Press-fit connections

The electrical properties of press fit connections are at least equivalent to, if not superior to, soldered connections. Process quality can be monitored by creating a force/travel diagram during the press fit. 

Figure 5.11 A schematic diagram of the ASPEC-GC-ECD equipment. HPl and HP2, high pressure six-way valves LPl 1, low pressure three-way valves RG, retention gap RC, retention column Tl, press fit coimection between RG and RC T2, three-way press fit connection for solvent vapour exit [117].

Tribology The frictional properties of a material become important for press-fit connections. 

If tribologic forces are too great, then the PTH barrel can be pushed out of the board or otherwise damaged. Trial boards and pressing parameters should always be assessed before full manufacturing commences. Only very small changes or imperfections can interfere with the typically high yields of press-fit connections. 

Ocket,T., and Verhelst, E., Lead-Free Manufacturing Effects on Press-Fit Connections, paper presented to the International Center for Electronic Commerce (ICEC) Proceedings, Zurich, September 2002. 

It is possible to place a deactivated silica capillary in the transfer line (Section 1.2.3) and to connect the analytical column to the latter. Obstructing this capillary by jabbing it into a septum when changing the column avoids stopping the pumps of the mass spectrometer. Be aware though, as mentioned previously, all press-fit connections constitute potential sources of leakage. 

Gas Chromatograph -- A Varian 6000 equipped with two constant-current/pulsed-frequency electron capture detectors, a 30-m x 0.53-mm ID DB-5 fused-silica open-tubular column (1.5-/xm film thickness), and a 30-m x 0.53-mm ID DB-1701 fused-silica open-tubular column (1.0-/im film thickness), both connected to a press-fit Y-shaped fused-silica inlet splitter (Restek Corporation, Bellefonte, Pennsylvania), was used to analyze for the nitroaromatic compounds. The columns were temperature-programmed from 120°C (1.0-min hold) to 200°C (1-min hold) at 3°C/min, then to 250°C (4-min hold) at 8°C/min injector temperature 250°C detector temperature 320°C helium carrier gas 6 mL/min nitrogen makeup gas 20 mL/min. 

Figure 5.1 Disassembled view of the spectroelectrochemical cell. (1) Tightening brass cap (threaded inside). (2) Brass ring required to tighten the cell. (3) Working electrode (brass rod with platinum soldered to the base). (4) Auxiliary electrode platinum wire with the tip made flush to the teflon base of the cell. (5) Pseudoreference electrode silver wire, also made flush to the teflon. (6,7) Luer-lock-type injection ports. (8) Cell body, top part aluminium, lower part teflon. (All three electrodes and both filling ports are press fitted into the cell body, so that they can be replaced if needed.) (9) Teflon spacer, determines the pathlength of the cell and masks the reference and counter electrodes from the incident beam. (10) Calcium fluoride window (Wilmad, standard 38.5 x 19.5 x 4mm). (11) Rubber gasket. (12) Hollow brass cell body with threaded inlet and outlet ports (Swagelock) for connection to circulating bath. (13) Two-mirror reflectance accessory (Thermo-SpectraTech FT-30). (14,15) Mirrors.

A key element in cost-effective sensor housings is the electrical connection between the circuit board and the outer connector. Good connections can be made very easily using press fit technology, which can simultaneously make the electrical connection and position the circuit board inside the housing (Fig. 5.8.9). This is a dry cold process adding only minimal costs. When used properly, press fit plugs can be used as the mechanical fixture and not only the electrical connec-... 

Because of the lower ductility of the fluorocarhon materials (e.g., TFE, CTFE, FEP), snap-fit and press-fit joints are seldom nsed. Rivets or studs can be used in forming permanent mechanical joints. These can be provided with thermal techniques on the melt-processable grades. Self-tapping screws and threaded inserts are used for many mechanical joining operations. In holted connections, some stress relaxation may occur the first day after installation. In such cases, mechanical fasteners should he tightened thereafter, stress relaxation is negligible. 

The dielectric layer is metallized at one side (e.g., a silver electrode is screened on the mica insulators in mica capacitors), then cut into rectangular pieces. The pieces are stacked with an offset of the alternative layers. The end caps are connected using press fitting and conductive pastes. Then the leads are connected and one of the sealing procedures follows. 

Experiments studying the corrosion behaviour of pipes and pipe connections made of the steel 1.4301 (SAE 304 UNS S30400) were carried out in cold drinking water in field tests lasting five years [34]. Table 20 contains data for pipes in various heat treatment states. The pipe connections were made of the same material as the pipes. Pressed fittings with a non-metallic seal and solder fittings were tested. The chemical composition of the solders used is shown in Table 21. 

Successful assembly of a press-fit backplane rests in designing a hole size small enongh to create a solid connection with the pins while ensnring that the hole is large enongh to permit the insertion of the pin withont fractnring the hole barrel. 

The notion of a gas-tight seal as the product of a proper press-fit is crucial to connection reliability. If an electrical contact is to be rehable, the interface between the two mating surfaces must remain chemically and mechanically stable. The gas-tight, smeared, metal-to-metal contact attained during the press-fit operation mitigates oxidation of either contact (FTH barrel or press-fit pin) and prevents fretting corrosion, which is a common failure mechanism for mechanically mated contacts, especially those subjected to vibration. Press-fit interconnection is considered at least as rehable as a soldered connection and there is no solder joint to degrade or crack with time. 

Barrel finish can have a profound impact on the press-fit operation. If a PTH barrel is too thin or poorly sized for the compliant pin, the pin may pierce the barrel wall or break internal connections to it. OSP-copper finish—since it is a watery, thin topical coating—adds no appreciable thickness to the PTH lands or barrel, so its control in high-aspect-ratio holes is not an issne in terms of press-fitting. Electroless/immersion surface finishes are generally thin and self-limiting in thickness, and as with OSP-copper, there no appreciable change in PTH hole diameter adding httle impact to the press-fit process. 

The connecting link consists of two connecting pins press fitted into one pin link plate, the required number of center fink plates, and a cover plate. Either cotters or a spring clip may be used to hold the cover plate in place. The cover plate should be an interference fit on the pins to give the connecting link about the same strength as the pin links in the chain. 

In most cases, the connector for flat-top chains is just a connecting pin. The connecting pin is usually either knurled or enlarged on one end to retain the pin in one barrel of the top plate. Sometimes the pin is jnst a straight pin and relies on a press fit in one end barrel to retain it. 

These directions cover only single-strand roller chains and connecting links with slip fit cover plates. If the chain is multiple-strand roller chain or if the connecting link has a press fit cover plate, see the ACA publication Connect and Disconnect Guide for ANS Roller Chains. Additional information can also be obtained from the chain manufacturer. 

Many engineering steel chains are very large and the press fits of the pins in the sidebars are very heavy. Connecting such chains into strands for installation must be carefully planned. This is both for safety and to avoid damaging the chains. The forces needed to install the pins are so large that pressing equipment is usually needed to disconnect and connect these chains. 

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