Hot Melt Glue Applicator

Abstract

A hot melt glue applicator including a console for housing controls and a tank containing hot melted glue and at least one glue carrying hose connected with an external glue gun. The device includes separate heaters for the tank, the hose and the gun, an improved solenoid pump for the gun, an automatic fluid pressure release device to prevent hose failure due to high expansion rate of the melting glue, and a pneumatic pump for pumping the glue through the glue carrying hoses to the gun in which seals and packings are eliminated.

Description

BACKGROUND OF THE INVENTION

This invention relates to an improved hot melt glue applicator. Paperboard cartons, corrugated cartons, book bindings and paper bags are commonly fabricated by means of glue which holds the seams and the sides of the various cartons or bags together. Experience has shown that it is best to use a glue which exists in the solid state at room temperatures since such glues provide more permanent and strong bonds for the cardboard or paper seams. To accomplish this hot melt glue applicator devices have been provided. Such devices normally include a heater tank adapted to receive glue in a solid particulate form, melt the glue and maintain it at a temperature which is appropriate for use. Normally, this temperature is between 250.degree. F. and 450.degree. F. A pump mechanism of some type is normally included to pump the glue from the heated tank through a hose to a glue applicator gun. The glue applicator gun is a nozzle arrangement adapted to discharge controlled amounts of glue at a controlled rate.

When operating at elevated temperatures with a viscous material such as glue, numerous problems are encountered. For example, because the melted glue expands in volume between 10 percent and 25 percent when changing from the solid to the liquid state, the glue carrying conduits, pump or gun may fail or burst unless some pressure release means is provided. Also, because the glue is normally a highly viscous substance, means for controlling and dispensing the glue from the applicator gun are difficult to provide. It is with problems of this sort that the improved hot melt applicator of the present invention successfully overcomes.

SUMMARY OF THE INVENTION

In a principal aspect the present invention is the improvement of means for mounting a liquid glue pump above a glue heater tank in a hot melt glue applicator of the type having a melt tank, a pump, and at least one glue gun connected with the tank by means of the hose means. The pump includes drain ports directed into the tank so that the glue leaking from the unsealed pump passes directly back into the tank. As an additional feature of the invention the glue gun includes improved solenoid means for dispensing glue in controlled amounts from the gun discharge orifice.

It is thus an object of the present invention to provide an improved hot melt glue applicator.

It a further object of the present invention to provide a hot melt glue applicator which substantially eliminates the problems caused by expansion of glue changing from the solid to the liquid state.

One further object of the invention is to provide an improved glue gun in combination with a hot melt glue applicator.

Still another object of the invention is to provide a glue applicator having a pump which does not require seals and packing.

These and other objects, advantages and features will be set forth in greater detail in the description which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

In the detailed description which follows reference will be made to the drawings comprised of the following FIGS.

FIG. 1 is a top plan view of the heater tank and console, attached glue hose and glue gun, the console having its cover removed;

FIG. 2 is a rear elevation of the unit set forth in FIG. 1;

FIG. 3 is a left-hand end view of the unit shown in FIG. 2;

FIG. 4 is a right-hand end view of the unit shown in FIG. 2;

FIG. 5 is an enlarged cutaway top view of the pump for the glue applicator system;

FIG. 6 is an enlarged cutaway cross-sectional side view of the pump shown in FIG. 5;

FIG. 7 is an enlarged cutaway cross-sectional view of the glue applicator gun of the invention;

FIG. 7a is an end view of the plunger for the gun of FIG. 7; and

FIG. 8 is a circuit diagram of the pneumatic system for the applicator.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The following description is directed to the mechanical components comprising the glue applicator of the invention. The electrical circuitry and control arrangement for the heater components is described in a copending application entitled "Glue Applicator Heater Circuit" by Theodore H. Davey, filed Sept. 17, 1968, Ser. No. 760,164. Thus, the description of the electronic components of this glue applicator system will be generally functional except where one skilled in the art may find difficulty practicing the invention. There, of course, the description will be more specific. However, the description of the mechanical components comprising the invention will be structurally and functionally described to clearly set forth the subject matter of the invention.

