Zinc Plating Using Split Rail Technology

Thomas Regout (Byron Center, MI), an operating unit of CompX Interna- tional, Inc., is a market-leading manufacturer of precision ball bearing slides for office furniture and electromechanical storage. The company also produces related products such as filing frames, and recently started production of television swivels and ergonomic products for the office environment. The company is known for being the low-cost producer for medium- to high-end applications, where design, quality and durability are the most important considerations.

Nearly all manufacturing processes have historically been in-house, with plating one notable exception. In 1999, however, facing heightened demand and its recent acquisition by CompX, the company resolved to take a new look at how plating, a critical and highly visible aspect of manufacturing, was accomplished.

The requirements were stringent. As a supplier to Steelcase, Herman Miller, Hayworth and other leading office furniture makers, plating quality and consistency were paramount. Throughput and the product range were equally important. The company wanted the capacity to finish 40 million pieces per year, with components ranging from 1.5-3 inches wide and 12-30 inches long.

Two equipment types and numerous suppliers were considered. The goal was the fast-track manufacture and installation of a system that would deliver high throughput at 95% uptime or greater with minimal maintenance and minimal space requirements.

Several types of automatic hoist systems were examined but removed from consideration due to high cost. A split rail return-type machine design submitted by one company was favored early in the process until a new split rail design, engineered by Price Walgren, demonstrated a capacity of 60,000 drawer slide channels per 10-hr shift, compared to the rival’s 36,000 pieces. The square footage and capital costs of the two systems were virtually the same.

Price Walgren manufactures both automatic hoist and split rail machines, which allowed Regout to contrast the performance, operation costs and maintenance requirements of both. Also, while the split rail technology is updated compared to other systems of this type, it had three successful split rail systems installed that Regout could actually see in operation.

The split rail system is distinctive because it offers a degree of process versatility, applying two finishes. The sequence of tanks and cycle times are fixed, however, this system adapts well to a wide range of plating processes. Also distinguishing the equipment is reliable, hydraulic operation on lift, lower and transfer operations and a wide body design that facilitates operator access to the tanks and the center of the machine where ventilation is located. This makes maintenance safer and less time consuming since everything is easier to access.

The wide body design also allows for rack-length hoods that run in the “full up” position to be on the inside of the machine so that ventilated fumes are directed away from workers. This improves the work environment and allows operators to effectively see what is happening with the process. In practice, the feature can make a big difference. Tank maintenance, for instance, is generally done at night. Adding baskets of zinc balls to plating baths with a hood in the way all the way around is not an easy or safe task. With this system servicing is easier as well.

The rack package on the line is 36-inches wide by 78-inches long by 8-inches deep. Variable platform elevations and a specially designed indexing rack allow parts to be loaded and unloaded from a stationary position. Six workers unload 1,000 pieces per hour from racks that hold 100 pieces each.

Regout’s split rail system plates acid zinc on mild steel with either clear or black chromate. The rails can run simultaneously, each in a 45-sec cycle. Polypropylene tanks, manufactured by Tri-Mer corp., are 90-inches deep and are pre-piped for easy installation and maintenance. The system’s removable tank covers allow for reduced ventilation sizing and have only updraft exhaust hoods at the entry and exit of the tanks.

A dual-purpose monorail hoist spans the length of the system and is instantly available in the event a rack falls into a tank. Custom engineered for this system, it is highly preferable to the alternative, which is having two workers standing on top of the machine and manually retrieving the fallen rack. Used with a safety harness, the monorail also functions similarly to the lanyard systems firefighters use, providing easy machine access without safety risk.

The line uses all liquid chemistry and has automatic chemical replenishment via diaphragm pumps and dedicated lines to eliminate the hazards of manual delivery, the risk of splashing and spillage and the need to assure that safety gear will be used properly and the risk that chemical could be added to the wrong tank. A drum and tote washing station for safe cleaning is part of the system configuration.

As on many systems, the acid zinc tank has sand filtration, which continuously filters impurities. Periodic back flushing is automatic, so filtration is highly efficient at all times. No regular operator maintenance is required. Other waste treatment steps are handled in conjunction with plant-wide requirements. Steps include neutralization and precipitation of metal hydroxide solids, lamella clarifier, sand filtration, filter press and sludge drying. Waste is contained in segregated PVC and CPVC piping. Nothing contacts the floor anywhere in the plant.

The split rail system includes an in-line convection oven for drying parts. The oven runs on a separate load/unload loop, shuttled from the machine. This allows operators to work more ergonomically, away form the plating tanks.

Control for the split rails is by an Allen Bradley PLC 503 with PanelView operator interface screen. The system governs the hydraulics that control machine movement and monitors process temperatures and overall process status.

The split rail was engineered for high-volume, high-repeatability plating of small parts. It is a modular system that offers a simple and cost-effective alternative to automatic hoist systems for applications that do not demand high levels of process flexibility. The system has performed as promised, consistently performing at greater than 95% uptime efficiency.