EP1558909A1

EP1558909A1 - Device for testing the scratch resistance of surfaces

Info

Publication number: EP1558909A1
Application number: EP03769378A
Authority: EP
Inventors: Andreas BÜRGEL; Georg Lamp; Robert Maleika; Leslaw Mleczko
Original assignee: Bayer MaterialScience AG
Current assignee: Covestro Deutschland AG
Priority date: 2002-10-25
Filing date: 2003-10-13
Publication date: 2005-08-03
Also published as: US20040092215A1; US6852018B2; TW200422613A; CN1708679A; JP2006504084A; AU2003278073A1; DE10249725A1; WO2004038385A1; CA2505149A1

Abstract

The invention relates to a device for testing the scratch resistance of surfaces of a sample body by means of a gas flow mixed with solid particles. Said device comprises at least one exchangeable pipe (1) for guiding the gas flow to a sample holder (2) containing the surface to be tested. In order to produce the gas flow, a ventilator is provided at the entrance to the pipe or a suction device (3) is provided at the exit of the pipe, and a dosing device (7) is provided at the entrance to the pipe or downstream along the pipe for dosing the solid particles in the gas flow. The pipe is elbowed in the region of the exit of the pipe, the elbowed pipe part comprising an opening (6) at the elbow, at which the sample holder (2) is detachably connected to the pipe (1), or instead of the opening (6), a sample holder (2) is provided inside the elbowed pipe part at the elbow. The opening containing the sample holder or the sample holder located inside the pipe is positioned in such a way that the gas flow is oriented towards the sample holder.

Description

Device for testing the scratch resistance of surfaces

The invention relates to a device for testing the scratch resistance of surfaces. The scratch resistance is tested by means of a gas stream mixed with solid particles, which flows over the surface to be tested. The north direction is used in particular for the practical simulation of scratching processes on automobiles while driving through dirt particles, flying sand or the like. in the headwind.

Different, partially standardized, ner driving tests for the scratch resistance of

Surfaces are known from the prior art. It is common to all these ner drives that the surface of test specimens is scratched by solid bodies of high hardness either with several contact points, for example through loose or bound particles, or with only one contact point, for example a diamond tip, by a touching relative movement. In all described ner drives, an analysis of the optical and / or topographical properties of the surface is generally carried out after scratching the surfaces. This is done e.g. by measuring the optical turbidity, the gloss or by examining it in a light, scanning electron or atomic force microscope.

The sand trickle method (DLΝ 52 348) is one of the standardized ner methods for testing scratch resistance. In the sand trickle method, the surface of a test specimen is scratched by a well-defined standard sand that falls through a downpipe from a height of 1650 mm. The amount of sand is set at 3 kg. The speed of impact of the sand results directly from the drop height

(neglecting air permeability) at 5.69 m / s. Particularly with a view to simulating the abrasive load on the surfaces of vehicle parts in the wind due to flying sand, dirt particles or the like. however, the speed of impact of the sand sprinkling process is too slow. The impact velocity of particles in the airstream is usually between about 30 km / h and 200 km / h, ie between 8.33 ms and 55.56 m / s. Another standardized test method is the friction wheel method, also called the Taber Abraser test (DIN 52 347). In the Taber Abraser test, the surfaces of the test specimens lying on the turntable of the wear tester are subjected to sliding wear by two friction wheels rotating in the opposite direction. The friction wheels from Teledyne Taber (USA), type CS 10 F, consist of a defined fine-grained abrasive that is embedded in rubber. To simulate the abrasive load on the surfaces of vehicle parts in the wind due to flying sand, dirt particles or the like. The Taber Abraser test has the disadvantage that the contact pressure of the wearing medium on the test specimen is optional

2.7 N or 5.4 N, is too large compared to the range relevant for automotive applications. Model estimates of the pressure force of particles in the airstream result in values of around 0.5 N. This pressure force also only occurs over a period of less than 1 μs.

