DIN 53509 “Testing of rubber – Determination of resistance to ozone cracking – Part 1: Static stress” is used to determine the resistance of synthetic rubber to cracking by exposing specimens to a specified ozone concentration and to elongation stress.
Introduction to DIN 53509
DIN 53509 was developed by the Working Committee NMP 434 “Testing of the Physical Properties of Rubber and synthetic Rubber” under the German Committee for Testing Standards for Materials (NMP) with reference to the international standard ISO 1431-1:1989. In addition to reference to Part 1 of the above standard, ISO 1431-2:1982 with dynamic stress determination content and ISO 1431-3:2000 with reference method for ozone concentration determination were adopted. The preferred method of determination of ozone concentration recommended in this standard is not the chemical method as DIN 52509-2, but a ultraviolet photometric method.

DIN 53509-0 “Testing of rubber – Determination of stability against ozone cracking – Part 1: Static stress”

DIN 53509 differs from ISO 1431-1:1989 in the following ways:

– Relative air humidity should be less than 65% under normal conditions, only limit the upper limit. However, if the product will be used in humid conditions, it should be tested at 80~ 90% relative humidity.

– In order to ensure sufficient supply of ozone, the ratio of the sample surface to ozone flow rate shall not exceed a value of 25 s x m-1,

– In Method A, the trial time is proposed to be 72 hours instead of 48 hours,

– In Method B, no limit is required for 96 hours,

– In method A, the use of a crack table to determine the rating is no longer specified. However, it is necessary to explain whether cracks are generated or not after the test. If a film (photograph) is required,

– If necessary, a T50-dumbbell sheet specimen of only 2 mm width is allowed to determine whether cracks have begun to form,

-It is also allowed to test specimens that are subjected to a number of different tensile stresses at the same time, namely, Annalus specimens and rectangular specimens bent into a ring.

DIN 53509-0 “Testing of rubber – Determination of stability against ozone cracking – Part 1: Static stress”

1. Scope and purpose of application
The test method specified in this standard is used to determine the crack resistance of synthetic rubber by placing the sample under the specified ozone concentration and exposing it to elongation stress. Ozone is the main cause of damage to synthetic rubber after exposure to the natural atmosphere for a period of time. But ozone can also be produced indoors, especially in areas with electrical discharges and sources of ultraviolet radiation. The crack resistance of the material is related to the concentration of ozone and the elongation stress of the material. Other factors include temperature, air humidity, sunlight, impurities and sediments in the air, etc.

All secondary factors related to material exposure to the atmosphere are not considered when static tests are performed in accordance with this standard, only constant elongation and constant ozone concentration, temperature and air humidity are considered. It is only desirable that the specimen can be tested under static stress.

It is only desirable that the specimen can be tested under static stress.

This test method is not suitable for determining the light resistance of synthetic rubber materials.

DIN 53509-0 “Testing of rubber – Determination of stability against ozone cracking – Part 1: Static stress”

2. References to this standard
The various references used in this standard are either dated or undated. These references, which are cited in the standard text, are indicated. A citation standard with a publication date is a later modified or revised version of the standard. Undated standard version refers only to the last version (including modified version) of the relevant standard

DIN 7716 Rubber and gum products – Requirements for storage, cleaning and maintenance.

DIN 50014? Air conditioning and its technical application-standard air conditioning equipment

DIN 53502? Tests on synthetic rubber and fabrics with a synthetic rubber layer — test specimens — manufacturing practice

DIN 53509–2? Tests on rubber and synthetic rubbies-Accelerated ageing of synthetic rubbies-Determination of ozone concentration (recommended method)

DIN 53509-0 “Testing of rubber – Determination of stability against ozone cracking – Part 1: Static stress”

Step 3: Terminology
1. Critical elongation

The so-called critical elongation rate refers to the maximum elongation rate that can be subjected to ozone under specified conditions without cracking.

4. Basis of this test method
Put the sample into the fixture of the laboratory to lengthen it to the specified size, stay at the specified temperature and air humidity for a certain time, and use the air with the specified ozone concentration to circulate through the surface of the sample during the test. Finally, the cracks are evaluated.

The following methods can be used to conduct the test:

Method A

The crack pattern is evaluated after a predetermined stress time at a predetermined elongation rate.

Method B

The stress time at crack generation was measured at a predetermined elongation rate.

Method C

A minimum of four different elongation rates was used to determine the stress time at the time of crack formation.

