NL2004165C2

NL2004165C2 - System and method for performing tribological tests.

Info

Publication number: NL2004165C2
Application number: NL2004165A
Authority: NL
Inventors: Benjamin Mckay; Erik-Jan Ras; Martin Christiaan Havranek
Original assignee: Avantium Holding B V
Priority date: 2010-01-28
Filing date: 2010-01-28
Publication date: 2011-07-29

Description

P30123NL00/NBL

System and method for performing tribological tests

The invention pertains to a system and a method for performing a plurality of tribological tests in parallel. Each of said tribological tests involves an interaction between a test 5 specimen and a counter body, possibly in the presence of a lubricant. A combination of a test specimen and a counter body that interact with each other in a tribological test, and a lubricant if one is present, is referred to as a “tribological unit”.

Tribological tests are for example used to determine the wear resistance of a material, coating and/or surface layer, and/or to determine the effectiveness of lubricants and/or 10 additives or other components of lubricants. The lubricants to be tested can be in liquid form, a gel-like form, a solid form or any other suitable form. They can be added to the surface of the test specimen and/or the counter body, or they can be embedded in the material of the test specimen and/or the counter body.

Tribological tests can also be used to determine friction properties of combinations of 15 materials, and/or the reduction of friction by a lubricant or lubricant additive. Tribological tests are also known to be used to study surface fatigue properties, for example in bearing materials.

Tribological tests as such are known. A commonly used test is for example the “four-ball test”. In this test, three balls are arranged in a triangle, and the fourth ball is put on top. The 20 fourth ball is then made to spin, while a mechanical force pushes it against the three other balls. The three other balls can be stationary, or they can have the freedom to spin as well. After a predetermined period of time, the wear of all four balls is analysed.

Other known tribological tests involve rotating a pen in a V-shaped groove, moving a pin (with a sharp or rounded tip) over a flat surface or moving, in particular oscillating, a ball 25 (either rotating or non-rotating) over a flat or curved surface.

Attempts have been made to provide a system that is suitable for carrying out a plurality of tests in parallel. For example, US7150182 discloses high throughput screening methods for lubricating oil compositions. In this known method, a plurality of four ball tests or pen-groove tests is carried out in parallel. To this end, the test set up comprises a plurality of 30 suitable test assemblies, each test assembly being adapted to carry out a single four ball test or pen-groove test. Each test assembly comprises its own load application unit for providing the required mechanical load for carrying out the test.

The known test set ups are rather complicated.

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The object of the invention is to provide an improved system for performing a plurality of tribological tests in parallel.

This object is achieved with the systems according to the claims 1 and 15, and with the method according to claim 22.

5

In a system and method according to the invention, multiple tribological units are subjected to tribological tests at the same time. A test specimen can be for example a flat panel, a curved panel, a ball, a sharp cone, a rounded cone, a cylinder. The counter body can also be selected from a large variety of sizes and shapes, for example a flat panel, a curved 10 panel, a ball, a sharp cone, a rounded cone, a cylinder. It is possible that after the test, the test specimen shows wear, the counter body shows wear or that both show wear. Materials that can be used for test specimens and/or counter bodies include metallic materials, non-metallic materials, coated materials, materials having undergone a surface treatment (e.g. surface hardening), ceramic materials, diamond, sapphire, ruby, steel, aluminium, polymers. 15 In the system according to the invention, three holders are provided. Each of the three holders is adapted to hold a test specimen or a counter body. The holders can be dedicated to holding a specific type of test specimen, a specific type of counter body or they can be adapted to hold different types of test specimens and/or counter bodies.

The holders are arranged on a load plate or on a counter plate of the system according 20 to the invention. The load plate and the counter plate are arranged relative to each other in such a way that the tribological units that are to be tested can be accommodated between them. It is possible that all three holders are on the load plate, that all three holders are on the counter plate, or that two of them are arranged on one plate and the other holder on the other plate.

25 The load plate and the counter plate can be arranged horizontally, vertically or be oriented at an angle. The load plate can be arranged above the tribological units, below the tribological units or next to the tribological units. Likewise, the counter plate can be arranged above the tribological units, below the tribological units or next to the tribological units. The load plate and the counter plate do not need to have the form of a flat plate. They can for 30 example alternatively have the form of a tripod or a box. It is not necessary that the load plate and the counter plate have the same shape.

In a possible embodiment, the system according to the invention comprises three pairs of holders, each pair of holders retaining a tribological unit. The individual holders of a pair are arranged at two different plates: one holder is arranged at a load plate and the other 35 holder of the same pair is arranged at a counter plate. The load plate has three holders arranged on it, and the counter plate also has three holders arranged on it. The holders are aligned such that the test specimen and the counter body of a tribological unit assume the -3- desired position relative to one another. This alignment can be achieved by aligning the holders as such, and/or by aligning the load plate and the counter plate relative to each other.

The holders can be dedicated to hold either the test specimen or the counter body, but it is also possible to use universal holders in which a test specimen can be arranged as well 5 as a counter body. It is not necessary that all test specimens are arranged on the load plate and all counter bodies are arranged on the counter plate, or the other way around. It is very well possible that for example two test specimens and one counter body are arranged in the holders of the load plate, and two counter bodies and one test specimen in the holders of the counter plate, or the other way around.