Therefore, referring to FIGS. 1 through 4, there is shown the complete applicator system. The components of the applicator are mounted on a frame 10. Positioned on the frame 10 and attached thereto by means of bolts 12 is a heater tank 14. The tank 14 is surrounded by insulating materials 16. Heater units 18 surround the tank 14 to provide heat for melting solid particulate glue material placed in the tank 14. A screen 20 is placed in a receiving receptacle at the bottom of the tank 14 in the path of a central melt discharge opening 22 at the bottom of the tank 14. Screen 20 serves to filter out materials which are foreign or unmelted before they pass into the pump assembly (described later). Various sizes of screen 20 may be utilized depending upon the glue being used, etc. The filter screen 20 may be removed by rotating or unscrewing the attached filter assembly handle 24 and lifting the screen from the tank 14.

Glue which has been melted in tank 14 passes through the opening 22 in the bottom of the tank 14, into a conduit 26 and finally into the pump assembly generally shown at 28. The pump assembly 28 is also maintained at a constant and controlled temperature by means of a heater element 30 positioned longitudinally along the assembly 28. Pump assembly 28 is driven by air motor 32. The liquified glue is pumped from the tank 14 through pump assembly 28 and into discharge glue hoses as at 34 and 36. An air supply conduit 40 provides air to drive the air motor 32.

A fluid pressure release cylinder 38 cooperates with the pump assembly 28 to provide a glue bypass for relief of pressure due to the expansion of the glue when changing from the solid to liquid state, or when cooling after the device is turned off. The air motor and relief cylinder controls and operation is more fully described below in relation to FIG. 5 and FIG. 8.

Control conduits as at 42 and 44 connect with separate glue applicator guns. Thus, glue hose 34 and control conduit 42 both connect with the same glue applicator gun. In the device illustrated, provision is made for the inclusion of four glue hoses and their corresponding control conduits and guns, a hose being connectable to nipple outlets 41a, 41b, 41c and 41d. Lead wires 43 from the heater and sensing elements for the tank 14, the control conduit lead wires as at 42, and lead wires as at 45 from the hose as at 34 all connect with the electronic control components positioned beneath the air motor 32. Power for heating the hoses and the separate glue guns is provided to each separate hose and glue gun; whereas, control leads are provided only to one hose 34 and its corresponding glue gun. It has been determined that sensing the temperature in one of the hoses and a connected gun is sufficient to control the temperature of all of the hoses and guns in the applicator since the characteristics of each hose and gun are all substantially identical. For this reason as illustrated in FIG. 1 the hose 34 and control conduit 42 include extra lead wires for the control circuitry. The control circuitry provides constant temperature readings and temperature settings in the tank 14, hose as at 34 and gun. Resistance heaters are used in each case.

Referring now to FIGS. 4 and 5 there is shown in greater detail the glue pump assembly 28. The pump assembly 28 is, of course, driven by the reciprocating type air motor 32. The pump assembly 28 includes a housing 46 which defines the cylinder of the glue pump. A piston rod 48 is connected by means of a coupling 50 to a reciprocating drive rod 52 of the air motor 32. The rod 48 rides in a bushing 54 threadably secured at one end of the housing 46. No seals are provided between the bushing and the rod since the pump assembly 28 is positioned over the tank 14 and a pair of drain ports 78 and 80 are provided which allow leakage of glue to flow back into the tank 14.

Attached to the end of the piston rod 48 is a valve stem 56. The valve stem 56 rides freely within a slidable piston sleeve 58 and seals against the sleeve 58 during the pressure stroke of the pump. A ball check valve 60 which leads from the conduit 26 and tank 14 is provided at the entrance to the cylinder of the housing 46. A second ball check valve 62 is positioned in an outlet opening 64 of the housing 46. Opening 64 leads to the nipple connections 41a-- d for the glue hoses.

Thus, as the piston rod 48 is drawn back into the air motor 32 causing the valve stem 56 to seat against the piston sleeve 58, glue is drawn into the chamber of the housing 46 and also forced through the second valve 62 and outlet 64 and ultimately into the hose 34 which is connected to the fitting 41a. On the return stroke the piston sleeve 58 rides back on the valve stem 56 permitting the glue to flow through openings in the piston sleeve and into the region traversed by the piston valve sleeve 58 as it moves forward.

