The air consumption of a spray gun is a measured value that represents the quantity of air utilized when a specific air pressure (around 0.25 - 0.35 MPa) is applied to the inlet port of the spray gun, at the time of spray operation. In other words, the air consumption is a numeric value that indicates the amount of compressed air that is required to achieve an adequate finish for the coating film. In each manufacturer's catalogue, air consumption is usually converted to an air pressure value and expressed in units of L/min. In order that this value may be compared with the quantity of air discharged from a compressor, the quantity of air discharged from the compressor should ideally be greater than the air consumption. As well, in the event that several spray guns and other air-powered equipment are utilized simultaneously, then the appropriate compressor should be selected in accordance with the total air consumption of the combined equipment load. Apart from the above facts;

• On certain occasions, if the spray gun is used for intermittent operation (for example, sprayed for 10 seconds then stopped for 20 seconds), then it is acceptable for the compressor to only discharge a smaller quantity of air. Please consult with the manufacturer for additional details.
• Extra precautions must be taken as the volume of air may drop significantly due to the following reasons, even though the compressor may normally produce a sufficient volume of air: the air hose is too narrow or too long; the metal connecting fittings are too small or the transformer opening is too small. In the event that the coating finish is not satisfactory, the air consumption should be checked first.

(Reply from: Meiji Air Compressor MFG. Co., Ltd.)

A tank that is filled with compressed air is used to pressurize the paint for transport (generally used to supply paint to the pressure-fed spray gun). The maximum pressure of this compressed air is referred to as the maximum working pressure of the paint pressure feed tank. As the paint pressure feed tank is a pressurized container, it can be extremely dangerous if the internal pressure ever exceeds the maximum working pressure. In order to avoid this risk, the following equipment must be installed onto the pressure feed tank: a safety valve, through which air can escape once the pressure reaches a certain level; a pressure gauge that displays the air pressure within the tank; a regulator that controls the air pressure, maintaining it at a constant value; and a relief valve for use in releasing pressure from the tank when the lid is to be opened, or for other purposes. Extreme danger may persist and accidents may occur if the tank is used under conditions in which any of these devices are broken. Therefore, this important safety-related equipment must be inspected on a regular basis. In order to use any paint pressure feed tank that has either a capacity or a maximum working pressure that exceeds specifics levels (40 L, 0.2 MPa), a pressure resistance certificate for Class 2 pressure containers must be obtained. The Japan Boiler Association is responsible for issuing this certificate.

(Reply from: Meiji Air Compressor MFG. Co., Ltd.)

HVLP (High Volume Low Pressure) spray guns can be roughly classified into 2 categories:

1. Low pressure warm air guns: paint is sprayed on the object by using a large amount of warm air produced by a turbine (blower).
2. Low pressure atomization guns: paint is sprayed on the object by using the following procedure: this system uses compressed air supplied by a compressor. The relatively high-pressure air within the air circuit is then reduced somewhat, especially within the spray gun itself. The pressure within the air cap is then set to 70 KPa or less and then spraying is performed.

For the gun type described in 2) above, the volume of spray air used is greater than that used by regular spray guns. The term "LVLP" refers to spray guns in which air volume has been minimized in order to conserve energy (i.e., the volume has been reduced from High to Low).

It is sometimes necessary to use a more creative method of atomization, as LVLP guns atomize paint by using only a small amount of low-pressure air. In some cases, LVMP (Low Volume Medium Pressure) guns are utilized, which spray paint using air at lower pressures than those used by regular spray guns, but not necessarily as low as 70 KPa.

(Reply from: Meiji Air Compressor MFG. Co., Ltd.)

The "Type of Coating Equipment" is indicated on the vertical axis and the "Coating Objects" are indicated on the horizontal axis. The standard transfer efficiencies are then shown for each category. However, these values are only general standards of reference, which only describe general tendencies and can thus vary depending upon the particular coating conditions.

(Reply from: Asahi Sunac Corporation)

Transfer efficiency can be greatly affected by several factors, such as the shape of the object to be coated, the hangering method and the coating method. Typical transfer efficiencies for several general categories of shapes of coating objects are introduced below.