10 The three holders on each plate are preferably arranged relative to each other in such a way that their positions form the corners of an equilateral triangle. In other words, a circle can be drawn through their positions (so they are not arranged on a straight line), and they are evenly distributed over said circle. So, seen that way, the positions of the holders on each plate are 120° apart from each other. This relative position helps to obtain an even distribution 15 over the mechanical load over the three tribological units that are tested in parallel.

The holders can be of any suitable type, shape and size. They can comprise a clamp to hold the test specimen or counter body in a fixed position, but it is also possible that the holders are mere recesses in which a test specimen can be arranged. In that case, the test specimen or counter body can be retained in the holder for example by gravity, by magnetism 20 or by mechanical means.

Further, in the system according to the invention, a mechanical load is applied to the tribological units. This load can be induced by the mass of any elements of the test system that are arranged above the tribological units, for example the load plate.

It is also possible that the system comprises a load application unit, that is adapted to 25 apply a mechanical load to the tribological units during the testing. The load application unit applies a mechanical load instead of or in addition to any mechanical load that is induced by mass of any elements of the test system that are arranged above the tribological units, if such elements are present. The mechanical load applied by the load application unit will often involve a force being applied that is directed towards the counter plate, so the test specimen 30 and the counter body are pressed against each other. The load application unit can for example use a a spring, a hydraulic cylinder, a pneumatic cylinder, a latch and/or a weight to generate the mechanical load. The load that is applied by the load application unit is transferred to the three tribological units via the load plate.

The mechanical load causes a normal force (i.e. a force perpendicular to the contact 35 surface of the test specimen and the counter body) at the contact surface of the test specimen and the counter body. Due to this normal force, friction occurs between the test specimen and the counter body. This friction could lead to wear of the test specimen and/or -4- the contact body. A lubricant that is present in the contact area will reduce this friction to a larger or lesser extent, depending on the effectiveness of the applied lubricant.

The system further comprises a driver. The driver makes that the test specimen and the counter body move relative to each other during the test. Tribological tests usually involve 5 relative motion between the test specimen and its associated counter body. The driver provides this movement, for example by moving the load plate and/or the counter plate, and/or by moving the holders relative to the plate they are mounted on. The movement can be a rotation, a translation or a combination of rotation and translation. The movement can be continuous or intermittent. In particular for translatory movements, the movement can involve 10 an oscillation. It is however also possible that rotational movement involves an oscillation.

It is possible for the holders to be moveable relative to the load plate or the counter plate to which they are connected.

It is possible for the holders to be fixed onto either the load plate or the counter plate. In that case, the driver actuate the load plate, the counter plate or both. In this case, the driver 15 could for example comprise an x-y-table or an x-y-z—table or a shaker table.

It is possible that the driver moves the load plate and/or the counter plate, and also moves the holders relative to the plate they are mounted onto.

In the systems according to the invention, the load plate and the counter plate are tiltable relative to each other. This is particularly advantageous because it allows that a single 20 load application unit is used to provide the required mechanical load to all three tribological units, or that the mass of a single element (for example the load plate) is used to provide a mechanical load for all three tribological units, as will be explained below. This reduces the complexity of the test system as a whole.

Generally, in high throughput testing, the three tribological units will be subjected to 25 different test conditions, or different materials and/or lubricants will be applied in the tribological units. Therefore, it can be expected that different amounts of wear will occur in the three tribological untis that are tested at the same time.

It is desirable tha, the test conditions during the entire testing are known. This applies in particular for the amount of mechanical load that is applied to each of the tribological units, as 30 this mechanical load has a relatively strong impact on the amount of wear that occurs during testing. For this reason, known test set ups for parallel tribological tests generally have a dedicated load application unit for each tribological units.

In the system according to the invention, this is no longer necessary. By allowing a relative tilting between the load plate and the counter plate during the test, the tribological unit 35 remains in contact with both the load plate and the counter plate, despite the change of height of the tribological unit that can occur due to wear that may occur.

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The relative tilting of the load plate and the counter plate prevents that if one tribological unit wears more than the other two, the mechanical load on those other two will increase and the mechanical load on the fast wearing tribological unit will reduce. This would result in a faster wearing of the two (initially) slow wearing tribological units and a slower wearing of the 5 (initially) fast wearing tribological unit. In the system according to the invention however, because of the relative tilting of the load plate and the counter plate, all test specimens will remain in fully loaded contact with their respective counter bodies during the entire test, so that the different rates of wear of the parallelly tested tribological units do not influence each other.

10 This makes it possible that the load application unit applies a mechanical load to all tested tribological units via the load plate without the wear rates of the simultaneously tested tribological units influencing each other, and/or that the mass of a single element arranged above the tribological units provides the mechanical load for all tribological units, again without the wear rates of the simultaneously tested tribological units influencing each other.

15

In embodiments in which a load application unit is present, it is possible that a joint is provided between the load plate and the load application unit, which joint allows a relative angular displacement of the load plate and the load application unit. This allows the load application unit to remain stationary when the load plate tilts due to uneven wear in the 20 parallelly tested tribological units. The joint can for example be a ball joint.

It is possible that the load plate and/or the counter plate are provided with a temperature control unit for controlling the temperature of one or more tribological units during the testing. Such temperature control unit can comprise a heater and/or a cooler. The load 25 plate and/ or the counter plate can be provided with channels through which a warm or cold fluid can be made to flow. Alternatively or in addition, electrical heaters and/or Peltier elements can be used. They can be arranged adjacent to the load plate and/or counter plate, or accommodated in the load plate and/or counter plate. The temperature control unit further comprises one or more sensors to measure the temperature, and a data processor, that 30 receives the data from the sensors, and uses these data to control the settings of the heater and/or cooler.

