EP0125771A2

EP0125771A2 - Method and apparatus for sealing welded seams of automobiles

Info

Publication number: EP0125771A2
Application number: EP84302241A
Authority: EP
Inventors: Larry Soutar
Original assignee: Nordson Corp
Current assignee: Nordson Corp
Priority date: 1983-05-11
Filing date: 1984-04-02
Publication date: 1984-11-21
Also published as: ES532415A0; ES8504521A1; CA1214363A; JPS6041568A; EP0125771A3

Abstract

The invention relates to a system for applying sealant material to the welded seams of an automobile body. The apparatus of the invention includes a reciprocating piston pump for supplying the material under pressure from a reservoir to an overhead distribution manifold. From a manifold the material is supplied to a plurality of extrusion guns through drop lines, each of which includes a volumetric metering gear pump for maintaining a constant flow rate to said guns irrespective of pressure changes which may occur in the distribution manifold.

Description

This invention relates to the sealing of welded seams of automobile bodies wherein finishing requirements dictate that the welded seam be covered with a sealant either before or after the body is primed and painted.
At the present time, some form of welded seam sealer is used to cover and protect very nearly every welded seam or joint of an automobile body. This seam sealer is applied for purposes of excluding water or air, preventing leaking, and combating corrosion. Presently, most commercial sealers comprise a vinyl plastisol or epoxy that is pumped via a reciprocating piston pump to a manually operated extrusion gun. Depending upon the volume of material consumed, the sealant is supplied either from a 55 gallon drum operable to feed a manifold system to which multiple guns are attached, or the sealant material is supplied from a five gallon can operable to supply only a single extrusion gun.
Prior art commercial welded seam sealant systems have generally been unsatisfactory because of large variations in the amount of deposit supplied to a seam. The problem is particularly acute at the beginning or end of each application when the flow control valves of the hand guns used for applying the sealant are opened or closed. Each opening and closing of the valves of the extrusion guns results in pump surges and pressure fluctuations which in turn cause wide flow variations of sealant pumped from the guns. Because of these wide flow variations, operators tend to apply excessive amounts of material in order to insure adequate coverage of all areas of the seams. This excessive application of material results in a messy or sloppy appearance which detracts from the quality and appearance of the resulting welded seams. In addition, the excess material commonly washes off in the phosphate paint priming wash and becomes redeposited on exterior surfaces of the automobile thereby causing paint blemishes in the resulting product. In addition, the excess sealant material frequently contaminates the paint primer system.
For some time now automotive company engineers have been engaged in an extensive effort to find some means for providing a constant bead of sealant material with a predictable uniform size which would apply a complete covering of the welded ` seam without any excess of visible sealant material to mar the appearance of the finished product and contaminate subsequent finishing operations. To that end, those engineers have attempted in one instance to solve the problem by inserting fluid pressure regulators into each extrusion gun supply system immediately upstream of each of the extrusion guns. Those pressure regulators though did not solve this problem, primarily because the viscosity of the material was too great for regulators to operate effectively.
Still another attempt which has been made, but which has so far proven to be a failure, has been the use of a sealant tape cut to length and manually placed into the various welded seams. This tape sealant approach has proven to be too expensive to be practical because of the expensive form in which the sealant is delivered, i.e., the tape. Additionally, the tape requires significantly greater labor time to apply than is required to apply liquid through an extrusion gun.
It is therefore the general object of this invention to provide an improved method and apparatus for applying sealant to a welded seam of an automobile so as to effectively cover that seam without the use of excessive sealant material.
This object is achieved in accordance with the invention by using a metering gear pump in the sealant supply system to each of the extrusion guns of an automobile welded seam sealant applicator system, so as to accurately meter and control the volumetric deposition of sealant material from the gun. The sealant material may be either a hot melt sealant which is solid at room temperature and applied in a molten state or a cold unheated sealant. In either event, the metering gear pump in the supply systems to each of the extrusion guns elimintes pressure surges and uneven flow variations from the bead of material applied by the extrusion guns. Thereby, only so much sealant is applied to.a welded seam as is required to adequately cover that seam without the application of excess material.
Hence sealer redeposition in the phosphate wash or in the primer paint system is mainly avoided.
In one preferred embodiment, the system for applying the sealant to the welded seam of an automobile comprises a 55 gallon drum from which sealant material is pumped by a conventional reciprocating piston pump. This reciprocating piston pump supplies the sealant material to an overhead manifold line from which there extends a plurality of drop lines. Each drop line terminates in a manually or a robotic operated extrusion gun. According to the practice of this invention an electric motor driven metering gear pump is connected to each of the drop lines so that sealant is supplied to each of the extrusion guns through a metering pump at a fixed and constant pressure without any pump surges or pressure fluctuations. Thereby, an even and precise amount of sealant is extruded from each gun at a predetermined and accurately controlled rate.
The invention will now be further described by way of example with reference to the accompanying drawing which is a partially diagrammatic illustration of an embodiment of a sealant application system in accordance with the invention for applying sealant to welded seams of an automobile.
