CN114486727A - Friction control and binding sealants for press-fit windows - Google Patents

Abstract

The invention relates to a friction control and captive sealant for pressed into a window. An improved method of sealing a window into an opening in a body uses a lubricant comprising polymer particles suspended in a volatile, low viscosity, low surface tension carrier liquid. The carrier liquid is applied to one or both of the window and the sidewalls of the opening and the window is pressed into the opening to evaporate the carrier liquid, leaving the polymer particles to fill interstitial surface voids while enabling intimate mechanical contact of the sidewalls of the window with the sidewalls of the opening. Although having broader applications, the present disclosure is particularly useful in optical characterization techniques based on raman effects and fluorescence probes used in process monitoring and control.

Description

Friction control and binding sealants for press-in windows

technical field

The present disclosure relates generally to optical measurement probes, and in particular, to probes constructed with windows suitable for in-line process control and other applications, and more particularly, to methods for incorporating such windows into probes Improved technology for bulk or process vessels.

Background technique

Optical characterization techniques based on the Raman effect and fluorescence have become important tools in process monitoring and control involving hazardous materials, pharmaceuticals, and other industries. In such applications, it is typical to introduce probes with sealed windows into the process flow to facilitate remote connection to analytical equipment, for example via optical fibers.

Current immersion window designs used by spectroscopic analysis systems rely on several techniques for sealing the window to the probe body. The two most common categories are elastomeric seals, which include O-rings, gaskets, adhesives, etc., and metal seals. O-rings and other elastomer seals have temperature, air tightness and chemical compatibility issues.

Metal seals can be subdivided into soft solder, metal spring seals (eg C-rings) and crimps. For C-rings, standard metal C-rings can be used as seals. However, this type of seal has problems achieving a high level of hermeticity, has difficulty getting the window flush with the probe body housing, and leaves many microvoids and dead volumes that trap the sample material, allowing The technology is not suitable for life science applications due to contaminant transfer.

Generally speaking, metal seals are the most desirable type, offering the potential for high temperature resistance, high pressure resistance, hermetic sealing, long life and robustness. A bonding material, usually a metal alloy or a low melting glass-like material, is used to seal and hold the window in place by brazing, sintering or fusing. Brazed window seals are common in the spectroscopic probe industry. As shown in FIG. 1 , such an arrangement includes a window 102 , such as a sapphire window, which is typically brazed to the surrounding probe body 104 using gold or gold alloy 106 . This technique has all the advantages of the metal seals listed above, plus the fact that the edge of the window is sealed so that the surface is flush with the outside of the probe, without any special styling of the window itself. However, this technique can create undesirable thermal stress between the window and the probe body 104, and the choice of material limits the application space due to corrosion resistance.

An alternative to brazed windows is the crimp window shown in FIG. 2 . In this case, the window 202 is tapered and pressed into the probe body 204 . The interface may or may not have a malleable metal such as gold to aid in sealing. This method is cheap and fast, but has the disadvantage of reducing the compression on the window as the probe body expands at high temperature, potentially leading to seal failure.

The crimp window technique described in US Pat. No. 6,831,739 and incorporated herein by reference uses a specially shaped window that is pressed directly into the probe body to form a permanent and airtight seal of the window and probe body material sealing and corrosion resistance. However, this approach presents difficulties in achieving the correct combination of sealing and window retention without damaging the window or probe body during manufacturing. The shape and surface finish of the window and probe body, as well as the indentation dynamics, must be very tightly controlled. In particular, to obtain an adequate seal, the window must plastically deform the probe body housing with sufficient holding force so that the window does not come out, but the press-in force is low enough to prevent shear stress on the window, The shear stress may cause the window to crack. In practice, it has proven difficult to satisfy all these requirements simultaneously.

Therefore, there is still a need for further contributions in this technical field.

