What is a trapezoidal thread
A trapezoidal thread is a type of running thread, the profile of which has the shape of an equilateral trapezoid. Its main purpose is the transfer of rotary motion into translational motion with the ability to withstand significant axial loads. Thanks to this geometry, it is widely used in machine tools, lifting mechanisms, jacks, presses and other devices where strength and reliability of work are important. The angle at the top of the trapezoid thread is usuallyi.e 30°, which provides a good combination of smoothness of movement, wear resistance and the ability to work under heavy loads. Such carving is marked with a symbol Tr, followed by the diameter and pitch (for example, Tr40×7). In the industry, the trapezoidal thread is considered the "golden mean" between the strength of the rectangular thread and the universalmetric. It combines relative ease of manufacture and high operational characteristics, which makes it popular in mechanical engineering.
To better understand the role of the trapezoidal thread (Fig. 1), it is important to compare it with the most common types:
- Metric thread
Used in conventional bolted connections. It has a triangular profile at an angle of 60°. Its main advantage is universality and standardization. But it is not designed to transmit large forces in the mechanisms, rather it serves to fix parts.
- Rectangular thread
It has a rectangular profile. It is ideal for transmitting loads with minimal efficiency losses, but its production is more difficult and expensive. The processing of such a thread requires high-precision equipment, and the fracture strength may be lower.
- Trapezoidal carving
Occupies an intermediate place. It is easier to manufacture than a rectangular one, but at the same time it can withstand much more load than a metric one. That is why it has become the standard in structures where durability, smoothness of movement and endurance are required.
Design features
The trapezoidal carving is distinctive profile form in the form of an equilateral trapezoid. Unlike a metric thread with a sharp triangular contour, a trapezoid thread has a wider contact surface between turns. This allows for a more even distribution of the load, reduces the pressure on individual areas and increases the service life. The upper and lower bases of the trapezoid form the support surfaces, the sides are responsible for the smoothness of the movement, and the angle of the profile determines the ability to withstand the load and affects the durability. Thanks to these features, the trapezoidal thread provides high efficiency in mechanisms operating under significant axial loads. In the design of the trapezoidal thread are important profile angle, pitch and diameter. The standard is an angle of 30 degrees, which is considered the optimal compromise between strength, smoothness of movement and ease of manufacture. The pitch of the thread determines the distance between adjacent turns and directly affects the speed of movement of the nut. A small pitch provides high precision and smoothness, while a large pitch allows for fast movement with fewer revolutions. The diameter of the thread determines its load capacity: the larger it is, the greater the load the screw can withstand. The combination of these three parameters is selected according to the operating conditions of the mechanism. Depending on the requirements for the mechanism, the trapezoidal thread can be performed in different variations. A right-hand thread is the most common: the nut moves forward when turned clockwise. The left-hand thread is used where self-unscrewing is possible under load in the opposite direction. The one-way thread has only one turn and is characterized by high precision and smoothness of operation, but at the same time ensures slow movement of the nut. The multi-turn thread consists of several parallel turns, which allows you to get a much larger stroke of the nut in one turn of the screw. This option is used in cases where the feed speed is important.
Basic standards and classification
Trapezoidal thread belongs to specialized threaded connections, therefore its use is strictly regulated by international and national standards. They define profile geometry, pitch parameters, tolerances, and marking rules. This is important, because even minor deviations can cause the mechanism to malfunction. The most common are international standards ISO and FROM, which ensure the unification of the production of parts in different countries. For example, ISO 2904 and ISO 2906 regulate the profiles and basic parameters of trapezoidal threads, while DIN 103 is widely used by European manufacturers. Both standardization systems allow you to choose a thread taking into account operating conditions, load and durability. In Ukraine, Soviet regulations, based on nand Soviet GOSTs, but is gradually integrated with international standards. The profile of the trapezoidal thread was established by GOST 9484-81, it is an equilateral trapezoid with an angle at the top of 30o (Fig. 2, a). The notation in the form of TrD×P is most often used, where Tr indicates a trapezoidal profile, d is the outer diameter of the thread in millimeters, and P is the pitch of the thread.
