Taking a look at automated spray control:

Figure 1 Wasted chemicals, scrap, and other related costs can increase the negative financial impact of poor spray performance.

After years of working hard to improve efficiency, you've wrung every bit of available savings out of your production line. From automation to staffing to supplies, you've made manufacturing as lean and focused as possible.

But you may have missed an untapped source of savings in your spray control system.

Industrial manufacturing plants spray thousands of gallons of expensive chemicals, and water, every day. Yet they often overlook the effectiveness of their existing spray systems, because even when a spray system is not operating efficiently, it still continues to deliver fluid.

Spray systems often are regarded as simple on/off valve and regulation systems. In reality, though, spray nozzles are precision components designed to yield very specific performance under specific process conditions. Just because nozzles are spraying doesn't mean that they are spraying precisely, and precision spray performance makes a difference in throughput, quality, and bottom-line profits.

If a spraying system is not calibrated, monitored, and maintained properly, it can drain a surprising amount of money from your operations. Wastewater costs can amount to tens of thousands of dollars annually, even in a system with relatively "minor" performance problems (see Figure 1). If wastewater is captured, treated, and recirculated, waste costs can double or even triple.

Moreover, a spray system that is not performing at maximum efficiency can produce many related expenses resulting from:

• Excess chemicals.
• Fluid mixing, reclaiming, and treating.
• Energy waste during fluid delivery.
• Scrap resulting from overspray or poor spray coverage.
• Unscheduled production downtime.
• Unnecessary labor in maintenance and operations.

Spray system inefficiencies that seem minor actually can cost a company hundreds of thousands of dollars per year.

Evaluating Your Current Spray System

How can you quantify precision spray control in your facility? Understanding the value of spray automation requires getting a handle on the costs associated with a production line spray system. In assessing your current system's performance, begin by evaluating your costs for labor:

• Are you spending too much time operating, monitoring, or documenting the performance of your spray system? If you're not monitoring it, how do you know if the flow is optimal?
• Is manual intervention required to adjust nozzles for batch or process changes?
• Is excessive cleanup of overspray required?

Figure 2 Spray patterns from worn nozzles often look almost identical to those from new nozzles, even when they are spraying 20 percent or more over specification.

Also examine the costs of water, chemicals, and electricity. Remember that spray patterns from worn nozzles often look almost identical to those of new nozzles, even when they are spraying 20 percent or more over specification (see Figure 2). Also consider environmental issues such as byproduct disposal and emissions costs.

Finally, evaluate your productivity. If your spray process directly affects product quality, even a slight increase in your reject rate can be extremely expensive. If your spray process has an impact on production rate, then precision spray control can affect the bottom line.

Once you understand your spraying costs, you can begin the process of controlling and automating your spray system.

Is Your Spraying System a Candidate for Automation?

Your company might benefit from spray automation if any of the following criteria are true:

• You need to control the flow rate for the spray system based on conveyor speed or line speed.
• You need sprays that can automatically change with product size, shape, or coating viscosity.
• Variations in the spray process affect the quality of your product.
• You need to monitor and inspect the spray system frequently to ensure optimal performance.
• Your spray system is physically enclosed, making inspection difficult.
• Your process frequently requires you to choose among multiple spray setups.
• You automatically need to shut down your spray system or production line under certain conditions.
• Coating coverage is critical to the quality of your product.
• Coating costs are a concern to you.
• Liquid overspray on equipment, on floors, or in the air is creating a hazardous work environment.
• You want to reduce maintenance costs associated with your spray system.
• You face challenges in meeting emissions regulations and are forced to buy costly permits.

Dedicated Spray Control

Traditionally, the spray functions of a manufacturing facility have been controlled manually or with programmable logic controls. Another option is a dedicated spray controller with predefined, pretested spray control nozzles and built-in nozzle performance data.

Dedicated spray controllers provide fast response times of 1 millisecond or less, which can help optimize the performance of air-atomizing nozzles and automatic spray guns. These controllers monitor all of the following parameters:

• Liquid pressure.
• Atomizing air pressure.
• Fan air pressure.
• Spray gun cycle time.
• External conditions such as temperature and humidity.
• Liquid level.
• Flow rates.
• Conveyor speed.
• Spray system integrity (such as checking for worn, plugged, or missing spray nozzles).

A dedicated spray controller can sense spray system variations and adjust other system components to compensate. For example, a worn orifice often will cause line pressure to decrease. A spray controller can detect this and adjust the pump so that adequate flow and coverage are maintained.
Variations that cannot be corrected immediately by a dedicated spray controller can trigger alarms or promptly shut down the entire system to prevent waste.

Most important, dedicated spray controllers can link spray performance to your most important production variable. For instance, if it is possible to measure precisely color, temperature, water content, size, texture, weight, or any other key variable that is directly related to fluid delivery, the spray controller can monitor this measurement and adjust the spray appropriately. In this way, you can control the spray system and monitor the integrity of your system in real time.

Figure 3 To reduce oil consumption and lubricant misting, one stamper used mobile spray carts with a dedicated spray controller and air-atomizing spray nozzles to generate a fine mist of drawing oil on the metal parts before stamping.

Spray controllers are available with different features, but some of the more important ones to keep in mind are:

• Compact size if needed for integration into work areas.
• The proper input/output mix for spray and fluid applications.
• Fast response time to help ensure precise spraying.
• Alarm priority, enabling trigger signals to interrupt the microprocessor when needed.
• Software designed for precision spray control.
• Ability to integrate with existing plant control systems.

Case Study

An automotive stamper that produces a variety of stampings needed an even coating of lubricant without generating mist that some spray lubricant systems produce. The stamper also needed to reduce its oil consumption significantly.

To solve the problem, the stamper used mobile spray carts with a dedicated spray controller and air-atomizing spray nozzles to generate a fine mist of drawing oil on the metal parts before stamping (see Figure 3). Precise timing of the spray and consistent part coverage were critical for product quality, while low liquid and atomizing air pressures prevented misting and overspray. A dedicated spray controller helped this stamper maintain product quality and reduce oil consumption by approximately 40 percent.

William J. Kohley is vice president of AutoJet Technologies, the spray control division of Spraying Systems Co., P.O. Box 7900, Wheaton, IL 60189-7900, 630-665-5000, fax 630-665-0139, bill.kohley@autojet.com, www.autojet.com.