In E.W.J. Mardles, J Oil Color Chem. Assocn. (1928), 11, pages 230-259 and in P.H. Shipway and I.M. Hutchings, Surface and Coatings Technology (1995), 71 (1), pages 1-8 describe methods in which abrasive particles are blasted onto a sample surface by an air stream. With these methods, comparatively high relative speeds occur between the wear medium and

Sample surface of up to 77 m / s. A disadvantage of these methods, however, is that the angle of attack cannot be varied. In the processes described in the standards ASTM G 76 - 95 and ÖNORM M 8126, a particle stream is also directed onto a surface at high speed. However, all of these methods have in common that the outlet of the nozzle tube or the like, which the

Gas particle stream leads to the sample surface, is spaced from the specimen, which is kept free in space. This means that the gas particle stream flows freely between the outlet of the nozzle tube and the sample surface, which can lead to turbulence and turbulence in the area of the sample surface. A well-defined flow and thus a reproducible scratching of the

The sample surface is therefore not given. The object of the present invention was to provide a device for testing the scratch resistance of surfaces which does not have the disadvantages mentioned.

According to the invention, the object is achieved by the features of claim 1.

The invention relates to a device for testing the scratch resistance of surfaces of a test specimen by means of a gas stream mixed with solid particles, at least comprising a tube, which is exchangeable, for directing the gas flow onto a sample holder with the surface to be tested, whereby to generate the Gas flow, a blower is provided at the pipe inlet or a suction device at the pipe outlet and a metering device at the pipe inlet or downstream along the pipe for metering the solid particles into the gas stream, the pipe being angled in the area of the pipe outlet and the angled pipe part at the angle opening on which the sample holder is detachably connected to the tube, or a sample holder is provided on the angle instead of the opening inside the angled tube part, the opening being positioned with the sample holder or the sample holder in the interior of the tube such that the gas flow a is aimed at the sample holder.

The sample holder is used to attach the test surface to the side opening of the tube, which is located at the angle in the angled part of the tube, ie in the direction of flow behind the angle. The side opening is positioned so that the gas flow is directed at the sample holder with the surface to be tested. Alternatively, a sample holder can also be provided in the interior of the tube, which is also positioned such that the gas stream loaded with particles is directed onto the sample holder. In this alternative, no opening is provided on the angle. The sample holder can be, for example, a plate or a cuboid on which the surface to be tested is applied or with the aid of which the sample surface is pressed against the pipe opening. The sample holder is accordingly detachably connected to the tube. It can be fastened, for example, by means of a screw or clamp connection or by springs by means of pressure or tension. In this way, the sample holder can be reproducibly attached to the opening. If a suction device is used to generate the gas flow, the suction pressure can possibly be strong enough to press the test specimen against the opening, so that no additional fastening means is necessary.

The tube through which the gas stream containing solid particles is passed is interchangeable, i.e. it is detachable with the other components of the device, in particular the metering device, the sample holder and the suction device or the like used for gas flow generation. connected. This has the advantage that the tube can be exchanged for another tube with a different angle by simple handling. In this way the flow angle at which the sample surface is checked can be varied. The angle of the tube, and thus the angle of flow, is preferably 5 to 90 °.

The tube can have any cross sections. However, it preferably has a square cross section. The diameter of the tube is essentially constant over the entire length of the tube. In order to achieve a uniform flow profile, which is necessary for scratching the surface as homogeneously as possible, and thus for a high degree of reproducibility, the ratio of the diameter to the length of the pipe is decisive, the relevant length of the pipe being the distance between the dosing device and the opening or the sample holder with the test surface. Accordingly, the diameter of the tube and the length of the tube between the metering device and the opening are preferably in a ratio of 1: 5 to 1: 100, particularly preferably 1:20 to 1:30, to one another. In the case of a square cross section, the diameter of the tube is to be understood as the edge length of the tube. In particular, In particular, by using a square cross section, changes in cross section, and thus local changes in speed, in the area of the angle, ie in the area of the sample surface, can be avoided.

A particular advantage of the device according to the invention is that the sample holder is attached to the side opening in the region of the tube angle in such a way that it completely covers the opening. The tube is thus closed with the exception of the openings at the inlet and outlet of the tube and, if appropriate, an additional opening for metering the solid particles into the gas stream. The sample surface to be tested faces the inside of the tube and is therefore from the

Environment shielded. If the tube were not connected to the sample, but directed towards the sample at a distance, the gas flow between the tube outlet and the sample would flow freely. The flow profile of the gas stream would be distorted as it exits the tube. There would be turbulence in the area of the sample surface and thus inhomogeneous scratching of the sample surface.

