NL1037176C2

NL1037176C2 - Explosion proof electronic device and method of manufacturing such a device.

Info

Publication number: NL1037176C2
Application number: NL1037176A
Authority: NL
Inventors: Jan Marinus Geluk
Original assignee: J M Geluk Beheer B V
Priority date: 2009-08-05
Filing date: 2009-08-05
Publication date: 2011-02-08

Description

Title:

Explosion proof electronic device and method of manufacturing such a device

Field of the invention 5 The present invention is directed to an explosion proof electronic device, said device comprising electronics which electronics are comprised by a housing, wherein said housing comprises at least one opening for enabling access to an interior of said housing.

In addition, the present invention is directed to a method of 10 manufacturing such an explosion proof electronic device as mentioned hereinabove.

Background of the invention

Explosion-proof electronic devices, such as lighting devices for offshore applications and heavy industry, are widely used in locations where fire safety 15 is of major importance such as oil refineries, drilling platforms, etc. Electrical installations in such applications should often comply with the ATEX guidelines issued by the European Union. The ATEX guideline applies to all locations where there is a risk of explosions; it has been in force since 1996. The guideline relates not only to the risk of gas explosions, but also, for example, to the risk of dust 20 explosions, and applies to apparatuses and other electrical systems. The object of these guidelines is to safeguard the health and safety of personnel working in such locations. ATEX is short for the French expression "atmosphère explosive" and refers to explosive atmospheres, the definition of which is: a mixture of combustible substances in the form of gases , vapours, mists and dust under atmospheric 25 conditions in which a combustion process after ignition will spread over the entire as yet not combusted mixture.

Explosion protection techniques are classified into Ex and EEx classes under the ATEX guidelines. Among the Ex classes that can be distinguished there is, for example, Ex e, which is a classification for equipment that is designed 30 such that its components cannot cause any sparks or high temperatures in normal use and that it is insulated from its surroundings. The equipment should in addition be impact-resistant so as to be able to withstand as much as possible any external forces released in the case of an emergency.

Another explosion protection is classified sub Ex d, wherein a 1037176 2 device is provided with a pressure-resistant envelope such that components that cause sparks or high temperatures in normal use and that may come into contact with the explosive atmosphere inside the device cannot cause combustion or explosion outside the pressure-resistant envelope.

5 The explosion safety techniques classified under Ex m serve to ensure that potentially flammable components are encapsulated or encased in a moulding compound. The flammable atmosphere is thus separated from the flammable components while at the same time the surface temperature of the encapsulated components can be kept under control.

10 In Ex m class explosion proof electronic devices of the prior art, often the moulding substance used for encapsulating the electronic is a resin. This has several disadvantages. Not only the electronics encapsulated by the resin become inaccessible for maintenance, but also the use of a resin for electronic devices that produce a large amount of heat does not take away the hazard of 15 explosion due to contact between flammable components and air. In fact, due to (frequent) thermal expansion of the electronic device encapsulated by the resin, fractures and small cracks may develop in the resin making the encapsulation not completely airtight.

Another approach used in prior art is the use of a gel instead of a 20 resin. A gel is a liquid substance with a high viscosity. Because of the liquid nature of the gel, fractures or cracks in the gel will not occur. A disadvantage of using a liquid substance such as a gel, is that a gel is not very shock proof and may leak from the device over time.

25 Summary of the invention

The present invention seeks to provide a solution to the above mentioned problems of the prior art, and to provide an explosion proof electronic device having a long lifetime.

This and other objects of the present invention are achieved in that 30 there is provided an explosion proof electronic device, said device comprising electronics which electronics are comprised by a housing, wherein said housing comprises at least one opening for enabling access to an interior of said housing, wherein said electronics is embedded in a first moulding substance, wherein said at least one opening is sealed with a second moulding substance, wherein said first 3 moulding substance is of a liquid nature, and wherein said second moulding substance is of a solid nature.

The present invention provides a hybrid solution wherein the electronics of the device are embedded in a first moulding substance of a liquid 5 nature. Near the openings in the housing, a second moulding substance of a solid nature is present for sealing the opening. This prevents the first moulding substance from leaking from the housing, and in addition it improves the robustness of the device and the electronics. The device becomes more shock proof, which is a particular advantage for an explosion proof device.