Data of critical elongation for a certain stress time

5. Test equipment (instrument)
5.1 Sample fixture

The fixture material shall not affect the measurement of ozone concentration. Suitable for aluminum and stainless steel manufacturing. Sharp blunt edges should be avoided on the fixture. The fixture should be shaped to ensure that the surface of the synthetic rubber sample can be in contact with the ozone-containing air in the laboratory to allow air flow over the surface of the sample. Use a threaded vise to clamp the strip specimen and use it to elongate the specimen to 80%. The unclamped length of the specimen should be at least 40 mm in the unstretched state.

The dumbbell sheet specimen needs to be applied such a fixture, the chuck is in the shape of a claw, the width of the specimen used for elongation is 5 mm, this part is 50 mm long before elongation, can be stretched to 90 mm (80% elongation). The maximum elongation of the annular specimen is about 20% when the fixture shown in Figure 1 is applied.

The corresponding fixture shall be applied to the finished product. Because the hardness of the finished product is large and the strength of the fabric is enhanced, the required elongation can not be achieved with the strip sample. The section of the finished product can be wound around a mandrel, so that the satisfactory elongation can be achieved. The elongation can be controlled by a pre-made scale line on the device.

Note: THE processing surface should be protected from ozone on the finished product sample.

1. Test chamber

The inner wall of the test chamber shall be made of a material that will not adversely affect the measurement of ozone concentration, such as stainless steel.

The test chamber should ensure a temperature of ±2°C and a relative air humidity of (55±10) % when carrying out the sample. An observation hole is provided on the test chamber so that the sample can be observed without opening the chamber (uninterrupted ozone supply).

Protect the specimen from direct effects of sunlight and ultraviolet rays.

The test chamber should be designed according to the minimum 10 cm3 free space (volume) of the test chamber per cm2. The free space (volume) of the test chamber here refers to the volume in the test chamber after the chuck and fixture are removed.

The flow rate of ozone-containing air through the test chamber should reach the calculation requirements of 12 ~ 16 mm/s, and the minimum fluid velocity should reach 8 mm/s. This calculated fluid velocity is equal to the quotient of the volume flow rate (volume/time) divided by the effective cross-sectional area of the air flow.

In order to ensure that the ozone concentration tolerance, temperature and relative air humidity specified in sections 7.1 and 7.2 of this standard are met throughout the chamber, a filter plate is required to distribute the inlet air or other equipment with the same function is used.

DIN 53509-0 “Testing of rubber – Determination of stability against ozone cracking – Part 1: Static stress”

It is recommended to install an auxiliary fan in the test box to strengthen the circulation of air, so that the surface of the sample can be significantly accelerated by (600±100) mm/s, so as to better distribute the air in the test box.

Note 1 When auxiliary fan is not used, the test results may be different, which should be explained in the test report.

Remark 2 It is critical to ensure the uniformity of ozone distribution in the test chamber and to avoid the jig blocking the flow of air flow. In order to better solve the problem, other methods can be used, for example, the fixture can be installed on a rotary table, so that the test process is periodically exposed to a certain area of the test box. Similar information and data can be found in the ISO /DIS1431-1:1986 standard.

In addition to using fresh air into the test chamber, you can also use circulating air plus part of the fresh air, the recommended amount of fresh air is not less than 3 x the volume of the test chamber/hour.

In order to prevent the disturbance of the established test conditions, it is required to extract 1 ~ 3 liters of air volume flow rate (LUft-volume EndurchFluss) per minute at the outlet of the test chamber and conduct ozone analysis according to DIN53509-2.

1. Ozone generation equipment can use ultraviolet lamp or discharge tube as ozone source, in the discharge tube to produce static discharge. Air or oxygen can be supplied. Especially when the discharge tube is used to inject air to produce ozone, it needs to be kept very dry (up to 0.3 grams of water per cubic meter of air). Ozone generating equipment shall ensure that the ozone concentration, temperature and relative humidity of the air flow before entering the test chamber meet the relevant test conditions specified in Section 8 of this standard and can maintain these test conditions during the test. The ozone concentration can also be adjusted by changing the voltage of the UV lamp or discharge tube and the amount of fresh air fed.

The ozone source used is required to have sufficient power. Because it is hoped that each time in the opening of the test box door, replace the new sample or observe whether the crack occurs above the sample, after closing the box door, at the latest, the ozone concentration should be adjusted again within half an hour.

