Common Fault Analysis and Solutions for Bending Machines
I. Mechanical Bending Machines
Fault 1: Excessive clearance between the slide and guide rail, producing abnormal noise.
This fault is caused by long-term use of the guide rail, resulting in increased clearance due to wear. It is necessary to inspect the wear level of the guide rail and determine whether to replace it and readjust it to the required clearance based on the degree of wear.
Fault 2: Failure of the backgauge transmission. The failure is due to the disengagement of the key bar between the transmission shaft and the synchronous pulley or slippage of the synchronous belt.
For this type of fault, the key bar and synchronous belt need to be reassembled, and the electrical components should be checked.
Fault 3: Excessive deviation in parallelism between the backgauge beam linear guide and the mold centerline.
For this fault, the "X" axis synchronous belt needs to be loosened and readjusted to within the parallelism tolerance range, and then reinstalled.
Fault 4: Loose connection between the hydraulic cylinder and the slide, causing inaccurate bending angles or the machine unable to find the reference point.
For this fault, the connection nut between the slide and the hydraulic cylinder needs to be checked and tightened again.
II. Hydraulic Bending Machines
Fault 1: Lack of pressure in the hydraulic system.
1. Check if the solenoid coil of the proportional relief valve is powered and if the voltage of the proportional solenoid coil meets the requirements. If not, check for related electrical issues.
2. Check if the cartridge valve is stuck or if the main spool is stuck, and whether the damping orifice is blocked. If any of these are the causes, disassemble the relief valve, clean it, and reinstall it.
3. Three-phase power phase shifting, causing motor reversal.
Fault 2: Slow-down or prolonged pause of the slide during rapid movement.
1. Check if the oil level in the tank is too low and if the filling port is submerged. Inadequate filling may occur if the upper chamber of the cylinder is emptied during rapid movement. Refill the oil properly.
In general, oil leakage in hydraulic bending machines can be caused by design and manufacturing issues, as well as equipment maintenance and upkeep. Oil leakage situations in practice are complex, often resulting from a combination of various causes and circumstances. However, most oil leaks in the hydraulic system of hydraulic bending machines are caused by seal failures.
1. Poor Quality of Pipelines
Hydraulic bending machines use various types of pipelines, including steel pipes, copper pipes, rubber hoses, nylon pipes, and plastic pipes. If inferior pipelines are used in the hydraulic system of a bending machine, they have low pressure-bearing capacity and a short service life, leading to oil leakage shortly after use. Poor-quality rigid pipes are characterized by uneven wall thickness, resulting in decreased pressure-bearing capacity. Inferior rubber hoses have poor rubber quality, insufficient tensile strength of the steel wire layer, and loose braiding, leading to reduced pressure-bearing capacity. Under the impact of hydraulic pressure, the pipelines are prone to damage and oil leakage. Therefore, when purchasing hydraulic pipes, it is necessary to choose pipes produced by reputable manufacturers that meet the pressure requirements and have a suitable service life.
2. Improper Installation of Pipelines
During the installation of rigid pipes, they should be bent with the specified bending radius; otherwise, the pipelines will experience different internal stresses, gradually leading to leakage under the action of hydraulic pressure. If the bending radius of rigid pipes is too small, the outer wall of the pipeline becomes thinner, and wrinkles appear on the inner wall, resulting in high internal stress at the bending point and significantly reduced strength. In the case of flexible hoses, improper bending radius or hose twisting can cause hose damage and oil leakage. When hydraulic hoses are improperly installed, slight twisting may reduce their strength and cause detachment at the joints, leading to bubbling at the hose joints. Excessive twisting of hoses during installation or use can easily damage the hoses under high pressure.
When flexible hoses are excessively stretched or deformed during installation, the layers may separate, reducing their pressure-bearing capacity. Under high pressure, hoses may experience longitudinal shrinkage or elongation, typically within a range of +2% to -4% of their normal length. If the hoses are too short during installation, they will be subjected to significant tensile stress during operation, leading to failures such as rupture or detachment. Additionally, if the span of the hose is too large, the weight of the hose itself and the weight of the hydraulic fluid will exert a greater tensile force on the hose, which can also lead to the aforementioned failures.
Under low-temperature conditions, improper bending or repair of hydraulic hoses can cause cracks on the outer surface of the hoses, resulting in oil leakage. Cracking of the hose's outer surface is more common in extremely cold winters, especially when hydraulic hoses are bent in very cold weather or low-temperature states. During use, if cracks are found on the outer surface of the hose, it is necessary to promptly inspect if there are cracks on the inner rubber of the hose. If cracks are present, the hose should be replaced immediately.
3. Leakage at Pipeline Joints
Oil leakage in the hydraulic system of bending machines most commonly occurs at pipeline joints. The fundamental reason is poor sealing at the joints, where the sealing oil pressure is lower than the peak hydraulic pressure. In such cases, disassembling, cleaning, and re-tightening the joints can solve the problem.
4. Oil Leakage Due to Damaged Rubber Seals
(1) Excessive gap between sealing surfaces. There is always a certain gap between moving sealing surfaces. During operation, under the pressure of hydraulic oil, a portion of the rubber seal is squeezed into the gap. When the working pressure is constant, the gap between the sealing surfaces expands, increasing the portion of the rubber seal being squeezed and the shear force it bears, making it more susceptible to tearing.
