Common faults and repairs of sand grinders

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I. Reduced flow rate or absence of cooling fluid for mechanical seals A. Reduced cooling fluid flow rate 1. Impurities in the cooling fluid get trapped on the filter screen at the oil inlet by the electric oil pump, resulting in difficulties in oil intake and a reduced amount of oil discharged. Solution: Open the cover on top of the machine base, pull out the inlet hose of the electric oil pump from the oil tank, and remove any debris from the filter screen. 2. When the compression amount of the mechanical seal spring or the spring pressure is too high, the temperature of the coolant increases. Coupled with the poor thermal stability of the electronic components in the electric oil pump, the operating frequency of the electric oil pump decreases and the flow rate of the coolant is reduced. Solution: Reduce the number of springs. Note that the reduction in the number of springs must be a multiple of 2: 2, 4, or 6, and the reduction should be done symmetrically. ” B. No coolant is ejected from the oil cover on the frame. 1. The electric oil pump is not working (no vibration in the oil pump). a. The plunger in the electric oil pump is stuck by impurities in the oil and cannot move (at the moment the pump is started, touching the electric oil pump reveals that its electromagnet moves for a brief instant; after that, there is no movement or only very slight vibration). Solution: Remove the oil outlet cover from the electric oil pump, check whether the plunger is stuck, and clean it thoroughly. b Damage to the electronic components inside the electric oil pump (in this case, the power indicator light for the electric oil pump turns red). Solution: Replace the pump or repair the electronic circuitry within it. c The 24V DC air switch in the electrical box provides protection (in this case, the solenoid valve does not operate either and no sound is produced). Solution: Check whether there is any short circuit in the solenoid valve and the electric oil pump. The 24V DC regulated switching power supply has no output; the green indicator light on the regulated switching power supply does not illuminate. Solution: Check whether the 220V AC circuit breaker has tripped due to protection mechanisms Has the overcurrent protection of the main motor’s thermal relay been activated? If it needs to be started (at this time, the two normally closed terminals beneath the red button of the thermal relay are already connected; one of them does not have 220V voltage, while under normal conditions both terminals are energized), it can be started by pressing the button, or it will recover automatically after half an hour. 2. The electric oil pump moves (it vibrates) but no circulating coolant is produced. Solution: The intake filter is completely clogged, or the check valve inside the electric oil pump is not functioning; clean the filter or the check valve in the oil pump. II. Coolant flows out from beneath the housing cylinder. If any oil leaks out from beneath the cylinder, there’s no need to worry that it will get into the material. The reason is that when the sanding machine is in operation, the pressure of the material inside the cylinder is higher than that of the coolant in the oil cover; therefore, it is only possible for the material to enter the coolant in the oil cover. When the sanding machine is shut down and not in use, the oil cannot enter the cylinder due to the tension of the oil; at this time, it is the sealing surfaces of the mechanical seal’s stationary and rotating rings that prevent the material from entering the oil. A. Oil leakage at the coolant connector on the oil cover – This can be observed directly with the eye, or by pressing a tissue against the base of the connector to check whether oil appears on the tissue Solution: Remove the connector, wrap a small amount of fine linen or cotton yarn around the base of the connector’s threads, and then apply a small amount of PTFE tape on top. B. Leakage at the oil seal area of the frame: After confirming that there is no leakage at the coolant connector on the oil cover, wipe away any remaining oil beneath it. Place a piece of white paper about 25 centimeters long and 4 centimeters wide under the oil cover, and after starting the main unit, observe whether any oil appears on the paper after 20–30 minutes If there are traces of oil, carefully observe whether it is engine oil or butter How can one determine whether it is residual oil or a leak from the skeleton oil seal, based on the location of the oil stains on white paper? Solution: The skeleton oil seal and the rotating ring of the mechanical seal are dynamic seals, which allow a small amount of oil leakage; it is normal for one drop to leak per 30–40 minutes. If too much oil leaks, the skeleton oil seal needs to be replaced. At this point, attention should be paid to observing the mating position between the moving ring of the mechanical seal and the skeleton oil seal. Are there any deep wear marks on the outer circumference of the moving ring? If so, the rotating ring and the skeleton oil seal should be replaced together. C. When the coolant in the oil cover on the machine base returns to the oil tank, it splashes onto the machine base cover. Due to the surface tension of the oil, it spreads in all directions and flows down along the discharge pipe area. Solution: Add a plastic film cover under the oil cover to prevent the oil from splashing everywhere. III. Materials entering the coolant (the color of the coolant changes according to the color of the materials). A. Could it be that the compression amount of the mechanical seal spring is too great, or the elasticity of the spring is excessive, resulting in high friction temperatures at the sealing surfaces of the moving and stationary rings? This destroys the lubricating oil film on these surfaces, leading to dry friction and a significant reduction in the sealing performance; as a result, the materials leak into the coolant under the effect of centrifugal force. Handling procedure: Before installation, the relevant parts should be wiped clean; the shaft must also be cleaned. When installing the discharge end cover (at this point, the stationary ring has already been mounted on the discharge end cover), the stationary ring must not come into contact with the shaft, so as to prevent the 90-degree sharp edge of the stationary ring from scraping off metal particles from the shaft surface, which could then accumulate on the sealing surface. Special attention should be paid to the first 5 minutes after turning on the main machine. In particular, during the first 2 minutes, listen for any high-frequency squeaking sounds coming from the mechanical seal area (Excessive spring compression or elasticity can also cause squealing.) If this occurs, it is due to dirt on the two sealing surfaces during the installation of the mechanical seal. Without installing the dispersing disc, start the machine and touch the stationary ring seat with your hand. After about 20 minutes, the temperature of the stationary ring seat should be around 50–55 degrees Celsius. If the temperature rises to 55–60 degrees Celsius within just 2–5 minutes after startup, the machine must be shut down immediately for inspection. Under normal conditions, the compression amount of the spring is around 3 mm; if it is too large, the spring seat or the adjusting shims for the O-ring that compresses the moving ring can be thinned. If the spring compression is less than 2–3 mm while the temperature of the stationary ring seat is very high, the number of springs should be reduced. Note that the reduction in the number of springs must be a multiple of 2: 2, 4, or 6, and the reduction should be done symmetrically. ” B. The spring force of the mechanical seal is too low or the compression amount is insufficient; as the rotating ring turns along with the shaft, due to bearing clearance, shaft deflection, and machine vibration, the rotating ring cannot remain in close contact with the stationary ring at all times, resulting in material leaking into the coolant. Solution: After removing the dispersion disc, the discharge sieve ring, and the discharge plate, start the main machine for 20–30 minutes. Then check the temperature of the static ring seat; it should be below 45 degrees Celsius. In particular, if the temperature is below 40 degrees Celsius, there is a risk of material leaking into the cooling fluid. Thin shims of 0.25~2 mm can be added behind the rotating ring of the mechanical seal, as well as in front of and behind the O-ring used for the rotating ring and the spring seat of the mechanical seal; this increases the pressure on the sealing surfaces of the rotating and stationary rings. The temperature of the stationary ring seat should be around 50~55 degrees when touched by hand. C. The gap between the rotating ring of the mechanical seal and the shaft is filled with material and dries out, preventing the rotating ring from moving freely. Material leaks through the sealing surface into the coolant, causing the coolant to change color. Solution: After installing the rotating ring, wind 6–8 layers of raw adhesive tape around the gap between the rotating ring and the shaft (the tape should be twisted into a rope shape, but not too tightly; excessive or tight winding will also prevent the rotating ring from moving freely), thereby preventing material from entering that gap and allowing the rotating ring to move freely. IV. Coolant (oil) entering the material: Under normal circumstances, it is difficult for oil to enter the material; oil may enter the material only when the static ring O-ring seal and the mechanical seal are severely damaged, and this occurs during shutdown. B: After installing the mechanical seal, the unit was put into use without conducting a no-load test (that is, without testing it without components such as the dispersion disk), and it was not possible to observe whether there was oil leakage from the mechanical seal. Solution: When installing the moving ring, it is important to ensure that there is sufficient clearance between the two pin holes on the moving ring seat and the two pins on the spring seat, so as to allow for smooth movement without any jamming. When testing the machine without a load, one can feel a very slight twisting motion when touching the stationary ring seat with their hand. When the torsion is excessive, oil may leak from the gap between the stationary ring seat and the discharge end cover. If oil leaks from the gap between the stationary ring seat and the shaft, it indicates that the machining precision of the mechanical seal surface is insufficient, and re-grinding is required. If oil leaks out from the gap between the static ring seat and the discharge end cover, it is because the clearance between the two drive pin holes in the dynamic ring seat and the two drive pins in the spring seat is too small, resulting in poor flexibility. When testing the machine without load, one can feel a significant twisting force when touching the static ring seat, and oil will leak out from the gap between it and the discharge end cover. V. The feed pump (diaphragm pump) does not operate, and no material comes out from the discharge pipe. A. After pressing the pump start button, no sound from the solenoid valve can be heard; however, the main motor can be jogged. a The 24V DC air switch in the electrical box provides protection; when the pump starts, the green indicator light comes on, but the electric pump does not operate and no oil is sprayed from the oil cover. Solution: Check whether there is any short circuit in the solenoid valve and the electric oil pump. b The 24V DC regulated switch-mode power supply has no output, and the green indicator light on the regulated switch-mode power supply is not lit. Solution: Check whether the 220V AC circuit breaker is in protective mode Has the overcurrent protection of the main motor’s thermal relay been activated? If it needs to be started (at this time, the two normally closed terminals below the red button are already connected; one of them does not have 220V voltage, while under normal conditions both terminals are energized), it can be activated by pressing the button, or it will recover automatically after half an hour. c. The 24V DC regulated switching power supply has no output, and the green indicator light on it is not lit. Solution: Check whether the 24V DC regulated switching power supply is damaged. d. No sound from the solenoid valve is heard after pressing the pump start button (at this time, oil is spraying inside the working oil cover of the electric pump). Solution: The solenoid valve is damaged. If there are no spare parts available, the intake pipe can be connected directly to the pressure regulator. After pressing the pump start button, the sound of the solenoid valve can be heard; however, no exhaust sound from the diaphragm pump is audible (at this time, oil is being sprayed from the working oil cover of the electric pump). Ⅰ. The O-ring of the internal main control valve in the diaphragm pump swells, preventing the main control valve from sliding freely. Replace the O-ring of the main valve inside the diaphragm pump. The reason for the swelling of the O-ring in the main control valve inside the diaphragm pump is that, during shutdown and cleaning, a solvent was accidentally spilled on the diaphragm pump; this solvent seeped into the main control valve through the threads connecting the silencer to the exhaust port of the diaphragm pump (the solvent could also enter the main control valve via the tiny pores on the outer surface of the silencer attached to the diaphragm pump), causing the O-ring to swell. Solution: Wrap Teflon tape around the muffler’s connecting threads, and put a half-used polyester bottle over the muffler. Ⅱ. There is material behind the main control valve, directional valve, and diaphragm backing (rubber) inside the diaphragm pump. The reason is that the screw used to tighten the diaphragm in the diaphragm chamber has loosened, allowing material to enter the diaphragm backing (rubber), as well as the directional valve and main control valve, which has resulted in damage to the rubber seals and prevented the diaphragm pump from functioning. Solution: Remove the inlet and outlet pipes, open the diaphragm chamber covers on both sides, replace the damaged seals, and tighten the compression screws on the diaphragm. f. After pressing the pump start button, a sound from the solenoid valve can be heard. When adjusting the pressure and air flow rate, pressure is indicated on the small pressure gauge. However, no exhaust sound from the diaphragm pump can be heard, or there might be just one or two sounds before it stops. On the surface, it seems that the diaphragm pump is damaged. The reason for this phenomenon is that after the diaphragm pump discharges the material, the material gets blocked at the check valve in the inlet pipe leading to the cylinder. Due to the counterforce, the diaphragm pump is unable to continue operating. This phenomenon occurs more frequently in vertical sand mills, where material sedimentation is more likely to happen. VI. Abnormal operation of the feed pump (diaphragm pump) resulting in low output (at this time, a venting sound can be heard from the diaphragm pump’s silencer). A. The air pressure is too low, or the flow rate of compressed air adjacent to the pressure regulator is set too low. B. The feed pipe below the diaphragm pump is blocked by dry material, resin, or other foreign objects. For materials such as fabric, cotton yarn, and plastic braided straps, the following handling method should be followed: The material to be processed must be thoroughly mixed. If thorough mixing is not possible, the flow rate of sanding during the first pass should be increased (to serve as a means of pre-dispersing the material), thereby preventing sedimentation and blockages. C. The feed pipe is cracked or the pipe joint is leaking air. D. The check valve seats or balls for material inlet and outlet inside the diaphragm pump are abnormally worn, preventing the check valves from closing. The main cause of abnormal wear is the presence of many small beads in the material, which wear out the check valve. E. In the diaphragm pump, the check valve balls for inlet and outlet are stuck by foreign objects, preventing the balls from moving up and down freely. VII. Damage to the mechanical seal
A. The coolant fails to circulate, or excessive pressure from the mechanical seal spring causes the coolant temperature to rise. Handling method: Refer to: 1. Solutions for reduced or no flow of coolant in mechanical seals: B. Impurities in the coolant; damaged filter screen at the oil inlet. Solution: Drain the coolant and clean the tank. Filter the coolant, then add it back to the tank. Finally, install a new filter screen. C. Impurities are present on the sealing surface during assembly, or the stationary ring of the mechanical seal removes metal from the shaft surface or other impurities, which are then carried to the sealing surface. Solution: During installation, pay attention to keeping it clean; do not press the stationary ring against the shaft – it must remain suspended above the rotating shaft. D. The cooling water pressure is too low, resulting in no flow of cooling water inside the copper coiled tube in the fuel tank. Solution: Open the upper cover of the chassis and touch the two cooling water pipe connectors with your hand. When water is flowing normally, there is a temperature difference between the two connectors – one is hot and the other is cold. If they are all hot, it can be determined that the water pressure is too low or there is a blockage. VIII. The main motor will not start. A. The load is too high (the viscosity of the material is high or too much grinding medium has been used); when the main unit attempts to start, the motor emits a dull sound and the thermal relay activates. At this point, the indicator light of the 24V switching power supply inside the electrical cabinet does not light up, and the feed pump also cannot start. Solution: Open the electrical enclosure to check whether the current setting on the thermal relay is too low. If it isn’t, adjust the viscosity of the material or the amount of grinding media used. B. If the material has high viscosity or too many grinding media are added, if the feeding speed of the diaphragm pump is too fast, or if the set values for temperature or pressure are exceeded, the red light on the control panel will turn on. At this time, the indicator light of the 24V switching power supply in the electrical box is on, and the feed pump cannot be started either. Solution: Adjust the viscosity of the material or the amount of grinding media according to process requirements and production conditions, as well as the feeding speed of the diaphragm pump (by adjusting the air flow rate). C. The thermal relay is faulty; in this case, the indicator light of the 24V switching power supply inside the electrical enclosure does not light up. Solution: Replace the thermal relay. D. The thermal relay’s frequent-start protection is activated; the main motor current is less than the set value of the thermal relay. Solution: Replace the thermal relay. E. During the startup of the main motor, the current is very high; the motor emits a dull noise, and the thermal relay activates immediately to provide protection. Solution: The conversion between star and delta modes is not proper; check the AC contactor and auxiliary contacts. F. The 220V air switch is providing protection, or the 24V DC regulated power supply is damaged and thus no output is available; the indicator light of the 24V power supply inside the electrical cabinet does not light up. Solution: Replace the 24V regulated switch DC power supply. IX. Excessive load when starting the main motor: A. High viscosity of the material, excessive amount of grinding media, or too fast feeding speed of the diaphragm pump (in this case, the pressure inside the cylinder exceeds 0.05 MP). Solution: Reduce the viscosity of the material, decrease the weight of the grinding media, or slow down the feeding speed of the diaphragm pump (by adjusting the air flow rate). B. The main machine fails to start immediately after the feed pump is activated (at this point, the pressure inside the cylinder increases; when starting up, the main motor produces a relatively dull sound). Solution: Remove the discharge plug or rotate the gland above the check valve to relieve pressure. When it is known that there is material inside the cylinder, first start the main machine; then, while holding down the green button, activate the feed pump (this method is particularly suitable for materials with high viscosity). C. The discharge screen is severely clogged, resulting in little or no discharge. Solution: Remove the grinding media, disassemble the dispersion disc and the discharge screen, and use a thin blade to clean the gaps in the discharge screen.
