In general, the surface of the thread is characterized by the outer (or inner) surface accuracy, the median diameter, the pitch, the profile height, and the position of the profile angle.
When the thread is rolled, the mechanism for forming each parameter is different, and each method of rolling the thread has its own characteristics (the dimensional chain is also different), so the precision of forming the thread parameters is also different.
1 When a threaded 1.1-size chain is formed on a double roller machine to form a thread, a secondary-type dimensional chain can be formed. For example, a static dimensional chain system is formed when three roller threaded rollers are used to roll threads, as shown in (b).
r,. One or three rollers cooperate with the distribution radius of the hole axis relative to the blank, the foot numbers i =1, 2, 3, respectively corresponding to the corresponding roller rollers; h, the threaded roller axis fits the journal with respect to the roller axis The radial displacement value of the axis (=1, 2, 3) r.,.
a rolling head with a shaft reference radius; da.? needle diameter; t, a threaded roller wall thickness; u? formed by the axis of the axis deviation from the axis of rotation of the threaded roller (handle) axis of rotation; below the double roller As an example of the axial feed of the threaded roller when the machine is rolling the thread, the accuracy of forming the thread parameters is analyzed. In practice, the BHrH type roller (for thread rolling on the solid blank) and the HBrr type roller are used. (for thread rolling on hollow blanks). In both cases, the diameter of the rolling thread is formed by a dynamic dimensional chain such as a threaded roller, which is formed by all the dynamic component links of the static dimensional chain during the threading process. The static dimensional chain component is the fixed size of the threaded roller and The eccentric axis distribution angle for each blank's variable size, such as 1.1.1 affects the thread parameter error factor in the equations (), parameter r,. , u and n are invariant to the thread being rolled, and the parameter r.,. , da., t, the shape error range of each of the blanks is different, but considering the high precision of these parameters, the above error is negligible, which means that the rolling thread causes the main error of the diameter error. The factor is hi. In addition, hi is a closed loop of two other size chains, namely a roll disassembly and a resizing chain.
Figure 6-2 shows Ch according to analysis and research oA 螟 pattern (roller rolling Wish1... solution measures; rved.h Qiu: w.cnki.net Received: 2003*?16 according to analysis, One of the main ways to improve the dimensional accuracy of the rolled thread diameter is to ensure that h has a relatively high stability when the rolling head is working. For this reason, it is necessary to increase the precision (fan gear, center wheel, etc.) involved in forming the part size h. Reduce the number of rings of the above size chain.
(e, ? eccentricity; burning-eccentricity axis arrangement angle) t, e, and r, fixed part error, can be compensated by manufacturing, thermal deformation, elastic deformation error.
When the threaded roller is mounted on the machine tool, it is assumed that the axis deviation of the spindle-rotation axis of the blank is m as shown in (a), and the following dimensional chain is formed.
(o) The axis of symmetry deviation of the axis. Thus u in the equation () can be substituted into the equation using (m + n) in equation (2).
In the process of rolling the thread, n is the source of the bending deformation of the process system components, and the total value of the deformation of the blank-roller contact section is equal to n. Generally, the blank is the weakest link in the process system, and it is subjected to the bending force. At this time, the additional force necessary for the bending value n of the blank is received by the threaded roller and is close to the main shaft. During the entire cycle of rolling work, these rollers are subjected to strong loads. These rollers have relatively large forces and operate under relatively heavy conditions. As a result, after determining that the threaded rollers meet the service period, the rollers are more than others. The component is damaged first. In addition, due to the bending of the axis of the blank, the rolled thread will produce a local taper, the result will be accompanied by pitch error and tooth half angle error. Obviously, the closer the roller surface formed on the spindle axis is to the axis of symmetry, the smaller the bending deformation of the components of the process system, and the smoother (uniform) the working conditions of all the rollers on the roller, therefore, in order to improve the service life of the thread roller, The parameters of the threaded thread must be such that the spindle is not coaxial with the axis of rotation of the roller (used in practice) and is coaxial with the axis of symmetry of the roller. For this reason, the value and direction of the displacement u can be reasonably adjusted on the front plate of the roller.
2 Application examples In the petroleum equipment machine, the thread on the valve shaft (material 20X13) (T26X5LH?8g, T30X6?7e) can be formed by rolling with a three-column threaded roller (BHTH). Through the experimental calculation, the thread roller is used. It is 5200~6500m long. Studies have confirmed that this roller surface symmetry axis is relatively close to the spindle axis. According to the theoretical method described, controlling the proper position of the mounting threaded roller can increase the life of the roller by 1.36 times (average).
The diameter dimension deviation Ad of the rolling thread is determined by the diameter dimension chain, and the rank of the function can be formed as a function symbol of the corresponding parameter change caused by the shape.
