Mandrel removal

Stress/strain submodel Stresses within the composite that occur during winding, as a result of heating/cooling, or upon mandrel removal are evaluated in the stress/strain submodel. 

The implementation of mandrel removal is of particular interest in winding model formulation. When the mandrel is removed, there is no radial stress [Pg.407]

In the Usui process for producing tapered pipes, the glass fibre reinforcement is wound round a tapered mandrel to make a preform. This is inserted into the mould in the centrifugal machine and the mandrel removed. Resin is poured in and the mold tilted to a pre-determined angle and then rotated until the resin has cured. 

The shape of the component must permit mandrel removal. Long, tubular shapes will generally have a taper. Different mandrel materials, because of differing thermal expansion and differing laminate layup percentages of hoops versus heUcal pUes, will demonstrate varying amounts of difficulty in removal of the part from the mandrel. 

Downward extmsion of a bubble into a water bath and over an inner water-cooled mandrel is used in a few instances for polypropylene and polyesters. The water is removed prior to slitting and winding. 

Electroforrning is the production or reproduction of articles by electro deposition upon a mandrel or mold that is subsequendy separated from the deposit. The separated electro deposit becomes the manufactured article. Of all the metals, copper and nickel are most widely used in electroforming. Mandrels are of two types permanent or expendable. Permanent mandrels are treated in a variety of ways to passivate the surface so that the deposit has very Httie or no adhesion to the mandrel, and separation is easily accompHshed without damaging the mandrel. Expendable mandrels are used where the shape of the electroform would prohibit removal of the mandrel without damage. Low melting alloys, metals that can be chemically dissolved without attack on the electroform, plastics that can be dissolved in solvents, ate typical examples. 

The eouplings should be earefully mateh-marked before removal from the balaneing mandrels. 

For new rotors, where the elements have not yet been put on the rotor, other techniques can be used. First, the components can be individually balanced on a precision mandrel. Precision means that the runout is a few tenths of a mil (.001 inch). The runout high spot should be scribed on the mandrel. The new component now can be reasonably well-balanced. As the component is removed from the mandrel, the mandrel mark should be transferred to the component. When all the components are completed, the shaft is checked for runout. The high spot should be marked. As the components are stacked onto the shaft, the marks on the shaft are aligned with those transferred to the component. This works well with keyless rotors (no key between shaft and component). Experience has shown ihat in most cases with keyless rotors when the stacked rotor is put in the balance machine and checked, the residual unbalance is within the acceptable tolerance. If not, the rotor must be unstacked and the problem located. It must be remembered, however, if the components were properly balanced and the rotor comes out with unbalance, there must be a proh-... 

A laminate is a bonded stack of laminae with various orientations of principal material directions in the laminae as in Figure 1-9. Note that the fiber orientation of the layers in Figure 1-9 is not symmetric about the middle surface of the laminate. The layers of a laminate are usually bonded together by the same matrix material that is used in the individual laminae. That is, some of the matrix material in a lamina coats the surfaces of a lamina and is used to bond the lamina to its adjacent laminae without the addition of more matrix material. Laminates can be composed of plates of different materials or, in the present context, layers of fiber-reinforced laminae. A laminated circular cylindrical shell can be constructed by winding resin-coated fibers on a removable core structure called a mandrel first with one orientation to the shell axis, then another, and so on until the desired thickness is achieved. 

Bellows Nickel bellows can be made by electrodeposition onto a grooved cylinder. In this case, the nickel coating cannot be slid off, and so the substrate must be removed destructively. The grooved cylinders or mandrels are frequently of aluminium alloy which is dissolved away in caustic alkali when the nickel deposition is completed. Uses include pressure switches, flexible couplings, and pressure transducers . 

The nozzle of original design was fabricated from a niobium alloy coated with niobium silicide and could not operate above 1320°C. This was replaced by a thin shell of rhenium protected on the inside by a thin layer of iridium. The iridium was deposited first on a disposable mandrel, from iridium acetylacetonate (pentadionate) (see Ch. 6). The rhenium was then deposited over the iridium by hydrogen reduction of the chloride. The mandrel was then chemically removed. Iridium has a high melting point (2410°C) and provides good corrosion protection for the rhenium. The nozzle was tested at 2000°C and survived 400 cycles in a high oxidizer to fuel ratio with no measurable corrosion.O l... 

The refractory metals for which CVD is commonly used to produce free-standing shapes are tungsten, niobium, rhenium, tantalum, molybdenum, and nickelb lb lb l (see Ch. 6). Shapes presently produced include rods, tubes, crucibles, manifolds, ordnance items, nozzles, and thrust chambers. They are usually deposited on a disposable mandrel of copper, molybdenum, or graphite which is subsequently machined off or removed chemically by etching. 

The removal of uncured assemblies or cured products from a former, mandrel or mould. 

The glass helices may be purchased from the Scientific Glass Apparatus Company, Bloomfield, N. J., or the American Instrument Company, Silver Spring, Md. Wire helices are readily made from No. 18 B. and S. gauge copper or Nichrome wire, by simultaneously winding two strands side by side on a j-in. steel mandrel. The spirals are cut into single helices by means of a thin emery wheel and then removed from the mandrel. 

To ease part removal, mandrels may be constructed from water-soluble materials (sand), plaster, or an assemblage of metal shells that is collapsible or segmented [6], Tube mandrels constructed with a high-quality surface finish and a slight taper are often used for cylindrical parts. 

This requirement is imposed by adding a radial stress at the cylinder inner diameter that is equal but opposite in magnitude to the contact stress between the mandrel and cylinder. The contact stress corresponds to the radial pressure at the interface at the time the mandrel is removed. 

A unique and considerably more elaborate multiaxial test employs a thick-walled hollow sphere test specimen which may be pressurized internally or externally with a nearly incompressible liquid. Figure 20 illustrates the essential features of the test device as described by Bennet and Anderson (5). The specimen is prepared by casting propellant in a mold fitted with a sand-poly (vinyl alcohol) mandrel inside the sphere which may be removed easily after curing. A constant displacement rate instrument drives the piston to pressurize the chamber and apply large deformations. The piston s total displacement volume is transferred to... 

The electroplating process is sometimes used to build up a thick coating of metal on a mandrel or mold. In this process, called electroforming, the mandrel is removed once the buildup is complete. Electroforming can produce intricate shapes whose dimensions and surface textures can be reproduced with great fidelity and detail. 

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