SUMMARY OF THE INVENTION

According to one aspect of the present disclosure, a method of sealing a window into a body having an aperture, the aperture having sidewalls, the method comprising: providing a window having a front surface, a back surface, and sidewalls, comprising A lubricant of polymer particles is applied to at least the sidewall of the window or the sidewall of the aperture and the window is pressed into the aperture in the body to allow the carrier liquid to evaporate, leaving behind the polymer particles to fill the interstitial surface voids , and at the same time, close mechanical contact between the side wall of the window and the side wall of the opening can be achieved. The sidewalls of the window are conformal to the sidewalls of the opening in the body, and the lubricant includes polymer particles suspended in a volatile, low viscosity, low surface tension carrier liquid. In at least one embodiment, the windows and apertures are circular.

In one embodiment, the polymer particles range in size from 0.25 to 16 microns. In one embodiment, the nominal size of the polymer particles is 2 to 4 microns. In one embodiment, the carrier liquid is an alcohol or cyclohexane. In at least one embodiment, the carrier liquid is ethanol. In one embodiment, the lubricant has a mixing ratio of polymer to carrier liquid of 1 :300 by weight. In another embodiment, the lubricant has a mixing ratio of polymer to carrier liquid of 1 :200 by weight.

In another embodiment, the polymer is polytetrafluoroethylene (PTFE) particles and the lubricant is PTFE particles suspended in a volatile, low viscosity, low surface tension carrier liquid.

In another embodiment, the window is composed of sapphire. In one embodiment, the front and back surfaces of the window are substantially parallel to each other. In another embodiment, the side walls of the window and the side walls of the aperture are tapered complementary to each other. In yet another embodiment, the taper of the side walls of the window and the side walls of the aperture is in the range of 1 to 5 degrees. In one embodiment, the side walls of the window and the side walls of the aperture have a 3 degree locking taper. In one embodiment, the sidewalls of the window have a surface finish in the range of 1 to 3 microns. In one embodiment, the sidewalls of the openings in the body have an average roughness of 4 to 8 microns RA.

In at least one embodiment, the body is comprised of a metal or metal alloy. In one embodiment, the body is part of an optical measurement probe. In another embodiment, the body is part of a processing vessel. In at least one embodiment, the force applied to the window during pressing of the window into the aperture in the body is at least 50% less than the maximum tensile stress on the window. In another embodiment, the force applied to the window during pressing of the window into the aperture in the body is at least 70% lower than the maximum tensile stress on the window.

Description of drawings

The described embodiments and other features, advantages, and disclosures contained herein, and ways of achieving them, will become apparent, and will be better understood, by reference to the following description of various embodiments of the present disclosure taken in conjunction with the accompanying drawings. The present disclosure, in the accompanying drawings:

Figure 1 shows a cross-section illustrating a prior art bonding technique in which a window, typically sapphire, is brazed to the surrounding probe body, typically with gold or a gold alloy;

Figure 2 shows a different prior art in cross section in which a tapered window is pressed into the probe body;

3 is a diagram illustrating an improved crimping method with the addition of binding lubricants and sealants for friction control in accordance with the present disclosure; and

Figure 4 is a photomicrograph showing PTFE fines applied to the Raman probe tip leaving only PTFE after evaporation of the alcohol carrier liquid.

Detailed ways

The present disclosure relates to an improved method of sealing a window into a body having an aperture having sidewalls. The present disclosure may be well suited for applications in Raman effect and fluorescence based optical characterization techniques where sealed windows are used in the probe body and in the walls of the process vessel.

The method of the present disclosure improves upon crimp window technology by including a lubricant for controlling the amount of friction experienced during press-in. Ideally, the lubricant will disappear completely after the process is complete, or use a material that is chemically and thermally compatible with the probe's intended application environment.

According to the present disclosure, there is provided a window having front and back surfaces and side walls, wherein the side walls of the window are conformal to the side walls of an aperture in a body. A lubricant consisting of polymer particles suspended in a volatile, low viscosity, low surface tension carrier liquid is applied to one or both of the side walls of the window and the aperture, and the window is pressed. into the opening to allow the carrier liquid to evaporate, leaving residual polymer particles behind to fill the interstitial surface voids while allowing the sidewalls of the window to be in close mechanical contact with the sidewalls of the opening. The windows and apertures may be generally circular in peripheral shape.