10 The liquid first moulding substance fits perfectly to the electronic components and ensures optimal conditions for heat transfer between the electronic devices and the first moulding substance. Since the first moulding substance is of a liquid nature, fractures or cracks will not occur and air tightness of the solution is guaranteed. The solid second moulding substance that seals off the openings of the 15 housing efficiently prevents the first moulding substance from leaking from the housing to the exterior thereof.

In addition to the above, if the electronics of the device need to be accessed from the outside, this is possible in the present solution simply by destroying the second moulding substance in order to reach the electronics 20 embedded in the first moulding substance. After repairs have been executed, the device is simply sealed off by simply replacing the solid second moulding substance near the openings of the housing. The explosion proof device of the present invention thus becomes reusable, and can be recycled.

The advantages of the invention are best achieved if the electronics 25 of the device are submerged in the first moulding substance. However, to some extent the advantages are already achieved if the electronics are only partly embedded in the first moulding substance, at least with those parts of the electronic device which develop most of the heat submerged in the first moulding substance.

The second moulding substance may, according to an embodiment 30 seal only the openings in the housing. However according to a further embodiment, the second moulding substance may fully surround the first moulding substance such as to encapsulate the first moulding substance completely. The latter of these two embodiments provides a robust solution and protects the environment efficiently from any explosions triggered in the devices, while at the same time protecting the 4 device against shock waves and other forms of brutal force acting on the device from the environment.

A particular embodiment which is fairly easy to manufacture is formed by an explosion proved electronic device as described hereinabove, wherein 5 said housing comprises a container for receiving said electronics, and a cover for covering said container, said cover being detachably or permanently fixed to said container, wherein said container is filled with said first moulding substance for embedding said electronics, and wherein said second moulding substance is present between said cover and said first moulding substance for sealing an 10 opening of said container which is covered by said cover.

In this case, the electronics are simply placed in the housing of the device, the housing is partly filled such as to submerge the electronics in the first moulding substance, after which a layer of resin is added to the housing and the cover is placed onto the housing to close it.

15 According to a further embodiment the housing may further comprise heat control means for exchanging heat with the environment of the device. These heat control means may comprise any of a group comprising a cooling unit or cooling element, a heat transfer unit, one or more cooling ribs, a heat sink unit, a heat exchanger unit, passive cooling means or active cooling means. 20 The heat control means of this embodiment may be mounted on the exterior side of the housing. It is noted that with the solution of the present invention it is not necessary to fix the heat control means directly to the printed circuit board (PCB) or to the components that produce most of the heat in the device. By submerging or embedding the electronics in the first moulding substance, heat exchange between 25 the components and the first moulding substance is optimized. The first moulding substance effectively transports this heat to the walls of the housing, or to the second moulding substance, for transporting it to the exterior side of the housing and to the heat control means. In addition to this heat transfer process, it is noted that the first and second moulding substances provide a body having a heat capacity 30 taking part in distribution of the heat produced by the components. The heat is more equally distributed throughout the device.

As will be understood by the skilled person, the electronics may be mounted on a printed circuit board, although this is not a requirement. A device according the present invention may be any explosion proof device, such as 5 explosion proof devices falling under the Ex m classification. In particular the explosion proof electronic device of the present invention may be a lighting arrangement, such as an industrial lighting arrangement.

The first moulding substance may be any liquid moulding 5 substance, in particular a gel. The second moulding substance may be any suitable moulding substance, but may in particular be a resin. Examples of gels or resins that may be used as first or second moulding substances can be of various chemical substances (often polymers), dependent on the application of the device, such as polyepoxide of epoxy, polyurethaan, polyethyleen, polyesther, polystyreen, 10 polyamide or polyacrylamide.

According to a second aspect of the invention, there is provided a method of manufacturing an explosion proof electronic device, wherein said device comprises electronics which are comprised by a housing, wherein said housing comprises at least one opening for enabling access to an interior of said housing, 15 said method comprising the steps of: at least partly filling said housing with a first moulding substance for embedding said electronics in said first moulding substance; and sealing said at least one opening with a second moulding substance; wherein said first moulding substance comprises a gel, and wherein said second moulding substance comprises a resin.

