This invention relates to the testing of tobacco filling power and its object is to measure firmness of a cigarette tobacco stream.

During the manufacture of cut tobacco or ^τ filler ^τ 5 forma ing cigarettes, it is necessary to make measurements of the cut tobacco to predict the firmness of the cigarettes that will be made from it so that the manufacturing process can be controlled. The usual measurement is filling power. 10 In the known cylinder volume method for testing the filling power of cut tobacco, a typical test consists of placing a 50g sample of cut tobacco, equilibrated to a standard moisture content, in a vertical 6θmm

•» diameter cylinder and compressing it axially for 5 ^{■**■ '} minutes with a freely moving piston of 3 kg. weight. The volume of the tobacco at the ..end of 5 minutes divided by the sample weight, i.e. the specific volume in ml/g, is known ^' as the filling power. -'

This method does not give a representative value of 0 filling power when the same tobacco is used in cigarettes for two reasons:

First, the cigarette is typically 8 mm diameter, so that strands that have a length of similar magnitude will produce different mechanical effect when contained

in a cylinder of 60 mm diameter.

Second, the axial compression produces radial forces in the cylinder which inhibit free compression by the piston due to the friction between the tobacco and the cylinder walls.

, Furthermore, the filling power is not the most suitable measurement for a -cigarette which is manufactured to a constant volume and weight, i.e. constant specific volume. A more relevant measurement is the long term firmness or residual radial pressure after a fixed time, when a fixed weight of cut tobacco has been compressed to a fixed cigarette volume-

An object of the invention is to provide: ^* a method and apparatus for measuring the long term firmness or residual radial pressure of an elongate volume of cigarette tobacco or a cigarette rod.

It is also desirable to be able to predict the short term firmness or finger firmness, i.e. the immediate radial pressure for a given small displacement or sq-ueeze, as sensed by the smoker.

According to the present invention a method of , measuring the firmness of a cigarette tobacco having elongate form comprising compressing a sample length of the tobacco transversely of the length thereof into a circular cross-section of cigarette reference size, measuring the compressed load (P) after a predetermined interval by which time the cσmpressive load has

levelled off, and ascertaining the load/area relationship which represents the desired residual radial pressure representing long term firmness.

In the present invention the test by applying load which tends towards a radial compression results in a more accurate assessment of the filling power.

The principle involved is based on the parameters V and where V is the specific volume or inverse of density and K is the bulk modulus of elasticity of units N/m ² per unit volumetric strain and is a measure of the firmness of the sample. The invention takes into consideration that V and K are sensitive to the shape of the sample and accordingly in the ^: resent invention the measurements are effected on a measurement volume which simulates the shape of a cigarette or preferably a plurality of cigarettes e.g., four. Ϊ

The sample preferably has a length corresponding to the length of several cigarettes e.g., 4 or 5 cigarettes, preferably about 300 mm.

The invention further comprises an apparatus for ^■ ' carrying out this method comprising a) a first female die member having a U-shaped slot therein,

b) a second male die member having a semi-circular sectioned groove therein capable of forming with said

- h - U-shaped slot a cavity of cylindrical section having a cigarette reference size, c) means to move the dies relative to each other between open and closed positions, and d) means to measure the force of compression between the dies.

In a preferred constructional form of the invention upper and lower dies are provided, the lower die is seated on load measuring cells connected to a common readout device and has a U-shaped groove into which the upper die is slidingly engaged, the upper die being vertically movable by a pair of screw devices that are connected together for simultaneous operatiorv and the movement being measured by a t ansformer device. The invention will now be further described by way of example with reference to the accompanying drawings in which:

FIGURE 1 is a perspective view of an apparatus made in accordance with the invention, and FIGURE 2 is a sectional view of the cooperating dies of the apparatus with a dynamic model superimposed thereon.

A frame 10 has a platform 11 on which two load cells 13, 1 are fixed e.g., Sangamo Weston Load cells D 96/50. A lower female die 16 rests on the cells 13 _. 14 and has a slot 17.-the bottom of which has the transverse shape and size of one half of a cigarette

and a length equal to three cigarettes. The slot has a tapered opening 18 at its upper end to facilitate entry of the tobacco sample. An upper male die 20 is shaped at its under edge with a semi-circular groove 21 corresponding transversely to the other half of a cigarette and of the same length as the lower die.. The upper die is a flat rectangular member having a thickness nearly equal to-the width of the U-shaped slot 17 so as to be slidable in it. The upper die 20 does not touch the sides of the slot 17 so as not to affect the loading measurement.

The upper die is fixed to the lower ends of two stems 23, 24 of screw devices 25, 26 operab-le by thumb screws 27, 28 which are connected together by a belt 30 which is preferably a toothed belt so that they provide a parallel vertical motion to the upper die 20. The cells ^* 13, 14 are connected to a digital readout 31.

The upper die 20 is also connected to the stem 33 of a linear variable displacement transformer 34 which is carried by a part 10A of the frame 10 and is. ^' , connected to a multimeter 35.

The compression load on the tobacco is measured by the cells 13, 14 and displayed on the digital readout 31 (e.g., Sangamo C44) in Newtoπs. The relative vertical displacement between the upper and lower dies is sensed by the linear variable displacement

transformer 34 which transduces displacement to d.c. voltage which is displayed on the multimeter 35.

Tobacco behaves according to the model as shown in FIGURE 2. In the dashpots _r and _c the force is proportional to piston velocity (Hewtons/unit velocity) and" in the springs K _e and K _r the force is proportional to displacement (New tons/unit displacement). The viscous dashpots decrease their viscosity as the moisture content of the tobacco increases. So that at low moistures the dashpots resist motion and firmness is predominantly the finger firmness determined by spring rate ^' K _e . At high moistures, the dashpots are soft and firmness is predominantly the residual firmness determined by the lower rate spring K _r . In use, a fixed weight m of equilibrated tobacco filler equivalent to four or five cigarettes is spread into the lower die 16 and the upper die 20 is lowered until the tobacco is compressed into a cylindrical cigarette shape of diameter I), typically 8 mm .

After approximately 10 minutes, the.»vertical force £ on the lower die has substantially levelled off and is read. This force represents the residual force in spring _r . The residual force P can be used as a comparative measurements for a fixed die size and fixed weight of tobacco. By dividing the measurement by the projected

area A of the cylinder the residual radial pressure of the filler is obtained.

The upper die 20 is then given a small further displacement of approx. 15_ of diameter, i.e. typically 8u and the additional force S. noted. The force divided by the displacement D gives the spring rate of j _E .

The measurement P can be used as a comparative measurement for a fixed die size, weight of tobacco and small displacement.

Alternatively, the small displacement results in a small change A x D in the volume n of the cigarette, so the short term elasticity or finger elasticity can be described as the bulk modulus of elasticity K = ^p x ^v It is natural that firmness will increase with bulk density, so a firmness index can be defined based on the specific bulk volume V = JJ or inverse" .of density valid for small changes in _Ϊ or jn. ^' , ^' ,

• I

Residual firmness = residual pressure x _E x V = _E I Joules/kg.

Finger firmness - ^• finger elasticity' x V

=!K Joules/kg.