Full Construction Technical Standards for Kiln Car Manufacturing in Fired Brick Plants

1 General Provisions

1.1 Scope of Application
These standards apply to the complete process of new fabrication and refurbishment of dedicated kiln cars for tunnel kiln fired brick production lines, covering all procedures: kiln car structural design, steel structure welding, base leveling, refractory and insulating layer masonry, running gear assembly, sealing structure installation, complete car commissioning, and factory acceptance. Kiln cars operate under prolonged high temperatures (maximum kiln temperature 1050°C), alternating thermal cycles, heavy-load pushing, and track reciprocating motion. These standards specifically address common industry issues such as frame deformation, lining cracking and heat leakage, wheel jamming, sand seal air leakage, car deviation, and cross‑flow affecting brick firing quality.

1.2 Basic Technical Requirements

• Rated load per car: meeting full‑load stacking of fired bricks, with a single‑car capacity ≥35 t.
• Operating conditions: adapted to thermal cycles from ambient to 1050°C, with resistance to thermal shock, extrusion, and deformation.
• Dimensional tolerances: overall dimensions, coaxiality of four wheels, and joint gaps all standardized to ensure interchangeability across the entire kiln car fleet.
• Service life: steel frame service life ≥8 years under normal conditions; major overhaul interval for refractory lining ≥2 years.

2 Technical Standards for Kiln Car Structural Design

2.1 Overall Structural Design
The kiln car adopts a main beam + secondary beam + deck plate frame steel structure, consisting of six modules: running mechanism, steel frame, thermal insulation base, refractory load‑bearing surface, side sand seal systems, and front/rear end face sealing. Simplification of structure or reduction of section thickness is prohibited.

2.2 Steel Section Selection Standards

• Main load‑bearing beams: National standard 30# thickened I‑beams, thickness ≥14 mm, to resist longitudinal pushing forces and vertical loads, preventing bending deformation under prolonged heavy load.
• Transverse secondary beams: 20# channel steel, spacing controlled at 400 mm ±20 mm, to evenly distribute deck loads.
• Frame bottom plate: 6 mm thick checkered steel plate, fully welded to prevent insulation layer detachment.
• Towing end plate: 20 mm thick reinforced steel plate, positioned at the continuous pushing point to avoid end extrusion deformation.
• Sand seal side plates: 8 mm thick heat‑resistant steel plate, with thermal expansion clearances to prevent warping at high temperature.

2.3 Thermal Expansion and Anti‑Deviation Design

• Bidirectional expansion joints are in both refractory lining and steel structure to relieve high‑temperature expansion stresses.
• Wheels adopt standard gauge design with four‑wheel coaxial layout to inherently avoid deviation and rail gnawing.
• An insulating protection plate is installed under the frame to shield running components (axles, bearings, etc.) from kiln heat radiation.

3 Welding Construction Standards for Steel Frame

3.1 Pre‑Welding Preparation
All sections shall be deburred, and oxides, rust, and grease removed after cutting. The frame shall be assembled and positioned on a jig platform to ensure overall length and width tolerance ≤ ±3 mm. Assembly without a jig is forbidden to prevent inherent distortion.

3.2 Welding Process Requirements

• Welding method: CO₂ gas‑shielded welding, with full and firm weld beads. Double‑layer full welding at connections between main and secondary beams; spot welding or intermittent welding is prohibited.
• Weld quality: weld height ≥6 mm, free from slag inclusions, porosity, cracks, undercut, etc. Critical load‑bearing welds shall be 100% visually and non‑destructively inspected.
• Stress relief: after complete welding, the car shall be left to stand for 24 hours to release internal welding stresses; next processes shall not start immediately.
• Overall correction: after standing, the frame shall be leveled; flatness error ≤2 mm/m, diagonal height difference ≤3 mm.

3.3 Prohibited Defects
Splicing short pieces for main beams, concentrated welding on one side, and omitting stress relief are strictly forbidden. These practices will cause beam bending and weld cracking within 1‑3 months of service, leading to total car scrapping.

4 Technical Standards for Kiln Car Base (Steel Surface) Treatment

4.1 Post‑Welding Grinding and Cleaning
All welds shall be ground smooth to remove weld spatter and sharp edges. Dust, slag, and debris inside the frame shall be thoroughly cleaned to avoid affecting insulation layer adhesion and to prevent carbonization and blistering at high temperature.

4.2 Anti‑Corrosion and Thermal Insulation Base Coating

• External non‑heated areas of the frame shall be coated with high‑temperature‑resistant anti‑rust primer to prevent corrosion during outdoor storage.
• The upper surface (masonry base) shall be covered with a 5 mm thick high‑temperature refractory fiber felt to block heat conduction from steel structure to refractory bricks, reducing frame temperature and preventing softening deformation.
• Base leveling: the fiber felt shall be laid flat without wrinkles, ensuring a level substrate for subsequent insulation and refractory brick masonry to avoid uneven stress and cracking.

