JPH0426969B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing short metal fibers, particularly ultrafine short fibers suitable for use as a base material for composite materials.

In general, there are various types of fibers such as short metal fibers, glass fibers, carbon fibers, and asbestos. Among these fibers, metal fibers are most suitable for friction materials such as brake linings and clutch plates, and structural composite materials such as filters, conductive FRP, electromagnetic shielding FRP, and noise shielding plates.

However, the metal fibers used for this type of application must be extremely fine, with a diameter of 100 microns or less and a length of 10 mm or less, and must also have good physical properties such as tensile strength as reinforcing fibers. Therefore, it is difficult to easily mass-produce them, and the manufacturing cost is extremely high, except for special products such as lead fibers, making it impossible to meet the wide-ranging demand described above.

That is, when manufacturing ultrafine metal short fibers, generally a cast ingot is rolled to make a wire rod, this wire rod is drawn using a drawing die, etc., and this drawing and annealing are repeated many times to obtain the diameter as described above. The method used was to stretch it into fibers and then cut it at the end.This extremely time-consuming process and the need for large-scale equipment resulted in low productivity and very slow production. The cost was increasing.

Note that, as a method for producing relatively long and thick metal fibers such as steel fibers for reinforcing concrete, there is a method of milling an ingot. However, this method involves intermittent machining by rotating a cutter with a plurality of cutting blades attached to its outer periphery, which poses a problem in terms of production speed. In addition, this method requires high precision of machines and tools, and slight deviations in precision (for example,
Runout of the spindle, clearance between the arbor and cutter inner diameter, groove depth of the carbide tip, blade width, runout of the outer circumference of the cutting edge due to installation errors, etc.) directly affects the dimensions and physical properties of the product, so as mentioned above, There was a problem in that it was difficult to mass-produce thin and short fibers without variation.

The present invention was created through repeated research in view of the above-mentioned circumstances, and its purpose is to improve physical properties such as elastic modulus, abrasion resistance, electrical and thermal conductivity, wettability, and sinterability. An object of the present invention is to provide a method for mass-producing ultra-fine short metal fibers having dimensions and shapes extremely efficiently and inexpensively.

To achieve this objective, the present invention utilizes the natural cracks of the material by turning a columnar block with relatively low ductility, such as brass, under predetermined conditions, and produces acicular short fibers with a non-circular cross section. It is designed to divide and create.

That is, the feature of the present invention is that when obtaining short metal fibers, a columnar block made of a material with low ductility such as brass is used as a raw material, and the columnar block is cut by a depth corresponding to the length of the fiber to be produced. Turning was performed under the following conditions at a cutting speed of approximately 86 to 276 m/min, a feed rate of approximately 0.05 to 0.3 mm/rev, and a tool rake angle of approximately 0 to -40°, and the fiber axis was aligned with the cutting direction. The purpose of this method is to separate and create acicular short fibers with a non-circular cross section that forms a right angle.

When the tool rake angle is approximately 0 to -10°, the lower limit of the feed rate is approximately 0.07 to 0.1 in the entire cutting speed range.
mm/rev and the value gradually increases as the tool rake angle becomes more positive.

When the tool rake angle exceeds approximately -10° and reaches approximately -20°, the cutting speed is set to less than the upper limit, and the lower limit of the feed rate is set in the range of approximately 0.05 to 0.07 mm/rev and increases gradually as the tool rake angle approaches positive. value.

When the tool rake angle exceeds approximately -20° and reaches approximately -30°, the cutting speed should be approximately 158 m/min or less, and the feed rate should be approximately 0.05 mm/rev or more when the cutting speed is at the lower limit.
When the cutting speed is approximately 158m/min, the feed rate should be approximately 0.05~
During 0.075mm/rev, the cutting speed is from the lower limit to approx.
Between 158 m/min and approximately 0.05 mm/rev or more, the faster the cutting speed and the larger the negative tool rake angle, the smaller the value.

When the tool rake angle is negative and exceeds about -30°, the cutting speed should be set to about 158 m/min or less, and the feed rate should be adjusted to about 0.05 to 0.1 mm/min when the cutting speed is at the lower limit.
rev, cutting speed is approximately 158 m/min, the feed rate is approximately
Between 0.05 and 0.075 mm/rev, and when the cutting speed is between the lower limit and about 158 m/min, it is between about 0.05 and 0.1 mm/rev, and the higher the cutting speed, the smaller the value.

