WO2012158494A1

WO2012158494A1 - Adhesive dispensing applicator and valve assembly with needle and valve member in interference fit

Info

Publication number: WO2012158494A1
Application number: PCT/US2012/037459
Authority: WO
Inventors: Victor de LEEUW
Original assignee: Nordson Corporation
Priority date: 2011-05-13
Filing date: 2012-05-11
Publication date: 2012-11-22
Also published as: DE112012002070T5

Abstract

An adhesive dispensing applicator (10) includes a nozzle (18), a valve seat (36), and a valve assembly (1 6) including a needle (54) and a valve member (60) coupled to the needle (54) in an interference fit. The interference fit between the needle (54) and the valve member (60) of the valve assembly (16) may be produced by press fitting or shrink fitting a pin shank (66) of the valve member (60) into a bore (58) of the needle (54). The interference fit is produced without the use of adhesive or solder materials that are subject to premature fatigue failure or failure by chemical attack during operation of the adhesive dispensing applicator (10).

Description

ADHESIVE DISPENSING APPLICATOR AND VALVE ASSEMBLY WITH NEEDLE AND VALVE MEMBER IN INTERFERENCE FIT

Cross-Reference to Related Application

[0001] This application claims the priority of U.S. Provisional Patent Application No. 61 /485,935, filed on May 13, 201 1 (pending), the disclosure of which is incorporated by reference herein.

Technical Field

[0002] This invention generally relates to valve assemblies for adhesive dispensing applicators adapted to apply adhesive onto a substrate.

Background

[0003] Liquid adhesive, such as temperature and/or pressure sensitive adhesive, is applied onto various substrates in the manufacturing of packaging containers, hygienic articles, and other products. In some applications, adhesive dispensing applicators are used to rapidly dispense a stream of liquid adhesive or a plurality of dots of liquid adhesive onto a substrate. The liquid adhesive is dispensed at room temperature or at an elevated temperature such as 200 °C for hot melt adhesives. An adhesive dispensing applicator for these applications generally includes a valve assembly with a valve member adapted to selectively engage a valve seat formed or otherwise secured in a nozzle. In one common example, the valve member is a carbide ball attached to a needle of the valve assembly by soldering or adhering with an adhesive material. However, these carbide ball valve members are subject to multiple failure modes.

[0004] For example, adhesively bonding or soldering the carbide ball valve member to the needle may result in premature fatigue failure. In operation, a typical adhesive dispensing applicator can cycle the valve member at a continuous rate of 250 Hz or higher. At these high cycling rates, the coupling formed by solder or adhesive material may experience fatigue failure much more rapidly than the carbide ball valve member or the valve seat.

[0005] Additionally, the solder or adhesive material used to form the coupling of the valve member and the needle may be subject to chemical attack and subsequent premature failure. Some liquid adhesives that may be dispensed by the adhesive dispensing applicator are highly chemically reactive or aggressive. With highly chemically reactive liquid adhesives, the solder (e.g., gold-nickel) or adhesive material forming the coupling may be prematurely dissolved by chemically reacting with the liquid adhesive to be dispensed.

[0006] There is a need for an adhesive dispensing applicator and valve assembly that reduces or eliminates the likelihood that the coupling between the valve member and the needle will prematurely fail.

Summary of the Invention

[0007] In one embodiment of the invention, a valve assembly for use with an adhesive dispensing applicator includes a needle and a valve member. The needle includes a distal end and a bore at the distal end. The valve member is secured in the bore in an interference fit.

[0008] In one aspect, the valve member is pin-shaped and includes a pin shank inserted into the bore. The pin shank includes an outer diameter larger than an inner diameter of the bore. The pin shank also includes a distal end and a proximal end, the distal end being rounded or tapered from the outer diameter and configured to engage a valve seat in sealing engagement. The proximal end is tapered to assist with insertion of the pin shank into the bore.