Rice. 1 Trapezoidal thread
Rice. 2 Profile (a) and examples of notation (b) trapezoidal thread
For example, the marking Tr20×6 means that the thread has a diameter of 20 mm and a pitch of 6 mm. In the case of a multi-turn thread, one more parameter is added — stroke, i.e., the complete movement interval in one revolution (Fig. 2, b). Then the marking can look like this: Tr20×6(P2), where it is indicated that the thread is three-pass with a pitch of 6 mm and a stroke of 20 mm, that is, after the outer diameter, the thread stroke is indicated, in brackets - the letter P and the value of the thread pitch, for example: Tr. For a trapezoidal thread, a choice material plays a key role, because it is subjected to significant loads and friction. The most common material is steel, which provides strength, durability and withstands high mechanical loads. Alloy or hardened steels are used for components operating in high-wear environments. Bronze and brass are used where wear resistance and smoothness of operation are important, for example, in the lead screws of machine tools. Stainless steel is required for aggressive environments or the food industry, where corrosion resistance is required. Polymers should be noted separately - they are used for light loads, reduce the weight of the structure and do not require intensive lubrication.
.jpg)
Rice. 3 Trapezoidal thread (product appearance Pin with trapezoidal thread DIN 975)
Materials and manufacturing technology
Trapezoidal thread is widely used in industry due to its strength, reliability and versatility, but it is the material and manufacturing technology that determine its durability and efficiency. The choice of material directly depends on the operating conditions: loads, temperature, environmental impact, as well as requirements for wear resistance and accuracy. In addition, the method of thread production is equally important, because the quality of the surface, the accuracy of the profile and the cost of the finished part depend on it.
Popular materials steel, bronze, brass, stainless steel and modern polymers are used for making trapezoidal threads. Steel is considered universal and the most common option, as it provides high strength and can withstand significant loads. Alloyed or hardened steels with increased resistance to wear are used for parts that must work in difficult conditions. Bronze is noted for its excellent anti-friction properties, so bronze nuts in combination with steel screws are often used in machine tool construction. This allows you to achieve smoothness of movement, minimize friction and extend the service life of the screw-nut pair. Brass is used less often, but it also has good anti-friction characteristics and is resistant to corrosion, which makes it appropriate in some mechanisms of medium power. Stainless steel is used where equipment operates in wet or aggressive environments, such as in the chemical or food industry. For less loaded mechanisms, in order to reduce weight and cost, polymer materials that do not require lubrication and work well with metal elements are increasingly used.
Manufacturing technologyI trapezoid thread is determined by requirements for accuracy and quantity of products. Turning, milling and grinding remain the traditional methods. Turning is the most common method of thread cutting, especially when it comes to one-off or small-batch production. Milling is used when it is necessary to produce medium-sized parts with increased accuracy. Grinding provides the best surface quality and high profile accuracy, but this method is the most expensive and is used mainly in cases where particularly strict requirements are placed on the part. Modern technologies have significantly expanded the possibilities of trapezoidal thread production. The use of numerically controlled (CNC) machines allows the production of threaded parts with high precision, repeatability and minimal errors. This is especially relevant for serial production, where not only quality is important, but also speed of processing. Another promising technology is metal 3D printing. Thanks to additive manufacturing, it became possible to manufacture complex parts with integrated trapezoidal threads without additional machining. This method is actively used to create prototypes and unique products, as well as in industries where rapid development of individual solutions is required.
Thus, the materials and manufacturing technology of a trapezoid thread determine not only its mechanical properties, but also the field of application. The correct selection of material in combination with the optimal production technology makes it possible to create reliable, durable and economically feasible units that can work effectively in a wide variety of conditions.
