Impregnation
process for crossties and switch ties
according to AWPA
standards
1) Raw
Material Reception.
The
process starts when the raw wood is received, it is inspected and sorted
according to size, type of wood and humidity level.
2)
Wood pilling for natural seasoning.
Once the wood is sorted it is pilled perpendicularly allowing air to flow
between the wood pieces, this helps acquire uniform dryness.
3)
Load sorting for impregnation process.
Once the wood reaches the humidity levels required for impregnation (25%
softwood and 40% Hardwood) it is properly
arranged onto wagons for easy transportation into the retort.
4)
Impregnation Process, Reuping or Lowry
(empty cell).
The preservative temperature its verified (175 Fº to 195 Fº ) so the wagons
can be introduced into the retort. The impregnation process consists in:
A) Determining the preservative amount (class 1 creosote) that would be injected, so we can reach penetration and the retention required.B) Retort Filling The work tank and retort valves are opened. The Transfer pumps start to pump the preservative into the retort. This process takes about 45 minutes.
C) Injection period After the retort is filled with preservative the pressure process begins. Transfer valves are closed, and injection valves are opened, the preservative reaches a maximum pressure of 140 psi (maximum pressure during process) and it is maintained until most of the liquid is injected into the wood.
D) Vacuum Cycle After the injection period is completed a vacuum cycle begins reaching a vacuum level of 22" (sea level). This is accomplished with the help of 2 pumps, the first one is a vacuum pump and the other acts as a booster, so they can reach the required vacuum level.
E) Retort emptying process. Once the vacuum cycle is over the pumps are turned off and the valves are closed, the pressure is relieved with a valve. Afterwards the preservative is recirculated to the work tank.
5)
Final product storage.
When the load exits the retort the treated wood is sorted and stored according
to its dimensions and it is ready for inspection.
6) Final product shipment.