The gas flow, for example an air flow, is generated by overpressure with the aid of a compressor, blower or the like or by negative pressure with the aid of a vacuum pump or a suction device or the like. Solids particles can be added to the gas flow in a regulated or unregulated manner, but preferably distributed over a certain period of time. This can be done, for example, using a gravimetrically controlled metering device. Alternatively, a funnel based on the hourglass principle can also be used as a metering device. A control valve is attached to the pipe to regulate the flow rate. The flow rate of the gas stream mixed with solid particles is preferably adjustable in the range from 1 to 100 m / s, particularly preferably from 5 to 50 m / s. With a suitable choice of the suction device or the blower for generating the gas flow, higher flow velocities are also possible. The device is suitable, for example, for testing surfaces made of glass, metal, ceramic or plastic, for example paints. The materials mentioned can also serve as a substrate which is provided with a coating to be tested made of glass, metal, ceramic or plastic, for example lacquers.

For example, granular solids can be used as particles, for example made of sand, metal or metal oxide. The particle size is preferably from 10 to 2000 μm. The density of the solid particles is preferably from 500 to 22000 kg / m ³ , particularly preferably from 1000 to 10000 kg / m ³ .

Amounts of particles of 1 to 10 g are usually metered into the gas stream. Depending on the type of particles and the surface to be tested, however, any desired smaller or larger amounts can also be used. The loading of the gas stream with solid particles is preferably from 0.1 to 500 g / m ³ .

The invention is explained in more detail below with reference to the attached FIG. 1.

FIG. 1 shows a diagram of a preferred embodiment of the device according to the invention.

An air flow flows through the square tube 1 with an inner edge length of 36 mm and is generated with the aid of a suction device 3. At the upper end of the vertically arranged tube 1, a where defined mass of sand or the like is via a funnel 7. fed. The funnel 7 has a height of 50 mm and an outlet opening of 2 mm at an opening angle of 40 °. The funnel is positioned by means of spacers above the inlet opening of the tube 1, so that air can flow laterally into the tube opening. By varying the height of the spacers, the width of the gap through which air enters laterally, and thus the speed, can be varied. As a result, the particles can be mixed into the air flow if necessary be optimized so that the most homogeneous possible distribution is achieved by turbulence of the air flow in the pipe entry area.

In the embodiment shown in FIG. 1, the vertically arranged tube 1 has an angle of 45 ° at the lower end, at which an opening 6 is located.

The opening 6 with a size of 57 x 34 mm is in particular below the angle, i.e. in the direction of flow behind the angle, on the outer side of the square tube 1. At the opening 6, a sample holder 2 is attached to the tube. The opening 6 with the sample holder 2 is thus positioned at the angle that the gas flow is directed at the sample. The sample holder 2 is in particular detachably connected to the tube 1. In the illustrated embodiment, the sample holder 2 is a plate, e.g. is pressed against the opening of the tube with the help of spiral springs. In this arrangement, the surface to be tested on the sample holder 2 points into the interior of the tube 1 and thus forms an inner surface of the tube at the opening 6. The air flow mixed with particles therefore flows onto the sample surface at a defined angle of 45 °. The tube 1 is detachable with the exhaust hose 8 or the like. connected. In particular, the pipe 1 is connected to the exhaust hose 8 with the aid of screw or flange connections. This makes it possible to easily replace the tube 1 by a tube with a different angle. The length of the vertically arranged pipe part, and thus the

The length of the tube between metering device 7 and opening 6 or sample holder 2 is 1 m.

With the help of a control valve 5, which is attached to the exhaust hose 8 in the embodiment shown, the volume flow, and thus the flow velocity, is regulated. In the suction device 3, the particles with which the air stream has been mixed are separated by a cyclone and by filters. The flow rate of the exhaust air cleaned in this way is detected by a thermal flow sensor 4. example

Using the device shown in FIG. 1, specimens with a surface made of Makrolon® polycarbonate from Bayer were tested for their scratch resistance. The surface was not additionally scratch-resistant coated. The specimens had a size of 40 x 60 mm with a thickness of 2 mm. The opening of the tube is 34 x 57 mm, which corresponds to the area of the test surface. Quartz sand with a grain size distribution of 125 to 250 μm was used as the solid particle. 3.5 g of quartz sand with a density of 1500 kg / m ³ was metered into the air stream with the aid of a funnel with a height of 50 mm and an outlet opening of 2 mm at an opening angle of 40 °. The time span in which the quartz sand trickled into the pipe via the funnel was - depending on the selected flow velocity of the air flow - a maximum of 15 s. This corresponds to the duration of the abrasive load on the test surface.