[0009] In another aspect, the proximal end of the pin shank defines an end diameter less than the inner diameter of the bore. The outer diameter of the pin shank is larger than the inner diameter of the bore by an interference within the range of about 0.003 millimeters to about 0.019 millimeters. In another aspect, the pin shank and the bore define a substantially smooth surface finish of less than about 1 .0 micrometers such that the pin shank is configured to be press fit into the bore by the application of a force to the pin shank. The needle may be formed from a material having a coefficient of thermal expansion sufficient to enable the bore to be heated to expand the inner diameter to be larger than the outer diameter of the pin shank during a shrink fit of the pin shank into the bore.

[0010] In yet another aspect, the valve member is composed of a hardened ceramic and the needle is composed of stainless steel. The coupling of the valve member in the bore by interference fit includes no adhesive or solder materials subject to premature fatigue failure or chemical attack during operation of the valve assembly. [0011] In another embodiment, an adhesive dispensing applicator includes an applicator body with an adhesive inlet. The applicator also includes a nozzle coupled to the applicator body. The nozzle includes an internal passage communicating with the adhesive inlet and a discharge orifice communicating with the internal passage. The applicator further includes a valve seat positioned between the internal passage and the discharge orifice. A valve assembly is at least partially positioned within the internal passage and includes a needle and a valve member. The needle includes a distal end and a bore at the distal end into which the valve member is inserted and secured with an interference fit. The valve assembly is adapted to be driven in a

reciprocating manner so that the valve member intermittently engages the valve seat to control flow of adhesive through the discharge orifice.

[0012] In another embodiment, a method of assembling a valve assembly for use with an adhesive dispensing applicator includes machining a bore into a distal end of a needle and machining a valve member to be larger in size than the bore. The method also includes inserting the valve member into the bore to provide an interference fit between the valve member and the bore. The interference fit is configured to resist impact forces and other forces applied to the valve assembly that would disengage the valve member from the needle.

[0013] In one aspect, machining the bore further includes reaming the bore from the needle such that the bore defines a generally cylindrical shape having an inner diameter. Machining the valve member further includes grinding the valve member to include a generally cylindrical pin shank having an outer diameter larger than the inner diameter of the bore. Grinding the valve member may also cause the valve member to include a tapered proximal end having a diameter smaller than the inner diameter of the bore, thereby to assist with insertion of the pin shank into the bore.

[0014] In another aspect, the bore includes a top end and the valve member includes a proximal end. In this regard, inserting the valve member further includes applying a force to press fit the valve member into the bore until the proximal end of the valve member abuts the top end of the bore.

Alternatively, inserting the valve member further includes heating the needle to an elevated temperature to expand the bore to be larger in size than the valve member, moving the valve member into the bore until the proximal end of the valve member abuts the top end of the bore, and cooling the needle from the elevated temperature to shrink the bore and produce the interference fit between the valve member and the bore.

Brief Description of the Drawings

[0015] FIG. 1 is a perspective view of an adhesive dispensing applicator including a valve assembly constructed according to an illustrative embodiment of the present invention.

[0016] FIG. 2 is a front view of the valve assembly and nozzle of the adhesive dispensing applicator of FIG. 1 .

[0017] FIG. 3 is a cross-sectional side view of the valve assembly and nozzle of FIG. 2 taken along line 3-3.

[0018] FIG. 4 is a detailed cross-sectional side view of encircled area 4 showing the needle and valve member of the valve assembly and the nozzle of FIG. 3.

[0019] FIG. 5 is a side cross-sectional view of the needle and the valve member of the valve assembly of FIG. 3 prior to press fit insertion of the valve member.

[0020] FIG. 6 is a side view of the valve assembly of FIG. 5 during press fit insertion of the valve member into the needle.

[0021] FIG. 7 is a side cross-sectional view of the needle and the valve member of the valve assembly of FIG. 3 prior to shrink fit insertion of the valve member.

