When installing foam insulation, there is a metal to metal contact between a mixing chamber and two side seals, one for each chemical. These parts MUST be perfectly smooth to prevent the fluids from leaking between the joining faces of each part.The fluids are under pressure up to 2000 psi. and are heated to 165*F.
When metal parts are in direct contact and friction is the result, lithium grease is injected into the front of the gun assembly. This is what is referred to as the “chemical housing”, or the “wet end”. The lithium grease also acts as a binding inhibitor in the mixing chamber and a lubricant for the metal to metal contact between the moving parts.
Image | Artist Simulation
The original design of the side seals has an under cut around the perimeter that allows for the lithium grease to build-up in this under cut. As the mixing chamber and side seals move back and forth, the lithium grease is contacted to the chemical residue and causes crystallization of the grease build up in the under cut. As the parts continue to move back and forth, the crystallization is pressed into the mating joint which causes scoring of the parts. This scoring results in scratches that continue to deepen over time. This is the cause of the fluids leaking.
Once the leaking has begun, production stops. For production to resume, the gun must be replaced with a second gun which can cost between $2,400.00 – $2,700.00 depending on when and where it was purchased. Or it is necessary to disassemble the gun, clean and polish or replace the mixing chamber and side seals. This can take up to 1 – 2 hours depending on how severe the scoring, and how long the leaking occurred. If the parts are replaced, the mixing chamber will cost approximately $200.00 and the side seals another $45.00 per pair. When adding tax and shipping, these parts are close to $250.00.
Some contractors purchase as many as 10 – 12 sets of mixing chambers per month, and these overhead costs are added to the contract and passed to the customer.