20

Brief description of the drawings

The invention will be further explained by means of a number of specific embodiments, with reference to the enclosed drawings, wherein: figure 1 illustrates a first embodiment of the present invention; 25 figure 2 illustrates a second embodiment of the present invention; figure 3 illustrates a third embodiment of the present invention; figure 4 illustrates a method of the present invention.

Detailed description 30 Figure 1 illustrates an embodiment of the present invention, and in particular illustrates an explosion proof electronic device 1. Electronic device 1 consists of a housing 2 comprising a container part 4 and a cover 3. In the container part 4, a printed circuit board (PCB) comprising electronics 6 is mounted in a known manner by means of screws 9 and 10 which fix the printed circuit board 5 to fixing 6 means 11 and 12 which extend from the housing into the interior thereof. It will be understood by a skilled person that fixing the electronics to the housing is not mandatory, and the manner of fixing the printed circuit board to the housing by means of screws 9 and 10 is merely an example and should not be interpreted as 5 limiting on the invention. Printed circuit board 5 may be fixed to the housing differently, e.g. by means of clamping or glueing.

The electronics 6 on printed circuit board 5 are powered by power from a power line 15 which? extends into the housing 2 through an opening 13 in the cover 3. An output signal from the electronic device leaves the housing via cable 16 10 which is led through opening 14 of the cover 3 to the exterior of the housing. Cover 3 of the housing is fixed to the container 4 thereof by means of a small amount of glue 20 between the container 4 and the cover 3. The container 4 comprises a large opening at the top, which is in use covered by the cover 3. From the outside, any open space between the cable 15 and the edge of the opening 13 is closed by 15 means of a flexible ring 17. Similarly, flexible ring 18 closes any possible play between cable 16 and the edges of the opening 14.

In accordance with the invention the interior of the housing 2 is filled with a first moulding substance 22 in the form of a gel. The electronics 6 on printed circuit board 5 are submerged in the gel. On top of the gel 22, a second moulding 20 substance 23 in the form of a resin seals off the large opening of the container 4 and the openings 13 and 14 in the cover 3 of the housing.

On the exterior side of the container 4, heat control means 21 in the form of cooling fins are mounted to container 4. Any heat which is produced by the electronics 6 on the printed circuit board 5 is conveyed through the gel 22 and/or 25 resin 23 from the components of the electronics 6 to the housing 2, and from there to the heat control means 21 which stimulate heat transfer to the environment.

A further embodiment of the invention is illustrated in figure 2. Figure 2 again discloses a printed circuit board 5 with electronics 6 in a housing 2. The housing 2 consists of a container part 4 and a cover 3. A power line cable 15 30 and a signal line 16 for the output signal extend through a hole in the container part 4 between the interior and exterior of the housing. Although not illustrated in figure 2, the skilled person may understand that printed circuit board 5 may be fixed to the housing 2 by means of any suitable fixing means.

The cover 3 closes the container 4 at any slit between the cover 3 7 and container 4 may be closed by means of glue which fixes the cover 3 to the container 4. A standard flexible closing ring 25 closes any possible play between the cables 15 and 16 and the opening of the housing 2.

In the present embodiment, the electronics 6 and printed circuit 5 board 5 are submerged in the first moulding substance 28, which may be a gel. This first moulding substance 28 is fully encapsulated by a solid resin 29 such that the first moulding substance 28 is not in contact with the interior walls of the housing 2. This embodiment is robust and protects the electronics from any exterior forces from the outside of the device, while at the same time protecting the environment from 10 any (unlikely) possible explosions that may be triggered from within the device in the electronics 6.

Figure 3 discloses a further embodiment of the present invention comprising a housing 2 consisting of a container 4 and a cover 3. The cover 3 is fixed to the container 4 by means of screws 40 and 41 which extend through the 15 cover 3 and walls of the container 4. Power line 15 enters the interior of the housing through a hole 13, which is closed from the outside by a flexible ring 17. Signal line 16 leaves the interior of the housing through a hole 14 which is closed from the exterior part of the housing by means of a flexible ring 18. Inside the housing, electronics 6 is mounted on a printed circuit board 5, which is submerged in a first 20 moulding substance 33. At the upper side of the container 4, near the opening covered by cover 3, a solid resin 37 seals the opening of container 4. In addition small parts of moulding substance 35 and 36 seal the openings 13 and 14 from the interior side of the housing.

