PART 2: Automatic spraying machines Washington DC

The previous article in this series stated that many companies look to automation of their finishing process as a means to overcome some of the many problems associated with manual spray applications. The necessity to increase production, decrease rejects and improve material costs, as well as a shortage of qualified finishing personnel, encourages automation as a finishing solution. These all lead to "bottlenecks" in productivity and shipping.

Spraying machines are the most common method of finishing since they are the most versatile and the most compatible with current hand-spraying materials and techniques. There are three types of automatic spraying machines:

• Widebelt — where the parts are placed on a horizontal conveyor.
• Vertical — the parts are hung on an overhead monorail.
• Moulding — long narrow parts are placed on a narrow conveyor and passed through fixed position spray guns at high speeds. Due to space limitation this editorial will only deal with the most common of these three, the widebelt, since the other two types are more specialty applications.

There are many manufacturers of spraying machines worldwide, but only five companies are well represented in the United States. All five companies are headquartered in Europe and have sales/service facilities in North America. Spraying machines, like all machinery, vary widely in price, which usually correlates with productivity, longevity and sophistication. When purchasing an automatic spray machine, be sure the company has a long history of service in the United States and is financially stable enough to withstand the serviceable life of the machine, which can be 15 to 20 years.

Spraying machines are available in four styles with many different model variations:

1) Reciprocating

Reciprocating or oscillating spray machines have one or two arms with four spray guns mounted on each arm. The guns oscillate back and forth across the part in a motion perpendicular to the forward motion of the conveyor. These spray machines are the most common type found since they operate at a speed range of 10 to 25 fpm. This speed is the typical range of most automatic finishing lines.

2) Rotational

This style of machine will have up to 10 guns mounted on the spokes of a "wagon wheel" carriage. The guns rotate in a circular motion as the parts pass under the carriage. Most manufacturers recommend this style of machine for stains or very low solids coatings only. If higher solids coatings are used, a reciprocating style machine is typically preferred. The many passes with 10 guns over the part makes this machine ideal for very uniform application of spray (no wipe) stains.

3) Elliptical

Twelve to 16 guns are mounted on an elliptical "race track" carriage. This is a large spray machine capable of spraying at line speeds up to 40 fpm. The large number of guns all spraying in the same direction minimizes overspray turbulence in the cabin. It is commonly used for high-speed and high-volume production requirements.

4) Robotic

The CNC robotic spray machine is designed for the ultimate finish quality. The machine has one or two spraying arms that allow surface spraying to be accomplished by transverse reciprocation or a "cross-hatch" pattern. In addition to the surface guns, an independent gun sprays the edges with programmed "recipes." Robotic spray machines are used for high-quality finishing of office furniture, very high-gloss finishing and residential dining tables.

Reciprocating and rotational spray machines usually have dry paper filtering systems. The larger reciprocators will also offer "water-wash" filtration versions when line speeds approach 25 fpm. Elliptical and robotic spray machines use water filtration only, due to high speeds and high-quality requirements. The smallest reciprocator will use a paper conveyor. This is an excellent solution when spraying at low or intermittent line speed or when spraying adhesives since the machine does not have to be cleaned after spraying. Larger spray machines typically have plastic or fiber glass conveyor belts that allow the parts to sit directly on the conveyor when spraying. An automatic belt cleaning and coatings recovery system is a standard feature on these machines. Spraying directly on the belt greatly improves edge coverage and coatings transfer efficiency. These spray machines also utilize a photo-diode light reading bar to precisely locate the part on the conveyor. This positioning allows the computer to calculate the exact timing and pattern of spray around the part regardless of its shape.

Some of the many benefits of automatic spraying are: double the transfer efficiency over manual spraying; greatly reduced rejects due to precise control of the spray application, reduced coating cost and VOC; possibility to reclaim coatings; great reduction of dust or "trash" on the finished part; and reduction of labor costs.

Most of the machinery vendors have demonstration and test facilities in the United States, where a customer can "test drive" a machine using his coatings and parts before making a decision. We encourage you to take advantage of this service to be sure you are pleased with the operation and performance of the spray machine. Be sure it satisfies — you will have it a long time.