Construction Requirements for Phosphate Bricks of Rotary Kiln

Applicable: Phosphate-bonded high-alumina wear-resistant bricks for transition zone and cooling zone of cement rotary kiln

1. Pre-construction Preparation

1. Mortar requirements (top priority): Special phosphate refractory mortar must be used. Ordinary refractory mortar, high-alumina cement or silicate mortar are prohibited. Phosphate mortar is corrosive and shall not be in direct contact with the shell steel plate. An isolation layer (high-alumina refractory mortar / fiber mat) can be arranged on the back of bricks.

2. Brick inspection: Bricks shall be free of chipping, cracks and delamination. Remove dust, oil stains and accumulated water on brick surfaces. Damp bricks shall be dried before laying; bricks with visible water are not allowed for construction.

3. Shell base treatment: Remove rust and slag from the shell steel plate, and ensure roundness meets requirements. Mark setting-out lines, including circumferential joint reference lines and expansion joint positions.

4. Ambient conditions: Construction temperature: 5～35℃. Stop construction when the temperature is below 5℃. Keep the work area rainproof and waterproof; water ingress and dampness are strictly forbidden during curing.

5. Mortar mixing: Mix strictly in accordance with the manufacturer’s proportion. Do not dilute by adding water arbitrarily. Mix mortar on demand and discard once initial setting occurs. Use separate tools for different mortars to avoid cross contamination.

2. Construction Technology Requirements (Circular Laying for Rotary Kiln)

1. Laying method: Circular laying is preferred. Construct symmetrically in sections (5～6 m per section). Start laying from the kiln bottom and build synchronously on both sides. Rotate the kiln body with support arch frames to guarantee concentricity. Straight through joints are forbidden. Longitudinal staggered joints shall be no less than 1/2 of the brick length.

2. Joint thickness control: Cold joint thickness: 2～3 mm. Mortar filling rate ≥95%. Brick joints shall be neat and the inner arc surface of kiln smooth. Scrape off excess mortar immediately; do not refill joints after mortar hardens.

3. Operation method: Apply mortar following the principle of “stable dipping, low fitting, short pulling and compact rubbing”. Seat bricks with rubber hammer gently. Heavy striking with sledgehammer is forbidden to prevent hidden cracks inside bricks. Bricks shall be tightly attached to shell pads without gaps.

4. Closing bricks: Prearrange and trial-fit closing bricks for each ring. Tighten closing bricks from both sides toward the middle. It is forbidden to cut thin or hammer closing bricks forcibly. Closing positions shall avoid the lower stressed area of the kiln.

3. Expansion Joint Arrangement (Indispensable due to thermal expansion of phosphate bricks)

1. Reference value: Reserve 6～8 mm expansion joint per meter of masonry; drawings shall prevail if specified. Fill joints with refractory fiber board. Do not fill expansion joints with phosphate mortar, otherwise bricks may crack or fall off under thermal extrusion.

2. Arrange circumferential and longitudinal expansion joints evenly, away from closing brick positions.

4. Curing Requirements (Phosphate bricks are air-hardening, WATER CURING IS FORBIDDEN!)

1. After masonry completion, conduct air curing at ambient temperature for 24～48 hours. Ventilate mildly; avoid strong cold wind, rain spraying and water sprinkling for curing (completely different from castables).

2. Do not rotate the kiln or vibrate the lining during curing. Remove support arch frames only after mortar reaches initial strength.

5. Baking Schedule (Critical, slow heating rate required)

Baking can start only after qualified curing, with low heating rate:

Ambient temperature → 150℃ (heat slowly to discharge free water) → hold at 300℃ → then gradually raise to normal kiln temperature.

Rapid heating or sharp temperature rise is prohibited, which will cause joint cracks and large-area lining falling off.

6. Prohibited Items

1. Do not mix ordinary refractory mortar or cement-based mortar

2. Do not spray water for curing or allow rain soaking

3. Do not form straight through joints or insufficient mortar filling

4. Do not fill expansion joints with mortar

5. Do not rotate kiln or vibrate lining during curing

6. Do not let mortar contact shell steel plate directly

7. Acceptance Criteria

Joint thickness, mortar filling rate, staggered joints, expansion joints, closing bricks and lining roundness shall comply with drawings and GB 50211. The surface shall be free of cracks and empty joints.