CH673786A5 - - Google Patents

Description

673 786

PATENT CLAIM Electrostatic spray gun with an insulating body to which a handle is attached and in which there is a paint supply channel that ends in a spray nozzle made of plastic material attached to the insulating body, which also forms the valve seat of a needle valve, the valve needle of which is made of plastic material a valve rod is seated, which runs through the paint supply channel and on the end means of a sealing arrangement facing away from the spray nozzle can be displaceably and displaceably protrudes out of the insulating body, a high-voltage electrode being arranged in the paint supply channel and a metal part coming into contact with it upstream of the high-voltage electrode being provided for earthing the paint flow , characterized in that the sealing arrangement (5, 6, 7) and the part of the valve rod (8) passing therethrough consist of high-voltage-resistant insulating material and that the metal part as a lacquer insertion piece (20) is one is made of plastic material paint supply hose (19) is connected to the spray nozzle (13) facing away from the end of the paint supply channel (24).

DESCRIPTION

The invention relates to an electrostatic spray gun according to the preamble of the claim. By reducing the current flowing back to the earth, it is possible to spray dyes with low resistance or metal pigment content (lacquers giving a metal effect) electrostatically with high effectiveness.

It is known that the rear metallic part, which is used to hold the electrostatic spray gun, in the case of a manual execution of the metal handle, must be earthed in accordance with the safety regulations. In the embodiment already considered traditional, this holding part, the handle, is continued into a cylindrical body made of some insulating material. The high-voltage electrode is built into this insulating material body, which charges the lacquer material which is passed through the channel formed in the insulating body by direct contact or indirectly via the air. The paint material channel is closed by means of a valve or opened for the spraying process. The valve can be placed in the handle itself or in the vicinity thereof; in this case the channel section following the valve is open to the front of the spray nozzle. If the valve is now in the closed state, the outflow of the lacquer material located in this channel section is prevented exclusively by the capillarity and the vacuum that may have arisen; the paint material should not actually drip out of the nozzle. However, in spite of all measures, it may happen that a small amount of dye emerges from the nozzle opening due to the effect of thermal dilation, mechanical movement or vibration, as a result of which the spray head and the spray cap provided with fine bores are contaminated, which causes both the electrostatic effect and the fineness of atomization may be impaired.

In order to avoid these shortcomings, the valve is arranged directly behind the outlet opening in the nozzle in more modern embodiments.

In this embodiment, the long valve rod made of insulating material runs in the middle of the straight dye channel and its front conical part enters the opening of the nozzle which widens to form a valve seat, as a result of which the paint material channel is blocked off immediately behind the outlet opening and in this way the front the duct section lying on the valve and filled with paint material, which is also open after the valve is closed, is omitted.

In this embodiment, a metal rod connects to the rear 5 part of the long rod made of insulating material; In view of the fact that this rod is sealed with a stuffing box, from which the escape of the liquid is prevented, the valve can be operated from the outside. The metal rod that is brought out is in contact with the end of the paint material channel that is closer to the handle, specifically where the paint flows into the channel of the insulating material body. In view of the fact that the handle is grounded, the metal rod in contact with the paint material forms the grounded point of the paint material channel.

The high voltage electrode, which is also in contact with the paint material, is closer to the front end of the paint material channel. The coating material is electrically charged by means of this electrode. However, since the coating material itself 20 has a low electrical conductivity, the current flows from the high-voltage electrode via the coating material channel to the grounded location, which results in a loss. If the resistance of the coating material is low, a relatively large amount of electricity flows to the earth. 25 For safety reasons, the generator supplying the high voltage is designed in such a way that a maximum of 0.2-0.7 mA current can be generated even in the event of a short circuit; at the same time, the high voltage drops to zero. The current flowing through the paint material channel to earth can significantly increase the load on the generator, as a result of which the voltage can drop significantly, but this entails the decrease in the electrical charge of the atomized paint material; with coating materials with very low resistance, there is even no need for charging. If the 35 color effect is caused by grains or pigments in the paint material - these paint materials are known under the name "metallic effect paints" - it can happen that these metal particles form a chain in the electrical force field formed in the channel and a total short circuit cause. 40 The current flowing to earth via the paint material channel can be reduced by keeping the resistivity of the paint above a predetermined limit or by modifying the channel dimensions; this means that the cross-section is reduced and the channel is lengthened. The last 45 method mentioned is based on the application of the relationship relating to the ohmic resistance, the value 1 / q, where 1 denotes the channel length and q the cross section. The channel dimensions can only be changed to a significant extent if the paint material valve is arranged in the vicinity of the handle, since the narrowed cross section substantially reduces the flow rate; The lengthening of the channel can only be carried out in such a way that the originally linear channel is transformed into a wave or spiral. Otherwise the 55 tubular body of the spraying device would have to be extended to a multiple of the original length. However, the valve rod can only be guided in a straight channel.

