Electrostatic spraying devices with hazardous condition warning

Details Electrostatic spraying devices with hazardous condition warning Electrostatic spraying devices with hazardous condition warning

1997-03-21

1999-08-03

Chin, Peter

Coating apparatus

With means to apply electrical and/or radiant energy to work...

Electrostatic and/or electromagnetic attraction or...

118620, 118621, 118300, 118663, 118668, 118707, 118708, 118712, 239691, 427458, 427475, 427483, B05B 5025

Patent

active

059320117

DESCRIPTION:

BRIEF SUMMARY
This invention relates to electrostatic spraying devices.
In spraying certain objects, problems may arise if an imbalance of electrical charge occurs between the object and the device since there is a risk of an electrical discharge which could result in the operator receiving an electrical shock and/or the production of a hazardous situation if flammable solvents are present (eg as part of the formulation being sprayed). The risk can be minimised by ensuring that there is good electrical continuity between the device and the object being sprayed, for instance by making an electrical connection to the object to provide an earth return path between the object and the device.
According to a first aspect of the present invention there is provided an electrostatic spraying device provided with contact means for providing a primary charge return path between the device and an object to be sprayed. and means for testing a circuit established between the device and the object to be sprayed.
The testing means may be constituted by means for determining the resistance or impedance of the circuit so established.
The testing means may be arranged to detect charge return to the device via the primary charge return path; preferably however the testing means is constituted by means for detecting charge return to the device via routes other than the primary path.
According to a second aspect of the present invention there is provided an electrostatic spraying device provided with contact means for providing a primary charge return path between the device and an object to be sprayed. and means for detecting charge return to the device via an operator holding the device.
Preferably the device also includes means for producing an output signal in response to detection of charge returning via routes other than said primary path.
In this way, the existence or otherwise of a secure and effective primary charge return path can be established. If an effective primary charge return path is not established, there will be a tendency for charge to return to the device via other paths. For instance, in the absence of an adequate primary charge return path. as spraying proceeds charge will build up on the object being sprayed and tend to repel further electrically charged spray droplets which, in turn, may deposit on the operator with consequent return of charge to the device via a route other than the primary path.
Detection of charge return via routes other than the primary path allows detection of an inadequate primary path and other conditions in which the return of spray current via the primary charge path is affected. The existence of a defective primary charge return path may be attributable to an inadequate connection being made to the object. Other conditions that may result in charge return via routes other than the primary path include: overspraying in which deposition of charged spray on to objects other than the intended target occurs; and spraying carried out by an operator wearing insulating footwear.
Thus, for example, if the earth return path is defective as a result of an inadequate connection with the object to be sprayed. this can be detected and signalled to the operator during spraying; if appropriate. the defect can then be remedied before spraying continues to the point where a substantial charge imbalance develops.
The contact means for providing the charge return path conveniently includes an electrical conductor in the form of a lead terminating in connector means for connection to a convenient site on the object to be sprayed.
To provide additional security, the conductor lead preferably comprises twin conductors connected between the device and the connector for attachment to the object to be sprayed so that the two conductors form a loop in such a way that. if one conductor is damaged with consequent impairment of the integrity of the primary charge return path, the break in the loop can be detected and a warning produced and/or spraying terminated automatically.
The conductor or conductors of the contact

REFERENCES:
patent: 3851618 (1974-12-01), Bentley
patent: 3894272 (1975-07-01), Bentley
patent: 4586657 (1986-05-01), Johnson et al.
patent: 4682735 (1987-07-01), Mommsen
patent: 5138513 (1992-08-01), Weinstein
patent: 5397605 (1995-03-01), Barbieri

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