Figure 4 illustrates a method for manufacturing an explosion proof 25 electronics device in accordance with the present invention.

In step 45, the electronic device is assembled by mounting a printed circuit board with electronics inside a housing, in a manner known to the skilled person. Optionally required power cables and/or signal cables are extended through the housing through openings therein, and are connected to the electronics.

30 In step 48, the openings through which the cables extend, and any other openings except a main opening of the housing which is to be covered by a cover, are sealed by means of the second moulding substance. This is done by adding amounts of the second moulding substance or resin to the interior side of the housing around the openings through which the cables extend. Preferably this is 8 performed in a manner such that the printed circuit board is not in contact with the second moulding substance. It is noted that step 48 is optional, and may not be required for example in the embodiment disclosed in figure 1.

Step 48 may also be replaced by a different step (e.g. in case of the 5 embodiment disclosed in figure 2, wherein the bottom of the interior side of the housing is filled with a first layer of the second moulding substance, underneath the printed circuit board (but preferably not in contact therewith).

In step 49, the printed circuit board is submerged in the first moulding substance, which is in the form of a gel. Then, in step 50, on top of the first 10 moulding substance a layer of the first moulding substance seals off the main opening to the container part of the housing. In step 53, the cover of the housing is fixed to the container part thereof.

The invention may be practised otherwise than as specifically described herein, and the specific features of the embodiments described in the 15 application should not be interpreted as limiting on the invention. The invention is only limited by the features of the claims appended herewith.

1 0 3 7 1 7 6

Claims

An explosion-proof electronic device, the device comprising electronics, which electronics is comprised of a housing, wherein the housing comprises at least one opening for providing access to an interior of the housing, in which the electronics are embedded in a first molding substance wherein the at least one opening is sealed with a second molding substance, wherein the first molding substance is of a liquid nature, and wherein the second molding substance is of a solid nature.

The explosion-proof electronic device according to claim 1, wherein the electronics are immersed in the first molding substance.

An explosion-proof electronic device according to claim 1 or 2, wherein within the housing, the first casting substance is surrounded by the second casting substance.

Explosion-proof electronic device according to one or more of the preceding claims, in which the second casting substance is only present in the vicinity of the at least one opening, for sealing the at least one opening.

5. Explosion-proof electronic device according to any one of the preceding claims, wherein the housing comprises a container for receiving the electronics and a cover for covering the container, the cover being removable or permanently fixed to the container, the container being filled with the first molding substance for embedding the electronics, and wherein the second molding substance is present between the lid and the first molding substance for sealing an opening of the container which is covered by the lid.

An explosion-proof electronic device according to any one of the preceding claims, wherein the housing comprises heat management means for exchanging heat with an environment of the device.

An explosion-proof electronic device according to claim 6, wherein the heat management means comprises at least one element of a group comprising a cooling unit or cooling element, a heat transfer unit, one or more cooling fins, a heat sink unit, a heat exchange unit, passive cooling means or active cooling means. 1037176

An explosion-proof electronic device according to claim 6 or 7, wherein the heat management means are placed on an outer side of the housing.

9. An explosion-proof electronic device according to any one of the preceding claims, wherein the electronics are placed on a printed circuit board, and in which the printed circuit board is embedded in the first casting substance.

An explosion-proof electronic device according to any one of the preceding claims, wherein the device is a fixture for a lighting device.

An explosion-proof electronic device according to any one of the preceding claims, wherein the first molding substance is a gel.

An explosion-proof electronic device according to any one of the preceding claims, wherein the second casting substance is a resin.

13, Method of manufacturing an explosion-proof electronic device, wherein the device comprises electronics contained in a housing, wherein the housing comprises at least one opening for providing access to an interior of the housing, the method comprising the steps of of: at least partially filling the housing with a first molding substance for embedding the electronics in the first molding substance; and sealing the at least one opening with a second casting substance; wherein the first molding substance comprises a gel, and wherein the second molding substance comprises a resin.

The method of claim 13, wherein the step of at least partially filling the housing with the first molding substance comprises immersing the electronics in the first molding substance.

15. Method as claimed in any of the claims 13 or 14, wherein the first casting substance is immersed in the second casting substance for surrounding the first casting substance comprising the electronics by the second casting substance. 1037170