1) External Coating of Box-Shaped Objects (i.e., refrigerators, vending machines)

In general, all four sides and both top and bottom surfaces are coated. On most occasions, ON-OFF operations are performed between coatings for different objects. Transfer efficiency is 70 - 80%.

2) Internal Coating of Box-Shaped Objects (i.e., Microwave ovens)

This type of coating requires good penetration power for the coating of inner corners. Robots (including equipment having 3-axis motion) are mainly utilized as the automatic coating machinery. It appears that paint powder overspray (recovered powder) is often utilized for coating the rear surfaces (class B surfaces). Transfer efficiency is high, approximately 80 - 90%.

3) Panel Shaped Objects (i.e., guard rails)

As a specific example, guardrails are often hung vertically and coated using a continuous coating method (no ON-OFF spray operation), with a coating film thickness of 50 - 60μm.

4) Mesh Objects (i.e., chain link fences)

For mesh objects, coating is often performed by hanging multiple objects (2 - 3 sheets) in parallel. In general, transfer efficiency is low, ranging from 20 - 35%.

5) PCM Coating

Coating is performed on cutout sheets that are laid out horizontally. Several guns are mounted above the objects and coating is performed using short reciprocating strokes. Transfer efficiency is approximately 90 - 95%.

(Reply from: Asahi Sunac Corporation)

A variety of methods are available to improve the transfer efficiency.

However, this section only introduces the overall factors that can affect transfer efficiency, as the transfer efficiency for each specific coating application will vary in accordance with the particular combination of different conditions involved.

1) Coating Conditions

2) Paint Conditions

3) Other Factors

In addition to the above factors, the following factors can be taken into account:

Type of cator -- air electrostatic, rotating atomization electrostatic, air wrap electrostatic or other types.

Automatic coating equipment -- robots, reciprocators, fixed guns or other types.

"Density, orientation and other factors" when installing jigs for objects to be coated.

* The basic factors above have been used solely to illustrate their effects upon the improvement of transfer efficiency. For actual coating operations, other conditions, such as the appearance of the finish and the film thickness uniformity, must be taking into consideration, in order to determine the best-fit conditions.

(Reply from: Asahi Sunac Corporation)

Although the particular details to be evaluated will vary depending upon the coating line, I will explain some basic checkpoints here.

Step 1

When designing an entirely new coating line and even when implementing robots on an existing line, the first step is to draft a coating line layout based upon the coating requirement specifications. When drafting the layout, it is necessary to maintain a long-term perspective with respect to coating specifications, in order to be able to utilize the coating line for as long a time as possible. In this age of rapidly changing market demands, there is no point in even drafting a layout if it will require significant modifications soon after the start of operations. The layout should be drafted from a perspective of being non-obsolescent for at least 3 - 5 years. In the event that an appropriate layout cannot be devised, for any reason, it is recommended that flexibility be added to the facility in a manner that will minimize the amount of future modifications. In this sense, the implementation of robots is more advantageous than the implementation of other automatic equipment.

Step 2

Tasks must be specified for each robot and piece of equipment (including automatic equipment and peripherals) within the layout. At the same time, the function of each piece of equipment within the entire coating line must be determined, as must their combination with the prior and subsequent processes of each particular line. In addition, the maximum and minimum task loads should be determined for each piece of equipment, prior to operation. The understanding of these task loads will, for example, allow each piece of equipment to adapt to any changes in the quantity of production output or task details.

Step 3

The positioning of all equipment, including the spatial relationships between robots, should be determined. As well, if any people (human operators) are involved, their tasks must be specified for each piece of equipment. In particular, all details of human involvement, including exactly where, how and when human operators should be involved in operations, must be clarified. In addition, the most effective combinations of equipment and the best matching of their functions must be determined. The clarification of these factors will enable task details to be better understood, thus allowing for an accurate determination of the actual number of human operators required.

Step 4

After the completion of Step 3, it is important to meet directly with the manufacturers of the facility, the robots and the automatic machinery. In this meeting, the flexibility of the specifications, including the software, as well as compatibility with the planned layout should be discussed, along with the details of specifications for each piece of equipment. However, it is also necessary for you to explain the coating specifications and the purpose of the coating line to the manufacturers, presenting your own ideas without being too particular about the initial layout plan. In doing so, you may gain an enhanced understanding of the actual capabilities of each particular manufacturer.