5 Masonry Construction Standards for Insulation Layer + Refractory Brick Lining (Core Procedure)
The deck adopts a three‑layer composite structure: bottom insulation layer + middle transition insulation layer + top refractory load‑bearing brick, total thickness ≥180 mm, laid in staggered joints; continuous vertical joints are prohibited.

5.1 First Layer: Lightweight Thermal Insulation Layer

• Material: lightweight clay insulating bricks, thickness 80 mm.
• Construction: wet‑laid with refractory mortar, joint thickness 2‑3 mm. Main function: isolate high kiln temperature to protect underlying steel frame and running wheels.
• Prohibition: ordinary red bricks are strictly forbidden as substitute; otherwise, bottom temperature will exceed limits and damage bearings and axles.

5.2 Second Layer: Refractory Fiber Insulation Transition Layer

• Material: 10 mm thick high‑temperature ceramic fiber blanket, fully laid over the entire surface.
• Function: further block heat conduction and buffer thermal expansion stresses of refractory bricks, reducing cracking probability.

5.3 Third Layer: High‑Alumina Refractory Load‑Bearing Brick (Top Layer)

• Material: second‑grade high‑alumina refractory bricks, thickness 90 mm, high compressive strength for direct stacking of green bricks.
• Masonry requirements: staggered joints between upper and lower layers; vertical through‑joints prohibited; joint thickness ≤2 mm, with full mortar filling without voids.
• Expansion joints: 15‑20 mm expansion gaps reserved in both transverse and longitudinal directions, filled with refractory fiber cotton to prevent brick arching and fracturing due to mutual extrusion at high temperature.

5.4 End Face Sealing Masonry Requirements
The front and rear end faces of the kiln car shall be built with a tongue‑and‑groove interlocking sealing structure instead of flat butt joints, reducing air leakage gaps between cars, stabilizing kiln firing temperature, and ensuring brick quality.

6 Assembly and Construction Standards for Running Gear (Wheels + Axles + Bearings)

6.1 Wheel Technical Standards

• Material: ZG340‑640 heat‑resistant cast steel; ordinary gray cast iron is prohibited. The tread shall be induction hardened with a hardened layer depth of 3‑5 mm to improve wear resistance.
• Machining accuracy: coaxiality error of wheel bore ≤0.2 mm; tread free from taper and out‑of‑roundness.
• Assembly: after mounting all four wheels, diagonal height difference ≤2 mm to ensure even load distribution and prevent excessive wear on individual wheels.

6.2 Axle and Bearing Assembly Standards

• Axles: 45# quenched and tempered carbon steel with high bending strength; ordinary carbon steel axles that may bend under heat are prohibited.
• Bearings: special high‑temperature bearings with high‑temperature grease; bearing housings equipped with independent oil injection holes.
• Thermal expansion clearance: 1.5 mm expansion clearance reserved between hub and shaft shoulder to prevent metal expansion seizing and causing car jamming.

7 Installation Standards for Side Sand Seal Systems
The sand seal structure is critical for preventing cold/hot air cross‑flow, directly affecting kiln temperature stability and energy consumption.

• Sand seal plate installation: full welding fixation is prohibited; use bolted connection through slotted holes to allow thermal expansion and avoid warping and scraping against the sand seal trough.
• Gap control: single‑side clearance between sand seal plate and trough controlled at 3‑5 mm; excessive gaps cause air leakage, while insufficient gaps cause friction and rail sticking.
• Plate seam sealing: joints between sand seal plates shall be filled with refractory sealing cotton to eliminate side air leakage.

8 Overall Commissioning and Factory Acceptance Standards

8.1 No‑Load Test Run
The kiln car shall undergo three round‑trip test runs on standard tracks, with smooth operation, no sticking, no abnormal noise, no deviation, and no rail gnawing. Check wheel loading – no wheel shall be suspended; operation shall be stable without bouncing.

8.2 Sealing Performance Test
When two adjacent cars are coupled, the end gap shall be ≤2 mm without obvious air leakage points. The sand seal plates shall be vertical with no tilt or deformation.

8.3 Dimensional and Visual Inspection

• Overall dimensions shall be uniform to ensure interchangeability across the fleet.
• Refractory masonry shall be firm without looseness or cracks; expansion joints shall be properly filled.
• Steel structure shall be free from deformation, weld cracks; protective guards shall be fully installed.

8.4 Delivery Documentation
Each car shall be accompanied by an inspection report including material certificates, weld inspection records, four‑wheel coaxiality measurement data, and masonry dimension records.

9 Common Construction Defects and Rectification Plan

10 Concluding Remarks by Brictec
As the core transfer equipment in tunnel kiln fired brick production lines, the construction quality of kiln cars directly determines kiln energy consumption, finished brick yield, and operational maintenance costs. Strict adherence to the full‑process technical standards – from structural design, steel welding, base treatment, refractory lining, running gear assembly to complete car commissioning – can thoroughly eliminate frequent failures such as deformation, heat leakage, deviation, and air cross‑flow, effectively extending service life and ensuring continuous, stable, and low‑cost operation of the entire fired brick production line.