Retractable rod screens

Details Retractable rod screens Retractable rod screens

2001-11-13

2004-09-07

Rosenbaum, Mark (Department: 3725)

Solid material comminution or disintegration

Apparatus

Comminuting surface provided with openings to permit...

C241S089200

Reexamination Certificate

active

06786439

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention generally relates to grinders and hammermills, and, more particularly to grinders with a screen adjacent to a rotating hammermill.
Grinding machines, including those utilizing grinding means such as hammermills, grinders, drum chippers, and wheel chippers, are used for varying applications. These applications can include, amongst others: grinding tree stumps and slash from logging operations; grinding construction debris from buildings damaged by natural disasters, such as hurricanes or floods; shredding animal feeds, grinding used automobile tires, grinding wood, and grinding landfill material for compaction or disintegration purposes.
Many different kinds of grinders and hammermills are known in the prior art, including U.S. Pat. No. 4,997,135 to Zehr and U.S. Pat. No. 5,720,440 to Bonner et al. Generally, these grinders/hammermills utilize a hammermill assembly formed of a rotatable shaft to which radially extending hammers are affixed, interfitted within a semicircular hammer mill screen, such as is shown in FIG. 3 of Bonner (U.S. Pat. No. 5,720,440).
In use, the material to be ground is dropped into a hopper from which it passes into the screen chamber containing the rotating hammermill hammers, where it is broken apart and/or pulverized. Other configurations of grinders and shredders exist, each with a hammermill and a screen. The hammermill screen serves as a sieve, allowing ground material smaller than the sieve hole size of the hammermill screen to pass through, or literally to be thrown through the screen into a chute and onto some sort of discharge system, conveyor, auger, or other device by which it is carried away. Hammermill/grinder screens shown in the prior art include: screens having screen holes (Bonner), a “grate” (Zehr), a plate/grate system (Graveman), and curved ribs and spaced bars (Williams).
A typical problem with such grinding devices arises when a piece of material becomes lodged between the hammermill screen and the hammers, causing a jam. Material may also become wrapped around the hammermill, or clogged in the holes of the hammermill screen, and wrapped around the screen. The prior art method of relieving such a jam is, as described in Bonner, disassembling the grinding device in order to manually dislodge the material jammed therein. This step is time consuming and labor intensive. Some grinders are designed so that the screen of the grinder is in the shape of a section of a cylinder, which is removed by rotating it from adjacent the hammermill to a position in the feed intake of the hammermill. Even though the screen is typically made of thick metal, it may have been bent during operation, and rotating it and removing it is a demanding and time consuming job.
SUMMARY OF THE INVENTION
The present invention is an improved screen, particularly for hammermills, horizontal grinders, tub grinders, shredders, and other grinding apparatuses. The device of the invention can be utilized in any shredder or grinder which uses a rotating hammermill with an adjacent screen through which material is ejected.
The device is an improved grinding apparatus for use in grinding or commuting material. The improved grinding apparatus includes a frame for supporting the grinding apparatus, an inlet for receiving material to be ground, and a grinding means which is operatively connected to the inlet and typically mounted on a drive shaft. The grinding means is typically a hammermill and comminutes material to a smaller size. The device also includes a screen mounted around the hammermill or grinding means, and thus defining a screen chamber around the hammermill. Material enters the hammermill and is struck by hammers of the hammermill and driven through or into the screen. The screen of the improved grinding device is formed from a number of bars which extend parallel to and adjacent to the grinding means. The bars have a long axis, and the long axis of the bar is parallel with the long axis of the hammermill or grinding means. One or more of the bars may be extracted from the screen chamber, and inserted into the screen chamber by pulling or pushing on the bar, in a direction parallel with the long axis of the bar.
A bar extraction means is also utilized. Typically, the bar extraction means would be formed from a bar extraction tool of various designs. Bar extraction tools can be formed based on propulsion from hydraulic cylinders, mechanical pullers which use leverage or mechanical advantage, electrically driven screws, or pneumatically driven drives. The bar extraction tools of the invention attach to the bars which form the screen chamber and either push the bars into place around the hammermill, or pull them out of the hammermill region. The grinding device of the invention can be configured to include one extraction tool which is attachable sequentially to each of the bars around the hammermill, and is thus able to insert or remove any of the bars around the hammermill. The bar extraction tools can be configured so that there is one bar extraction tool for each of the bars around the screen chamber of the hammermill. The device of the invention may also include a first end wall and a second end wall which are attached to a right rail and a left rail of the frame. The first and second end walls further define the screen chamber. The first and second end wall contained openings, called bar passages, through which the bars pass in and out of the screen chamber, and on which the bars rest for support and positioning around the hammermill.
In one form, the present invention is utilized on a particular type of grinding apparatus known as a tub grinder. This tub grinder is utilized for comminuting a supply of material. Such a tub grinder will have a frame supporting the grinder's components, and may have the frame mounted on a locomotion means such as tires or treads. One type of tub grinder has a rotatable drum assembly which is mounted to the frame, with the drum assembly configured to rotate in relation to the frame. Although the device works equally well with stationary tubs, one configuration of the device operates with a rotating drum. The drum assembly has a rotatable sidewall adjacent to the frame, as well as a stationary tub bottom surface inside the side wall. The side wall is open at the top and able to receive the supply of material into a rotating drum space defined therein. The device of the invention also works with horizontal grinders, and other types of hammermills.
Although the operation of the device is described in use primarily with a tub grinder, it would work equally well with a variety of grinder configurations. The bottom surface of the tub grinder includes an opening in which the hammermill assembly is mounted. The hammers of the hammermill assembly typically extend into the rotating drum space, in the case of a drum grinder, and grind material which is brought into contact with the hammers of the hammermill. The rotatable drum assembly attaches to the frame and its rotation causes material to be pushed into the hammers in the hammermill opening, and by agitation prevents the bridging or arching of material over the hammermill. Such a tub grinder has a drive mechanism for rotating the rotatable sidewall, which causes material inside the sidewall to be pushed into contact with the hammermill assembly. Versions of hammermills with non-rotating drum assemblies are also possible, and may go by the name of shredders, horizontal grinders, chippers and mills. The retractable rod screen of the invention may also be utilized with these non-rotating drum assemblies.
The grinding mechanism of the invention comprises a hammermill assembly having a rotatable hammermill with attached hammers. Positioned below such a rotatable hammermill is a hammermill screen which is attached to the frame of the grinder, which may be a tub grinder. The hammermill screen comprises a plurality of bars mounted in the frame compartment adjacent to the hammermill. The bars act as any hammermill screen does, and are for impa

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