High-temperature mold steel

Measurement of a number of properties requires sheet stocks of PFA, from which specimens are punehed out and conditioned before testing. The sheet is prepared by using a chase in the shape of a picture frame with the adequate depth to produce a finished thickness of 1.5 0.25 mm. A fairly thick (0.13-0.18 mm) aluminum foil is sprayed with a high-temperature mold release agent before being placed smoothly over a flat steel plate (>1 mm thick). The chase is then placed over this plate-assembly. An amount of polymer sufficient to produce the sheet is placed in the middle of the chase in the form of a mound. A second sheet of aluminum foil is placed on top of the polymer granules and the top steel plate is added to the assembly, which is then put in a preheated (380 5°C) compression molding press. 

Allyl diglycol carbonate (CR-39) is the most highly scratch resistant of the transparent plastics. Unlike most of the other transparent plastics that are TP, CR-39 is a TS plastic that has been in use for over a half century in applications such as bullet-proof shields, high temperature steel blast furnace eye and face guards, aircraft window side panels, etc. Processing methods include injection molding and casting. 

Schematic diagrams of (top) stacked dried PF resin-soaked kraft paper (brown) plus a metal foil (optional), a pattern or veneer sheet (red) and a translucent sheet (blue) (middle) compression molding between highly pol-ished heavy steel platens under high temperature and pressure (bottom) a sheet of Formica laminate.

The surface temperature of each mold half should be held within + 4 F. At the high temperatures at which nylon RIM tools are operated, this requirement necessitates the use of more coring than is sometimes used for urethane tools. In steel tools. 75 inch diameter circulating oil core holes, spaced at 2.5 Inches on centers and located roughly 2-inches from the cavity surface have worked quite well. An average temperature difference of about 5°F can be... 

Smooth surfaces of each polymer were also prepared (without additives) by pressing samples of the powdered polymers against a highly polished stainless steel surface in a Carver press at 16,000 p.s.i. Circular disks 1 inch in diameter and weighing several grams were formed in this way. PS and the PVeC copolymer were compressed at room temperature, PAM at 120° C.,and PMMA at 150° C. The pressure was maintained until smooth polymer surfaces were obtained. The mold and stainless steel piston were cleaned prior to use, so that contact angles could be measured on the polymer surfaces without further surface treatment. 

Since absorbed water can cause catalyst decomposition and hence incomplete polymerization and since lactam monomer flakes are highly hygroscopic, the melting of monomer is carried out under appropriately controlled temperature and humidity conditions. All additives are also completely dried and then mixed with the monomer in stainless steel vessels while flushing with inert gas under thermostatically controlled temperature. Molds can be of the single type fabricated from silicone rubber, epoxy, or sheet steel or the more expensive tool steel used in tight tolerance cast-to-size parts casting. 

Molds can range from hardwood for short runs to filled and unfilled high temperature polyester (TS) and epoxy resins, cast solid urethane, sprayed metal, cast aluminum, cast porous aluminum, and machined steels. The... 

Injection molds are machined from a variety of tool steels and then hardened or in some cases plated with chromium, nickel, or proprietary materials. Large molds use prehardened tool steels because they cannot be hardened after machining. 124 Stainless steel is employed for some smaller molds, particularly those used for optical and medical parts and for corrosion resistance. Since they provide better heat transfer and, thus, shorter molding cycles, materials such as beryllium copper are used as inserts in critical areas. Injection molds are usually cooled or heated with water, although oil or electric heater cartridges are employed for high-mold temperatures. Mold-temperature controllers pump water into the manifolds and then into cooling fine machine into the molds. 

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