128-cavity mold designed for easy maintenance.

A new "maintenance-friendly" 128-cavity mold, supplied by JK Molds, Inc., Upland, Calif., fills in less time, requires no more clamp tonnage than the 64-cavity mold that it replaces, and occupies less space as well. The system combines some minor alterations to the hot-runner system with a reportedly unique "converter" piece between the tips and the cavities, providing a four-drop system with replaceable inserts.

The new mold, used to make syringe caps for a major medical supplier, replaces a 64-cavity mold that employed a single hotrunner probe per part. The molder had experienced cracking of cavities and manifolds and was looking to increase productivity.

'CONVERTER' INSERT

The hot-runner system for the mold was supplied by Enrietti of Italy, represented here by A.L.B.A. Enterprises, Torrance, Calif. Typical multi-tip hot-runner systems, in which multiple cavities are fed from one block, have the disadvantage that cavities cannot be shut off individually. In a four-drop manifold system, if one cavity is damaged due to gate blockage, all four cavities in the block go down. To get around this problem, JK Molds developed a simple converter piece, or interchangeable insert, that fits between the hot-runner probe and the cavities. The converter is actually a seat with four holes, each of which accepts a hot-runner tip that feeds into a cavity. The system enables an individual cavity to be shut off by blocking off the hole.

Essentially, this converter changes the four-drop hot-runner system into a single-drop system because the interchangeable inserts allow one, two, three, or four parts to be run off the same probe without affecting the integrity of the parts. To accommodate the converter piece, Enrietti lengthened the tips at the end of the probe. Another advantage claimed for the Enrietti system is that beaters are located at the tips, providing more effective heating. Also, all components, including the tips, are replaceable--not cast-in. (CIRCLE 8)

Each four-tip probe is equipped with one temperature controller for a total of 32 temperature zones in the mold. Fewer temperature zones may result in a greater loss of cavities from damaged controllers than would be the case with individual control of the tips, acknowledges Jack Kelly Jr., president of JK Molds. On the other hand, fewer controllers also mean fewer potential problems and lower equipment costs.

The system is also said to provide advantages in cooling. In a traditional four-drop system, it's not possible to feed cooling water around each individual cavity, Kelly says, because each cavity is contained in one block. Water passes around all four parts, cooling only the outside of each part. By contrast, because the converter changes the four-drop system back to a single-drop one, it allows 360' cooling around individual cavities, cores, and strippers. Basically, the tool has a standard configuration from the hot-runner system down, says Kelly.

LOWER TONNAGE, EASIER MAINTENANCE

Using one probe to fill four parts reduces both the size of the mold and the required clamp tonnage. The 128-cavity mold measures 18.5 x 20 in. with a 16-in. stack height--significantly smaller than the 64-cavity mold. With the new system, four parts occupy a much smaller area in the mold than did one using a single probe per part.

It also requires less plastic at each gate location, reducing the pressure build-up during injection and permitting the use of a smaller press. The 128-cavity mold is being run on a 320-ton press, the same as the 64-cavity mold that it replaces. At the same time, injection time decreased, from 6.9 sec for the 64-cavity mold to 6.5-6.7 sec for the 128-cavity mold.

In addition, maintenance is much improved. If a cavity is damaged, it can easily be blocked off with a blank insert--the same as with a single-probe system--without affecting the remaining parts. Also, potential downtime is drastically reduced. JK Molds reports that during testing, it completely disassembled the hot half of the mold and the runner system, replaced a cavity, and reassembled the mold in just 4.5 hr. The same job on the 64-cavity mold would have taken a week, according to the customer. (CIRCLE 9)