FI66089B - PROCEDURE FOR ORDERING FOR FREQUENCY OF FRICTION HAVING SKIV- AND BANDFORM MATERIAL - Google Patents

Description

1 6 5089

Method and apparatus for measuring friction of sheet and strip-like materials

The invention relates to a method and a device for measuring the friction of plate and strip-like materials by pulling a test strip over a corner piece.

In general, knowing the coefficients of friction between material pairs under different conditions is necessary in many applications. For example, in addition to tool design and function, as well as the mechanical properties of the sheet material, the success of forming sheet metal products is affected by surface reactions between the sheet and the tool, depending on surface to-10 chromatography, lubricant viscosity, and lubricant and surface chemical composition. The recent shift to easily removable lubricants and high-strength sheet metal increases the risk of sheet and tool sticking. According to studies, in the automotive industry of Japa-15, more than 70% of tool repairs are due to cutting and subsequent adhesion of sheet material to the tool surface.

Most commonly, friction and sticking are investigated by simple sliding or strip drawing tests, e.g., by pulling 20 sheet metal strips to be examined between planar or cylindrical tools. Their weakness is the type of loading that does not correspond to the practice of the test strip; only the peaks of surface roughness are in the plastic state. However, in molding processes, the roughening of the surface associated with plastic deformation and the rupture of the natural oxide film covering the surface have a major effect on the friction behavior. Therefore, methods have been developed in which the plate can be modified during the experiment, e.g. by pulling and bending the sheet metal strip over a fixed corner piece. In these experiments, however, it is not possible to distinguish between the energy expended in plastic work and the friction losses, so that the actual coefficient of friction cannot be determined.

In the friction measurement test which is the starting point of the invention, the test strip is pulled over a fixed cylindrical piece of friction 5 according to Fig. 1 by pulling. The load mimics the situation at the critical points of the shaping tools (rounding radii and traction ridges). The test strip is subjected to plastic deformation by means of a retention force F2, whereby the surface quality corresponds to practical molding. The force F 1 required for bending and straightening the strip 10 is then determined in a separate experiment by pulling the test strip over the bearing friction roller. The friction losses are thus subjected to a force F ^ for which the equation PM = P1 - Pb - P2 ’

In order to calculate the coefficient of friction, it is also necessary to know the total normal force F ^ °, which can be calculated by means of the tensile and retention forces. When the forces F ^ and F ^ ot are known, the coefficient of friction can be calculated from the equation μ = F ^ / F ^ ot.

The forces acting on the test strip when the strip is pulled over a fixed friction piece are considered in more detail below. Using the notations in Figure 2, it is observed that when the test strip is pulled over a friction piece of radius r, the work done by the force increment dF on the sliding distance r d0 is equal to the corresponding friction work v yFNrdO, where F ^ means normal force against the sliding surface. So

25 dFr d0 = wF „rdO C N

Since F ^ = FdO, dFrcdO = yFrdOdO or f - 4de c 1 is obtained: f 3 6 ΰ 08 9

Integration over the contact angle (δ) gives

Frpb 4 S ΪΓ- = S or f2 o u - 1 Γ ° In Λ "Fbl

The bending and straightening force depends on the load, material and dimensions of the test strip.

As stated above, in the friction measurement method on which the invention is based, two separate tests have to be performed: one for measuring tensile and retaining forces and the other for measuring bending and correcting forces. The object of the invention is to develop a previously known friction measurement method and device so that the friction of a test strip can be determined in one measurement so that the measurement result can be read immediately from the output data of the calculator unit of the device. The characteristic features of the invention are set out in the appended claims.

Applications of the invention include, for example, the classification and development of lubricants, the classification of sheet material / tool-friction pairs, and studies on surface topography (especially tool surface roughness), molding geometry (tool radius, plate thickness) and process variables (e.g., speed, surface pressure, or temperature).

In the following, some embodiments of the invention will be considered in more detail with reference to the accompanying drawings. 25 In the drawings FIG. 1 shows the principle of a friction measurement method when pulling a test strip over a fixed friction piece.

