JPH0447260B2 - - Google Patents

Description

[Detailed Description of the Invention] "Objective of the Invention" The present invention aims to calculate the true friction coefficient at the interface between a workpiece and a tool during plastic working by determining the force acting perpendicularly to the rolling direction and the force acting parallel to the rolling direction. The objective is to accurately evaluate the friction characteristics in plastic working by determining the detected values of force and force.

INDUSTRIAL APPLICATION FIELD The present invention relates to a testing machine and a testing method for evaluating the frictional characteristics of the interface between a tool and a workpiece in plastic working.

BACKGROUND ART In plastic processing such as rolling, extrusion, and forging, lubricants are often used for purposes such as reducing processing force, improving product quality, and preventing damage to tools. In addition, it is not uncommon for tools to be subjected to special surface treatments, such as by heat treating them or coating them with different materials.

To explain mandrel rolling, which is one of the hot steady plastic working processes to reduce the wall thickness of a tube between a slotted roll and a mandrel bar, as an example, in order to reduce the frictional resistance of the mandrel bar, the surface of the mandrel bar is Usually, a graphite-based lubricant is applied. However, if the lubrication condition is poor and the coefficient of friction becomes high, not only will the shape of the rolled tube deteriorate, but the tube material and mandrel bar will seize, causing damage to the inner surface of the tube and the surface of the bar. It may also be difficult to remove the mandrel bar from the rolled tube. Furthermore, in the method that has been widely adopted in recent years of restricting the speed of the mandrel bar to a constant level during rolling, the success or failure of machining depends on the quality of the lubrication, as excessive load on the bar due to poor lubrication can cause the bar to break. It's no exaggeration to say that.
However, the selection of lubricants and the determination of lubrication conditions currently rely on experience. For this reason, there is a strong desire to establish a method for easily evaluating the friction coefficient and durability of lubricants for mandrel rolling, and the seizure resistance between pipe materials and mandrel bars.

Furthermore, even in unsteady plastic working, such as forging, where working conditions such as reduction rate and load change during one working process, a lubricant is usually applied to the surface of the die or mold. Even in these processes, if the friction coefficient of the lubricant is high, the product value will decrease due to insufficient filling of the material in the mold, and if the rolling reduction rate increases, the material will seize on the mold and the mold will be damaged due to galling. As mentioned above, there is a need to establish a method for easily evaluating the friction coefficient and durability of lubricants and the seizure resistance of molds and materials.

The conditions of the contact interface between the tool and the workpiece in plastic working as described above are such that extremely high pressure acts over a large contact area, and a new surface is exposed as the workpiece undergoes plastic deformation. Furthermore, in hot working, the contact interface is exposed to high temperatures.

Traditionally, basic testing machines such as the four-ball type and Teimken, which are published in pages 371 and below of the Lubrication Handbook edited by the Japan Society of Lubricants, and their improved machines have been widely used for lubricant evaluation tests. The ring compression method is sometimes used to evaluate commercial lubricants.

Problems to be Solved by the Invention However, in tests using basic testing machines such as the four-ball type and Teimken, and their improved machines, the contact area that applies the load is the contact between elastic bodies, and the contact area is small due to point or line contact. Although the load is small and locally high, there is no large exposure of the newly formed surface due to plastic deformation, and the test results merely elucidate the friction phenomenon, making it difficult to properly evaluate the friction characteristics in actual plastic working. Not good.

In addition, in the ring compression method, the surface elongation and exposure of new surfaces in simple compression are small compared to actual plastic working, so the ranking of lubricant lubricity based on the friction coefficient measured by this method and the actual The ranking determined based on the processing force and seizure resistance during extrusion processing etc. is often reversed, and the evaluation of the friction coefficient, durability and seizure resistance of lubricants is not properly performed for actual processing. It's hard to say that there are.

Therefore, in order to simulate actual plastic working, processing is performed using special equipment that is the same size or a fraction of the operating equipment, and the friction coefficient due to processing force is evaluated and the relationship between the tool and the workpiece is evaluated. Although burn-in properties are sometimes evaluated, these facilities have the drawbacks of being usually large, expensive to produce, and complicated to operate.

"Structure of the Invention" Means for Solving the Problem A plate-shaped workpiece is rolled between a rotating rolling roll and a fixed plate-shaped tool, and an acting force acting perpendicular to the rolling direction and a rolling direction are applied. A friction lubrication test method characterized by detecting both the force acting on the tool in parallel with the force acting on the tool and evaluating the friction characteristics at the interface between the tool and the workpiece during plastic working.

Effect By detecting the rolling force P perpendicular to the rolling direction and the frictional force F parallel to the rolling direction, the friction coefficient μ can be determined from the law of friction as μ=F/P.

From the change in the coefficient of friction μ over time, it is possible to evaluate and determine the durability, durability, seizure resistance, etc. of a lubricant film on the tool surface.

We can test and evaluate both steady plastic working and unsteady plastic working.

EXAMPLE To further explain the present invention as described above, the testing machine according to the present invention rolls a plate-shaped workpiece between a rotating rolling roll and a fixed plate-shaped tool. Firstly, a large plastic deformation is applied to the workpiece, and secondly, a high pressure is generated at the contact interface between the newly exposed surface of the workpiece and the tool surface, causing relative slippage between the workpiece and the tool. This creates a state close to the contact state between the tool and workpiece in actual plastic working, and in this state, the force acting perpendicular to the rolling direction and the force acting parallel to the rolling direction on the tool By using a mechanism that simultaneously detects force and calculating the true coefficient of friction at the interface between the workpiece and the tool from both detected values, it is possible to accurately evaluate the friction characteristics in plastic working.

To explain the present invention with reference to the accompanying drawings, FIG. 1 shows an example of the principle relationship of the present invention. A plate-shaped tool 1 with At the same time that the force P acts on the roll 2 or the tool 1, a force F parallel to the rolling direction acts on the tool 1 due to friction at the interface between the workpiece 3 and the tool 1. When these respective forces P and F are detected by the load detectors 4 and 5, the workpiece 3 is affected by the law of friction.
The friction coefficient μ at the interface between the tool 1 and the tool 1 is determined by μ=F/P. By tracking the change in the friction coefficient obtained in this way over time from the start of rolling, it is also possible to evaluate the sustainability and durability of the lubricant film 6 on the tool surface, as well as the seizure resistance between the workpiece 3 and the tool 1. . roll 2
If a cylindrical roll for sheet rolling is used, the rolling conditions during roll rotation are constant, making it possible to perform tests in steady plastic working. If a roll is used, testing in unsteady plastic working becomes possible.

Additionally, hot testing is possible by heating the material to a predetermined temperature in a heating furnace in advance. roll 2
By changing the distance between the tool 1 and the tool 1, the magnitude of plastic deformation, the pressure acting on the contact area between the tool 1 and the workpiece 3, and the contact area can be changed, and the rotation speed of the roll 2 can also be changed. can change the relative sliding speed between the tool 1 and the workpiece 3.

Furthermore, by making the shape of the tool 1 simple, it becomes easy to apply the lubricant 6, to change the surface treatment of the tool 1, to change the material, and to replace the tool 1, making it easy to conduct tests under various lubrication conditions. You can also do it.

Note that in order to evaluate the friction characteristics over a longer period of time, a long workpiece 3 may be used, or a short workpiece 3 may be rolled in multiple passes. Further, in FIG. 1, the force acting on the roll 2 is detected as the rolling force P, but the force acting on the tool 1 may also be detected.

Next, to explain the present invention in more detail using a specific example, FIGS. 2 to 4 show the configuration of a test machine manufactured by the present inventors, and as shown in FIG. The lower roll set opposite to the upper roll 14 in a commercially available twin roll rolling mill is replaced with a fixed block 11 and installed on a bearing 18,
A tool 13 machined into a plate shape is fixed in the tool holding part 12 of the fixed block 11, and the tool 13 is
A compression type load cell 16 is attached to the exit side of the roll housing 15 as shown in FIG. Press the fixed block 11 and press the fixed block 11
is fixed in the rolling direction, and the frictional force acting between the tool 13 and the workpiece located between the roll 14 and the tool 13 as described above is detected. The force perpendicular to the rolling direction is detected by a roll rolling force detection load cell 17 attached to the upper part of the roll housing 15.

