Routine maintenance and common fault repair of multihead weigher

Author: Smartweigh–Multihead Weighter

Multihead weigher is a mechanical automation equipment with microprocessor as the key, which is basically developed in the measurement and verification of static data scales. Metrological verification and delivery of materials, granular materials, edge materials, ball materials, etc. It is divided into two working modes, one is batch seasoning, which is characterized by gap feeding, and the deviation is controlled at around 0.1%; the other is rotary seasoning for flow monitoring, and the deviation is generally controlled at 0.2% Between ~0.5%, it can control a certain amount of raw material water flow to add raw materials of required quality to the middle and downstream equipment, so as to continue the whole process of production. The editor takes the French Schenck weight loss of the continuous feeding method as an example, and mainly introduces the basic principles of the structure of the multihead weigher, daily maintenance and common fault repairs.

1multihead weigher structure, principle and operation steps of multihead weigher Equipment, conductive soft connection, weighing controller, etc. As shown in the figure (1), the load sensor is the key component of the multihead weigher, and a solid high-resolution resistance strain gauge sensor is mostly used. Its structure is a standard bridge circuit method, and strain force is applied to one of the bridge arms. The resistor sheet is pasted on the steel material. When the load is applied, the output voltage of the bridge circuit is positively correlated with the change of the bridge arm resistor after adding the standard bridge voltage. The multihead weigher selects two inductors to change the load into a working voltage data signal and transmit it to the automatic control system.

1.1.1 Sound card rack The sound card rack is the support point frame for other components and equipment, and the weight sensor is installed on it. 1.1.2 The stirring equipment (motor) is mainly used to assist the unloading of raw materials with poor circulation. It is generally composed of a simple drive motor of an arch-breaking arm machine with spiral auger blades or nail teeth. According to the rotation of the arch-breaking arm , to prevent railway bridges or bonding conditions of raw materials. 1.1.3 Measurement verification warehouse The measurement verification warehouse is the medium for weighing raw materials. The selection of raw materials should be determined according to the characteristics of the raw materials, and its capacity should be selected according to the 3min feeding amount under the processing technology of the maximum conveying total flow.

1.1.4 The screw conveyor (motor) screw conveyor is more excellent than other closed feeding equipment. It can not only transport raw materials evenly, but also avoid the flying and gushing of powder raw materials. The principle of frequency converter is used. Changing the speed ratio of the motor makes continuous adjustments to the slicing rate. 1.1.5 The weighing controller metrological verification control equipment is composed of a fully intelligent multihead weigher dial and a fully automatic automatic control system, which is used for the setting of various main parameters, the query of the content of the alarm information and the operation of the weightless weighing scale. and approval, etc. 1.1.6 Conductive flexible connection The inlet and feed ports of the multihead weigher should generally be air-tight conductive flexible connections to ensure that the connection between the discharge tank and the subsequent equipment does not hinder the weighing.

1.2 The principle of the multihead weigher and the whole process The multihead weigher measures the damage to the quality of the raw materials in the measurement and verification bin per unit time according to the two strain-resistor type weight sensors installed at the bottom of the fixed bracket, and compares the total flow of specific materials with the total flow of settings. For comparison, use the frequency converter to control the speed ratio of the screw feeding motor, so that the total flow of the material is in line with the preset value. The work of the multihead weigher is divided into two parts: a) Feeding process: when the quality of the raw materials in the measurement and verification bin is less than the lower limit set by the control board, the control board sends out a command to open the pressure regulating valve at the lower end of the discharge tank, and the raw materials enter the measurement and verification bin. At this time, it is impossible to measure the flow rate according to the sensor, and the control board is working in the capacity situation, that is, the open-loop control situation, to maintain the DC variable frequency electromagnetic speed regulation motor speed to be the same as before charging, because the entire charging process is very short, and the linearity b) Weighing link: when the filling reaches the limit of the warehouse weight, the control panel outputs a data signal to turn off the pressure regulating valve, the measurement and verification warehouse terminates the feeding, and enters the weighing operation, that is, the closed-loop control system. The reduction of the bin weight tested by the sensor per unit time is the raw material flow rate. According to the comparison with the preset value of the flow rate, the DC frequency conversion rate control of the motor is carried out. The linearity of this link is relatively high. When the bin weight is less than the lower limit value, repeat the above The whole process.

See Figure (2) as shown. 2. The usual maintenance of the multihead weigher (take Schenck as an example) The multihead weigher is a seasoning machine and equipment with a high degree of automation technology measurement verification. Basically, it will not be harmed by the mechanical equipment transformation of the scale body and the feeding organization, and it has both static and Characteristics of data scales and dynamic scales. Therefore, after a period of continuous production and operation (3 months), a series of refined management and maintenance must be carried out.

2.1 Static data maintenance First check the conductive soft connection interconnected with the multihead weigher, and replace it if damaged or brittle. According to the maximum range of the scale body identification plate, the relative standard weights are prepared in advance, and 25%, 50%, 75%, 100% of the maximum range can be calibrated. 2.1.1 Tare weight correction a) Press the function key, operate the selection key and search for Calib. Functions;b) Press Enter, actually operate the selection key, look for Tw:Tare; c) Press {C}{C}, the program flow will start automatically, after it is stable, press Clear, press Cancel.

