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  HONG KONG SPRAYING AND MACHINERY INDUSTRIAL CO. LTD.              

  

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   PRODUCT
   PRETREATMENT

    SPRAY BOOTH

   FRAME SPRAY BOOTH

   CLEAN ROOM

    OVEN

   OVERHEAD CONVEYOR

   FLAT & MESH CONVEYOR


  COLUMN & CHAIN    

       CONVEYOR


   POWDER COATING

   SPRAY ROBOT

   CONVEYOR

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HONG KONG OFFICE
Address: No 7-8, 11/F Block A, Vigor Industrial Building, 14-20 Cheung Tat Road, Tsing Yi
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 Tel:  24317981
 Fax: 24320126
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 E-mail: sales@hkspraying.com.hk
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       PRODUCT            CONTACT              ¤¤¤å

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           OVEN ¡@

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METHODS FOR CURING 

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 AIR DRYING 
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PRINCIPLE OF OPERATION

Paints get cured under room temperature as

1. volatile thinner evaporates and paints become dried

2. dry thinner oxides as a film by oxidizing polymers

3. hardening paints get hardened by hardeners in paints

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DRAWBACK

a. high humidity makes violate thinners harder to evaporate and poor paint film quality is resulted (discoloured or dusty paint film). Air-conditioners and dust filtering system are required to improve paint film quality.

b. high room temperature can make paints easier to evaporate, less dust on paint film but poor flash-off 

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 CURING BY HEATING
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Curing oven can be divided into 3 types

1. Low temperature oven

oven temperature: <100¢J, it is used to speed up the curing time of self-cured paints

2. Medium temperature oven

oven temperature: 100-150¢J, it is used to cure paints that require condensation reaction or polymerization

oven temperature should not be >150¢J, otherwise, coating will get yellowing and brittle

3. High temperature oven

oven temperature: >150¢J, it is used for powder coating or electrophoretic coating

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  HEATING METHODS FOR CURING OVEN

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 CONDUCTION & CONVENTION HEATING (HOT AIR OVEN)
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PRINCIPLE OF OPERATION

Heating with gas or liquid to:

1. by conduction: transfer heat from the heating tubes to the paint substrates with gas or diesel

2.  by conduction & convention: transfer heated gas to the paint substrates 

      

ADVANTAGE

Hot gas circulates evenly in the oven to

a.  make objects evenly cured, even for objects with recessed areas

b. speed up paints volatile

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DISADVANTAGE

a. Hot gas oven heats up objects from outside to inside, which results in: low rising temperature, low heat transfer efficiency, high power consumption, long oven size, high dust prevention requirement

b. (outside) coating cures first than the inside part so pimples or bubble marks will easily deposit on the coating surface

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 STATIC OVEN & TUNNEL OVEN  
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1. Heating by convention "horizontal hot air circulation" & equipped with "interlock hot air supply" to avoid the risk of sudden temperature rise

2. Oven temperature: ambient to 220¢J, thermostatic, self-timing with explosion proof window

3. Perfect insulation: oven outside temperature is less than 40¢J, so heat loss can be minimized

4. Control panel composed of: master switch, thermostatic, automatic drying timer with alarm, indication lights and explosion-proof window

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 RADIATION HEATING (INFRARED OVEN ) 
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3 WAVELENGTHS OF INFRARED OVEN

1. Near infrared (short wave):

wavelength:  0.75-2.5£gm

radiator temperature: 2000-2200¢J

radiation efficiency: high

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2. Medium infrared (medium wave):

wavelength:  2.6-4.0£gm

radiator temperature: 800-900¢J

radiation efficiency: medium

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3. Far infrared (long wave):

wavelength:  >4.0£gm

radiator temperature: 400-600¢J

radiation efficiency: low 

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 CURING PRINCIPLE   
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1. when the wavelengths of infrared match with that of the vibration of paint molecules, paint molecules can absorb the infrared and the paint will be cured, otherwise, the objected can only be heated and cured by the evaporation of thinner inside

2. as the  wavelengths of the vibration of paint or water molecules is normally >4.0£gm, we need to heat up the inner part of the object by near infrared (short wave) and cure the coating by far infrared (long wave)

3. distance between the infrared reflector and the object should be 120-300mm, otherwise radiation efficiency will be adversely affected

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  ADVANTAGE
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As object is cured from inner to outside coating by infrared oven which means the object and coating is heated at the same time which will result in a

a. higher rising temperature, higher heat transfer efficiency, lower power consumption

b. faster thinner evaporation, better coating quality, shorter oven size, lower dust prevention requirement

