GB1595396A - Apparatus for coating surfaces of objects with pulverulent substances - Google Patents

Description

(54) APPARATUS FOR COATING SURFACES OF OBJECTS WITH PULVERULENT SUBSTANCES (71) We, INSTITUT FRANCAIS Du PET ROLE, a body corporate organised and existing under the laws of France, of 4 avenue de Bois-Preau, 92502 Rueil-Malmaison, France, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The invention relates to apparatus for coating surfaces of objects with pulverulent substances, and is more particularly concerned with improvements in or modifications of the invention of our earlier Patent No. 1,517,598 (hereinafter referred to as 'the main patent').

The main patent is directed to an apparatus for depositing a homogenous layer of a pulverulent substance on a surface of an object, the apparatus comprising processing means arranged to subject the pulverulent substance to a sudden pressure drop and to deliver a pulverulent fluid formed by solid particles of the substance suspended in a carrying gas, a storage chamber connected to receive the pulverulent fluid from the processing means, means for spraying said particules of the pulverulent fluid, a pipe connecting the spraying means to the storage chamber, and means for controlling the flow of pulverulent fluid in said pipe.

Due to the use of a storage chamber, the apparatus according to the main patent is perfectly suitable for a substantially continuous operation, even when the supply of the pulverulent substance is discontinuous.

A preferred embodiment of the present invention described hereinbelow comprises a simplified version of the apparatus described in the main patent, this simplified version being particularly suited to discontinuous operation, although its continuous operation is not excluded.

According to the present invention there is provided apparatus for coating a surface of an object with a homogeneous layer of a pulverulent substance, the apparatus comprising a processing device arranged to subject the pulverulent substance to a sudden pressure drop and to deliver a pulverulent fluid composed of solid particles of the pulverulent substance suspended in a carrying gas, the device having therein a passageway for the pulverulent substance, a spraying device for spraying the particles of the pulverulent fluid, a pipe connecting the processing device to the spraying device, and a receptacle, open at its upper portion, for receiving the pulverulent substance, the processing device being positioned above the bottom of the receptacle with said passageway extending substantially vertically.

The invention will now be further described, by way of exemplary and non-limiting example, with reference to the accompanying drawings, wherein: Figure 1 diagrammatically shows apparatus embodying the invention; Figure 2 illustrates means for processing a pulverulent product, which means forms part of the apparatus of Figure 1; and Figure 3 shows in more detail an embodiment of a receptacle for the pulverulent product, such receptacle forming part of the apparatus of Figure 1.

As in the main patent, and for sake of a better understanding of the following description, there is considered, by way of example, the case where the apparatus embodying the invention is used for coating the surface of a plate with a protective layer formed from powdered TEFLON (trade mark for polytetrafluoroethylene).

This plate is indicated by the reference P in Figure 1, which diagrammatically shows the whole apparatus embodying the invention.

This apparatus comprises the combination of three main elements: a receptacle 1 for the pulverulent product, fed from a storage tank, a device 2 for processing the pulverulent product, placed just above the receptacle 1 and delivering a pulverulent fluid consisting of particles of the pulverulent product suspended in a carrying gas, and a device 3 for spraying the solid particles of pulverulent product onto the surface of the plate P, the spraying device 3 being connected to the processing device 2 by a pipe 4.

The spraying device 3 will not be described in detail and may be of any known type. In particular, the device 3 may comprise a socalled 'electrostatic gun' (sold in particular by such firms as SAMES and RANSBURG) and so devised as to electrically charge the solid particles of the pulverulent product by means of an electrostatic generator (not shown) to which the gun is connected. Preferably, and as shown in Figure 1, the spraying device 3 comprises a gas inlet connected to a pipe 23 delivering a pressurised gaseous fluid, such as the carrying gas, providing for a regular spray of the pulverulent fluid.

Figure 2 is a cross-sectional view of the processing device 2 which creates a pressure drop to which the pulverulent product is subjected.

The device 2 comprises a tubular body 5 arranged vertically and provided at its upper part with means for connecting it to a pipe 4, which means may comprise, for example, a thread 6. From the bottom to the top of Figure 2, the body 5 comprises a bore 7 of large diameter, extended by a convergent conical section 8 having an apex angle 25, followed by a cylindrical portion 9 of smaller diameter at most equal to the inner diameter of the pipe 4. Inside the body 5, in the section of larger diameter, is placed a tubular element 10 whose bore 11 has a diameter at most equal to that of the cylindrical portion 9.

The upper end of the element 10 has a conical external surface 12, converging in the same direction as the conical portion 8, and whose apex angle 2z is smaller than the apex angle 28.

The element 10 is secured to the body 5, for example by means of a thread 13 and a locking nut 14. The body 5 and the element 10 define between their conical portions an annular groove 15 opening into the cylindrical bore formed by the cylindrical portions 9 and 11, through an annular slot 24 of width e.

A source (not shown) of pressurised gas, such as compressed air, is connected to the annular groove 15 by a pipe 16, one end of which is secured to the body 5 and communicates with space 15.

At the lower end of the device 2 is secured an element 17 diverging towards the bottom of the ligure and whose action will be explained later.

Figure 3 shows a preferred embodiment of the receptacle 1, with which is associated a tank portion 18 for storing the pulverulent product, this tank portion being defined between a wall 19 and an intermedlate wall 2 placed above the bottom 21 of the receptacle at a certain distance x therefrom. A vibrating system 22, of any known type, is fastened to the bottom 21 of the receptacle 1.

When using the apparatus, the device 2 is placed above the receptacle 1, with the element 17 at a distance xl, slightly greater than x, above the bottom 21.