The present invention will be explained below based on the accompanying drawings.

FIGS. 1 and 2 show an embodiment of the method for producing ultrafine short fibers according to the present invention. In producing the ultrafine short fibers, a columnar block 1 such as a cast ingot is used as a raw material. The columnar block 1 in this embodiment is suitably made of a material with low ductility such as brass, most preferably free-cutting brass. Next, the end of the columnar block 1 in the axial direction is gripped by a holding means such as a chuck, and the columnar block 1 is rotated at a predetermined speed and number of rotations via this holding means, and the end face of the columnar block 1 is rotated. 2,
The cutting edge 4 of the tool 3 is set to a predetermined depth of cut l and rake angle θ and brought into contact with each other, and a predetermined feed f is applied to the tool 3 in the direction of the block axis.

By doing so, the thin layer 5 on the surface of the metal block 1 is continuously scraped off by the cutting edge 4 of the tool 3. If the rake angle, cutting speed, and feed rate of the tool are not set appropriately, the collected thin layer may flow out for a long time along the rake face, resulting in curved or curled flow chips or free chips. It becomes a serrated chip with a series of serrations and depressions on the surface side.

In the present invention, the columnar block 1 is made of a material with relatively low ductility, such as brass, and the tool rake angle, cutting speed, and feed rate are set to constant conditions, as will be described later. Therefore, as before, when the surface layer of the columnar block is scraped up to a certain amount on the cutting edge 4 and this rises, due to an unstable phenomenon, it is scraped along the approximate interface between the scraped layer and the surface layer of the columnar block. The layer scraped along the crack is instantaneously broken and separated, creating needle-shaped short fibers 6 with fiber axes perpendicular to the cutting direction and a non-circular cross section. Each of them is released continuously, one by one, independently.

FIG. 3 shows the short fiber 6 in an enlarged manner.

Although FIG. 1 shows that the tool 3 is fed in the axial direction, it may be fed in a direction perpendicular to the axis, that is, in the radial direction. In that case, it goes without saying that the feed and depth of cut will have an inverse relationship to that shown in FIG.

The present invention employs constant turning conditions in the production of short fibers, that is, basically, the depth of cut is made to match the length of the fiber to be produced,
And, the tool rake angle θ is approximately 0 to -40°, and the feed amount f
about 0.05~0.3mm/rev, cutting speed V about 86~
The speed will be 276m/min. If this condition is not met, chips will be serrated or flow-shaped, making it impossible to produce the desired short fibers industrially and stably.

First, the rake angle θ is an important condition that affects the thickness, shape, and strength of the fiber, and it is preferable to make it as negative as possible. The reason why the upper limit of the rake angle is set to 0° is because when the rake angle is set to the positive side, the chipped layer flows easily along the rake face without being compressed, resulting in a flow type chip.
If the rake angle is increased to a negative value, the layer that has been scraped and is accumulating on the cutting edge will be compressed and deformed, promoting instability and making it easier to crack, so it is necessary to use thin and hard fibers. Moreover, at the same time, a rough surface 61 can be formed on the free surface of the short fiber 6 as shown in FIG. The rough surface 61 has a ridge shape running along the fiber axis, thereby increasing the surface area and increasing the frictional resistance. However, if the rake angle is extremely large, serrated chips are likely to occur in areas where the feed is large, and when the feed is small, flow-type chips occur, making it impossible to produce fibers. Therefore, the negative upper limit of the rake angle should be −40°.

Next, as the feed f is decreased, the fiber cross-sectional area tends to become smaller, and the smaller the feed and the more negative the rake angle, the thinner the short fibers can be. However, if the feed rate is too small, the longitudinal side edges of each fiber will tend to form a series when it leaves the cutting edge 4, resulting in a flowing chip. Should be set to a range. According to the studies carried out by the present inventors, even if the rake angle is within the above conditions, the minimum feed rate is about 0.05 mm/rev. The upper limit of feed is approximately 0.3 mm/rev in view of the fiber thickness.

