abstract：The two-flange connection from input to output is an important part of the cross shaft universal coupling, which is directly related to the reliability of the entire transmission chain and the performance and life of each component in the transmission chain, and users tend to ignore or misunderstand this The authenticity and importance of the problem. The following will comprehensively analyze several typical flange connection types and related factors.

One. Comparison of flange connection type and performance

     Nowadays, manufacturers generally adopt three types of flange connection: end face keying with ordinary bolt group connection, end face gear with ordinary bolt group connection and reaming with reaming bolt group connection.

 

1.Comprehensive Analysis of the Connection Types of End-face Keys with Ordinary Bolt Groups

 

    In the past, limited by the backward manufacturing level, the flange connection type with end face keyed with ordinary bolt group (see Figure 1) is easier to manufacture, but has many disadvantages

Figure 1

     （1）The problem of too large gap between key and keyway: The gap between key and keyway should be smaller and tighter, but on-site installation will be more difficult, and the keyway and positioning stop are prone to interference, which makes installation more difficult, so it is necessary to enlarge the key and keyway The gap between the key and the keyway results in an angle between the key and the keyway, the actual contact area is smaller, and the large-load forward and reverse operation can easily further increase the gap between the key and the keyway after being squeezed.

    （2）The problem of too large size of common bolt group and insufficient pre tightening torque: about 25% of the running load of flange connection depends on the friction between two flanges after pre tightening of common bolt group. However, the site space is narrow, the size of ordinary bolt group is large, and the applicable wrench can not be used due to interference. It is understood that the pre tightening torque of bolt group is generally less than 50%. This will be very unfavorable to the locking of ordinary bolt group, and will increase the extrusion stress between the key and keyway.

    （3）The problem of flange fork head strength and rigidity too weak: the depth of the end face keyway is about 50% of the flange thickness, which obviously reduces the flange strength and rigidity. In addition, due to the large size of the bolt group, the neck diameter of the flange fork head is too small (see Figure 1 φ225). Compared with the bushing fork head (see Figure 2 φ240), the strength and rigidity of the fork head bearing hole are quite different , The flange fork will break first when running with over-heavy load. In addition, the cross shaft and bearings installed on the flange fork head and sleeve fork head in the long-term operation are under the same working conditions. The cross shaft and bearing on the flange fork head have large deformation due to the weak rigidity of the flange fork head and other reasons. The operating life will be shorter than 30%.

Figure 2

2.Comprehensive Analysis of the Connection Type of Face Gear with Ordinary Bolt Group

    

    In the last century, foreign manufacturers first used the flange connection type of end face gear with ordinary bolt group (see Figure 3).

Figure 3

    Although it looks like a tall and exotic product at first glance, there are also many shortcomings. In addition to the high manufacturing difficulty and cost, because the pressure angle of the end tooth profile reaches 20°, the ordinary bolt group increases a lot of extra pulling force during heavy load operation, which is likely to cause the bolt group to fail. Other disadvantages are similar to the end face key connection type. Nowadays, manufacturers choose this connection type less and less, and it is a connection type that cannot be used if it is not used well.

 

3.Comprehensive Analysis of the Connection Type of Reamed Hole with Bolt Set for Reamed Hole

 

    Reamed hole with reamed hole bolt group connection type (see Figure 4) The shear strength of the reamed hole bolt pin is used to transfer the load.

Figure 4

    In the past, due to the backward traditional processing conditions, the reaming method of flange was drilling and reaming, which made the interchangeability poor and the market promotion difficult. But with the popularity of CNC machine tools, the problem of interchangeability has been completely solved. At present, the interchangeability of products produced by different manufacturers in different batches can meet the requirements. Through the optimization design of Yueqing Sanfeng transmission, more and smaller olive shaped reaming bolts (see Fig. 5) are selected to expand the diameter of bolt hole distribution circle, so that the force is better. At the same time, the diameter of flange fork neck can be increased (see Fig. 4, φ 240). The flange end face is completely undamaged due to no keyway, unlike other connection types, so the flange fork is damaged The results show that the strength and rigidity of the bearing head are obviously improved, and the comprehensive use effect is good, especially for the products with high-speed dynamic balance requirements. The overall performance and bearing service life are increased by more than 20% compared with other connection types. At the same time, the connection type is easier to install, and the suitable wrench can be used to pre tighten the bolt group in place easily and flexibly.