(2) Excessive working pressure and the influence of oil pressure pulsation. If the working pressure is too high, more of the rubber seal will be squeezed into the gap, intensifying the abrasion and cutting effects on the rubber seal. Increased oil pressure pulsation frequency will increase the cutting frequency of the rubber seal, causing fatigue cracks.
(3) Influence of working temperature. High working temperatures soften the rubber, reducing its elasticity and contact pressure with the sealing surface, resulting in poor sealing performance. Additionally, high temperatures accelerate the aging of rubber seals, further reducing their elasticity and strength. On the other hand, low temperatures make the rubber hard and brittle, making it prone to cracking under external forces, especially shear forces, leading to rupture.
(4) Rough sealing surfaces. The smoothness of sealing surfaces greatly affects the service life of rubber seals. Rough surfaces accelerate the wear of rubber seals.
(5) Material and dimensional accuracy not meeting requirements. Different rubber materials used for rubber seals have different characteristics, some are not heat-resistant, some are not oil-resistant, and some are not cold-resistant. If mixed in unfavorable working environments, rubber seals may prematurely fail. The dimensional accuracy between the rubber seal and the sealing surface should also meet certain standards. Excessive interference or clearance will result in poor sealing performance.
5. Oil Leakage Caused by Contamination in the Hydraulic System of Bending Machines
The contamination in the hydraulic system of bending machines can have various causes. During the processing, assembly, testing, storage, and transportation of the hydraulic system and components, harmful substances such as molding sand, chips, abrasives, welding slag, rust flakes, dust, fibers, and rubber fragments may not be thoroughly removed and cleaned before and after the assembly of the hydraulic system, leading to their presence in the system. During operation, windblown sand, dust, and moisture can enter the system through filling ports. When the working temperature of the hydraulic oil exceeds a certain value, the oil will oxidize and deteriorate.
Contamination in the hydraulic system of bending machines can result in increased wear of hydraulic components, decreased sealing performance, reduced volumetric efficiency, and internal and external leakage. The clearance between the mating surfaces of hydraulic components is generally between 5 to 15 μm. For valve components, when contamination particles enter the mating surfaces, they interact, scratch the surfaces, and generate new abrasive particles, intensifying wear and enlarging the clearances, leading to internal leakage or oil bypass within the valve. For pump components, contamination particles can increase the wear on the moving parts (such as the pistons and cylinder bores, cylinder bodies, and distributor plates of piston pumps; the top of the blades and inner surfaces of the stator in vane pumps), causing increased clearances and increased leakage, resulting in reduced volumetric efficiency of the pump. For hydraulic cylinders, contamination particles can accelerate the wear of sealing devices, significantly increase leakage, reduce power, and even cause cylinder barrels or piston rods to be damaged and scrapped. For hydraulic hoses, contamination particles can intensify the wear on the inner walls of the hoses, and even scratch the walls. This is particularly true when the fluid flow is high and unstable (fast flow and large pressure pulsation), which can cause the material on the inner wall of the hose to be impacted and peeled off, ultimately leading to hose rupture and oil leakage.
When water is present in the hydraulic oil, it can cause the formation of emulsions, reducing the lubrication and anticorrosion properties of the hydraulic oil and accelerating the wear and corrosion of hydraulic components and the inner walls of hydraulic hoses. When there are a large number of air bubbles in the hydraulic oil, the bubbles will be compressed in high-pressure areas, and the surrounding oil will rapidly flow into the space previously occupied by the bubbles, causing strong hydraulic impacts. Under the impact of high-pressure liquid mixtures, the inner walls of hydraulic components and hydraulic hoses can be corroded and peeled off. All of these situations can eventually lead to internal and external leakage of hydraulic components and hydraulic hoses.
Additionally, the external surfaces of hydraulic components and hydraulic pipelines often come into contact with moisture, oil sludge, and dust. If the protective layer is damaged, corrosion can easily occur, resulting in reduced strength of hydraulic components and hydraulic pipelines, leading to oil leakage from areas of high pressure, high temperature, stress concentration, or severe bending and twisting of hydraulic pipelines.
6. Oil Leakage Caused by Excessive Oil Temperature
The temperature of the hydraulic system in bending machines is generally maintained between 35 to 60°C, with a maximum temperature not exceeding 80°C. Under normal oil temperature conditions, the hydraulic oil performs well in various aspects. However, when the oil temperature becomes too high, the viscosity of the hydraulic oil decreases, the lubricating oil film becomes thinner and more susceptible to damage, the lubrication performance deteriorates, mechanical wear increases, and the volumetric efficiency decreases, leading to increased internal leakage of the hydraulic oil. At the same time, leakage and wear can cause the system temperature to rise, which in turn exacerbates leakage and wear, potentially creating a vicious cycle that quickly leads to the failure of hydraulic components. High oil temperature accelerates the aging of rubber seals, reducing their sealing performance and ultimately causing seal failure and oil leakage. Moreover, high oil temperature accelerates the aging of rubber hoses, causing them to become stiff and develop cracks. Under the influence of high temperature and high pressure, such hoses can eventually burst and leak oil. Therefore, it is important to control the oil temperature of the system within a normal range.
