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Automatic chip processing goes underground.

Our division consist of three plants, with Otsego being, by far, the largest. The decision to modernize the chip-collection, chip-processing, and cutting-fluid system, without interrupting production, presented major challenges.

Our first experience with a chip-handling system occurred when we built one of the smaller plants. We installed a Harpoon conveyor chip-collection system from Prab Conveor Co, Kalamazoo, MI, during construction. These conveyors have reciprocating plows attached to a shaft in the bottom of a 24" X 24" liquid-tight trough. They feed into a parts separator and a chip wringer. Coolant, flowing into the conveyors along with the chips, is drawn off and recycled back to production machines. This worked so well that a similar system was built into a second plant constructed several years later.

Originally, the Otsego plant had coolant sumps on each machine, tote bins to collect chips, and forklifts to move the bins. The chip-processing system consisted of a bar-end separator and a centrifuge with connecting conveyors. It was state-of-the-art when the plant was built in 1966, but left a lot to be desired when measured against today's standards.

The original chip-handling method had become costly in many ways. It was labor intensive, created a host of housekeeping problems, and resulted in a measurable amount of machine downtime for chip removal. We also lost a significant number of finished parts--small parts, in particular, would fall into tote bins along with the chips. These were carried to chip processing, went through the bar-end separator, and were carried away with the scrap.

Monitoring coolant quality in machine sumps also was time consuming. One man could check about 20 sumps per day. This worked out to checking each machine about once a week. It was not an ideal control program.

Looking for better ways

Based on experience gained in our two smaller plants, management asked us to look at the economics and practicality of modernizing the chip-handling and coolant systems at Otsego. There were some major hurdles. For one, the plant was operating three shifts per day, so it wasn't practical to shut the plant down during installation of a new system because lost production would cost too much.

Also, we decided that we couldn't afford a single centralized coolant-storage system for several reasons. With approximately 37,000 gal of coolant in the system, a central tank would be large and expensive. Because of a high water table, it would have to be above ground, taking up a large amount of floor space. Also, if such a large amount of coolant became contaminated, the cost of disposal, clean-up, and replacement would be monumental.

With these thoughts in mind, we tentatively laid out a system based on using the same type of conveyors installed in the other two plants.

As we envisioned it, the new system would consist of six north-south conveyor runs, 180 ft of east-west collection conveyor, and another 50 ft run to move chips from the production are to the chip-processing system, a total of about 1100 ft of Harpoon conveyors. At this point, we called in Prab and proceeded to jointly engineer details of the new system.

Final design

Each of the six conveyor runs in the production area also serves as a sump for approximately 7500 gal of coolant. To keep the coolant in each conveyor isolated, Prab designed an upward slope at the discharge end. Coolant drains into a 1500 gallon sump and then is pumped through overhead piping back to the production machinery.

A side benefit of elevating the end of the conveyor is that chips discharged onto the cross-conveyor are well drained. This increases efficiency of the entire system and reduces the amount of liquid handled by downstream chip-processing equipment.

Screens are installed at the base of each machine at the point where coolant drains down into the conveyor. These catch finished parts that have been dropped, saving a large amount of product formerly hauled away with the scrap.

We installed a dump site, where the system enters the chip-processing area, for chips from machines operating outside the main production floor. This accommodates the small percentage of production equipment--short run machines and cut off saws--best served by tote pans. These are carried to the dump station by forklift. The chip-processing equipment, located beyond the chip-collection system, involves some specialized machinery that has worked very well.

Chips are elevated from the Harpoon conveyor by a Scrapveyor, which is basically a slide-drag conveyor with pivoting flights. These flights swing down at the discharge point to shed anything clinging to them. This effectively eliminates any problem of scrap carryover.

The Scrapveyor discharges into a bar-end separator--the only part of the original system used in the new installation. It is, essentially, an air-classifier containing an oscillating conveyor. Chips are blown across a threshold while solid material falls through an opening.

From the bar-end separator, a drag conveyor elevates the chips and distributes them to one of two newly-designed to a moisture level under two percent, one of our original system-design goals.

These centrifuges, rated at 4 tons/hr for brass chips, are built on a diagonal axis providing a straight-lien gravity feed for chips. This design eliminates a choke point found in horizontal centrifuges. It also keeps motors and drives out of the chip-flow path, preventing potential operating problems and simplifying routine maintenance.

Dry chips are collected from the centrifuge discharge ports by a pair of counter-rotating screw conveyors mounted in a single trough and driven by a single motor through a reduction gear. They feed dry scrap into a blower that carries it about 50 ft into a compartmented outdoor storage silo.

All aspects of the system are operated and monitored from a main control console located in the chip-processing room. With the Allen-Bradley PLC 2/20 programmable controller, we can start or stop each of the individual Harpoon runs, which have separate hydraulic power packs. We also can spot jams, which occur infrequently, and control various other elements of the chip-processing equipment.

Coolant is monitored through a central system made up of the six self-contained Harpoon lines and one master makeup tank. The tank receives coolant draining from the chip wringers, which is freshened with new coolant before being used to topoff the individual lines.

Our feed water is processed through an automatic deionizer. Its location, near a loading dock for convenient handling of chemicals, also isolates the deionizing process from the rest of the plant.

Installing the system

Installation of this entire system was a coordinated ballet involving our production-engineering and maintenance staff, the equipment supplier, and an experienced contractor.

The six in-floor conveyor runs required digging a trench 40" wide X 36" deep, running the length of the plant. To make room for trench construction and conveyor installation, without interrupting production, we moved a complete line of machines over a weekend. Since each machine was self-contained, this involved changing the fixed power, air, and coolant supply lines to flexible lines and moving the machines into the adjoining aisle.

By starting each segment of the move on a Friday, we were able to have the line running in its temporary location on Monday. This process was repeated for each conveyor run and, with practice, became a smooth operation.

The bottom line

Payback is still being evaluated because we are finding benefits in many areas. Plant housekeeping is greatly improved and, as people are reassigned, the indirect labor involved in scrap collection and processing is dropping substantially.

Coolant monitoring takes only minutes, instead of days, and we are maintaining a much more accurate measure of coolant condition. Also, we are able to experiment with different coolants because the fluid is isolated in a single production line. This means we do not have to get into an all-or-nothing decision when new developments in coolant come along.

There also are many less tangible elements. Machine setup is faster because there are no chips to clean off the tool plate. There is no periodic machine shutdown to clean out accumulated sediment. Greater safety results from better housekeeping.

This system also is very efficient in its use of floor space. The plates covering the in-floor conveyors serve as aisles and, in effect, the whole system hasn't taken any production space.

While we can't accurately measure all factors until we've developed more of an operating history, we feel sure that our original measurements of cost-effectiveness will be attained. This means the system should pay for itself in about two years.

For more information, circle 545.
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Author:Kreuger, John
Publication:Tooling & Production
Date:Oct 1, 1985
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