The present invention relates to a pellet press comprising a roller supporting shaft with a longitudinal axis, the shaft having at a roller support side an end part with a diameter DEP supporting a bearing roller member rotatable about the shaft, wherein the shaft is provided with a cooling channel having an inner diameter Di and extending along the longitudinal axis, and a cooling duct extending coaxially within the cooling channel and having an outer surface situated at a distance from a cooling channel wall, the cooling channel and the cooling duct being closed at the roller support side.

Background art

In WO 2016/195484 a pellet press is described with a supporting shaft and a perforated drum mounted rotatably thereon via a drive member having two spaced-apart bearings. A single roller is provided on the shaft within the drum. The first bearing of the drive member is a radial bearing, the second bearing of the drive member is an axial-radial bearing situated at a larger radial distance from the drum rotation axis than the radial bearing. An axially movable locking bushing is placed around the shaft between the bearing housings of the axial and the axial-radial bearings, the bushing engaging both casings.

When pelletizing kneadable material with a high viscosity, the bearings of the pellet press can generate too much heat, which may cause the viscosity of the lubricant to become too low to maintain effective lubrication. As a result, the bearings can become damaged and the pellet press requires repairing. Furthermore, when the lubricants becomes too liquid, they may seep into the drum of the pellet press, contaminating the pellets. This is especially undesirable when the pellets are to be used as animal feed, since contaminated feed needs to be discarded.

Due to the position of the bearings inside the pellet press and the height of the temperature reached by the bearings, air ventilation has proven insufficient.

An alternative cooling solution is described in US6,299,430, in which the shaft of a pellet press is provided with a cooling medium supply and return passage, providing fluid cooling of the shaft. Heat conduction from the bearings to the cooled shaft results in a lowering of the bearing temperature.

Summary of the invention

It is an object of the invention to provide a pellet press with more effective bearing cooling. It is another object of the present invention to provide for an improved method of pelletizing.

Hereto the pellet press according to the invention is characterized in that the roller supporting shaft further comprises at least one bearing cooling channel having first and second radial sections that respectively extend from a roller support side position and from an upstream position of the cooling channel wall, in a radial direction through the end part of the shaft, to an outward end part position near the bearing, and with a third axial section extending through the end part in the axial direction and interconnecting the first and second radial sections, and a fluid seal, situated between the outer surface of the cooling duct and the wall of the cooling channel at an axial position between the axial positions of the first and second radial bearing cooling channel sections.

Due to the at least one bearing cooling channel extending up to the outward end position close to the surface of the roller supporting shaft where the bearing rolling member is supported on, cooling liquid passes through the roller supporting shaft in close proximity to the bearings. This results in an effective heat exchange between the lubricated bearing and cooling liquid, increasing lubrication effectiveness and reducing roller bearing member failure. Furthermore, due to the improved cooling capacity, the operating temperature of other components of the pellet press is reduced, positively impacting their lifespan as well.

Through the addition of multiple bearing cooling channels, a higher cooling capacity can be reached, allowing the production capacity and/or speed of the pellet press to be increased. Preferably the cooling system is set up to be able to cool the bearing support shaft back from 200°C to 70°C, providing a more pleasant and safe environment to work in for the operator, due to a reduction in heating of the surroundings of the pellet press. Beneficially, if the cooling capacity is sufficiently high to maintain a temperature of the lubricant in the bearing roller member below 120°C, food grade lubricants can be used, eliminating the risk of contaminating animal feed produced with the pellet press. Furthermore, the added cooling capacity of the shaft results in a reduced power consumption by the pellet press, contributing to a lower CO2 emission.

An additional advantage provided by the design of the cooling assembly is that assembly and demounting of the cooling duct inside the cooling channel can be performed by simply inserting the cooling duct together with the fluid seal from a shaft mounting side of the roller support shaft, which is opposite from the roller support side. Thus the implementation of the fluid seal enables ease of manufacturing and maintenance.

The cooled bearings in the proximity of the bearing cooling channels according to the invention can be the bearings that support the drive member of the drum or the bearings supporting the roller inside the drum or both.

