Training for Proofmaster M/S/Automat Functional principle for airtightness testing July 2017
Airtightness measurement 1. Measuring principle 2. Behaviour of the watch under vacuum 3. Behaviour of the watch under pressure 4. Use of supports 5. Definition of watch parameters 6. Minimum deformation 7. Remarks
1. Measuring principle One measuring chamber is placed under vacuum or pressure. The watch will be more or less deformed, depending on the structure of the materials used for the casing. During the measuring cycle, the system sensor monitors the watch s return and deformation. If the deformation return is within a defined tolerance, the watch is considered tight.
2. Behaviour under vacuum Cutaway of a watch Watch casing Glass Bezel Middle Back For easier comprehension, the internal components of the watch are not shown (the movement, dial, hands, etc.).
During evacuation (removal of air from the tank) the watch tends to inflate. Schematic presentation
Behaviour of the watch during the measuring period. Watch is tight The watch retains its deformation during the measuring period. Leak Watch is not tight The depression between the tank and the inside of the middle stabilizes, and the watch takes its original shape.
3. Behaviour under pressure During pressurization of the tank (air entering the tank), the watch tends to compress. Schematic presentation
Behaviour of the watch during the measuring period. Watch is tight The watch retains its deformation during the measuring period. Leak Watch is not tight The pressure between the tank and the inside of the middle stabilizes, and the watch takes its original shape.
4. Using watch supports The position of greatest deformation is between the support s round posts. It is therefore necessary to choose the smallest possible support (to ensure the lever effect), while ensuring the watch s stability once it is placed. Ideal situation: The support points are near the watch radius s halfway point. Too much support: Part of the back s deformation is lost and cannot be measured by the sensor.
5. Definition of watch parameters Glass diameter The three possible settings for Proofmaster There are three different size categories that can be configured, depending on the watch s behaviour. It is therefore possible for a watch of a large diameter (> 40 mm) to be categorized as a watch between 20 mm and 40 mm, for example. Later in this documentation, we will explain how to select the right category based on the watch s measured deformation. Ø less than 20 mm Ø between 20 mm and 40 mm Ø greater than 40 mm
Materials The three possible settings in Proofmaster There are three different configurable categories, based on the type of construction and materials used for the watch casing. For example, a very fine steel watch may easily behave like a plastic watch in terms of deformation and is therefore in the Soft category. On the other hand, a plastic watch may be in the Standard or Hard category if its construction is solid, thick or rigid, displaying less deformation. Another factor that plays a very important role is the properties of the glass. Logically, a flat glass should deform more than a domed glass. However, it is difficult to anticipate the right category with certainty without making an initial measurement, which would allow discovery of which category the watch is in. When it doubt, it is possible to set the category to Hard and then read the initial deformation values that Proofmaster shows on the screen. Later in this documentation, we will explain how to categorize the watch according to its deformation level. Soft Standard Hard For a watch with large deformation For a watch with normal deformation For a watch with little deformation
Airtightness limit As explained in the previous chapter, the watch deforms under vacuum and under pressure. After a certain stabilization time, the machine checks whether the watch continues to deform or stabilizes, to check whether it shows a leak or not. The tightness limit is expressed in %/min and depends on the quality of free air in the watch or, more simply, on the size of the watch. The exact formula for precise calculation of the leak limit in correlation with standard ISO 22810 in 2140mm relation to the volume of free air in the watch is as follows: - 3 = lllll ii %/mmm VVVuuu oo ffff aaa Standard tightness limit in correlation with standard ISO 22810: -2.0%/min with Ø < 20 mm -1.0%/min with Ø between 20 mm and 40 mm -0.5%/min with Ø > 40 mm
Test mode The test mode selected has a direct effect on the measurement resolution, the stabilization time and the measuring time. Prod (Production) Std (Standard) Lab (Laboratory) Fast test mode for production with reduced precision. Normal test mode with enough precision for reliable measurement. Very precise measurement with long measurement period for laboratory trials and tests.
