WO2004006627A1

WO2004006627A1 - Nozzle tip

Info

Publication number: WO2004006627A1
Application number: PCT/SE2003/001179
Authority: WO
Inventors: Stefan Springmann
Original assignee: Sandvik AB
Current assignee: Sandvik AB
Priority date: 2002-07-04
Filing date: 2003-07-04
Publication date: 2004-01-15
Anticipated expiration: 2005-01-04
Also published as: AU2003245219A1; SE0202141D0; EP1552725A1

Abstract

The present invention relates to nozzle tip for use in a three-tube filling machine for the production of heating elements in an its enterity continuous concave shape, that increases the material flow per time unit and therewith increases the productivity rate in the production of tube-shaped heating elements. Closer determined, a nozzle tip, where the number of guide wings can be varied, where said guide wings lay between concave radii and where the free surface between the guide wing and the element tube, determinant for the flow of the filling media, is maximized for a maximum flow of filling media.

Description

Nozzle tip

Technical Area of the invention

Background

Heating elements in tubular shape for heating purposes in different connections, such as e.g. domestic appliances, equipment for the chemical industry and so on, are characterized by that these elements have very small dimensions regarding the diameter. Heating elements are usually dimensioned originating from among others the desired heating effect and the disposal installation space. These tube-shaped heating elements will be filled with a suitable filling media, which is bedding in and fixates the resistance wires in the center of the tube. This has to be done with outmost possible precision, because the least deviation form- the center could lead to breakdown of the heating element.

Nowadays, for the production of tubular elements in filling machines the so- called three-tube-filling principle is used. The element tube is placed in the filling machine and will be overlapped the filling mechanism. The filling media is running between the inner- and the outer tube. A valve stem adjusts the flow. A so-called nozzle tip with strapping rings has the function to center the resistance wires. In the closed position the valve stem will overlap over the strapping rings and stops the further flow of filling media. Determining for the amount of filling media, which can be filled in per time unit is the area of the gap between the nozzle tip and the element tube. The dimensions of the nozzle tip have to be adjusted to the dimensions of the heating element, which requires that they are custom-made. Given parameters for the dimensioning of the nozzle tip are the inner diameter of the element tube and the largest diameter for the in the center of the element placed coil of heating wire with terminal pins. In conventional design the nozzle tip can be manufactured of different metallic materials, such as stainless steel, ceramics and/or hardmaterial. Today, the limiting factor for the flow of the filling media is the gap between the wings of the nozzle tip and the element tube.

Summary of the invention

It is therefor an object of the invention to provide a nozzle tip in a design, which increases the material flow per time unit and thereby increases the production rate in the manufacturing of tube-shaped heating elements. Closer determined, a nozzle tip, where the number of guide wings can be varied, where said guide wings lay between concave radii and where the limiting factor for the flow of the filling media is the gap between the wings of the nozzle tip and the element tube is maximized for a maximum flow of filling media. It is another object of the invention to provide a nozzle tip which can be produced in an simplified process and in all material, that are used toady, such as stainless steel, ceramics and/or hardmaterial.

Short description of the drawings Figure 1 shows an explanatory sketch over the three-tube-filling principle. Figure 2 shows top view, sectional view and perspective of A - is a conventional nozzle tip and B - is a nozzle tip in a design according to the present invention. Figure 3 shows alternative embodiments of the nozzle tip according to the present invention, where

A - has three guide wings B - has four guide wings

C - has five guide wings

D - has six guide wings. Figure 4 shows overview over the parameters for the calcualtion of the geometry of the nozzle tip, where

C is the outer diameter of the bar, tube and the finished nozzle tip

B is the diameter of the sealing ring

A is the diameter of the centre bore hole, which is equal for sealing ring and nozzle tip V is the wall thickness between the base of the concave cavity and the centre bore hole

CB is the width of the guide wing

CK and C_D the arc area between the corner points of two adjacent guide wings α is the aperture angle, outgoing from the centre of the of the nozle tip and cutting the corner points of two adjacent guide wings

R is the optimum radius for the concave cavity

B is the longest distance between C and CK

Detailed description of invention

It has surprisingly shown that the nozzle tip with a design according to the present invention solves these problems. The nozzle tip is principally executed in such way, that between the guide wings concave radii are introduced, which leave the guide wings out. The upper limitation fort his radius is infinite, i.e. in practice near an unbend line. This embodiment could in its optimum shape presuppose a number of guide wings of three. Three guide wings are supposed to be the minimum number in order to be able to maintain their function in the filling tube, i.e. to guarantee the centration. The maximum number of guide wings is attained, when no larger area than in the conventional design can be attained. A further limitation lays in the wall thickness for the radii between the guide wings. Since the width of the guide wings at the top can be minimized to very small dimensions without missing their function, as a consequence the wall thickness in the concave radius' deepest point in relation to the inner bore. The design with a concave radius between the guide wings gives the possibility of increasing respectively variation of the following parameters: free surface between filling tube and guide wing number of guide wings the width of the guide wings at the top - manufacturing method.