The invention also provides a system that can be used to test more than three tribological units, in particular to test a multiple of three tribological units. Preferably, the 35 number of tribological units tested in parallel is a power of three (3, 9, 27, etc.).

For example, in an embodiment of such a system nine tribological units are tested.

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In such an embodiment, three sample holding sets are present. Each sample holding set comprises a load plate with holders and a counter plate, and at least three holders, like the load plate and the counter plate of the previously described wear tester for three samples. Possibly, the load plate of each sample holding set has three holders, and the counter plate 5 of each sample holding set comprises three holders as well.

The load plate and the counter plate of each sample holding set are tiltable relative to each other.

The sample holding sets are arranged adjacent to each other. It is possible that each sample holding set has its own load plate and counter plate, but it is also possible that the 10 counter plates or the load plates of the sample holding sets are integrated into a single counter plate or single load plate. The single counter plate or the single load plate has nine holders, and is referred to as “assembly load plate” or “ assembly counter plate”, respectively.

In the system for performing nine tribological tests in parallel, the sample holding sets are preferably arranged on a circle, so not on a straight line. More preferably, each sample 15 holding set is arranged at an angle of 120° from the adjacent sample holding sets, so that they form the corners of an equilateral triangle.

It is possible that each sample holding set is provided with its own load application unit.

It is however also possible that a single load application unit is used for all three sample holding sets. This makes the system cheaper and easier to control.

20 If only a single load application unit is used, it is particularly advantageous if the sample holding sets are arranged on a circle, at an angle of 120° from each other. If the load application unit is then arranged such that it applies the mechanical force at the centre of this circle, the load is evenly distributed over the sample holding sets.

When a single load application unit is used, preferably a load distribution plate is 25 provided. This load distribution plate transfers the force that is applied by the load application unit to the sample holding sets.

In a possible embodiment, the load plates of the sample holding sets are tiltable relative to the load distribution plate. This allows an even load distribution to be maintained even when different wear rates occur in the different tribological units that are tested 30 simultaneously. In an other possible embodiment, the counter plate is tiltable relative to the load distribution plate.

Instead of or in addition to a mechanical load that is applied to the tribological units via a load application unit, the mass of elements of the test system that are arranged above the tribological units can be used to provide a mechanical load to the tribological units.

The invention will be explained in more detail under referral to the drawing, in which non-limiting embodiments of the invention are shown. The drawing shows in: 35 -7-

Fig. 1: several examples of tribological units for typical tribological tests,

Fig. 2: a system according to the prior art,

Fig. 3: the mutual position of the holders,

Fig. 4: an exploded view of a first embodiment of a system according to the invention, 5 Fig. 5: an exploded view of a second embodiment of a system according to the invention,

Fig. 6: an exploded view of a third embodiment according to the invention,

Fig. 7: a fourth embodiment of a system according to the invention.

10 Fig. 1A-F show several examples of tribological units for typical tribological tests. Each tribological unit comprises a test specimen 1 and a counter body 2.

In fig. 1 A, the test specimen 1 is a flat plate of a metallic or polymeric engineering material. A ball shaped counter body 2, for example made of ruby, is during the tribological test rolled back and forth over the test specimen 1. The rolling is caused by a relative 15 translating, oscillating movement of load plate 4 and counter plate 5. During the movement, a force F is applied, that pushes the counter body 2 against the test specimen 1. This results in a normal force at the contact surface between test specimen and counter body, which normal force induces friction. A lubricant, in liquid, semi-liquid or solid form, can be applied to the contact surface between the test specimen 1 and the counter body 2 before or during the test. 20 It is also possible that a lubricant is present in matrix material of the test specimen and/or counter body.

After the test, the surface of the test specimen 1, and preferably also the surface of the counter body 2, is examined for wear and possibly other types of damage. This can be done in order to establish the wear resistance of the combination of materials of the test specimen 25 1 and the counter body 2, but for example also in order to establish the effectiveness of a certain lubricant.

In the example of fig. 1 A, the test specimen 1 is arranged in a holder 6 of a counter plate 5. The holder 6 in this example is a recess, in which the test specimen 1 is accommodated during the test. When the test specimen 1 is arranged in the recess of the 30 counter plate 5, the counter body 2 is put on top of the test specimen 1. If desired, a lubricant is added or present in the counter body and/or the test specimen. Then, load plate 4 is arranged on top of the counter body 2. In this example, the load plate has no holders to engage or position the counter body 2. The skilled person will however understand that as an alternative, it is possible that the load plate is also provided with holders, in this example to 35 retain the counter bodies 2.

The load plate 4 has a certain mass, that causes a force F onto the counter body 2 and the test specimen 1, resulting in a normal force (i.e. perpendicular to the contact surface of -8- test specimen and counter body) - and therewith in friction - between the test specimen 1 and the counter body 2.

In addition or as an alternative, a separate load application unit can be provided. This load application unit supplies a part of force F as indicated in fig. 1 A, or all of this force. In the 5 latter case, the weight of the load plate 4 is borne by further components of the system, instead of by the tribological unit.

In a possible embodiment of a system according to the invention that is suitable to run tests with the set up shown in fig. 1 A, the counter plate 5 comprises three recesses to serve as holders 6, and the load plate rests on top of three counter bodies 2.

10 The skilled person will understand that different materials can be selected for the counter body 2 and the test specimen 1 than the ones mentioned above. It is also possible that the ball shaped object is the test specimen and the flat plate is the counter body, depending on the choice of materials for both.

15 Fig. 1B shows a set up for a tribological test which is generally used in the same way as the set up of fig. 1A.

In the example of fig. 1B, the load plate 4 is provided with holders 3. The holders 3 in the load plate 4 are in the example of fig. 1B formed by recesses in which a ball shaped object, which is in this example the test specimen 1, can be accommodated.

20 In the example of fig. 1B, the holders 6 of the counter plate 5 are formed by clips, that hold a flat object, which is in this example the counter body 2.

In this example, an oscillating relative movement of the load plate and the counter plate induces a rolling of the ball shaped test specimen 1 relative to the flat counter body 2. The movement can be a translation, a rotation or a combination of a translation and a rotation.

25 The wear or other damage resulting from this on the test specimen and possibly also of the counter body is studied and evaluated.

In a possible embodiment of a system according to the invention that is suitable to run tests with the set up shown in fig. 1B, the counter plate 5 comprises three sets of clips to serve as holders 6, and the load plate 4 has three recesses to function as holders 3.

30 The skilled person will understand that different materials can be selected for the counter body 2 and the test specimen 1 than the ones mentioned in relation to fig. 1 A. It is also possible that the ball shaped object is the counter body and the flat plate is the test specimen, depending on the choice of materials for both.

35 Fig. 1 C shows a test set up for a tribological test which is generally used in the same way as the set up of fig. 1A.

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In the example of fig. 1C, the ball shaped object is the counter body 2, and the flat object is the test specimen 1. The test specimen 1 is arranged in a recess in the counter plate 5, that serves as a holder 6. The holders 3 of the load plate 4 are formed by grippers, that have a stationary jaw 3a and a moveable jaw 3b. The jaws 3a, 3b fix the ball that forms the 5 counter body 2 between them so that it does not roll over the test specimen 1 when the load plate and the counter plate oscillate relative to each other.

The skilled person will understand that the ball shaped object can also be fixed relative to the load plate 4 in different ways, for example by means of one or more rings.

In a possible embodiment of a system according to the invention that is suitable to run 10 tests with the set up shown in fig. 1B, the counter plate 5 comprises three recesses to serve as holders 6, and the load plate 4 has three grippers as holders 3.

The skilled person will understand that different materials can be selected for the counter body 2 and the test specimen 1 than the ones mentioned in relation to fig. 1 A. It is also possible that the ball shaped object is the test specimen and the flat plate is the counter 15 body, depending on the choice of materials for both.

Fig. 1 D again shows a test set up for a tribological test which is generally used in the same way as the set up of fig. 1A.

In the example of fig. 1D, the counter body 2 is a rounded pin, that is connected to the 20 load plate 4 by means of a bolt. Instead of a pin with a rounded tip, a pin with a sharp tip or a pin with a conical tip can be used as well.

In the example of fig. 1D, the flat test specimen 1 is held between two jaws 6a, 6b. It is possible that one jaw is stationary and the other one moveable, or both jaws can be moveable.

25 In a possible embodiment of a system according to the invention that is suitable to run tests with the set up shown in fig. 1D, the counter plate 5 comprises three sets of jaws 6a,6b to serve as holders 6, and the load plate 4 has three holes through which a bolt can be fitted.

The skilled person will understand that different materials can be selected for the counter body 2 and the test specimen 1 than the ones mentioned in relation to fig. 1 A. It is 30 also possible that the pin is the test specimen and the flat plate is the counter body, depending on the choice of materials for both.

Fig. 1E again shows a test set up for a tribological test which is generally used in the same way as the set up of fig. 1A.

35 In the example of fig. 1E, the test specimen 1 is arranged on the load plate 4. A magnet 7 prevents it from falling off the load plate 4, while stops 8a,8b prevent sideways movement of the test specimen 1.

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Magnet 9 holds the counter body 2 in place. Stops 10a,10b prevent sideways movement of the counter body 2. Magnet 9 is arranged in the counter plate 5.

In a possible embodiment of a system according to the invention that is suitable to run tests with the set up shown in fig. 1E, the counter plate 5 comprises three sets of magnets 9 5 and stops 10a,10b to serve as holders 6, and the load plate 4 has three sets of magnets 7 and stops 8a,8b to serve as holders 3.

The skilled person will understand that different materials can be selected for the counter body 2 and the test specimen 1 than the ones mentioned in relation to fig. 1 A. It is also possible that the pin is the test specimen and the flat plate is the counter body, 10 depending on the choice of materials for both.

Fig. 1F shows a four ball test as is known in the art, wherein the three lower balls 12 are arranged in the counter plate 5 and the upper ball 11 is connected to the load plate 4.

15 The skilled person will understand that other shapes and other combinations of shapes are possible than the ones shown in fig. 1. For example, both the test specimen and the counter body can be flat plates, or both can have a curved surface in the area of contact.

Also, “pin and V-groove”-like combinations can be used. The skilled person will also understand that features of the embodiments shown in fig. 1A-1F can be combined. For 20 example, the gripper of fig. 1c can be combined with the magnet and the stoppers of fig. 1E.

Tribological units of the types shown in fig. 1 are known as such from the art. In order to speed up testing, it is desirable to perform tribological tests on multiple tribological units at the same time (i.e. “in parallel”). In the known systems for performing tribological tests in parallel, 25 a separate load application unit, for example in the form of a spring or a hydraulic or pneumatic cylinder, is assigned to each tribological unit.

An example of a known system is shown in fig. 2A.Test specimens 1 are arranged in recesses 14 of plate 15. On top of each test specimen 1, a ball shaped counter body 2 is arranged. Each of the tribological units is provided with a lubricant 17. A plurality of cylinders 30 16 is provided.

During the test, each cylinder 16 pushes a ball shaped counter body 2 against a test specimen 1. The plate 15 with the recesses 14 and the test specimens is oscillated in order to obtain a relative movement between the test specimens and the counter bodies. The force F provided by the cylinders 16 results in friction between the test specimens 1 and their 35 associated counter bodies 2, which results in wear of the test specimen 1 and/or the counter body 2.

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In this example, three different types of lubricant 17a, 17b, 17c are applied. The test specimens 1 are of the same material in all three tribological units. Also, the counter bodies 2 are the same in all three tribological units.

Fig. 2A shows the situation at the beginning of the test. Fig. 2B shows the situation in 5 the known system at the end of the tests. In tribological unit on the left, hardly any wear has occurred. Apparently, the lubricant 17a applied in this tribological unit was effective under the circumstances of the test. In the tribological unit in the centre, the lubricant 17b was not so effective: the test specimen 1 lost quite some material due to wear. In the tribological unit on the right, a substance in the lubricant 17c was aggressive to the material of the counter body 10 2, causing the counter body 2 to loose material instead of the test specimen 1. Fig. 2B

illustrates that uneven amounts of wear and/or other types of material loss and uneven wear rates can occur in the group of tribological units that are tested simultaneously.

The known system of fig. 2 is quite complex, due to the plurality of cylinders that all 15 have to be controlled individually. This complexity can be reduced by replacing the cylinders by a single cylinder (or other type of load application unit) and a load plate, that distributes the mechanical load applied by the cylinder over the tribological units that are tested in parallel.

However, if no further measures would be taken, the results of the tribological tests would be rendered unreliable. This is caused by the uneven wear that can occur in a group of 20 tribological units that is tested simultaneously.

As can be seen in fig. 2B, the height of the tribological unit changes due to wear that occurs in the test specimen 1, the counter body 2 or both. However, in order to transfer the mechanical load from the load application unit to an individual tribological unit, the load plate has to remain in contact (either directly or via intermediate elements) with said tribological 25 unit.

Furthermore, it is advantageous if the mechanical load on each tribological unit is known throughout the duration of the test. Preferably, the mechanical load on each tribological unit is constant throughout the duration of the test.

With embodiments of the current invention it is possible to achieve this.

30 In the system according to the invention, the tribological units are arranged between a load plate and a counter plate. A combination of a load plate and a counter plate is shared by three tribological units. In an advantageous embodiment, the three tribological units that share a combination of a counter plate and a load plate are not arranged on a straight line, so their top ends together always define a plane, as well as their bottom ends do. By allowing 35 the load plate and the counter plate to tilt relative to each other, the three tribological units remain in contact with both the counter plate and the load plate, irrespective of their change in height due to the wear they experience.

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In order to obtain an even distribution of the load of the load application unit over the tribological units, the three tribological units that share a counter plate and a load plate are arranged on a circle, at mutual angles of 120°. The relative positions of such group of three tribological units could also be described as the forming the corners of an equilateral triangle.

5 This is illustrated in fig. 3.

Fig. 3 shows the tops 20 of three tribological units that share a combination of a counter plate and a load plate. These tops 20 form the corners of equilateral triangle 23, and they are arranged on circle 22. The centre of the circle 22 and the circumcentre of the triangle 23 coincide at 21.

10 A mechanical load that is applied at the centre point 21 will be evenly distributed over the three tribological units.

Instead or in addition, it is possible that the mechanical load is applied at one or more different locations on the load plate. In that case, it is advantageous if the load is applied such that still an equal distribution over the tribological units is achieved.

15

Fig. 4 shows an exploded view of a first embodiment of a system according to the invention.

The system of fig. 4 comprises a counter plate 30, that is provided with three recesses 31. The recesses 31 positioned in such a way that they are on the vertices of an equilateral 20 triangle. The recesses 31 are adapted to retain a test specimen 1. On top of each test specimen, a ball shaped counter body 2 is arranged. The counter bodies 2 protrude above the top surface of the counter plate 30. The recesses 31 can retain a lubricant if desired.

In the embodiment of fig. 4, the system is provided with a temperature control unit. The counter plate 30 is provided with a circulation system 32 through which warm or cold fluids 25 can flow. The fluids heat or cool the counter plate 30, and therewith influence the temperature under which the tribological tests are carried out. The skilled person will understand that also other types of heaters and/or coolers can be used, such as electrical heaters or Peltier elements. Also combinations of different types of heaters and/or coolers are possible.

The temperature control unit further comprises one or more sensors to measure the 30 temperature, and a data processor, that receives the data from the sensors, and uses these data to control the settings of the heater and/or cooler.

The counter plate 30 is fixed to a driver in the form of a shaker table 35. This shaker table moves the counter plate 30 relative to the load plate during the testing in one or more directions. The movement can involve an oscillation, a translation, a rotation or a combination 35 thereof. The load plate can be stationary, or it can move as well. If the load plate moves as well, the movement is such that there is relative movement between the load plate and the counter plate.

