Agitating – Mortar mixer type – With heating or drying
Patent
1991-03-15
1993-03-02
Hornsby, Harvey C.
Agitating
Mortar mixer type
With heating or drying
432106, 432110, 34136, B28C 122
Patent
active
051903717
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method of producing a bituminous or asphalt paving mixture.
So far, practically all bituminous paving mixture has been produced by either one of two different methods, namely the so-called "batch-mixing" and the so-called "drum-mixing", respectively. Batch-mixing is a discontinuous method of production which is suitable for use in connection with production plants from which relatively small amounts of a bituminous or asphalt mixture of varying, further specified compositions are to be delivered during a day to many different purchasers. In the known batch-mixing, stone and sand fractions are metered according to the purchaser's recipe or specifications by means of metering apparatus, and the materials so metered are transported to a drying drum where the materials are dried and heated to a temperature of about 160.degree.-180.degree. C. Then the materials are sieved into 4-6 fractions and stored in a hot silo or buffer silo. From the hot silos a portion or batch of 2000-4000 kg is weighed out, and filler, bitumen and other additives are weighed out as a certain percentage of the stone and sand material according to the recipe presented. When all components have been weighed out, the materials are mixed for about 30-50 seconds in a special mixing apparatus. The mixture is now ready for use and may be transported to a product silo where it may be collected by the purchaser.
Drum-mixing is a continuous method of production which is suitable for use in connection with production plants from which large amounts of bituminous or asphalt paving mixtures of rather uniform compositions are to be supplied, for example in connection with large civil engineering projects or for purchasers of large asphalt mixture amounts. In drum-mixing, aggregate, such as stone and sand fractions are metered continuously in accordance with a recipe or specifications by means of metering apparatus, and the metered materials are continuously passed to a drying drum through which they may flow substantially continuously. In the first part of this drum the materials are dried and heated to a temperature of 160.degree.-180.degree. , and in the last part of the drum, filler, bitumen and any additives are continuously added. The dried and heated materials are mixed with the additives in the last part of the drum so that finished mixture is discharged continuously from the outlet end of the drum.
It will be understood that the known production plants for paving mixtures are rather inflexible, as a certain plant only permits either production of relatively small amounts of mixtures of various compositions or continuous production of a large amount of a paving mixture of the same composition. Therefore, a paving mixture manufacturer who wants to be able to produce large as well as smaller amounts of paving mixtures of a desired compositions has to invest in at least two different plants for batch-mixing and drum-mixing, respectively.
The invention provides a method which renders it possible to produce large amounts as well as relatively small amounts of paving mixture of different compositions in a rational manner in the same plant.
The method according to the invention comprises supplying aggregate, for example sand and/or gravel, into a first section of a rotating drying and mixing drum at an inlet end thereof, introducing at least one further component, for example using paving material, a binder, such as bitumen and/or recycled material into a second section of the drum between said inlet end and an opposite outlet end of the drum, mixing said component with the dried aggregate in the drum, and discharging the mixture at the other end of the drum, and the method according to the invention is characterized in supplying the aggregate to the drum in portions, drying each portion in said first drum section, transferring a first portion to the second drum section after drying such portion and prior to supplying a second portion of aggregate into the drum, and mixing the dried first portion of aggregate with s
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Alexander Reginald L.
Hornsby Harvey C.
Pedershaab Maskinfabrik A/S
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