The long-term stability of ultra-precision equipment depends not only on factory machining accuracy, but also on scientific post-production storage and regular precision maintenance. As the core load-bearing benchmark for semiconductor inspection equipment, linear motor platforms, industrial CT, and femtosecond laser equipment, the granite gantry is an integrated ultra-precision component with a large span. Even adopting high-density black granite base material featuring stable modulus and excellent damping performance, it may still suffer from benchmark surface damage, abnormal stress and precision drift due to improper storage, handling collision, environmental disturbance and incorrect cleaning methods, which directly affect the measurement and motion output of the entire equipment. Many enterprises only attach importance to factory inspection during procurement while ignoring subsequent storage and maintenance, resulting in abnormal precision attenuation of high-precision gantries after a period of service and causing high rework and downtime losses. Based on extensive practical experience in large-scale granite gantry projects, UNPARALLELED Group sorts out implementable standardized specifications for gantry component storage, transportation protection, on-site operation maintenance and periodic calibration, helping users maintain the original precision of components for a long time.
Different from small granite measuring tools, large granite gantries feature heavy self-weight, long span and complex stress conditions of column and beam composite structures, and their storage posture significantly affects the internal stress state. Many customers randomly place gantries in an inclined manner, with single-sided padding or direct floor placement during storage. Although no visible surface damage occurs, latent internal stress has already been generated. Under long-term unreasonable support, the gantry beam will undergo slow creep deformation, which is invisible to the naked eye and can only be detected during assembly and commissioning when flatness and verticality exceed tolerances, leading to extremely difficult repair work.
A qualified storage site is the primary prerequisite. The floor of the storage area must have sufficient bearing capacity to avoid ground settlement and local collapse. The site shall be kept away from vibration sources such as stamping equipment, crane passages and fan units, as continuous low-frequency vibration will disturb the internal stress distribution of stone materials. Outdoor stacking is prohibited to prevent erosion from direct sunlight, rain and salt fog; drastic temperature cycles will cause uneven thermal deformation of large-span gantries. Coastal factories need to strengthen moistureproof measures, as high humidity will not only accelerate corrosion of metal embedded parts, but also change the local physical state of components via long-term moisture penetration into stone micropores. The ideal storage environment shall be close to the working conditions of a constant-temperature workshop to avoid sharp fluctuations in temperature and humidity.
In terms of support methods, single-point support, single-sided support and inclined vertical placement are strictly forbidden. Large granite gantries require uniformly distributed multi-point flexible support at positions corresponding to the designed stress points, avoiding weak suspended beam areas to disperse overall self-weight and eliminate local concentrated stress. Support pads shall be made of suitable hardness granite or polymer buffer materials, and hard steel blocks are prohibited from direct contact with precision benchmark surfaces. Precision assembly benchmark surfaces shall be covered with special dust-proof protective films without strong adhesive glue, preventing residual glue from penetrating into stone pores after film removal. Non-processing side surfaces shall be well dust-proofed with clear product marking to avoid dislocation of lifting points and collision during hoisting. Multi-layer stacking of gantry components is strictly prohibited under any circumstances, as the weight of upper components will cause irreversible compression deformation and damage to lower ones.
Lifting and transportation are high-risk links in precision maintenance, even for short-distance handling. Most precision damage occurs during secondary transportation rather than factory production. Lifting points must strictly follow the factory marked positions without random adjustment, so as to avoid internal stress caused by stress distortion during hoisting. The lifting and lowering speed shall be well controlled to prevent collision, dragging and rolling. Precision ground benchmark surfaces shall be fully covered with protective plates, and ropes are not allowed to directly contact precision machined surfaces. The gantry shall be slowly placed on preset support pads after transportation instead of being dropped violently. After positioning, immediate precision re-inspection is not recommended. The internal stress of large granite gantries needs sufficient standing time to release, and precision detection can only be carried out after the component temperature is fully balanced with the ambient temperature.
After formal on-site service, daily maintenance mainly focuses on three aspects: standardized cleaning, environmental control and external impact avoidance. Many on-site operators use ordinary rags, sandpaper or hard scrapers to clean granite benchmark surfaces, or adopt strong acid and alkaline cleaning agents, which easily scratch nano-level ground surfaces, form micro pits and damage the original flatness. The correct cleaning method is to use dust-free soft cloth matched with special neutral cleaning agents to remove surface dust and micro oil stains. In semiconductor workshop environments, residual cleaning agent precipitates must be avoided. The surface shall be dried in a timely manner after cleaning to prevent long-term liquid retention in grooves and gaps of metal embedded parts.
During equipment operation, overload on granite gantry benchmark surfaces is forbidden. Random stacking of toolings and workpieces on precision benchmark areas will change the component stress state under long-term additional load. Meanwhile, workshop environmental management shall be strengthened to reduce short-term drastic temperature fluctuations. Welding sparks and metal debris from surrounding equipment maintenance shall be prevented from splashing on the gantry surface, as residual iron scraps in stone pores will form rust stains and contaminate the benchmark surface.
In addition to physical protection, periodic precision calibration is an indispensable part of maintenance. The precision of granite gantries will not remain permanent. Regular calibration mechanisms must be established to cope with long-term load, environmental changes and equipment renovation. The calibration cycle is formulated in accordance with international metrological standards including DIN, ASME, JIS and GB as well as actual equipment working conditions. Professional testing tools such as laser interferometers, electronic levels and roughness testers are adopted to verify core indicators including beam flatness, verticality between beams and columns, and position accuracy of key mounting holes. All calibration instruments must be certified by metrological institutions to ensure traceable test data. Once precision deviation is detected, on-site self-grinding and repair are prohibited. The repair of large gantries requires professional constant-temperature workshops and senior grinding technicians, and blind on-site grinding will directly lead to component scrapping due to insufficient on-site conditions.
Long-term shutdown storage maintenance is often neglected by users. Granite gantries shall not be exposed directly during equipment shutdown. All working surfaces need thorough cleaning, and anti-corrosion protection shall be implemented for exposed metal parts such as threaded sleeves and sealing inserts. Precision benchmark surfaces shall be covered with dust-proof pads and integral dust covers to isolate dust and moisture. Regular environmental inspection is required to check for condensation and water accumulation.