WO2010149556A1

WO2010149556A1 - Core box with air vents integrated in pins

Info

Publication number: WO2010149556A1
Application number: PCT/EP2010/058509
Authority: WO
Inventors: Paul Thijssen; Jan Van Peteghem
Original assignee: Bekaert Combustion Technology B.V.
Priority date: 2009-06-23
Filing date: 2010-06-17
Publication date: 2010-12-29
Also published as: CN102802835A; US20120090563A1; EP2445662A1

Abstract

The invention relates to sand casting and more specifically to sand casting of a heat exchanger element with pins and/or fins. The invention provides a core box for sand casting of workpieces comprising pins and/or fins. The core box molding surface comprises at least one air vent and pins and/or fins. The at least one air vent is integrated in at least one pin or fin.

Description

CORE BOX WITH AIR VENTS INTEGRATED IN PINS

Description

Technical Field

[0001] The present invention relates to sand casting and all casting processes where sand core are used, and more in particular to a sand casting for production of pin finned workpieces.

[0002] The invention further relates to such workpieces, e.g. heat exchanger elements provided with a dense array of pinned fins.

Background Art

[0003] Heat exchanging surfaces are commonly provided with pin fins. These pin fins provide an enlargement of the heat exchanging surface, as more surface of the heat exchanger is in contact with the cooling or heating fluid.

[0004] A further enlargement of the heat exchanging surface can be obtained by using thinner and thus also shorter pins which also allows more pins on the same surface area, thereby obtaining a greater surface content, as described in EP1722172. Still more enlargement of the heat exchanging surface is however limited by the inter pin or fin spacing, reduction below which it is impossible or impracticable to go with present manufacturing methods in an effort to increase surface area.

Disclosure of Invention

[0005] It is an object of the present invention to escape the limitations of the sand casting process for further enlargement of the heat exchanging surface. More precisely, the object of the present invention is to provide an improved sand casting method enabling the enlargement of the heat exchanging surface.

[0006] In making sand cores or molds for subsequent casting purposes, the sand mixture is delivered to the core box cavity by means of compressed air. This core box is provided with a number of fixed pins or fins with a particular heat exchanger geometry. The terms "particular heat exchanger geometry" refer to the fact that the pins or fins have about the same geometry of the pins or fins in the heat exchanger which will be made by means of the sand core or sand mold. Although other geometrical are not excluded, the pins or fins have a cylindrical form with a diameter of maximum 3.0 mm or have a frusto-conical form with an average diameter of maximum 3.0 mm. It is general practice in molding such core to provide air vents in the molding surfaces of the core box in positions which will do the most good in obtaining sound cores. When a blast of airborne sand is received by the core box, the air must be rapidly vented while the sand remains entrapped within the core box cavity. In the currently available pins and/or fins sand casting technology the air vents are located in between three neighboring pins or in between two neighboring fins and have a diameter of minimally 4 mm. This means that a possible enlargement of the heat exchanging surface is restricted by those 4mm. [0007] The present invention mitigates this restriction by providing air vents in or integrated in the pins and/or fins. An aspect of the present invention provides a core box for sand casting of workpieces comprising pins and/or fins. The core box molding surface comprises at least one air vent and pins and/or fins. The at least one air vent is integrated in at least one pin or fin. The integration of the air vents in the pins and/or fins allows a densification of the pin and/or fin array, which thereby enlarges the heat exchanging surface. This is especially useful when relatively big air vents are needed for sufficient venting in the core box, but a large heat exchanging surface of the cast heat exchanger is desired.

[0008] US-A1 -2003/0173049 discloses a method and an apparatus for making a sand mold utilizing reverse purge air through a core box and to harden the binder in the sand mold proximate the ejection pins. In a particular embodiment, the ejection pins are hollow tubes functioning as vents.

