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March 25, 2003
IMPRINTING PRESSURE
First, imprinting force or pressure is not an exact science, just a rough approximation. Even then we are only considering static not dynamic pressure. Just as the pressure in your car tires is static to be measured when cold and your blood pressures are static to be measured at rest. At the current state of the art, the specifications call for an imprinting static force or weight ranging from 500 to 1000 lbs per foot of imprinting roller length for soils ranging from soft to hard. This weight range corresponds roughly to an imprinting pressure range of 15 to 30 psi.
Here is the way I convert from pounds per foot to pounds per square inch.
Assumptions:
• That only 3/4 of one imprinting tooth is fully in contact with the soil per foot of roller length.
• That the tooth is made from a 10-inch length of 6" x 6" angle iron.
• That the tooth width in soil contact is 4.24 inches.
• That the tooth/soil contact area is given by the product: ¾ x 10 x 4.24 = 31.8 in. 2
• That the unloaded (without ballast) weight of the seeding imprinter is 500 pounds per foot of roller length and that the weight of ballast is 500 pounds per foot.
Then the imprinting pressure without ballast is:
Pressure (no ballast) = 500 lb
31.8 in 2 = 15.7 psi
And:
Pressure with ballast = 1000 lbs
31.8 in 2 = 31.4 psi
Finally:
Pressure without ballast = 15.7 or about 15 psi
Pressure with ballast = 31.4 or about 30 psi
So, in conclusion the current specs. call for a range in static imprinting force of 500 to 1000 lbs per foot of imprinting roller length corresponding to an imprinting pressure range of about 15 to 30 psi.
The Imprinting Foundation
1616 E. Lind Road
Tucson, Arizona 85719