US20200164479A1

US20200164479A1 - Method of abrading a test track with a bituminous surface

Info

Publication number: US20200164479A1
Application number: US16/630,065
Authority: US
Inventors: Pierre Cormier; Jerome Mahe; Frederic Peyrin
Original assignee: Arteme; Compagnie Generale des Etablissements Michelin SCA
Current assignee: Arteme; Compagnie Generale des Etablissements Michelin SCA
Priority date: 2017-07-10
Filing date: 2018-07-10
Publication date: 2020-05-28
Also published as: FR3068714A1; WO2019012419A1; FR3068714B1; EP3652381A1; CN110892113A

Abstract

A method for breaking in the surface condition of an asphalt test track for vehicles, comprising: modifying the condition of the surface of the test track with a treatment machine; placement on the treatment machine (1) of at least one rotary abrasive disc (4); and moving the treatment machine on the test track so as to reduce the friction coefficient to achieve a friction level corresponding to that of a broken-in track.

Description

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a method for breaking in the surface condition of a test track for vehicles, said track being of asphalt, comprising the provision of a treatment machine comprising a rotary head bearing at least one friction element for modifying the condition of the surface of said test track, the placement on the treatment machine of at least one rotary abrasive disc and the treatment of the surface to be modified.

PRIOR ART

The manufacturers of road surfacings continually develop new products in order to improve the quality of the roads. Generally, the aim is to increase the durability of the surfacings as well as their mechanical qualities in order to obtain a better vehicle road-holding. To this end, the aim is therefore most often to increase the friction coefficient of the surfacing.
For their part, the constructors and motor vehicle equipment suppliers have to be able to test their vehicles and components in the most realistic and repetitive conditions possible. In particular, with regard to the tyres, the European Union Regulations R117 and R228 specify, in their Annex 5, the method for measuring the wet grip index of the tyres. This method provides notably for the average maximum braking force coefficient of a test tyre to be within specific ranges of values. Some standards thus provide friction coefficient values for the surfacings of the tracks on which the tests are carried out.
Because of the ever improving qualities of the new surfacings on the one hand, and the objectives of performing tests representative of road conditions on older surfacings, the newly constructed test tracks may not respect certain requirements with respect to the friction coefficient. Various approaches have therefore been tried in order to treat the surface of the new surfacings of the tracks in order to make them rapidly conform, at acceptable costs. The known methods are essentially based on the following principle: rubbing a rubber pad with or without abrasive particles to obtain the ground wear.
Given the large surfaces to be treated, the method has to be simple, effective and adaptable to long tracks. Currently, no truly conclusive method is available.
The polishing machines are also well known. For example, the document US20070272223 describes a polishing machine comprising a rotary friction surface provided with bristles. These bristles can be covered with abrasive particles such as silicon carbide for example. This type of machine is used for example to polish concrete grounds.
The document WO2005113198 illustrates an example of a polishing brush comprising bristles encrusted with metal abrasive particles. These abrasive bristles are for example used in order to polish concrete grounds.
There is still a need to establish a method that makes it possible to break in a new test track of which the friction coefficient of the coating does not make it possible to perform representative tests.
To mitigate these various drawbacks, the invention provides different technical means.

SUMMARY OF THE INVENTION

The main objective of the invention consists in defining a surface treatment method that makes it possible to lower the level of grip of a new test track to bring it within a determined target, such as, for example, a target provided by the current regulation.
To do this, the invention provides a method for breaking in the surface condition of an asphalt test track for vehicles, comprising the following steps:

- provision of a treatment machine comprising a rotary head bearing at least one friction element, for modifying the condition of the surface of said test track;
- placement on the treatment machine of at least one rotary abrasive disc;
- application of movements of the treatment machine on the test track so as to reduce the friction coefficient to achieve a friction level corresponding to a target value.

