Automotive Tire Screws Locking Principles and Precautions

Automotive Tire Screws Locking Principles and Precautions

Car Tire Screws Locking Principles and Precautions

Tire screws this let a lot of people have ignored the small things. The car's tire screws are very important just because it does not require special maintenance; usually, if it is not replaced, the tires can not use, so many people will ignore them, and even a lot of people never disassemble the tire screws. We look at the accident video or pictures on the network; sometimes, there will be a high-speed car wheel flying out of the accident, which is mainly due to the tire screws broken or loose. So what exactly is the use of tire screws in a car? How is it installed? What is its fastening and self-locking principle? What are the precautions in use? Today, we will discuss tire screw-related topics.

First of all, let's take a look at what is a tire screw, what role it has. Tire screws are screws that are installed on the wheel hub and connect the wheel, brake disc (brake drum), and the wheel hub. Its function is to connect the wheel reliably, the brake disk (brake drum), and the hub. As you know, the weight of the car is ultimately borne by the wheels, so the connection between the wheels and the body is realized through these screws. So, these tire screws bear the,e weight of the whole car and also have to transfer the torque output from the transmission to the wheels, which are subjected to both tensile force and shear force at the same time in the work of the dual role.

Steel Vibration-Damping Hex Head Screws for Sheet Metal: These steel screws are zinc plated to resist corrosion in wet environments. A rubber washer cushions the screw to resist loosening from vibration. They have a hex head for a secure grip with a wrench and a flange to reduce the risk of crushing thin metal. Screws penetrate 0.025" and thinner sheet metal. Length is measured from under the washer.

Hex Head Screws with Flat Washer: A freely rotating but permanently attached washer distributes pressure over a wider area than a flange, preventing damage to your material's surface. They are also known as Sems screws. Made from 18-8 stainless steel, these screws have good chemical resistance and may be mildly magnetic. Length is measured from under the head.

Hex Head Screws with Lock Washer: Also known as Sems screws, these screws have a permanently attached but freely rotating tooth lock washer that bites into the mating surface for vibration resistance. The zinc plating provides corrosion resistance in wet environments. Length is measured from under the head.

Match the thread spacing of mating components. Coarse threads are the industry standard; choose these screws if you don't know the threads per inch. Fine threads are closely spaced to prevent loosening from vibration.

Screws for Joining Sheet Metal to Wood: Able to penetrate overlapping sheets, these screws have a secure hold in wood. The hex head allows for a firm grip with a wrench, while a rubber washer provides a watertight seal. They're corrosion-resistant-coated steel to resist corrosion in wet environments and minimize reactions between dissimilar metals. Length is measured from under the washer.

The structure of a tire screw is straightforward: it consists of a screw, a nut, and a washer. According to the different structures of the screw, it can also be divided into single-head bolts and double-head bolts. Most cars nowadays have single-head bolts, and double-head bolts are generally used in small and medium-sized trucks. There are two types of single head bolts, one is the hub bolts + nuts, bolts with interference fit fixed installation in the hub, and then by the nut to fix the wheel, the general application of Japanese and Korean cars are more, the vast majority of trucks also use such a way. The advantage of this approach is that the wheel is more straightforward to locate, dismantling the wheel is more accessible, and has higher security. The disadvantage is that the tire screw replacement is more troublesome; some need to dismantle the wheel hub; the other is the wheel fixation bolts, threads directly processed in the hub, tire screws directly screwed in the hub, generally in Europe and the United States Department of the small cars are more often used. The advantage of this approach is that the tire screws are more accessible to disassemble and replace; the disadvantage is that the security is a little worse; if the tire screws are repeatedly disassembled many times, it will damage the threads on the wheel hub, then you have to replace the wheel hub.

