Abnormal wear of Diesel forklift tires and preventive measures

There are generally six abnormal wear situations of forklift tires during use: The first is abnormal wear in the middle of the tire crown; The second is the excessive wear on both shoulders of the tire crown. The third is abnormal and uneven wear on the inner (or outer) side of the tire crown of the steering wheel. The fourth is that the tire crown shows serrated wear. The sixth is local wear of the tire crown. The main manifestations are uneven tread wear, delamination between fabric layers, loose and broken cord, and the resulting tire body rupture. When a forklift is in motion, the forces acting on various parts of the tires are rather complex: there is a vertical reaction force in the vertical direction, and longitudinal and transverse reactions in the tangential direction, which cause the tires to have overall or local relative slippage in these directions, leading to tread wear and deformation. Tensile and compressive forces occur inside the carcass, causing material fatigue and thereby reducing its strength. Shear stress is generated between the fabric layers. When this stress exceeds the adsorption force between the fabric layer and the rubber layer, the cord will become loose. During tire deformation, frictional heat is also generated between the outer and inner tires. Some of the heat is dissipated into the air, while the rest accumulates, causing the tire temperature to rise and its performance to decline. This leads to an increase in abnormal tire wear, resulting in loose and broken cords and tire body rupture.

I. Types of Wear: Abnormal wear of forklift tires during use generally includes six situations: The first is excessive wear in the middle of the tire crown; The second is the excessive wear on both shoulders of the tire crown. The third is abnormal and uneven wear on the inner (or outer) side of the tire crown of the steering wheel. The fourth is that the tire crown shows serrated wear. The sixth is local wear of the tire crown. The main manifestations are uneven tread wear, delamination between fabric layers, loose and broken cord, and the resulting tire body rupture. When a forklift is in motion, the forces acting on various parts of the tires are rather complex: there is a vertical reaction force in the vertical direction, and longitudinal and transverse reactions in the tangential direction, which cause the tires to have overall or local relative slippage in these directions, leading to tread wear and deformation. Tensile and compressive forces occur inside the carcass, causing material fatigue and thereby reducing its strength. Shear stress is generated between the fabric layers. When this stress exceeds the adsorption force between the fabric layer and the rubber layer, the cord will become loose. During tire deformation, frictional heat is also generated between the outer and inner tires. Some of the heat is dissipated into the air, while the rest accumulates, causing the tire temperature to rise and its performance to decline. This leads to an increase in abnormal tire wear, resulting in loose and broken cords and tire body rupture.

Ii. Causes of Wear (1) Improper Use ① Under certain load and driving conditions, the tires of forklifts have an appropriate tire pressure. When the tire pressure is lower than the standard value and the forklift is driven, the radial deformation of the tires increases, and excessive deflection occurs on both sides, causing the tire crown to touch the ground on both sides, the inner wall of the tire side to be compressed, the outer wall of the tire side to be stretched, and the cord inside the tire body to undergo significant deformation and alternating stress. Periodic compression deformation will accelerate the fatigue damage of the cord, increase the relative sliding between the cord layer of the tire and the tire and the ground, increase the heat generated by friction, cause the tire temperature to rise sharply, reduce the tensile strength of the rubber, loosen the cord and cause local delamination. When encountering obstacles and being impacted, a blowout will occur. The uneven pressure on the tread causes severe wear on the shoulder of the tire, resulting in a "bridge effect", and the tread appears toothed or wavy. The concave parts of tire treads are prone to embedding nails and stones on the road, causing mechanical damage. The rolling resistance of the carcass increases, and the fuel consumption rises. Tests show that when the tire pressure is 20% to 25% lower than the standard value, fuel consumption increases by 20% accordingly. When driving with tire pressure higher than the standard value, the center of the tire crown touches the ground, reducing the contact area between the tire and the road surface, increasing the load per unit area, and intensifying the wear in the middle of the tire crown. When the cord of a tire is overly stretched, the stress on the cord of the tire body increases, the fatigue process of the cord accelerates, causing the cord to break and resulting in an early blowout of the tire. Under certain loads and tire pressures, as the vehicle speed increases, the deformation frequency of the tires, the vibration of the tire body, and the circumferential and lateral twisting deformation of the tires (forming rest waves) also increase accordingly. The heat generated per unit time due to friction increases, and the