Next, the cutting speed v affects productivity, and the faster the cutting speed, the greater the number of fibers produced. However, on the other hand, the higher the cutting speed, the narrower the fiber generation area. This is thought to be because the increasing speed increases the breaking strain of the material, making it difficult for the chips to separate. According to the experiments conducted by the present inventors, it has been found that when the rake angle is 0 to -40° and the feed rate is 0.05 mm/rev or more, the practical range of productivity is about 86 to 276 m/min.

Note that the rake angle θ also affects the cross-sectional shape of the fiber, and as the rake angle becomes more negative under constant conditions of cutting speed and feed, the width of the upper base decreases and the width of the lower base increases. Therefore, by setting the rake angle, it is possible to manufacture anything from a trapezoidal shape to a triangular shape. Further, the length of the short fibers 6 corresponds to the depth of cut of the tool 3 in the axial direction as shown in FIG. 1, and corresponds to the width of the cut in the radial direction. Therefore, by adjusting them, it is possible to manufacture anything from relatively long to extremely short.

The above-mentioned basic conditions are the basic conditions, but in order to stably produce the desired short fiber without variation, within the framework of the above-mentioned basic conditions, the following relationship between the tool rake angle, cutting speed, and feed amount is required. should be set to .

Under these conditions, desired short fibers can be produced with high efficiency and good yield.

When the tool rake angle is approximately 0 to -10°, the lower limit of the feed rate is approximately 0.07 to 0.1 in the entire cutting speed range.
mm/rev and the value gradually increases as the tool rake angle becomes more positive.

When the tool rake angle is more than about -10° and up to about -20°, the cutting speed should be lower than the upper limit, and the lower limit of the feed rate should be in the range of about 0.05 to 0.07 mm/rev, and the closer the tool rake angle is to positive. Take a gradually increasing value.

When the tool rake angle exceeds approximately -20° and reaches approximately -30°, the cutting speed should be approximately 158 m/min or less, and the feed rate should be approximately 0.05 mm/rev or more when the cutting speed is at the lower limit.
When the cutting speed is approximately 158m/min, the feed rate should be approximately 0.05~
During 0.075mm/rev, the cutting speed is from the lower limit to approx.
Between 158 m/min and approximately 0.05 mm/rev or more, the faster the cutting speed and the larger the negative tool rake angle, the smaller the value.

When the tool rake angle is negative and exceeds about -30°, the cutting speed should be set to about 158 m/min or less, and the feed rate should be adjusted to about 0.05 to 0.1 mm/min when the cutting speed is at the lower limit.
rev, cutting speed is approximately 158 m/min, the feed rate is approximately
Between 0.05 and 0.075 mm/rev, and when the cutting speed is between the lower limit and about 158 m/min, it is between about 0.05 and 0.1 mm/rev, and the higher the cutting speed, the smaller the value.

Next, examples of the present invention will be shown.

A free-cutting brass rod with an outer diameter of 60 mm (Pb: 2.98%, Fe: 0.23%, Fe+Sn: 0.30%,
Remaining Zn, tensile strength 38.4Kg/mm ² , elongation 23.6%,
The average cutting speed was 86 using a cutting tool with a P-class carbide throw-a-chip (12.7 mm x 4.8 mm) attached to the holder.
~276m/min, feed rate 0.021~0.306mm/rev, rake angle 10°, 0°, −10°, −20°, −30°, −40°
The cutting depth was set to 5 mm, and ultrafine short fibers were produced by the method shown in FIGS. 1 and 2.

FIG. 4 shows the influence of turning conditions on short fiber production at this time. In FIG. 4, the desired ultrafine short fibers were obtained in the area surrounded by diagonal lines. In FIG. 4, the portions surrounded by solid lines on the right side of each cutting speed display represent fiber generation. From the results shown in Fig. 4, as mentioned earlier, the conditions of cutting speed of about 86 to 276 m/min, rake angle of about 0 to -40°, feed rate of 0.05 to 0.3 mm/rev are satisfied, and the cutting speed and rake angle are It can be seen that it is necessary to give the above relationship to the feed amount and the feed amount.

In other areas, that is, areas where the rake angle is negative to the strength and the feed rate is large, the chips will be serrated, and if the rake angle is too large or the feed is too small, the chips will be flow-type chips, producing the desired short fibers. It's difficult.

