METHOD FOR ASSEMBLING A NEEDLE VALVE

Description

[0001] The invention relates to a method for assembling a needle valve according to the preamble of claim 1.

[0002] Needle valves with one or more valve needles and a corresponding number of valve seats are used, for example, to apply fluids such as adhesives, sealants, insulating materials, or other viscous materials to workpieces with high precision in the form of material beads or dots. Increasingly thinner valve needles are being used for this purpose, which close correspondingly small outlet openings on the respective valve seat. The use of such valve needles with small diameters and correspondingly small valve seats places high demands on the precision of needle valve assembly. In particular, it is difficult to position and fix the respective valve seat with respect to the associated valve needle in such a way that the valve needle can sit on it precisely, ensuring good sealing performance.

[0003] A method of the type mentioned above is known to the applicant from its operational practice. Various needle valves are known from DE 19 621 835 A1, DE 691 26 667 T2, US 2009 / 0107398 A1, US 5 618 566 A, and US 2019 / 0337008 A1.

[0004] It is therefore an object of the invention to provide a method for assembling a needle valve which enables better positioning of the valve seat or seats with respect to the valve needle(s).

[0005] This object is achieved according to the invention by a method having the features of claim 1. Advantageous developments of the invention are the subject of the dependent claims.

[0006] The invention is based on the applicant's experimental discovery that self-centering of a valve seat with respect to its associated valve needle can occur if the valve needle, while a valve seat plate carrying the valve seat is fixed to the housing in which the valve needle is guided for longitudinal displacement, performs an oscillating movement that corresponds to the movement it performs during operation when it is repeatedly lifted off the valve seat and placed onto it at regular intervals. In a first step, the valve seat plate is attached to the housing using fastening means. Contrary to the usual procedure, however, the valve seat plate is not fixed to the housing in the first step, but only fastened to the extent that it still has limited mobility with respect to the housing.Then, in a second step, each valve needle is set into the oscillating movement, and in a third step, the valve seat plate is fixed to the housing while the valve needle(s) move back and forth.

[0007] It is preferred that the at least one valve needle is moved back and forth at a frequency of 10 Hz to 100 Hz, preferably from 30 Hz to 70 Hz and more preferably from 45 Hz to 55 Hz, since frequencies around 50 Hz have proven to be the most effective. After the first step, the valve seat plate is expediently fixed in the first spatial direction with respect to the housing, while it has limited mobility in the two other spatial directions. It can then move sideways in order to be able to center each valve seat with respect to the associated valve needle. The fastening means are expediently screws passed through the valve seat plate, which are screwed into the housing in the first step until a first torque is reached and in the third step until a larger second torque is reached.

[0008] Hard metal is preferred as the material for each valve needle and valve seat. Hard metal is chemically resistant to the materials regularly used to coat the needle valve. Hard metal is a metal matrix composite material in which hard materials in particle form are held together by a metal matrix. Hard materials used are, in particular, metal carbides or metal nitrides, such as tungsten carbide, titanium carbide, titanium nitride, niobium carbide, tantalum carbide, or vanadium carbide. It is then also preferred that the valve seat plate has a base plate made of metal, preferably stainless steel, which supports the at least one valve seat. In particular, all valve seats can be combined into a single hard metal component that is accommodated in the base plate, which in turn is attached to the housing.Stainless steel, in particular, exhibits high elasticity, which is advantageous for securing the component to the housing in the third step, whereas hard metal is more brittle. If screws are used to secure the component to the housing, they are best passed through the base plate.

[0009] The needle valve can be equipped with only one valve needle and one valve seat. However, it is preferred that it has several valve needles extending parallel to one another in the first spatial direction, which are preferably arranged in a row so that a straight line extending perpendicular to the first spatial direction can be drawn through all the valve needles.

[0010] The invention will be explained in more detail below with reference to an embodiment shown schematically in the drawing. Fig. 1 a schematic sectional view of a needle valve and Fig. 2 an exploded view of the needle valve according toFig. 1 .

[0011] In Fig. 1 1 shows a schematic cross-sectional view of a needle valve 10 having a housing 12 and a valve needle 16 made of hard metal, which is guided in the housing 12 so as to be longitudinally displaceable in a first spatial direction 14. A valve seat plate 18 is fixed to the housing 12 by means of fastening means 20, which in the exemplary embodiment shown here are screws 20. The valve seat plate 18 has a base plate 22 made of stainless steel and a valve seat block 24 with a valve seat 26 assigned to the valve needle 16, on which valve seat an outlet opening 28 for a fluid that can be applied by means of the needle valve 10 can be closed and opened by moving the valve needle 16 back and forth and thereby lifting it off and placing it on the valve seat 26. The valve seat block 24 is received in the base plate 22 and has a shoulder 30 so that it can only be inserted into the base plate 22 from the side facing the housing 12.It is made in one piece from the same hard metal as the valve needle 16.

