Inserts force required

The impact of different surface finishes on press fit connectors is another factor to be considered when selecting PWB surface finishes for products such as backplanes. The plastic deformation of the Sn plating, the hardness of the surface finishes, along with the dimensional tolerances of the pin and through-holes, the design of the connector pins (and their mechanical compliance), and the mechanical properties of the PWB, all affect the insertion force required (and consequently the retention force) for the press fit connectors. Typically, the difference in the insertion force among the different surface finishes (Ni/Au, TAg, I-Sn) is not significant (<10%). 

Penetration force is a measure of the force required to insert a needle through the rubber septum. When a needle pierces a rubber closure it inherently generates a number of rubber particles and this phenomenon is termed fragmentation. 

Similarly, the force required to stop a unit volume of flow (which a body inserted into the flow does) is given by f = ma. Multiplying both sides by dx we get I... 

Bueche illustrated glass transition as follows [16]. In measuring the force necessary to force a needle into a polymer, like polystyrene, at various temperatures, there is a relationship between the force required to insert the needle and the temperature [16]. As the temperature is being lowered, maximum resistance to penetration is reached at Tg. 

Pull-out strength n. Of threaded inserts in plastics moldings, the force required to pull the insert out of the molding. It may be expressed as the force per unit area of the engaged outside surface. 

Figure 22.11b shows the distribution of system stiffness in the radial direction (perpendicular to the needle) at the needle entry point (z = 500 mm). The figure shows that system stiffness is quite uniform although absolute values are low. Recall that, for this prototype, system stiffness is limited by the low forces of the handmade DBAs. Developing higher stiffness requires actuators with higher force output. To meet the clinical requirements on needle insertion forces, it is estimated that the number of active layers must increase from 2 to 30, which is technically feasible with proper actuator manufacturing techniques [24]. 

The Pb of Sn-Pb solder-coated barrels is known to reduce the force required for press-fit connector insertion and seating. Although Sn-Pb coating is one of the best surface finishes for pressing, if it is thick, then the press-fit connector pin may skive a thin shver of solder and push it out the secondary side of the PWB (see Fig. 49.8). Very often these slivers... 

The mechanics of microneedle insertion are fundamentally important to practical applications. Only microneedles with the correct geometry and physical properties can be inserted into tissues. When the force required for insertion is too large compared with needle strength, microneedles can break or bend before insertion occurs. Two mechanical events play a critical role in microneedle insertion the force required to insert microneedles and the force needles can withstand before fracturing. The fracture force must be larger than the insertion force for the microneedles to be functional. 

There is however some evidence not in accord with this hypothesis. Experiments by Lai (1970), which included treatment of existing natural rubber gum-stock vulcanizates to both, separately, insert and remove poly sulphide links, did not show any dependence of strength on the nature of the cross-link. Mention may also be made of observations on carbon black loaded natural rubber vulcanizates cured by conventional accelerated sulphur and by EV systems (Des-ramault and Brydson, 1970). Plots of tensile strength against 300% modulus (the force required to extend the sample 300% in a conventional tensile test (not an equilibrium modulus) showed no dependence on the type of cross-linking. 

In this method, a thin wire ring is inserted below the interface (which can be either a liquid-vapour or liquid-liquid interface) and held horizontal. It is then pulled up through the interface and the force required to detach it from the interface, F, is measured by a balance. The surface tension is then given by the following ... 

Improved machinability and reduced insertion force for the rubber stoppers Lubrication of rubber stopper closures prevents their conglomeration as well as reduces the friction between the stoppers and the machinery such as hopper. This improves the flow behavior of the stoppers while they move along the high-speed packaging lines. Lubrication also lowers the friction between the vial and rubber stoppers, reducing the force required to properly insert the stopper on the vial. 

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