The freeness of pulp is designed to give a measure of the rate at which a dilute suspension of pulp (3 g of pulp in 1 L of water) may be drained. The freeness, or drainage rate (see TAPPI T 221 “Drainage Time of Pulp”), has been shown to be related to the surface conditions and swelling of the fibers. Besides these factors, the result is dependent also on conditions under which the test is carried out, such as stock preparation, temperature, and water quality.
The procedure was originally designed to yield a test value suitable primarily for the control of manufacture of ground wood. It is also widely used to follow the changes in drainage rate of various chemical pulps during beating and refining. Treatments which produce a large proportion of fines may sometimes cause an anomalous rise of freeness (false freeness) usually at values below 100 mL.
Freeness values do not necessarily correlate with the drainage behavior of pulp material on a commercial paper machine.
The freeness tester consists of a drainage chamber and a rate measuring funnel, mounted on a suitable 1support. The apparatus is manufactured to drawings and specifications and each instrument is inspected and calibrated before delivery. Some instruments may have a coating of marine varnish on the surface
The screen plate is 112.0 + 0.5 mm – 0.0 mm in diameter, 0.51 mm ± 0.05 mm (0.020 in.) thick and has perforations of 0.51 mm diameter spaced 625 per 1 in. (about 97 per cm ) of surface. The plate is mounted so that the 2 2 burr of the punched perforations is downward
Weight: 15 Kgs (40lbs)