This method makes it possible to modify the friction characteristics of the track in order to obtain a range of predetermined characteristics, for example specific wet grip characteristics.
It should be noted that this method has no significant influence on the depth of the macrotextures (MTD, according to the standard EN13036-1) and consequently does not affect the drainage characteristics. As described later in this document, the other tests trialled all have a negative impact regarding this descriptor.
According to an advantageous embodiment, the method comprises a preliminary step of preparation consisting in eliminating the bituminous binder on the surface of the aggregates by hydrostripping. Such a step makes it possible to obtain favourable results with shorter implementation delays.
According to an advantageous embodiment, the friction element is an abrasive disc with bristles impregnated with abrasive particles.
The bristles advantageously have a height greater than 15 mm.
The form factor of the bristles is advantageously between 1/50 and 1/10, and more preferentially between 1/40 and 1/30.
For example, the height of the bristles is advantageously less than 60 mm. The diameter of the bristles is advantageously between 2 and 4 mm.
Unexpectedly, this configuration makes it possible to obtain particularly advantageous results. The tool used makes it possible to perform work over all the perimeter of the aggregates, and not only their top surface.
Advantageously, the abrasive particles of the bristles are of silicon carbide (SiC), ceramic or tungsten carbide type.
These particles, covering or embedded in the bristles or filaments, make it possible to interact optimally with the aggregates of the surfacing.
According to an advantageous embodiment, the speed of rotation of the rotary discs is between 1000 and 1500 revolutions/minute and more preferentially substantially 1200 revolutions/minute.
According to another advantageous embodiment, the speed of movement of the machine is between 0.5 and 15 metres/minute and more preferentially between 5 and 10 metres/minute.
The fact that the friction is generated by rotary discs makes it possible to avoid giving the abrasion a directional aspect.
The number of passes of the machine is preferably between 1 and 10 and more preferentially between 2 and 6.
Advantageously, the average contact pressure of the bristles of the abrasive discs is between 1 and 5 bar, preferably between 2 and 4 bar.
According to an advantageous embodiment, a working load of preferably between 200 and 400 kg and more preferentially between 260 and 300 kg is applied to the treatment machine.
According to another advantageous embodiment, the machine comprises a sensor giving an indication concerning the trend of the treatment, such as, for example, a sensor of pendulum type (such as a “British Pendulum Tester” sensor). This configuration makes it possible to simply control the progress of the method.
The invention also provides a tyre test track surface treatment machine for implementing the breaking-in method previously described, comprising a rotary head bearing at least one friction element capable of modifying the condition of the surface of said test track, wherein the friction element is an abrasive disc with bristles impregnated with abrasive particles, and wherein the form factor of the bristles is advantageously between 1/50 and 1/10, and more preferentially between 1/40 and 1/30.

DESCRIPTION OF THE FIGURES

All the details of realization are given in the following description, complemented by FIGS. 1 to 9, presented purely as nonlimiting examples, and in which:

FIG. 1 is a schematic representation of an example of a surface treatment machine;

FIG. 2 is a bottom view of the machine of FIG. 1, equipped with brushes with abrasive bristles;

FIG. 3 is a schematic profile view of a brush with abrasive bristles;

FIG. 4 is a schematic representation in perspective of a filament of which the brush with abrasive bristles is composed;

FIG. 5 is a bottom view of an example of an abrasive disc;

FIG. 6 is a schematic representation in profile view of a loaded carriage in polishing position and provided with a pad;

FIG. 7 is a table illustrating the effects observed on the surfacing for different types of polishings;

FIG. 8 is a table summarizing the types of tyres used for the comparative tests;

FIG. 9 is a summary table of the variations in μ_ASTMobtained for each of the tests carried out.

DETAILED DESCRIPTION OF THE INVENTION

As has been seen previously, the grip levels sought for the vehicle and/or tyre test tracks are for example defined in standards.
The method needs to be able to cover all the range of values 0.5<μ_ASTM-16pces<0.9, and more preferentially the values 0.6<μ_ASTM-16pces<0.8.
Various polishing techniques were tested on a track which was specially constructed for this study. The various results obtained show that the breaking-in technique using a resurfacer equipped with brushes with abrasive bristles of great height is most effective for achieving the target sought in terms of μ_ASTMlevel. The analyses have made it possible to construct a two-fold demonstration:
i) on the one hand that the technique makes it possible to achieve a target grip through the range previously cited;
ii) the known tyre behaviour tests performed on a new track treated with the method according to the invention made it possible to obtain tyre classification results comparable to those previously obtained on regulatory or other test tracks.

