Application of special frequency converter for the

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Key words: block forming machine, vibration technology, Che brick machine special frequency converter

in the field of construction industry, the commonly used wall materials in China can be divided into two categories, namely, solid clay bricks and new wall materials. Solid clay bricks (commonly known as red bricks) made of clay as the main material by sintering process have a long history because of their simple process equipment, It has been the main wall material in China for a long time; New wall materials such as non clay bricks and building blocks made of cement, sand, fly ash, coal gangue, slag and other industrial wastes or construction waste through mixing, vibration, pressing and other processes. Similar new wall materials have been gradually promoted and popularized in China in recent decades. Among them, concrete blocks are the most commonly used and later data processing. "No solid" is the abbreviation of prohibiting the use, sale and production of solid clay bricks. Compared with new wall materials, solid clay bricks have adverse factors such as digging soil and destroying fields, wasting energy, polluting the environment and so on. Therefore, the state has issued many hard indicators and policies to encourage the use of new wall materials and gradually ban solid clay bricks. According to relevant national regulations, clay bricks will be banned in all cities (towns) in China after 2010, which will provide a huge market space for new wall materials

1. Classification of brick machine equipment (new wall materials)

according to different molding processes, brick machine equipment can be divided into brick press and block molding machine. Brick presses that shape bricks (blocks) through high-pressure extrusion are collectively referred to as brick presses; Brick machines that shape bricks (blocks) through vibration extrusion are collectively referred to as block forming machines. Among them, the block forming machine has a high degree of automation, a large variety of blocks (bricks) that can be produced and a large output. It plays a leading role in the brick machine equipment and is the most widely used. Note that the following discussion is only about the block forming machine. In the following discussion, the word "brick machine" refers to the block forming machine, which is hereby brought to the attention of readers

2. Vibration technology of block forming machine

a full-automatic block forming machine is mainly composed of belt conveyor, vibration forming machine (host), plate feeder, brick discharging machine, stacking machine, control cabinet, hydraulic pump station, etc., of which the vibration forming device is the core part of the block forming machine, and its performance directly determines the advantages and disadvantages of the machine itself and the formed blocks

3. Theory of vibration forming technology

the block forming machine relies on vibration and pressure to form and compact the concrete mixture in the mold box, so the selection of vibration parameters is very important to the performance of the block. Vibration parameters include vibration frequency, amplitude and acceleration. From the perspective of concrete vibration technology, the optimal vibration frequency and amplitude are different for different vibrated materials. The vibration frequency should be as close to the natural frequency of the aggregate in the material as possible to make it produce resonance. At this time, the attenuation is the smallest and the amplitude is the largest. The aggregate particle size of the block concrete mixture is 3~10mm, and the ideal vibration frequency is 100~125hz, but it can not reach such a high vibration frequency for the block forming machine, mainly considering the service life of the vibration system, especially the bearing. The vibration parameters commonly used by domestic block forming machines are as follows: the vibration frequency range is 45~55hz; Amplitude 1~2.2mm; The vibration acceleration is 10~18g

4. Classification of vibration technology

according to the different positions of vibration sources, block forming machines can be divided into table vibration machines and mold vibration machines. The model that the vibration source directly acts on the vibration table is called the vibration table, and the model begins with "QT". The model with the vibration source installed on the mold box is called the mold vibrator, and the model begins with "QM". Due to the advantages of large output and low average loss of block vibration power, the bench vibrator has become the mainstream model of domestic brick machine manufacturers. Figure 1 and Figure 2 are the schematic diagram of platform vibration and mode vibration mechanism respectively. Take the table vibrator as an example. Generally, the vibrator is driven by an electric motor or a hydraulic motor. Through the two shafts with eccentric blocks in the vibrator, the high-speed rotation in the opposite direction is generated. The centrifugal forces in the horizontal direction offset each other, and the centrifugal forces in the vertical direction overlap each other, so as to produce vertical directional vibration. When there are few shaped blocks, a vibration source can be set under the mold box; When there are many shaped blocks, two or more vibration sources can be set

5. Motor drive and hydraulic motor drive

at present, whether the vibrator is driven by motor or hydraulic motor, there are obvious disadvantages:

1) disadvantages of motor drive

· the motor is frequently and directly started (3-4 times per minute), the starting current is large (5-7 times the rated current), the motor temperature rises (above 70 ℃), and the bearing grease is easy to melt and cause motor damage