Further, in difference to the conventional design the guide wing according to the present invention can be executed in such manner that the guide wing itself and the valve stem will be manufactured separately and be joined with suitable means. This allows a more simplified manufacturing of the guide wing and leads to the possibility of recycling of the valve stems (see figure 2, embodiment B).

Description of preferred embodiments

The outer diameter C of the nozzle tip should be such that the nozzle passes free through the element tube with a gap of between 0.05 and 0.3mm. The coil should pass free in a tube, the so-called inner tube, with an inner diameter of between 0.2 and 0.5 mm larger than that of the coil and the terminal pins largest diameter. The diameter of the inner tube determines the diameter of the bore A. The flow of the filling media will be adjusted by the valve stem. The valve stem should pass free in the element tube with a gap of between 0.1 and 0.3 mm. The inner diameter of the valve stem determines the diameter B of the sealing ring. The bore diameter A is equal for the sealing ring and the concave nozzle.

The other outline measures can be determined in different ways. In the following some embodiments of the nozzle tip according to the present invention with an optimum concave radius, outgoing from the determined geometrical measures such as width of the wing and the smallest wall thickness. This is most suitable for sintered types in among others hardmaterial or production by spark machining. For the second, the manufacturing with predetermined concave radius, even here with the width of the wing and the material thickness as limitations. This is most suitable for conventional production by e.g. milling usually outgoing from round material with diameter C in order to minimize the use of different tools.

In order to obtain the largest possible free area between the wings, the number if wings can vary. At least three wings are required in order to obtain a centration of in the element tube. Conventional nozzle tips are often deigned with four wings in order to obtain a well-defined gap between the nozzle tip and the element tube. An improved number of guide wings can give a larger free area, but requires smaller concave radii.

Design with optimum concave radius

Several geometrical parameters are preset.

The number of wings can vary. This is included in the calculations with the parameter x.

The centre of the radius of the in its entirety continouos concave recess is positioned outside the circumference of said nozzle tip.

In order to obtain a centration at least three evenly distributed over the circumference C wings are required. In order to obtain the largest possible free area it can be necessary to increase the number of wings. With an increased number of wings, it is expected that the concave radius will be diminishing. The arc length C_B over the four wings of a diameter C should be between 0.6 and 1.5mm with superiority to amounts between 0.8 and 1.2mm over every wing. The wall thickness V between the base of the concave cavity and the center bore with a diameter A should be at least 0.3mm. Outgoing form the given values for C, A, CB and V the optimum radius for the concave cavity can be calculated.

With C, A and V the depth F for the lowest point of the concave cavity outgoing from the diameter C can be calculated with:

F = (C-A)/2-V

The from the diameter C removed arc length Co between the corner points of two adjacent wings, will be calculated with C, CB and the parameter x the number of wings to:

C_D = ( TT ^■ C- x ^• C_B ) / x

Now the opening angle α between two from the center of the nozzle tip outgoing lines and which cuts the corner points of two adjacent wings will be calculated to:

α=(2 C_D- 180°)/(π-C)

The chord CK, laying between the corner points of two adjacent wings will be calculated to:

C_κ = C-sin(α/2)

The largest distance between C and C_κ at the length Cκ/2 will be:

b = C/2 V( (C/2)²-(C_K/2)²) The largest distance f between the chord and the deepest point of the concave cavity will be calculated to:

f = F - b

Finally, with f and CK the optimum radius R for the concave cavity can be determined to:

R = ((C_K / 2 )² + f² ) / ( 2 f )

Design with given concave radius

Even here a number of geometrical parameters are predetermined.

