Field of the invention

The present invention relates to an improved method of manufacturing a vessel for containing fluids, in particular pressure vessels, and to an improved vessel for containing a fluid. Vessels for containing fluids may be applied in hydraulic systems, such as heating systems, cooling systems, and in systems for distributing potable water. The invention further relates to a method of connecting a nipple to a metal sheet, and to an assembly manufactured with said method.

Analysis

In vessels for hydraulic systems of the prior art, the outside of the vessel is generally coated. The coating is generally performed with a powder coating process. The powder coating process requires a preparation step of cleaning the metal parts, in particular removing any oil, soil, lubrication greases, metal oxides, welding scales etc. The cleaning step is generally performed with cleaning baths. The vessels are submerged in the bath, which contains a liquid of a certain chemical.

Vessels for hydraulic systems are generally manufactured in a range of different sizes and shapes due to market demands for varying sizes and shapes. The cleaning operation and the powder coating operation of a production line for a hydraulic vessel generally needs to be flexible enough to accommodate different sizes (and shapes) of vessels, because it would be too costly to install a different production line for each size of vessel. This flexibility can only be provided if the cleaning and coating process is arranged to accommodate the largest vessel which is being produced.

The baths of the cleaning process should thus be capable of holding the largest vessels, while for the majority of the production time smaller vessels are submerged in the baths. The baths generally need to be heated, which implies that for substantial portion of the time a too large volume of cleaning liquid is heated. From an energy point of view, this is disadvantageous.

The coating process comprises the spraying of the coating onto the metal surface of the metal parts that make up the vessel. This is performed in a ventilated space. The space needs to be adapted to the largest size of vessel which is manufactured. For the smaller vessels, the space will be too large, which is inefficient.

After the coating is sprayed onto the parts, the parts generally need to be cured in a cure oven. When the vessels vary in size, the size of the cure oven needs to be adapted to - - the largest vessel in the line. However, for smaller vessels, the cure oven is too large and thus not efficient in the use of energy.

Furthermore, the cleaning and coating process comprises a substantial number of manual operations, such as the operation of the baths, the coating process and the oven. This is costly and prone to errors. The coating process also requires intensive monitoring and inspections by personnel, which is cumbersome.

The present invention is based on the insight that for manufacturing vessels, it provides advantages to pull the coating process forward in time to a moment prior to deforming the metal sheet.

The present invention is further based on the insight that one of the problems in pulling the coating step forward in time is that nipples which are connected to the vessel often result in adverse effects on the coating of the vessel wall. This is due to the fact that the nipples are connected to the vessel by a welding operation. The heat of the welding disadvantageously affects the coating. Due to this reason, the coating step often has to be performed after the nipple is welded to the vessel, which makes it difficult or impossible to pull the coating step forward in time.

Summary of the invention

The invention relates to a vessel for containing a fluid, the vessel comprising:

- a piece of metal sheet forming a part of a wall of the vessel, wherein an opening is provided in the metal sheet,

a nipple comprising a pen, a shoulder and a through hole, wherein the pen extends through the opening in the metal sheet, the shoulder covering an area of the metal sheet around the opening on one side of the metal sheet, wherein the nipple is connected to the metal sheet via a weld connection between the pen and a rim of the opening on the opposite side of the metal sheet as the shoulder.

The present invention results in a connection between the metal sheet and the nipple which is esthetically clean. The weld is not visible from the outside. Visible effects of the weld operation in the metal sheet on the side of the shoulder may be covered by the shoulder. In particular, adverse visible effects on the coating are prevented. This advantageously allows the coating to be performed prior to the connecting of the nipple to the metal sheet. Other advantages are also be achieved, such as a simple connection.

In an embodiment of the vessel, a end face of the pen is substantially flush with one side of the metal sheet. In an embodiment, at least part of the metal sheet is curved. In an embodiment, the pen has a smaller diameter than the shoulder. In an embodiment, the shoulder engages the surface of the metal sheet piece without being attached to the metal sheet piece. - -

In another embodiment of the vessel, the metal sheet is provided with a coating on at least one side thereof, in particular on the side which is covered by the shoulder.