According to an embodiment, the roller supporting shaft has a main section of a smaller diameter Do than the diameter DEP of the end part, the end part comprising a cylindrical bearing support surface and a ring-shaped, radially oriented end surface, where the radial bearing cooling channel sections are provided by drilling from the bearing support surface to the cooling channel and the axial bearing cooling channel section is provided by drilling from the ring shaped end surface in an axial direction.

By drilling the channel sections from the outside surface of the roller support shaft inwards, the ease of manufacturing of the radial bearing cooling channels is improved. If additional cooling capacity turns out to be required at a later moment, additional cooling channels may be added to the roller support shaft as and when required. This manufacturing method also allows for existing shafts being retrofitted with a cooling system according to the invention. According to a further embodiment, at the bearing support surface and at the radially oriented end surface, the bearing cooling channel sections are closed by a plug member.

The plug members ensure that the cooling system is a closed system, separated from the lubrication system. The plug members close off the drilled cooling channels and ensures that the cooling water cannot mix with the roller lubricants and/or contaminate the kneadable material.

According to an embodiment, the fluid seal comprises at least one O-ring.

Due to equal pressure on both sides of the seal when the cooling system is running, the seal can be relatively thin and flexible. This allows the rings seal to be a simple O-ring.

According to a further embodiment, the shaft is at a shaft mounting side provided with a rotatable coupling comprising connector members for connecting a fluid supply duct and a fluid return duct to the cooling channel and to the cooling duct respectively.

The rotatable coupling allows the shaft itself to rotate when required, as an emergency system when a rotational force on the shaft becomes too high in order to prevent damage, for example due to a friction force between the roller and perforated drum mounted on and driven via the shaft exceeding a maximum force.

According to an embodiment, the pellet press further comprises a cooling member and a pump connected to the cooling channel and the cooling duct for supplying cooled cooling fluid to the channel or duct, a temperature sensor for measuring a cooling fluid temperature of heated return fluid coming from the cooling channel or cooling duct, and a controller for controlling the rotation speed of a drive member which is mounted on the roller supporting shaft via the bearing and adapted to rotate a perforated drum supported on the end part of the shaft around the longitudinal axis L depending on the measured temperature.

The cooling member receives the heated cooling fluid exiting the roller support shaft and cools the fluid back to a predetermined lower cooling temperature before the pump pumps the cooling fluid back into the roller support shaft. The cooling member and pump thus allow for recycling of the cooling fluid. In a preferred set-up the cooling member comprises a radiator and a fan. This set-up has the advantage that hot air, released in the radiator, can be led away via an exhaust to a desired location, for example outside, allowing a comfortable working temperature being maintained in the working facilities around the pellet press.

Through the addition of the temperature sensor measuring the heated return fluid, the condition of the pellet press is monitored and the controller can adjust the rotation speed of the drum to maintain the temperature at the bearing roller member resulting from the drum rotation within an optimum range. As previously stated, at bearing roller member temperatures which are too high, damage is risked due to lubricant becoming less effective. At bearing roller member temperatures which are too, the viscosity of the lubricant increases becomes too high, also having an adverse effect on the effectiveness of the machine. Thus in order to keep the pellet press optimally operating, the temperature of the bearing roller member needs to be kept optimal. Through the addition of the temperature sensor providing feedback to the controller, the controller can automatically adjust operation parameters of the pellet press to maintain this optimum temperature.

Further, the controller may be adapted to adjust the roller rotation speed and/or distance between the roller and the drum. Alternative or additional to the controller controlling the rotation speed of the drum, the controller may also be connected to the cooling member and/or pump and adapted to adjust a cooling rate and/or pumping speed at which the cooling member or pump operates depending on the measured temperature.