2.1.2 Correction of static data a) Press the function key, operate the selection key, and search for Calib. Functions;b) Press Enter, the actual operation selection key, look for CW:WeightCheck;c) Press, the program flow will start automatically, after it is stable, there will be two lines of display information, the above display information is the standard weight quality necessary for calibration, The information shown below is the quality of the raw material in the hopper today. Place the standard weight of a certain quality necessary for calibration on the top of the hopper; d) Press, the program flow will start automatically, after it is stable, press Clear, press Cancel, the calibration is over, and the standard weight is removed. 2.1.3 The standard weights are adjusted one by one to the full scale, and the displayed information on the scale calibration interface of the control panel is of the same quality as the standard weights added to the scale body, and then click to calibrate the full scale on the scale calibration interface. , the deviation is less than 0.1%.

2.2 Dynamic maintenance 2.2.1 Adjust the four corners of the multihead weigher with standard weights Put 25kg standard weights on each of the four multihead weighers to check whether the deviation is within the allowable range, if there is no error value range of 0 Within .1%, it is also necessary to adjust the two weight sensors and the tightening anchor bolts of the scale body to make the deviation meet the requirements. 2.2.2 Dynamic correction a) First set about 50% of the rated range (can not be lower than 30%), start the feeder; b) Press the function key, the actual operation selection key, look for Calib. Functions; press enter, and actually operate the selection key to find AdaptVol. Disch, press to enter; c) Wait for the marked value of the displayed information to change smoothly and in a small range, press Clear, press Cancel; d) Continuous cutting operation for at least 10min, the material discharged from the multihead weigher inlet and outlet must be electronically with a higher precision level Weigh this material, compared with the preset value, the deviation is less than 0.5%. 3. Maintenance of common faults 3.1 It is found that the quality of the specific powder equipment displayed on the operation panel of the operation panel has drift, and the range is 4g of positive and negative. Large fluctuations a) Check whether the weightless weighing scale is affected (such as whether the cables are fastened, whether the cover is dirty, whether the windows and doors are open); b) Clear the powder equipment in the measurement and verification warehouse, and peel it again , Static data calibration; c) Dynamic calibration of the weightless weighing, found that the error exceeds 1%; d) Replacement of the weight sensor, the load sensor belongs to high-precision components, the load exceeds its maximum value, it is very easy to permanently destroy, Should be suspended around the scale body“Prohibit climbing”Signs, place guardrails.

If the common faults in the above process are still not cleared, it should be considered that when the weightless weighing is not needed for a long time, it is recommended to use 4 clamping devices to connect with the fixed bracket of the measurement and verification chamber, so that the weight sensor is suspended in the air and cannot bear the force. 3.2 The output of the weightless state measurement verification bin is small, and the flow rate of the lifting multi-tube screw conveyor is still ineffective, and the situation is becoming more and more serious a) Check whether the software control board of the self-inspection system has any problem codes; The manhole door was observed and stabbed, and it was found that the warehouse wall was smooth and clean, there was no dirt inside, the powder equipment was not wet and cold, and the fluidity was good, so the material blockage of the powder equipment was removed; c) There is positive pressure inside the multihead weigher system software , After inspection, it is determined that the conductive soft connection at the upper end of the feeding port has a positive pressure condition, and the observation hole of the feeding port pipeline is opened, and a lot of powder equipment emerges. Due to the analysis, there is heat flow on the lower part of the connecting equipment, which makes the conductive soft connection wet and cold, resulting in the deposition of powder equipment.

Therefore, when cleaning the equipment in the lower section of the weightless scale, the feeding port of the weightless scale should be sealed with a packaging bag to prevent the powdery raw materials from returning to moisture and agglomeration in the weightless state. 3.3 During the whole process of continuous feeding of the screw-type feeding motor, the frequency of the soft starter is changed from 10Hz to 35Hz, and the motor speed is unstable. Check whether the raw material is stuck in the lower screw feeder; c) calibrate the static data and dynamic calibration of the weightless weighing; d) check the two weight sensors, and accurately measure whether the bridge arm resistors are consistent with the specific values, and the standard value The distance is not too big; e) Suspect that the weight sensor is corroded and cause common faults in discrete systems, replace the new weight sensor, and the common faults remain; f) Replace the soft starter, and everything works normally for three days, after the 4th day The common faults are still; g) When checking the grounding protection, it is found that when the shielded cable of the sensor connected between the control box and the weightless scale is moved in the cable trunking body, the motor speed is sometimes very stable, and the common faults of the shielded cable are completely eliminated. Analyzing the reason, because the shielding layer of the shielded cable of the weightless weighing sensor is damaged, it is affected by the fluctuation of the power supply voltage of the AC power supply system and the output harmonics of the soft starter, resulting in the influence of the working voltage of the sensor to transmit the data signal.

In addition, when the sensor shielded cable is routed in the cable trunking body, it should be placed separately from the communication and AC cables or routed through an independent conduit. 4 Summary Because the multihead weigher is a seasoning machine and equipment with measurement verification, the seasoning precision is high, the automatic automatic control system is complicated, and the common fault conditions are various, so it is not easy to accurately check the common fault locations. The editor thinks that only when we usually pay more attention to the maintenance of machinery and equipment, have the courage to develop in combination with the actual situation, and objectively analyze and comprehensively distinguish when we encounter difficulties, can we continue to accumulate work experience and ensure that we are problem-oriented in common fault inspections. , reducing the time of fault detection.

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