However, if too much polymer is present, the window may substantially "float" on the polymer layer and may not be adequately retained or sealed. According to at least one embodiment of the present disclosure, as shown in FIG. 3, the fit dimensions are controlled such that the window 302 achieves close mechanical "window-to-shell" contact after being pressed into the body 304, wherein the residual polymer particles 306, 308 are at least The interstitial surface voids in the window 302 and the body 304 are partially and in some embodiments substantially pressed into and at least partially filled.

The lubricant can be a very dilute suspension of polymer micropowder in a volatile, low viscosity, low surface tension fluid that wets the surface, distributes the polymer powder evenly, and evaporates rapidly, leaving behind polymer particles sparse distribution. The surface finish of the housing and window allows the polymer to be applied to the surface during the press-in process and then cold flow into the voids of the microstructure, enabling direct contact of the window to the housing, but at the same time being squeezed and bound polymer, which fills microscopic voids and creates an airtight seal that is resistant to high temperatures and chemicals. Thus, the polymer particles (eg, micropowders) can be any suitable polymer, including thermoplastic, thermoset, elastomeric and semi-crystalline materials, which can remain suspended in a carrier liquid and have suitable cold forming properties. In at least one embodiment, the particles may be graphite rather than polymers.

The particles are sized small enough to fill interstitial surface voids, microscopic crevices and gaps within and between the windows 302 and/or bodies 304, and large enough for suitable cold forming properties. In at least one embodiment, the polymer particles can range in size from 0.25 to 16 micrometers (μm). In certain embodiments, the polymer particles may have a nominal or average size range of 2-4 μm. The carrier liquid can be an alcohol, such as ethanol, or cyclohexane. The window may be a sapphire window, wherein the front and back surfaces of the window are substantially parallel to each other. The taper of the side walls of the windows and apertures may be in the range of 1-5 degrees. In certain embodiments, the side walls of the windows and apertures may have a locking taper of about 3 degrees. In at least one embodiment, the sidewalls of the windows can have a surface finish in the range of 1-3 μm, and the sidewalls of the openings in the body can have an arithmetic mean roughness (Ra) of 4-8 μm Ra. The body may be constructed of metal or metal alloys.

)。在这样的实施方案中，PTFE颗粒的尺寸范围可以为0.25至16微米(μm)。在某些实施方案中，PTFE颗粒的标称或平均尺寸范围可以为2-4μm。在其它实施方案中，聚合物可以是线性聚乙烯(PE)、聚丙烯(PP)、聚酰胺(PA)、聚酰胺6,6(PA66)、聚酯、聚烯烃(如聚α-烯烃(PAO))、或另一种合适的聚合物。在另一个实施方案中，聚合物可以是具有粘弹性的热塑性弹性体。In at least one embodiment according to the present disclosure, the polymer is polytetrafluoroethylene (PTFE, eg, powder form)

). In such embodiments, the PTFE particles may range in size from 0.25 to 16 micrometers (μm). In certain embodiments, the nominal or average size range of the PTFE particles may be 2-4 μm. In other embodiments, the polymer may be linear polyethylene (PE), polypropylene (PP), polyamide (PA), polyamide 6,6 (PA66), polyester, polyolefin (eg, polyalpha-olefin ( PAO)), or another suitable polymer. In another embodiment, the polymer may be a viscoelastic thermoplastic elastomer.

Applicants conducted tests using at least one embodiment disclosed herein. The tests described herein show that the diluted PTFE lubricants of the present disclosure are capable of reducing the indentation force to less than 70% of the maximum tensile stress on the window, which is the most brittle component, while maintaining at least 50% of the maximum holding force . In one embodiment, the indentation force may be less than at least 50% of the maximum tensile stress on the window. The following test experiments provide details on the preparation and use of friction reducing solutions (ie, lubricants) for assembling crimp windows in probe body tips used in Raman spectroscopy applications. Two different window seal surface finishes, lapped and non-lapped, were tested.