Conclusive Characteristics

- Rate of advance: 0.5 m/min;
- Number of passes to be performed: ≥4;
- μ lowering rate: 0.07 pt μ_ASTMper pass.

Track Used to Determine the Effective Criteria

A track of 550 m²was specially constructed in an area of low activity of a tyre test centre. It consists of two different surfacings (Sol1 and Sol2) taken from wet braking tracks. After preparatory work which consisted in eliminating the bituminous binder from the surface of the aggregates by hydrostripping and delimiting the working zones, the track was handed over to test polishing methods.
The choice of road surfacings is geared towards the following solution:

- Sol1: track with low microroughness and open macroroughness favouring water evacuation; surface of 5×60 m²;
- Sol2: track with high microroughness and closed macroroughness; surface of 5×50 m².

Tests Carried Out

Several distinct approaches were tested, according to two test families:
A1) pad with high load (high pressure);
A2) pad with low load with SiC (low pressure);
B1) sanding machine with tyre tread;
B2) sanding machine with abrasive discs;
B3) sanding machine with rotary brushes equipped with bristles impregnated with abrasive particles.
Pad with High Load (High Pressure)
A pad of large dimension comprising a bottom friction surface provided with a plurality of tyre treads arranged in parallel, serves as a working surface. To improve the effectiveness, loads are placed on the pad. The pad forms a kind of trailer without wheels, pulled by a tractor or other vehicle of high traction power. FIG. 6 schematically illustrates an example of a pad on which loads are placed.
The idea behind the HP pad technique is therefore to create a device which makes it possible to cause the rubber to rub on the surfacing to be broken in with the right pressure and for long enough.
The study began with the production of a specific carriage. The carriage consists of a robust metal frame, which can be manipulated by a “standard” tractor (for lifting and transportation) and placed on rubber pads. For the pressure exerted, the carriage weighs in all 2200 kg. The carriage rests on 4 pads of 6.5×24.0 cm²=637 cm²; the contact pressure=3.4 bar.
The implementation of the HP pad gave rise to a certain number of incidents. The sprinkling system had to be modified to reduce the risk of destruction through burning. The pads were wearing out very quickly. Then, shims had to be added to extend the life of the pads. All that combined with a fairly uncomfortable working posture for the operator, who had to spend his or her time watching behind him or her. The result of that was that productivity was very mediocre. An average of eleven passes per day were completed during the tests.
The implementation made it possible to rapidly identify two defects on the first batch of pads which were manufactured: stripping by delamellization; wear by burning.
t can be estimated that the necessary number of passes needs to be of the order of 2000 to achieve the asymptote of the different grounds. It is also probable that the number of passes should be dependent on the ground treated. It must be stressed that the implementation of the HP pad technique brings a working situation that is particularly difficult for the operator, making the solution difficult to industrialize.
Pad with Low Load with SiC (Low Pressure)
This approach is comparable to the preceding one for the main support, namely the pad. It is however used without load placed on the pad. To replace the load, an intermediate material is used, acting between the pad and the ground. The test therefore involves arranging a layer of SiC on the ground before performing the passes with the pad.
The technique works at an average contact pressure that is extremely low P=0.03 bar. The surface is approximately 4 m²and the weight is of the order of 250 kg.
The use of powder needs to respect the conventional polishing techniques. We start with a large particle size and end with a fine particle size. For these tests, three particle sizes had been procured: 10, 5 and 3 μm. After treatment, cleaning the treated zone was not easy.
Looked at from the viewpoint of the aggregate used in the surfacing, the slipped length is significantly greater than the HP pad technique. On each pass, an aggregate undergoes 2 m of slipped length.
It can be reported that the technique was not effective. From the viewpoint of the μ_ASTMfriction coefficient and regardless of the ground watched, the technique does not give a result. This is probably linked to the indentation phenomenon. The LP pad+SiC technique works essentially on the surface of the aggregate, and the tyre, for its part, touches unworked zones. As a first approximation, it is thought that there would need to be approximately 5000 passes to manage to bring the p level to the expected target. The technique is highly polluting. Once the polishing work is finished, the elimination of the SiC is relatively difficult.