[0012] When assembling the needle valve 10 from the Fig. 2shown individual parts, the valve seat block 24 is first inserted into the base plate 22 and together with it forms the valve seat plate 18. This is placed against the housing 12 from below, and the screws 20 are pushed through the base plate 22 and screwed into threaded screw holes 32 in the housing until they are subjected to a first predetermined torque. The valve seat plate 18 then rests almost immovably against the housing 12 in the first spatial direction 14, but still has some play in the two other spatial directions that are perpendicular to the first spatial direction 14 and to each other. The valve needle 16 is then set in an oscillating movement that corresponds to a sequential opening and closing of the needle valve 10 at a frequency of approximately 50 Hz.During this oscillating movement of the valve needle 16, the screws 20 are tightened until a predetermined second torque is applied, which is greater than the first torque. During tightening of the screws 20, the constant lifting of the valve needle 16 from the valve seat 26 and the subsequent seating causes the valve seat 26 to self-center relative to the valve needle 16, so that the valve seat 26 can be positioned very precisely relative to the valve needle 16.

[0013] In the illustrated embodiment, the needle valve 10 has only one valve needle 16 and the associated valve seat 26. It goes without saying that the method according to the invention can also be applied to needle valves that have multiple valve needles and a valve seat for each valve needle. In this case, the valve seat block has, for example, several valve seats arranged in a row, while the design of the needle valve is essentially the same as shown in the drawing.

[0014] In summary, the invention relates to a method for assembling a needle valve 10, which has a housing 12, at least one valve needle 16 guided longitudinally displaceably in the housing 12 in a first spatial direction 14 and a valve seat plate 18, wherein the valve seat plate 18 has a valve seat 26 assigned to each valve needle 16, at which valve seat an outlet opening 28 for a fluid can be closed and opened by a back and forth movement of the respective valve needle 16.According to the invention, it is provided that the valve seat plate 18 is fastened to the housing 12 by means of fastening means 20 in a first step, so that it is movable to a limited extent with respect to the housing 12, that in a second step each valve needle 16 is set into a back and forth movement in which it is alternately placed on the valve seat 26 assigned to it and lifted off therefrom and that the valve seat plate 18 is fixed to the housing 12 in a third step, while the at least one valve needle 16 moves back and forth.

Claims

1. Method for assembly of a needle valve (10), which has a housing (12), at least one valve needle (16) that is guided in the housing (12) to be longitudinally displaceable in a first spatial direction (14), and a valve seat plate (18), wherein the valve seat plate (18) has a valve seat (26) for each valve needle (16), assigned to the latter, on which seat an outlet opening (28) for a fluid can be closed and opened by means of a back and forth movement of the valve needle (16), wherein in a first step, the valve seat plate (18) is fastened to the housing (12) by means of fastening means (20), so that it has limited mobility with reference to the housing (12), characterized in that in a second step, each valve needle (16) is put into a back and forth motion, during which it is alternately set onto the valve seat (26) assigned to it and lifted up from it, and that in a third step, the valve seat plate (18) is fixed in place on the housing (12) while the at least one valve needle (16) moves back and forth.

2. Method according to claim 1, characterized in that the at least one valve needle (16) is moved back and forth at a frequency of 10 Hz to 100 Hz, preferably of 30 Hz to 70 Hz, and further preferably of 45 Hz to 55 Hz.

3. Method according to claim 1 or 2, characterized in that after the first step, the valve seat plate (18) is fixed in place in the first spatial direction (14) with reference to the housing (12), and has limited mobility in the two other spatial directions.

4. Method according to one of the preceding claims, characterized in that the fastening means (20) are screws that are passed through the valve seat plate (18), which are screwed into the housing (12) until a first torque is reached during the first step, and until a greater second torque is reached during the third step.

5. Method according to one of the preceding claims, characterized in that each valve needle (16) and each valve seat (26) are produced from hard metal.

6. Method according to claim 5, characterized in that the valve seat plate (18) comprises a base plate (22) composed of metal, preferably of stainless steel, which carries the at least one valve seat (26).

7. Method according to one of the preceding claims, characterized in that the needle valve (10) has multiple valve needles (16) that extend parallel to one another in the first spatial direction.

8. Method according to claim 7, characterized in that the valve needles (16) are arranged in a row.