Peeling machines

Fig. 2. Illustrations of forces to which adhesive bonds are subjected, (a) A standard lap shear specimen where the black area shows the adhesive. The adherends are usually 25 mm wide and the lap area is 312.5 mm. The arrows show the direction of the normal apphcation of load, (b) A peel test where the loading configuration, shown by the arrows, is for a 180° peel test, (c) A double cantilever beam test specimen used in the evaluation of the resistance to crack propagation of an adhesive. The normal application of load is shown by the arrows. This load is appHed by a tensile testing machine or other...

Peel tests are accompHshed using many different geometries. In the simplest peel test, the T-peel test, the adherends are identical in size, shape, and thickness. Adherends are attached at thek ends to a tensile testing machine and then separated in a "T" fashion. The temperature of the test, as well as the rate of adherend separation, is specified. The force requked to open the adhesive bond is measured and the results are reported in terms of newtons per meter (pounds per inch, ppi). There are many other peel test configurations, each dependent upon the adhesive appHcation. Such tests are well described in the ASTM hterature. 

PTFE mouldings and extrudates may be machined without difficulty. Film may be obtained by peeling from a pressure sintered ring and this may be welded to similar film by heat sealing under light pressure at about 350°C. 

While detail may be found in the ASTM D-3330 or PSTC-1 and PSTC-2 standards, the peel test is typically carried out as follows The tape is conditioned at 23°C and 50% relative humidity for 1 day. Next, the tape is rolled down with a weighted standard roller onto a clean test substrate (usually polished 302 stainless steel), allowed to dwell for a specified time (usually 1 min), and then clamped with the testing fixture in the test machine and peeled at a specified rate. 

The United. States Department of -bgrieultarc have recontly devised a machine for the peeling ol cilriii fruits and the expression therefrom of the eaaential oil. Although only iu the experimental stage, it piomiaea to be very auecesstnl. 

Adhesion tests can be broken into two categories qualitative and quantitative. They vary from a simple Scotch tape test to a complicated flyer tape test, which requires precision-machined specimens and a very expensive testing facility. Quantitative (such as peeling) tests have been developed for coatings on plastics (12), but not to the same extent for metal-to-metal systems. The quantitative testing systems in limited use, mainly in the electronics industry, are not commonly present in production plants but have been used to aid in process development. For quality control purposes, qualitative tests for metal-to-metal adhesion (13) are usually adequate. The adhesion of some plated metal parts is improved with baking for 1 to 4 h at relatively low (120 to 320°C) temperatures. 

Separation in these devices known as winnowing machines [3], is achieved due to the difference between trajectories of coarse and fine particles in the separation zone (Fig. lb). Their operation and efficiency are strongly affected by the stochastic factors of the process, in particular by uncertainties in feeding and particles aerodynamic interactions. In most cases coarse particles prevent proper classification of fines. Separation efficiency of these devices is usually low. They are normally used for separation of solid particles according to densities (e.g. grain from peel), rather than by size. Sometimes crossflow separation in horizontal streams is used in combination with other separation principles. 

In peel tests, the polyurethane is bonded to a metal strip. The bonded area is 25 x 25 mm. The sample is conditioned, and an initial length of approximately 1.5 mm is stripped from the plate using a knife. The sample is mounted in a tensile strength machine and the polyurethane stripped from the plate. Figure 9.4 shows the sample configurations used. 

Specialized copolymer latices, which are inherently and permanently tacky, are available as pressure-sensitive emulsions. They are mechanically stable and have excellent machinability. They are compatible with many other PVAc latices and, therefore, can be easily blended with other resins for modification of surface tack, peel strength, and creep. 

The cleavage test utilizes a specimen where the load is intentionally placed on one edge of the bonded area. The test method is described in ASTM D 1062. The specimen is usually loaded at a rate of 0.05 in/min until failure occurs. The failing load is reported as breaking load per unit area in pounds per square inch. A standard test specimen is illustrated in Fig. 20.9. Because cleavage test specimens involve considerable machining, peel tests are usually preferred where possible. 

Peel tests were conducted on universal testing machines at 23°C at a test speed of 10 mm/min. In the fixed arm peel test there was a requirement that the peel fixture was attached to the test machine through a fnction-free linear bearing system. This enabled the direction of force on the peel arm to remain vertical whilst the peel fracture was propagating. A number of peel angles were used in the fixed arm test, but all laboratories included a configuration where the peel angle was 90°. 

Only the EMC extractor (see Eigure 3.9-3.10) and recently, some similar machines from FOMESA (7) and OIC (8) allow a simultaneous collection of rasped peel for oil recovery and juice in separate streams. The juice passes from the extractor to a so-called finisher to remove the coarse pulp particles. Then the juice can be bottled as fresh juice or it can be used for the production of juice concentrate. If necessary, the pulp content of the juice can be further reduced by centrifugation, using so-called desludger type centrifuges (AEEA EAVAE and TETRA PAK (9), WESTEAEIA SEPARATOR (10), etc.). 

Ecuelle method, machines are used to prick or cut the outermost layer of the peel, taking care not to touch the zest, since this contains enzymes that can degrade the constituents of the oil. 

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