Using the testing machine of the present invention as described above,
First, we will describe an example of a test method and test results that simulate steady plastic working using cylindrical rolls. Carbon steel (0.2%C) is used as the workpiece, heated at 1000℃ in an electric furnace.
The temperature was raised to . The shape is 15mm thick, 40mm wide, and long.
The length is 150mm, and the tip has a taper of approximately 10° to improve biting performance. The tool 13 is made of alloy steel (5% Cr-
1% Mo), the distance between the roll 14 and the tool 13 was set to 7 mm (reduction ratio 53%), and the test was conducted by driving a roll with a diameter of 130 mm with a DC motor at a rotation speed of 20 rpm.

Figures 5 and 6 show test results when water-soluble graphite-based lubricants A and B are applied to the tool surface in advance to a thickness of about 50 μm, and the rolling reduction, which is the output from the load cell 17 over the course of rolling time, is shown in Figures 5 and 6. Power P,
The friction force F and the friction coefficient μ, which are output from the load cell 16, are shown as the calculation results of μ=F/P. That is, in FIG. 5, it can be seen that the friction coefficient during rolling is almost constant and its value is also extremely low, indicating that a stable lubrication state is obtained. On the other hand, in Figure 6, the friction coefficient increases immediately after rolling starts.
The friction coefficient increases to 0.2, and the friction coefficient fluctuates little by little during rolling, and the plate material actually seizes on the tool 13 at this point.

As described above, it has been found that by the test method according to the present invention using a cylindrical roll, it is possible to accurately evaluate the friction coefficient and durability of a lubricant, and the seizure resistance between a tool and a workpiece.

Next, we will describe an example of a test method and test results that simulate unsteady plastic working using eccentric rolls whose rolling reduction rate changes as the rolls rotate.
130 mm, eccentricity 6.5 mm, the distance between the roll and tool is 2 mm to 15 mm (reduction rate 0 to
80%). The above A was used as the lubricant, and the other conditions were the same as above. FIG. 7 shows the change in the friction coefficient with respect to the rolling reduction ratio as a result of the test. From this figure, it can be seen that as the rolling reduction rate increases, the friction coefficient also increases, and seizure occurs between the workpiece and the tool at a rolling reduction rate of approximately 58%.

As described above, the present invention can evaluate the friction coefficient and durability of the lubricant and the seizure resistance between the tool and the workpiece when the rolling reduction rate changes sequentially in the test method using eccentric rolls. It's obvious. Of course, evaluation under similar conditions can also be achieved by using the cylindrical roll made of a material whose plate thickness changes successively in the longitudinal direction.

The test method has been described above using the method of evaluating lubricants using the tester of the present invention as an example. However, if the test is performed without lubricant, the friction characteristics of the tool material can be evaluated. It is clear that the lubricity of each surface layer can be evaluated individually by conducting tests.

Effects of the Invention According to the present invention as explained above, a large plastic deformation is caused to the workpiece by rolling the workpiece in the form of a plate between a rotating rolling roll and a fixed plate-like tool. At the same time, a high pressure is generated at the contact interface between the newly exposed surface of the workpiece and the tool surface, and a relative slip is applied to the workpiece and the tool to prevent the tool and the workpiece during actual plastic working. It is possible to simultaneously detect the force acting perpendicular to the rolling direction and the force acting on the tool parallel to the rolling direction, and from the detected values of both, the true state at the interface between the workpiece and the tool can be determined. By calculating the coefficient of friction of This is a highly effective invention.

[Brief explanation of the drawing]

The drawings show the technical contents of the present invention, and FIG. 1 is an explanatory diagram of the principle relationship of test and measurement in the present invention, FIG. 2 is a front view of a test machine manufactured according to the present invention, etc., and FIG. The figure is a side view, FIG. 4 is an elevation view, and FIGS. 5, 6, and 7 are graphs showing the test results. Therefore, in these drawings, 1 is a tool, and 2 is a tool.
is a roll, 3 is a workpiece, 4 is a rolling force detector, 5
1 is a friction force detector, 6 is a lubricating film, 11 is a fixed block, 12 is a tool support part, 13 is a tool, 14 is a roll, 15 is a roll housing, 16 is a load cell for friction detection, 17 is a load cell for detecting rolling force, 1
8 indicates bearings.

Claims (1)

[Claims] 1 A plate-shaped workpiece is rolled between a rotating rolling roll and a fixed plate-shaped tool, and both the acting force acting perpendicular to the rolling direction and the acting force acting on the tool parallel to the rolling direction are A friction lubrication test method characterized by detecting and evaluating the friction characteristics at the interface between a tool and a workpiece during plastic working.