Cast Polyurethane (CPU), widely known in the industry as “liquid rubber,” is an advanced product manufactured by pouring a liquid reaction mixture directly into a mold. As a major branch of the polyurethane family, its unique two-phase structure—comprising both soft and hard segments—endows it with exceptional mechanical, physical, and chemical properties.
By perfectly bridging the high elasticity and shock-absorbing capabilities of rubber with the rigidity of plastic, CPU has become indispensable across the national economy, penetrating sectors such as chemicals, electronics, automotive, defense, aerospace, medical, and construction.
The Chemical Matrix: 3 Core Raw Materials of CPU
A top-tier CPU product relies on a rigorously engineered formulation consisting of three primary components, often supplemented by specific functional additives:
1. Polyols (The Flexible Soft Segment): Polyols form the soft segment of the CPU matrix, providing the product’s fundamental flexibility. Industrial applications primarily utilize polyether polyols and polyester polyols.
2. Isocyanates (The Rigid Hard Segment): Acting as the hard segment, isocyanates deliver the necessary rigidity and structural strength. The most common types used in CPU production include Toluene Diisocyanate (TDI), 4,4′-Diphenylmethane Diisocyanate (MDI), 1,5-Naphthalene Diisocyanate (NDI), and Paraphenylene Diisocyanate (PPDI).
3. Chain Extenders (The Curing Catalysts): For polyurethane elastomers, chain extenders are generally divided into amines and alcohols. Diamine extenders are predominantly used in TDI-based elastomer production and are categorized into aromatic and aliphatic diamines. Crucially, CPU products must utilize aromatic diamines; aliphatic diamines have excessively high reactivity, causing rapid gelling when reacting with isocyanates, making them completely unsuitable for the casting process.
To further improve processing performance, enhance product characteristics, or reduce costs, manufacturers often incorporate additives such as plasticizers, fillers, colorants, and catalysts, along with stabilizers like antioxidants, wear-resistant agents, and flame retardants.
The Standard CPU Casting Workflow:
Generally, the prepolymer and chain extender are metered from storage tanks and pumped into a mixing head. Once uniformly mixed, the liquid is injected into a mold where it undergoes polymerization and curing before finally being demolded.
From Railways to Aerospace: The Expanding Applications of CPU
Because polyurethane elastomers exhibit outstanding resistance to wear, oil, tearing, chemical corrosion, and radiation—coupled with excellent adhesion to other materials and superior shock absorption—their application potential is limitless:
Transportation and Railways: This sector represents the largest consumption of PU abroad, utilizing the material for automotive bumpers, steering wheels, and dashboards. In railway infrastructure, it is critical for solid tires, marine fenders, locomotive fuel tank rings, and the heavy-duty shock-absorbing pads placed beneath train sleepers.
Heavy Machinery: Polyurethane has become a key structural material in engineering machinery, widely used for oil-resistant, wear-resistant, and shock-absorbing seals. It is also essential for transmission belts, wear linings, steel pipe straightener trough liners, and steel-rolling rubber rollers.
Textiles and Sports: In the textile industry, CPU is molded into spinning, printing, and grain processing rollers. In sports, it forms the foundation of PU running tracks, ski boot pulleys, and roller skate wheels.
Defense and Aerospace: Thanks to its extreme resilience, CPU is deployed in military applications, including airtight artillery pads, armored vehicle bulletproof plates, and missile nose protective covers.
Master the Pour with Precision Engineering
Understanding the chemistry of CPU is only the first step. Executing the precise metering of prepolymers and chain extenders from the tanks to the mixing head requires absolute mechanical perfection.
Supported by a dedicated workforce of over 50 employees and a specialized subsidiary, Machine à polyuréthane Haifeng translates complex chemical reactions into highly profitable, automated production lines. As a globally recognized expert en machines pour le polyuréthane, we engineer high-pressure and low-pressure elastomer casting equipment equipped with intelligent PLC closed-loop systems, guaranteeing perfect stoichiometric ratios and flawless dynamic mixing.
Agir en tant que fournisseur de solutions dans le domaine du polyuréthane, we are ready to elevate your manufacturing capabilities. Contact our engineering team today to architect the perfect CPU casting solution for your factory floor.