Fields of application
Machine tool construction
One of the most important industries where trapezoidal threading is integral is machine tool construction. It is used in lead screws, which are responsible for the accuracy of movement of calipers and tables of machine tools. Due to the large contact area of the profile, high wear resistance is ensured, as well as uniform distribution of loads. For example, in lathes, the lead screw allows you to automatically move the caliper during thread cutting, and in milling machines, it ensures smooth and precise movement of the table in three directions. The use of bronze nuts in combination with steel screws allows to achieve maximum accuracy and durability of mechanisms. Without a trapezoidal thread, modern machine tool construction is simply impossible, because it provides the necessary accuracy and reliability during many years of operation.
Lifting devices and jacks
Another area where the trapezoid thread shows its strengths is in lifting mechanisms. In screw jacks, it is the trapezoidal profile that allows you to create huge lifting forces with relatively little effort on the handle or drive. Thanks to its self-braking properties, such a thread does not allow the load to fall on its own, which makes it safe and reliable in operation. A similar principle is used in lifts for cars and in large industrial mechanisms, where it is necessary to move heavy structures. It is worth emphasizing that it is the trapezoidal thread that allows for a balance between ease of control, smooth running and high load capacity.
Presses and industrial equipment
In industrial presses and equipment where large axial forces must be created, the trapezoidal thread is a key element. It is able to withstand significant loads without premature wear, ensuring the durability of structures. In mechanical presses, screws with such a thread are used to create the pressure necessary to form metal or other materials. In laboratory and production installations, threaded pairs with a trapezoidal profile allow precise adjustment of compression or displacement forces. Due to this, they remain in demand even at a time when hydraulic and pneumatic systems are widespread. The trapezoidal thread is often chosen where reliability, simplicity of design and lack of complex maintenance are required.
Household mechanisms
Although the trapezoidal thread is associated mainly with industry, it is quite often found in household appliances as well. Typical examples are car jacks, adjustment mechanisms in furniture or office chairs, and some household appliances. Its use is based on simplicity and safety: even in the absence of complex drives, the mechanism can effectively perform its functions. In the furniture industry, it allows you to create adjustment systems with smooth and safe movement, and in medical equipment - to lift and fix parts of structures without the risk of sudden operation. Household examples confirm the versatility of this type of thread: it can work both in high-tech machines and in ordinary devices that we encounter every day.
Advantages and disadvantages
The trapezoid thread combines characteristics that make it a unique element in mechanical engineering and mechanics. It can withstand significant axial loads, work in friction conditions and at the same time ensure smooth movement. That is why it is used where the usual metric thread would not cope with the task. However, like any engineering element, a trapezoidal thread has not only advantages, but also certain disadvantages that must be taken into account at the design stage. Let's consider in more detail its strength and durability, efficiency in work and possible limitations.
Strength and durability
One of the main advantages of the trapezoidal thread is its ability to withstand high mechanical loads. Due to the special geometry of the profile, the contact area between the turns of the screw and the nut is much larger than that of the metric thread. This means that the pressure on the surface is distributed more evenly, and therefore the risk of deformation or premature wear is reduced. In combination with the right choice of material (for example, steel + bronze), an impressive durability of the assembly is achieved. In machines or jacks, such a thread can work for years without the need for replacement, if the operating conditions are observed and proper lubrication is provided. It is thanks to this that the trapezoidal thread is considered the standard for responsible mechanisms, where reliability is in the first place.
Efficiency and smoothness of work
Another advantage is a fairly high coefficient of effectiveness compared to a rectangular thread, which, although more effective in transmitting forces, is more difficult to manufacture and less durable. The trapezoidal thread is considered to be the optimal compromise: it provides sufficient efficiency for power transmission and at the same time guarantees a smooth ride. This is especially important for mechanisms where precise and controlled movement is required, such as in machine tool lead screws or control systems. Due to the geometry of the profile, the thread works more softly, without jerks, which makes it convenient and safe to use even in household mechanisms. An additional advantage is the property of self-braking: in many cases, the thread is able to hold the load without reversing, which allows you to do without complex locking devices.
