Tools hardening/platings

A hard, mst-resistant shaft of at least 0.25 micrometer finish is usually required. Common shaft surfaces are hardened tool steel, chrome plate, high strength bronze, and carbide and ceramic overlays. Test results over a broad speed range from 0.05 to 47 m/s (10 to 9200 fpm) iadicate that a coefficient of friction of 0.16—0.20 and a wear factor of 14 X 10 m /N(70x 10 ° in. min/ft-lb-h) are typical for dry operation of weU appHed grades of carbon—graphite (29). 

Even without heating it is likely that in the course of each pass there will be some release of volatile material—like water vapour, plasticizer, extender, or processing aids (anti-static agent or lubricant). There must be opportunity for such substances to be vented and carried away the die or tool must be capable of resisting attack by volatiles (suitably plated if they are corrosive), and designed to prevent an accumulation of released materials. Special hardened... 

Once all departmental activities are satisfied, with redesign and resamples if necessary, metal should be cut for the full production tool, but on the understanding that further purchaser evaluations must be completed before tool acceptance (or, for example, before a mould is finally plated or hardened). 

Steel. The extrusion process being continuous, both erosion and corrosion are significant factors. Hence the dies must be made of a high-quality tool steel, hardened so that the areas that contact the plastic material do not erode. Additionally, many dies have a dense, hard chrome plating in the area where plastic melt contacts the die. 

Ejection of a molded plastic article from a mold can be achieved by using ejector pins, sleeves, or stripper plates. Ejector pins are the most commonly used method because they can be easily fitted and replaced. The ejector pins must be located in position where they will eject the article efficiently without causing distortion of the part. They are worked by a common ejector plate or a bar located under the mold, and operated by a central hydraulic ejector ram. The ejector pins are fitted either to the bottom force or to the top force depending on whether it is necessary for the molding to remain in the bottom half of the female part or on the top half of the male part of the tool. The pins are usually constructed of a hardened steel to avoid wear. 

The workrest plate, also known as work rest blade, work blade, or workplate, needs to be highly wear-resistant and consists of tool steel or cast iron with hardened surfaces, cemented carbide inserts or coatings of PCD, or other hard material. Workrest plate angle is important for grinding force directions and process stability. 

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. 

The one-impression mould was made by Penton Tools Ltd of High Wycombe (part of the Guinness group). It is a conventional two-plate injection mould incorporating a side core to produce the front sliding cover channel. The mould was made from mild steel with hardened-steel cavity inserts. 

Aluminum, steel, or beryllium-copper is used for the bottle cavity and neck ring. For polyolefin resins, aluminum No. 7075, as well as QC-7, is used. The surface is usually finished with No. 120-grit sandblast, which increases the venting of trapped air. For rigid resins, A-2 tool steel air-hardened to 52-54 HRC is used. The surface finish is highly polished with chromium plating. Cast beryllium-copper is often used for minute detail. As with the parison cavity, water lines are drilled as closely together as possible, perpendicular to the cavity axis. 

Unlike injection blow molds, which are mounted onto a die set, extrusion blow molds are fitted with hardened-steel guide pins and bushings to ensure that the two mold halves are perfectly matched. Dies, mandrels, blow-pin cutting sleeves, and neck-ring striker plates are made from tool steel hardened to 56-58 HRC. 

Tooling Plates. The outermost item in the stack is termed a caul plate or carrier plate. These are thick, oversized metal plates, generally made of % in. (9.525 mm/0.375 in.) thick steel.The 4130 alloy of steel is often chosen due to its precision machining capabiUty for placement of the holing holes. Sometimes a hardened aluminum alloy is chosen, but is not highly recommended due to its high in-plane expansion. The purpose of the caul plate is to provide a stable base to transport the ML-PWB stack. 

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