Additionally, the invention provides a method of pelletizing a kneadable material in a pellet press comprising a drum with a perforated wall, at least one roller within the drum that is rotatable about an axis and cooperating with an inside surface of the drum to press material through the perforations in the drum wall and drive means to rotate the drum and the axis of the at least one roller rotate relative to each other about a shaft with a drum rotation axis, wherein the shaft is configured to adjust a distance between the at least one roller and the inside surface of the drum, to control the gap width there between and wherein the shaft is provided with a cooling channel having an inner diameter Di and extending along the drum rotation axis, and a cooling duct extending coaxially within the cooling channel and having an outer surface situated at a distance from a cooling channel wall, the cooling channel and the cooling duct being closed at a roller support side. The method of pelletizing comprising the steps of: - feeding the material into the drum and kneading the material by rotating the drum at a drum rotation speed,

- forcing the material through the apertures in the drum wall with the roller, which has a roller rotation speed, and

- running cooling fluid through the cooling channel and the cooling duct to cool down the shaft, characterized in that the method further comprises measuring a cooling fluid temperature of heated return fluid coming from the cooling channel or cooling duct, and adjusting the drum rotation speed, the roller rotation speed and/or the distance between the roller and the drum depending on the measured temperature.

Short description of drawings

Embodiments of a pellet press according to the present invention will be described by way of example, with reference to the attached drawings, in which

Fig. 1 shows a cross section of a pellet press with cooled drive member bearings according to the invention;

Fig. 2 shows a detailed view of the shaft in section II of Fig. 1 ; and Fig. 3 shows a perspective view of the shaft section of Fig. 2 Description of embodiments

Fig. 1 shows a pellet press 100 having a roller support shaft 10 with a longitudinal axis L, a shaft mounting side 11 , for being supported by a machine frame (not shown) and a roller support side 19 having an end part supporting a perforated drum 90 that is rotated around the longitudinal axis L via a drive member 48. The drive member 48 is mounted on the support shaft 10 via an axial- radial bearing 20, positioned near the end part 19 of the shaft 10, and a radial bearing 21 , positioned near the shaft mounting side 11 . For providing a rigid construction, the drive member 48 is formed in one piece of cast iron.

At the end part 19, a roller 80 is mounted on the support shaft 10 to be rotatable around a roller axis R that is spaced at a distance from the longitudinal axis L. The roller 80 is driven by frictional engagement between the outer roller surface 81 and the inner drum surface 91 via the kneadable material that is squeezed in the gap between the roller 80 and the drum 90 prior to being extruded through the perforations of the drum to form pellets.

The pellet press 100 is provided with a cooling system, which is shown to comprise internal cooling channels and ducts 30, 32, 34 in the roller support shaft 10, a cooling member 42, a pump 40, a temperature sensor 44 and a controller 46. The internal cooling channels and ducts 30, 32, 34 are connected to the cooling member 42 via a rotatable coupling 15, having connector members 17 for connecting a fluid supply duct 7 and a fluid return duct 8 to the internal cooling channels and ducts 30, 32, 34, allowing a cooling fluid such as water being circulated and reused. The pump 40 is located between the cooling member 42 and the supply duct and is adapted to pump the cooling fluid into the internal cooling channels. The temperature sensor 44 is arranged in the fluid return duct 8 for measuring a cooling fluid temperature of heated return fluid coming from the internal cooling channels 30, 32, 34. With an output, the temperature sensor 44 is connected to the controller 46, which is arranged to control the rotation speed of the drive member 48 with respect to the roller support shaft 10 and the pumping rate of the pump 40 depending on the measured temperature. The rotatable coupling 15 of the cooling system allows for a rotation of the roller support shaft 10 within the machine frame, with respect to the fluid supply duct 7 and fluid return duct 8, which rotation may occur as a safety feature preventing overload in the event that a friction force between the drum 90 and the roller 80 exceeds a predetermined maximum force. Details of the internal cooling channels and ducts 30, 32, 34 inside the roller support shaft 10 are further discussed in reference to Figs. 2 and 3.