Step 5

Evaluate the compatibility of the specifications with respect to each facility and equipment line. Check to ensure that there is some flexibility in the degree of compatibility, according to the detailed specifications for the coating process and the production method for coated products.

Step 6

After following all of the above steps, the final step is to perform tests based on the specifications and determine the final requirements. Subsequent to this testing, the appropriate automatic equipment will be selected. This selection process includes pricing negotiations with each manufacturer. However, environmental protection measures must be taken into account when selecting the equipment, as such measures have now become a critical issue within the coating industry.

(Reply from: Asahi Sunac Corporation)

Drying ovens can be classified according to the heat source and the method of drying, as follows:

As described in Section 2, the appropriate curing system should be selected by answering the questions using a "YES / NO" methodology, for each coating condition. However, this section only lists materials and drying methods below, for your reference.

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

Powder coating shall be used as the example for answering these questions.

1. Initial Costs

1. Costs of securing a location to set up the coating facility.
2. Costs of applications to the local government offices
3. Costs for electricity, gas, compressed air, steam and other utilities
4. Costs for wastewater treatment facilities
5. Facility implementation costs ... pretreatment equipment, coating booths, coating equipment, water drainage type drying ovens, drying ovens for baking, exhaust gas treatment equipment, conveyor systems and wastewater treatment facilities.
6. Coating costs
7. Costs for pretreatment liquids
8. Labor costs

2. Operating Costs

1. Electricity costs
2. Water costs
3. Gas costs
4. Sludge (industrial waste) treatment costs
5. Paint costs
6. Costs for removing paints
7. Costs for pretreatment liquids
8. Costs for replaceable parts
9. Maintenance costs
10. Repair costs
11. Labor costs
12. Logistics costs

<Ways to Reduce Operating Costs> (The relationship to initial costs must be also taken into consideration.)

1. Change motors to those with energy saving specifications.
2. Increase the degree of automation as much as possible.
3. Increase paint recovery rates (improve transfer efficiencies).
4. Decrease recoating rates by reducing dust defects and poor coating quality.
5. Improve conveyor efficiency by maintaining the conveyors in good condition.
6. Use low temperature chemical pretreatment agents.

(Reply from: OSAME Co., Ltd.)

(Perform standard pretreatment procedures and use the same drying oven used in the existing facility.)

The questions will be answered using a "propane gas tank" as the coating object.

(1) Facilities required: powder coating booths, recovery equipment, rotation equipment, reciprocators and powder coating guns

(2) Space required: 5m × 4m

(3) Initial costs: 15 million - 20 million yen. For solvent coating, 2 coats are required, thus increasing costs by 30 - 40%.

(4) No documentation need be submitted to local government offices.

(Reply from: Nordson Co., Ltd.)

Yes, very thin films can now be created. The average particle size of paint powders ranges from 30 - 35 μm, thus resulting in films 40 - 150 μm in thickness, for each coating operation. In addition, coating films of 300 - 2000 μm in thickness can be produced by preheating objects prior to their being coated. In recent years, fine particle paint powders have been developed, which enable the production of very smooth, thin film coatings having average film thicknesses ranging from 23 - 35 μm.

(Reply from: Japan Parker IONICS)

Equipment Maintenance

For proper maintenance of equipment, it is particularly important to check the electrical grounding conditions. A checklist should be created and inspections should be performed on a regular basis.

For electrostatic guns, inspections to detect any abnormal electrical discharge must be performed on a regular basis. Apply a voltage to the gun tip and perform grounding by touching a ground conductor to every surface of the gun. In addition, this inspection should be performed immediately, if a gun is either dropped or receives an impact, possibly from the motion of a reciprocator or other equipment.

Safety Measures for Operators

Important precautions for operators (i.e., protective clothing and gear) are listed below.

1. Operators and other persons who enter the coating room (coating booth) must wear shoes and working clothing that prevents the buildup of electrostatic charge.
2. The soles of electrostatic preventative shoes must not be dirty or covered with foreign material, such as paint. The shoes must always be checked to ensure that they are clean.
3. Electrostatic preventative shoes must be stored separately from regular shoes.
4. Operators of hand-held guns must always hold the gun grips with their bare hands.
5. It is strictly prohibited to bring any ignition sources, such as lighters or matches, into the coating room (or into paint supply or storage rooms).
6. As a basic precaution, operators engaging in coating operations in the coating booth must always wear dust prevention masks that are compliant with official certification standards. Operators should also wear other respiratory protectors suitable for specific operations, such as air supply masks, whenever necessary.
7. Work shoes, clothes, gloves and respiratory protectors must be maintained and stored in a clean environment. In particular, respiratory protectors must be stored in dedicated lockers. As well, filters must be replaced on a regular basis, or earlier if necessary, depending upon the results of regular inspections with consideration for the given workload.

(Reply from: Japan Parker IONICS)

The answer to this question is different for each of the 2 following situations:

1. The short answer is that it is possible to perform powder coating in a booth that is used for liquid coating. However, it is necessary to consider that the following problems may occur:
   • As it will be difficult to recover paint powder for reuse, some degree of cost increase is inevitable.
   • Paint powder cannot effectively be collected by the existing ventilation systems used in liquid coating booths, therefore some powder overspray may be discharged into the atmosphere with the exhaust air.
   • The frequency of booth cleaning and maintenance must be increased in order to maintain the performance of the ventilation system.
   Although the above problems do occur, in reality, it appears that there are many situations in which powder coating is performed in liquid coating booths for a variety of reasons, such as "performing small lot multi-color production."
2. It is not possible to perform the reverse of this situation, i.e. liquid coating cannot be performed in a powder-coating booth.

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

1. Regular inspections conducted by specialized manufacturers: Fans, pumps, compressors, burners, burner equipment and boilers.
2. Inspection of the coating systems:
   • Check for loose nuts and bolts.
   • Check for excessive chain expansion.
   • Inspect measuring instruments.
3. Replaceable parts (capabilities and functionality must be maintained):
   • Clean each filter and replace if necessary.
   • Inspect drive belts and replace if necessary.
   • Confirm the operational validity periods of safety devices, etc.
4. Perform operator inspections using the manuals for each system.
5. Perform cleaning of each system.

(Reply from: OSAME Co., Ltd.)

Under the Industrial Safety and Health Law, it is stipulated that a business enterprise must appoint an operations chief to maintain and manage the coating facilities, such as the coating booths and the drying equipment (for more information, please refer to the relevant law, above).

(Reply from: Matsushita Environmental & Air-conditioning Engineering)

When examined in accordance with the 3 perspectives described below, it is apparent that maintenance inspections should always be performed for coating equipment.

In addition, with respect to "how and where maintenance inspections are to be performed," please carefully read and understand the operations manual issued by your coating equipment manufacturer, prior to performing inspections.

The first perspective is the protection of coating operators from accidents.

As its sources of power, coating equipment primarily utilizes electricity and compressed air supplied by a compressor. The following operations are performed: "coating of objects with atomized paint" and "compressing the paint under high pressure, then supplying it."

However, the coating equipment cannot perform these operations alone and cooperative action is required from humans or robots.

In other words, the continuous use of coating equipment under poor conditions, such that air or paint leakage occurs or equipment does not function correctly because equipment maintenance inspections were not performed, may cause unexpected accidents that may seriously affect the health of coating equipment operators.

The second perspective is the continual ability to obtain a uniform quality of coating.

In order to demonstrate stable optimal performance and obtain a uniform coating quality (including the coating finish) on an everyday basis, it is mandatory that the coating equipment be maintained in top operating condition.

A satisfactory coating quality cannot be achieved by using coating equipment that operates inconsistently or has paint leaks.

The third perspective is the extension of the service life of the coating equipment.

As with automobiles, if you "use it as much as you like but ignore it after use," the service lifespan of coating equipment will definitely be reduced.

The most efficient means of ensuring a longer service lifespan for coating equipment is to perform daily maintenance, to inspect regularly for defects and to repair any such defects at the earliest opportunity.

(Reply from: Anest Iwata)