Proofmaster S / M Software Test modes: LAB / PREC* / STD / PROD and what a measurement resolution of: 5% / 15%* / 25% / 40% means. Explanation with graphic example of the differences and effects on the measurement result precision / * PREC mode / 15% of on Proofmaster M Example: Pressure 2.0 bar / 100 µm absolute deformation / Max. negative tolerance: - 1% of return from deformation / Final result: + 1.0%/min. = O.K. Pressure Watch deformation in µm Pressurization phase Stabilization phase Measurement phase Depending on selected test mode Tolerances and final result Result: (example) - +.01%/min. of 100 µm LAB mode = very precise/long Final result + 1.0% Measurement resolution: +/-5% = Min. value: +0.95% Max. value: +1.05% STD mode = standard mode Final result + 1.0% Measurement resolution: +/-25% = Min. value: +0.75% Max. value: +1.25% Def. 0%, no successive deformation PREC* mode = precise AND long PROD mode = fast measurement Final result + 1.0% Final result + 1.0% Absolute deformation 100 µm (= 0.10 mm) Max. negative tolerance - 1%/min. of 100 µm Measurement resolution: +/-15% = Min. value: +0.85% Max. value: +1.15% Measurement resolution: +/-40% = Min. value: +0.60% Max. value: +1.40% Time Automatic Variable, depending on test mode Key: Pressure: * / Deformation: / Max. negative tolerance: / Final result (example):
6. Minimum necessary deformation of -0.1 to -0.8 bar Minimum necessary deformation under vacuum A B C D E G Deformation limit [µm] F H A B C D E F G H I I Test pressure [bar]
Minimum necessary deformation pressure range 0.1 to 1 bar Deformation limit [µm] A B C D E F G H I I H F E G D C B A Test pressure [bar]
The charts can be used to define the behaviour categories (material/diameter combination) of the various watch modules. This is for defining an adequately precise category for the watch s behaviour in various test situations. There are nine combinations for categorizing a watch, and each category requires that a minimum deformation be reached to launch measurement. Example with the following parameters: Diameter = 20 40 mm Material = Standard Pressure = 0.5 bar Minimum necessary deformation pressure range 0.1 to 1 bar Once the test is launched, it is possible to see deformation of the airtight watch of 1.8µm at 0.5 bar. The test is interrupted, because with the combination of configured parameters (diameter, material, pressure), the minimum deformation of 2µm has not been reached. Observing the chart to the right, with the configured parameters, we need to reach deformation of at least 2µm to perform the test. With detected deformation of just 1.8µm, the parameters need to be adjusted. Deformation limit [µm] Test pressure [bar] The new, adjusted category for this watch is: diameter 20 mm with Standard material. This new category requires minimum deformation of 1µm at 0.5 bar, much less than at 1.8 µm. Independently of the configured diameter, it is necessary to check that the tolerance in %/min still corresponds to the watch s physical dimensions. Proofmaster can automatically change the tolerances if the diameter is changed during programming. Depending on the standard, a small watch has a limit of -2%/min, a normal watch of -1%/min, and a large watch of -0.5%/min. These values are only for reference and can be adjusted according to your needs and different situations.
Minimum necessary deformation pressure range 1 to 10 bar Deformation limit [µm] A B C D E F G H I I H F E G D C B A Test pressure [bar]
7. Remarks Protective adhesives placed on the watch s back and/or glass may change the result. We strongly advise removing adhesives before the test, to ensure high-quality measurement. The helium valves found on some diving watches can open during a vacuum test. In that case, the machine will detect a large leak. To perform a vacuum test on a watch head without a movement installed inside, the crown can t just be placed. It must be fastened or, ideally, screwed to ensure that the pressure cannot detach it or eject it from its original position. To prevent traces of wear or scratching, there is a Proofmaster M Automat equipped with a rubber pad to eliminate this problem, which occurs rather often when the watch is being placed or removed. A watch that has been worn must thermally stabilize for about 15 minutes before measuring. Thermal fluctuations have a negative effect on the test results. Do not measure watches if they have been exposed to the sun too long or have been held in one s hand too long. A tested watch can be measured a second time after a time period 3 times greater than the length of the test conducted beforehand. The physical size and materials used in constructing the watch casing do not directly define a precise category. A plastic watch may behave like a small steel watch, etc. On the other hand, the limit in %/min is directly linked to the size of the watch casing or precisely to the amount of free air inside the watch casing.
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