Preprocess

Q1.
Is it possible to process several different types of metal alloys within the same coating operation line, even though each alloy is composed of different materials?
A1.
  1. The purpose of pretreatment is to "degrease" and perform "chemical conversion" on the surface of the metal to be coated.
    The "degreasing" process can easily be performed for different metal alloys by adjusting a few minor conditions. However, "chemical conversion" cannot usually be performed unless the appropriate chemical reagents are utilized for each particular type of metal alloy.
  2. As well, the chemical reagents and their conditions of usage vary even among ferrous materials, depending upon the particular type, such as bright steel sheeting, zinc steel sheeting, black annealed steel and castings.
  3. However, for vehicle pretreatment lines a chemical agent has been developed that can be utilized to pretreat both iron and aluminum.
  4. The following examples indicate the different metal alloys that can be pretreated using the same tribasic zinc phosphate pretreatment line as is used for bright steel sheeting:
    • Stainless alloys: Can be degreased and coating is possible. However, careful attention must be given to the adhesion characteristics.
    • Aluminum alloys: Can be degreased, etched and coating is possible. However, careful attention must be given to the aging of the chemical reagent used.
    • Black annealed steel, treated steel sheeting and castings: Standard coating can be performed.

(Reply from: Nippon Paint Plant Engineering)

Q2.
After pretreatment, what criteria are utilized to determine whether the pretreatment has been performed properly?
A2.
  1. The purpose of pretreatment is to improve both the adhesion and the corrosion resistance of the coating film. Therefore, the effectiveness of both of these characteristics are determined by evaluating the coating film itself, after the coating material has dried.
  2. With respect to adhesion, adequate degreasing must be performed during the pretreatment stage and all foreign material must be removed from the surface.
  3. Furthermore, in order to increase corrosion resistance, a chemical conversion process must be performed on the metal surface. Therefore, it is necessary to select the most appropriate chemical reagent for each particular metal to be treated.
  4. In each situation, a final assessment is made on the actual pretreatment line, to determine whether or not the required characteristics have been achieved.

(Reply from: Nippon Paint Plant Engineering)

Q3.
I understand that pretreatment may be performed by either spraying or by dipping. Please tell me about the special features of each method and how each is used.
A3.

Please refer to the table below:

No. Item Spraying Dipping
1 Background Information The development of pump technology has facilitated a high degree of automation, allowing for the rapid development of this method. Brush application, manual dipping and bath treatment (for rust removal, etc.)
2 Washability Certain physical effects can be expected as a result of the pressure and quantity of spray utilized, which contributes to the removal of foreign material and can improve washing efficiency. Can be used for objects with surfaces having simple shapes, such as flat sheeting - in other words, surfaces that can easily be reached by the paint spray.
3 Productivity As conveyor systems have advanced and grown, the development of level conveying, automatic conveying and high-speed conveying have resulted in significant enhancements to the utility of this method. Can be used for the bulk treatment of small parts. This method requires a vertical conveyor system.
4 Drying Properties, Drainage Properties Hot air drying and continuous drying can be performed. There are some restrictions with the hot air drying process. On certain occasions, the washing process must be separated from the drying process.
5 Preparations for Coating In most cases, a continual feed into the coating line is possible. In most cases, loading must occur separately from the washing process and the shape must be changed into one that facilitates easy coating.
6 Potential, Expandability In terms of productivity, this method still provides superior results. It is desirable to use this method together with the dip method, in order to improve both washability and product quality, in terms of the coating pretreatment. In terms of the coating pretreatment, this method still provides superior product quality. Further productivity improvements and enhancements in conveyor technology are required.
7 Applications Suitable for large objects that have flat, simple shapes. Suitable for small objects that have complex, three-dimensional shapes.

(Reply from: Parker Engineering Co., Ltd.)

Coatings

Q4.
Can any type of paint be applied through the electrostatic coating process?
A4.

Yes, basically, any type. In general, the electrostatic coating process can be used with no problems with either liquid or powdered melamine, acryl, epoxy and urethane resin coating materials. These coatings materials can be utilized for the industrial coating of metal, wood and plastic. However, one precaution must be taken when performing liquid electrostatic coating, with respect to the electrical resistivity (more accurately, the value for volume resistivity). If the volume resistivity of the coating material is less than 7.0 MΩcm, then the passageway for the coating material must be insulated, as the electrostatic charge may leak away through the coating material itself. Coating materials that may be subject to this phenomenon, include water-borne coatings and color clears that contain dye. As well, with respect to metallic coating materials, even though the electrical resistivity is greater than 7.0 MΩcm, some of the electrostatic charge may occasionally leak away through the aluminum powder contained within the coating material. Therefore, in some cases when electrostatic coating is performed, the entire passageway for the coating material must be insulated.

Moreover, even though an electrostatic charge can be successfully applied to the following materials, the electrostatic effect will not occur: coating materials composed of large-sized particles, such as those used in construction; and high viscosity coating materials that may not become atomized unless a very high pressure is applied, such as heavy corrosion preventative coatings. Therefore, there is no advantage in attempting to apply these materials via the electrostatic coating process.

(Reply from: Ransburg Industrial Finishing K.K.)

Q5.
What precautions should we take in order to improve transfer efficiency?
A5.

The following precautions should be taken, in order to improve transfer efficiency:

  1. Regardless of whether air atomization or airless atomization is employed, it is important to minimize the air or liquid pressure, as much as possible.
  2. Use the most appropriate jig. It is best to use a metal jig that conducts electricity. However, ensure that the particular jig used will not attract excess coating material.
  3. When wraparound is expected, ensure that the appropriate spacing is used between adjacent objects to be coated.
  4. The electrical resistivity should be adjusted to the most appropriate value for the particular electrostatic coating equipment used. A solvent is usually used to reduce the resistivity. However, if the resistivity is already too low, another method should be utilized.
  5. In the event that the electrical resistivity is "0" or near zero (for example, when using a water-borne coating material), then a water-borne electrostatic system must be utilized.

For more information, please consult the manufacturer of the particular electrostatic coating equipment utilized by your company.

(Reply from: Asahi Sunac Corporation)

Drying

Q6.
What can I do to reduce energy consumption?
A6.

Steps to Reduce Energy Consumption

No. Item Step
1 Understanding Energy Usage <Low initial costs>
Utility
1.water, 2.electricity, 3.compressed air, 4.heat source: electricity, gas, oil
2 Understanding the Costs of Each Energy Source <Low operating costs>
Total estimated operating costs for each energy source listed under item No 1. : Yen/year, Yen/hour
3 Understanding Consumable Products <Verification of operating lifespan> (utilization of washable parts)
Filters, packing, machine parts, instrument parts
4 Energy Consumption Analysis <Reducing the accumulated heat, heat released and volume of air discharged>
Analyses of heat load data during temperature rises
Analyses of heat load data during normal operations
Improvements to oven design
5 Understanding Production Conditions <Operating in accordance with operational conditions and situations>
No load, full load
6 Instrumentation for Energy Management <Improvements in operating efficiency>
Inverters, hygrometers, densitometers

(Reply from: Parker Engineering Co., Ltd.)