The ozonated air from such ozonating equipment shall not contain carbon oxide, oil, dust and other impurities.

Ozone concentration control equipment

The e fluctuating ozone concentration in the test chamber can be recorded at any time and anywhere using suitable equipment operating on the basis of electrochemical or photometric methods. Test such equipment according to the method recommended by DIN 53509-2.

DIN 53509-0 “Testing of rubber – Determination of stability against ozone cracking – Part 1: Static stress”

6. Sample
Sections 6.1.1 to 6.1.3 of this standard specify the specimens to be applied. The most commonly used sample is Streifenproben.

The strip specimens and dumbbell sheet specimens can adjust the elongation more accurately than the annular specimens.

6.1 Shape and size of the specimen

6.1.1 Strip sample

The thickness is (2±0.2) mm, and the length is not less than 10 mm; The length is not specified. If the clamping length is not specified, it should be ensured that the length is not less than 40 mm in the unextended state.

6.1.2 Dumbbell sheet sample size is shown in the figure.

Picture is missing

FIG. 2 dumbbell sheet

6.1.3 Annular specimen

The thickness was (6±0.3) mm and the side length or diameter was (60±0.3) mm.

Such annular specimens require a special fixture (see Section 5.1) with a maximum elongation of about 20%.

6.2 Manufacture of the sample

Manufacture specimens according to standard DIN 53502. Can be processed from vulcanized rubber sheet or by the product of the appropriate size of the sample, especially for the latter directly from the product of the sample need to pay attention to the processing shall not damage the vulcanized surface layer (vulcanized film).

Note: IF THE sample of the product cannot be manufactured according to Section 6.1 of this standard, the test can also be carried out directly with the product.

6.3 The number of samples. At least three samples should be used each time.

6.4 Pretreatment of sample test

6.4.1 Pretreatment of the sample without elongation

DIN 53509-0 “Testing of rubber – Determination of stability against ozone cracking – Part 1: Static stress”

DIN 53509-0 “Testing of rubber – Determination of stability against ozone cracking – Part 1: Static stress”

Test specimens should wait at least 16 hours after vulcanization and no longer than 4 weeks at the latest. The period between vulcanization and the start of testing should not exceed three months as far as possible. On the other hand, the trial shall be started no later than two months after the supply to users. If the test is conducted at a different time, a separate contract shall be signed and indicated in the test report.

If it is necessary to place vulcanized rubber with different mixed structures together, it should be noted that in contact with another vulcanized rubber, the mixing additive should be replaced as much as possible (first, ozone protective agent), which can affect the performance of ozone resistance. For this, aluminum foil can be padded between the various synthetic rubber parts.

When storing, attention should be paid to DIN 7716, which stipulates that the storage temperature should be controlled to better maintain the temperature at (23±2) °C.

6.4.2 Pretreatment under tensile condition

The surface to be evaluated shall be intact and clean. Requires the removal of weathered skin from the surface.

Such a part of the specimen will produce severe deformation after being clamped through the clamp mouth (see Section 5.1 of this standard). Therefore, the part should be coated with a coating of ozone-resistant paint (such as a polyester based on chlorinated chloride) before clamping. The dividing line between the painted surface and the non-painted surface should not be perpendicular to the tensile direction of the specimen, but should be inclined, otherwise, serious cracks will occur on the dividing line. Ozone-protective coatings such as silicone grease (Silikonfett) that may adversely affect the properties of synthetic rubber should be avoided

Before the sample is exposed to ozone, it should be clamped in the jig to reach the tensile state specified in this standard (see Sections 7.4 and 8 of this standard) for 48 to 72 hours. In the case of arbitration (in Schiedsf? lle) should be adjusted according to DIN50014-2350-2 to handle tensile state (70-72) hours (pre-elongation) under standard ambient conditions.

Hand contact with the specimen should be avoided both during conditioning and subsequent testing.

The test results of samples under the same conditioning conditions and stress conditions need to be comparable.

DIN 53509-0 “Testing of rubber – Determination of stability against ozone cracking – Part 1: Static stress”

7. Stress conditions
7.1 Ozone concentration

This standard specifies that the ozone concentration used in the test is mainly (50±5) pphm (pphm is the abbreviation of part perhundred millions). 1pphm is equal to 1 volume share of ozone in 108 volume shares of air). In addition, ozone concentrations of (25±5) pphm, (100±10) pphm and (200±20)pphm can be applied to perform the test.