The relationship between the cross-sectional area of the short fibers and the turning conditions under the appropriate conditions is as shown in FIGS. 5 and 6.

FIG. 5 shows the relationship between feed and cross-sectional area. The smaller the feed, the smaller the cross-sectional area becomes. However, in the region where the feed is large, the influence of the cutting speed and rake angle on the cross-sectional area changes. Figure 6 shows the relationship between rake angle and cross-sectional area.

Furthermore, FIG. 7 shows the results of examining the fiber productivity at the upper and lower limits of the cutting speed, and it can be seen that the productivity is highest when the feed is reduced and the cutting speed is increased. The number of short fibers produced using a rotating shear blade or flat milling cutter is Q=Z・N
(Z = number of teeth, N = number of cutter rotations), and in actual production equipment, the cutter diameter is 300φ, Z = 50,
It is thought that N = 210 (V = 200 m/min), and therefore Q = approximately 10,000 pieces/min, but with the present invention, approximately 2 million pieces/min can be produced even with experimental equipment, and from this It can be seen that it is possible to achieve a remarkable productivity improvement of about 200 times compared to the conventional method.

According to the present invention as described above, it is possible to uniformly produce large quantities of short fibers that are equipped with a substance suitable for a base material for composite materials, have ultra-fine dimensions and a large surface area, and also use inexpensive raw materials with a low degree of processing. It can be manufactured directly from raw materials, and the machines and tools are simple, so it can be provided at a cost that is not much different from that of raw materials.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing an example of the method for producing short metal fibers according to the present invention, FIG. 2 is an enlarged cross-sectional view showing the fiber production mechanism, and FIG. 3 is a partial view of the short metal fibers obtained by the present invention. An enlarged perspective view, FIG. 4 is a graph showing the relationship between manufacturing conditions and short fiber production area in the present invention, FIG. 5 is a graph showing the relationship between feed and cross-sectional area, and FIG. 6 is a graph showing the relationship between rake angle and cross-sectional area. The graph shown in FIG. 7 is a graph showing short fiber productivity according to the present invention. 1... Columnar block, 3... Tool, 6... Short fiber, θ... Tool rake angle, f... Feed, V... Cutting speed.

Claims (1)

[Claims] 1. To obtain short metal fibers, a columnar block of a material with low ductility such as brass is used as a raw material,
This columnar block is cut at a depth of cut corresponding to the fiber length to be manufactured and at a cutting speed of approximately 86 to 276 m/min.
Feed rate approx. 0.05~0.3mm/rev, tool rake angle approx. 0~
Turning is performed under the following conditions within each range of -40°,
A method for producing short metal fibers, which comprises separating and creating acicular short fibers with a non-circular cross section, the fiber axis of which is perpendicular to the cutting direction. When the tool rake angle is approximately 0 to -10°, the lower limit of the feed rate is approximately 0.07 to 0.1 in the entire cutting speed range.
mm/rev and the value gradually increases as the tool rake angle becomes more positive. When the tool rake angle is more than about -10° and up to about -20°, the cutting speed should be less than the upper limit, and the lower limit of the feed rate should be in the range of about 0.05 to 0.07 mm/rev, and the closer the tool rake angle is to positive. Take a gradually increasing value. When the tool rake angle exceeds approximately -20° and reaches approximately -30°, the cutting speed should be approximately 158 m/min or less, and the feed rate should be approximately 0.05 mm/rev or more when the cutting speed is at the lower limit.
Approximately 0.05 to 0.075 when the cutting speed is approximately 158m/min
mm/rev, the cutting speed is approximately 158 m/rev from the lower limit.
min, the value should be smaller as the cutting speed is faster and the tool rake angle is more negative at approximately 0.05 mm/rev or higher. When the tool rake angle exceeds approximately -30° and is negative, the cutting speed should be set to approximately 158 m/min or less, and the feed rate should be adjusted to approximately 0.05 to 0.1 mm/min at the lower limit of cutting speed.
rev, about 0.05 ~ at cutting speed of about 158 m/min
During 0.075mm/rev, the cutting speed is from the lower limit to approx.
Between 158 m/min and approximately 0.05 to 0.1 mm/rev, the faster the cutting speed, the smaller the value.