will appreciate that I have described 
only a single modification of an electrical reisstance alloy spring 30 
utilized as a heater of a multi-section hose, but that other materials and 
other spring configurations could be utilized in such an electrical 
resistance heater to obtain the same temperature or differing temperatures 
in the same or different heated hose environments. Therefore, I do not 
intend to be limited except by the scope of the following appended claims: