Influence of Parameters on the Properties of Groundwood

In the mechanical defibration of wood by grinding, several process parameters

Have significant influences on the final properties of the stone groundwood.

Among these, the most important include:

_ Moisture of the wood logs

_ Logs feeding speed or grinding pressure respectively

_ Pulp stone rotational speed

_ Temperatures

_ Process consistency

_ Surface profile of the pulp stone

_ Specific grinding energy consumption

Basically, it can be said that an increase in grinding pressure produces a groundwood

With better dewatering behavior (high freeness) and less strength properties,

Assuming that all other parameters are kept constant. Such pulps are coarse

Groundwoods, whereas pulps with low freeness are fine groundwoods. Increasing

The pulp stone speed, and keeping all other conditions constant, produces a pulp

With shorter fibers and lower freeness.

From a practical standpoint, the efficiency of the grinding process will be

improved by increasing both parameters – grinding pressure and pulp stone

Speed. However, the relationship between both of these parameters can be held

Constant and high-quality groundwood produced.

The temperature relationship during grinding also affects the properties of the

Final groundwood. Functions which describe the temperature relationship in

grinding include:

_ Temperature of the pit pulp

_ Temperature of the shower water

_ Temperature at the end of the grinding zone

In practice, the temperature of the pit pulp is used to control the grinding process,

with typical shower water temperatures of 60–75 °C being used in atmospheric

Grinders.

The pit consistency, in practical terms, is set from 1.0% to 2.5%, and interacts

With the pit temperature. Increasing the pit consistency also enables the pit temperature

To be increased, at constant shower water temperature. Depending on

Either the pit consistency or possible stone immersion in the pit (Fig. 4.6), a certain

Amount of pit pulp is transported with the stone and passes back into the

Grinding zone. Here, regrinding takes places, so that the pulp suspension from

The grinder pit is passed to the grinding zone instead of the shower water.

A deeper immersion of the stone into the pit, or a higher weir height in the pit,

Leads to a larger quantity of circulating pulp. The stone surface will be lubricated

By pulp particles and appears duller than it really is, and this in turn reduces the

Freeness of the pulp.

Grinding Processes

Fig. 4.6 Pulp stone immersion and weir height in grinding.

Дата добавления: 2015-10-21