The basic of the powder coating oven design is to find out the necessary heat. Need to calculate the heating up time (from the start of the switch to the time to reach the temple temperature) sweep heat, the necessary heat per hour during production operation, according to the calculation results to decide the capacity of the heater (such as the burner) and the capacity of the circulation fan.
(1) Heat when heating up The heat when heating up is calculated as follows.
① powder coating oven body heating Q1 = specific heat capacity of iron × mass related to the powder coating oven × (average temperature of the entity – room temperature)
②Heating of air duct system Q2 = specific heat capacity of iron × mass related to air duct × (average temperature of air duct – room temperature)
③Drying indoor conveying chain heating Q3 = specific heat capacity of iron × conveying chain mass × (drying indoor temperature – room temperature)
④Drying indoor air heating Q4 = specific heat capacity of air × air mass inside the powder coating oven × (powder coating oven temperature – room temperature)
⑤ Heat addition of discharged air Q5 = specific heat capacity of air × discharged air when heating up × (air powder coating oven temperature – room temperature)
The total heat required during heating up QH= Q1+ Q2+ Q3+ Q4+ Q5
The heating up time is quite different during winter and summer, so it is necessary to change the starting (ignition) moment of the powder coating oven with the season.
(2) Heat during production operation
① coated material heating Qa = specific heat capacity of iron × mass of coated material per hour × (drying temperature – inlet temperature)
②Hanging tool heating Qb = specific heat capacity of iron × mass of hanging tool per hour × (drying temperature – inlet temperature)
③ evaporation heating Qc = solvent evaporation
④ powder coating oven entity heat dissipation Qd = entity area × heat dissipation coefficient × (duct outer wall temperature – room temperature)
⑤ Heat loss Qe of air duct = area of air duct × heat dissipation coefficient × (outer wall temperature of air duct – room temperature)
⑥ heat loss of exhaust Qf = specific heat capacity of air × air mass discharged per hour × (powder coating oven temperature – room temperature)
(7) Heat loss of the entrance and exit of the powder coating oven Qg = specific heat capacity of air × average wind speed × area of the opening section × (powder coating oven temperature – room temperature)
The total heat required for production operation QR= Qa+ Qb+ Qc+ Qd+ Qe+ Qf+ Qg. Considering the safety factor, a safety rate of 30%~50% needs to be added to the total heat QR.
When indirect heating is used, in addition to the above load, a heat exchanger has to be added, and the heat load of the combustion furnace material.
The above calculated heat time required when heating up and production operation, must be designed and selected with a larger heating device than both QH and QR.
According to the above theory to calculate the thermal power is very troublesome, and thermal conductivity, heat dissipation, heat storage and other coefficients of a wide range, but also to take according to experience. The domestic unit (company) summed up many years of experience and came up with the following empirical formula, which can be used as a reference for powder coating oven design. When the oven temperature is 180 ℃, powder coating oven volume × 3 × 860 = Q180 (million kcal / h), in the oven temperature of 140 ℃, powder coating oven volume × 2.2 × 860 = Q140 (million kcal / h). For example, baking for 180 ℃ electrophoresis paint powder coating oven (50m × 2.8m × 3.4m), its heating power is (50 × 2.8 × 3.4) × 3 × 860 = 1.22 million kcal / h. Baking for 140 ℃ is the medium or top coat powder coating oven (42m × 2.8m × 3.4m), its heating power is (42 × 2.8 × 3.4) × 2.2 × 860 = 1.22 million kcal/h.
