Improving Productivity Through Good Racking Design

Q: I suspect there is an opportunity for increasing productivity on my line by improving racking procedures, but I’m unsure where to start. Do you have recommendations? 

A. One of the things you’ll notice if you study many finishing lines is that despite having the most technologically advanced equipment in place, many finishing lines are underutilized; producing less parts for which they were designed.

Three real-life examples that I’ve witnessed come to mind. First, imagine two, six-foot chains hanging 10 feet apart on a monorail conveyor. The two free ends of the chains are brought together and attached to a single one-inch square steel bracket hanging in the center. Every 10 feet of conveyor has one, one-inch bracket being coated. I saw it myself.

In another instance, I saw a monorail conveyor with ‘C’ hooks hanging from it with enough space between each hook that when coupled with the slow line speed, the person loading parts had time to sit down on a five-gallon bucket and pick up a magazine and read, while waiting for the next hook to come by. The person would then get up and hang a 10" square sheet metal piece on a single hook and sit back down to continue reading. As you might have guessed, the company is no longer there.

Last, but not least, a company that was breaking sales records, working overtime and struggling to keep up, asked me to consult with them on replacing a piece of finishing equipment. In the process, I discovered that by improving their racking, they could also increase their parts production by 100% to over 500%, depending on the part size. Unfortunately, they didn’t think that improved racking was important enough, and they chose to ignore a cost-benefit of hundreds of thousands of dollars in increased production year over year.

Note that each of these three examples of massive lost parts production have nothing to do with the finishing equipment. They have everything to do with the lack of good management and good parts racking.

The best finishing manager I ever met, who ran the fastest and most productive line I’ve ever seen, once said to me, “Racking is an absolute given in every job quote — it’s not an option.” Why would he say that? Because when finishing lines can cost between $1,500 and $2,500 per hour, wise managers use good parts racking to fill every inch of available line space.

So, given that proper racking will make or break a job, let’s look at the obstacles that can inhibit good parts finishing, and the best hook and rack solutions to overcome them.

Obstacles that Inhibit Parts Finishing:

• Wasted line space due to poor parts density
• Draining wash liquids from parts
• Holding parts without holes
• Controlled positioning for accessibility of wash, paint, and cure
• Parts blowing off of hooks
• Releasing trapped air pockets
• Masking parts on the rack
• Parts floating off of hooks if submerged in a tank
• Broken or Missing hooks resulting in inaccurate part counts per cycle
• Loss of electrical ground due to paint build-up from lack of cleaning

Part Hook Design Features:

1. Parts heavy enough not to blow off a hook with high-pressure wash or float off a hook when submerged, should be hung on a hook with a ‘V’ bottom. Even the slightest ‘V’ will provide more part control than a ‘U’ shaped bottom, and will always push the part to the exact same center location, ensuring a longer-lasting electrical ground. Customer tests have not always shown that square wire on edge holds a better ground than round wire.
2. For lightweight parts that need to be controlled for any of the reasons listed above, parts hooks should be designed to achieve and maintain a minimum two- or three-point spring tension contact with the part at all times. Hooks with three points of contact are better than two points in order to maintain part position, hold parts in close proximity to one another for maximum part density, and control the part position for draining liquids and releasing trapped air pockets.
3. Although not as advantageous as hooks with three points of contact, hooks with at least two points of contact will prevent parts from floating or blowing off of the hooks and will help to ensure continuous electrical grounding by scratching off limited amounts of paint build-up from the hooks until such time as the hooks are cleaned. In addition, at least two points can be designed to ensure that the part makes contact at the same electrical ground points on the hook for a much longer time.
4. For parts that have no holes or require special masking, custom multiple-point spring tension hooks can be made to accommodate almost any shape. Furthermore, conductive silicone masking has been developed to hold parts making electrical contact through the mask.
5. Hooks should be attached to racks without welding, when possible, for replacement and to eliminate annealing (or softening) the hook at the weld points, causing broken and missing hooks which negatively impact part counts. If welds are required, locate them away from the hook’s stress points.
6. If high temperatures are used for cleaning, the parts hooks should be made of a high-grade spring stainless with an annealing temperature high enough to help withstand flash fires if they occur in the cleaning process.

Rack Design Features

Proper racking can increase throughput on average from 100% up to 500%, depending on the part size when compared to individual hooks. Therefore, make parts racks as full as possible, taking advantage of every possible inch of space. Based on different volumes and sizes of parts, it may be more efficient to have dedicated high-density racks for specific parts, or, to design the racks with adjustable hooks and crossbars for change-over. Also, remember that electrostatically charged paint particles reach beyond the line of sight. So, shoot for the maximum number of parts possible and adjust backward if necessary.

Before deciding on the rack design, step back and look at your parts processing beyond the actual coating line, taking into consideration all other operations such as masking, sanding, deburring, washing, etc., leaving enough room around the part to accommodate the operation without removing the part from the rack if possible. Re-handling a part between operations is always expensive.

Racks should always hang in a vertical position pivoting from one center point to eliminate excess stress on the rack as it moves up and down inclines and declines. If you have a monorail conveyor with inclines/declines, calculate your optimum rack width based on the steepest degree of incline or decline (30 degrees, 45 degrees, etc.) to get your center-hung racks as close together as possible on the steepest inclines/declines, leaving approximately one inch between them.

In conclusion, there are huge savings to be gained by implementing the proper parts hooks and racking. The benefits include: an average of up to five times increased parts density, higher quality, reduced rejects, minimum re-handling of parts, and much more efficient use of finishing line resources including labor. All of these can be achieved for the smallest capital investment you’ve ever made!