I started with a ship full of max-level veterans, and I'm just a complete noob.

Jiang Ming's consciousness sank into the void and quickly locked onto that familiar name.

[System Prompt: Connecting to a late pioneer of early vacuum tube and radar physics. Duration: 15 minutes. Countdown begins.]

Pioneer's somewhat impatient voice rang out: "Not again? What's the matter this time, that's so serious?"

"Senior, the grinding precision of the seal is up to standard, but when it was installed on the test bench and ran for eight minutes, a micro-leakage started to appear."

Jiang Ming spoke very quickly, rattling off the whole issue of thermal expansion in one breath.

"The coefficients of linear expansion of rubber and metal differ by an order of magnitude. When the temperature rises during operation, micro-gaps will appear at the interface. I need to know how to compensate for this."

The pioneer paused for three seconds, then spoke with a hint of sternness:

"You should have thought of this sooner."

"The linear expansion coefficient of fluororubber is more than ten times that of ordinary carbon steel. If you put these two materials together without considering temperature changes, it's simply reckless."

"There is only one direction for compensation, and that is over-compensation."

"You must calculate the initial interference fit of the seals based on the actual operating temperature range of the rotary vane pump."

"The rubber is in a slightly compressed state when assembled at room temperature. After the pump starts running and heats up, both the metal and the rubber will expand, but the rubber expands faster."

"As long as the initial interference is calculated accurately, the amount of compression released by the rubber after heating will be just enough to achieve zero-gap fit with the metal surface."

Jiang Ming's mind raced: "Senior, what is the specific value of the interference fit?"

"Calculate it yourself!"

The pioneers rejected the offer without hesitation.

"You have the approximate range of the material's coefficient of expansion, the pump's operating temperature, and the heat conduction formula that Qian Xuesen taught you. That's enough."

"However, I must remind you of a fatal detail."

The pioneer's voice lowered:

"Your fluororubber is a second-grade industrial product, with a purity of only 92%, and the composition of impurities is unknown."

"This means that its actual inflation coefficient will be larger than the theoretical value."

Jiang Ming pressed further, "How much larger?"

"Go try it yourself, I'm not your rubber."

The pioneer's answer was cold and decisive.

System notification: The duration of a single psychic session has reached fifteen minutes. The connection has been disconnected.

Jiang Ming took a deep breath in the void.

The direction is clear: adopt an interference fit and back-calculate the initial compression amount.

But another problem arises.

What happens when metal and rubber come into direct contact and undergo repeated thermal cycles?

Jiang Ming vaguely remembered that in the vacuum sealing design of later generations, the metal and the elastomer would never come into direct contact.

He needs to find someone to confirm this conjecture.

[System prompt: Connect to other unlocked historical figures?]

Jiang Ming looked at the network diagram and spotted another name that was faintly lit next to the pioneer of vacuum tubes.

The late colleague's academic field was: vacuum systems engineering and materials interface physics.

Previously, we hadn't connected because we didn't need it, but now, it just so happens to be in their area of ​​expertise.

connect!

System notification: Psychic dialogue initiated, duration 15 minutes per session.

A young voice, speaking rapidly and with an academic air, rang out: "Who are you? How did you find me?"

"Junior Jiang Ming is modifying a Soviet rotary vane pump and has encountered a problem with the material compatibility at the sealing interface."

Jiang Ming went straight to the point: "What problems might arise when fluororubber seals are in direct contact with a carbon steel pump shaft during repeated thermal cycles?"

There was a two-second silence on the other end, followed by a violent outburst of emotion: "Direct contact? Are you crazy?!"

"The metal surface has microscopic roughness, which will repeatedly scrape the rubber surface like a file during thermal cycling."

"After only a few cycles, the rubber sealing surface will begin to peel off microscopically. These debris will fall into the vacuum chamber and become a source of venting, directly contaminating the vacuum environment!"

Jiang Ming's heart tightened: "Then how should we solve this?"

"A very thin layer of vacuum grease is applied to the contact interface as a buffer layer."

The fellow disciple's answer was resolute:

"Vacuum grease can fill the micro-grooves on the metal surface, forming a lubricating film and preventing the rubber from being directly worn."