[0022] FIG. 8 is a side cross-sectional view of the needle of FIG. 7 undergoing expansion during a heating process.

[0023] FIG. 9 is a side view of the valve assembly of FIGS. 7 and 8 during shrink fit insertion of the valve member into the heated needle.

Detailed Description

[0024] FIG. 1 illustrates one embodiment of an adhesive dispensing applicator 10 for dispensing a liquid adhesive according to the invention. The adhesive dispensing applicator 10 includes an applicator body 12 with an adhesive inlet 14 and an outlet (not shown), a valve assembly 16 disposed within the applicator body 1 2, and a nozzle 18 coupled to the outlet of the applicator body 12. The adhesive dispensing applicator 10 may also include a drive mechanism (not shown) for moving the valve assembly 16 and a stroke adjustment mechanism 20 adapted to modify a stroke length of the valve assembly 16. The drive mechanism may be electrically or pneumatically actuated to move the valve assembly 16. One exemplary drive mechanism for electrical actuation of a valve assembly 16 is described in U.S. Patent No.

7,178,704 to Saidman, the disclosure of which is incorporated by reference in its entirety herein.

[0025] FIGS. 2-4 show further features of the valve assembly 16 and nozzle 18 of the adhesive dispensing applicator 10. The nozzle 1 8 includes a nozzle body 30 having a proximal body portion 30a positioned within the applicator body 12 and a distal body portion 30b extending beyond the outlet and outside the applicator body 1 2. The nozzle body 30 includes an internal passage 32 terminating at a discharge orifice 34 in the distal body portion 30b. In an exemplary embodiment, the discharge orifice 34 defines an orifice diameter D₀ of about 0.40 millimeters. The distal body portion 30b further includes a valve seat 36 formed by a tapering portion of the internal passage 32 adjacent the discharge orifice 34. The proximal body portion 30a further includes a seating flange 38 and a seal member 40 such as an O-ring, the seating flange 38 positioning the nozzle body 30 at the outlet of the applicator body 12. The nozzle 18 of the exemplary embodiment is formed of 303 stainless steel. However, the nozzle 18 could alternatively be formed from other grades of stainless steel, tungsten carbide, or another structural material suitable for the application needs. The shape and the size of the nozzle body 30 and the internal passage 32 may be modified in other embodiments of the adhesive dispensing applicator for different dispensing applications.

[0026] The valve assembly 1 6 includes an elongate body having a needle flange 50, a drive portion 52 positioned proximal to the needle flange 50, and a needle 54 extending distally from the needle flange 50. The drive portion 52 is adapted to operatively engage the drive mechanism and the stroke adjustment mechanism 20 such that the valve assembly 16 may be driven to move in a reciprocating manner proximally and distally. The needle 54 also includes a distal end 56 and a bore 58 drilled and reamed into the needle 54 and extending in a proximal direction from the distal end 56. The valve assembly 16 further includes a valve member 60 inserted into the bore 58 and extending beyond the distal end 56 of the needle 54. The needle 54 and the valve member 60 are located within the internal passage 32 of the nozzle body 30 such that the valve member 60 may be brought into intermittent contact with the valve seat 36 to thereby open and close flow through the discharge orifice 34 as the valve assembly 1 6 is driven to move in a reciprocating manner. The valve member 60 is advantageously press fit or shrink fit into the bore 58 of the needle 54 so that the valve member 60 is reliably retained at the distal end 56 of the needle 54 without the use of adhesive or solder. The process for press fitting or shrink fitting the valve member 60 into the bore 58 is described in further detail with reference to FIGS. 5-9 below.

