Bearings to Die For

Die casting spray system slides on non-metallic bearings

An automatic system that sprays lubricant on dies between die casting cycles incorporates non-metallic, self-lubricating square bearings to simplify design and eliminate the need for bearing lubrication. The mechanism uses a 3-sided Duralon bearing made by Rexnord Corporation, Downers Grove, IL.

Used to help automate die casting cells, the system sprays water-soluble lubricant on the halves of the open die between cycles, after the part is extracted. This lubricates the die to facilitate part extraction. Additionally, the lubricant further helps prevent sticking by cooling thin-walled sections and other areas that tend to be hotter than the rest of the die.

The spray unit is mounted to the top of a die casting machine’s fixed platen. Between cycles, its spray arm extends down between the dies and sprays in a pre-determined pattern that can be varied to suit the design of the die. Different manifolds are available either to sweep and dwell in multiple positions for general die spray or to spray in a singular dwell location. Extra mounting positions allow for different nozzle positions, and multiple lube manifolds are available as well. The system manufacturer says its manifolds typically reduce cycle times by 15%, compared to hand spray, and increase safety by removing the operator from between the dies.

During setup, the operator can move the upper part of the machine, which includes the spray arm and manifold, forward or back to a position that will allow the spray arm to reach the specific die being installed. When dies are changed after a run, the motor-driven unit is moved back to allow the die to be removed and a new die installed. In previous designs, the company used a type of cam follower to act as a roller on which the upper part of the machine could move. A spokesperson for the system manufacturer says, “We wanted something that didn’t require lubrication and could be used fairly inexpensively. We also wanted an open bearing to simplify assembly.”

To meet these requirements, the firm’s engineers selected Duralon bearings. The bearings are constructed from a filament-wound fiberglass epoxy resin matrix with a woven Teflon and polyester fiber bearing element. The process allows the bearings to be finished in the three-sided square configuration needed to make assembly easier. The open shape rides on a rail that is bolted against a plate, so the rail can be supported along its length. According to the manufacturer, the portion of the machine and manifold supported by the bearings weighs as much as 400 or 500 pounds on a standard machine.

Depending on the size of the machine, either two or three bearings are used per side. The bearings are designed to ride on 3/4-in. square drill rod. A brass scraper in front of the bearings keeps the bars free from small amounts of excess metal or “spit” that can escape from the dies under pressure, as well as any other dirt or grit that could accumulate. A major reason for using this type of bearing is its self-lubricating qualities. While standard metal bearings would have required periodic maintenance, the Duralon bearings operate maintenance-free.

—SG