In another embodiment of the vessel, the shoulder covers an area of the metal sheet of which the appearance on the side of the shoulder is affected by the weld connection.

The present invention further relates to a method of manufacturing a vessel for containing a fluid, the method comprising:

providing a coated metal sheet and creating a hole in the metal sheet, providing a nipple comprising a pen, a shoulder and a through hole and inserting the pen of the nipple into the hole in the metal sheet from one side of the metal sheet,

- welding the nipple to the metal sheet part from the opposite side as the side from which the nipple is inserted.

In an embodiment, the method comprises welding the nipple to the metal sheet by directing a laser beam from the opposite side of the piece of metal sheet to the region where the pen adjoins a rim of the opening.

In an embodiment, the method comprises forming the metal sheet into a vessel part, wherein the weld is located on the inside of the vessel part.

The invention further relates to an assembly comprising a metal sheet part and a nipple, wherein:

- the metal sheet part comprises an opening, wherein a ridge which defines the

opening is bent,

- the nipple comprises a pen and a shoulder, wherein the pen extends through the opening and is bent around the ridge of the opening.

In an embodiment of the assembly, the nipple has a pen and a shoulder, and wherein the pen is folded around the bent ridge of the hole.

In an embodiment of the assembly, at least one side of the metal sheet is coated.

In an embodiment of the assembly, at least the part of the metal sheet which engages the nipple is coated, wherein the coating is flexible and acts as a seal against leakage. The flexible coating is clenched between the metal sheet and the nipple.

In an embodiment of the assembly, the assembly is free of any gasket between the metal sheet and the nipple. Because the flexible coating prevents leakages between the metal sheet and the nipple, the assembly does not need a gasket, resulting in a simpler construction.

In an embodiment of the assembly, the nipple is manufactured from stainless steel or brass, and wherein the metal sheet is manufactured from steel.

In an embodiment of the assembly, the ridge of the hole curves over an angle of approximately 70-90 degrees. - -

In an embodiment of the assembly, the bent ridge of the hole is curved and defines a substantially trumpet shape.

In an embodiment of the assembly, the shoulder engages the metal sheet.

In an embodiment of the assembly, the shoulder has a curved surface which gradually goes over in the pen, and wherein the curved shoulder engages the curved ridge.

In an embodiment of the assembly, the folded end of the nipple engages both the outer side of the metal sheet as the inner side of the metal sheet, thereby forming two fluid- tight connections between the pen and the metal sheet.

The invention further relates to a method of connecting a nipple to a metal sheet, the method comprising:

providing a piece of metal sheet,

creating a hole in the piece of metal sheet,

bending a ridge of the hole so that the ridge projects from the surface of the metal sheet,

- inserting a nipple into the hole, wherein an end of the nipple extends beyond the bent ridge of the hole,

folding a ridge of the end of the nipple outward and around the bent ridge of the hole, thereby forming a fixed connection between the metal sheet and the nipple.

Typically, the folding will be performed with a spinning operation. The folded part clamps the ridge of the hole.

In an embodiment of the method, the nipple has a pen and a shoulder, and wherein the pen is inserted into the hole from the opposite side as the side from which the ridge of the hole projects, and wherein the pen extends beyond the bent ridge of the hole.

In an embodiment of the method, the method comprises the step of coating the metal sheet on at least one side prior to the connecting of the nipple to the metal sheet. The flexible coating may be applied to the metal sheet prior to the making of a hole in the sheet.

In an embodiment of the method, the coating is a flexible coating which acts as a seal between the metal sheet and the nipple. In use, the flexible coating prevents leakages and obviates the use of a separate gasket between the metal sheet and the nipple.

In an embodiment, the nipple is manufactured from stainless steel or brass, and wherein the metal sheet is manufactured from steel.

In an embodiment of the method, the ridge of the hole is bent over an angle of approximately 70-90 degrees.