The unit of ozone concentration can also be used in mg/m 3. The conversion relationship between the two units is as follows:

The unit of the pressure p in the formula is pa. The unit of temperature is K(thermodynamic temperature). The following simple conversion relationship can be used at standard ambient pressure and temperature of 20°C:

50 pphm(V/V) =1 mg/m 3.

Note: Because the ozone concentration in the natural atmosphere is much lower than that actually used in the test, the product is exposed to a lower ozone concentration in the practical application, and the actual interaction is better. Ozone concentration units can be referred to in the introduction to this standard.

7.2 Temperature and relative air humidity

The main test temperature was (40±2) °C. Temperatures of (23±2) °C and (30±2) °C are also recommended.

The relative air humidity in the test chamber recommended by this standard should reach (55±10) % during the test. If you want to use other relative air humidity, you need to sign the contract and indicate it in the test report.

7.3 Stress time

The crack generation diagram (Rissbild) is evaluated after one or more of the following stresses have been applied for hours:

(1.9 2), (3.9 4), (7.8 8), (15.5-16), (23.5-24), (47-48), (71-72), (95-96),

For test method A(see Section 9 of this standard), the main stress action time is (47 to 48) hours.

The longest stress action time (95-96 hours) should be selected for test methods B and C.

One of the main stresses used for test method C critical elongation is (95-96) hours..

7.4 Elongation of the sample

One or more of the following elongation % may be selected during the strip specimen test:

(5 + 1), (10 + 1), 15 + / – 2), (20-2), (30 + 2), (40 + 2), (50 + 2), (60 + 2), (80 + 2).

For test method A and test Method B, 20% is recommended if only one elongation is selected.

The maximum selected elongation when bending the annular specimen on the fixture of FIG. 2 is about 20%.

There is a great relationship between the crack tendency and the elongation of the specimen. It is hoped that the elongation of the actual application can be used as much as possible for the test of the product.

DIN 53509-0 “Testing of rubber – Determination of stability against ozone cracking – Part 1: Static stress”

8. Implementation of the test
Figure 3 shows the system diagram of equipment layout when the test is actually carried out.

Start the test chamber is empty, has not yet loaded the sample, first close the switch, make it to meet the requirements of section 7 of this standard stress conditions such as ozone concentration, temperature and relative air humidity. Then put the samples in the fixture treated before section 6.4.2 into the test chamber.

It is necessary to return to the aforementioned test conditions at the latest half hour (30 minutes).

As far as possible, the peephole installed in the test chamber is used to evaluate the specimen. Only at this time, artificial light is allowed to facilitate the evaluation of the specimen. Test interruption and unnecessary opening of the test chamber should be avoided as far as possible, and the opening time should be shortened as much as possible when it is unavoidable. Other test results are obtained because the specimen is subjected to frequent stress reduction and relaxation processes that can lead to prolonged interruption of ozonation. When opening the test chamber, the loss of ozone and the interruption of ozone generator work should be avoided. Because almost every time the test chamber is opened, that is, it takes 30 minutes after each interruption of the test to resume the test conditions required by the regulations again.

The test can be conducted by any of the following three methods:

Method A

According to the sample macro grinding observation evaluation. The strip specimens shall reach the specified elongation, mainly 20%, in accordance with Section 7.4 of this standard. The maximum elongation of annular specimens is about 20%. This method requires the stress time specified in Section 7.3 of this standard to be achieved, mainly 48 hours.

Method B

This approach allows the adoption of one or more of the elongation rates given in Section 7.4. If you only use one, use 20%. The maximum elongation of annular specimens is about 20%. Stress time was selected as specified in Section 7.3. After the action time, to determine whether the sample cracks. The intermediate time is usually used to evaluate the elongation data according to the period of priority crack detection.

Method C

At a minimum, this method uses the four elongation rates specified in Section 7.4. After the stress time is determined according to Section 7.3, the sample is checked for cracks. For each specimen, the stress time at which the initial crack was detected, the elongation data related to the critical elongation range, and the intermediate time can also be used for evaluation.

For all the above measurement methods, the sample was clamped on the fixture when the observation was made.

DIN 53509-0 “Testing of rubber – Determination of stability against ozone cracking – Part 1: Static stress”

9. Assessment
The evaluation work requires that the surface to be evaluated be unprocessed and unprotected. Cracks at the edge of the specimen are not considered in the evaluation.