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Load plate 40 is put on top of the counter bodies 2. In this embodiment, the load plate 40 has a flat bottom surface, without any specific holders.

On top of the load plate 40, a joint 50 is arranged that allows the load plate 40 to tilt relative to the counter plate 30 when an uneven amount of wear or an uneven rate of wear 5 occurs between the tribological units that are tested. In this example, the joint comprises a lower ring 51 that rests on top of the load plate 40. The lower ring 51 has a conical inner surface 52. The joint 50 further comprises a joint body 53, that has a conical outer surface 54 that matches the conical inner surface 52 of the lower ring 51. The joint body 53 can be arranged in the lower ring 51 such that the conical inner surface 52 of the lower ring and the 10 conical outer surface 54 of the joint body 53 adjoin each other. This construction allows relative tilting of the lower ring 51 relative to the joint body 53. The skilled person will understand that other types of joints that allows this movement, such as a ball joint, could be applied as an alternative for the type of joint described above.

In this embodiment, on top of the joint body 54, a weight 60 is arranged. The weight 60 15 adds to the mechanical load already exerted on the tribological units by the mass of the joint 50 and the load plate 40. The skilled person will understand that in variants of this embodiment, the weight 60 can be left out.

The embodiment of fig. 4 further comprises guides or supports that prevent the load plate 40, the joint 50 and the weight 60 from moving along with the counter plate 30. These 20 are not shown in fig. 4 for reasons of clarity.

Fig. 5 shows a partly exploded view of a second embodiment of a system according to the invention. In this embodiment, nine tribological units can be subjected to tribological tests simultaneously.

25 In this embodiment, the same components can be recognised as in the embodiment of fig. 4.

In the embodiment of fig. 5, three groups of tribological units are present, each group having three tribological units. The groups are indicated by the circles A, B and C. Like in the embodiment of fig. 4, the tribological units are accommodated in recesses 31 of a counter 30 plate 30. The three recesses 31 in which the tribological units of the same group are accommodated form the corners of an equilateral triangle. Preferably, the circumcentres of the three triangles also form the corners of an equilateral triangle.

Like in fig. 4, the counter plate 30 is fixed to a driver, in this case a shaker table 35.

In the embodiment of fig. 5, the system is provided with a temperature control unit. The 35 counter plate 30 in the embodiment of fig. 5 is provided with a combined heater/cooler 32. The heater/cooler 32 can be such that it heats or cools the entire counter plate 30, but - 14- alternatively, a separate heater and/or cooler can be provided for each three recesses 31 that together accommodate a single group of tribological units.

The temperature control unit further comprises one or more sensors to measure the temperature, and a data processor, that receives the data from the sensors, and uses these 5 data to control the settings of the heater and/or cooler.

Each group of three tribological units has its own load plate 40, its own joint 50 and its own weight 60. So, the system of fig. 5 comprises three load plates 40, three joints 50 and three weights 60. Not all of them are visible in fig. 5 because of the perspective view.

The system of fig. 5 further comprises a load distribution plate 70. The load distribution 10 plate 70 has three connection points 71 via each of which a weight 60, a joint 50 and a load plate 40 associated with the same group of three tribological units can be connected to the load distribution plate 70. Preferably, the three connection points 71 are the corners of an equilateral triangle.

An additional force F can be applied to the load distribution plate, for example by a 15 spring, an actuator or a pneumatic or hydraulic cylinder. Advantageously, such an additional force would be applied to the load distribution plate between the connection points 71. If the connection points are corners of an equilateral triangle, then preferably the additional load F is applied to the load distribution plate at the circumcentre 72 of said triangle. That way, the additional load F is distributed equally over the three groups of tribological units.

20 The embodiment of fig. 5 further comprises guides or supports that prevent the load plates 40, the joints 50 and the weights 60 from moving along with the counter plate 30.

These are not shown in fig. 5 for reasons of clarity.

In the embodiment of fig. 5, an assembly counter plate 30 is used, that comprises recesses 31 for accommodating all nine tribological units. Instead, three individual counter 25 plates can be used, each provided with recesses or other types of holders to retain a group of three tribological units.

The embodiment of fig. 5 allows tilting of the load plates 40 relative to the counter plate 30 and relative to the load distribution plate 70. This makes that the load plate can follow the changes in height of the tribological units (caused by wear or other types of material loss) 30 without loosing contact with them.

In a variant to the embodiment shown in fig. 5, an assembly load plate can be used. Such an assembly load plate engages all nine tribological units that are tested simultaneously. In such an embodiment, each of the three groups of three tribological units has its own counter plate, which is tiltable relative to the assembly load plate.

35 The skilled person will understand that in variants of the embodiment of fig. 5 and in the variant described above, both the counter plate and the load plate can be provided with holders, or that only the load plate can be provided with holders. The skilled person will also - 15- understand that these holders can be of any suitable type, for example the ones shown in fig.

1. Also, different types of test specimens and counter bodies can be applied.

Fig. 6 shows a partly exploded view of a third embodiment of a system according to the 5 invention. This third embodiment is similar to the embodiment shown in fig. 5.

Fig. 6 clearly shows square, plate shaped test specimens 1 being arranged in the nine recesses 31 of the counter plate 30. Like in fig. 5, there are three groups of tribological units, each group comprising three tribological units. Each group has its own load plate 4 and joint 50.