The starting up and the operation of the apparatus involves the following sequential steps: a) the amount of pulverulent product required for coating the surface of the plate P to be processed is introduced into the tank portion 18 of the receptacle 1; b) the spraying device 3 and processing device 2 are fed simultaneously with pressurised gas, such as compressed air, through pipes 23 and 16, respectively, and the spraying device is energised. The flow of air from the annular groove 15 to the pipe 4, through the slot 24, as shown by arrows in Figure 2, creates, in the lower part of the device 2, a reduced pressure zone which is delimited by the element 17.

c) the vibrating system 22 is then actuated, thereby transferring the pulverulent product from the tank portion 18 to a position just below the element 17. The pulverulent product is then sucked up into the processing device 2 and subjected to the action of the reduced pressure which disaggregates the agglomerates of pulverulent product and, at the outlet of the device 2, there is obtained a pulverulent fluid consisting of particles of pulverulent product in suspension in the carrying gas. This fluid flows through the pipe 4 and is then sprayed by means of the device 3, the air fed through the pipe 23 forming a steady jet resulting in the formation of a uniform deposit on the surface of the plate P.

When the whole amount of pulverulent product has been consumed, the compressed air, which continues to flow, provides for a complete and efficient cleaning of the device 2, the pipe 4 and the spraying device 3.

Advantages of the above-described apparatus are those of a simple design, resulting in a limited bulk, and the automatic cleaning resulting from the flow of the carrying gas in the absence of pulverulent product, this cleaning being made easier by the fact that no part of device 2 is in the flow path of the pulverulent fluid.

In addition, it should be noted that the relative position of the receptacle 1 and device 2 avoids any likelihood of blocking of the latter by a large agglomerate which would have not been disaggregated by the action of the reduced pressure.

Modifications may be made to the above described embodiment without departing from the scope of the invention. In particular, it is possible to make use of a control device, not shown in the drawings, whereby the vibrating system 22 is actuated only when the apparatus is fed with pressurised gas. Preferably, such a control device would also make possible to discontinue the supply of pressurised gas only after a certain delay has elapsed after the operation of the vibrating system 22 has been stopped.

In the case where the apparatus is adapted for continuous operation, it would be possible to provide for continuous or periodic feeding of the receptacle 1 with pulverulent product by any automatic or manual transfer means.

WHAT WE CLAIM IS: 1. Apparatus for coating a surface of an object with a homogeneous layer of a pulverulent substance, the apparatus comprising a processing device arranged to subject the pulverulent substance to a sudden pressure drop and to deliver a pulverulent fluid composed of solid particles of the pulverulent substance suspended in a carrying gas, the device having therein a passageway for the pulverulent substance, a spraying device for spraying the particles of the pulverulent fluid, a pipe connecting the processing device to the spraying device, and a receptacle, open at its upper portion, for receiving the pulverulent substance, the processing device being positioned above the bottom of the receptacle with said passageway extending substantially vertically.

2. Apparatus according to claim 1, wherein the processing device comprises a substantially vertical tubular body provided at its upper part with means for connecting it to said pipe and whose bore comprises at its upper part a first cylindrical portion of a diameter at most equal to that of said pipe, at its lower part a second cylindrical portion whose diameter is larger than that of the first portion and, in its intermediate part a conical portion for connection of the two cylindrical portions, the processing device also comprising a tubular member placed and maintained inside said second portion of the bore of said body, said member having a bore of a diameter at most equal to that of the first portion of the bore of said body, and having at its upper part an external conical surface which delimits, with the conical portion and a section of the second cylindrical portion of the bore of said body, an annular groove communicating, through an annular slot, with the upper portion of the bore of said body, said groove communicating also with a source of pressurised gas through a pipe having one end secured to said body.

3. Apparatus according to claim 2, wherein the external conical surface of said tubular member has an apex angle smaller than that of the conical portion of the bore of said body.

4. Apparatus according to claim 1, claim 2 or claim 3, wherein the processing device comprises an element delimiting a reduced pressure zone, said element having a hollow conical shape widening out downwardly and being secured to a lower portion of the processing device.

5. Apparatus according to any one of the preceding claims, wherein the receptacle comprises a wall maintained at a certain distance above the bottom of the receptacle and dividing the receptacle into two compartments, a first of the compartments forming a storage tank for the pulverulent substance and the processing device being placed above the second compartment at a distance from the bottom of the receptacle at least equal to that separating said wall from the bottom of the receptacle, and transfer means for transferring the pulverulent substance from the first to the second compartment.

6. Apparatus according to claim 5, wherein the transfer means comprise a vibratory system capable of subjecting said receptacle to vibratory motions in a direction parallel to the bottom of the receptacle.

7. Apparatus according to claim 5 or claim 6, that comprises a control device whereby said transfer means can be operated only when the processing device is fed with pressurised gas.

8. Apparatus according to claim 7, wherein the control device is operative to stop the supply of pressurised gas to the processing device only after a certain delay time has elapsed after stopping of the operation of the transfer means.

9. Apparatus according to any one of the preceding claims, which comprises means for feeding the receptacle with the pulverulent substance.

10. Apparatus for coating a surface of an object with a homogenous layer of a pulverulent substance, the apparatus being substantially as herein described with reference to the accompanying drawings.

11. A method of coating a surface of an object with a homogeneous layer of a pulverulent substance, in which there is used apparatus according to any one of the pre

Claims (1)

1. ceding claims.

   12. An object having a surface coated with a homogeneous layer of a pulverulent substance by a method according to claim 11.