working performance of the tires declines. In severe cases, the fabric layer may break and the tread may peel off, accelerating the wear and damage of the tires. Under a certain tire pressure, overloading the tire will increase its deflection deformation, and the stress on the cord fabric and cord will increase. This can easily lead to the cord breaking, loosening and delamination of the cord fabric at the tire wall. The force on the cord of the tire body will exceed the design allowable stress and the ground contact pressure of the tire, generating more heat, raising the temperature of the tire body and reducing its load-bearing capacity. At the same time, due to the contact between the tire shoulder and the ground, wear occurs. Especially when encountering obstacles, even a small stone can cause the tire crown to burst. Practical experience has shown that when driving on turns and uneven roads, if the tire load exceeds 20%, the driving range will be shortened by 35%. When it exceeds 50%, shorten by 59%. When it exceeds 100%, shorten it by more than 80%. ④ Road conditions also have a significant impact on the service life of tires. They affect the friction between the tires and the ground as well as the dynamic loads the tires are subjected to. ⑤ High temperatures will reduce the tensile strength, elongation and hardness of rubber, decrease the adhesion strength between rubber and cord, and also accelerate the aging of rubber. For tires exposed to high temperatures, especially those that have aged, when they skid sideways or roll over obstacles, it is very easy for the tire crown tread to tear. Due to the aging of the sidewall rubber causing cracks and severe deformation of the sidewall leading to the separation of the cord from the rubber in the carcass layer, once a local area of the tire is subjected to sudden load, a blowout is very likely to occur. When tires are corroded by grease, acidic or alkaline substances and exposed to high temperatures for a long time, their physical and chemical properties will change, their load-carrying capacity will be greatly reduced, and they are also highly prone to blowouts during use. In addition, tires that have been corroded by oil may experience blocky peeling of the air seal layer, small areas of rubber detachment at the tire orifice, and the separation of the tire cord from the rubber. Since the patch cannot be compatible with oil-impregnated rubber, even if the damage wound on the tire is very small, there is no possibility of repair. Due to the different loads distributed to the front and rear axles, the distinct working characteristics of the drive wheels and steering wheels, and the varying road conditions, the wear conditions of each tire are inconsistent. If tires of the same factory, size, structure, grade and pattern are not replaced on both sides of the same axle, it will accelerate the wear of the tires. During use, if proper matching and regular rotation are not paid attention to, resulting in uneven load on the tires, it will also accelerate tire wear. (2) Changes in the technical condition of the driving mechanism ① Changes in the camber Angle of the wheels. When the gap between the main pin and the main pin bushing is too large and the main pin hole of the rear axle is excessively worn, the camber Angle of the wheel will deviate from the design value. If the lateral reaction force generated by the ground on the tire reaches the adhesion limit of the wheel, lateral sliding will occur between the wheel and the ground, and the wheel plane will deviate from the direction of wheel travel, resulting in side deviation, or even relative sliding. Lateral frictional force is generated on the contact surface, causing uneven wear of the tire. ② Changes occur in the anterior beam. The toe-in is designed to reduce or eliminate the deviation of wheels from a straight line caused by the camber of the wheels. The toe-in value is generally 8 to 10mm. When the wheel is tilted outward to a certain extent, if the toe-in is too small, the tread and crown will wear in a serrated pattern from the inside to the outside; if the toe-in is too large, the tread and crown will wear in a serrated pattern from the outside to the inside. ③ There are changes in tire balance and wheel alignment. Poor static or dynamic balance of tires, inaccurate wheel alignment, loose hub bearings, excessive rim shape and position tolerances, mismatched ball joints of tie rods, and excessive clearance of pin bushings can all cause wheel jolting, jumping or swaying, leading to uneven wear of the tire crown in a wavy or disc-like pattern. Improper adjustment of the drum clearance of the service brake, uneven braking force on each wheel or braking drag can also cause abnormal wear of the tire tread. (3) During the operation of a forklift with poor driving skills, if the operation is improper, such as starting quickly, the slippage between the tires and the road surface increases, and emergency braking is frequently used during driving and operation, it will cause an increase in the driving resistance of the tires, resulting in local wear of the tire tread and crown. A single emergency brake can wear off a pattern height of 0.9mm, which is equivalent to the wear amount after driving 4,000 kilometers under normal conditions. When driving, carelessly passing over obstacles can cause local deformation of the tires or scratch the tread, leading to their damage.

Iii. Preventive Measures for Abnormal Wear and Tear (1) Strengthen the maintenance of tires and follow the "Four Diligations" (i.e., frequently check tire pressure, frequently check tire temperature, frequently dig stones, and frequently plug small holes). Inflate the tires according to the specified pressure and regularly check and adjust the tire pressure under cold conditions and certain loads, at least once a month. In summer, due to the high ambient temperature, if the tire temperature is found to be too high, the frequency of stopping should be appropriately increased. Avoid direct sunlight on the tires. It is advisable to park the forks in a shady place and do not use cold water to cool them down or release air to reduce pressure. When parking outdoors for a long time in winter, wooden boards should be placed under the tires. Do not accelerate immediately when starting. Wait until the tires get warm before returning to normal driving. Metal pieces, glass and crushed stones and other debris embedded between the tire treads should be removed in a timely manner. After removing the embedded debris, if the wound has reached the tire body, a new tire should be replaced. It is necessary to check the tires in a timely manner for punctures, cuts, bulges and cracks, etc. If there are deep holes, they should be filled with raw rubber. (2) The maintenance quality of raising the chassis should be enhanced. Timely inspection and correction of wheel alignment should be carried out to ensure that the toe-in and camber angles meet the design requirements. Check if there are any cracks, deformations or obvious corrosions on the rim. If so, repair or replace it with a high-quality rim in time to ensure that the rim matches the tire. Add grease in a timely manner as per regulations and adjust the clearance of the hub bearing, the ball joint of the tie rod and the main pin bushing to the design value. Keep the tires balanced. If they are unbalanced, a dynamic balance test should be conducted on the wheels. Regularly check the valve exhaust to determine if oil has entered the tires. Once oil is found in the tires, remove the tires immediately for cleaning and check the air seals at the same time. When changing tires in winter, place the tires in a greenhouse to restore their elasticity. When installing the rims, apply soap solution to the tire orifice to prevent damage to the orifice. The new model should be worn out and driven for about 200 kilometers before it can be used normally. The clearance between the brake shoes of the service brake should be adjusted to the design value without any drag. There should be no oil leakage from the hub oil seal and the brake hydraulic cylinder to prevent oil from dripping onto the tires and wetting the rubber. The lateral and radial swing amounts of the wheel assembly should meet the requirements. (3) Improve driving skills. When starting, slowly lift the clutch pedal and start smoothly. The maximum speed during driving should not exceed the speed limit of the tire grade. During driving, sudden acceleration, braking and steering should be avoided as much as possible. When driving, be cautious of large, sharp and sharp materials scattered on the road. When encountering obstacles such as stones and pits, one should slow down or avoid them. (4) Reasonable selection and matching of tires: The tire specifications for forklifts should be determined based on the static loads generated by the forklift's own weight and the weight of the goods, as well as the dynamic loads produced during the forklift's operation, taking into account the road surface and vehicle speed factors. Tires should be mounted on rims of specified specifications. The same axle should be equipped with tires of the same brand, specification, pattern and grade. When changing tires, the entire vehicle should be changed on the same axis. The tires used should be compatible with the maximum designed speed. When changing tire positions, the front wheels should be fitted with tires that have less external injuries and less wear as much as possible. After the tire position is changed, the air pressure should be readjust according to the requirements of the new tire position. The appropriate tread pattern should be selected based on the driving conditions. When installing patterned tires, pay attention to the marking of the wheel's rolling direction. (5) Pay attention to the balance of cargo loading and prevent tire overloading. Do not compensate for tire overloading by increasing tire pressure.