In an embodiment of the method, the bent ridge of the hole is curved and defines a substantially trumpet shape. In another embodiment, the shoulder has a curved surface which gradually goes over in the pen, the method comprising inserting the nipple into the hole until the curved shoulder engages the curved ridge.

In an embodiment, the method comprises folding the end of the nipple until said end engages both sides of the metal sheet.

The present invention provides a method of manufacturing a vessel for containing a fluid, the method comprising the subsequent steps of:

providing a flat piece of metal sheet, wherein the flat piece of metal sheet has previously been coated on at least one side,

- forming the coated flat metal sheet into a three dimensional metal part by deep

drawing the flat sheet of metal.

The words "metal sheet" are intended to refer also to a metal sheet with a somewhat greater thickness, i.e. a metal plate.

In an embodiment, the deep drawing step is carried out without the use of a lubricant.

In an embodiment, the coating is a flexible coating. In an embodiment, the coating is slippery and scratch resistant. In an embodiment, no subsequent step of removal of lubricant is carried out.

In an embodiment of the method, the coating is a Polyurethane (PUR) coating. PUR coating was found to be corrosion resistant and scratch resistant. The PUR coating protects the metal sheet during the deep drawing process. The deep drawing process is carried out without a lubricating oil, which becomes possible due to the application of the coating.

In an embodiment of the method, the metal sheet is formed into substantially one half of a vessel during the deep drawing.

In an embodiment, the method comprises:

providing a hole in the metal sheet,

inserting a nipple comprising a through hole into the hole,

welding the nipple to the metal sheet with a laser beam.

In an embodiment, the method comprises:

o providing a hole in the metal sheet,

o providing a nipple comprising a pen, a shoulder and a through hole and

inserting the pen of the nipple into the hole in the metal sheet from one side of the metal sheet,

o welding the nipple to the metal sheet part from the opposite side as the side from which the nipple is inserted

or

o creating a hole in the piece of metal sheet, - - o bending a ridge of the hole so that the ridge projects from the surface of the metal sheet,

o inserting a nipple into the hole, wherein an end of the nipple extends beyond the bent ridge of the hole,

o folding the end of the nipple outward and around the bent ridge of the hole, thereby forming a fixed connection between the metal sheet and the nipple. By combining the deep drawing step without lubrication with one of the nipple-metal sheet connections disclosed herein, it becomes possible to first coat a flat piece of metal sheet and subsequently deep draw the flat piece of metal sheet into a 3D shape and connect the nipple to the flat piece of metal sheet. Coating flat pieces of metal sheet is much easier and cheaper than coating 3D vessels, for the reasons described in the analysis underlying the invention, see above. Hence, the coating step is pulled forward in the production process, i.e. to the phase wherein the metal sheets are still flat, resulting in a clear improvement in manufacturing of the vessels. The connecting of the nipple may take place prior to deepdrawing or after deepdrawing.

In an embodiment, the method comprises welding the nipple to the metal sheet part from the opposite side as the side from which the nipple is inserted. In an embodiment, the metal sheet is not coated after the deep drawing thereof.

In an embodiment, the method comprises:

- providing a nipple comprising a pen and a shoulder and inserting the pen of the nipple into said opening from one side of the metal sheet,

- welding the nipple to the metal sheet by directing a laser beam from the opposite side of the piece of metal sheet to the region where the pen adjoins a rim of the opening.

In an embodiment, the method comprises forming the piece of metal sheet into a three dimensional part prior to the connection of the nipple to the metal sheet, in particular by deep drawing the piece of metal sheet.

In an embodiment, the method comprises providing the piece of metal sheet with a coating prior to deep drawing the piece of metal sheet.

In an embodiment, the method comprises inserting the pen into the opening until an end face of the pen is substantially flush with one side of the metal sheet.

In an embodiment, the method comprises engaging the shoulder with the surface of the metal sheet without attaching the shoulder to the metal sheet.

The invention further relates to a vessel for containing a fluid, the vessel comprising the assembly of the metal sheet part and the nipple.

