EPMMA Characteristics and Applications for Lost Foam Pattern Materials

I. Basic Chemical Composition of  White Pattern Materials

1. Styrene

Each ethylene molecule combines with one benzene molecule to form one styrene molecule. The benzene ring is exceptionally stable — it is difficult to undergo addition, oxidation, or decomposition reactions.

Structural formula：

2. Methyl Methacrylate (MMA)

It has a molecular chain structure that is highly prone to cleavage.

Structural formula：

II. Commonly Used White Pattern Materials

A polymer resin based on the above two components, when impregnated with a foaming agent, acquires expansion properties and thus becomes an expandable pattern material.

1. EPS

Expandable Polystyrene (EPS): A polymer resin composed solely of styrene monomers, containing 92% carbon. It exhibits very poor vaporization, leaves a large amount of solid residue, requires significant carbon addition, and produces considerable carbon slag defects. It is considered the lowest-grade pattern material.

2. STMMA（Copolymer Material）

Expandable Copolymer of Methyl Methacrylate and Styrene (EPMMA): Contains 63% carbon. It has excellent vaporization, leaves minimal solid residue, requires very low carbon addition, and produces very few carbon slag defects. It is widely used in ductile iron and carbon steel products.

STMMA—FD (FD Material): A copolymer with a lower proportion of methacrylate, containing 82% carbon.

FD material decomposes catalytically and, compared with ordinary EPS, effectively reduces carbon slag, making it an ideal pattern material specifically for gray cast iron.

3. EPMMA

Expandable Polymethyl Methacrylate (PMMA):  A polymer resin composed solely of methyl methacrylate monomers, containing 45% carbon.

It undergoes extremely thorough thermal decomposition at high temperatures, with a very high degree of vaporization and minimal solid residue.

The carbon addition requirement is very low, and carbon slag defects are extremely rare, making it the most ideal pattern material.

Applications: Suitable for materials and products sensitive to carbon addition and carbon slag defects:

1. Low carbon steel series

2. Stainless steel series

3. High-quality ductile iron products

EPMMA、STMMA、STMMA—FD，Comparison Diagram of Combustion at Ambient Temperature and Pressure

EPMMA Carbon Addition Value Test Statistics Table

III. Main Characteristics of EPMMA Materials

1. Complete Decomposition and High Vaporization (requiring a correspondingly higher gas generation). The pattern material decomposes rapidly due to the “zipper-like” decomposition of the methacrylate.

2. Compared with STMMA (copolymer material), EPMMA generates more gas per unit time and vaporizes faster. Consequently, a faster venting rate is required to ensure that gases produced during decomposition and combustion are discharged in time. 

IV. Approaches to Overcome “Metal Reflux” and Achieve Smooth Pouring

Improve Venting Efficiency and Increase Venting Speed

1. Increase Venting Power    

(1) Increase venting capacity, i.e., ensure sufficient vacuum pump power or adequate total system power.    

(2) Maintain a sufficiently high and relatively stable casting negative pressure

2. Reduce Venting Resistance

(1) Venting resistance mainly comes from the coating.    

(2) Use ultra-high-permeability coatings to improve coating permeability, thereby reducing venting resistance and    increasing venting efficiency.

3. Pay Attention to Venting Ducts and Flask Design    

(1) Increase the diameter of venting ducts and ensure gas exhaust paths have no “bottlenecks.”    

(2) Optimize flask design: negative pressure zones should be dense rather than sparse; maximize the number and total area of vent holes; avoid overly fine sand screens. For connections to venting ducts, consider both diameter and quantity.

IV. Approaches to Overcome “Metal Reflux” and Achieve Smooth Pouring

Extend Pattern Drying or Curing Time to Reduce Total Gas Generation

Extending the pattern drying time to over 30 days reduces the volatile content to a very low level, which correspondingly decreases the total gas generation.

V. Summary

The solid residues generated from pattern decomposition cannot be discharged from the mold cavity, which is an inherent limitation of the lost foam casting process. Promoting complete vaporization of the pattern to minimize solid residues is the most effective way to reduce carbon addition and carbon slag.

As a high-end pattern material, EPMMA’s high vaporization is its advantage, and its large gas generation is an inherent characteristic. By implementing proper process measures to ensure a smooth pouring process, its benefits of low carbon addition and minimal carbon slag can be fully realized, creating greater potential for the mass production of high-end lost foam products.

20 Steel and 25 Steel Products

Grade B Steel Products

Anode Steel Claws (Carbon Content below 0.15%)

Ductile Iron Products