The length of the tube between the tube inlet opening with the metering device and the sample surface was 1 m. The tube inner edge length was 36 mm. The angle of attack was 45 °. The air flow was generated with the aid of a suction device.

In each case 3 sample surfaces were tested with flow velocities of 10, 20, 30 and 40 m / s in order to test the reproducibility of the tests. The loading of the air stream with particles was at 10 m / s 18 g / m ^3, at 20 ms 9 g / m ³ at 30 m / s 6 g / m ³ and at 40 ms 4.5 g / m ^3.

After scratching the surface, the optical turbidity was checked using a

Turbidity meter from HunterLab, model D25D2P, measured according to ASTM Dl 003-95. A cloudy, transparent sample is illuminated with a parallelized light beam and the proportion of the light diffusely scattered by the sample is determined in comparison to the total intensity. In these measurements, a circular section of the sample surface was taken with a light beam

25 mm diameter examined. The measurement results are summarized in Table 1. The optical haze in% corresponds to the proportion of light diffusely scattered by the sample compared to the total intensity of the light. The dependence of the optical turbidity on the flow velocity can be clearly seen, the measured values being very reproducible. The relative standard deviation is less than 2.3%.

Table 1: Optical turbidity depending on the flow velocity.

In order to test the homogeneity of the scratching, additional measurements of the optical turbidity were carried out on a sample which was scratched with an inflow velocity of 40 m / s and an inflow angle of 45 °, the diameter of the light beam using an aperture to 10 mm was reduced. This makes it possible to examine smaller sections of the sample surface, with lower turbidity values due to the measurement technology. Optical turbidity was measured at 12 measuring points in the form of a 3x4 matrix on the sample surface of 34 x 57 mm. The measured values are summarized in Table 2. The measurements show the high homogeneity of the scratching on the tested surface. The relative standard deviation was 1.83%.

Table 2: Optical turbidity at various measuring points on the test surface

Claims

claims

1. Device for testing the scratch resistance of surfaces of a test specimen by means of a gas stream mixed with solid particles, at least comprising a tube (1) which is exchangeable, for directing the gas flow onto a sample holder (2) with the surface to be tested, whereby to generate the Gas flow a blower is provided at the pipe entrance or a suction device (3) at the pipe exit and a metering device (7) at the pipe entrance or downstream along the pipe (1) for metering the solid particles into the gas flow, characterized in that the pipe (1) in the area of the tube outlet is angled and the angled tube part has at the angle an opening (6) at which the sample holder (2) is detachably connected to the tube (1), or instead of the opening (6) inside the angled tube part at the angle a sample holder is provided, the opening (6) with the sample holder (2) or the sample holder in the interior of the tube being pos It is ionized that the gas flow is directed towards the sample holder.

2. Device according to claim 1, characterized in that the angle of the tube (1) in the region of the opening (6) is 5 to 90 °.

3. Device according to one of claims 1 or 2, characterized in that the diameter of the tube (1) and the length of the tube (1) between the metering device (7) and the opening (6) in a ratio of 1: 5 to 1: 100, preferably 1:20 to 1:30, to each other.

4. Device according to one of claims 1-3, characterized in that the tube (1) has a square cross section.

5. Device according to one of claims 1-4, characterized in that the tube (1) has a control valve (5) for regulating the flow rate.

6. Device according to one of claims 1-5, characterized in that the flow velocity of the gas stream mixed with solid particles is adjustable in the range from 1 to 100 m / s, preferably from 5 to 50 m / s.

7. Device according to one of claims 1-6, characterized in that the particle size is from 10 to 2000 microns.

8. Device according to one of claims 1-7, characterized in that the density of the solid particles from 500 to 22000 kg / m ³ , preferably from 1000 to 10000 kg / m ³ .

9. Device according to one of claims 1-8, characterized in that the loading of the gas stream with solid particles is from 0.1 to 500 g / m ³ .