Shell mold

CASTOR OIL (Ricinns communis Emiharbiiiceae) CAS HOOI-79-4). Castor oil is obtained from a short lived perennial tree that occurs wild in tropical Africa and perhaps in India. Cultivation of the tree is widespread not only in the tropics but also in temperate regions, where it is often grown as an ornamental plant In the tropics it becomes a iree 36 feet tall, with large coarse leaves often of reddish color, and green flowers. An annual herbaceous variety is grown widely and produces a superior oil. The seeds, borne three in each of the smooth or prickly capsules, have a hard molded shell. These seeds are ejected violently from the mature fruit. 

To avoid damage and ensure long life, the flanges should be about 50% thicker than the mold shell itself and metal plates should be incorp-... 

The cam controlled temperature controller sets the cure cycle for the epoxy. Once the epoxy is introduced, the temperature is held for about 12 hours then the temperature is slowly raised to 60 C (this takes about 3 hours). The cure at 60 C takes 8 hours. Then the temperature is raised to 80 C. (This takes about 2 hours.) The magnet and the mold are maintained at 80 C for at least 8 hours. The outer molding shell can be removed after the magnet temperature has dropped to room temperature. The pour and cure temperature schedule for the A magnet (one of the one-meter diameter solenoids) is shown in Fig. 3. (Note the epoxy was not held at 50 C for 12 hours before starting the cure.)... 

This cast aluminum rotational mold can be modified using inserts so that either a BBQ-Donut Half (Figure 1.175) with steps of invert or a half with motor and umbrella holder can be molded. The mold consists of 10 mold shells. 

In the construction of prototypes, molds are used where the mold shells are manufactured in the metal spraying procedure. This is only possible for easy and flat contours due to the metal spraying procedure. 

FIGURE 1.176 Prototype mold with carbon fiber molded shells... 

These molds can be made from CNC-milled or casted aluminum mold shells (a combination between both methods is possible as well). A mold made from a combined cast aluminum and CNC-milled shells can be manufactured. In addition, a lot of different materials in a mold (aluminum with steel) can be used for the manufacture of mold shells. 

The production steps of both applications differ from each other significantly. The complete construction of the mold shells and the design of the form separation and flanges have to be determined for the production of a machined aluminum mold. The manufacture of a mold begins mostly with the production of a positive model (per sample, drawing, or 3D data). 

For an economical rotational production, it is necessary to machine the mold shells to a certain wall thickness, which means to machine on both sides. This will ensure an equal and fast heat penetration of the mold wall. 

The use of mold shells manufactured in an aluminum casting is advantageous for large and deep mold shells or for necessary follow-on molds. For the manufacture of aluminum casting mold shells, the casting molds made from sand or sand/ceramic molds have to be manufactured first. The aluminum casting process, shown in Figure 1.179, is done by hand. 

Negative molds are needed when manufacturing such casting molds. These correspond to the required mold shells and already have the necessary mold flanges and mold thickness (mostly between 7 and 12 mm). 

To give the mold halves the necessary stability and uniform clamping, a steel frame is attached above the flanges. Manual clamping devices, pneumatic cylinders, or similar closures are installed to this frame. Furthermore, additional protection for the often fragile, thin-walled mold shells is offered. The steel frame can either be made out of bent or welded steel tube as seen in Figure 1.178, or out of flat materials. 

The wall thicknesses of the aluminum molds are very thick in comparison to the thin-walled sheet steel molds (1.5 to 3 mm). Wall thicknesses between 7 and 15 mm are used for casting molds (depending on the quality of the casting process). In the mold shells that are CNC milled out of an aluminum block material, a standardized wall thickness of 7 mm is established. 

For heating and cooling, different process systems can be used that need adapted electroplated mold shells ... 

Mold shells from sulphamate nickel with a wall thickness of about 3 to 4 mm, which are heated either with hot air or in a sand bed, where cooling is done through spraying with a water-air mixture or though cold air. 

Mold shells from sulphamate nickel with a wall thickness of about 4 to 5 mm, soldered onto the temperature control pipes made from steel, so that heating and cooling can be done using heat transfer oils (Figure 1.187). 

In order to meet the great demands of application technology and the design department on the construction, surface structures, dimensional stability of the slush mold skins, electroplated molds are made available. The goal is reached by using a complex and expensive model technology. Figure 1.188 shows the principle path from CAD data to the finished electroplated mold shell. 

The bath model is prepared (as described above), made electrically conductive, and put into a sulphamate nickel bath for an electroplated deposition. Depending on the size, geometry and required wall thickness, the model stays between three to seven weeks inside the electroplated hath including disruptions (to renew auxiliary anodes and insert covers). When reaching the required wall thickness, the process is ended and the mold shell is ground to the outer contour. If necessary, the flange surfaces have to be milled, and fixed bore holes have to be drilled. After thermal or chemical demolding of the bath models, the inner contour is cleaned, the mold is measured, values are compared to the CAD data, and a defined surface treatment is applied. 

The design of the positive models is of particular importance, because large-sized galvanized molds are often used in the aerospace industry, and mold shells of up to 9 m long and 3 m wide are currently manufactured in Germany. Bath models... 

The negative-stamping deep drawing allows for high production volumes with short cycle times. In addition, deep-drawing molds, which are manufactured using nickel mold shells, can be, in many cases, combined with subsequent work operations, namely ... 

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