Major Heat / Da Shu

Major Heat / Da Shu

July 23 - August 6: How Extreme Temperatures Test Slewing Ring Quality

The 12th solar term and the hottest period of the year

What is Major Heat ? It is the 12th solar term on the traditional Chinese calendar and the hottest period of the year, falling between July 22-24. In 2026, Da Shu begins on July 23, when the sun reaches 120 degrees of celestial longitude. The name tells the story: Da (great) + Shu (heat) - the peak of summer intensity.

In Chinese tradition, this is a season described as "steaming above, boiling below" - a blend of scorching sun, oppressive humidity, and sudden thunderstorms. Ancient scholars compared the accumulated heat to a stove brought into a room: the warmth builds gradually, and by Major Heat the thermal inertia has reached its peak.

For an industrial manufacturer, Major Heat is more than a calendar marker. It is a real operational stress test - one that affects material behavior, machining tolerances, and production schedules. At Anhui Yuanfeng, this season demands heightened attention across the entire production line.

1. Thermal Expansion and Clearance Tolerances

Steel expands with heat. For a slewing bearing with a 2,000 mm outer diameter, a 10-degree temperature swing can produce a dimensional change of roughly 0.14 mm - significant enough to shift internal clearance from the designed specification. During Major Heat, workshop temperatures can fluctuate by 15-20 degrees within a single day. A bearing fit measured in the cool morning hours may not represent actual operating conditions during the afternoon heat.

2. Induction Hardening Consistency

Induction hardening of the raceway surface relies on precise heating and quenching cycles. When workshop temperature climbs above 38 degrees Celsius, the cooling efficiency of the quenching medium can shift, potentially affecting hardened layer depth and surface hardness consistency.

3. Humidity and Corrosion Risk

Major Heat brings extreme humidity. The "soil is moist and the air is muggy" - as the ancient description goes - is a warning for metalwork. During monsoon-like rainy periods, corrosion risk on machined steel surfaces increases significantly.

The Chinese calendar divides Major Heat into three five-day phases: fireflies emerging from the grass, the earth becoming damp and muggy, and heavy rains arriving in succession. These ancient observations carry practical wisdom: extreme conditions, while challenging, prepare the ground for autumn harvest.

In manufacturing, the same principle applies. High temperatures reveal stresses in materials and processes that remain invisible in milder conditions. A production line that performs reliably through Da Shu is one designed with safety margin, monitored with care, and operated with discipline.

There is a traditional custom called "sending off the Major Heat boat" - launching a decorated vessel into the sea to dispatch summer heat and pray for a smooth harvest. For a manufacturer, this spirit of preparation - anticipating challenges before they arrive - is not a ritual but daily practice.

Extreme weather tests not only equipment but people. At our Hefei facility, summer workshops operate with adjusted schedules to avoid the most intense midday hours. Hydration stations are placed at every work area, and breaks are scheduled on a shorter cycle. Our heat treatment operators rotate in 45-minute shifts with dedicated cooling-down time - a practice we never compromise on.

Major Heat is traditionally a time for fu tea  - herbal infusions made from honeysuckle, prunella, and licorice. While we leave remedies to personal preference, the principle that working conditions should adapt to the season is one we take seriously.

Major Heat is the peak of the year warmth, but also the turning point. After Da Shu comes Li Qiu - the Beginning of Autumn. The ancient observation that "heat accumulates and does not rest" reminds us that every extreme is temporary, and that discipline maintained during the hardest conditions carries through to the harvest.

At Anhui Yuanfeng Slewing Rings Co., Ltd., we treat every season as part of our quality process - because a bearing that performs reliably through summer worst heat is a bearing you can trust all year round.

Editor & Layout: Daphne Hsu