Automotive tire screws are generally made of high-strength steel; in the head of the tire screws printed with the strength of the screw grade, there are 8.8, 10.9, and 12.9, several kinds, the greater the value of the higher strength. Here, 8.8, 10.9, and 12.9 refer to the performance level of the bolt labeling by two parts of the number, respectively, the nominal tensile strength of the bolt material value and flexural strength ratio value, generally with "X.Y," such as 4.8, 8.8, 10.9, 12.9 and so on. Performance level 8.8 bolt tensile strength of 800MPa, yield strength ratio of 0.8, yield strength of 800 × 0.8 = 640MPa; performance level 10.9 bolt tensile strength of 1,000MPa, yield strength ratio of 0.9, yield strength of 1,000 × 0.9 = 900MPa. Other and so on. Generally, the strength is 8.8 and above, and the bolt material for low-carbon alloy steel or medium-carbon steel is used by the heat treatment called high-strength bolts. Automobile tire screws are high-strength bolts, different models, and different loads; matching bolt strength is distinct, 10.9 is the most common, 8.8 is generally matched in the lower end of the model, and 12.9 is usually matched in heavy-duty trucks.

We look carefully, will find the car on the tire screws have installed four, five, six or even more, why is there such a difference? Is not the more tire screws, the safer it is?

The number of tire screws installed, the weight of the car, and the strength of the tire screws. Generally, in small vehicles, the weight is relatively light, with four tire screws being enough; in medium and large cars and SUVs, the car weight is more significant, generally needing at least five tire screws; and in the heavier models, more tire screws will be installed, and some trucks even have twelve tire screws, and the diameter of the bolts is also huge, the strength is very high, to adapt to the higher load capacity. However, we should not take the number of tire screws on the hero; the car's tire screws strength, number, etc., are precisely calculated and will take into account the car's worst working conditions, so there is a considerable margin of safety, in general, will not happen to break, loose and other phenomena, is almost safe. So no matter how many tire screws, can ensure driving safety, not the more the better, for example, some models use four 10.9 strength tire screws, another model uses five with the same diameter 8.8 strength tire screws, if the total strength calculation, four tire screws but higher.

Let's talk about the fastening and self-locking principle of tire screws.

Automobile tire screws generally use fine teeth of the triangle thread, bolt diameter between 14 ~ 20mm, thread pitch of 1 ~ 2mm. this triangle thread is theoretically self-locking: tire screws to the specified torque tightening, the nut and bolt threads fit each other, the huge friction between them can let the two remain stationary, i.e., self-locking. At the same time, the bolt undergoes elastic deformation, fixing the wheel and brake disk (brake drum) tightly to the hub. The use of fine pitch can increase the friction area between the threads, and the anti-loosening effect is better. Nowadays, more and more fine threads are used in automobiles, that is, its anti-loosening effect is better.

However, when the car is running, the wheels are subjected to alternating loads, and the tire screws are also subjected to continuous shock and vibration. In this case, in a moment, tire bolts and nuts between the friction disappeared, tire screws have the possibility of loosening; In addition, the car in the acceleration and braking, due to the direction of rotation of the wheel and tire screws in the opposite direction of the fastening direction, which will produce a "loosening torque", which will lead to tire screws loosening. Therefore, tire screws must have a reliable self-locking anti-loosening device. Now the car tire screws, the vast majority of friction self-locking anti-loosening device, such as the addition of elastic washers, wheels and nuts are processed into a matching taper or sphere, the use of spherical spring washers and so on. They can compensate for the gap caused by the tire screws in the moment of shock and vibration, which also prevents the tire screws from loosening.

There are also some models, the use of "inside the opposite outside" type of tire screws, that is, the left side of the wheel tire screws using the left-hand thread, the right side of the wheel tire screws using the right-hand thread, so that the tightening direction of the threads and the direction of rotation of the wheel to maintain the same, it is weakened or even eliminated the "loosening torque "to avoid automatic loosening of the tire screw. This kind of left-hand tire screws, generally in the head of the screw marked with a capital letter "L", or in the central position of the nut cut a groove, in order to distinguish from the right-hand bolt. This kind of left-hand thread tire screws were widely used in the early Dongfeng, Jiefang and other vehicles, and now there are still some medium and light trucks, light buses, small off-road vehicles and so on adopting such a design.

