How to Avoid a Hidden Batch Powder Coating Bottleneck
by Aaron Anderson
Customer Service Manager, Reliant Finishing Systems
When a company contacts Reliant about buying a new batch powder coating system, our first step is to identify their goals for production. Our discussion often begins with the largest part they plan to coat. Knowing what parts or assemblies must fit inside the coating equipment is important and helps us to determine overall throughput. A booth and oven can be physically large enough for the products they plan to coat and still result in a system that misses production targets.
We feel a better approach is to size a batch system around the customer’s production requirements and anticipated workflow.
We Consider Parts Per Shift, Not Just Part Dimensions
Suppose a manufacturer is bringing powder coating work in-house to improve their profitability and reduce turn-around times. They must coat 160 fabricated assemblies during an 8-hour shift to meet their goals. If 8 parts fit on a rack, the system must process 20 racks per shift. That means a completed rack must move through the operation every 24 minutes on average if the start-up and shut-down of the system take place before and after the shift.
Now let’s consider all the process steps. Manual pretreatment with a spray wand system may require up to 10-15 minutes per rack, depending on how large and complex the assemblies are. Drying them in a dry-off oven may take 10-15 minutes. Powder application might also require 10-15 minutes per rack or more. But if curing a rack of 8 assemblies takes 40-45 minutes, curing becomes a massive bottleneck unless the oven can hold more than one rack at a time. If the oven is going to pull double duty and alternate between drying and curing parts, throughput will grind to a crawl. Instead of meeting or exceeding the 24-minute cycle time, the powder coating department is stuck at 40-45 minutes per rack no matter what they do, and probably over an hour if the oven will also be used for drying.
If, on the other hand, the company invests in a separate drying oven that can process one rack at a time, along with a larger curing oven that can hold three racks simultaneously, the company could, on average, process one rack about every 15 minutes. This would provide the production capacity needed to meet their requirements while allowing for occasional rework, unplanned downtime, and other factors that are common in a busy production environment.
Why Your Powder Curing Oven Is So Important
Not all ovens provide the same results. Some are poorly suited to daily professional use. They typically don’t heat parts as quickly or uniformly and may not have the controls needed for consistently repeatable results. Other ovens may offer better performance and durability but include costly “bells & whistles” that are of limited value. At Reliant Finishing Systems, our goal is to provide ovens that offer the right balance of rugged dependability, strong performance, and practical features.
The performance of your oven depends on the heating system. A heat system’s effectiveness isn’t dictated solely by how many BTUs the burner can generate, it’s also linked to how the heated air circulates around the product inside the oven. Good circulation improves heat transfer and temperature uniformity, but excessive or uneven air velocity can disturb the coating before it gels or create hot and cold spots on the surface of the parts.
The goal is not simply more heat or more airflow, but controlled, well-distributed airflow combined with the appropriate amount of heat energy to efficiently reach and maintain curing temperatures. For this reason, all ovens provided by Reliant Finishing Systems include adjustable airflow ducting, and they are adjusted, calibrated, and tested by our technicians on-site at your facility to ensure safety and proper performance.
Why Hidden Curing Problems (And Bottlenecks) Are So Common
An error made by shops that are new to powder coating is treating oven air temperature as if it were part temperature. This is something we address throughout the sales process and during start-up and training, but we often encounter the issue when reviewing problematic coating systems from other manufacturers. In fairness, the root of the problem often isn’t the equipment, it’s the way the curing process is being handled.
Here’s an example:
The powder specifications require a certain time at a specified part-metal temperature (PMT), such as 12 minutes at 400°F for this example. The oven’s display reaches 400°F within 15 minutes, so the operator waits 12 more minutes, for a total of 27 minutes, then pulls the load out and goes on to the next one.
Nobody accounts for the fact that the part surface takes a good bit more time to reach the same temperature as the air temperature shown on the display, so even though the parts look good once they cool, they end up failing in the field or don’t pass a QC check. This creates rework or future break-ins due to warranty claims, reducing future throughput. These problems are directly related to curing but may not be immediately recognized as such.
Now, let’s assume a powder rep, equipment provider, or finishing consultant sees the problem for what it is and educates the company. Different parts will require different curing times to get proper results, regardless of the air temperature inside the oven. They explain that a sheet metal panel may heat quickly, but a heavy weldment can require much more time to absorb heat before the metal surface reaches the required cure temperature. For the panel, it may take only 5 or 10 more minutes, but the weldment may take an additional half hour to reach the curing temperature.
