JPH0620741B2 - Variable speed mixer for raw concrete - Google Patents

Description

Detailed Description of the Invention [Industrial applications]

According to the present invention, the drive source in the variable speed mixer is an electric motor, and the rotational speed of the electric motor can be adjusted to an optimum rotational speed corresponding to the load at the time of load and the best stirring blade peripheral speed. The present invention relates to a variable speed mixer.

2. Description of the Related Art As a conventional concrete mixer of this type, a mixer whose rotational speed can be changed in two steps (Jitsuko Sho 59-9854).
issue). A mixer whose rotation speed can be changed by a pole change motor (Japanese Patent Laid-Open No. 58-163614). A mixer using a hydraulic motor (Japanese Patent Publication No. 57-43405). A mixer whose rotation speed can be adjusted according to the load (Shokai 59-9808)
No.) and the like are known. However, in any of the mixers, it is not possible to select the rotation speed of the electric motor by increasing or decreasing the frequency of the frequency converter according to the present invention by the rotation speed selection means, and further, it corresponds to the load amount of the stirring blade for kneading the aggregate. There is no technical idea of adjusting the motor speed to an optimum value by adjusting the speed.

[Problems to be Solved by the Invention]

An object of the present invention is to provide a mixer for ready-mixed concrete, which is characterized in that the rotation speed of the electric motor of the drive source is controlled and adjusted most conveniently for kneading of ready-mixed concrete. To explain this in more detail, the relationship between the power consumption and the rotation speed of the electric motor is H = T × N / 974 [H: power (kw), T: torque (kg · m), N: rotation speed (R.
PM)]. Suppose now that the electric power when the load torque is T1 is H1 and the rotation speed is N1. On the other hand, if the load torque is increased to T2 and the rotation speed is constant at N1 = N2, the electric power H2 is larger than the electric power H1, but the rotation speed N2 is N2.
By decelerating to 1 × T1 / T2, H2 = H1 can be kept constant. Applying this, in order to adjust the load under load in each of the high-speed rotation range, medium-speed rotation range and low-speed rotation range and the optimum rotation speed of the motor corresponding to the best stirring blade peripheral speed, For example, in the case of the high speed rotation range, the rotation speed N of the electric motor is reduced so that the electric power H does not always exceed a certain value with respect to a large temporary torque T generated immediately after the gravel is put in, and the kneading progresses. The rotational speed N is gradually increased according to the load torque that gradually decreases. Then, the rotation speed N of the electric motor is increased until the peripheral speed of the stirring blade that is most convenient for kneading the fresh concrete is reached, and the kneading of the fresh concrete is continued in the desired rotation speed range.

[Means for solving problems]

The present invention has been made for the purpose of producing excellent raw concrete that cannot be obtained at all with a conventionally known variable speed mixer for raw concrete, in which a drive source is an electric motor, The rotation speed selection means is provided which can change the frequency to increase or decrease the peripheral speed of the stirring blade for kneading the aggregate and adjust the rotation speed to the optimum rotation speed of the electric motor. Generally, the rotation speed of the mixer when kneading ready-mixed concrete using a batcher plant is usually 10 to 20 R.PM with a tilting mixer in which the container rotates, and a forced mixing mixer in which the container is fixed and the stirring shaft rotates. Is usually 20 to 35 R.PM, and the number of rotations when kneading mortar with one mixer is usually 1.3 to 2.5 times the number of rotations at the time of concrete mixing. . The present invention, by configuring as in the following examples,
It has successfully solved many problems for producing the best ready concrete ideally with one mixer.