The number of wings can vary. In order to obtain a centration at least three wings evenly distributed over the circumference C are required. In order to obtain the largest possible free area it could be necessary to increase the number of wings. With four wings a good centration will be obtained, to produce more wings is unmotivated, because of that the milling radii have to been chosen smaller and smaller with increasing number of wings. The arc length C_B over the four wings of a diameter C should be between 0.6 and 1.5mm with superiority to amounts between 0.8 and 1.2mm over every wing. Here, a given amount CB shall not be underpassed. The wall thickness V between the base of the concave cavity and the center bore with a diameter A should be at least 0.3mm. Outgoing from a given concave radius RK the milling depth F_R will be calculated for a given C_B. With C, A and V the largest possible milling depth F_M. The concave nozzle will be produced with the least calculated milling depth F_R or F_M. The largest milling depth with a given wall thickness V will be calculated to:

F_M = C / 2 - A / 2 - V In most of the cases, the milling depth for a given arc length CB over the wing will be calculated in several steps in the same way as the optimum concave radius.

The from the diameter C removed arc length C_D between the corner points of two adjacent wings, will be calculated with C, CB and the parameter x the number of wings to:

Co = ( π ^• C - x ^■ C_B ) / x

α=(2 C_D-180^o)/(τr-C)

C_K=C sin(α/2)

The largest distance between C and C_κ at the length </2 will be:

b = C/2 V( (C/2)²-(C_K/2)²)

With given concave radius R_κ

FR = R_K V(R_K ²- (C_κ/2)²) + b

The limiting parameters for a nozzle tip with predetermined concave radius are the width of the wing and the wall thickness V. The most suitable production method is milling, outgoing from bar or tube with a diameter C in order to minimize the working steps, especially the cutting operations and the number of different tools said working.

The sealing ring and the nozzle tip can be manufactured in all known and already for the manufacturing used materials. The manufacturing from as well as bar, tube or sintering is possible. With adapted production methods the sealing ring and the nozzle tip can be manufactured s one peace as conventional nozzle tips. The use of concave instead of convex cavities between the wings of the nozzle tip simplifies the production process. A drawback with the convex shape of the cavities is that every single convex shape requires a tailor-made tool with adapted radius for every desired diameter B. However, with a concave shape of the cavities standard milling tools, such as endmills with endradius or radial mills be used. All nowadays produced dimensions can be manufactured with the same milling tool. The cavity between the guide wings increases additionally by milling three or four evenly over the circumference distributed concave ways. This forms the guide wings.

Since the so-called valve tube should stop or limit the flow of filling media, the gap between the inner diameter of the valve tube and the diameter B should not be larger than 0.1 mm. In order to simplify the production, the nozzle tip can be divided into two segments. The nozzle tip as describes above and the sealing ring replace the pin with the diameter in the conventional nozzle. The sealing ring and the nozzle are similarly to the nozzle tip forced over the so- called inner tube and are fixated by gluing or soldering or other suitable type of fixation. The area for the flow of the filling media around the sealing ring is equal to the area around the pin B in a conventional nozzle. The area for the flow of the filling media increases between the guide wings because of the in its enterity continuous concave shape of the area between the guide wings. This leads to an increased flow of filling media per time unit and allows increased filling rates. The area, which will be passed by the flowing filling media, will approximately be duplicated.

Claims

1. Nozzle tip for directing the flow of filling media in a three-tube filling machine for the manufacturing of electrical heaters, said nozzle having a cavity allowing the filling media to pass, the filling media to sourround the coiled resistance heating wire characterized in, that said cavity has the shape of an in its entirety continouos concave recess.

2. Nozzle tip according to claim ^characterized in, that said in its enterity continuous concave cavity is shaped such, that the depth of the in its entirety continouos concave recess is determined by the minimum wall thickness between the center bore hole and base of the concave recess.

3. Nozzle tip according to claim 1, characterized in, that said in its enterity continuous concave cavity is shaped such, that the centre of the radius of the in its entirety continouos concave recess is positioned outside the circumference of said nozzle tip.

3. Nozzle tip according to claim 1 to 3, characterized in, that said nozzle tip has at least three guide wings.

4. Nozzle tip according to claim 1 to 3, c h a r a c t e r i z e d in, that nozzle tip has four, five or six guide wings.

5. Method of manufacturing a nozzle tip comprising the steps of

- providing a blank in the shape of a bar or a tube

- machining said blank to form external cavities such that each of said cavities adopt the shape of a in its enterity continuous concave recess in order to reduce the cross sectional area of said blank thereby providing a nozzle tip.