Adhesives automatic dispensing

The adhesive should be processed through automatic dispensing equipment. 

Header systems with manual or automatic dispensing valves have been designed to carry adhesives and sealants over long distances within the plant. Distances of as much as 300 ft are not uncommon with drops at points of application. Figure 17.7 shows a modular header system. Adhesives and sealants are nearly ideal materials for application by robots. Robotic application is commonly used in the automobile industry to increase quality and to reduce labor and material cost.7,8... 

Remove the adhesive film carefully from the Pyrosequencing plate and place it in the pyrosequencer. Close all levers and click run on the plate run set up. The pyrosequencer will now automatically dispense enzyme, substrate and nucleotides in the predetermined dispensation order. The progress of each individual well can be monitored at any time by selecting the relevant well on the 96-well plate map on the screen. 

When the shear stress of a liquid is directly proportional to the strain rate, as in Fig. 2.4a, the liquid is said to exhibit ideal viscous flow or Newtonian behavior. Most unfilled and capillary underfill adhesives are Newtonian fluids. Materials whose viscosity decreases with increasing shear rate are said to display non-Newtonian behavior or shear thinning (Fig. 2.4b). Non-Newtonian fluids are also referred to as pseudoplastic or thixotropic. For these materials, the shear rate increases faster than the shear stress. Most fllled adhesives that can be screen printed or automatically dispensed for surface-mounting components are thixotropic and non-Newtonian. A second deviation from Newtonian behavior is shear thickening in which viscosity increases with increasing shear rate. This type of non-Newtonian behavior, however, rarely occurs with polymers. ... 

The flow properties of an adhesive are largely controlled by its inherent viscosity and by the alteration of its viscosity through the addition of diluents and fillers. How properties are important for screen-printing, automatic dispensing, and capillary flow, and can be tailored by the type of filler, amount of filler, and the particle-size distribution. 

Viscosity, a measure of the flow properties of a liquid, is important as an incoming receiving and acceptance test for adhesives. During automatic dispensing, measuring... 

Typically, an automatic dispenser is used to apply enough adhesive to completely cover the underside of a die. Bondline thicknesses of 1.0 to 1.5 mils and fillets of 50% to 75% of the die thickness are recommended. The star pattern of dispensing is suggested to achieve optimum coverage. A surface-roughness tester, such as a Brown Sharpe Surface Roughness Measuring... 

Two of the most difficult types of adhesives to dispense are Cyanoacrylate adhesives and Anaerobic adhesives. Cyanoacrylates cure by interaction with the surface moisture on a component part. Anaerobics remain liquid in the presence of oxygen but automatically cure once enclosed in a joint. 

Butyl rubber is used in preformed, hot melt adhesive rods which can be fed through various types of automatic dispensing equipment. Butyl provides both strength and flexibility to the adhesive rope before application, flow control during application, and improves the properties of the adhesive bond. A formulation for a typical rope or coil form of hot melt adhesive is shown in Table 8. 

One of the most commonly used semi-automatic dispense systems is the pressuretime method and this is extensively used for a wide range of production engineering applications. The adhesive is stored in a pressurised vessel and pressure is applied to force the adhesive to the dispensing tip. There are two distinct variations of the pressure-time method ... 

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