[0009] Coming back to the present invention, the pins used here can have any appropriate diameter. Preferably, the pins have a diameter of 3.0 mm or smaller. This enables a further enlargement of the heat exchanging surface of the heat exchanger element produced with the core box according to the present invention. [0010] In a preferred aspect, the at least one air vent is integrated in the base section of the pin or fin. Such air vent can cover the complete circumference of the base section of the pin or fin. In an alternative preferred aspect, one or more air vent(s) can cover only part of the circumference of the base section of the pin or fin. As such, more than one air vent can be present at the base section of the pin or fin.

[0011] In another preferred aspect, the at least one air vent is integrated in the surface of the body of the pin or fin. Such air vent can cover the complete circumference of the body of the pin or fin. In an alternative preferred aspect, the air vent can cover only part of the circumference of the body of the pin or fin. As such, more than one air vent can be present at the body of the pin or fin.

[0012] In still another preferred aspect, the at least one air vent is integrated in the top surface of the pin or fin. In case fins are being cast, more than one air vent can be present at the top of the fin. A further advantage of this preferred embodiment is that the body of the pin and/or fin is part of the required walls of the air vent.

[0013] The integration of the air vents in the pins and/or fins makes it now possible to make more dense arrays of pins and/or fins. This more dense array of pins and/or fins in the core box for sand casting enables the enlargement of the heat exchanging surface of pin and/or fin containing heat exchanger elements produced by use of such core box.

[0014] An aspect of the claimed invention provides a sand cast heat exchanger element comprising walls. The walls of the heat exchanger element are provided with pins and/or fins which enlarge the heat-exchanging surface. The pins and/or fins are forming an array, wherein that array comprises equal to or more than 250 pins and/or fins per square meter.

[0015] Such heat exchangers have more heat exchanging surface, for a slightly increased heat exchanger weight, which allows an equal or even better thermal inertia of the system and also the reaction time stays the same or becomes even better.

[0016] Another aspect of the present invention provides a method for the production of a pinned and/or finned heat exchanger element. This method comprises following steps. First, a pinned and/or finned core box is provided. This core box comprises at least one air vent. This at least one air vent is integrated in at least one of said pins and/or fins. Then, a mixture of sand and binder is shot into said core box. The sand-binder mixture is subsequently left to harden. In cold box processes, catalyst gas for hardening is led through the air vents. Thereafter, the core box is removed, thereby obtaining a sand core. This sand core is then placed in a moulding box. Molten metal is poured into said moulding box thereby obtaining a heat exchanger element around said sand core. Thereafter the cast heat exchanger element is cooled; whereafter the sand core is removed.

[0017] Another aspect of the present invention provides the use of the core box according to the present invention for the production of a pinned and/or finned heat exchanger element.

[0018] In a further aspect, the present invention provides the use of the heat exchanger element as defined by the present invention.

[0019] A further aspect provides a heating boiler provided with a heat exchanger element according to the present invention.

[0020] Definitions

[0021] The term 'core box' should be understood to be every mould used in sand casting in which air vents are being used: e.g. core box, pattern, mould box or other mould.

[0022] The term pitch should be understood as the distance from the centers in between two neighboring pins and/or fins.

Brief Description of Figures in the Drawings

[0023] Example embodiments of the invention are described hereinafter with reference to the accompanying drawings in which [0024] - Figure 1 shows a top view of a pinned core box for a heat exchanger element.

[0025] - Figure 2 shows a cross section taken along line M-M' of figure 1. [0026] - Figure 3 shows a cross section of a pinned core box with an exemplary air vent configuration according to the present invention. [0027] - Figure 4 shows a cross section of a pinned core box with another exemplary air vent configuration according to the present invention.

[0028] - Figure 5 shows a cross section of a pinned core box with still another exemplary air vent configuration according to the present invention.

[0029] - Figure 6 shows an exemplary heat exchanger element according to the present invention.

[0030] - Figure 7 shows a cross section taken along line VII-VM' of figure 6.

[0031] - Figure 8 shows a cross section taken along line VIM-VIM' of figure 6.

[0032] - Figure 9 shows an alternative pin with integrated air vents.

Mode(s) for Carrying Out the Invention

[0033] Examples of a pinned or finned core box for sand casting, air vent arrangement, sand cast heat exchanger elements and a method for production of such heat exchanger elements will now be described with reference to Figures 1 to 8.

