Let a robot do the job

Spraying, stencilling and striping packs of panels is a messy necessity for wood based panel manufacturers. An Oregon firm is doing something about that with robotic methods it developed for other industries.
It all results in a painless automatic procedure that the company says does the job, conserves paint, limits messy spray booth clean-up, saves money and is safer.
Precision Technologies, a division of Eugene, Oregon’s Willamette Valley company, already has five of its automated spray booths, and several other lines, in operation in North American panel plants.
This represents the newest arrow in the company’s quiver, which includes such  specialities as resin and catalyst mixing and metering, extrusion heads and systems, finger- joint application systems, polyurethane mixing and a host of other robotic solutions. In the wood panel business, they serve plywood, OSB, and siding manufacturers.
As an example, they have two installations in the US’ newest OSB mill, J M Huber in Broken Bow, Oklahoma.
That 20ft x 20ft x 14ft robotic spray booth uses six-axis industrial application robotic arms by Motoman,West Carrollton, Ohio.
A four-stage down-draft air filtration system has accessible ‘tunnels’ in the bottom of the booth to easily access the filter media and the air can be safely released back into the plant with no outside venting required. This also has the advantage of saving heat energy in cold winter climates.
The system sends a signal to the operator when filter changes are required. The two-stage floor filtration rolls are changed weekly, or as needed. The third stage cartridge is changed monthly and the final stage fibre filter is changed quarterly.
Infeed and outfeed vestibules allow additional airflow to maintain a slight negative pressure within the booth to contain the material.
Of course the fact that these are water-based paints simplifies the air handling problems; there are no toxic fumes. Variable frequency drives on the fan motors automat- ically increase fan speed to maintain constant airflow as filters begin to load. Air flow is adjustable up to about 18,000ft3/minute.
Stencilling the loads to apply logos or grademarks is another part of the development. Stencils are automatically cleaned between loads. This allows the stencil face to come in direct contact with bundles.
The company designs stencils and has them cut from 1/4in aluminium by a local water-jet cutter which operates at 60,000psi. They are anodised to close the pores and thus prevent paint sticking to them.
The end stripe operates separately from the stencil system, but shares some of the controls. It can be placed in line either before or after the stencilling and will apply up to six stripes about 1in wide, with 2in between.
In operation, the load moves to the spraying position and stops. Stripe guns spray the leading end as programmed, the load moves forward, stops, and the trailing end is sprayed. Nailing lines can be applied in the same manner.
Using the same robotic principles, cardboard side protectors can be applied to the sides of 4ft x 8ft tongue and grooved units. In this case, vacuum heads pick up the material and place it against the load, hold it in place and staple it.
The company has developed a system for spraying T&G too, to be sure the grooves are sprayed. There is articulation so it will spray downward in one pass and upward in another.
Precision Technologies’ general manager, Eldon L Owen, enthusiastically describes the company’s system. “We thought the timing was good due to rising costs. We needed to get our spray booths more efficient, with increasing volumes. Our painters were 65 to 70% efficient. Paint that you can’t use, you still have to clean up.”
Mr Owen estimates that the average mill, using 100,000 gallons of paint annually, would save US$60,000 to US$80,000 a year, not including clean-up. Individual costs are about US$225,000 for a spray booth, US$65,000 for a stencil system, and US$45,000 for a striping system.
The system uses only four guns so there is less maintenance. Former spray booths had 10 to 12 guns. Mr Owen recommends weekly head changes because of the high volume. The robot simply brings the heads down to a trap door where they are removed and replaced in seconds.
The spray heads work 10in to 12in from the material and run at 800psi to 1,300psi. There is very little over-spray. Paint is filtered in a high pressure filter.
Mr Owen said that if a 0.019in tip wears to 0.002in, it will increase paint flow by 20%.
In operation, a forklift operator places bundles onto the spray booth rollcase and picks up the bundles on the offbear rollcase. Everything else is automatic.
As the bundles move toward the booth they are automatically scanned for location, height, width and possible skewing. As they move in, the robot verifies these  measurements and the stopping position. The computer makes the proper corrections for the load and directs the robot to begin. After painting, the bundle moves out.
The computer system is stand alone, but it can be tied into a plant computer. Allen- Bradley controls are used.
“You do not have wet waste to clean up,added Mark Matteson, sales administrator. “Just pull the filters out and change them. Another nice thing about the efficiency of this booth and the way that it’s filtered is that you don’t have to vent through the roof. You can have the air coming from the mill and being exhausted back into the mill. This is a real advantage in a cold country – you don’t have to pull the air in from the outside, heat it up, and send it out the back,said Mr Matteson.
Mr Owen declared: “Our whole goal was to increase the efficiency of the mills, reduce their clean-up and increase speed. Speed has gotten to be a factor with these larger mills. I think we paint a 4ft x 8ft, 38in high stack in 70 seconds.”
Mr Matteson continued: “When you have a degree of accuracy on a robotic arm of 5/1000, you can use fewer spray guns and you’re closer to the load. You can reduce the pressure, you don’t have as much bounceback or splatter. All those things add up.”
The system employs electric guns, so on  and off timing can be highly accurate, based on  robot speed.
Precision Technologies completely assembles and operates each unit on their shop floor, along with necessary programming. After final inspection it is disassembled to the least degree possible to ease re-erection at the mill. Loads are generally 40ft long.
Mr Owen said: “We developed an automated stencil system that pushes the stencil against the load and it cleans itself every time it paints. It comes back into a wash mechanism in between loads. It gets washed and squeegeed and the water for that is  recycled until it reaches a set tolerance content when it needs to be changed.”
This is water-based paint with wax and resins.
The division employs about 35 people, including five engineers. The forest industry makes up 40% of its work.