10 The use of square, plate shaped elements as test specimen or counter body has the advantage that they do not rotate in their holders. This way, uncontrolled (and therewith generally undesired) relative motion between the counter body can the test specimen is reduced or even prevented. Instead of square test specimens and/or counter bodies, this also works with rectangular and triangular test specimens and/or counter bodies, and with test 15 specimens and/or counter bodies in the shape of a polygon. The skilled person will understand that such test specimens and/or counter bodies can also be used in the other embodiments of the invention.

In the embodiment of fig. 6, all load plates 40 are provided with three holders 45 for the ball shaped counter bodies 2. The holders 45 comprise an upper ring 41 and a lower ring 42, 20 between which a ball shaped counter body 2 can be clamped. The holders 45 are connected to a load plate 40 by means of screws 43.

The embodiment of fig. 6 further comprises a load distribution plate 70. All three joints 50 are connected to this load distribution plate 70. In this embodiment, the weights 60 are arranged on top of the load distribution plate 70, right above the load plates 40. Bolts 61 25 connect the weights 60 to the load distribution plate 70.

Below the load distribution pate 70, guide pins 73 are arranged. They extend downwardly, and fall in slots 74 of a load plate 40. These slots are wide enough to allow the load plate 40 to tilt relative to the load distribution plate 70, but small enough to prevent undesirable rotation or sideways movements of the load plate 40 relative to the load 30 distribution plate 70. In this example, bolt 75 connect to the guide pins 73 to the load distribution plate 70. For reasons of clarity, fig. 6 only shows three guide pins 73, but they extend between the load distribution plate 70 and all three load plates 40.

The embodiment of fig. 6 further comprises pins 80. They extend through the load distribution plate 70, so that the load distribution pate 70 can move in a vertical direction 35 relative to the pins 80. The pins 80 are connected to a frame 85, so they prevent sideways movement and rotation of the load distribution plate 70 relative to that frame. The frame can be stationary, in which case both the load distribution plate 70 and the three load plates 40 - 16- are stationary as well. The relative movement of the test specimens and their associated counter bodies 2 can then be obtained by moving the counter plate 30, for example by mounting the counter plate 30 in a shaker table.

The embodiment of fig. 6 allows tilting of the load plates 40 relative to the counter plate 5 30 and relative to the load distribution plate 70. This makes that the load plate can follow the changes in height of the tribological units without loosing contact with them.

In a variant to the embodiment shown in fig. 6, an assembly load plate can be used. Such an assembly load plate engages all nine tribological units that are tested simultaneously. In such an embodiment, each of the three groups of three tribological units 10 has its own counter plate, which is tiltable relative to the load plate.

The skilled person will understand that in variants of the embodiment of fig. 6 and in the variant described above, both the counter plate and the load plate can be provided with holders, or that only the load plate can be provided with holders. The skilled person will also understand that these holders can be of any suitable type, for example the ones shown in fig. 15 1. Also, different types of test specimens and counter bodies can be applied.

Fig. 5 and fig. 6 show embodiments in which nine tribological units are tested simultaneously. These embodiments can be used to make systems that test more tribological units at the same time. For example, three systems according to fig. 5 or fig. 6 can be 20 arranged adjacent to each other, preferably such that each system is at the corner of an equilateral triangle. The load distribution plates of the three systems can then be connected to each other by second load distribution plate, to which for example a load application unit can apply a mechanical load. This mechanical load can then be distributed evenly over all tribological units that are tested simultaneously.

25

Fig. 7 shows a fourth embodiment of a system according to the invention.

In the embodiment of fig. 7, an assembly load plate 40* is provided. Three counter plates 30 are present. Between the load plate 40* and each of the counter plates 30, three tribological units 100 are accommodated. Support 110 holds the counter plates 30. The 30 support is essentially parallel to the assembly load plate 40*.

Joints 50 allow tilting of the counter plates 30 relative to the support 110 and relative to the assembly load plate 40*. Pins 111 allow movement of the counter plates to and away from the support plate 110. The construction is such that the counter plates 30 can tilt relative to the support 110, despite the pins 111. This can for example be achieved by 35 arranging the pins 111 in relatively wide holes or slots in either the counter plates or the support.

- 17-

The support 110 is held in place relative to the assembly load plate 40* by frame 115. Assembly load plate 40* can move in a horizontal direction, towards and away from the support 11 and the counter plates 30. Guides 105 are provided to control this movement.

The assembly load plate 40*, the counter plates 30 and the support 110 are arranged 5 vertically in this embodiment.

Cylinder 120 exerts a mechanical load on the load plate 40*, that distributes the load evenly over the tribological units.

Frame 115 is moved up and down in an oscillating movement, while the assembly load plate 40* does not move in a vertical direction. This induces a relative movement between the 10 test specimen and the counter body in each of the tribological units 100.

Claims

A system for performing multiple tribological tests in parallel, wherein each of the tribological tests is performed in a tribological unit comprising a test element, a counter-body and optionally a lubricant, wherein each of the tribological tests an interaction between a test element and a counter-body of a tribological unit, which system is adapted to receive three tribological units, wherein the system comprises: a load plate, a counter plate, three holders, which holders are arranged on the load plate or on the counter plate, each of the three holders is arranged to hold a test element or a counter-body, the load plate and the counter plate being arranged relative to each other such that the tribological units to be tested can be accommodated between them, a drive unit which is arranged to hold a relative movement between the test element and the counter body of a tri cause a biological test unit, which system is arranged to apply a mechanical load to the tribological units by means of: the mass of elements of the system which are arranged above the tribological units, if such elements are present, and / or load applying unit, for testing and applying a mechanical load on all three tribological units via the load plate, characterized in that the load plate and the counter plate are tiltable with respect to each other.