According to the current state of the art, such methods for lengthening the channel are known in which the 60 channel is formed after the lacquer valve formed in the handle by a plastic tube which runs inside the insulating tube body in a spiral or corrugated line and the front of which End to the nozzle through which the paint flows out, is connected and the high-voltage electrode is arranged in the middle. In this way, the length of the channel between the electrode and the grounding point is extended to about 1 m, while in the aforementioned solution this length is max. Can be 0.1m.

673 786

At the same time, however, the length of the insulating tubular body - which is approximately 0.15-0.2 m - remains unchanged. The most contemporary solutions are currently widespread in the passenger car industry and are used in particular for spraying paints which cause metallic effects.

However, there is still a lack in this system

that the paint channel, in which a considerable amount of liquid paint is now accumulating, is open to the outlet nozzle. In this way, the risk of paint dripping out is much greater when the paint valve is closed.

The object of the invention was to develop a system in which the advantages of the extended paint channel made of a plastic tube and the valve built into the nozzle and blocking the path of the paint at the nozzle are combined.

The solution according to the invention is defined in the patent claim. the insulating tube is preferably formed, has good insulating properties and is provided with a corresponding wall thickness. All these requirements are met with a tube made of e.g. B. meets polyethylene. Such a tube has a metallic inlet connection which is connected to the handle in a metallic manner and forms the grounding point of the paint channel system.

Another advantage of the proposed solution is that the extension of the paint channel formed by the insulating tube lies outside the spray device, which means that the tube is replaced in the event of a blockage, in contrast to the previous embodiments in which the tube forming the channel extension is installed in the insulating body , is relieved.

The invention is explained in more detail using an advantageous exemplary embodiment, with the aid of the drawing.

The single figure shows a spray gun according to the invention in longitudinal section.

In a grounded metal handle 1 there is an air valve 2 which can be opened by pulling an operating lever 3. By opening the valve 2, the compressed air supplied via the connecting piece flows via a channel 15 formed in the insulating body 4 from a space delimited by a plastic cap 14 via an annular opening 16 and atomizes the paint flowing out of the circular nozzle opening 17. The paint passes from a container 26 under compressed air through a hose 27 and a metal nozzle 20 fastened in a metal bracket 21,

a long plastic tube 19 bent into a circle and a plastic socket 18 into the insulating body 4 or into a lacquer channel 24 formed there, which can be shut off at the front by means of the plastic needle valve 8 in the nozzle 13. When the operating lever 3 is actuated, a metal rod 9 is moved backwards with the aid of a spring plate 10 against the force of a spring 11; as a result, the front conical end of the long insulating rod 8 opens the paint outlet opening 17 of the nozzle 13. The electrical charging of the paint is ensured by a high-voltage generator 28 via a high-voltage cable 29 via the high-voltage electrode 12, which is built into the paint channel 24 is.

The lacquer channel 24 formed in the insulating body 4 is pressure-tight and pressure-tight along the valve rod 8 against the earthed handle 1 or 25, the metal rod 9 connected thereto in metallic fashion via the lip seal 5 made of high-voltage-resistant insulating material and the elastic rings 7 present in the plastic stuffing box 6 High voltage isolated completed. In this way it can be ensured that the current can flow from the high-voltage electrode 12 via the insulating connector 18 and the long plastic hose 19 to the metal connector 20 which is in metallic connection with the handle 1 and which forms the grounding point of the paint channel.

M

1 sheet of drawings