· the contactor acts frequently, the passing current is large, and the contact is easy to age

· when the electric voltage is low, it is difficult to start the motor with load

· the running time of the motor each time is 2~4s, the average power factor is low, and the line loss is serious

· when the motor is directly started, the mechanical impact is large, and the requirements for all mechanical accessories are high

2) disadvantages of hydraulic motor drive

· electric 1 According to the stress (strain) cycle times when the sample is broken, it can be divided into: low cycle fatigue test and high cycle fatigue test can be transferred by motor oil pump hydraulic valve pipe hydraulic motor, and finally converted into mechanical energy to drive the vibrator to work. There are too many energy conversion and transmission processes, and the output of roasted blocks reaches more than 10000 tons, which is not efficient

· the hydraulic system has high cost, heavy maintenance workload and many vulnerable parts

· compared with motor drive, the pressure rise of hydraulic system is slow and the vibration acceleration is not high

· when the vibrator does not operate, the motor and oil pump have been idling, wasting electric energy

6. Frequency modulation and vibration technology of frequency converter

how to excite and how to adjust the vibration frequency has always been the concern of brick machine manufacturers. Since the motor frequency conversion technology has been widely used, the vibration forming method of using frequency converter to adjust the motor speed to drive the vibrator has been paid attention to by many brick machine manufacturers

7. Application status of frequency converter in block forming machine

in the 1990s, building materials equipment manufacturers represented by Bessel in the United States and OMAC in Germany applied motor frequency conversion and speed regulation technology to block forming machine. Taking Bessel V-shaped block forming machine as an example, the two optional vibration systems smartpac and posapac adopt frequency converter speed regulation, which can preset different vibration frequencies and vibration accelerations according to the products. The control of start, acceleration, deceleration and shutdown is flexible, which greatly enhances the forming quality and performance of the products. The following table shows the technical requirements of the vibration forming system for the frequency converter:

for the application of the frequency converter, the difficulty of the above technical requirements mainly lies in the control of acceleration and deceleration time. If the acceleration time is too short, the starting current will surge, affecting the motor temperature rise; If the deceleration time is too short, the motor is often in the power generation state, and the electric energy feedback will cause the frequency converter to give an overvoltage alarm. On the contrary, increasing the acceleration and deceleration time will reduce the production efficiency of the block forming machine

8. Application of Che series special inverter for brick machines

after many on-site debugging, our R & D and technical personnel have made corresponding software and hardware improvements on the basis of the company's original Che series vector inverter according to the motion characteristics of the vibration system, thereby developing Che series special inverter for brick machines. The biggest feature of this series of frequency converters is that they can eliminate the braking unit and braking resistance on the premise of meeting the vibration technical requirements. At present, this series of brick machine special frequency converter has been successfully applied to a Construction Machinery Co., Ltd. in Quanzhou. The following is the production data comparison of the block forming machine produced by this company before and after using Che series special frequency converter:

9. The advantages of frequency modulation and vibration of frequency converter

it can be clearly seen from the above data that compared with the direct drive of motor or hydraulic motor, Using frequency converter technology in vibration system has unparalleled advantages of the first two:

· it can easily realize the needs of frequency modulation of vibration system and meet the requirements of production process

· fast acceleration and deceleration, save molding time, and increase the switching contactor pick-up and capacity

· small starting current and less electric shock

· the motor starts smoothly with small mechanical impact

· low temperature rise of motor, which is conducive to long-term stable operation of motor

· high energy transfer efficiency, saving electric energy

· the masonry has good compactness and smooth and beautiful surface

· the inverter has a unique AVR function, which can output enough voltage to drive the motor even when the electric voltage is low

10. Application prospect of frequency converter in block forming machine

it can be said that most domestic brick machine manufacturers are not unfamiliar with frequency modulation and vibration technology of frequency converter, but for the consideration of cost and technical reliability, most manufacturers have not made mass production of this technology. However, with the increasingly fierce market competition and the continuous improvement of process requirements, seeking technological innovation and improving product performance has become an important issue for brick machine enterprises. Facts have proved that the frequency modulation vibration technology of frequency converter has more advantages than other vibration technologies, and the market application conditions have become mature. At present, it is a favorable opportunity to vigorously promote the application. (end)

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