Sanding Machine

The machine is electrical and requires a standalone set to power it as far as the track.
An example of sanding treatment machine 1 and of its different elements is illustrated schematically in FIGS. 1 to 4. In the example illustrated, the machine 1 has a rotary head 2 and is mounted on wheels 8. The rotary head comprises three friction elements 3 (4=220 mm). Each of the friction elements 3 is rotated about its central axis. The speed is adjusted by variable speed drive to a rotation speed of 1200 rpm. The friction elements 3 comprise brushes 4 provided with bristles 5. As illustrated in FIG. 4, at least a portion of the bristles 5 is coated with abrasive particles 6. The set of the three brushes 4 is rotated about the central axis 7 of the machine (of the order of 100 rpm), thus generating a double rotation movement of the abrasive discs 4.
The abrasive particles 6 are advantageously composed of SiC, of ceramics or of tungsten carbide.
The machine used in the tests has an autonomous driving system with adjustable speed. The machine is piloted by an operator by radiocommunication. The operator has to be situated within a perimeter of 5 m around the machine. Other operating parameters are adjustable: the deballasting weight and the sprinkling. As is known, the device presented is used for brightening or cleaning tasks. In these cases, the bristles do NOT include abrasive particles.
The implementation requires the availability of an electrical generator set. The time required to assemble the equipment is relatively short but necessitates lifting equipment to rapidly transport the machine. During use, a continuous sprinkling is necessary. It makes it possible to discharge sludge and ensures the cooling of the interface and of the ground. One or more loads 9 or weights can be applied to the machine in order to increase the effectiveness of the polishing.
The tests were performed with a “Blastrac” model 780RS polishing machine.
Sanding Machine with Discs with Tyre Tread
For this test, the abrasive discs 4 are composed of portions of tyre tread. The diameter of the discs used was 220 mm. The height of the tread was 8 mm.
The tests were very quickly stopped. The join between the pad and the machine was not sufficiently strong and the discs were torn away.
Sanding Machine with Grain Abrasive Discs
FIG. 5 schematically illustrates an example of a grain abrasive disc used for this test. These discs are composed of a resin in which “grains” of tungsten carbide are integrated. Depending on the density and the particle size of these grains, the degree of abrasiveness is controlled.
Sanding Machine Using Brushes Comprising Bristles Encrusted with Particles (SiC)
FIGS. 2, 3 and 4 (previously described) illustrate an example of a device for these tests.
The tests were done with a fixed rate of advance of the order of 0.5 m/min. Additional tests were carried out at a speed of 10 m/min. A double rotation is advantageously used. The pressure is situated between 0.2 and 0.3 bar.
This test configuration made it possible to achieve the target sought in terms of p level. Moreover, comparative tests with tyres of known relative grip performance levels on one of the treated zones delivered results identical to those obtained on the “conventional” tracks (FIG. 8).
From an effectiveness point of view, the technique based on a brush with abrasive bristles of great height is the most effective for lowering the μASTM.

Main Results

The many technical difficulties to be overcome to create the prototypes, perform the tests in good conditions of safety, monitor the effects obtained, then compare with prior results providing a guarantee of the authenticity of the observed effects, shows that developing a breaking-in method is a particularly complex and lengthy process, the results of which are totally unpredictable.
FIG. 7 schematically illustrates the main effects produced on the surfacing with the methods tested. The first illustration represents the profile of the surfacing prior to breaking-in. The aggregates or pebbles form a rough surface. The next two illustrations show the particularly limited effect of the pads (pad+SiC and HP pad). The last illustration shows the effect of the abrasive disc, working only on the surface. Finally, the penultimate illustration presents the effect obtained with brushes whose filaments comprise abrasive particles in their mass (SiC for the tests carried out). It is observed that the bristles make it possible to reach all the reliefs, on the top and on the sides, for a particularly conclusive three-dimensional effect with respect to the targeted aim of reducing the friction coefficient.
FIG. 9 shows the friction coefficient values obtained. The advantageous results from the brush with abrasive bristles of great height described previously are confirmed.
This table makes it possible to draw many conclusions:

