The Mandrel

This component is essential for obtaining the correct geometry of the part. It can be metallic (steel or aluminum), plastic, or even made of chalk, and it can be fixed or removable. When it is fixed, it stays inside the piece, becoming an integral part of it, whereas if it has to be removed, it will be possible to extract it, provided that its shape allows for this or, if it has been made with an appropriate material, it could be unwound. Irrespective of its material and shape, the mandrel has to be able to bear the stresses exerted upon it by the tension of the filament winding on the mandrel (this is another extremely important parameter for obtaining a high-quality product). 

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Testing of Painted Products. The enhancement of paint adhesion is one of the principal functions of conversion coating (20—22). A group of tests based on product deformation is used to test the painted product. The appHance and cod-coating industries use the mandrel bend, the cross-hatch adhesion test, and the direct and reverse impact tests. Adhesion after a water soak is judged using a cross-hatch test performed on the exposed surface. 

Pipe and Tubing. A typical die for extmding tubular products is shown in Figure 4. It is an in-line design, ie, the center of the extmded pipe is concentric with the extmder barrel. The extmdate is formed into a tube by the male and female die parts. The male die part is supported in the center by a spider mandrel. Melt flows around legs of the mandrel and meets on the downstream side. The position of the female die part can be adjusted with bolts adjustment is requited to obtain a tube with a uniform wall thickness. 

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. 

Plating solutions used in nickel electroforming are primarily the Watts bath and the nickel sulfamate bath. Watts baths exhibit higher stress and require additives for stress control, which may affect other properties. Sulfamate baths produce much lower stress and are preferred where purer nickel or nickel—cobalt deposits ate needed. ASTM specifications are available that describe the mandrels and plating solutions (116,162). 

Such defects result from abnormal manufacturing operations such as insufficient lubrication between the metal and the mandrel during the tube-forming process. The lubricant may have been contaminated. Measurement indicated that some of these defects penetrated 8% of the tube wall thickness. Defects of this type can act as corrosion-initiation sites in a sufficiently aggressive environment. 

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-... 

In the past a limitation on this process was that it tended to be restricted to shapes which were symmetrical about an axis of rotation and from which the mandrel could be easily extracted. However, in recent years there have been major advances through the use of collapsible or expendable cores and in particular through the development of computer-controlled winding equipment. The latter has opened the door to a whole new range of products which can be filament wound - for example, space-frame structures. Braiding machines for complex shapes are shown in Fig. 4.76. 

Solid-Type Stabilizers. (See Figure 4-180.) These stabilizers have no moving or replaceable parts, and consist of mandrel and blades that can be one piece alloy steel (integral blade stabilizer) or blades welded on the mandrel (weld-on blade stabilizer). The blades can be straight, or spiral, and their working surface is either hardfaced with tungsten carbide inserts or diamonds [57,58]. 

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... 

A numerically controlled filament winder has been designed and constructed. The distance between the head-stock and tail-stock is six feet. Clearance between the centers emd the body of the winder is adjustable, but a specimen several feet in diameter could presently be fabricated. The mandrel and carriage are each driven by one horsepower, direct current motors with a maximum 2000 revolutions per minute. Three phase, 480 volt alternating current is transformed to a 90 volt, direct current power supply. A gear... 

Position Feedback Encoders generate 512 pulses per revolution of the motor. One pulse correlates to the me2tsurement of 0.023 degree in angular displacement of the mandrel. 

Mandrel Speed Manipulation The speed of the mandrel determines the rate of fiber lay down. To control angular velocity, a proportional control algorithm was programmed... 

The variable ERRORmj n represents the error in the position of the mandrel over an increment in TIME, in seconds. ERRORman is calculated by subtracting the actual pulses accumulated, PULSEman, from the desired number of pulses that would be generated under perfect control. The desired number of pulses for perfect control is determined by the set point speed, RPSman, revolutions per second and the mechanical gear reduction. The constant 15630 is the product of encoder counts per revolution and the thirty to one gear reduction of the mandrel. 

The speed of the motor for the mandrel is accurately controlled to at least 0.1% of the set point speed. The gain, Kman, was selected to be. 1 by observing an acceptable response to a 10% change in the set-point. 

At the start of the wind, the mandrel is also positioned at a reference point. For the initial pass the change in mandrel position is proportional to the counts. For subsequent peisses, a reference PU LS Em AN REF is determined. It is the count at the start of the pass. The rotational, incremental change of the mandrel can then be determined by subtracting PULSEman REF from the actual count PULSEman-... 

The desired carriage position is relative to the measured mandrel s circumferential position and can be visualized with the aid of Figure 5. The count PU LS Eman continues to increment. This is expressed by the ordinate, in terms of units of the circumference. The first peiss, the first dwell and the second pass are shown schematically. The desired locus of the two relative positions result in the line segments represented in bold print. The reference condition for the mandrel position at the start of the pass is PULSEman ref- The actual mandrel s position after an increment of time is PULSEman- The desired carriage position is PULSEqarwant- The two previous conditions are represented by the darkened arrow on the sketch. 

Figure 5. Two-dimensional representation of the relative motions of the carriage and the mandrel.

BAND WIDTH is the width of the roving on the surface of the mandrel. CIRCUMFERENCE is the circumference of the mandrel. 

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