[0027] In the exemplary embodiment, the valve assembly 16 is formed of a stainless steel having a high degree of corrosion resistance and desired magnetic properties. For example, the valve assembly 16 may be formed from Chrome Core® 18-FM stainless steel commercially available from Carpenter Technology Corporation of Wyomissing, Pennsylvania. It will be understood that other types of steel or metal may be used to form the valve assembly 16 in other embodiments, as long as the bore 58 in the needle 54 is capable of receiving the valve member 60 in a press fitting operation or a shrink fitting operation. As shown in FIG. 4, the needle 54 may be larger in outer diameter at the bore 58 than proximal to the bore 58. For example, the outer diameter of the needle 54 may be about 3.0 millimeters along its length except for adjacent the bore 58, where the outer diameter is enlarged to about 3.42 millimeters. The outer diameter of the needle 54 may also slightly taper inwardly at the distal end 56 as shown in FIG. 4.

[0028] Also in the exemplary embodiment, the valve member 60 is pin- shaped and formed of a hardened ceramic material such as Silicium Nitride (Si₃N₄). The valve member 60 could alternatively be formed of nickel or another material in other embodiments, but the ceramic material is easy to machine with conventional grinding equipment to the tight tolerances required for press fitting and shrink fitting. The ceramic material also reliably withstands between 700 million to one billion duty cycles (i.e., impacts against the valve seat 36) or more before wearing out and requiring replacement of the valve assembly 16 in the adhesive dispensing applicator 10 or replacement of the entire adhesive dispensing applicator 1 0.

[0029] The valve member 60 includes a distal end 62, a proximal end 64, and a pin shank 66 extending between the distal end 62 and the proximal end 64. For simplicity in manufacturing the valve member 60 and the corresponding bore 58, the valve member 60 defines an outer diameter that is constant along the pin shank 66 and tapers inwardly only adjacent to the distal end 62 and the proximal end 64. The proximal end 64 of the valve member 60 is tapered inwardly to ease the insertion of the pin shank 66 into and through the bore 58. The distal end 62 of the valve member 60 is rounded into a generally hemispherical shape configured to selectively abut the valve seat 36 in the nozzle 18. It will be appreciated that the particular shape and size of the distal end 62 and the proximal end 64 relative to the pin shank 66 may be modified in other embodiments without departing from the scope of the invention. For example, the distal end 62 could be modified to define a conical shape or any other shape that mates with the valve seat 36 to cut off adhesive flow through the nozzle 1 8.

[0030] In the foregoing description of the valve assembly 16 and the following description of the processes for manufacturing the valve assembly 16, dimensions and directional terminology are provided for illustrative purposes only and do not limit the respective elements or methods to the exemplary embodiments shown. To this end, the exemplary embodiment of the valve assembly 16 may be reconfigured for use in various adhesive dispensing applicators and nozzles.

[0031] FIGS. 4-6 illustrate the valve assembly 16 during various states of a press fitting process. As shown in FIG. 5, the ceramic valve member 60 is machined by grinding to have an overall pin length of about 9.20 ± 0.05 millimeters and a pin shank diameter of about 2.380 ± 0.003 millimeters. The distal end 62 of the ceramic valve member 60 is machined by grinding to define a hemispherical shape having a radius of curvature R of about 1 .19 millimeters. The proximal end 64 of the ceramic valve member 60 is tapered inwardly at about a 15 degree angle from the pin shank 66 for about 1 .00 millimeters of length such that the proximal end diameter D₃ of the valve member 60 is about 1 .844 millimeters.

[0032] Similarly, the needle 54 is machined by drilling and reaming at the distal end 56 to form the bore 58. The bore 58 includes a bore length L₂ of about 7.00 ± 0.05 millimeters from the distal end 56 to a top end 70 of the bore 58. The bore 58 defines an inner diameter D₂ of about 2.369 ± 0.005 millimeters. Thus, the pin shank diameter is always machined to be slightly larger than the inner diameter D₂ of the bore 58 such that the valve member 60 forms an interference fit with the bore 58. In this regard, the interference fit between the bore 58 and the valve member 60 is within the range of about 0.003 millimeters to about 0.01 9 millimeters depending on the exact size of each member within the specified tolerances. As shown in FIG. 6, a force is then applied to the distal end 62 of the valve member 60 to insert the valve member 60 into the bore 58. The force is applied until the valve member 60 is fully seated in the bore 58 as shown in FIG. 4, for example with the proximal end 64 of the valve member 60 engaging the top end 70 of the bore 58. In the exemplary embodiment, the force F-i that is applied to press fit the valve member 60 into the bore 58 is about 50 N/meter. After the press fitting process, the ceramic valve member 60 is reliably retained in the bore 58 of the needle 54 by the interference fit between the pin shank diameter and the bore inner diameter D₂.

[0033] In another embodiment, FIGS. 4 and 7-9 illustrate the valve assembly 16 during various states of a shrink fitting process. As shown in FIG. 7, the ceramic valve member 60 is machined by grinding to have an overall pin length L₃ of about 9.20 ± 0.05 millimeters and a pin shank diameter D of about 2.380 ± 0.003 millimeters. Similar to the previous embodiment, the distal end 62 of the ceramic valve member 60 is machined by grinding to define a hemispherical shape having a radius of curvature R of about 1 .1 9 millimeters. Once again, the proximal end 64 of the ceramic valve member 60 is tapered inwardly at about a 15 degree angle from the pin shank 66 for about 1 .00 millimeters of length such that the proximal end diameter D₅ of the valve member 60 is about 1 .844 millimeters.

[0034] Similarly, the needle 54 is machined by drilling and reaming at the distal end 56 to form the bore 58. The bore 58 includes a bore length L of about 7.00 ± 0.05 millimeters from the distal end 56 to the top end 70 of the bore 58. The bore 58 defines an inner diameter D₆ of about 2.369 ± 0.005 millimeters. Thus, the pin shank diameter D₄ is always machined to be slightly larger than the inner diameter D₆ of the bore 58 such that the valve member 60 forms an interference fit with the bore 58, at least at room temperature. As shown in FIG. 8, the needle 54 is then heated to expand the inner diameter of the bore 58 to an expanded inner diameter D₇. The heating process is shown by lines 71 . Exemplary expansions of the bore inner diameter at various temperatures are provided in the following table. Table 1 : Expansion of Diameter During Heating of Needle

[0035] In the exemplary embodiment with a roughly 2.38 millimeter diameter bore 58 and valve member 60, the maximum difference between the pin shank diameter D₄ and the inner diameter D₆ of the bore within the provided tolerance ranges is about 0.019 millimeters. Consequently, the needle 54 is heated to a temperature of at least 800 degrees Celsius so that the expanded inner diameter D₇ of the bore 58 is about 2.3884 ± 0.0050 millimeters. Then the pin shank 66 of the valve member 60 is inserted into the bore 58 with a minimal insertion force F₂ as shown in FIG. 9 until the proximal end 64 of the valve member 60 abuts the top end 70 of the bore 58 (as shown in FIG. 4). As the needle 54 cools back down toward room temperature, the bore 58 shrinks such that the pin shank 66 engages the bore 58 in an interference fit. After the press fitting process, the ceramic valve member 60 is reliably retained in the bore 58 of the needle 54 by the interference fit between the pin shank diameter D₄ and the bore inner diameter D₆.

[0036] Although the exemplary embodiment described above for shrink fitting reliably retains the ceramic valve member 60 in the needle 54 during dispensing operations at room temperature, the ceramic valve member 60 is also reliably retained in the needle 54 if the valve assembly 16 is to be used in the dispensing of hot melt adhesives, which may have an operating

temperature of up to 200 degrees Celsius. In such applications at 200 degrees Celsius, the bore inner diameter D₆ expands by about 0.0044 millimeters as shown in Table 1 above, but the pin shank diameter D also expands by approximately 0.001 1 millimeters. Thus, the interference fit between the valve member 60 and the bore 58 is loosened by about 0.0033 millimeters. As such, for valve assemblies 16 adapted to be used in hot melt adhesive applications, the amount of crimping in the interference fit between the valve member 60 and the bore 58 (i.e., the difference in room temperature diameters of the bore inner diameter D₆ and the pin shank diameter D ) must be at least 0.0033 millimeters to avoid loosening of the valve member 60 during operation at 200 degrees Celsius. It will be appreciated that similar calculations may be made for other embodiments of the valve assembly 1 6 having differing shapes and sizes.