The invention further relates to an assembly of a metal sheet and a nipple, the assembly comprising: - -

- a piece of metal sheet, wherein an opening is provided in the metal sheet,

- a nipple comprising a pen, a shoulder and a through hole, wherein the pen extends through the opening in the metal sheet, the shoulder covering an area of the metal sheet around the opening on one side of the metal sheet, wherein the nipple is connected to the metal sheet via a weld connection between the pen and a rim of the opening on the opposite side of the metal sheet as the shoulder.

The assembly can be a vessel or a different assembly than a vessel. Brief description of the figures

In the following, the aspects, features and advantages of the present invention will be elucidated further by reference to the annexed Figures illustrating exemplary

embodiments. In the Figures, the same parts or parts having the same function have been identified with the same reference numeral.

Figure 1 shows a diagrammatic sectional view of a connection between a wall of the vessel and a nipple according to the invention.

Figure 2A shows a diagrammatic sectional view of a step in the method according to the invention.

Figure 2B shows a diagrammatic sectional view of another step in the method according to the invention.

Figure 2C shows a diagrammatic sectional view of another step in the method according to the invention.

Figure 3A shows a diagrammatic sectional view of a step in another embodiment of the method according to the invention.

Figure 3B shows a diagrammatic sectional view of another step in the embodiment of figure 3A.

Figure 3C shows a diagrammatic sectional view of a further step in the embodiment of figure 3 A.

Figure 3D shows a diagrammatic sectional view of yet another step in the embodiment of figure 3A.

Figure 4 shows a diagrammatic sectional view of a step in the embodiment of figure

3A.

Detailed description of the invention

Turning to figure 1 , a wall 10 of a vessel for holding a fluid is shown which is formed by a metal sheet 10. The metal is generally steel. Vessels for hydraulic systems generally are constructed to hold a fluid, i.e. a liquid or a gas. Generally, the vessel comprises at least - - one opening allowing the fluid to enter and/or leave the vessel. Often, the opening is provided in the form of a nipple. The design and construction of the opening and in particular the connection of the nipple to a wall of the vessel is subject to several constructional requirements. One requirement is generally that there may be no leakage.

Vessels are often manufactured from metal sheet. The metal sheet 10 is coated with a PUR coating, i.e. Polyurethane coating, at least on the side which is intended to form the outside 12 of the vessel. In an embodiment of the invention, the coating is provided on both sides of the metal sheet.

The application of PUR coating has as an advantage that it can be carried out in a closed environment. This allows any toxic gasses which are created as a result of the coating process to be funneled off and treated with a gas treatment device. The gasses may be burned and any heat that is created during the burning may be used in the coating process or used in another manner.

The coating process is performed directly downstream of the rolling process. This has as an advantage that the metal sheet is protected against corrosion and damage such as scratching due to the handling directly after its formation as metal sheet. Therefore, the metal sheet is less likely to become damaged or to corrode prior to the making of the vessel from the metal sheet. Another coating may also be used. The metal sheet has a thickness 15.

A nipple 1 is connected to the metal sheet 10. The nipple 14 comprises a through hole 16. The nipple has an outer diameter 17. The nipple further comprises thread 18, which is located on the outside and which is present to allow a conduit to be mounted to the vessel. The nipple further comprises a pen 20 and a shoulder 22. The pen is a section of the nipple having a reduced outer diameter 19 with respect to the diameter 17 of the shoulder 22. The pen is a tubular section of the nipple having a wall thickness 53. The shoulder 22 has a substantially same diameter 17 as the outer diameter 17 of the thread 18. The shoulder 22 protrudes outwardly from the pen 20 over a distance 25. The total thickness of the shoulder 22 and the pen 20 is indicated as 26

The through hole 16 in the nipple 14 defines a fluid opening which allows fluid connection between one side of the metal sheet and an opposite side of the metal sheet, which in use corresponds to the inner space in the vessel and the outside.

A hole 30 is provided in the metal sheet 10. The hole is defined by a rim 32 in the metal sheet. The hole is a circle, but may also have another form, such as square shaped. The hole has a diameter 29.