Possible restrictions
Despite all its advantages, the trapezoidal thread has its weaknesses. First of all, it is the complexity and high cost of manufacturing compared to the usual metric thread. The technological process requires precise equipment and tools, especially when it comes to large diameters or multi-way profiles. Another limitation is increased friction compared to ball screw pairs (BSPs), which reduces efficiency during high-speed movements. In such conditions, the mechanism may heat up, require more intensive lubrication and wear out faster. In addition, over time, due to natural wear of the profile, backlash may appear, which reduces the accuracy of work. For high-precision mechanisms, special nuts with clearance compensation must be used, which complicates the design. It is also worth considering weight and dimensions: massive screws with a trapezoidal thread increase the size of nodes, which is not always acceptable in modern compact equipment.
Therefore, the trapezoidal thread is a reliable and time-tested option for transmitting significant forces, which provides a balance between durability, smoothness of movement and relative ease of maintenance. At the same time, its limitations force engineers to carefully approach the choice: where maximum accuracy and speed are required, it is better to use alternative solutions, but in most cases, the trapezoidal thread remains the optimal choice.
How to choose a trapezoidal thread
Choosing a trapezoidal thread is a task that requires taking into account a number of factors, because the durability of the mechanism, its efficiency and operational safety depend on the correctness of the decision. Engineers and designers approach this issue comprehensively, evaluating not only the geometric parameters of the thread, but also the working conditions, the nature of the loads, the environment in which the node will function, as well as the accuracy requirements. On the one hand, the trapezoid thread is universal and can be used both in machine tool construction and in household appliances. On the other hand, the wrong choice of profile or material can lead to rapid wear or even an emergency situation. To avoid such problems, you should focus on three key criteria: load, material and scope of application.
Selection by load
The first and most important parameter when choosing a trapezoidal thread is the level of loads it must withstand. If the unit will work in difficult conditions with a large transmission of forces, you need to choose a thread with a larger diameter and an appropriate pitch. For jacks or presses, massive screws with a large profile are usually used, which can withstand tons of load without breaking. In machines where precise positioning and smooth movement are required, a thread with a smaller step is used, because it allows for controlled and gradual movement of parts. Special attention should be paid to multi-turn threads: they provide faster movement of the nut in one turn of the screw, but require careful selection under the load, since the distribution of forces in them is different from single-turn threads.
Selection of material
An equally important factor is the material from which the carving is made. Steel, which provides high strength and durability, is suitable for most universal tasks. However, if the mechanism works in a wet or aggressive environment, it is better to choose stainless steel, which is resistant to corrosion. A combination of a steel screw and a bronze nut is often used for screw-nut pairs. This allows you to significantly reduce friction and increase the service life. In less loaded mechanisms, you can use brass or even polymers, which work well without lubrication and provide sufficient smoothness of movement. The choice of material directly affects not only the durability, but also the cost of the product, so it is important to find the optimal balance between reliability and economy.
Orientation to the field of application
The third aspect is the field of use itself. For machine tool construction, the priority is accuracy and the absence of backlash, so a thread with a small pitch and high-quality surface treatment is chosen here. In lifting devices, the key parameter is load capacity and safety, therefore, it is necessary to use massive profiles with the property of self-braking. In presses and other industrial equipment, preference is given to durability and the ability to withstand huge loads, while in household appliances, simplicity, ease of use and lack of complex maintenance come to the fore. It is important to remember that a trapezoidal thread is always a compromise between precision, strength and efficiency, so its choice should be based on a clear understanding of the operating conditions.
A correctly selected trapezoidal thread allows you to achieve maximum performance of the mechanism, avoid premature wear and ensure safe operation of the equipment. In other words, the competent choice of this element is the foundation of the reliability of the entire structure.
Operation and maintenance
A trapezoidal thread, like any other mechanical element, requires proper care and regular inspection to ensure long-term and safe operation. It is subjected to significant axial loads and constant friction, therefore, without proper maintenance, even the highest quality material quickly wears out. In order for the thread to perform its functions for many years, it is necessary to observe three key aspects: systematic lubrication, condition control and timely replacement in case of wear. Correct operation allows not only to extend the service life of the unit, but also to avoid emergency situations that may occur when the threaded pair is destroyed.
