GB2059805A - Screen retaining device for hammer mills - Google Patents

Abstract

Disclosed is an improved screen retaining device for use in size reduction mills designed to grind, shred, or fluff various materials. A bottom pivot point 28 for the retaining device causes the screen to be squeezed against the bottom wear bar of the mill when the retaining device is fixed in place. The retaining device includes a bottom retainer bar 24 with a roller chain supports 32, a top retainer bar 36 and chains pinned at the bottom. The improved design provides uniform contact along the circumference of the screen to prevent screen leakage. <IMAGE>

Description

SPECIFICATION Screen retaining device for hammer mills Background of the Invention 1. Field of the invention: This invention relates to a screen retaining device for hammer mills and more particularly to a screen retaining device for hammer mills used to grind, shred, or fluff various materials such as cereal grains, tobacco, and wood pulp.

2. Description of the Prior Art: In the grinding of cereal grains, for example, in a hammer mill the primary grinding takes places when the grain is driven against a breaker plate. The grain is actually caused to be driven against the breaker plate by means of the rotating hammers. The hammers also drive the grain against a screen where the final reduction takes place through the striking of the grain by the hammers. The size of the reduced grain which is discharged from the mill is determined by the diameter of the perforations in the screen.

In prior art hammer mills the screens are seated under a stop bar at the bottom of the mill and rest on steel rings bolted into the side of the mill. The lower screen retainer is hinged at the bottom wear bar of the mill. The screen is also attached to an upper retainer member which is adjustably fixed to the upper wear plate of the mill. While in certain cases the prior art screen retainer performed satisfactorily, many times screen leakage would occur because of the absence of uniform contact around the entire circumference of the screen. Further, if a screen backing grid were to be used in the prior art design, additional structure was needed. This additional structure interferes with screen removal thereby causing additional mill downtime when the screens are replaced to permit changes in the partice size of the material being reduced in the mill.

Summary of the Invention The screen retaining device of the present invention overcomes the foregoing problems of the prior art by providing a screen retaining device which provides uniform contact along the entire circumference of the screen while acting as a back-up grid for the screen. The screen retainer is comprised of a bottom retainer bar. Pinned to the bottom retainer bar at predetermined intervals along the length thereof are the first segments of a plurality of articulated support members. The length of the articulated support members is determined by the length of the screen and the support members extend to an upper retainer bar to which the last segment of each member is pinned. The screen is supported on the support members in a manner so when the lower and upper retainer bars are fixed to the mill, the screen is pressured against the bottom wear bar of the mill.The bottom retainer bar is pivotably connected to the bottom of the mill housing. The upper retainer bar is fixed to the mill upper wear plate by conventional means.

The retainer of the present invention provides uniform contact along the surface of the screen thereby minimizing screen leakage while acting as a screen backup grid without the necessity of introducing additional structure which can complicate screen removal.

Brief Description of the Drawings Figure 1 is a front elevation view, partly in section, of a hammer mill incorporating the screen retaining device of the present invention, and Figure 2 is an elevational view of the screen retaining device.

Description of the Preferred Embodiment Referring to Fig. 1 a conventional hammer mill generally designated as 10 includes a plurality of hammer plates 1 2 which are rotated through shaft 1 4 by a conventional electric motor, not shown. Rotatably mounted to plates 1 2 are a plurality of hammers 1 6.

Hammers 1 6 are typically four-point, hardface. In a typical mill sixty-four hammers are used for fine grinding while thirty-two are used in coarse grinding operations. The material to be reduced is introduced into the mill through inlet 1 8 by conventional material handling equipment, not shown. Breaker plate 20 is mounted across inlet 1 8 so that the material to be reduced is forced to strike the plate to accomplish the first size reduction.

Material is caused to be carried through the mill by means of a conventional air intake system, not shown. After contacting the striker plate the material enters the interior of the mill where final size reduction accompolished.

Mounted outside the diameter of plate 1 2 is screen 22. Hammers 1 6 drive the material against screen 22 causing the final size reduction. The final size of the material is determined by the diameter of the perforations in screen 22. When the material is reduced to the size of the perforations, it is discharged from the mill through screen 22 and is collected by conventional material handling equipment, now shown.

The screen retainer of the present invention includes a bottom retainer bar 24 which is pivotably mounted to mill frame support 26 through pivot 28. Pinned to bar 24 are the first links 30 of three lengths of No. 40 roller chain supports 32. Chain supports 32 extend the length of each screen 22 and at their opposite ends links 34 are pinned to top retainer bar 36. Top retainer bar 36 is fixed by bolts 38 to the top wear plate 40. It can be seen when top retainer bar 36 is fixed to wear plate 40, screen 22 is pressured against bottom wear plate 42. Also, the lengths of chain supports 32 provide uniform contact along the entire circumference of screen 22.

The foregoing describes a novel screen retainer which minimizes screen leakage while acting as a screen grid.

While I have described a certain preferred embodiment of my invention, it will be understood that it may otherwise be embodied within the scope of the following claims.

Claims (3)

1. A screen retaining device for hammer mills and the like comprising: a) A first retainer bar, said first retainer bar adapted to be pivotably attached to the frame of said mill; b) A plurality of articulated screen support members, each of said articulated support members having the first segments thereof fixably attached to said first retainer at selected points along the length thereof, said articulated screen support members adapted to extend along the circumference of said screen to be supported; and c) Second retainer bar said second retainer bar means have the last segments of each of said screen support means fixed thereto and said second retainer bar means adapted to be fixed to the frame of said mill.

2. The screen retaining device of claim 1 wherein said articulated screen support means are roller chains.

3. A screen retaining device substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawings.