Coating apparatus – With treatment of coating material – Of recirculated coating material
Patent
1992-09-02
1994-08-16
Ball, Michael W.
Coating apparatus
With treatment of coating material
Of recirculated coating material
118300, 2391022, B05B 108, B05C 500
Patent
active
053383605
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a device for use in applying a liquid material consisting of a solder paste, a glue or another viscous liquid or liquid dispersion in discrete small quantities to selected points on a substrate, for instance an electric circuit board.
More particularly, the invention relates to such a device of the kind comprising a supply of said material, an outlet, connected to said supply by means of a conveying conduit, and means for intermittently forcedly discharging the material in successive small quantities through the outlet and applying each such quantity to a selected point on a substrate, placed in front of the outlet and movable in relation thereto.
2. Description of Related Art
Devices of the above kind are previously known which, similar to the device according to the invention, are primarily intended to be used for applying a solder paste or an electrically conductive glue on electric circuit boards before placing components intended to be surface mounted thereon, but which, similar to the device according to the invention, may be used also for applying other viscous liquids or liquid dispersions on any suitable kind of substrate.
A troublesome disadvantage of these known devices has been found to be that, both during the use of the devices as well as, and above all, during interruptions in their use, a sedimentation may easily occur in the conveying conduit extending between the supply and the outlet. This sedimentation may result in that the material discharged through the outlet will have quite another composition than intended. Moreover, the sedimentation in the conveying conduit may also cause heavy cloggings in said conduit, especially in the case of extended breaks in the use of the devices.
SUMMARY OF THE INVENTION
The invention has for its purpose to provide a new and improved device of the kind initially specified which avoids the above disadvantages of the known devices in a favourable manner.
The device, according to the invention proposed for the above purpose, is primarily characterized in that the conveying conduit is formed as a closed loop which contains means for feeding the material in a circulating flow therethrough and past the outlet which comprises a discharge opening, provided in the wall of the conveying conduit and through which the material may be discharged in successive small quantities by the aid of means for intermittently transiently increasing the internal pressure in the conveying conduit within a zone thereof, located in the vicinity of the discharge opening.
By forming the conveying conduit in the above manner, it is possible, in an easy manner, effectively to eliminate the risk of a sedimentation of the material within the conveying conduit, existing in the known devices. Thus, the invention makes it possible to ensure that the material discharged through the outlet will have the desired composition and that any clogging will not occur in the conveying conduit, even after longer breaks in the discharge of material through the outlet.
The continuous circulation of the material in a closed loop within the conveying conduit also causes a certain homogenization of the material. In order to intensify this homogenization, the means serving to feed the material through the conveying conduit may advantageously be arranged to subject the material to a homogenizing mechanical treatment when it passes said means. For this purpose, the feeding means may preferably be formed by a screw pump or a gear pump.
In order to counteract any tendency of the material to adhere to the conveying conduit, this conduit may suitably be provided with an internal liquid repellent coating which for instance may consist of polytetrafluoroethylene. Alternatively, the entire conveying conduit may consist of a liquid repellent material.
Moreover, in order to make it possible to place the substrate at a longer distance from the outlet than otherwise possible, the outlet may lead into an ejector nozzle by which the
REFERENCES:
patent: 4667877 (1987-05-01), Yao et al.
patent: 4828886 (1989-05-01), Hieber
Ball Michael W.
Crispino Richard
Qenico AB
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