Analysis of causes and preventive measures for base settlement and cracking of NGW-L11-5.6 planetary reducer

(1) Preliminary geological survey and basic design

1. Detailed geological survey : Before equipment installation, conduct a comprehensive geological survey of the installation site to understand the soil structure, soil properties, groundwater level, etc., and accurately evaluate the bearing capacity and stability of the foundation. For sites where there may be weak soil layers, its distribution range and thickness need to be determined in advance to provide an accurate basis for subsequent design.

2. Reasonable foundation design : Design the appropriate foundation form and size based on the weight, working load, vibration characteristics and other factors of the NGW-L11-5.6 reducer. It can adopt the form of independent foundation, raft foundation or pile foundation to ensure that the foundation can evenly distribute the equipment load. For heavy equipment, the foundation burial depth should be appropriately increased to improve stability, and a certain safety factor should be reserved in the design.

3. Foundation reinforcement : If the foundation conditions of the site are poor, the following measures can be taken:

   • Replacement and filling method : dig out the weak soil layer, replace it with high-strength materials such as sand, gravel, lime soil or concrete, and compact it in layers

   • Grouting reinforcement : Inject cement slurry or chemical slurry into the foundation to fill the voids in the soil and improve the bearing capacity.

   • Pile foundation reinforcement : Micro piles, static pressure piles, etc. are used to transfer the load to the deep stable soil layer.

(2) Quality control of foundation construction

1. Material selection and quality control : Use high-quality concrete and steel materials. It is recommended that the concrete strength grade should not be lower than C25. Strict inspection and sampling testing of incoming materials should be carried out to prevent the use of unqualified materials.

2. Standard construction technology :

   • Carry out foundation construction in strict accordance with the construction specifications to ensure that the formwork is firmly installed, the dimensions are accurate, and the steel bar binding specifications are

   • Concrete pouring needs to be vibrated and compacted, and the pouring temperature and curing conditions must be controlled to avoid cracks in the foundation due to temperature stress or improper curing.

   • The foundation surface needs to be chiseled and cleaned of oil and dust. It cannot be leveled directly on a smooth cement surface.

3. Curing period requirements : The curing period of the concrete foundation shall not be less than 28 days, and the equipment can be installed only after the strength reaches 80% of the design value. During the maintenance period, the foundation settlement needs to be monitored, and subsequent processes can only be carried out after the settlement rate is stable (settlement for 7 consecutive days ≤ 0.1mm/d).

4. Secondary grouting process : A secondary grouting layer should be reserved at the base of the reducer, with a recommended thickness of 30-50mm. For large reducers, it is recommended to use secondary grouting technology to fix the anchor bolts to achieve rigid connection.

(3) Accuracy control of installation base

1. Base rigidity guarantee :

   • Prioritize the steel base plate (base plate) and do not drop the reducer directly on the concrete.

   • The bearing capacity of the base must exceed 1.5 times the total weight of the reducer and load.

   • Install reinforcement ribs to increase rigidity, and use cast iron or steel structure bases if necessary

2. Installation surface accuracy requirements :

   • Surface roughness≤Ra3.2

   • Flatness ≤0.1mm/m (high-precision occasions ≤0.05mm/m)

   • Level deviation ≤0.1/1000

3. Leveling method : It is recommended to use the shim leveling method - arrange pairs of slanted shims (flat shims + slanted shims) at the four corners and the middle stress point of the base, with the number of shim groups ≤ 3 layers, and fixed by spot welding to prevent slippage during operation. Use a frame level or laser level to measure in two mutually perpendicular directions, axial and radial.

(4) Anchor bolt tightening specifications

1. Bolts Selection : Use high-strength bolts of grade 8.8 or above to ensure connection reliability.

2. Tightening sequence : Use diagonal staged tightening method (such as 50% pre-tightening and then 100% final tightening, or 40% → 70% → 100%). It is strictly forbidden to tighten the bolts on one side at one time to avoid 'warping' of the base caused by unilateral tightening.

3. Torque control : Use a torque wrench to apply force according to the standard torque marked by the manufacturer. Excessive tightening may cause housing deformation or thread slippage.

4. Anti-loosening measures : It is recommended to use thread glue, spring washers or double nuts to prevent loosening caused by long-term vibration.

(5) Operation monitoring and maintenance

1. Settlement monitoring : Set up settlement observation points around the base, regularly use laser levels and steel rulers to measure height difference changes, establish monitoring data files, and take timely remedial measures if abnormalities are found.

2. Regular inspection :

   • Check the tightening status of the anchor bolts every 500 hours of operation and re-test the levelness.

   • Check whether there are cracks or damage on the surface of the base and repair them in time

   • Check whether the connection between the equipment and the foundation is loose

3. Vibration and temperature monitoring : Install vibration sensors and temperature sensors in key parts of the reducer to establish baseline data. When the effective value of vibration speed is >4.5mm/s or the shell temperature exceeds 85℃, the machine needs to be shut down for inspection.

4. Load control : Reasonably control the operating load of equipment to avoid overload operation and reduce the impact of equipment vibration on the foundation. The maximum working torque should be less than 2 times the rated output torque of the reducer.

(6) Special measures to prevent cracking

1. Set settlement joints : When the building length is long or the foundation soil quality is greatly different, settlement joints are reserved to divide the building into independent units and control and adjust the elevation of each part.

2. Enhance structural stiffness : Set up reinforced concrete ring beams, reinforce the openings in the walls, or use structural columns to strengthen them; for situations where load differences are large, box foundations, pile foundations, raft foundations, etc. can be used to strengthen the overall rigidity of the foundation.

3. Crack prevention :

   • Strictly control the concrete mix ratio and pouring quality to avoid shrinkage cracks

   • Take good drainage measures and keep the foundation pit dry during construction to avoid rainwater soaking and softening the foundation.

   • Carry out grouting repairs on cracked areas to prevent water erosion and aggravation of settlement.

4. Shock absorption measures : For working conditions that produce large vibrations, shock absorbers or shock-absorbing foundations can be installed to reduce the impact load on the base.