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The machining and drilling of the heat exchanger tube sheet

Release time:

2025-04-24

The machining and drilling of the heat exchanger tube sheet is a technical operation with high requirements for precision and craftsmanship. The following is a detailed explanation of the key steps and precautions:

I. Preparation before Machining

1.Material and Drawing Confirmation

- Material Selection: Common materials include carbon steel, stainless steel (such as 304/316), titanium alloy, etc., which should be selected according to the corrosiveness of the medium.
- Drawing Review: Check the technical requirements such as hole diameter tolerance (usually ±0.1mm), hole pitch accuracy (±0.05mm), and surface roughness (Ra≤3.2μm).

2.Tooling and Fixture Design

- Use a special indexing plate or CNC rotary table to fix the tube sheet to ensure a stable clamping and prevent machining vibration.
- For large tube sheets (diameter > 2m), multi-point support is required to reduce deformation.

3.Tool Selection

- Drill Bit Type: Carbide-coated drill bits (suitable for high-hardness materials), gun drills (for deep hole processing), and step drills (for forming multiple hole diameters at once).
- Parameter Matching: Adjust the geometric angle of the drill bit according to the material (for example, for stainless steel, the rear angle should be increased to reduce friction).

II. Key Steps of Drilling Process

1.Positioning and Marking

- Use laser projection or CNC programming to determine the hole positions to ensure that the hole group distribution meets the design requirements (such as triangular/square arrangement).
- Pre-drill a center hole (Φ3 - 5mm) as a guiding reference.

2.CNC Programming Optimization

- Path Planning: Adopt spiral feed or peck drilling (G83 cycle) to reduce cutting heat and avoid chip clogging.
- Sequential Processing: Rough drilling (leaving a margin of 0.2 - 0.5mm) → Fine reaming/boring (to ensure size and smoothness).

3.Cooling and Chip Removal

- High-pressure internal cooling system (pressure > 5MPa) directly cools the drill tip to extend the tool life.
- Regularly clean the chips to prevent winding (especially for aluminum/copper materials).

4.Precision Control

- Real-time Monitoring: Use the machine tool probe (such as Renishaw) to online detect the hole diameter and position to compensate for the thermal deformation error.
- Post-processing Inspection: Use a coordinate measuring machine (CMM) to inspect the hole pitch in full and spot-check the hole diameter with a plug gauge.

III. Common Problems and Solutions

1.Hole Position Deviation

- Cause: Loose fixture, machine tool backlash.
- Countermeasure: Regularly calibrate the machine tool accuracy and use a hydraulic fixture to enhance rigidity.

2.Hole Diameter Out of Tolerance

- Cause: Drill bit wear, improper cutting parameters.
- Countermeasure: Check the drill bit wear every 50 holes processed. For stainless steel, it is recommended that the rotational speed is ≤80m/min and the feed is 0.1mm/r.

3.Rough Hole Wall

- Cause: Poor chip removal, too small rear angle.
- Countermeasure: Increase the number of tool withdrawals. For fine processing, use a reamer (Ra can reach 1.6μm).

IV. Advanced Processes (Special Requirements)

1.Deep Hole Processing (hole diameter to depth ratio > 10)

- Use BTA deep hole drill + high-pressure cooling, with a shock-absorbing guide sleeve.

2.Composite Tube Sheet (Overlay Weld Layer)

- First machine the base layer (carbon steel), then perform overlay welding of the stainless steel layer and then secondary fine processing to avoid delamination.

V. Safety and Maintenance

Operating Specifications: Wear protective glasses to avoid long chip winding.
Equipment Maintenance: Clean the guide rail chips per shift and replace the spindle grease regularly.

Through the above fine process control, the drilling quality of the heat exchanger tube sheet can be ensured to meet the requirements of standards such as ASME or GB151, significantly improving the sealing performance and service life of the heat exchanger.