But why do heavy-duty trucks as well as small cars not use this design now? This is mainly because, heavy-duty trucks generally use dual tires and mounted, single-nut fixed way to install tires, tire nuts using a spherical spring washer, can prevent the nut from loosening itself; and in the small car, because it is accelerated and braked faster, so whether it is accelerated or braked will produce a loosening torque, the use of the left-handed tire screws is not very meaningful. Therefore, these two models no longer use left-hand threaded tire screws, which is conducive to reducing the number of parts and components, easy to disassemble and repair.

So what do we need to pay attention to when disassembling tire screws? When disassembling, we should pay attention to the diagonal uniform loosening, so that the wrench is perpendicular to the tire screws, to avoid the tire screws being subjected to bending moments, which in turn cause the screws to break. When installing, pay attention to the diagonal installation, diagonal sub-even tightening, do not tighten at once, not to mention the screws are installed on one side of the wheel, so as to make the screws even force, to avoid deformation of the wheel rim. After dropping the jack and landing the wheel on the ground, use a torque wrench to tighten the tire screws to the specified torque, generally between 15 to 20 kg force, if too loose the screws are easy to loosen, too tight will tighten the wheel rim deformation, and even lead to the screws stretching and breaking. If there is no torque wrench, the average adult man just hold the end of the tire wrench with both hands and torque it as hard as he can, this force is enough.

In addition, try not to use the air cannon tool fastening tire screws; this air cannon tool generally has too much torque, which will lead to tire screws stretching, and even stretching to the yield point of the tire screws, resulting in irreversible plastic deformation of the tire screws, so that the tire screws can not be banned anymore, must be replaced. There are tire screws that do not repeatedly disassemble; each disassembly is an injury to the threads, the friction between the bolt and the nut will become smaller and smaller, the self-locking effect of the bolt is weakened or even disappear, the tire screws will not be able to tighten, generally disassembled more than ten times of tire screws on the recommendation of the replacement. There are also tire screws that should not be coated with butter so that although the future disassembly is easy, the butter will reduce the friction between the threads, and reduce the self-locking effect of the screws, resulting in the possibility of screw loosening.

The installation of automobile wheels mainly relies on tire screws, which are reliably connected to wheels, brake discs (drums), and hubs through a specific locking principle.

The design and installation of tire screws follow certain principles and precautions to ensure safety and longevity. First of all, tire screws usually use fine tooth triangular threads, bolt diameter between 14 ~ 20mm, and pitch 1 ~ 2mm. This design makes tire screws in tightening to the specified torque, and the nut and bolt threads fit each other to form a vast friction to achieve the self-locking effect, that is, to maintain a static and motionless state. At the same time, the bolt undergoes elastic deformation, which holds the wheel and brake disk (drum) tightly to the hub. Using a fine pitch increases the friction area between the threads and improves the anti-loosening effect.

However, when the car is in motion, the wheels are subjected to alternating loads and constant shock and vibration, which may cause the friction between the tire screws and nuts to disappear instantly, thus creating the possibility of loosening. In addition, when the car accelerates and brakes, due to the direction of rotation of the wheel is opposite to the tightening direction of the tire screw, it will produce a "loosening moment", which will further lead to the loosening of the tire screw. Therefore, tire screws must have a reliable self-locking and anti-loosening device. Most modern automotive tire screws use friction self-locking anti-loosening devices, such as the addition of elastic washers, wheels, and nuts processed into matching taper or sphere, the use of spherical spring washers, etc. These measures can be compensated for the tire screws in the shock and vibration caused by the gap to prevent the screws from loosening.

Precautions include ensuring that the tire screws are tightened by the specified torque, regularly checking the tightness of the tire screws, especially after driving on uneven or poor road conditions to see if the tire screws have loosened, and replacing deteriorated washers or damaged screws promptly. In addition, tire screws should not be tightened or disassembled with unsuitable tools or methods to avoid damaging the threads or causing safety hazards.

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