[0037] In both of the exemplary embodiments described for

manufacturing the valve assembly 16 (press fitting and shrink fitting), the outer surface 72 of the pin shank 66 and the inner surface 74 of the bore 58 are machined to have a substantially smooth surface finish. For example, the surface roughness of the outer surface 72 of the pin shank 66 may be about 0.4 micrometers, while the surface roughness of the inner surface 74 of the bore 58 may be about 0.8 micrometers. Therefore, the reliable retention of the valve member 60 in the needle 54 is caused primarily by the interference fit between the elements rather than by frictional engagement of the pin shank 66 and the bore 58. However, it will be understood that the surface roughness of the respective outer and inner surfaces 72, 74 may be increased in other embodiments to assist with retaining the valve member 60 in the needle 54. Furthermore, retention features such as corresponding detents and indents in the pin shank 66 and the bore 58 may also be provided in other alternative embodiments.

[0038] Regardless of whether the valve member 60 is press fit or shrink fit into the needle 54, the interference fit between the pin shank 66 and the bore 58 advantageously ensures that the valve member 60 is retained within the needle 54 for the entire lifespan of the valve member 60. The coupling between the valve member 60 and the needle 54 does not use adhesive or solder material to form the joint, so the risk of premature failure of the coupling caused by premature fatigue failure or chemical attack is eliminated with the exemplary embodiment of the valve assembly 16. To this end, the valve assembly 16 has improved reliability over conventional designs. Furthermore, the process for forming the valve assembly 16 is simplified and more cost effective.

[0039] While the present invention has been illustrated by the description of specific embodiments thereof, and while the embodiments have been described in considerable detail, it is not intended to restrict or in any way limit the scope of the appended claims to such detail. The various features discussed herein may be used alone or in any combination. Additional advantages and modifications will readily appear to those skilled in the art. The invention in its broader aspects is therefore not limited to the specific details, representative apparatus and methods and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the scope or spirit of the general inventive concept. What is claimed is:

Claims

claimed is:

1 . A valve assembly for use with an adhesive dispensing applicator, the valve assembly comprising:

a needle including a distal end and a bore at said distal end; and a valve member secured in said bore with an interference fit.

2. The valve assembly of claim 1 , wherein said valve member is pin-shaped and includes a pin shank inserted into said bore, said pin shank including an outer diameter larger than an inner diameter of said bore.

3. The valve assembly of claim 2, wherein said pin shank includes a distal end and a proximal end, said distal end being rounded or tapered from said outer diameter and configured to engage a valve seat in sealing engagement, said proximal end being tapered to assist with insertion of said pin shank into said bore.

4. The valve assembly of claim 3, wherein said proximal end defines an end diameter less than the inner diameter of said bore, and wherein the outer diameter of said pin shank is larger than the inner diameter of said bore by an interference within the range of about 0.003 millimeters to about 0.019 millimeters.

5. The valve assembly of claim 3, wherein said pin shank and said bore define a substantially smooth surface finish of less than about 1 .0 micrometers such that said pin shank is configured to be press fit into said bore by the application of a force to the pin shank.

6. The valve assembly of claim 3, wherein said needle is formed from a material having a coefficient of thermal expansion sufficient to enable said bore to be heated to expand the inner diameter to be larger than the outer diameter of said pin shank during a shrink fit of said pin shank into said bore.

7. The valve assembly of claim 1 , wherein said valve member is composed of a hardened ceramic and said needle is composed of stainless steel.

