Richard H Henley of A.I.M. Associates wrote the following story circa 1992-1993 under sub-contract to Lampe Communications, Orchard Lake Michigan. Mid-West Conveyor contracted Lampe for this story and other assignments. This story was the cover feature on three major trade journals: Material Handling Engineering, APICS and Products Finishing. George Robinson took photographs with existing plant lighting. Shot in medium format.

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Tired legs are a certainty for someone who tours the aircraft parts finishing center at Boeing in Wichita, Kansas. The 1,000,000 sq ft facility is possibly the largest of its type in the world.

Not only is it big, the diversity of parts carried on the four-inch power and free overhead conveyor system is news to those who think the advantages of conveyor automation are only possible when the product loads are all alike. The system stores, routes and delivers to the production line. It is integral to the process. The system was built and installed by Mid-West Conveyor Company, Inc., Kansas City, Kansas who worked as a subcontractor under Harnischfeger Engineers, Inc., Milwaukee, Wisconsin.

The aircraft building includes more than the usual scene of a flock of great silver birds nesting quietly in a huge hanger. The fabrication and preparation of the parts prior to assembly are critical to aircraft construction.

The sheer size and diversity of parts treated in this finishing system presented challenges that brought out the best in the power and free conveyor system. If it is possible to totally test a conveying medium under every condition, the Boeing Wichita installation is about as close as one can get.

Nearly three miles of X-458 chain was installed, along with 23 drive units to power the two miles of carrier track, 244 switches, 159 stops, 38 lift/lowerator units and eight process hoods to handle the vast array of part sizes and surface treatment menus the Boeing challenge posed. Lift/lowerator units are often simpler and require less space in a power and free layout than a decline. Large parts, such as are found at Boeing, would have required many such incline/decline units for the cross-over and load/unload points. An ongoing consideration in power and free system arrangements is the general desire to put the system overhead and save valuable floor space. Loading/unloading using this procedure meets ergonomic considerations of being "handy at floor level."

Boeing pre-fabricates a wide range of metal parts and sub-assemblies for commercial 700 series aircraft. The parts, which will be used in all sections of the aircraft, are shipped by rail to Seattle for final assembly. Tens of thousands of structural parts and sub-assemblies, ranging from postage-stamp size to giant 48ft long wing sections, must be fabricated, inspected, prepped and then given a variety of surface treatments depending on the material and its application. The primary substances are aluminum and titanium.

Nearly 150 surface treatments are available to treat the thousands of parts manufactured. The majority are aluminum, which are anodized and painted, depending on their use in or on the aircraft.

Parts destined for use "below the waterline" receive additional treatment, much as an automobile is undercoated. Below the waterline refers to the part of the plane that may be exposed to splashing at takeoff/landing from salt-bearing ground water and snow- melting chemicals, rendering this part of the plane more prone to corrosion.

The carrier variances include: 75, six foot long wire basket models for transporting very small parts; 600, four ft long picture-frame type racks for small to medium hanging parts; 250, 24ft long picture frame type racks for hanging larger parts and 50, 48ft long load-bar type racks for the largest wing, skin and control surface type items.

The carriers are all made of titanium and aluminum except for the trolleys. Since titanium is relatively inert and will not contaminate any of the finishing baths or processes, it was used for that portion of the carrier immersed in the process tanks.

The bias-banking and parallel-banking capabilities of power and free allow Boeing to accommodate over-sized carrier lengths required for large aircraft parts. When transporting long carriers, the leading trolley passes by a first switch and enters a second switch or curve. The trailing trolley is diverted at the first switch. The entire carrier-load bar assembly is thereby changed from longitudinal travel and accumulation to parallel or side-by-side storage in "banked" fashion. The width of load becomes the length.

However, banking intermingled carrier lengths is not the only challenge. The short carriers (4ft-10inch) might be preceded and/or followed by a 24ft or 48ft carrier traveling in skewed, bank style.

A major consideration in the early stages of system design was the carrier lengths. Part of the solution that made the intermingling of sizes feasible was the common denominator of equals multiple lengths of the four ft nominal length (actually 4ft-10inch). Another difficulty overcome by system designers was limited total headroom available for conveyors. This problem resulted in a single trolley rig being used at each end of all load bars rather than tandem trolley arrangements, which would normally be used with such long loads. This provided the capability of conveying and accumulating the carriers in either direction of load bar travel. Most of the parts do not have an appreciable "thickness dimension," and a single trolley was sufficient for load separation in the parallel-banked condition.

The process uses a two-cycle flow path. On the first path everything goes through the same basic functions. Those operations: cleaning, Magnaflux and visual inspection are common to all parts. On the second cycle, the parts undergo final surface treatment according to a specific menu for the part. The conveyor is designed with flow path controls that interface with the HEI plant Host Supervisory System. Smart Eye readers scan carrier code plates for ID purposes. This information is communicated to Allen-Bradley PLC-5 Controllers that regulate tracking/flow path.

Because of the large number of aluminum parts, the trolleys and carriers must be electrically isolated during the anodizing process, which requires 3,600 amps.

Special transport hoods, each equipped with five parallel track sections, receive a "menu load" of carriers destined for the same sequence of treatments. The hoods were designed and built with integral ventilation systems to protect the carrier trolleys from the effects of chemical and heat exposure. A similar type transfer hood is used in the salt bath system where all carriers are cleaned before they are reused.

An automatically controlled bridge crane takes each hood and its load of "piggyback" power and free carriers through the cleaning baths. A hood might contain as many as 50 of the four ft carriers, five of the 48ft size, ten of the 24 ft or various combinations thereof.

The aircraft center at Boeing finishes a diverse range of part sizes, from tiny to huge. The number of different parts is great. But the company was able to install a single conveyor to transport all these parts through the finishing process.

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