The pen 20 has an outer diameter 19 which corresponds to the diameter 29 of the hole, and is slightly smaller than the diameter 29 of the hole. The pen 20 fits into the hole - -

30, resulting in a small gap 36 between the outer wall 38 of the pen 20 and the inner side 40 of the hole 30. The shoulder has a greater diameter than the hole.

The dimensions of the different parts are related to one another and are provided as values without any dimension below. The metal sheet typically has a thickness of between 0,9 and 1 ,75. The gap may typically be approximately 0,1. The wall thickness 23 of the pen 20 may be 0,8 - 1 , preferably 0,9. The distance 25 may be between 1 ,8 and 2,3, preferably 2,1. The distance 25 is chosen as between 1 ,5 and 3 times the thickness of the metal sheet 10.

. The nipple has a length 42 and an inner diameter 44. The pen has a length 46 which corresponds substantially to the thickness 15 of the metal sheet.

The end face 48 of the pen 20 is flush with the inside 13 of the metal sheet.

The shoulder 22 has a face 23 which is oriented at right angles to a central axis 50 of the nipple 14.

Turning to figures 2A - 2C, a method of connecting the nipple 14 to the metal sheet 10 is further elucidated.

First, the metal sheet is coated with a PUR coating prior to the connecting of the nipple 14 to the metal part. Next, as can be seen in figures 2A-2C, the metal sheet 10 is formed three dimensionally and has a general shape of one half of a vessel for containing a fluid.

Generally, two halves of the vessel are formed. The vessel halves are formed by deep drawing. This is a known process for forming three dimensional parts from a flat sheet of metal. The process results in a high quality at relatively low costs. The coating which is applied is very flexible and very scratch- resistant. The PUR coating allows an upset (negative strain) of 45% and a strain of 65% during deep drawing.

During the assembly of the vessel, the two halves of the vessel are interconnected, often with a rubber ring for sealing.

In a next step, the pen 20 of the nipple 14 is inserted into the hole 30. The face 23 of the shoulder engages the outer side 12 of the metal sheet 10. When the nipple 14 is inserted into the hole 30, a laser beam 60 is used to weld the nipple 14 to the metal sheet. The laser beam 60 is provided on the inside 13 of the metal sheet 10 and directed at the region of the gap 36. The laser beam melts a small portion of the outer wall 38 of the pen 20 and the inner side 40 of the hole 30 and causes the outer wall 38 of the pen 20 and the inner side 40 of the hole 30 to become welded to one another.

A side effect of the laser beam 60 is that the coating of a part of the metal sheet 10 becomes damaged. If coating is provided on the inside, the damaged coating is visible on the inside 13 of the vessel. However, in use, the inside of the vessel is not visible to a user. - -

The coating which is provided on the outside 12 is also damaged in the region 64 of the hole 30. Here, the shoulder 22 covers said region 64 of the metal sheet which becomes slightly damaged due to the welding. Hence, this region 64 can not be seen by a user because it is covered by the shoulder 20 of the nipple 14. The distance 25 over which the shoulder protrudes from the pen is also dependent on the region 64 in which the welding operation leaves a noticeable change in appearance on the opposite side 12 of the metal sheet 10. Therefore, in an embodiment the distance 25 is chosen such that the shoulder covers the region 64 of the metal sheet 10 on the side 12 of which the appearance is affected by the welding operation.

After the nipple 14 is connected to the halve 10 of the vessel, the laser is removed and the two halves are interconnected to form a vessel.

The present invention has as an advantage that the coating of the vessels is no longer performed after the forming of the metal parts by deep drawing. This obviates a necessity for a flexible cleaning process and a flexible coating process.

The opening may be formed in the metal sheet when it is still flat or may be formed in the metal part after the forming into a three dimensional part. The hole may be created by drilling or by another suitable method.

The present invention comprises the step of welding the nipple to the vessel wall with a laser beam.

The welding is performed from the inside, i.e. the opposite side as the side from which the nipple is inserted. The welding is performed from the concave side of the metal sheet.

The present invention results in a reliable connection between the metal sheet and the nipple.