8. The valve assembly of claim 1 , wherein the coupling of said valve member in said bore by interference fit includes no adhesive or solder materials subject to premature fatigue failure or chemical attack during operation of the valve assembly.

9. An adhesive dispensing applicator comprising:

an applicator body including an adhesive inlet;

a nozzle coupled to said applicator body, said nozzle including an internal passage communicating with said adhesive inlet and a discharge orifice communicating with said internal passage;

a valve seat positioned between said internal passage and said discharge orifice; and

a valve assembly at least partially positioned within said internal passage, said valve assembly further comprising:

a needle including a distal end and a bore at said distal end; and

a valve member secured in said bore with an interference fit,

wherein said valve assembly is adapted to be driven in a reciprocating manner so that said valve member intermittently engages said valve seat to control flow of adhesive through said discharge orifice.

10. The adhesive dispensing applicator of claim 3, wherein said valve member is pin-shaped.

1 1 . The adhesive dispensing applicator of claim 10, wherein said valve member includes a pin shank inserted into said bore, said pin shank including an outer diameter larger than an inner diameter of said bore.

12. The adhesive dispensing applicator of claim 1 1 , wherein said pin shank includes a distal end and a proximal end, said distal end being rounded or tapered from said outer diameter and configured to engage said valve seat in sealing engagement, said proximal end being tapered to assist with insertion of said pin shank into said bore.

13. The adhesive dispensing applicator of claim 12, wherein said proximal end defines an end diameter less than the inner diameter of said bore, and wherein the outer diameter of said pin shank is larger than the inner diameter of said bore by an interference within the range of about 0.003 millimeters to about 0.01 9 millimeters.

14. The adhesive dispensing applicator of claim 12, wherein said pin shank and said bore define a substantially smooth surface finish of less than about 1 .0 micrometers such that said pin shank is configured to be press fit into said bore by the application of a force to the pin shank.

15. The adhesive dispensing applicator of claim 12, wherein said needle is formed from a material having a coefficient of thermal expansion sufficient to enable said bore to be heated to expand the inner diameter to be larger than the outer diameter of said pin shank during a shrink fit of said pin shank into said bore.

16. The adhesive dispensing applicator of claim 9, wherein said valve member is composed of a hardened ceramic and said needle is composed of stainless steel.

17. The adhesive dispensing applicator of claim 9, wherein the coupling of said valve member in said bore by interference fit includes no adhesive or solder materials subject to premature fatigue failure or chemical attack during operation of the valve assembly.

18. A method of assembling a valve assembly for use with an adhesive dispensing applicator, the method comprising:

machining a bore into a distal end of a needle;

machining a valve member to be larger in size than the bore; and inserting the valve member into the bore to provide an interference fit between the valve member and the needle, the interference fit configured to resist impact forces and other forces applied to the valve assembly that would disengage the valve member from the needle.

19. The method of claim 18, wherein machining the bore and the valve member further comprises:

reaming the bore from the needle such that the bore defines a generally cylindrical shape having an inner diameter; and

grinding the valve member to include a generally cylindrical pin shank having an outer diameter larger than the inner diameter.

20. The method of claim 19, wherein machining the valve member further comprises:

grinding the valve member to include a tapered proximal end having a diameter smaller than the inner diameter of the bore to assist with insertion of said pin shank into said bore.

21 . The method of claim 18, wherein the bore includes a top end, the valve member includes a proximal end, and inserting the valve member further comprises:

applying a force to the valve member to press fit the valve member into the bore until the proximal end of the valve member abuts the top end of the bore.

22. The method of claim 18, wherein the bore includes a top end, the valve member includes a proximal end, and inserting the valve member further comprises:

heating the needle to an elevated temperature to expand the bore to be larger in size than the valve member;

moving the valve member into the bore until the proximal end of the valve member abuts the top end of the bore;

cooling the needle from the elevated temperature to shrink the bore and produce the interference fit between the valve member and the bore.