With the continuous upgrading of product quality in the domestic machinery industry and growing global demand for export castings, more and more foundries have transformed from traditional clay sand dry mold process to self-hardening resin sand casting process. Self-hardening resin sand process delivers castings with good surface finish, high dimensional accuracy and low scrap rate. It has a wide range of applications, reduces operational difficulty and labor intensity for workers, and improves workshop working conditions, making it a mainstream process for high-end export castings. However, the raw material cost of resin sand process remains relatively high. How to reduce costs through equipment selection and process optimization while guaranteeing casting quality has become a key topic in the industry.

Ⅰ.  Proper Selection of Production Equipment to Lay a Foundation for Cost Reduction

Equipment selection should not focus merely on purchase price, but also evaluate long-term operating costs. Three key points are listed below.

1. Attach importance to dust removal system configuration

   When selecting equipment, many foundries prioritize sand mixing and reclamation equipment while ignoring dust collectors. Dust removal performance directly affects the fine powder content of reclaimed sand. Poor dust control leads to excessive fine powder in reclaimed sand, which increases resin dosage and raw material consumption, and causes dust pollution in the workshop. A reliable dust removal system is critical to stabilize reclaimed sand quality and control resin consumption.

2. Balance equipment reliability and maintenance costs

   The machining and assembly capacity of equipment manufacturers determines operational stability. High equipment failure rates will increase spare part replacement frequency and lower equipment availability. It raises maintenance workload and costs, reduces production efficiency and indirectly increases casting production costs.

3. Rational control of equipment energy consumption

   On the premise of meeting process requirements, reasonably design installed capacity to avoid over-sizing equipment. Make full use of existing resources, push equipment to run at full load and improve energy utilization to save energy.

Ⅱ. Refined Control of Production Process, the Core of Cost Reduction

A well-designed process directly affects casting yield, product quality and material consumption, serving as the core of cost control for resin sand.

• Optimize LOI (Loss on Ignition) control of reclaimed sand

  LOI is a key indicator for measuring the film removal rate of reclaimed sand, closely related to gas generation of molding sand and porosity defects of castings. For conventional cast iron produced by furan resin sand, the industry generally controls LOI at around 3%. Some enterprises tighten the standard below 2.5%, which requires extra equipment, more sand reclamation cycles or large addition of new sand, significantly raising sand processing costs. Verified by mass production practice, LOI can be relaxed to 4% with proper on-site management without compromising casting quality.

• Accurate setting of key process parameters

  Determine the final strength of molds according to production rhythm, and avoid two extreme practices: blindly increasing strength which wastes resin and hardener, or cutting costs by lowering strength which causes severe fluctuation of casting quality.

The sand-to-metal ratio is recommended to be controlled at 2.2～3:1. An excessively high ratio increases consumption of resin and hardener, generates more waste sand blocks, burdens reclamation equipment and raises the risk of porosity. Too low a ratio may result in metal runout and casting deformation during pouring.

• Optimize molding process to improve casting yield

  Improving yield is the most direct and effective measure to cut casting costs. Special flasks with vent holes on flask walls are adopted for production, together with pattern plate molding using solid patterns. Ceramic runners and multiple dispersed ingates are applied in gating system. Coating shall be brushed evenly. Proper risers and vents are arranged to ensure smooth venting of cores and reduce casting defects.

III. Select Suitable Raw Materials to Secure Quality and Cost Control

Raw material quality affects auxiliary dosage and casting scrap rate, forming the foundation of cost management.

1. Selection of base sand

   Scrubbed sand is preferred, followed by washed sand. Untreated raw sand is prohibited. Scrubbed sand has low clay content and reduces resin consumption. Procurement shall follow the nearby sourcing principle to cut transportation cost and ensure stable supply. Base sand with low angularity coefficient is preferred. If conditions permit, visit sand manufacturers to check their production and quality control capacity, select sand sources through comparative tests, and balance delivered cost and molding sand performance.

2. Selection of resin

   Resin has a high unit price and greatly impacts total cost. Poor-quality resin degrades molding sand performance, increases casting rejects and forces higher resin addition. Resin selection shall not rely only on technical datasheets provided by suppliers. Sample inspection, investigation on resin manufacturer’s quality control capability and reference to application experience from peer foundries are recommended. Prioritize suppliers with stable quality and good reputation.

3. Selection of auxiliary materials

   Auxiliary materials including hardener, coating, release agent and flask sealing strips are not decisive for core casting quality, yet their impact on production cost cannot be overlooked. The addition amount of hardener directly affects curing speed, production efficiency and material expenses. Auxiliary materials shall match the performance of main materials while considering procurement and transportation convenience.

Practice proves that self-hardening resin sand casting can effectively control production costs through proper equipment selection, stable equipment operation, raw materials with stable quality and timely supply, refined process parameter control and complete tooling support. Moving forward, we will continuously optimize resin sand casting technology, and provide high-quality castings for global customers with consistent quality and controllable production costs.