Optimal Coating for Gearboxes

Graco's ProMix Easy and ProMix 2KS metering systems, along with G40 and AirPro spray guns, prove their value at Bonfiglioli's gearbox production facility in Forlì, Italy. One of the projects undertaken at Pieffeci Spa, an industrial engineering company headquartered in Turin, Italy, is the optimization of all stages of a coating process. To achieve this goal, Pieffeci works closely with all of its customers' coating units. One such customer is Bonfiglioli Spa. At its facility in Forlì, Italy, gearboxes are produced for self-propelled machines (chain and excavator head rotation), electromobility devices, and wind turbines. Among Bonfiglioli's customers are leading companies in the world's wind energy and earthmoving machinery sectors. Coating specifications with these customers are quite strict; accordingly, Pieffeci, working together with Bonfiglioli, carries out the necessary laboratory tests to meet these specifications. In recent times, demands for superior quality and performance have been increasing. While this is a challenging situation for Pieffeci, it is also an incentive for Bonfiglioli to improve its work. However, when coating parameters are kept under strict control by establishing a highly restrictive tolerance limit for nonconformity, painting results have reached the required level. Using appropriate equipment for metering, mixing, and spraying is also important. For this reason, Pieffeci turned to Graco and its distributor in Bologna, AS Divisione Verniciatura.

Step-by-Step Monitoring of the Coating Process

Coating gearboxes is complex because of the difficulty in protecting equally the surfaces exposed to excessive wear and corrosion as well as the weight and shape of the parts. When the material to be processed reaches the coating unit, each product is assigned a barcode to enable all steps to be traced. To reduce the number of color changes, components are grouped according to the shade to be applied.

Robotic Paint Spray Booths

The coating system comprises four paint spray booths separated by a flashing tunnel. The thickness required to coat gearbox components ranges from 40 to 400 microns in one to four coats; however, if the customer is to finish the part, only a single coat of 40-micron primer basecoat is applied in a single system. Normally, the first two booths apply the basecoat, while the last two apply the topcoat. However, when maximum production efficiency is achieved, the third booth can apply both basecoat and topcoat. Coating robots are located in the first three booths; in the fourth booth, the operator manually applies paint for touch-up in the event of small batches or prototypes or if visual inspection of a component yields negative results.

Graco's Metering Systems

Bonfiglioli's paint shop is equipped with Graco metering systems supplied by AS Divisione Verniciatura. Recently, the ProMix Auto metering system, which had been used successfully for over a decade in the first booth, was replaced with the ProMix 2KS. This newer and more powerful system has provided greater reliability in both quality and capacity. Together with Pieffeci's staff and Bonfiglioli's management, AS conducted a detailed evaluation of the paint shop to discover new ways to increase efficiency and productivity. Following this analysis, contrary to the previous arrangement, it was decided to place the mixer inside the booths. This process reduced pipe length and the amount of catalyzed product entering circulation and improved space utilization. Primer metering is managed by two ProMix Easy systems (previous 2K generation). One is dedicated to standard light gray basecoat, the other to yellow and black primers, which are required for certain technical properties that ensure surface protection and that, even if the topcoat is scratched, the color remains the same as the rest of the component. The ProMix Easy metering systems were set up with manual management in mind. However, a PLC was added that can manage both ProMix Easy units; in this way, both machines were converted into semi-automatic systems capable of limited interaction with the coating robots.

Advantages of the Automatic Application Process

The Bonfiglioli catalog contains 60 topcoat series; 17 of these are frequently used. These are kept in tanks equipped with a mixer and pump managed by the ProMix 2KS metering system in the coating management room, which also manages catalyst levels. A pump manages the remaining color series by drawing products directly from paint drums. Checks are performed based on the viscosity of the paints and the temperature and humidity levels in the heated tank in the coating management room. Pieffeci also changed the way product volumes are managed by increasing barrel lifting capacity from 30 kg to 200 kg where possible and installing several barrel lifts that ease the work of employees involved and increase facility safety. During the application phase, Graco's G40 automatic air-assisted spray gun is used. This lightweight gun delivers superior topcoat quality with tight spray pattern widths and excellent positional accuracy. Each robot has two guns; one for single-component and one for two-component products. Both are used 50 percent of the time. This choice is supported by the need to avoid continuous cleaning and loading operations of the guns. This feature means there are always two loaded and ready-to-use devices available. The greatest advantages obtained from the automation of the process are the savings obtained from paint and the reduction in color changeover times. Paint waste has been cut in half; the time required for color changeover has been reduced from 75 seconds to 43 seconds. Given that there are many changes throughout the day (approximately 40), the advantages gained in time and cost are quite evident.

Protection of Gearboxes

The drying oven is set up after the coating facility polymerizes the surfaces of the gearboxes for approximately one and a half hours. The following tunnel cools the processed parts before unloading; thus they can be immediately sent to packaging. The paint is cooled to below 40°C; then the gearbox can be placed in the bottom of the box in which it will be shipped. Before the unloading station, there is a mask stripping station to remove films and tapes that protect the flanges during processing, and an automatic station equipped with a robot for application of stainless steel oil that prevents flange oxidation. Graco was also consulted in automating the protective oil application station. Initially, the goal was to apply two different oils with two guns located at the robot's wrist. However, due to weight issues, only a single gun, the Graco AirPro, was installed. This situation has made it possible to adjust the spray fan and apply the least amount of well-sprayed product (approximately 10-20 cc/min) to small parts and more product to larger parts. The AirPro gun is frequently used in the automotive industry for processing limited surface areas requiring top-level quality. Pieffeci selected this highly powerful gun because the different oil types used have very different oil viscosities.

Results

Pieffeci's work with Bonfiglioli has contributed greatly to improving the efficiency and productivity of the gearbox coating process in Forlì. It provides evidence of how proper surface treatments can add value to the manufacturing industry and how important partners such as Graco and AS Divisione Verniciatura are in supplying metering, mixing, and spraying equipment for the relevant processes.   Marc Gijbels Product Marketing Manager IPD Graco