In this example, the cure cycle time may end up being 32-57 minutes instead of 27. If the company has been operating under the assumption that only 27 minutes are needed for curing, their entire plan for the powder coating department could be badly flawed.
Ideally, production planning should be based on a representative temperature profile of actual parts, preferably measured with thermocouples and a data logger. As mentioned above, a lightweight sheet metal part and an 800-pound fabricated assembly will behave very differently in the same oven. Taking readings with a test instrument, such as a Datapaq, will eliminate guesswork and ensure good results. It will also help identify curing-related issues before they can become hidden.
Look for Bottlenecks Outside the Oven
The curing oven is often the slowest step in the powder coating process, but not always. Shops with frequent color changes may lose substantial production time cleaning application equipment and blowing down the booth. A recovery system can reduce powder waste on long runs, but most batch operations don’t have the budget for reclamation equipment, especially if multiple colors will be sprayed and reclaimed. Booths with spray-to-waste operation usually make more business sense if powder colors and textures change frequently and/or the total amount of powder sprayed annually is limited.
Pretreatment can also limit output and inject rework. A manual wash enclosure and spray wand system may be more than adequate for moderate production demands, but prep cycle estimates must include realistic allowances for cleaning, rinsing, chemical treatment, and drying. Poor surface preparation cannot be overcome by using a better powder gun or longer curing routine. Similarly, defects due to applying powder to parts that are still damp cannot be undone by special curing techniques. Allow enough time for proper pretreatment.
Material handling deserves special attention. There are two facets to this issue. One involves inefficiencies due to poor racking or equipment layout, and the other involves unrealistic time estimates. In fact, erroneous handling time estimates may be the most common cause of throughput miscalculation. The amount of time it takes to hustle parts into the oven while the boss is looking on with a stopwatch may be wildly different from the amount of time it takes seven hours into an eight-hour shift at the end of the week. Managers often don’t allow enough time for manual handling of parts when estimating throughput, or they forget to tack this extra time onto every step of the coating process.
Rack dimensions, cart design, door opening sizes, equipment orientation, and aisle spacing can all affect batch system throughput. Operators should not spend excessive time dealing with staging issues in front of booths or ovens, maneuvering carts through tight turns, waiting on plant traffic, tediously hanging and repositioning parts, or pushing carts from one side of the finishing department to the other just to get parts to the next process.
Calculate Labor Along With Equipment Capacity
A new batch powder coating system capable of 20 racks per shift on paper may still fall short if the same employee must wash parts, move carts, spray powder, and load the oven.
Map the labor requirement at each step and identify where tasks overlap. Sometimes one or two additional racks or carts per hour creates more capacity than a larger piece of equipment because employees can prepare the next load while another is being processed.
This means equipment sizing and layout are financial issues as well as engineering ones. A few minutes of unnecessary handling per rack or travel time per cart, repeated over hundreds of shifts, can become a significant operating expense. Spending more on the frontside to prevent these kinds of inefficiencies is usually a no-brainer, but it means you need to spend time talking in detail about the fine points of your new system with the people who’ll be providing it instead of just asking for three quotes and picking one.
Design for Realistic Growth
Allowing for increased future capacity sounds great, but oversizing every component “just in case” increases purchase price, floor space requirements and operating costs. Instead, identify which components are difficult to expand later and which can be modified easily. Fortunately, batch booths and ovens from Reliant are fully modular, so it’s easy to increase their size at a later date if needed.
You can also allow floor space for future expansion as part of your plan. As an example, you may only have the budget for one oven, so you’ll need to use it for both drying and curing. By leaving an open area in your floor plan, you can easily add a second oven just for drying or curing once it becomes necessary.
Before requesting equipment quotations, estimate your maximum normal part size, maximum part weight, how many parts you think there will be per rack, and most importantly: the number of parts you need to coat per hour/shift/week/month. Be prepared to talk with the supplier about their estimate of the actual cure cycle for the heaviest representative load. You also need to be ready to talk about your expected color-change frequency, pretreatment requirements, and any limitations to available labor. By working through this information, you turn the equipment shopping process into a useful examination of the process you’ll be using, and you get a jump start on the engineering phase.
At Reliant Finishing Systems, we encourage customers to consider the complete sequence—load, pretreat, dry, coat, cure, cool and unload—before settling on equipment sizes and features. Our goal is to develop a balanced solution where the equipment’s capacity and performance allow you to meet your manpower targets and production requirements in a practical, cost-effective way that generates strong ROI for your company.
