Example 4 Baking of a Spray Painted Wing Bolt

The upper half of a 64 mm (2 2 in.) long shouldered wing bolt was spray painted to a wet film thickness of 30 pm (1.2

mils) with glossy bronze baking enamel, using toluene as the solvent. Before being painted, the parts were placed in aluminum racks incorporating 156 holes that accepted the wing bolts up to the shoulder on the body of the bolt, serving to mask the lower part from the paint. Parts were painted, air dried for 5 to 6 min, then baked at a production rate of 1500 pieces per hour. The operating conditions were the following:

Weight of each piece

0.032 kg (0.0702 lb)

Number of pieces per rack

156

Weight of rack plus load

5.089 kg (11.22 lb)

Pieces processed per hour

1500

Type of baking enamel

Glossy bronze

Solvent used

Toluene

Baking cycle

20 min at 150 °C (300 °F)

The requirements for the baking equipment included the following:

• Racks: aluminum sheet, 710 by 660 mm (28 by 26 in.) and 1.0 mm (0.040 in.) thick, with 13 rows of 12

equally spaced 9.5 mm (5 in.) diam holes (156 holes); weight 0.12 kg (0.27 lb)

• Oven: electrically heated single-compartment batch oven, 750 mm (30 in.) square and 622 mm (24.5 in.) high (inside dimensions), with shelves accommodating five racks of parts, which are placed in oven every 30 min

• Heat input: 13.3 kW/h, assuming that oven is at heat and that 15 min is required for load to reach oven temperature

• Exhaust air: 0.46 m3/s (98 ft3/min) at room temperature; 0.670 m3/s (142 ft3/min) at 150 °C (300 °F)

• Air recirculation rate inside oven: 3.8 m 3/s (800 ft3/min) at 150 °C (300 °F)

• Space for oven and controls: width, 1625 mm (64 in.); depth 915 mm (36 in.); height, 2135 mm (84 in.) Example 5: Baking of a Spray Painted Angular Welded Frame Assembly.

A welded frame assembly, angular in shape, 2 m (8 ft) long with each leg approximately 0.9 m (3 ft) long, was produced from 6.4 mm (4 in.) steel plate, and weighed approximately 410 kg (900 lb). The parts were spray painted to a wet film thickness of 30 pm (1.2 mils), using a glossy yellow baking enamel with xylene as the thinner. Before baking, the parts were air dried 10 to 20 min. The parts were supported during baking by special dollies designed to have minimum contact with the parts. Three parts were processed each hour. Operating conditions used in this process included:

Weight of each assembly

408 kg (900 lb)

Assemblies painted

3 per hour

Baking enamel

Glossy yellow

Solvent used

Xylene

Baking cycle

45 min at 135 °C (275 °F)

The requirements for the baking equipment included the following:

• Dollies: of steel construction, designed to support frame assemblies with minimum contact during finishing; 3 m (9 ft) long, 1 m (4 ft) wide, 380 mm (15 in.) high; weight 90 kg (200 lb). Nine required, three each in spray room, oven, and cooling area

• Oven: electrically heated walk-in batch oven with three compartments, each 1.5 m (5 ft) wide, 3.0 m (10 ft) deep, 2 m (6 ft) high

• Heat input: 95.6 kW/h, assuming that one dolly and part are replaced every 20 min and that 15 min is required for one dolly and part to reach oven temperature

• Exhaust air: 1.26 m3/s (267 ft3/min) at room temperature; 1.75 m3/s (370 ft3/min) at 135 °C (275 °F)

• Air recirculation rate inside oven: 30.68 m 3/s (6500 ft3/min) at 135 °C (275 °F)

• Space for oven and controls: width, 6.1 m (20 ft); depth, 3.4 m (11 ft); height, 3.0 m (10 ft)

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