[0034] Vents will be provided as is well known in core boxes in which cores are to be blown and in known manner would be provided with suitable means for preventing the escape of the sand particles with the escaping air.

[0035] Figure 1 shows a top view of a prior art pinned core box for casting of a heat exchanger element. X represents the horizontal pitch in between two consecutive pins. Y represents the vertical pitch in between two rows of pins. In this example, pins (1) have a conical shape, which is shown in figure 1 as two concentric circles, the inner one representing the top of the pin, the outer circle representing the base of the pin. In the prior art, air vents (2) are located in between the base sections of three neighboring pins. Figure 2 shows a cross section taken along line M-M' of figure 1.

[0036] Figure 3 shows a cross section of a pinned or finned core box for the sand casting of a heat exchanger element with an exemplary air vent configuration according to the present invention. In a first exemplary embodiment according to figure 3, the air vent's exit (3) covers the complete circumference of the body of the pin or fin. In an alternative exemplary embodiment according to figure 3, the air vent's exit (3) covers only part of the circumference of the body of the pin or fin. Alternatively, multiple exits (3) of the air vent cover multiple parts of the circumference of the body of the pin or fin.

[0037] Figure 4 shows a cross section of a pinned or finned core box for the sand casting of a heat exchanger element with another alternative air vent configuration. In a first exemplary embodiment according to figure 4, the air vent's exit covers the complete circumference of the base section of a pin. In an alternative exemplary embodiment according to figure 4, the air vent's exit (3) covers only part of the circumference of the base section of the pin. As such, more than one air vent is present at the base section of the pin or fin. Alternatively, multiple exits (3) of the air vent cover multiple parts of the circumference of base section of the pin.

[0038] Figure 9 shows another example embodiment of a pin with integrated air vents. Figure 9A shows a 3-D drawing of such a pin wherein multiple air vents are present in the collar of the pin. It must be understood that such pins are then integrated in the molding surface of the core box. Figure 9B shows a section according to line B-B'. It must be understood that the collar of the pin will be integrated in the molding wall of the core box.

[0039] Figure 5 shows a cross section of a pinned or finned core box for the sand casting of a heat exchanger element with still another alternative air vent configuration. In a first exemplary embodiment according to figure 5, the core box comprises pins and the air vents are located at the top in the center of the pin. As such, only one air vent is present at a pin. In a second exemplary embodiment according to figure 5, the core box comprises fins and the air vents are located at the top of the fins. As such, more than one air vent is present at the top of the fin.

[0040] An example embodiment provides a sand cast heat exchanger element comprising walls. The walls of the heat exchanger element are provided with pins and/or fins which enlarge the heat-exchanging surface. The pins and/or fins forming an array, wherein that array comprises equal to or more than 250 pins and/or fins per square meter. In this example the pin array is composed of pins with a diameter of 3mm, and the air vents located at the base section of the pins. The array has a horizontal pitch X of 5 mm and vertical pitch Y of 4,66 mm. This array provides 429 pins/m² and a heat exchanging surface of 303 m²/m³. Such heat exchanger element has a density of 30,3%. For comparison, current state of the art sand castings with air vents with diameter of 4mm and use of pins with diameter of 3mm, the array having a horizontal pitch X of 5,75mm and vertical pitch Y of 5,5mm, provide an array with 316 pins/m² and provide a heat exchanging surface of 223m²/m³. Such heat exchanger element has a density of 22,4%.

[0041] Another example embodiment of a sand cast heat exchanger element according to the present invention comprises a pin array of pins with diameter of 5,7mm with a horizontal pitch X of 8,5mm and a vertical pitch Y of 7,25mm wherein the air vents are located at the top of the pins. This provides an array with 162 pins/m² and a heat exchanging surface of 415m²/m³ and a density of 41 ,5%.

[0042] The density of the pin and/or fin array is an indication for the pressure drop which might be expected for this pin and/or fin array. As can be seen from the above examples of 3mm pins, the density is not strongly affected by the densification of the pin configuration.