When the thread is rolled, the contact area generates thermal displacement, and the periodic contact occurs according to the blank roller, the roller, the needle roller, the needle roller and the shaft contact pair, and during the plastic deformation, the blank is on the blank. The heat balance is quickly redistributed. Thus, the dimensional deviation due to thermal deformation can be determined by the following equation: the elastic deformation of the process system components that have an effect on the diameter dimension, including the blank (Ap, roller (2Ay), needle roller (Ad)). Or the roller shaft is bent (2Ar,). The diameter dimension offset is equal to: due to the elastic compressive deformation, the diameter dimension error is directional, and its direction is opposite to the thermal bending deformation direction, so they can partially compensate each other. If the rolling pressure and the component heat capacity are known, the dispersion range of the diameter size can be determined by using the formulas (3), (4) and the elastic theory and the known formula of the thermal deformation theory.
3 Conclusion The dimensional chain of rolling thread has its own characteristics (in quadratic form) and needs to be solved by systematic method. Through research and analysis, the parameters can be analyzed and revealed by increasing the parameters, positional accuracy and tool life of rolling threaded components. The essence and rolling thread conditions, in order to achieve the purpose of improving the accuracy of the threaded parameters and extending the service life of the equipment.
(Finish)
Tungsten carbide roller has characteristics of good wear resistance, high temperature red hardness, thermal fatigue resistance and thermal conductivity and high strength , have been widely used in high-speed wire rod, bar, rebar, seamless steel tubes, etc. Domestic production of tungsten carbide roller materials mostly WC- Co, WC- Co- Ni- Cr two series, and the content of Co, Co- Ni - Cr is in the range of 6wt% ~ 30wt%. From the use of perspective, tungsten carbide rollers has good mechanical properties, its flexural strength up to 2200 MPa or more, shock toughness up (4 ~ 6) × 10^6 J/ m^2, Rockwell hardness (HRA) is up to 78 to 90, widely in the high-speed wire rod rolling process, which is much higher than single-slot chilled cast steel or high speed steel rolls.Tungsten carbide is made of Tungsten Carbide Powder and binder phase (such as drilling, nickel, etc.), and then pressing and sintering, regardless of the conditions under cold rolled or hot rolled has excellent wear resistance, tungsten carbide rollers has been widely used in pre-finishing mill and finishing of high-speed wire rod currently. On the performance of tungsten carbide roller in hot-rolling wire rod , the material must meet the following requirements:
1. Sufficient anti-fracture strength;
2. Good abrasion resistance;
3. The smooth surface finish;
4. Excellent corrosion resistance, thermal fatigue, thermal cracking performance.
Tungsten carbide roller rings can working in bad conditions , small profile rolling (especially rebar rolling) process conditions is harsher than the high-speed wire rod, and therefore corresponds to the profile rolling ,tungsten carbide rollers recommend using high binder phase carbide.
Tungsten carbide roller material design
Pre-finishing all vehicles roller should ensure its high toughness, strength, rigidity and thermal conductivity, followed before considering its wear resistance. When designing each vehicles roller, pre-finishing materials should choose carbide grades of Co, Co- Ni- Cr binder content is high (greater than or equal to 25wt%) , requiring an average WC grain size of coarse (5μm ~ 6μm), to obtain a higher shock toughness, proper strength and hardness. For the finishing of the roller movements, particularly the last two rollers of the finish rolling, which suffered load is small, and high relative velocity of the material to be pressed (80 m / min ~ 120 m / min). In this case, the wear resistance of the roller to be the most important requirements, and must ensure the strength , timpact toughness and hardness of a reasonable match, so the binder of Co / Ni content ratio and the average grain WC control of particle size and other factors must have greater control in front of different pre-finishing rolling roll.
Tungsten carbide roller category
According to the structure of tungsten carbide rollers, it can be divided into solid tungsten carbide roller and composite tungsten carbide roller. Solid tungsten carbide rollers have been widely used in pre-finishing and finishing stands high speed wire rod mill (including fixed reducing the rack, pinch roller rack). Composite tungsten carbide roller is made of cemented carbide and other materials, and it can be divided into tungsten carbide composite roll rings and solid tungsten carbide Composite Roller. Tungsten carbide composite roll rings mounted on the roller shaft; solid tungsten carbide composite roller will be directly cast in the roll axis to form a whole, a large load is applied to the rolling mill.
Tungsten carbide roller production process control
Tungsten carbide rollers produced by powder metallurgy method, the key to its process control is the chemical composition of the material and the mixture was prepared, pressed molding, sintering and deep processing and other preparation process parameters.
1. Preparation of starting material (WC focus quality): As the WC raw material and quality control of the use of different levels of quality may fluctuate, resulting in adverse effects on microstructure.
2. Preparation of the mixture: Mixture preparation is the key to the production process of the roller, the roller of failure modes - trachoma, mainly generated by this procedure.
3. Pressing: roller pressing is an important process of the roller mill.
4. Sintering: roller sintering is to determine the final quality of the roller production processes, use of advanced low-pressure sintering technology, HIP sintering technology can greatly improve the performance of roller.
5. Deep processing: deep processing rollers have a greater impact on the quality and accuracy of the roller surface.
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