X. Excessive mechanical vibration
A. Running the equipment without any grinding media after installing the dispersion disc causes permanent deformation of the dispersion shaft. Solution: Replace the dispersion shaft. B. The height of the aircraft’s footrests is not adjusted properly; adjust them again. C. Too little grinding media is loaded. XI. Intact or crushed (commonly known as crushed sand) grinding media come out together with the material. A. If the intact beads come out along with the material in large quantities, it must be that the discharge screen ring has been worn out. Solution: Replace the discharge screen ring. B. It comes out with the material in small quantities; upon close inspection, it is in the form of fine sand, and the presence of such broken sand is extremely detrimental to the internal and external scrapers. 1. When the grinding media wear down to a size slightly larger than the gap between the inner and outer scrapers, the pressure inside the cylinder together with the gap between the bearings causes the dispersion shaft to vibrate. This forces the grinding media of appropriate size to move into the side of the scraper gap that is larger; as the dispersion shaft rotates, it carries these media to the side of the gap that is smaller, where they are crushed and then exit along with the material. This creates a vicious cycle that further increases the size of the scraper gaps, resulting in even more severe sand fragmentation. Solution: Regularly screen the grinding media. 2. Bubbles are present within the grinding media, and their insufficient strength causes them to be broken by the dispersing disk. Solution: Replace them with grinding media of higher strength, and regularly screen the grinding media. 3. Installing the dispersion disc in the reverse direction can also cause sand fragmentation. 12. Damage to internal and external scrapers: When there is excessive broken sand, the gap between the scrapers widens further. The size of the worn zirconia beads matches this gap, making it easy for the scrapers to become damaged. Solution: Regularly screen and grind the media to remove broken sand and beads smaller than 1 mm. 13. The main motor makes a muffled sound when starting, and it is very difficult to start. A. The motor is missing one phase of power supply. Solution: Use a multimeter to check that one pair of contacts in the AC contactor is damaged or has poor contact. When replacing the AC contactor, pay attention to the coil voltage of 220V; some coils have two A1 terminals and one A2 terminal. If both wires are connected to A1, the 220V AC circuit breaker will provide protection. B. During testing, the rotation direction of the spindle was reversed, and the wiring was changed incorrectly when adjusting the phase. (Only for star-to-triangle conversion) Solution: Wiring changes are not allowed between the AC contactor and the motor; changes can only be made on the incoming line. For this method, use one hand to press the blue plastic ring at the mouth of the compressed air quick-connect fitting downward, while using the other hand to pull out the air tube. If the blue plastic ring at the mouth of the compressed air quick-connect fitting is not pressed down firmly before pulling the tube out, it will result in damage to the compressed air quick-connect fitting. The equipment shuts down frequently during operation, and the thermal relay trips repeatedly as a protection mechanism. Solution: It can be observed that the pressure inside the cylinder is very high at the time of shutdown, and the current drawn by the main motor is also high. The reason is that when the feed flow rate is adjusted, the pressure of the compressed air is low; once the air compressor starts up, the pressure of the compressed air increases, the feed flow rate rises, which in turn causes an increase in pressure inside the cylinder. The minimum start pressure of the air compressor should be ~0.5 Kg higher than the pressure used by the sanding machine.