Figure 5（Patent No：ZL 2019 2 1730808.X）

Two. Comparative calculation of transmissible torque of two flange connection types

1.End face key with common bolt group connection type (see Figure 1)

 

（1）The end face key calculates the torque according to the allowable extrusion strength: (calculated according to the relevant weakest

         material)

         According to the extrusion limit calculation, take σp=σs·n (where n=2/1.5≈1.3), and substitute 45# steel σs=355 Mpa, σp=461.5 Mpa

         T=σp·D·l·h·(1-l/D) 2/2, substitute D=315 mm, l=315/3=105 mm, h=30 mm

         T =101.76 kN·m（Because the shear strength is much greater than the compression strength, it is calculated according to

         the compression strength.）

 

（2）The friction force is generated after the ordinary bolt group is pre-tightened, and the torque is calculated:

         Calculation of the clamping force produced by a single ordinary bolt: F= T·u/(K·d) (where u is 0.15 and K is 0.18)

         Substituting the 10.9 grade M22 bolt pre-tightening torque 660 N·m, F= 25000 N

         The maximum friction force generated after the ordinary bolt group is pre-tightened, the calculated torque:

         T=F·Z·r，代入Z=10，r=280/2=140 mm

         T= 35 kN·m

 

2.Reamed hole with reamed hole bolt group connection type (see Figure 4)

 

（1）Calculate the torque according to the allowable shear strength of the bolt group pin rod for reaming holes:

         Calculation of allowable shear stress of bolts: τ=σs/n is calculated according to the shear limit (n=3.8 in the formula),

         Substitute 10.9 grade bolts σs=900 Mpa, τ= 236.84 Mpa

         T=τ·π·m· d²·Z·r/4，Substitute m=1，d=17 mm，Z=24，r=285/2=142.5 mm

         T=183.85 kN·m

 

（2）Calculate the torque according to the allowable extrusion strength of the bolt group pin rod for reaming holes: (calculated

         according to the weakest material)

         According to the extrusion limit calculation, take σp=σs·n (where n=2/1.5≈1.3), and substitute 45# steel σs=355 Mpa,

         σp=461.5 Mpa

         T=σp·Z·r·δ·d, substitute Z=24, r=285/2=142.5 mm, δ=15 mm, d=17 mm

         T=402.47 kN·m (Because the extrusion strength is much greater than the shear strength, it is calculated according to

         the shear strength.)

（3）After the reamed hole is pre-tightened by the bolt group, the friction force is generated and the torque is calculated:
         Calculation of clamping force produced by bolts for single reamed hole: F= T·u/(K·d) (where u is 0.15, K is 0.18)
         Substituting the 10.9 grade M16 bolt pre-tightening torque 175 N·m, F=9115 N
         The maximum friction force produced by the bolt group pre-tightened for the reamed hole is calculated as the torque:
         T=F·Z·r，Substitute Z=24，r=285/2=142.5 mm
         T= 31.17 kN·m

3.Summary

 

    The allowable torque of SWF315 cross shaft universal joint is 156 kN·m. (For details, please refer to Yueqing Sanfeng Transmission 2020 product catalog, download URL: www.sanfengcn.com)
    The connection type of the face key with ordinary bolt group: the face key can transmit torque 101.67 kN·m, and the friction force generated after the ordinary bolt group is pre-tightened can transmit the torque 35 kN·m. Meet 88% of allowable torque.
    Reamed hole with reamed hole bolt group connection type: reamed hole bolt group pin rod can transmit torque 183.85 kN·m, reamed hole bolt group can transmit torque 31.17 kN·m after the friction force is generated , The sum of the two amounts to 215.02 kN·m, which can fully meet the requirements of use.
    The above verification proves that the reamed hole and the reamed hole bolt group connection type can transmit torque significantly better than that of the end face key.
Through bolt group connection type. (Physical test values are similar to verification calculations)

Three. Reamed hole flange size and bolt pre-tightening torque table

Note: 1. The mechanical properties of the bolt group should meet the requirements of GB/T3098.

