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Modular container mold cuts replacement costs.

A modular container mold design that permits the main mold frame to stay attached to the molding machine while replacing the specific core and cavity set has been developed by Plas-Tool Co., Niles, Ill. The mold's modular configuration is said to reduce investment costs by 35% to 50% when changing to a new container volume or wall thickness, because only the essential parts--i.e., an interchangeable cavity set that fits within the common frame, rather than the entire mold--need to be replaced.

The modular mold, which is suitable for HDPE and PP, is offered in five volume ranges from 0.3 to 120 liters. The first mold covers 0.3 to 3 liters and is for thin-wall (15-20 mil) containers; remaining groups consist of 4-8 liters, 10-25 liters, 40-80 liters, and 80-120 liters. Multiple cavities are available in the first two volume ranges. A selection of any volume or wall thickness within one of the five ranges is possible after the initial purchase of a complete mold, which consists of a mold frame and modules for cavity, core, and common lid.


During changeover, the last molded pail remains in the closed mold as core-module retainer screws are removed, releasing the core from the frame. As the press is opened, the core remains with the molded part in the cavity module, and a lifting hook is attached. Cavity retainer screws are then removed, releasing the cavity from the frame, and the cavity and core modules are lifted out together. A new volume module, consisting of cavity, core, and molded part, is then lifted into place, and cavity retainer screws are replaced. The mold is closed to the new shut height; core retainer screws are replaced; and lifting hook is removed. After the new module is in place, the mold is opened, the part is ejected, and shot volume and cycle are adjusted to the new part.

The system presents a number of advantages in ease of use and versatility, according to Plas-Tool president and chairman of the board John Von Holdt Sr. No adjustments in water or air lines are required for module changeover. Also, because the core and cavity are changed together with a molded part in place, the module is protected against abuse while it is in transit or storage.

Additional molds can be ordered that fit into a modular mold frame without local fitting required. New modules may be supplied in U.S. or metric units, as well as off-sizes within a volume range.

The modular concept is also said to simplify setup with hot runners, which are used with molds up to 8 liters. During changeover, the hot runner stays in place and remains in line with the mold. Also, a hot runner or heater can be changed without taking the mold out of the press.

"Common" parts of the mold--all mold plates, leader pins, bushings, hot-runner systems, ejector system, water and air system, screws, rack-and-opinion and gear mechanisms, mold outrigger support system, and cavity and core yoke rings--essentially become part of the molding machine and no longer constitute replacement costs of the mold. Further cost savings stem from the use of common lids within each volume category. Lids come either in plain or tamper-evident styles, with or without offset threaded pour spout for a metal cap.

Of particular benefit for thin-wall molds is improved concentricity, says Von Holdt. Thin-wall molds use a patented interlock system to ensure that steel expands equally at all angles under pressure. Tooling concentricity tolerance is [+ or -]0.25 mil and molded part tolerance is [+ or -]0.5 mil for the practical life of the mold. (CIRCLE 3)


In a separate development, Plas-Tool is now supplying molds for 1- to 6-gal containers with either a molded-on plastic handle or two holes to receive snap-in plastic handles. The molded-on plastic handle, available on containers below 3-1/2-gal capacity, is a free-swinging handle that is molded in the container mold. When the mold opens, the connecting plastic piece between the main container to the handle breaks, separating the container and handle as the part leaves the mold.

The new mold is said to address compaints from recyclers that metal handles left on containers often contaminate reprocessed material. The container design is said to have high hoop strength, allowing plastic handles to be used without the open container head "ovalizing" when lifted under full load.

Cost of the end products with plastic handles are the same as metal-handle containers, says the company. Tooling costs for molded-in plastic handles are about 10% higher than conventional snap-in molds. (CIRCLE 4)
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Title Annotation:Molds; Plas-Tool Co.'s modular container mold design
Author:De Gaspari, John
Publication:Plastics Technology
Date:Oct 1, 1991
Previous Article:Rotomolders meet military Q-C specs.
Next Article:Retrofit package to enhance injection molding performance.

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