A relief cylinder assembly 68 is attached to the pump assembly 28 and includes a piston rod 70 which is biased by means of air pressure through conduit 72 acting on piston 74. This piston is normally biased when the pump is being operated so that the piston rod 70 operates to close a bypass passageway 76. When the glue applicator is turned off, however, the air pressure acting on piston 74 is eliminated due to three-way poppet valve 75 in FIG. 8 which vents to the atmosphere. This permits the bypass passageway 76 to open and allowing expansion and contraction of the glue. The relief valve assembly 68 is thermostatically controlled by a thermoswitch 77 so that during heating of the glue when the glue expands, the relief valve assembly remains open to permit the glue in the hoses and pump to expand without rupturing the hoses.

Referring now to FIG. 6 there is shown the means by which glue leaking from the pump assembly 28 passes through the pair of drain ports 78 and 80 back into the tank 14. The amount of leakage is controlled by sizing the bushing 54 and piston rod 46. This allows some recirculation of the glue and eliminates a drip pan. A wall 82 defined in the housing 46 insures that excess leakage unable to drain down the port 78 will be retained in a pool defined by the wall 82 and will eventually drain down the drain port 78.

Referring now to FIG. 7 there is shown a typical glue hose and coil connected to a glue gun of the present invention. In particular a hose 34 connects with a fitting on a gun base 86. The hose consists of a tetrafluora ethylene tube covered by a stainless steel wire braid. A tape type heating element is wrapped around the wire braid and is covered by insulation. The entire assembly of the hose is enclosed in a fiber glass cloth tube.

The gun base 86 forms the framework upon which the gun assembly is constructed. Fluid glue passes through the hose 34 and through the discharge end of the gun base 86 into a nose piece 88. A cap 90 is attached to the nose piece 88 and holds a tip 92 in secure communication with the nose piece 88.

Positioned inside the gun base 86 is a spring biased plunger 94. Plunger 94 is biased by spring 96 so that the tip end 98 of the plunger 94 engages an orifice of an inner nose piece 100 which provides a path for fluid glue between the interior gun base and the orifice through the tip 92.

An electromagnetic coil 102 is positioned about the gun base 86. Upon activation of the coil 102 through coil leads 104, the plunger 94 is caused to rise permitting a flow of glue along the sides of the plunger, into the tip 92 and out of the orifice of the tip 92. In practice the plunger may be rapidly cycled up to 2,000 cycles a minute to permit glue flow through the tip 92 as required. The glue, of course, is under pressure up to 15,000 lbs. p.s.i. as provided by pump assembly 68.

The plunger 94 includes a central or axially disposed opening 106 for housing the spring 96 and also for receiving glue from the hose 84. The axial opening 106 is connected with the interior of the gun base 86 by means of a passageway 108 in the plunger 94.

The outer circumference of the plunger 90 includes four shallow flat portions 111 through 114 as illustrated in FIG. 7a. On the lower shank portion of the plunger 90 at the outside diameter, shank flat portions 116 and 117 are defined. This arrangement allows the fluid glue to flow down the sides of the plunger 94 and also makes four regions in which the volume between the plunger 94 and inside diameter of the gun base 86 is greater thus avoiding excessive fluid friction drag. Shank flats 116 and 117 also provide a region between the nose piece 88 and the lower part of the shank of the plunger 94 so that glue may easily flow from the tip 92. With a construction of this type the valve can be cycled at very high rates because of the low viscous drag. Rates up to 25,000 cycles per minute are thereby possible.

The upper end of the plunger 90 which engages the gun base 86 is also specially constructed. The upper end includes a narrow circular seat 91 having a reduced contact area between the plunger 90 and gun base 86. This has the advantage of providing a vacuum type breaking action when the electrical signal is removed from the coil 102. Thus, the spring 96 will quickly and firmly drive the plunger 94 to close the orifice of the tip 92.

