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Tooling innovations speed rotomolding cycles.

Tooling Innovations Speed Rotomolding Cycles

A number of improvements in rotational molds that are said to shorten cycle times have been unveiled by Kelch Corp., a producer of cast-aluminum rotational molds based in Cedarburg, Wis. Taken together, these tooling innovations are said to increase productivity significantly and reduce production costs. Among the specific advantages claimed are reduced manual labor required between cycles, decreased wear and tear on molds, and improved quality of parts.


One development, called the Snap-Sert, is a handling device for securing threaded inserts within a rotational mold that permits rapid installation and demolding of the insert. Previously, threaded inserts had to be screwed manually onto the locating pin prior to molding and unscrewed after each molding cycle. The new system allows molded-in inserts to be held securely in place during the molding cycle, and then released automatically upon demolding without unscrewing them from the locating pin. It is said to cut servicing time by 50-75%, depending on the number of inserts in a part.

Fast release is accomplished through the use of a locking/unlocking device on the locating pin, which extends into the mold cavity through the housing wall of the mold. The locking/unlocking device protrudes from the pin, and internal threads of the threaded insert are engaged when the bore of the insert is placed over the pin. This permits the threaded insert to be slipped on and off for convenient loading and unloading, yet prevents the insert from being displaced during the molding cycle.

When the Snap-Sert is placed perpendicular to the line of draw, a retractor mechanism allows the locating pin to be removed from the cavity to allow the part to be taken out. The device is said to allow the molded part to shrink freely away from the mold, thereby minimizing distortion around the insert.

Depending on its position in the mold, a Snap-Sert insert may cost between $85-$150 and can only be installed in a Kelch mold, according to the company.


The Common Grid has been developed to permit unlike molds that require similar cycle times to be attached and molded during the same cycle, maximizing machine capacity. This is said to be of particular interest to custom molders, who are required to run different-sized molds of the same cycle times simultaneously. Molds can be quickly attached and removed using a variety of quick-attach mechanisms that hold the mold securely to the Common Grid during the molding cycle.

The Common Grid reportedly can be used on any biaxial-type of rotomolding machinery and is custom-made to fit the molder's equipment. The number of molds that can be held on a grid depends on the size of the grid and size and configuration of the mold. Typically, a 6- to 8-ft-diam. grid can hold six or seven medium-sized molds, according to the company, resulting in significant cuts in cycle times for parts that otherwise would be molded individually.

Common Grids of diameters from 6 to 9 ft may cost between $850-$1000.


A clamping system called the Quarter-Turn Lock is said to allow for easy and rapid installation and retraction of cores, inserts, and fill ports. The device is said to be particularly effective in clamping the mold halves together at the parting flange, but also can be used to hold inserts, cores, and fill ports in place during molding, or to attach molds to a common grid. The device reportedly can work on all types of molds and parting lines. It's said to be retrofittable to existing molds and is compatible with Kelch's new Common Grid described above.

The locking device uses a pin that slips into a receptacle and then locks in place with a quarter turn. It can be released quickly with a simple turn of the wrist when demolding the part. One advantage of the system, according to Gary Guzikowski, Kelch's engineering manager for R&D, is to ensure that systems are strong and structurally sound. The Quarter-Turn Lock clamps molds onto the grid with a force of 1100 lb. Another advantage is lower framing costs, due to elimination of the top frame for small- and medium-sized molds. A typical lock for a parting-line closure may cost about $15 per clamp.


Using a proprietary coating called Duraline on the parting line reportedly can increase the life of a mold by 15-25%, depending on the use and care of the mold. Price of the Duraline coating must be quoted per job.

Another coating offered by the company, this one based on PTFE, is said to inhibit the resin from sticking to the parting line, thereby decreasing mold clean-up time by 50% relative to uncoated molds, and also decreasing wear and tear on the mold. Approximate cost of coating the parting line of a 24 x 18 in. mold with this material is $70-100, depending on the complexity of the parting line.

Although these coating systems were developed for aluminum molds, the company claims that they can be applied to other mold materials as well.

Because all of these new developments are supplied on a customized basis, actual prices must be quoted individually, says Sandy Scaccia, general manager of Kelch's Aluminum Molds Div.

PHOTO : (Left) Previously, threaded inserts had to be manually screwed onto the locating pin prior to molding and unscrewed after each molding cycle. But the new Snap-Sert (above) from Kelch Corp. is said to permit rapid installation and demolding of threaded inserts, cutting demolding time 50-75%.

PHOTO : The Quarter-Turn Lock clamping system is released with a simple turn of the wrist upon demolding the part. Kelch Corp. says the device ensures that systems are strong and structurally sound, lowering framing costs of some molds.
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Author:De Gaspari, John
Publication:Plastics Technology
Date:Apr 1, 1991
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