Synthetic resins have been used for the fabrication of moulds and cores for heavy and individual castings since the sixties. These cold curing resins generally are reaction products of combinations of furfuryl alcohol or phenol and urea with formaldehyde. Variations are based on polyurethanes and resoles.

All methods have been and will remain under constant development in consideration of their environmental compatibility. The emissions during sand conditioning and mould filling normally do not reach the permissible MAK (TLC) limits, and frequently even lie well below these limits.

Cold cure binder systems are presently classified according to four main process principles.

The introduction of these processes may undoubtedly be regarded as one of the greatest advances to take place in the foundry industry.

The furan Kaltharz process is the classical all-purpose method for the fabrication of all different grades of various castings. Specially modified, nitrogen-free furan resins are available for steel casting. Resins with a drastically reduced water content permit the fabrication of high-quality aluminum castings. All modern furan resins permit the use of large amounts of reclaimed sand, in many cases up to nearly 100 percent, even when adding just small binder dosages. This is also a contribution to environment protection and resource conservation. Organic acids and mixtures of organic acids with inorganic acids are used as hardeners (curing agents). In rare cases, curing can also be carried out by using pure inorganic acids.

Just like the furan binders, phenol-based resins may also be cured by adding acidic activators. These systems have proved to be reliable, particularly for the individual fabrication of heavy castings in steel, gray iron and nodular iron.

The Sinotherm 200 and Pentex methods are based on completely different curing principles. Sinotherm 200 resins are alkaline phenolic resoles that are cured by adding esters. This process is excellent for high-quality steel castings, since it does not involve phosphorous, nitrogen or sulfur.

The Pentex process involves a three-component system consisting of a modified, phenol-based synthetic resin, a polyisocyanate and a catalyst. The curing rate is controlled by the catalyst addition level. This process is particularly suitable for short and medium series steel and aluminum casting.