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Building a Better Powder Coating System: Racking

Posted on Wednesday, February 6, 2019

Every product that you coat has its own unique characteristics. And even though every product hangs differently on a rack, the temptation is to find a one-size-fits-all solution.

That instinct can actually cost you efficiencies and profits. In reality, an all-purpose rack is a no-purpose rack.  Read on to get “hooked in” to critical steps for better racking and more efficient powder coating. 

When a customized racking application makes sense, taking the time to plan out that system for optimal results pays dividends by cutting wasted time, wasted coatings, and wasted space. Often the most optimal solution is a balance between customization and flexibility within a single racking system. You want to create an efficient system, but you don’t want to completely straitjacket your processes unnecessarily. 

Space is always at premium

Efficiency in racking is about space density on the line. The more densely you can run your products down the conveyor, the more efficiency and cost savings you can gain. The goal with racking is to present a solid wall of products that passes by the coating sprayer for the most effective application. But how do you achieve that goal? You should always start with the products to be coated—what the coating requirements are and the operational limitations you are facing.

Though there is often a perception of minor trade-offs between speed and quality, there are many ways to gain throughput on the coating line without sacrificing quality. The gains you experience will come from increasing density within the rack, increasing density on the conveyor, increasing the speed with which you can load each rack, and increasing the efficiencies of rack transfer.

These four steps will guide you to optimal results: 
Step 1: Racking Suitability 
Step 2: Dedicated vs. Modular Racking 
Step 3: On-line vs. Off-line Racking 
Step 4: Optimizing Conveyor Space 

Step 1: Racking Suitability When should you choose racking? 

Before getting too far down the process of customizing a racking system, you should ask if racking is the best option. You should choose racking for applications with small- or medium-sized parts, long production runs, or families of parts in kits. Racking makes sense when there will be minimal touch-ups, you have cost-effective rack stripping, and there is sufficient plant space for rack storage. 

Another factor to consider is whether you can secure the part well. Will it be difficult to manage because of what it is made of, how heavy or light it is, how hard it is to clean, or the temperature of its curing process? Racks are not always good for heavier objects that would be better served and handled more safely individually, with hooks. On the other hand, very light parts can sometimes be more difficult to secure. 

One thing that well-designed racking systems can help with is consistent part presentation for cleaning, coating, and curing. Your racking goals should include more uniform coverage, increased transfer efficiency, limited overspray waste, and complete drainage of pretreatment solutions and rinses. These factors will naturally lead to fewer poorly coated products that require recoating.
 

Step 2: Dedicated vs. Modular Racking Which will work better for you? 

Dedicated racking means that only one part, or a small set of related parts, will run on that dedicated rack. Modular racks are more flexible in application because they can be reconfigured to accommodate a wider variety of parts. 

Dedicated racks will be more efficient than modular when you have large volumes of one product or small products collected in kits. Dedicated systems often have fixed hooks, clips, or pins that can be repaired or replaced if damaged. These racks maximize density, but since dedicated racks are custom racks, you have to consider how much storage space you are willing to use for them when they are not in use. An additional consideration in favor of dedicated racks is your ability to incorporate masking into hook or pin designs.

Modular racking allows for more flexibility across different parts and applications. They are designed to be able to coat a variety of parts by having removable crossbars and removable product holders. Though modular racks might not reach the density of dedicated racks consistently, there can still be other advantages. One advantage is that you will save storage space if you have one modular rack instead of two dedicated racks, for example. Other benefits include the ability to switch between standard and custom hooks relatively easily, and to incorporate shielded ground points as needed. 

Step 3: On-line vs. Off-line Racking Have you weighed all the factors? 

The key factors to consider when deciding between on-line and off-line racking are line speed, product mix, part window, size and weight of the rack, number of available personnel, plant space, and safety. On-line racking would seem ideal to maintain the pace of the loading personnel. However, there are many times when off-line rack loading can be more efficient. 

For instance, if the line speed is high and the products are small, a rack might have more spaces for products than the available personnel can load reasonably. Off-line racking can make sure that line density is high by having loaded racks constantly in a queue to be put on-line. Other advantages of off-line racking are that you can ensure ground points for electrostatics, minimize any hanger marks, apply masking more easily, place parts in an ideal position, and reduce the Faraday effect. 

In many cases, you should also consider moving off-line racking to the point of manufacture to increase efficiencies. Why handle the products twice when you only need to handle them once? And at the back end, racks can be taken to where the parts will be assembled for similar efficiency savings. 

Step 4: Optimizing Conveyor Space Have you looked into all the options?

There are a number of ways to increase density with modifications “above the hanger.” One highly effective and proven strategy is to add load bars to reduce rack to rack spacing, which may be currently limited if hanging from standard pendant or trolley centers. 

Another opportunity to increase density might be using rotators and indexers. These mechanisms allow you to load and unload from a single side of the conveyor, spray both sides of the rack from a single side of the booth, or spray geometrically challenging parts. 
Any elevation change in your line can also limit your ability to maximize line density for your racking system. One way around this is to use angle pivot tooling that rotates the rack sideways during elevation changes so that they can return to maximum line density when ready to be coated. 

What is the bottom line? 

Usually you cannot employ every strategy to maximize line density and racking efficiency. Each application is different, and each plant is configured differently. The tradeoffs between efficiencies and other costs are only fully understood with experience. 

Nevertheless, you can calculate potential savings by measuring your current throughput and comparing it to an optimized, or ideal, system. First you need to count your current throughput per hour on a common part you coat. Then estimate your throughput after applying all the efficiency gains you would be able to implement. Divide your new throughput by your current throughput for the percentage production increase. Then write down your yearly averages and multiply the rest of these factors: 

• Percentage Production Increase vs. Current 
• Running Hours Per Day 
• Production Cost of Running the Line Per Hour 
•Average Total Production Days Per Year 

Formula: % Increase x Hours/Day x Hourly Cost x Days = Potential Savings Sample: A 30% increase on 16 hours runtime/day at $150 cost per hour for 300 production days in a year = $216,000/ year in cost savings.
 

Designing an efficient racking system is often an afterthought. But on your larger projects the savings  can be substantial. Taking the time to consider all the factors in racking efficiency can pay off in increasing line density while balancing the requirements and limitations of your plant. 

by Scott Rempala, president of Mighty Hook

Author: PCT Editor