The grain harvesting stage is the "last mile" of grain production. As the core operating machine, the combine harvester directly determines the grain loss rate with its operation quality. According to relevant data from the Ministry of Agriculture and Rural Affairs, a combine harvester with standardized operation and scientific debugging can control the grain loss rate within 2%, while improper operation or unreasonable machine debugging may increase the loss rate to more than 5%. Combining industry technical specifications and frontline operation experience, this article explains the core points of reducing grain loss rate of combine harvesters from the aspects of machine debugging, operation specifications, model adaptation, and maintenance, providing professional reference for agricultural machinery practitioners.

I. Accurately Debug Core Components to Reduce Loss Risks from the Source

The debugging of core components of combine harvesters, such as the header, threshing and cleaning system, and conveying system, is the foundation for reducing grain loss. Different grain varieties (wheat, rice, corn), different maturity levels and field conditions have significant differences in the requirements for component parameters, which need to be adjusted in a targeted manner to avoid problems such as missed harvesting, incomplete threshing, and grain breakage caused by parameter deviations.

(1) Header System Debugging: Reduce Field Missed Harvesting and Grain Drop

The header is the first process of grain harvesting. Improper adjustment of the header can easily cause header losses (missed harvesting, grain drop), accounting for 30% to 40% of the total loss. The following parameters need to be focused on:

1. Header Height: Adjust according to the grain plant height and lodging situation. For wheat and rice harvesting, the header height is recommended to be controlled at 10-15 cm, which not only avoids ear residue caused by too high stubble, but also prevents too much straw from being brought in due to too low header, increasing the pressure of subsequent cleaning. For lodged crops, the header height can be appropriately reduced and adjusted in conjunction with the reel to reduce missed harvesting.

2. Reel: The rotating speed, height and front-rear position need to match the growth state of the grain. For normally growing grain, the reel speed should be 1.1-1.5 times the forward speed of the combine harvester, and the reel teeth should act on 2/3 of the height of rice and wheat plants to ensure smooth reel lifting and avoid grain drop caused by too fast speed or missed harvesting caused by ineffective reel lifting due to too slow speed. For lodged crops, the reel needs to be moved forward and lowered to enhance the reel lifting effect.

3. Operating Width: To ensure uniform feeding and reduce missed harvesting, the operating width is recommended to be controlled at about 90% of the header width. Avoid overloading of feeding volume caused by too wide operating width, which may lead to blockage and missed harvesting; at the same time, pay attention to the connection of adjacent operating belts to prevent the occurrence of "missed harvesting belts".

(2) Threshing and Cleaning System Debugging: Balance Threshing Rate and Breakage Rate

The threshing and cleaning system is the core link of grain harvesting, which directly affects threshing loss, breakage loss and cleaning loss. It needs to be adjusted in accordance with the principle of "improving threshing rate and cleaning efficiency on the premise of ensuring the breakage rate does not exceed the standard".

1. Threshing Drum: Rotating speed and concave plate gap are key parameters, which need to be adjusted according to grain varieties and maturity levels. When harvesting wheat, on the premise of ensuring the breakage rate ≤ 2%, appropriately increase the drum speed and reduce the concave plate gap, and control the inlet to outlet gap ratio at 4:1, which can effectively improve the threshing rate and reduce threshing loss; when harvesting rice, the drum speed is recommended to be controlled at 700-900 rpm, and the concave plate inlet gap is 20-30 mm to avoid grain breakage caused by too high speed. When harvesting corn, baffles can be installed on both sides of the ear picking roller and conveying trough to fill the gaps and reduce the loss of corn cobs; replace the ribbed concave plate with round steel bars to reduce the impact between grains and steel bars and lower the risk of breakage.

2. Cleaning Device: Including fan air volume, sieve opening and tail sieve position, it needs to be adjusted in conjunction with the threshing system. On the premise of ensuring the impurity content ≤ 3%, appropriately reduce the fan air volume, increase the sieve opening and raise the tail sieve position, which can reduce the grain blowing loss during the cleaning process. For grains with high humidity, the air volume can be appropriately increased to prevent sieve surface blockage and avoid grains being discharged with straw.

(3) Conveying System Debugging: Avoid Intermediate Grain Drop and Blockage

The conveying system (conveying trough, auger, elevator) is responsible for conveying the grain harvested by the header to the threshing system, and then conveying the cleaned grains to the grain tank. Its smooth operation directly affects intermediate losses. It is necessary to check whether the conveying trough scraper and auger blade are intact to avoid grain leakage caused by worn components and excessive gaps; adjust the conveying speed to match the header feeding speed to prevent grain accumulation and blockage, and reduce grain scattering loss caused by blockage.

II. Standardize Operation Specifications to Reduce Losses Caused by Human Factors

The operating level of combine harvester drivers has a significant impact on the grain loss rate. According to industry research, the operation loss rate of skilled drivers and novice drivers can differ by 2% to 3%. It is necessary to strictly follow the following operation specifications to reduce human errors.

(1) Reasonably Control Operating Speed

The operating speed needs to match the field conditions, grain yield and machine feeding capacity, avoiding blind pursuit of speed that leads to increased losses. Generally, the operating speed for wheat and rice harvesting is controlled at 3-5 km/h, and for corn harvesting at 2-4 km/h; when the grain yield is too high, humidity is too high or stubble height is too low, the operating speed needs to be reduced to ensure the machine works under rated load and reduce entrainment loss and blockage failures. Before operation, a low-speed test harvest should be carried out first, and the speed should be gradually adjusted to the normal speed according to the test harvest situation. It is strictly forbidden to use the walking gear for harvesting directly.