Figs. 2 and 3 respectively Fig. 2 show a detailed view and a perspective view of the shaft in section II of Fig. 1. The roller support shaft 10 has a main section 18 having an outer diameter Do which extends from the shaft mounting side up to the end part at the roller support side 11 , having a larger diameter DEP. A ring-shaped, radially oriented end surface 24 provides a transition between the main section 18 and the end part at the roller support side 19. An outer surface section of the end part directly adjacent to the ring-shaped, radially oriented end surface 24 forms a bearing support surface 22, having a length along the longitudinal axis L sufficiently long to support the bearing roller member 20 for having the drive member 48 is mounted on the support shaft 10.

The internal cooling channels and ducts inside the shaft 10 are shown in Fig. 2 with a cooling duct 32, a cooling channel 34 and a plurality of bearing cooling channels 30. The cooling channel 3432 is a cylindrical channel with inner diameter Di, preferably being between 40 - 70 mm, which extends along the longitudinal axis L in the centre of the shaft 10 from the shaft mounting side 11 towards the roller support side 19, extending along substantially the full length of the bearing support surface 22 when seen along the longitudinal axis L. The cooling duct is coaxial with the cooling channel 34 and positioned inside the cooling channel 34 having an outer surface 31 at a distance dw between 5 - 25 mm from an inner wall 33 of the cooling channel 34. The cooling duct 32 has a length which is shorter than a length of the cooling channel 34 and extends from the shaft mounting side 11 to a position past the ring-shaped radially oriented end surface 24 seen along the longitudinal axis L. The cooling channel 34 is closed at the roller support side 19. At the roller support side 19 the cooling duct 32 is along its outer perimeter provided with an O-ring 36 which seals the end of the cooling duct 32 against the inner wall 33 of the cooling channel 34, preventing cooling fluid from directly flowing from the cooling duct 32 via the cooling channel 34 to the fluid return duct 8. As a result, a section 35 of the cooling channel 34 which extends past the O-ring 36 and past the end of the cooling duct 32 at the roller support side 19 is closed off from the remainder of the cooling channel extending from the shaft mounting side 11 and is in open connection with the end of the cooling duct 32 at the roller support side 19 for distribution of cooling fluid into the multiple radial ducts 30b.

At the position of the bearing support surface 22 the roller support shaft 10 is provided with the bearing cooling channels 30 connecting section 35 to the upstream part of the cooling channel 34, forming a flow path for the cooling fluid through the cooling system. In this flow path, the end of the cooling duct 32 at roller support side 19 is upstream from the end of the cooling duct 32 at the shaft mounting side 11 and the end of the cooling channel 34 at the shaft mounting side 11 is upstream from the end of the cooling channel 34 at the roller support side 19.

Each bearing cooling channel 30 has first, second and third sections 30a, 30b, 30c. The first and second sections 30a, 30b are radial sections which each extend from a position in the cooling channel wall 33, radially outward toward an end position below the bearing support surface 22. The first sections 30a extend outward from the section 35, which, due to having a plurality of radial openings, forms a spray head. The second sections 30b extend outward from a position adjacent to the O-ring 36 on a side facing the upstream end of the cooling channel 34. The third section 30c of each bearing cooling channel 30 extends in the axial direction through the end part of the roller support side, interconnecting the end positions of the first and second radial sections 30a, 30b. Preferably, the end positions of the first and second sections 30a, 30b are between 5 and 50 mm from the bearing support surface 22. For ease of manufacturing, the first and second sections 30a, 30b are drilled radially inward from the bearing support surface 22 into the cooling channel wall 33 and the third sections 30c are drilled from the ring-shaped, radially oriented end surface 24 through the end position of the second radial sections 30b and into the first radial sections 30a. The resulting drill holes in the bearing support surface 22 and the ring-shaped, radially oriented end surface 24 are closed off with plugs 38, in order to ensure a closed cooling system in the shaft and prevent contamination of bearing lubricant and the kneadable material in the perforated drum 90.

The roller 80 depicted in Fig. 1 also comprises bearings, which may be cooled similarly, by extending the cooling system as described above.

The present invention has been described above with reference to a number of exemplary embodiments as shown in the drawings. Modifications and alternative implementations of some parts or elements are possible, and are included in the scope of protection as defined in the appended claims.