The welding process damages the wall to some extent. The coating will also become some what damaged as a result of the welding. The damaged region is limited in size and extends around the opening. However, this is not visible from the outside, because the shoulder of the nipple covers the wall section which adjoins the opening. Thus, any damages are covered by the shoulder.

The shoulder covers an area of the wall surrounding the opening. The shoulder may engage said area or may extend at a small gap from the wall.

Turning to figures 3A, 3B, 3C, 3D and 4, another embodiment of the invention is shown.

In figure 3A it is shown that the metal sheet 10 is curved and has the required form to be part of a hydraulic vessel. Prior to the curving of the metal sheet 10, the metal sheet 10 is provided with a flexible coating. The coating may be provided on both sides, or on a single - - side of the metal sheet, i.e. the side from which the nipple is later inserted or the opposite side.

The metal sheet 10 forms one half of a pressure vessel. A hole 30 is provided centrally in the piece of metal sheet. The flexible coating may be applied to the metal sheet prior to the making of the hole 30. The ridge 32 of the hole 30 is bent inward and forms a curved shape which resembles a trumpet shape. The ridge 32 is curved over an angle of between 60 and 90 degrees, so that the end face 40 of the ridge 32 extends at an angle a between zero and 30 degrees to the metal sheet 10 near the hole.

The curving of the ridge 32 results in a hole having a diameter 29.

In figure 3B it is shown that the nipple 114 is inserted into the hole. The nipple has a through hole 16, thread 18, an outer diameter 17 and an overall length 31.

The nipple 1 14 comprises a pen 20 and a shoulder 22. The shoulder 22 has a curved surface 123 and gradually goes over in the pen 20. The curved surface 123 may be a circular curve, but may also have another form. The pen 20 comprises an end 49 having an end face 48.

In figure 3C the nipple is shown in the inserted position. The curved surface 123 engages the curved area 64 of the metal sheet 10 around the hole 30. The pen 20 extends through the hole and extends beyond the ridge 32 of the metal sheet 10 over a length 51.

In a next step, shown in figure 3C, the pen 20 is folded outwards and around the ridge 32. This may be performed with a spinning operation. The folded pen 20 engages both the outside 12 as the inside 13 of the metal sheet and forms a watertight and air-tight connection with the metal sheet 10. The folded part clamps the ridge of the hole. The coating of the metal sheet is impressed by the folded pen, which creates a fluid tight connection. In an embodiment, the folded pen does not engage the end surface 40 of the hole of the metal sheet. In an embodiment, a separate gasket is not provided. The coating acts as a seal due to its flexibility. The contact area between the curved surface 123 of the shoulder and the curved area 64 of the metal sheet does not form a fluid-tight connection, i.e. the only fluid-tight connection is formed between the folded pen and the metal sheet.

Because the folded pen engages both side of the metal sheet two separate seals are provided, a first seal 72 on one side and a second seal 73 on the other side of the metal sheet.

In an embodiment, the metal sheet is coated on the inside 13. Because the nipple shields off the end surface 40, all uncoated metal surfaces are covered, either by the coating or by the nipple. This makes the assembly very practical to be used in a vessel for containing drinking water. In use, the water can not contact the blank metal of wall 10, and corrosion is prevented. - -

Figure 3D and figure 4 show the metal sheet 10 with the connected nipple 1 14. The pen 20 is folded round the ridge 32 of the hole and clamps the ridge 32 between two parts 70A, 70B of the pen 20. The curved surface 123 engages the region 64 of the metal sheet 10. It is possible that the region 64 is clamped against a part of the surface 123 of the shoulder 22 or against the entire surface 123 of the shoulder 22. The curved surface 123 may also have a slight gap with said region 64.

For completion of the hydraulic vessel, two halve of the hydraulic vessel are provided and interconnected, possible with a rubber ring to seal the connection. A membrane may also be provided in case of a pressure vessel, as well as other parts.

It will be obvious to a person skilled in the art that the details and the arrangement of the parts may be varied over considerable range without departing from the spirit of the invention and the scope of the claims.