[0043] A method for the production of such a pinned and/or finned heat exchanger element comprises following steps. First, a pinned and/or finned core box is provided. This core box comprises at least one air vent. This at least one air vent is integrated in at least one of said pins and/or fins. Then, a mixture of sand and binder is shot into said core box. The sand-binder mixture is subsequently left to harden. . In cold box processes, catalyst gas for hardening is led through the air vents. Thereafter, the core box is removed, thereby obtaining a sand core. This sand core is then placed in a moulding box. Molten metal is poured into said moulding box thereby obtaining a heat exchanger element around said sand core. Thereafter the cast heat exchanger element is cooled; whereafter the sand core is removed.

[0044] Figures 6 to 8 show a sand cast heat exchanger element (5) comprising walls (6) substantially of aluminium, said walls (6) enclosing at least one water carrying channel (7) and having at least one flue gas draft (10). At least one wall (6) forms a boundary between water carrying channel (7) and flue gas draft (10). The at least one wall is provided with pinned fins and/or fins (8,9) which enlarge the heat-exchanging surface and which extend in the flue gas draft (10). The pinned fins and/or fins form an array, wherein the array comprises equal to or more than 250 pinned fins and/or fins per square meter. In a first exemplary sand cast heat exchanger element the air vents in the core box were part of the pins as shown in figure 3. In an alternative exemplary sand cast heat exchanger element, the air vents in the core box were part of the pins as shown in figure 4. In a further alternative exemplary sand cast heat exchanger element, the air vents in the core box were part of the pins as shown in figure 5.

[0045] The illustrated exampled of the present invention the pins have a conical shape, although in another example, another shape e.g. completely cylindrical or dimples, could be present. It is clear to the man skilled in the art, that any shape of heat exchange enlarging structures can be used.

[0046] Thus there has been described a pinned or finned core box for sand casting, air vent arrangement, sand cast heat exchanger elements and a method for production of such heat exchanger elements. The invention further relates to a heat exchanger element with a very dense pinned fin and/or fin array having equal to or more than 250 pins and/or fins per square meter. The invention also provides methods for obtaining such a dense pinned fin and/or fin array, by modifying the air vents in the sand casting core box. This invention provdes thus a solution for the further enlargement of the heat exchanging surface in a pinned and/or finned heat exchanger element.

Claims

1. A core box for sand casting comprising at least one air vent and pins and/or fins of a particular heat exchanger geometry and being fixed to the core box, characterized in that said at least one air vent is integrated in at least one of said pins and/or fins.

2. A core box for sand casting according to claim 1 , wherein said at least one air vent being located at the base section of said pins and/or fins.

3. A core box for sand casting according to claim 1 , wherein said at least one air vent being located at the surface of the body of said pins and/or fins.

4. A core box for sand casting comprising pins according to any of the previous claims, characterized in that said pins and/or fins have a diameter equal to or smaller than 3 mm.

5. A core box for sand casting according to any of the claims 1 to 4, said core box comprising equal to or more than 250 pins and/or fins per square meter.

6. Method for the production of a pinned and/or finned heat exchanger element, said method comprising:

- providing a core box, said core box comprising pins and/or fins of a particular heat exchanger geometry and being fixed to the core box, said core box further comprising at least one air vent, wherein said at least one air vent is integrated in at least one of said pins and/or fins;

- shooting a mixture of sand and binder into said core box, which is subsequently left to harden;

- removing said core box, thereby obtaining a sand core;

- placing said sand core in a molding box;

- pouring molten metal into said molding box thereby obtaining a heat exchanger element around said sand core;

- cooling of the cast heat exchanger element; - removing said sand core.

7. A sand cast heat exchanger element comprising walls provided with pins and/or fins which enlarge the heat-exchanging surface, as obtained by the method of claim 6.

8. Use of the core box as defined in any of the claims 1 to 5 for the production of pinned and/or finned heat exchanger element.

9. Use of the heat exchanger as defined in claim 7 in a heating boiler.

10. A heating boiler provided with a heat exchanger element according to claim 7.