(2) Standardize Turning and Field Head Operation

When turning at the field head, stop the operation and turn by reversing to avoid the header continuing to harvest during turning, which may lead to grain missed harvesting or rolling. When operating to the field head, slow down in advance and turn after the header completely leaves the crop to reduce grain scattering at the field head. For irregular plots, the "circular" operation method can be adopted to avoid frequent turning, improve operation continuity and reduce missed harvesting.

(3) Operation Skills for Special Working Conditions

Faced with special working conditions such as lodging, high humidity and excessive weeds, the operation method needs to be adjusted to reduce losses. When harvesting lodged crops, operate in the reverse direction of the lodging direction and adjust in conjunction with the reel to enhance the reel lifting effect; for grains with high humidity, appropriately reduce the operating speed and increase the cleaning air volume to avoid incomplete cleaning caused by grain caking; for plots with excessive weeds, clean the field weeds in advance or adjust the header height to reduce the amount of weeds brought in and prevent the cleaning system from being blocked.

III. Adapt to Models and Operating Environment to Improve Loss Reduction Effect

Different grain varieties, planting modes and field environments have different requirements for combine harvester models. Choosing a suitable model is the premise of reducing losses. At the same time, adjusting the operation plan according to the operating environment can further reduce the loss rate.

(1) Key Points of Model Selection

1. Grain Variety Adaptation: For wheat and rice harvesting, full-feed combine harvesters are suitable, which have good threshing and cleaning effects and are applicable to plump grains with moderate humidity; for corn harvesting, special corn combine harvesters can be selected, which are equipped with ear picking rollers and peeling devices to reduce corn cob loss and grain breakage; for small plots or mountainous and hilly areas, small and light combine harvesters are suitable, which are easy to operate and turn, reducing missed harvesting.

2. Planting Mode Adaptation: For densely planted crops, models with suitable header width and strong feeding capacity should be selected to avoid low operation efficiency and more missed harvesting caused by insufficient feeding volume; for ridge crops, models with ridge distance adjustment function can be selected to ensure the header matches the ridge distance and reduce rolling and missed harvesting.

(2) Adaptation Adjustment of Operating Environment

1. Field Humidity: The grain loss rate is the lowest when the grain humidity is 15%-20%; when the humidity exceeds 25%, the grains are prone to caking, incomplete threshing and increased cleaning difficulty, and harvesting can be carried out after sun drying on sunny days; when the humidity is lower than 12%, the grains have increased brittleness and are easy to break, so the threshing drum speed should be appropriately reduced and the concave plate gap increased.

2. Plot Conditions: The linear operation method can be adopted for flat plots to improve operation efficiency and quality; for mountainous and hilly plots, reduce the operating speed and adjust the header height to avoid missed harvesting and grain scattering caused by terrain undulation; for muddy plots, crawler combine harvesters should be selected to prevent getting stuck and reduce missed harvesting caused by machine slipping.

IV. Strengthen Machine Maintenance to Ensure Operation Stability

The performance stability of combine harvesters directly affects the operation quality. Regular maintenance can avoid increased losses caused by component failures and extend the service life of the machine. Maintenance work should be done well before, during and after operation.

(1) Pre-operation Maintenance

Conduct a comprehensive inspection of all components of the machine, including the header, threshing drum, cleaning device, conveying system, etc., and replace severely worn scrapers, blades, reel teeth and other components; check the engine, gearbox, hydraulic system, etc., to ensure normal operation; clean up residual straw, grains and other debris in the machine to prevent blockage; debug the core component parameters in advance according to the grain variety to be harvested and make preparations for test harvest.

(2) In-operation Maintenance

During operation, stop and inspect every 2-3 hours, clean up straw and debris in the header, conveying trough, cleaning sieve and other parts to prevent blockage; check whether all components are firmly connected to avoid grain leakage caused by loose components; monitor parameters such as engine speed and hydraulic system pressure to ensure the machine operates under rated conditions and avoid failures caused by overloading.

(3) Post-operation Maintenance

After the operation is completed, thoroughly clean up residual grains, straw and debris in the machine to prevent mold and corrosion of components; check the wear of all components and repair or replace damaged components in time; carry out lubrication and maintenance on key parts such as the engine and gearbox; park the machine in a dry and ventilated place, take rainproof and dustproof measures, and make preparations for the next operation.

V. Industry Development Trend: Intelligent Upgrading Helps Reduce Losses and Improve Efficiency

With the improvement of agricultural mechanization and intelligentization levels, the intelligent upgrading of combine harvesters has become an important direction to reduce the grain loss rate. At present, mainstream domestic agricultural machinery enterprises have launched combine harvesters equipped with intelligent control systems, which can monitor parameters such as feeding volume, grain breakage rate and loss rate in real time through sensors, and automatically adjust the drum speed, fan air volume, operating speed, etc., to achieve precise loss reduction. Some models are also equipped with Beidou navigation systems, which can realize linear operation and automatic docking, reducing missed harvesting and field head losses. In the future, with the application of artificial intelligence and the Internet of Things technology, combine harvesters will achieve more precise working condition perception and parameter adjustment, further reducing the grain loss rate and promoting the grain loss reduction work in the grain harvesting stage to a new height.

To sum up, reducing the grain loss rate of combine harvester operation needs to take into account the four core links of machine debugging, operation specifications, model adaptation and maintenance, and at the same time rely on intelligent technology upgrading to continuously improve the operation quality. Agricultural machinery practitioners need to master relevant technical points proficiently, standardize the operation process, implement every detail in place, effectively hold the "last line of defense" in grain production, and contribute to ensuring national food security.