- the threshold of 0.7 μ_ASTMwas achieved by just one of the techniques implemented: the brush with bristles encrusted with particles of silicon carbide (SiC);
- the LP carriage+SiC did not have any effect from the μ_ASTMpoint of view;
- the grain 2000 sanding machine did not have any effect;
- the tests with a brush with abrasive bristles of great height make it possible to achieve the target 0.6<μ_ASTM<0.8 (that confirms the robustness of the technique);
- the reference plot shows a μ_ASTMof the order of 1. The measurement dispersion is of the order of 0.1 point;
- the HP pad presents a fairly slow polishing kinetic, the trend goes in the right direction but remains inadequate;
- the grain 500 sanding machine is more effective than the grain 2000 but achieves an asymptote fairly far from the final target.

REFERENCE NUMBERS EMPLOYED IN THE FIGURES

1 Surface treatment machine
2 Rotary head
3 Friction element
4 Abrasive disc or brush
5 Bristles
6 Abrasive particles
7 Rotation centre
8 Wheels
9 Load

Claims

1.-14. (canceled)

15. A method for breaking in a surface condition of an asphalt test track for vehicles, comprising:

(a) modifying the surface condition of the test track with a treatment machine comprising a rotary head bearing at least one friction element; and

(b) moving the treatment machine on the test track to reduce a friction coefficient to achieve a friction level corresponding to a target value,

wherein the at least one friction element is an abrasive disc.

16. The method according to claim 15 further comprising the step of hydrostripping the test track before step (a) to eliminate a bituminous binder on a surface of aggregates.

17. The method according to claim 15, wherein the abrasive disc comprises bristles impregnated with abrasive particles.

18. The method according to claim 17, wherein the bristles have a height greater than 15 mm.

19. The method according to claim 17, wherein a form factor of the bristles is between 1/50 and 1/10.

20. The method according to claim 17, wherein the abrasive particles are selected from the group consisting of silicon carbide (SiC), ceramic and tungsten carbide type.

21. The method according to claim 15, wherein a speed of rotation of the abrasive disc is between 1000 and 1500 revolutions/minute.

22. The method according to claim 21, wherein the speed of rotation of the abrasive disc is about 1200 revolutions/minute.

23. The method according to claim 15, wherein a speed of movement of the treatment machine is between 0.5 and 12 meters/minute.

24. The method according to claim 23, wherein the speed of movement of the treatment machine is between 1.5 and 5 meters/minute.

25. The method according to claim 24, wherein the speed of movement of the treatment machine is about 2 meters/minute.

26. The method according to claim 15, wherein a number of passes of the treatment machine on the test track is between 1 and 10.

27. The method according to claim 26, wherein the number of passes of the treatment machine on the test track is between 2 and 6.

28. The method according to claim 15, wherein a working load applied to the treatment machine is between 200 and 400 kg.

29. The method according to claim 28, wherein the working load applied to the treatment machine is between 260 and 300 kg.

30. A treatment machine for breaking in a surface condition of an asphalt test track for vehicles, comprising a rotary head bearing at least one friction element capable of modifying the surface condition of the test track,

wherein the friction element is an abrasive disc with bristles impregnated with abrasive particles, and

wherein a form factor of the bristles is between 1/50 and 1/10.

31. The treatment machine according to claim 30, wherein the abrasive particles are selected from the group consisting of silicon carbide (SiC), ceramic and tungsten carbide type.

32. The treatment machine according to claim 30, wherein the bristles have a height greater than 15 mm.

33. The treatment machine according to claim 30, wherein an average contact pressure of the bristles is between 1 and 5 bar.

34. The treatment machine according to claim 33, wherein the average contact pressure of the bristles is between 2 and 4 bar.