With reference to the drawing there is diagrammatically illustrated a system 10 for applying sealant to the welded seams of an automobile body and chassis 12. In general, all of the welded seams of an automobile body must be covered with a sealant material to exclude water or air and to combat corrosion. This sealant is either applied before or after the welding of the seams and either before or after any primer paint or any preparatory coating treatment of the body.
The apparatus generally indicated at 10 comprises a reciprocating piston pump 14 for pumping sealant material 16 from a drum or container 18 to a distribution manifold 20. This manifold generally extends parallel to an automobile production line 13 and is operative to supply pressurized sealant from the pump 14 to a plurality of drop lines 22 through which the sealant is distributed to multiple extrusion guns 24 located along.the production line. The guns 24 are illustrated herein as being of the manual type controlled from a manually operated trigger 26. One suitable gun is disclosed in U.S. Patent No. 4,245,759. The guns could as well though be automatically operable guns controlled and moved relative to the body by robots.
There is associated with each drop line 22 a volumetric metering pump 30. Each pump 30 comprises a two-speed DC motor driven gear pump. Since the gear pumps 30 and the motor M for driving the gear pumps are conventional commercially available items, they have not been illustrated or disclosed in detail herein.
The reciprocating piston pump 14 is a conventional pneumatic motor driven reciprocating piston pump. It may be either a single acting or a double acting pump, i.e., a pump which pumps on one of two strokes or pumps on both strokes. If the sealant material 16 is a hot melt material then a heated platen 40 will be suspended beneath the pump to heat and melt the hot melt sealant material which is solid at room temperature. One appropriate heated platen is disclosed in U.S. Patent No. 4,227,069. Alternatively, if the sealant is a cold sealant, i.e., liquid at room temperature, then the heated platen will be omitted and the pump 14 inlet simply inserted into the cold sealant 16 contained in the 'drum.
Irrespective of whether the pump 14 is single acting or double acting, there are pressure surges or variances associated with the reciprocation of the piston of the pump. At the end of each cycle of the piston there are conventional presssure drops. Heretofore, it has been the practice to supply the sealant material directly from the pump 14 to the extrusion gun 24 without the presence of any volumetric metereing pumps 30. As a result, pressure changes effected by reciprocation of the piston of the pump were transmitted through the distribution manifold to the gun. Those pressure changes resulted in varying flows of material from the gun. Additionally, pressure changes occurred whenever one gun of a plurality of guns operated from a common distribution manifold was opened or closed to initiate or terminate dispensing of adhesive material from that gun. These pressure changes, irrespective of their source, resulted in varying flow rates from the guns. The use of volumetric metering pumps upstream of the gun in each drop line 22 has been found to eliminate the pressure and flow variance which have heretofore been characteristic of automobile welded joint sealer systems.
The metering pumps 30 are conventional motor driven gear pumps such as the gear pump disclosed in U. S. Patent No. 4,009,974. In one preferred embodiment, this pump is motor driven by a two speed DC electric motor M. The use of a two speed motor has been found to be desirable if that motor is controlled from the trigger 26 of a manually operated gun 24 because it enables the operator of the gun to increase or decrease the rate at which material is dispensed from the gun in accordance with the needs or requirements of the application. Specifically, it has been found that when applying sealant with a manual gun to a straight welded seam, high speed application may be employed, but when applying the sealant to a rounded corner, a slower speed is required in order to effect complete coverage of the seam without application of excessive sealant material. Robot controlled guns may use an even greater number of motor speeds to drive the metering pump 30.
In use, the reciprocating pump 14 is actuated when the system is turned on and before the valves of any of the extrusion guns are opened. This results in viscous sealant material being supplied at a pressure substantially above that of the atmosphere from the drum 18 into the distribution manifold 20 and from the distribution manifold 20 through the metering pumps 30 to the extrusion guns 24. When the trigger 26 of a gun 24 is actuated so as to open the valve V contained internally of the gun 24, the motor M for driving the gear pump 30 is actuated and sealant material is dispensed from the gun at a controlled volumetric rate for so long as the trigger remains open. That rate will remain constant irrespective of any pressure fluctuations which may occur in the distribution manifold 20 because of the presence of the motor driven gear pumps 30. If more sealant is required, as for example because the gun is being moved at a fast rate over a straight section of welded seam, greater quantities of sealant may be obtained by adjusting the trigger 26 of the guns 24 to secure high motor speed. This trigger is preferably connected via a conventional electric control circuit to the motor M of the gear pump 30 so that by controlling the trigger, the actuation and speed of the motor M is controlled. The control circuit which connects the trigger 26 of each of the guns 24 to the associated motor M of the metering pump 30 through which a sealant is supplied to the gun 24 is a conventional electrical control circuit which could readily be supplied by a person skilled in this art. Accordingly, it has only been diagrammatically illustrated and represented by the dashed line 42 and the box labeled CC.
In lieu of a manual gun 24, the sealant may be dispensed from a conventional robot controlled automatic gun. In that event, the control circuit CC would be a part of a programmed control for the automatic gun, the robot, and the motor M for driving the metering pump 30 or a clutch operable between the motor M and the metering pump 30 for controlling actuation of the metering pump 30.
It will be appreciated that in some applications it may be desirable to insert a pressure regulator in line 22 between the distribution manifold 20 and the metering gear pump 30 to drop the liquid pressure to an acceptable inlet pressure for the particular gear pump 30.

