Agitating – Rubber or heavy plastic working – With specified feed means
Reexamination Certificate
1996-03-14
2001-07-31
Chin, Randall E. (Department: 1744)
Agitating
Rubber or heavy plastic working
With specified feed means
C366S156200
Reexamination Certificate
active
06267495
ABSTRACT:
TECHNICAL FIELD
The present invention generally relates to a device for blending solid particulate matter, and more particularly relates to an improved blender apparatus for high-precision metering of at least one particulate ingredient at low flow rates.
BACKGROUND OF THE INVENTION
Blending devices for blending various types of solid particulate ingredients, such as plastic pellets, are well-known in the art. Generally, these devices include a number of ingredient hoppers, each of which discharge ingredients into individual metering units. These metering units typically include a metering auger, the rotational speed of which can be varied to control the flow rate of the individual ingredients. The metering units discharge individual ingredients into some sort of common hopper at independently controllable feed rates which can be varied to produce the desired blend of individual ingredients. Typical feed devices are shown, for example, by U.S. Pat. No. 1,757,341 to Smit, U.S. Pat. No. 2,957,608 to Wahl, and U.S. Pat. No. 3,684,082 to Wardell.
Advances in material and compounding technologies have led to the production of ingredients for blending with a higher concentration of additive materials, such as pigments and antioxidants. These highly concentrated ingredients are usually more costly than the other materials in the blend and typically constitute a very low percentage of the total blend, which requires operation of at least one of the metering units at very low flow rates, often at 0.2 lbs./hr or less. When operating a metering unit at such low rates, it is desirable to achieve as small a short-term flow rate variation as possible. Ideally, it would be preferable to eliminate such short-term flow rate variations. In many situations it is necessary or important to maintain at least a minimum flow rate, despite the undesirable short-term fluctuations in flow rate. In such situations, it has been common to set the nominal or target rate well above the required minimum flow rate in order to ensure that the minimum rate is maintained despite short-term fluctuations in flow rate. Substantial cost savings could be achieved if the nominal or target rate could be set closer to the minimum rate while still ensuring that the minimum flow rate is maintained.
It has been discovered by Applicant that one of the primary causes of flow rate fluctuations at low flow rates is the rotation of the metering auger itself. Existing prior art metering devices typically are fed by circular, square or rectangular ingredient hoppers with the lower portion having converging walls mounted directly to the metering auger housing, as demonstrated by U.S. Pat. No. 1,757,341 to Smit. In this arrangement, the weight of ingredient particles in the hopper is supported almost entirely by the sloped walls of the ingredient hopper, with only a small fraction of the weight of the ingredients being reactive with (i.e. affected by) the auger. It has been found that upward forces resulting from the rotation of the auger cause perturbations in this small reactive volume of particulate matter just above the auger. At low metering rates these perturbations are sufficient to cause fluctuations in material feed to the auger, thus resulting in uneven operation.
Accordingly, it can be seen that a need yet remains for a blender apparatus capable of precise low-rate metering, which minimizes perturbations in the low-rate metering. It is to the provision of such a blending apparatus capable of providing such precision low-rate metering that the present invention is primarily directed.
SUMMARY OF THE INVENTION
Briefly described, in a preferred form the present invention comprises a blender apparatus including a number of individual ingredient metering units, at least one of which is capable of precision low-rate metering. Preferably, the individual metering units feed ingredients to a common hopper which can be used to store blended material for subsequent use, or serve as a reservoir of blend for feeding a processing machine.
The precision low-rate metering unit includes a vertical elongate tubular hopper over the throat of a metering auger housing, with the tubular hopper being substantially longer than a transverse dimension of the throat. This tubular hopper discharges ingredients by gravity feed to the metering auger. Because the tubular hopper does not have sloped walls, as do existing circular, square or rectangular hoppers, very little of the weight of the ingredient is supported by the hopper. Rather, nearly all of the weight of the ingredient acts to force the ingredient downward, into the auger housing. The tubular hopper thus acts to increase the quantity of material which is reactive with (influenced by) the auger, thereby Minimizing the effect of upward perturbations caused by the auger's rotation. This effectively increases the weight of the column (head) of material positioned over the auger and, as a result, upward forces on the column caused by the rotation of the auger are thus rendered smaller in relation to the weight of the column. By stabilizing the head pressure of material presented to the auger in this manner, the accuracy of the auger's metering is substantially improved.
Thus, it is an object of the present invention to provide a blender apparatus capable of precision metering of particulate materials at low flow rates.
It is another object of the present invention to provide a blender apparatus which achieves accurate and consistent blending despite perturbations caused by rotation of the metering auger.
It is a further object of the present invention to provide a blender apparatus which is durable in use, economical in manufacture and reliable in operation.
It is another object of the present invention to provide a blender apparatus that reduces production cost of products which utilize highly concentrated ingredients which are metered at low rates.
These and other objects, features, and advantages of the present invention will become more apparent upon reading the following specification in conjunction with the accompanying drawing figures.
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patent: 1757341 (1930-05-01), Smit
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Chin Randall E.
Deveau Todd
Process Control Corporation
Schneider Ryan A.
Troutman Sanders LLP
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