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 DISADVANTAGE  
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1. uneven oven temperature in infrared oven means different curing speed for objects with different shapes; so infrared lamp panel is more suitable for objects with different shapes

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2. as water molecules can absorb infrared, blower is required to blow away water molecules in order to speed up thinner evaporation

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  DIFFERENT INFRARED CERAMIC HEATERS

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 Infrared heating plate
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1. radiant ray is parallel to its horizontal ray and diffusion ray, this plane is suitable to cure plane objects because of even heat distribution

2. poor heat transfer on the back of the heating plate

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   Infrared heating lamp
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a. is less affected by radiant distance, smallest temperature difference for radiant distance of 200-600mm, so it is suitable for complex objects with different sizes

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  Infrared heating tube
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a. made of ceramics, insulation layer  in the middle, outside coated with far infrared coating

b. as this tube has thin heating layer and does not have resistance wire, heat distribution can be even  and there is no visual light loss which can ultimately improve the heat transfer 

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  MIX OF HOT AIR & INFRARED OVEN 

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 PRINCIPLE OF OPERATION 
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To let thinner out by infrared heating and to keep even oven temperature by  hot air convection  heating

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a. as metal can absorb radiant heat energy from infrared heating, therefore, in order to speed up the heating effect, we can get higher oven temperature (above 300 ¢J) and shorter oven tunnel at the same time

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b. this oven can maintain a stable oven temperature as there is an air insulation layer in the middle to guarantee the oven outside temperature is less than 40 ¢J - a good way to minimize heat loss and energy saving

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c. each section of our tunnel oven is checked with Oven Tracker -  to maintain stable oven temperature before delivery 

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 ADVANTAGE 
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have advantages of both infrared heating and hot air heating:

1. advantage of infrared heating

a. fast oven rising temperature

b. good coating quality

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2. advantage of hot air heating

a. even oven temperature: even curing speed for objects of different size

b. fast thinner evaporation

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  UV OVEN

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 ADVANTAGE 
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to cure objects by UV lamps

a. short curing time: ideal for paper, plastics or wood coating

b. low oven temperature for curing

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 DISADVANTAGE   
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a. short diffusion distances

b. only suitable for simple objects

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 ­^°ê OES ¼Ð·Ç
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1. ²Ä¤@­Ó¼o®ð¼Ë¥»©ó¥»¼t¼Ð·Ç¼QÏ@©â¨ú

2. ²Ä¤G­Ó¼o®ð¼Ë¥»©ó¨ª¥ß¨¤¾÷³õ¼QÏ@©â¨ú

  COMPONENT

VOC  

 OES Limit  Sampling with standard    Water-Wash Spray Booth    (Shenzhen: 7/1/98)

Sampling with Specially made   Water-Wash Spray Booth  (Chek Lap Kok:30/7/98)

Isopropyl alcohol

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400ppm  <0.1ppm <0.1ppm

n-butyl alcohol

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50ppm <0.1ppm <0.1ppm

Ethanol

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200ppm

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 0.5ppm

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<0.1ppm
Methylethyl ketone 1000ppm 6.8ppm 2.8ppm
Phosphoric acid 1mg/m3  0.2mg/m3 <0.05mg/m3

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Conclusion

The concentrations of five different parameters in the paint mist were measured at Shenzhen (7-1-98) and Chek Lap Kok (30-7-98) respectively and the results are presented. It is concluded that the VOC (including Isopropyl alcohol, n-butyl alcohol, Ethanol, Methylethyl ketone) and Phosphoric acid arepresent in an insignificant amount and within the OES limit.

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A note on the quoted OES listed in the above table

The full name of OES is Occupational Exposure Standard and it is a concentration of an specific airborne Substance averaged over a reference period at which there is currently no evidence that repeated or day after day exposure by inhalation, will be injurious to the Health of employees. The OES¡¦s should not be exceeded but if this does occur, effective measure should be taken to reduce the exposure as soon as practicable.

The OES quoted here is based on the EH40 which is a part of The Control of Substances Hazardous to Health (COSHH) regulations established by the Health and Safety Executive of UK. 

The objective of this regulation is to prevent disease at workplace due to exposure of hazardous substances.

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 ­»´ä OEL ¼Ð·Ç
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 ¤¤°ê°ê®a¼Ð·Ç GB/T 16157-1996
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