FIG. 2 shows the force components acting on the friction piece and the test strip.

FIG. 3 shows a block diagram of a friction measurement method 5 according to the invention.

FIG. 4 shows an alternative embodiment of the friction measurement method according to the invention.

FIG. 5 shows an apparatus for measuring the friction of a test strip FIG. 4 when the calculator unit is not shown.

FIG. 3, a replaceable cylindrical friction piece 10 is provided on the angle piece 9 attached to the measuring device so that it can rotate freely when measuring bending and straightening forces and is locked to rotate when measuring friction forces. The test strip 11 is attached to the hydraulic traction cylinder 1 and guided over the friction piece 10 to the attachment end of the braking cylinder 2 controlled by the electro-hydraulic servo valve 12. The test strip is attached to the traction and braking cylinders, eg with tensioners attached to the pull-20s. The traction speed of the cylinder 1 and the braking force of the cylinder 2 are adjusted by means of the hydraulic control unit 6 and the measuring and control electronics unit 3. When performing the test, the friction piece 10 is first allowed to rotate freely, whereby the sensors 7 and 8 provide the calculator 25 with signals of the traction and holding force acting during the friction measurement. The analog circuit 4 of the calculator unit then generates a coefficient of friction of the test strip, which is displayed on the calculator output unit 5, e.g. as a digital display.

30 FIG. The measurement method according to 4 differs from the method described above.

II

6 5089, so that in order to measure the bending and straightening forces, a separate angle piece 13 is arranged in the device, on which a sensitively rotating shaft 14 is mounted. The shaft 14 has the same radius as in the contact area between the friction piece 17 and the test strip. In order to measure the braking force, a third force sensor 15 is attached to the device, while the sensor 8 measures the holding force acting on the test strip with respect to the friction piece 17. The measurement signals from the sensors 7, 8 and 15 are fed to a calculator unit which, by means of an analog circuit 4, generates a coefficient of friction 10 which is immediately visible from the input unit 5.

FIG. 5 is based on FIG. 4. The body 18 of the device is constructed as a rectangular support frame divided into two parts by a cross member 20. In the lower part of the body, between the cross members 20 15 and 21, a test strip 11 is mounted A drive hydraulic cylinder 1 and an electro-hydraulic servo valve controlled brake cylinder 16 a friction piece 17 is attached, and an angle piece 13 on which a sensitive rotating shaft 14 is mounted are fixed to the upper beam 20 19 of the measuring device. The hydraulic unit 6 is located in FIG. 5, to the lower part of the body encased as indicated by dashed lines 22.

The invention is not limited to the embodiments described above, but the friction measurement method and apparatus may vary within the scope of the appended claims.

Claims (6)

A method for measuring friction of sheet and strip-shaped materials by pulling a lubricated or unlubricated test strip (11) over a friction body (10) attached to its angular body at a fixed contact angle, characterized therefrom, for measuring the bending and straightening forces (F F) of the test strip (11) at the test strips (11) as tensile and locking forces (F1, F2), a portion of the test strip (11) is simultaneously pulled over a lightly rotating shaft (10). , 14) and a portion above the Iästä friction body (10, 17). The radius of the stored shaft (10, 14) corresponds to the radius of curvature of the contact area between the friction body and the test belt. A method according to claim 1, characterized in that the braking force is kept constant or corresponding to a given varying normative value. 15 3. A method according to claim 1 or 2, characterized in that when measuring bending and straightening forces (Ffa) the effect of the counteracting forces of the rotating shaft (14, 10) is compensated. 4. A method according to any of the preceding claims, characterized in that the forces necessary for measuring the friction force of the test strip as well as bending and straightening forces are measured from the difference between either the before and after the friction body (10, 17) or the rotating body. the shaft (14, 10) acting forces (F F-F2'F2-F3) or from the torque which rotates the friction body (10, 17) / the rotating shaft (14, 10) or from the normal forces acting on the friction body and the rotating shaft . A friction measuring device for realizing friction measurement according to any of the preceding claims, comprising a tensioning device (1) for the test band (11),