          2. Choose olive-shaped bolts for reaming holes (Patent No.: ZL 2019 2 1730808.X), the use effect is better.

          3. The bolts used for reaming holes should be grade 10.9 for the specifications below M24, and grade 12.9 for the specifications

              of M24 and above. The tolerance of the pin is h6.      

          4. The pre-tightening torque of the bolt group is organized and edited according to the relevant mechanical design manual

              for your reference.

 

Four. Comprehensive analysis of anti-loosening performance of flange connection bolt group

1.Comparative detection of static anti-loosening of bolt group

 

   10.9 grade bolt set, with 10 grade ordinary nuts. Choose spring washers, flat washers, falling lock washers and without washers. After pre-tightening according to the normative torque, when loosened, all the above methods are still 85%-90% The pre-tightening torque. (Fine thread is about 5% larger)
    10.9-level bolt set, equipped with 10-level locknut (the head of the nut is equipped with a nylon ring to squeeze the thread, which cannot be repeatedly assembled and disassembled. The nylon ring is easy to age and has a limited life), without washers. Similarly, after pre-tightening according to the specified torque, the pre-tightening torque of 120%-125% is reached when loosened.
    10.9 grade bolt set, with 10 grade ordinary nuts coated with anaerobic glue, without washers. Similarly, after 24 hours of pre-tightening according to the specified torque, the pre-tightening torque is as high as 165%-170% when loosened (40% smaller for fine thread). Shanghai Kangda 5071 anaerobic adhesive was selected for the test, and the initial positioning was 30 minutes, and the maximum bonding strength could be reached after 24 hours.

 

2.Comparative detection of dynamic anti-loosening of bolt group

 

    After the two flanges are connected, when there is no relative displacement between the flanges during long-term heavy load and frequent forward and reverse operation, the various methods that have been statically tested above are used, and they are not easy to loosen and fail.

    If there is repeated relative displacement between the two flanges in operation (the greater the displacement and the more frequent the repeated movement, the easier the bolt group will loosen and fail), the bolt group with and without washers will loosen and fail at the earliest, and the anti-loosening nut will last longer , No loosening failure was found in the dynamic test of the bolt group coated with anaerobic glue.

 

3.Summary

 

    The bolt group anti-loosening detection more clearly illustrates the anti-loosening effect of the bolt group under various anti-loosening methods in static and dynamic. In view of the working characteristics of the cross-shaft universal coupling, the anti-loosening effect of the contact end face of the nut alone is very limited, and the anti-loosing effect of increasing the resistance of the threaded section will be better.
    After the cross-shaft universal coupling is connected with the bolt group of the shaft adapter flange under various working conditions, the bolt group must be anti-loosing and reliable. In addition to the proper anti-loosening technology and pre-tightening of the bolt group, the most The key is that there should be no repeated relative displacement when working after the two flanges are connected.

 

Five. To sum up

 

    Based on the comparative analysis of the contents of the above pages, in addition to the excellent performance of the cross shaft universal coupling, the overall quality of the flange connection is also very important. How to achieve high reliability of flange connection, longer product operating life, more convenient manufacturing and use, the choice of reaming holes and reaming holes with bolt group connection type has obvious advantages, and now foreign manufacturers have used a lot of similar products. After Yueqing Mitutoyo's transmission technology is optimized, the overall performance of the product will be more ideal, which will be of great significance to the operating reliability and life of the cross-shaft universal coupling.