Lubrication and maintenance
One of the most important factors in the longevity of a trapezoidal thread is lubrication. It reduces friction between the turns of the screw and nut, prevents overheating and wear of surfaces, and also protects against corrosion. Lubricants with increased viscosity are used in industrial mechanisms, which are able to stay in the threaded profile even under load. For high-precision machines, special lubrication systems are used, which automatically supply grease to the required areas. In household machinery such as jacks or adjusting devices, it is sufficient to periodically apply a thick lubricant by hand. In addition to lubrication, it is important to ensure cleanliness: the ingress of dust, chips or dirt into the profile of the thread dramatically accelerates its wear. Regular cleaning of the screw and nut, as well as protection against aggressive environments (moisture, acids, salts) is an integral part of care.
Check for wear
The threaded pair gradually wears out even if all operating rules are followed, so it is necessary to carry out its diagnostics regularly. The first symptom of wear is the appearance of backlash — an increase in the gap between the screw and the nut. This can lead to reduced accuracy of the mechanism and, in the case of lifting devices, to dangerous situations. In industrial conditions, the inspection is carried out with the help of special devices for measuring clearances and profile, while in household mechanisms, a visual inspection and checking the smoothness of movement is sufficient. It is also important to monitor the condition of the surface: the presence of burrs, cracks or traces of corrosion is a signal for immediate intervention. Regular inspection allows you to detect the problem in time and prevent serious breakdowns.
Replacement and repair
If significant wear or damage to the trapezoidal thread is detected, the question of replacement or repair arises. In industrial mechanisms, a complete replacement of the nut is usually carried out, since it wears out faster than the screw. This is more cost-effective and allows you to quickly restore the unit's performance. If the screw is damaged, it is usually repaired by regrinding or re-threading, but this option is possible only if the wear does not exceed the permissible standards. In domestic conditions, a complete replacement of the unit is often chosen, because repairs can be difficult and expensive. It is important to remember that the use of worn or damaged threads can lead to accidents, so saving on timely maintenance is inappropriate here.
Proper use and care of a trapezoid thread significantly extends its service life. Timely lubrication, regular condition checks and competent replacement of worn parts ensure the smooth operation of mechanisms and the safety of their use. In other words, attention to detail in this case determines the reliability of the entire structure.
FAQ: Questions and answers about trapezoidal threads
1. How does a trapezoidal thread differ from a metric one?
A trapezoid thread has a profile in the form of an equilateral trapezoid, and a metric thread has a triangular profile. The first is used to transmit forces and motion, the second is mostly used in fastening joints.
2. How to correctly read the designation TrD×P?
"Tr" means trapezoidal. "D" is the thread diameter in millimeters, "P" is the thread pitch. For example, Tr40×7 is a trapezoidal thread with a diameter of 40 mm and a pitch of 7 mm.
3. What materials are used for the manufacture of trapezoidal screws and nuts?
Carbon or stainless steel, bronze, brass are most often used. For light structures, it is possible to use polymers.
4. Why is the trapezoid thread considered reliable?
Due to the large contact area, it withstands significant loads, works smoothly, and has less wear compared to other types of threads.
5. How to choose the right trapezoidal nut or screw?
It is important to take into account the diameter, pitch, thread direction, product material and scope of application.
6. Is it possible to use a trapezoidal thread in highly loaded mechanisms?
Yes, that is exactly what it is intended for. It is often used where metric or other types of threads wear out quickly.
7. How to extend the service life of a trapezoidal thread?
Regular lubrication, cleaning from dirt, checking for backlash and correct selection of material will help to avoid premature wear.
8. What modern technologies for the production of trapezoidal threads are used?
Most often - high-precision processing on CNC machines, grinding, as well as 3D metal printing for the manufacture of non-standard parts.