The system of claim 1, wherein the positions of the corners form an equilateral triangle.

A system according to any of the preceding claims, wherein the load applicator unit is arranged with respect to the load plate such that the load applicator unit applies its load to or directly above or right below the center of the triangle formed by the positions of the holders of the load plate and / or the counter plate.

4. System as claimed in any of the foregoing claims, wherein both the load plate and the counter plate are provided with three holders, each of the three holders being adapted to hold a test element or a counter-body, wherein the positions of the holders on the same plate form the corners of an equilateral triangle, wherein each holder of the load plate can be aligned with a holder of the counter plate, such that each pair of mutually aligned holders can hold together a tribological unit 10.

5. System as claimed in any of the foregoing claims, wherein the system further comprises a coupling between the load plate and the load applying unit, which coupling allows a relative angular displacement of the load plate and the load applying unit.

A system according to any one of the preceding claims, wherein the drive unit is adapted to actuate the load plate and / or the counter plate to cause a relative movement between the load plate and the counter plate. 20

A system according to any one of the preceding claims, wherein the drive unit is adapted to actuate the holders of the load plate and / or the holders of the counter plate to cause a relative movement between the test element and the counter body of the tribological units. 25

A system according to any one of the preceding claims, wherein the position of the holders of the load plate is fixed relative to the load plate.

9. System as claimed in any of the foregoing claims, wherein the position of the holders of the counter plate is fixed relative to the counter plate.

10. System as claimed in any of the foregoing claims, wherein the drive unit is adapted to oscillate the holders of a holder pair with respect to each other.

11. System as claimed in any of the foregoing claims, wherein the drive unit is adapted to rotate the holders of a holder pair relative to each other.

12. System as claimed in any of the foregoing claims, wherein at least one of the holders is adapted to contain a lubricant.

13. System as claimed in any of the foregoing claims, wherein the system further comprises a lubricating unit for supplying lubricant to at least one tribological unit.

14. System as claimed in any of the foregoing claims, wherein the load plate and / or the counter plate is provided with a temperature control unit. 10

A system for performing multiple tribological tests in parallel, each of the tribological tests being performed on a tribological unit comprising a test element, a counter-body, and optionally a lubricant; wherein each of the tribological tests comprises an interaction between a test element and a counter body of a tribological unit, which system is arranged to receive a multiple of three combinations of a test element and a counter body, wherein the system comprises: at least one sample holding assembly wherein each sample retaining assembly comprises three sample retaining sets, each of the sample retaining sets comprising: a load plate, 20. a retaining plate, three holders, which holders are arranged on the load plate or on the counter plate, each of the three holders being arranged around a test element or to hold a counter-body, the load plate and the counter-plate being arranged relative to each other so that the tribological units to be tested can be accommodated between them, a drive unit which is arranged to allow relative movement between the test element and the counter-body of a tribological test unit which system is arranged to apply a mechanical load to the tribological units by means of: 30. the mass of elements of the system which are above the tribological units, if such elements are present, and / or a load application unit for applying a mechanical load to at least one sample holding set during testing, which load is applied to all three tribological units arranged in the sample holding set via the load plate of the relevant sample holding set, in which system the load plate and the counter plate of each sample retention set can be tilted with respect to each other.

16. System as claimed in claim 15, wherein the positions of the holders form the corners of an equilateral triangle.

17. System as claimed in claim 15 or 16, wherein the load applicator unit is arranged with respect to the load plate such that the load applicator unit applies its load at or directly above or right below the center of the triangle formed by the positions of the holders of the load plate and / or the counter plate.

A system according to any of claims 15-17, wherein both the load plate and the counter plate are provided with three holders, each of the three holders of each plate being adapted to hold a test element or a counter-body, the positions of The holders on the same plate form the corners of an equilateral triangle, in which each holder of the load plate can be aligned with a holder of the counter plate, such that each pair of mutually aligned holders can hold together a tribological unit.

A system according to any of claims 15-18, which system comprises three sample holding assemblies, which sample holding assemblies are arranged on a circle, each sample holding assembly being located at an angle of 120 ° from the adjacent sample holding assemblies.

A system according to any of claims 15-19, wherein the counter plates of a sample holding assembly are integrated in an assembly counter plate, and wherein the load plates of the sample holding assembly are tiltable with respect to this assembly counter plate.

A system according to any of claims 15-19, wherein the load plates of a sample holding assembly are integrated into an assembly load plate, and wherein the counter plates of the sample holding assembly are tiltable with respect to this assembly load plate.

A method of performing at least three tribological tests in parallel, wherein each of the tribological tests is performed on a tribological unit comprising a test element, a counter-body, and optionally a lubricant; wherein each of the tribological tests comprises an interaction between a test element and a counter body of a tribological unit, the method comprising the steps of: providing a test system having a load plate and a counter plate, 5. arranging three tribological units between the load plate and the counter plate, applying a mechanical load to the tribological units, such that a normal force occurs on the contact surface between the test element and the counter body of the tribological unit, the mechanical load being generated by the mass of an element of the system is arranged above the tribological units, if such an element is present, and / or by a load application unit that applies the mechanical load to the three tribological units via the load plate, 15. in each tribological unit, the movement of the test element and the counter-body relative to each other that the load plate and the counter plate tilt with respect to each other during the test. 20 -o-o-o-