Claims

1. Apparatus for dispensing viscous sealant material onto a welded seam of_an automobile, comprising a distribution manifold connected to a plurality of extrusion guns by a plurality of drop lines, and a primary pump for supplying sealant to the distribution manifold, characterised in that a plurality of volumetric metering pumps (30) are provided each of which is motor driven, and is operatively connected to one of the drop lines (22) so as accurately to control the rate of flow of sealant from the distribution manifold (20) to one of the said extrusion guns (24).

2. Apparatus as claimed in Claim 1 wherein the said primary pump (14) is a reciprocating piston pump.

3. Apparatus as claimed in Claim 1 or 2 wherein each of the said volumetric metering pumps is a motor driven gear pump.

4. Apparatus as claimed in Claim 1 or 2 wherein each of the said volumetric metering pumps is driven by a DC electric motor.

5. Apparatus as claimed in Claim 4 wherein each of the _DC electric motors is a two speed electric motor.

6. Apparatus as claimed in any of the preceding claims wherein each extrusion gun (24) is a manually operated gun having a valve, which is controlled by a trigger (26) associated wth said gun.

7. Apparatus as claimed in Claim 5 wherein each of said _DC electric motors is a variable speed motor, and in which a trigger (26) is provided controlling both the speed of said DC electric motor and a valve for the gun.

8. A method of applying sealant material to a welded seam of an automobile, comprising supplying sealant material from a bulk sealant reservoir to a distribution manifold at a pressure substantially greater than that of the atmosphere, supplying the sealant material from the distribution manifold to a plurality of sealant dispensing extrusion guns, each of the extrusion guns containing a flow control valve, and metering the flow of sealant material from the distribution manifold.to each of the said extrusion guns by means of a motor driven metering pump so as to maintain an even flow of sealant material from the said extrusion guns upon actuation of the said flow control valves irrespective of pressure changes which may occur in said sealant material contained in the distribution manifold.