Pipes and tubular conduits – Flexible – Braided – interlaced – knitted or woven
Reexamination Certificate
1999-07-22
2001-03-20
Hook, James (Department: 3752)
Pipes and tubular conduits
Flexible
Braided, interlaced, knitted or woven
C138S133000, C138S152000, C138S170000
Reexamination Certificate
active
06202701
ABSTRACT:
The present inventions relates to a hose for conveying free-flowing materials, in particular coating powder, consisting of an electrically non-conductive or poor conductive material.
Coating powders are usually conveyed pneumatically through plastic hoses from a reservoir to a spray gun. Friction of the powder particles at the hose inner wall may generate strong electrostatic charges on the inner side of the hose. Corresponding mirror charges are formed on the outer side of the hose, said mirror charges may at times become so strong that they cause disruptive discharges through the hose wall and/or discharges from the outer side of the hose to grounded parts of the coating assembly.
To avoid these undesired, sometimes dangerous effects, hoses made of an electrically conductive material were used for conveying coating powders. Hoses of this kind do, however, have the disadvantage that they have the tendency to form powder cake or sinterings on the inner wall of the hose, which in the worst case can fully obstruct the hose.
A hose of the described kind having an electrically non-conductive or poor conductive hose wall is known, integrated into which is a grounded wall member made of an electrically conductive material extending radially throughout the cross section of the wall (DE 31 45 702 A1, DE 12 76 207 U1). The object of the invention is to provide a hose of the above-mentioned kind, which does not generate electric discharges and which at the same time avoids the caking or sintering of powder material at the inner hose wall.
To accomplish this object a hose according to the present invention includes an electrically conductive wall member which is grounded on the outside and extends radially throughout the cross section of the hose, said wall member having a cross section with a large circumferential dimension at the outer surface of the hose wall, and a significantly smaller circumferential dimension at the inner surface of the hose wall.
It is especially advantageous when the wall member is formed sector-shaped, preferably triangularly like those found in the cross-section of a welding seam, wherein the apex of the triangle approximately coincides with the inner surface of the hose, and the base of the triangle approximately coincides with the outer surface of the hose.
In a hose according to the invention a favorable discharge of undesired charges is achieved towards the outside due to the friction of the free-flowing materials owing to the relatively large conductive surface on the outer side of the hose. Caking and sintering of the free-flowing material at the inner hose wall is practically excluded due to the minimized surface of the electrically conductive material on the inner surface of the hose.
In order to further reduce the risk of cakings or sinterings of the conveyed materials at the inner surface of the hose, the wall portion may be shaped preferably wedge-like as seen in its longitudinal extension, i.e. it may become progressively smaller in the longitudinal direction of the hose.
The electrically conductive wall portion preferably consists of a metal wire or a metal strand. Alternatively, the conductive wall portion can also consist of a plastic material that is made conductive by the addition of carbon. The electrically non-conductive material of the hose is, as known per se, a plastic material that is electrically non-conductive, preferably polyvinylchloride or polyurethane.
A hose according to the invention reliably conveys electrostatic charges generated in the hose by friction of the conveyed substances against the inner wall of the hose towards the ground without producing obstructive cakings or sinterings of the material on the inner side of the hose.
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patent: 3201507 (1965-08-01), Johnsen
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patent: 75 34 723 (1976-03-01), None
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patent: 31 45 702 (1983-05-01), None
patent: 32 02 854 (1983-08-01), None
Faegre & Benson LLP
Hook James
Wagner International AG
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