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4 Types of Tests for Coated Glass

4 Types of Standard Test for Coated Glass

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Coated glass is an industrial glass product onto which metal oxides are sprayed in the form of thin coatings (0.01 µm to 0.8 µm) that alter the light transmission, reflection, and absorption characteristics of glass.

Coated glass

The coated glass uses green and sustainable elements for high performance against heat ingress and better visual appeal.

The coated glass used for the exteriors of commercial and non-commercial buildings should meet the test requirement listed in this article.

Measurement of Performance

The performance factors and spectral details of the coated glass shall be determined using standard accepted spectrophotometer equipment. The exact size will be determined by the type of measuring equipment employed. The transmittance of the measuring sample must be measured using normal incidence light at the following wavelengths:

  1. 550 µm (representative wavelength for light and solar transmittance)
  2. 900 µm (representative wavelength for solar transmittance)
  3. R-reflectance measurement shall be made at 8 µm using radiation of nearly normal incidence for glass with a low emissivity coating.

1. Resistance Test

The coated glass is subjected to a water-saturated atmosphere at a constant temperature. The samples are exposed to condensation which may lead to surface degradation.

Test apparatus should have a provision of four test pieces, and the materials used for the inner walls shall be corrosion-resistant and shall not affect the test pieces. 

Test Procedure

  1. The water tank shall be filled with demineralized water, having conductivity lower than 30 µS/cm and a pH higher than 5. 
  2. The cabinet's internal temperature shall be controlled by means of the reference thermocouple keeping a temperature of the reference glass piece at 40 ± 1.5°C. 
  3. The test cabinet shall be in a room with an ambient temperature of 23 ± 3°C.
  4. Care shall be taken to ensure that draughts, dust, moisture, and solar radiation do not interfere with the test cabinet.
  5. The reference temperature shall be reached within 2 hours of commencing heating.
  6. Condensation shall be seen to form on the glass pieces. 
  7. The test is continued without interruption for the required time.
  8. Both the internal reference and the external air temperature shall be regularly checked.

Standard Test Requirements

  1. No defect greater than 3 mm in length.
  2. Maximum one defect between 2 mm and 3 mm in length.
  3. Maximum five defects between 1 mm and 2 mm in length.
  4. No staining of the coating, scratches, or clusters of pinholes greater than 1 mm.
  5. When compared with the reference test piece, there shall be no significant color change in both reflection and transmission. This observation shall be made within 20 s.
  6. The transmittance measured at 550 nm and 900 nm must vary from the corresponding measured value on the reference test item by no more than 0.03.

2. Acid Resistance Test

This test consists of subjecting the coated glass to a sulfur dioxide saturated atmosphere at a constant temperature. The samples shall have condensation continually forming on them. It is this condensation, together with the quantity of sulfur dioxide, that may cause surface degradation.

Test Procedure

  1. The test cabinet contains 2 liters of demineralized water having conductivity lower than 30 µS/cm.
  2. When the cabinet is closed, 0.2 liters of SO₂ shall be added, and the heating system switched on.
  3. The test consists of a repetition of 24 h cycles as shown in the figure.
  4. Each cycle consists of a high temperature plus condensation period and an ambient temperature without condensation period.
  5. The temperature shall increase to 40 ± 1.5°C in less than 1.5 h.
  6. During the next 6.5 h, the test pieces shall be subjected to condensation in the SO₂ atmosphere.
Acid resistance test graph

Standard Test Requirements

The transmittance measured at 550 nm and 900 nm shall not differ by more than ±0.03 nm from the corresponding measured value on the reference test piece.

3. Neutral Salt Spray Test

This test consists of subjecting the coated glass to a neutral, water saline atmosphere at a constant temperature. It is the water saline spray that may cause surface degradation. 

Test Procedure

  1. The test cabinet shall be prepared and run for a minimum of 24 hours before the test pieces are placed within it.
  2. The neutral salt solution is made up by dissolving NaCl in demineralized water having conductivity lower than 30 µS/cm to produce a concentration of 50 ± 5 g/l at 25 ± 2°C.
  3. The compressed air supplied to the spray nozzle shall be passed through a filter to remove all traces of solid matter or oil and shall be at an absolute pressure of 70 kPa to 170 kPa through a saturator at 40 ± 1.5°C.
  4. The spray nozzle shall be made of inert material with baffles to prevent the direct impact of spray on the test pieces. 

Standard Test Requirements

The standard requirement of a well-coated glass against neutral salt spray shall be the same as the condensation resistance test requirement mentioned above.

4. Abrasion Resistance Test

This test involves subjecting the coated surface of the coated glass to rubbing with a felt pad in dry condition. It is the type of pad, its loading, and the number of strokes that may cause surface degradation.

Test Procedure

  1. The metal finger shall be approximately 15 mm to 20 mm in diameter and shall be driven to produce a frequency of 60 strokes/min + 6 strokes/min alternating forwards and backward.
  2. The stroke length shall be 120 ± 5 mm. The strokes shall be parallel and ensure a constant pressure over the zone to be tested. 
  3. A circle shape with a diameter of 14.5 ± 0.5mm.
  4. The test sequence shall commence within 30 mins of the sample being cleaned.
  5. The felt pad's metal finger shall be lowered onto the glass surface, and a load of 4 N applied perpendicular to the glass surface via the felt pad.

Standard Test Requirements

  1. Ensure that the abraded area is uniform.
  2. The transmittance measured at 550 nm and 900 nm shall differ by not more than ± 0.03 nm from the corresponding measured value on the reference test piece.

Duration of Tests for Coated Glass 

The duration of the above tests shall be as per the following table:

FAQs

How to determine the performance factors and spectral details of the coated glass?

The performance factors and spectral details of the coated glass shall be determined using standard accepted spectrophotometer equipment. The exact size will be determined by the type of measuring equipment employed. The transmittance of the measuring sample must be measured using normal incidence light at the following wavelengths:
1. 550 µm (representative wavelength for light and solar transmittance)
2. 900 µm (representative wavelength for solar transmittance)
3. R- reflectance measurement shall be made at 8 µm using radiation of nearly normal incidence for glass said to have a low emissivity coating.

What is the standard test requirement of the resistance test of coated glass?

The standard test requirements of the resistance test of coated glass are:
1. No defect greater than 3 mm in length.Maximum one defect between 2 mm and 3 mm in length.
2. Maximum five defects between 1 mm and 2 mm in length.No staining of the coating, scratches, or clusters of pinholes greater than 1 mm.
3. When compared with the reference test piece, there shall be no significant color change in both reflection and transmission. This observation shall be made within 20 s.
4. The transmittance measured at 550 nm and 900 nm must vary from the corresponding measured value on the reference test item by no more than 0.03.

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