The method of assessment depends on which method (A,B, or C) given in Section 8 is applied. These three test methods

Methods can be used 6-8 times of magnifying glass to observe, to see whether the sample surface cracks. Method A can determine the degree and grade of crack without magnifying glass.

Method A is to check the specified elongation after the specified stress time (mainly 48 hours and 20%) to see whether cracks occur. If so, the cracks are evaluated according to the crack map automatically drawn by the equipment, so it is not necessary to use a magnifier. It is divided into the following assessment levels:

Grade 0: no crack

Class 1: short and narrow cracks

Class 2: Long, slightly wider crack

Class 3: Long, wide crack

It can also be divided into several intermediate levels. Figure 4 shows the typical crack distribution diagram of strip samples divided into grades 1-3.

DIN 53509-0 “Testing of rubber – Determination of stability against ozone cracking – Part 1: Static stress”

The length and width of the crack should be measured during the evaluation. It is also necessary to measure the depth of the crack in annular specimens.

In order to evaluate the crack map more accurately and study the effect of ozone protective agent, the cracks can be evaluated by referring to the following crack class-crack number and crack class-crack length tables.

Here, the strip sample is selected according to Section 6.1.1, and the length of the sample is 60 mm.
For Method B, the required stress time is obtained at the beginning of crack generation with the elongation specified in the standard (20% more). Both data need to be filled in the test report.

Method C is based on finding the elongation range at which the critical elongation is located. That is, the maximum elongation ε1% and minimum elongation ε2? Are measured within the specified stress time. %. No crack has been found in all tested samples at ε1. Cracks appear in all tested samples at ε2.

DIN 53509-0 “Testing of rubber – Determination of stability against ozone cracking – Part 1: Static stress”

Figure 5 shows an example of a graphical solution (line diagram) for the critical elongation of method C. The results of the experiment can be seen at a glance without the need for explanation. In the figure, the ordinate represents the elongation, and the abscissa represents the stress action time (both the ordinate and abscissa use logarithmic scale to represent the numerical value. The upper part of the slanted line in the figure represents the test time after the crack was observed. That is, the area where the crack occurs. However, the lower part of the diagonal line and the upper part of the dashed line indicate the test time when small cracks are found, that is, the area where no cracks occur. The region within the dashed line represents the critical elongation measured after the stress time reaches 96 hours. The advantage of using a line plot of the kind shown in FIG. 5 is that the relevant critical elongation can be easily estimated using an arbitrarily chosen stress time. However, this line calculation also has its limitations. The curve is related to the quality of synthetic rubber, that is, this line calculation cannot be applied to all synthetic rubber. If there are no other requirements, the critical elongation should be determined according to the maximum stress time (maximum 96 hours).

Method C Line calculation of critical elongation Graphical legislation

Method C Line calculation of critical elongation Graphical legislation

Dehnung in %: elongation %; Beansprungungsdauer in h: stress action time (hours); Gebiet mit Rissbildung: areas where cracks occur; Prufzeit, nach der erste Risse beobachtet wurden: test time after the discovery of the first crack; Prufzeit, bis zu der keine Risse beobachtet wurden: test time when no cracks are found; Gebiet ohne Rissbildung: areas where no cracks occur; Kritische Dehnung ε=4% fur 96 h Beansprungsdauer: critical elongation ε=4% after 96 h stress action time

1. Test report

In accordance with this standard, the test report needs to state:

– type, name and shape of the product;

– Where the sample is sampled on the finished product, if from the finished product;

– Shape and size of the specimen;

– Clamping method during finished product testing;

-Specific test method chosen (A, B or C).

DIN 53509-0 “Testing of rubber – Determination of stability against ozone cracking – Part 1: Static stress”

If the main test conditions for application are not the same, it should also be given:

– ozone concentration;

– temperature under stress;

– Time of stress action:

– Elongation when strip test and dumbbell sheet specimens are used;

– Maximum elongation of annular specimens and products;

– pre-stretch time;

– No auxiliary fan shall be applied;

– Methods for the determination of ozone concentration;

– The crack diagram is evaluated according to grade 0-4 or grade 0-6. For method A, the grade of A-D is used to evaluate;

– Stress time of the first crack in method B;

– Range of critical elongation (ε1,ε2) for method C at specified stress time;

– Existing line diagrams;

– where it differs from this standard;

– Test date.
D > 8