"How thick should I apply it?"

"It depends on your vacuum level target. If you apply it too thickly, the vacuum grease itself will release air; if you apply it too thinly, it won't provide any protection."

"I'm not sure about the exact number, but it should be in the single digits of micrometers. You'll need to find someone who knows more about high vacuum sealing to confirm."

[System notification: The duration of this single psychic session has reached fifteen minutes. The connection has been disconnected.]

Jiang Ming has one last chance to communicate with the spirits.

Without hesitation, he switched back to the vacuum tube pioneer.

[System notification: The third psychic summoning session has begun.]

"Senior, one last question: When applying vacuum grease to the sealed interface for cushioning, what is the maximum possible thickness for this coating?"

The pioneer was quite pleased with this question: "You finally figured it out."

"It cannot exceed five micrometers."

"Below this thickness, the outgassing rate of the vacuum grease can be ignored."

"Once it exceeds five micrometers, the lipid layer will slowly evaporate organic molecules under high vacuum, becoming the biggest source of pollution in the system."

"Moreover, the coating must be absolutely uniform; any area that is too thick is a ticking time bomb."

[System notification: You have exhausted your three summoning attempts for today.]

Jiang Ming opened his eyes.

The dormitory was pitch black, with only the table lamp emitting a faint light.

He rolled out of bed and quickly walked to his desk.

The information obtained from three psychic encounters in my mind quickly converged:

Interference fit, reverse calculation of working temperature, correction of expansion coefficient, and application of vacuum grease within five micrometers.

Jiang Ming took out his lecture notes, turned to the chapter on heat conduction, and compared it with the working temperature of the Soviet rotary vane pump that he had copied down.

"Maximum operating temperature: 120 degrees Celsius."

He muttered to himself as his pen flew across the scrap paper, writing formulas.

Pump shaft outer diameter, carbon steel linear expansion coefficient, fluororubber linear expansion coefficient.

Temperature difference: from room temperature of 20 degrees to working temperature of 120 degrees, a span of 100 degrees.

The formulas for the expansion of metals and rubber are laid out on paper.

He stopped writing after the third line.

The problem lies in the precise coefficient of thermal expansion of fluororubber.

The purity of the industrial grade II product is only 92%. Impurities will cause the expansion coefficient to be larger, but there is no data on how much larger it will be.

After a moment's thought, Jiang Ming made a bold decision.

He multiplied the theoretical expansion coefficient of pure fluororubber by a safety factor of 1.1, and used this to deduce the interference.

This means that assembly at room temperature will be tighter and more difficult, but it can ensure the sealing performance after high-temperature operation.

It's better to put in more effort during assembly than to have it leak during operation.

The pen tip landed back on the paper.

Without a calculator, he could only use the most primitive method of manual calculation, breaking down and verifying the steps one by one.

He checked each digit after the decimal point twice.

A pile of scrap paper filled with writing sat to one side.

He finally calculated the value at 2 a.m.

At room temperature, the inner diameter of the seal should be 0.015 mm smaller than the outer diameter of the pump shaft.

To ensure everything went perfectly, Jiang Ming took out a new sheet of paper and recalculated the calculations.

The results were completely consistent.

Jiang Ming breathed a sigh of relief and began to draw the revised blueprints.

In addition to the tolerance markings, he also specially drew a thin buffer layer on the sealing surface and noted:

"The vacuum grease buffer layer should be no more than five micrometers thick and must be applied evenly."

As the first rays of dawn appeared outside the window, Jiang Ming finally put down his pen.

Looking at the revised drawings, he did not show any relief.

The interference of 0.015 mm means that Lao Sun not only has to maintain extremely high grinding precision, but also has to precisely control the inner diameter within this tiny tolerance range.

And there's an additional, extremely difficult step:

A layer of vacuum grease, less than one-twentieth the thickness of a human hair, is evenly applied to the mirror-polished sealing surface.

Applying too much will cause it to release air and become ineffective, while applying too little will not provide any protection.

Jiang Ming put away the blueprints and gave a helpless, bitter smile.

"If Old Sun heard this request, he'd probably break his pipe in two."