Alkaline phenolic resin and its supporting curing agent contain no harmful elements such as nitrogen, sulfur and phosphorus. They can effectively avoid casting defects including blowholes and cracks, improve the surface finish of castings and feature environmental friendliness. They are suitable for the production of various castings, especially steel castings and ductile iron castings. An increasing number of foundries have adopted this process in recent years, and its scope of application keeps expanding.

The molding process is greatly affected by ambient temperature. Compared with other molding resins, alkaline phenolic resin is more sensitive to low temperatures. Many enterprises face problems such as higher resin consumption and insufficient sand mold strength during cold periods, which may disrupt normal production in severe cases. Drawing on abundant on-site application experience, Xinda enables stable production of alkaline phenolic resin-bonded sand at low temperatures through optimized material matching and standardized site management to meet production requirements.

Ⅰ. Control Resin Temperature to Stabilize Feeding and Sand Mixing

At room temperature (around 25 ℃), the viscosity of alkaline phenolic resin is generally below 100 mPa·s. A temperature drop will markedly increase resin viscosity and cause the following production issues:

1. Resin residue on the inner wall of drums is hard to clean;

2. Metering deviation occurs in sand mixers with reduced outlet flow;

3. Insufficient actual dosage leads to lower sand mold strength.

It is recommended to install heating and thermal insulation devices on resin storage drums to maintain the resin temperature at 25–30 ℃. This ensures stable viscosity and constant feeding flow for accurate dosage calibration, and promotes the reaction between resin and curing agent to achieve qualified sand mold strength.

Ⅱ. Adjust Sand Temperature to Guarantee Basic Sand Mold Strength

Sand mold strength rises significantly along with sand temperature and tends to stabilize above 25 ℃. When the sand temperature falls below 10 ℃, molds made purely of reclaimed sand have low strength and fail to meet molding requirements. Solutions for different production modes are as follows:

1. Small-batch production line for single or large castings: Long molding cycle and slow sand circulation make sand temperature close to ambient temperature. Qualified enterprises can retrofit sand mixing equipment with hot-air baking devices or add heating systems for sand silos;

2. Mass-production assembly line: Optimize the sand circulation process to send hot reclaimed sand immediately after shakeout back to the sand mixing procedure and reduce heat loss.

Ⅲ. Adjust the Ratio of Fresh Sand to Reclaimed Sand and Stabilize the Sand System

With the same resin addition rate, molds prepared with fresh sand show obviously higher strength than those with reclaimed sand. Comparative tests at a sand temperature of 0 ℃ prove that increasing the proportion of fresh sand can effectively raise the tensile strength of sand molds.

During low-temperature production, maintaining a steady supplement of fresh sand helps improve the quality of reclaimed sand, ensures stable operation of reclamation equipment, and achieves the goals of cutting resin consumption and stabilizing sand mold strength.

Ⅳ. Strengthen Management of Reclaimed Sand Treatment and Control Impurity Indicators

The treatment quality of reclaimed sand has a prominent impact on sand mold strength, and this characteristic is more noticeable in the alkaline phenolic resin sand system. Key indicators under control include:

1. Loss on ignition of reclaimed sand;

2. Dust content;

3. Clay content;

4. Moisture content.

Under low-temperature working conditions, inspection of reclamation, dust removal and dehumidification procedures shall be intensified to keep all indicators within the allowable process range and minimize strength fluctuation.

Ⅴ. Optimize Catalyst Selection and Blending to Adapt to Low-Temperature Curing Rate

Catalysts take direct part in the curing reaction and greatly affect curing speed and final sand mold strength. A single catalyst can hardly satisfy the requirements for stripping time and strength at low temperatures.

It is recommended to blend fast-acting and medium-speed catalysts for low-temperature production. The mixing ratio can be adjusted according to the workshop production rhythm to balance curing rate and comprehensive sand mold performance.

Xinda keeps focusing on supporting materials and application processes for alkaline phenolic resin-bonded sand. We have developed a complete and implementable technical solution targeting the pain points in winter low-temperature environments, helping steel and ductile iron foundries realize stable production, reduce material costs and guarantee casting quality. We will continue to provide on-site process and technical support and deliver eco-friendly and reliable integrated solutions for resin sand to our customers.