A removable cover or housing 120 having an arm extended coil connection portion 122 is also provided for the gun. The arm portion 122 includes a cover 123 which may be removed to expose the connections between the various leads to the gun. Moreover, the housing 120 and arm 122 may be entirely removed and interchanged with another housing and arm, the other arm being repositioned in relation with the housing for alternative modes of clamping the gun in relation to an assembly line or another package making machine. Such an alternative mode is illustrated in phantom in FIG. 7.

An advantage of the gun construction described results from the fact that the fitting 85 is positioned at a 45.degree. angle to the top of the housing 120 and coil 102. Thus, the hose may be easily attached in the manner illustrated in FIG. 7. In addition, as illustrated by the phantom lines in FIG. 7 the gun base may be rotated and an alternative housing 120 and attached arm 122 may be used in cooperation with the hose 84 and the remaining components of the gun without breaking any fittings or connections in the glue passage line.

Within the arm 122 is a sensor lead 124 connected with a temperature sensor 126. Heater leads 128 connect to a circumferential heater element 130 positioned on the gun base 86. A shield 132 protects the heater 130 and also serves to keep heat contained within the shields 132. These leads connect with connectors in the conduit which leads back to the control circuitry described before.

FIG. 8 illustrates the pneumatic air diagram for the unit. Filtered, lubricated and pressure regulated air enters through supply conduit 40 and into poppet valve 75. From a T connector 136 a conduit 138 connects with the relief cylinder assembly 68. Another conduit 140 connects through regulator 142 to the air motor 32. A gauge 144 provides constant monitoring for the air pressure to the motor 32.

Claims

It is claimed:

1. In a hot melt glue applicator device of the type having a melt tank for holding and melting glue, a pump for pumping said glue from said tank, at least one glue gun for dispensing said melted glue, hose means connecting said tank with said gun, and temperature and pressure control means for controlling the temperature of said melted glue and the rate of discharge of said glue from said gun, the improvement comprising, in combination; means for mounting said pump above said tank, said pump including drain ports directed into said tank such that glue in said pump passes directly into said tank when leaking from said pump.

2. The device as set forth in claim 1 wherein said pump is a reciprocating piston type pump including a cylinder, a valve connection with said tank, a valve connection to said hose means, said piston being driven by a piston rod connected with an external motor, a bushing being provided for said piston rod in said pump, the clearance between the piston rod and the bushing allowing leakage through said bushing and said drain port directly back into said tank.

3. The hot melt glue applicator device of claim 1 including release cylinder means as adapted to bypass said valve connections positioned intermittent said pump and said hose means, said release cylinder means including means for automatically actuating when said applicator device is not being operated to relieve expansion and contraction of said melt when being heated or cooled respectively.

4. The device as set forth in claim 3 wherein said control means includes thermostatic control means for said release cylinder means operable to maintain said release cylinder means in an open position while said glue is being heated thereby to compensate for expansion of said glue changing from a solid to a liquid state.

5. The improvement as set forth in claim 1 wherein said glue gun includes a solenoid with a plunger having at least one flat side on its outside diameter to allow fluid to flow down the side of said plunger and out an orifice of said gun disposed axially of said plunger, said plunger operative in response to said solenoid to alternately open and close said orifice thereby discharging said glue through said orifice.

6. In a hot melt glue applicator system of the type having a melt tank for holding and melting glue, a pump for pumping said glue from said tank, at least one glue gun for dispensing said melted glue, hose means connecting said tank to said gun, and temperature and pressure control means for controlling the temperature of said melted glue and the rate of discharge of said glue from said gun, the improvement comprising in combination; a glue gun including a solenoid with a plunger, said plunger having at least one flat side on its outside diameter to allow fluid to flow down the side of said plunger and out an orifice of said gun disposed axially of said plunger, said plunger operative in response to said solenoid to alternately open and close said orifice thereby discharging said glue from said orifice.

7. The improvement as set forth in claim 6 wherein said plunger has four shallow flats on its outside diameter for allowing fluid glue to flow thereby avoiding excess viscous drag.

8. The improvement as set forth in claim 6 wherein said gun includes a removable cover adapted to enclose said temperature and pressure control means on said gun and which also provides a clamping surface to mount said gun.

9. The improved device as set forth in claim 6 wherein said conduit is connected with said gun by means of a 45.degree. fitting interconnected with said hose means.