【Example】

A variable speed mixer of the present invention will be described with reference to the drawings. FIG. 1 shows load torque, electric power, and rotation speed when green concrete is kneaded by the variable speed mixer of the invention. FIG. 2 is an automatic control circuit for controlling the rotation speed of the variable speed mixer. FIG. 3 shows a tiltable variable speed mixer in which a container rotates. FIG. 4 shows a biaxial forced kneading variable speed mixer in which the container does not rotate. In the figure, the drive source of the variable speed mixer is the electric motor 1,
A speed reducer 3 is connected to the electric motor 1 directly or via a belt 2, and a rotating tool provided with a stirring blade 4 is connected to the speed reducer 3 to rotate. Regarding the procedure of using the mixer, first of all sand, water, an admixture, cement, and gravel measured by a measuring instrument, sand, water, and cement are put into the container 10, and the mortar is kneaded. In this first step, the inverter 6 supplies a high-frequency power source to the electric motor 1 in response to a command signal from the speed setter 5, and the electric motor 1
The stirring blade 4 rotates at a high speed (peripheral speed) suitable for kneading the mortar in accordance with the rotation. Next, the gravel and the admixture are charged into the same container 10 to knead the fresh concrete. In this second step, the speed setting device 5 receives a gravel charging start signal, and the stirring blade 4 of the stirring blade 4 is instructed. Decelerate to medium speed rotation suitable for kneading concrete,
Mix concrete. The signal to the speed setter 5 for decelerating to medium speed rotation is
A signal from a timer that sets the time may be used, and the timing may be adjusted to the start of the gravel throwing. Also, the admixture should be mixed in water beforehand and
You may throw in in a process. When the fresh concrete is kneaded, the electric motor 1 is further decelerated by the same control operation as described above, the stirring blade 4 is rotated at a low speed, and the concrete is discharged without being separated. In the third step, if it is desired to retain the mixed concrete in the concrete container 10, the low speed rotation is continued to maintain the quality of the fresh concrete. On the other hand, when an overload occurs in each process, the overcurrent detector 7 detects the current of the electric motor 1 and inputs it to the calculator 8. The calculator 8 calculates the input data for the overcurrent from the overcurrent detector 7 and the set value from the speed setter 5,
Issues a command to the inverter 6. The inverter 6 reduces the power supply frequency by a value corresponding to the overcurrent, and supplies it to the electric motor 1. The stirring blade 4 is decelerated as the electric motor 1 rotates. The relationship among the load torque, the electric power, and the rotation speed in the above kneading process will be described with reference to FIG. A two-dot chain line a indicates the rotation speed of the electric motor 1 when the electric power is adjusted so that the electric power always becomes a constant value H1 with respect to the load amount of the stirring blade, that is, the load torque that changes according to the load. When the electric power is a constant value H1 or less with respect to the constant rotation speed N1 which is the best stirring blade peripheral speed for kneading concrete,
Kneading of cocrete is continued at this rotation speed N1, but a temporary large torque T2 generated immediately after the gravel is introduced.
On the other hand, if the rotation speed of the electric motor 1 is kept constant at N1, its electric power is a constant value H such as H2 shown by the chain double-dashed line.
Greater than 1. However, by applying the relationship between the power consumption and the rotation speed of the electric motor to the rotation speed, the electric power is always a constant value H1.
Decelerate to N2 so as not to exceed. Similarly, as kneading progresses thereafter, the rotational speed gradually increases in accordance with the load torque that gradually decreases. Then, the rotation speed of the electric motor is increased until the peripheral speed of the stirring blade that is the best for kneading of fresh concrete is reached, and when the rotation speed N1 that is the best peripheral speed of the stirring blade is reached, power is supplied in the subsequent mixing. Rather than increasing along with the rotational speed a at which the constant value H1 is obtained, the kneading of the ready-mixed concrete is continued at the desired rotational speed N1 even when the electric power becomes less than H1. The upper limit value H1 of the electric power is determined in consideration of the characteristics of the electric motor, such as the temperature rise of the coil and the life of the bearing, so as to maximize the electric motor performance with respect to the load of the stirring blade. The overcurrent detector 8 may be a torque detector that mechanically detects the rotational torque generated at any position from the electric motor 1 to the stirring blade 4 in addition to the one by electrical operation. According to the experiment, the rotation speed of the stirring blade and the required time in the twin-screw forced kneading mixer with the nominal capacity of 1.0 m ³ were 4 in the first step.
High speed rotation of 5 to 50 RPM for 10 to 15 seconds, medium speed rotation of 30 to 35 RPM for 20 to 25 seconds in the second step, and discharging or staying the kneaded concrete 3rd
10 to 20 R.PM was suitable in the process. There are various embodiments of fresh concrete in terms of strength, slump, difference in maximum coarse aggregate diameter, etc., and the order and quantity of charging, and the most suitable rotation speed for each embodiment is within the respective rotation range in each step. Is also different. Therefore, a combination storage device 9 is connected to the speed setting device 5,
If the optimum number of rotations according to the mixture can be selectively set within each rotation range, more optimal kneading can be performed for each embodiment, so that higher quality green concrete can be obtained.

【The invention's effect】

The variable speed mixer of the present invention is constructed as described above and has the following remarkable effects. (1) Mortar is a high-speed rotation suitable for mortar kneading, and green concrete is kneaded at a medium-speed rotation suitable for green concrete kneading. Can be discharged and retained. (2) The electric motor drive provided with the frequency converter and the rotation speed selection means is efficient, and in addition to being able to quickly shift in response to the maximum torque generated immediately after the gravel is thrown or an overload such as a sudden generation, Since the number of rotations of the electric motor is selected according to the load in each rotation range and the best peripheral speed of the stirring blade, the electric motor can be downsized and power consumption can be saved. (3) By simply attaching a part of the device of the present invention to the existing constant rotation type ready-mixed concrete mixer installed in the batcher plant, the mixer can obtain the same performance as that of the variable speed mixer of the present invention. No need to replace or modify existing mixer. (4) In the first step, water, sand, and cement are stirred at a high speed suitable for mortar kneading, so that the process of dispersing cement and wetting the surface of the cement particles with water can be performed favorably and in a short time. Therefore, when the admixture is added afterwards for the purpose of improving the water reducing property, the addition time can be earlier than in the conventional constant rotation type mixer.
Due to the good dispersion of the cement, the water reduction is further improved.

[Brief description of drawings]

FIG. 1 is a load torque and a rotation speed when green concrete is kneaded by the variable speed mixer of the invention. FIG. 2 is an automatic control circuit for controlling the rotation speed of the variable speed mixer. FIG. 3 shows a tiltable variable speed mixer in which a container rotates. FIG. 4 shows a biaxial forced kneading variable speed mixer in which the container does not rotate. 1 ... Electric motor 3 ... Reducer 6 ... Inverter 8 ... Computing unit

Claims (1)

[Claims] 1. A mixer having an electric motor as a driving source of a stirring blade rotational force, wherein the electric motor is provided with a frequency converter, and the frequency of the frequency converter is increased or decreased in stages to arbitrarily select the rotational speed of the electric motor. In addition to the above, a variable speed mixer for ready-mixed concrete equipped with a rotation speed selection means for adjusting the motor rotation speed to the best stirring blade peripheral speed in the arbitrary rotation speed range.