We have been asked to apply a zinc phosphate to steel surfaces in one of our products. For a number of reasons, we do not want to use a dipping process. Does zinc phosphate have an alternate application method other than dipping? M.L.
Zinc phosphates are applied on steel surfaces using solutions of zinc phosphate, phosphoric acid and activators. These proprietary chemical solutions deposit a crystalline coating of zinc phosphate during the application process. During the initial steps in the process, the metal is cleaned to remove oily soils. They can be applied cold or hot. Although viable, the cold processes are not widely used.
Cold zinc phosphates are applied using brush, spray, dip or flow coating on steel. Cold phosphates are used in maintenance and in-the-field painting. There have also been thixotropic zinc phosphate pastes used in maintenance painting pretreatment.
Most OEM manufacturing plants use a hot zinc phosphate process. Hot zinc phosphates are applied by dipping or spraying. It is also possible to apply them using a multi-stage steam spray applicator. The advantage of dipping and spray processes is control of crystalline structure and coating weight.