Lubricant: PTFE powder, available from Micro Powders Inc, Terrytown, NY, USA, part number FLUO 300XF, with an average particle size ranging from 2-4 μm on average and 16 μm maximum in the ethanolic carrier liquid used to suspend the lubricant. Probe body tip sealing surface area: 0.035 square inches; sealing surface finish: 4μm or better. Probe window seal surface area: 0.023 square inches. Probe window sealing surface finish: lapped windows – 1 μm Ra or better; non-lapped windows – 1.5 μmRa.

Procedure: Apply the PTFE solution to the sealing surface of the probe body tip. For the lap window, the lubricant was a 1:300 mix by weight of PTFE to carrier liquid, and 2 μL (0.00067 grams (g) PTFE) to 3 μL (0.0010 g PTFE) of the lubricant solution was dispensed. For non-overlapping windows, the lubricant was a 1 :200 mix by weight of PTFE to carrier liquid and 3.0 μL of lubricant solution (0.001507 g PTFE) was dispensed. Window Press-In Force: <370 lbs.

Figure 4 is a photomicrograph showing the lubricant PTFE after application to the probe body tip and after evaporation of the ethanol carrier liquid, leaving only PTFE particles pressed into the window and microvoids in the body.

While various embodiments of the disclosed methods have been described in considerable detail herein, these embodiments are provided merely by way of the disclosed non-limiting examples described herein. Therefore, it will be understood that various changes and modifications may be made and equivalents may be substituted for elements of the present disclosure without departing from the scope of the present disclosure. This disclosure is not intended to be exhaustive or to limit the scope of the disclosed subject matter.

Furthermore, in describing representative embodiments, the present disclosure may have presented methods and/or processes in the form of a particular sequence of steps. However, to the extent that the method or process does not rely on the specific sequence of steps set forth herein, the method or process should not be limited to the specific sequence of steps described. Other sequences of steps may be possible and still remain within the scope of this disclosure.

Claims (15)

1. A method of sealing a window into a body having an aperture with a sidewall, the method comprising:

providing a window having a front surface, a back surface, and a sidewall, wherein the sidewall of the window conforms to a sidewall of an opening in a body;

applying a lubricant to at least the side wall of the window or the side wall of the aperture,

wherein the lubricant consists of polymer particles suspended in a volatile, low viscosity, low surface tension carrier liquid; and is

Pressing the window into the opening of the body to evaporate the carrier liquid to leave the polymer particles filling interstitial surface voids while enabling intimate mechanical contact between the sidewalls of the window and the sidewalls of the opening.

2. The method of claim 1, wherein the polymer particles range in size from 0.25 to 16 microns.

3. The method of claim 1, wherein the polymer particles have a nominal size of 2 to 4 microns.

4. The method of claim 1, wherein the carrier liquid is an alcohol or cyclohexane.

5. The method of claim 1, wherein the front surface and the back surface of the window are substantially parallel to each other, and wherein the sidewalls of the window and the sidewalls of the aperture are tapered complementary to each other.

6. The method of claim 1, wherein the taper of the sidewalls of the window and the apertures is in the range of 1 to 5 degrees.

7. The method of claim 1, wherein the sidewall of the window has a surface finish in the range of 1 to 3 microns.

8. The method of claim 1, wherein the sidewalls of the opening in the body have an average roughness of 4 to 8 microns RA.

9. The method of claim 1, wherein the body is part of an optical measurement probe or a process vessel.

10. The method of claim 1, wherein the polymer of the polymer particles is Polytetrafluoroethylene (PTFE).

11. The method of claim 1, wherein the lubricant has a 1:300 by weight mixing ratio of polymer particles to carrier liquid.

12. The method of claim 1, wherein the lubricant has a 1:200 mix ratio of polymer particles to carrier liquid by weight.

13. The method of claim 1, wherein the polymer of the polymer particles is an elastomeric polymer.

14. The method of claim 1, wherein the polymer of the polymer particles is an elastomeric polymer.

15. The method of claim 1, wherein a force applied to the window during pressing of the window into the aperture in the body is at least 50% less than a maximum tensile stress on the window.

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