Loss In Weight Blenders
Loss in weight blenders, functioning in a target weight mode, have been used for film and sheet extrusion for over 35 years. Designed for a combination of high accuracy metering and homogenous ingredient blending, they provide these features at the higher processing rates typical of the extrusion process.
Figure 12. Typical Loss Weight - Target weight Blender - Multiple individually weight ingredients are fed simultaneously into a batch hopper or mixer to individual proportional weights. The batch is mixed and discharged to the downstream process.
A typical target weight loss weight blender has each metering feeder mounted to an independent, load cell supported, weighing hopper. In some designs, the metering feeder is separated (de-coupled) from the weighing hopper to lessen the amount of "dead load" on the load cell. The purpose for this is to improve the resolution of the live load being weighed. This can be important when small amounts of a material are required in a formulation. However, de-coupling adds complexity to the system, is sensitive to poor material flow properties and can cause errors in the blend proportions if the principles of operation are not properly understood and followed.
For these reasons, the majority of loss weight feeder stations supplied to the industry utilize a feeder coupled to the weigh hopper. Each weigh hopper measures the weight of material leaving it. The weighing system is programmed for simultaneous and proportional metering of each ingredient. Since each ingredient is weighed using an independent load cell, each cell can be sized and spanned to maximize the resolution of the A/D conversions. This yields very precise and accurate weightiness.
Although metering is done proportionally
and simultaneously, this type of blender is programmed with a target, proportional weight for each ingredient
with the proportional feed rates set and derived from the weigh proportions. The material that is fed out of
the weigh hoppers is delivered to an active mixer. The feeding is paused after the target weights are
achieved and the loss weight hoppers are refilled if necessary in preparation for the next gravimetric feed
cycle. Since, unlike target rate blenders discussed next, refilling of the weigh hoppers is done while the
feed cycle is paused, the feeders always run in gravimetric mode. All material fed is weighed. After the
metered materials are mixed, the mixer discharges to the process and the next weigh cycle is started.
Refilling of the weigh hoppers while the feed cycle is paused allows for self-loading vacuum weigh hoppers
on this type of blender. This feature can be a significant advantage where adequate headroom is not available
for separate weigh hoppers with vacuum receivers above.
Loss In Weight Blenders: Applications and Modes of Operation
The Foremost Loss Weigh Blender is a unique blender for bulk-dry solids, which uses feeders to automatically meter materials, chosen by the user, into the user's process.
The blender is designed, standard, with three modes of operation. The Mode of operation that the blender is to run in is chosen by the user. These modes are:
- MAUNAL MODE: The operator has full control of the blender and can use specific buttons on the displays to run the system manually.
- GRAVIMETRIC MODE: The blender runs automatically, using the scaling functions of the blender to deliver the proper WEIGHT of each material, as set by the operator.
- VOLUMETRIC MODE: The blender runs automatically to deliver the proper RATIO of each material into the process.
Since the Gravimetric Mode uses the load cells to accurately weigh the material, it is the normal and recommended mode of operation. But, if the condition should ever arise, where the Gravimetric Mode is not functional, or practical, the blender can still be used to get blended material to the process. An operator need only change the mode of operation to the Volumetric Mode. The Volumetric Mode can also be used to purge the blender automatically.
Each Loss-Weight Blending System consists of the following standard components:
1. Two (2) to ten (10) combination vacuum/weigh hoppers. One for each component supplied complete with:
- Level switch
- High accuracy tension compression load cell ( 25, 50, 75, 100, 150, or 200 KG)
- Variable speed vibratory feeder ( 1 1/2”, 3”, 4’ or 6” wide)
- Positive shut-off slide gate (2”,3”, 4” 5” or 6”)
- 0.2, 0.6, 1.0, 1.5, 2.0, 3.0, 4.0, 6.0 or 8.0 cubic foot capacity
- Aluminum construction
- Refill via vacuum loader
2. One (1) Collection chute
3. All of the above components are rigidly mounted on a leg assembly for floor mounting. Includes all limit switches, scale components, compressed air connections and vacuum control valves for completely automatic operation. The vacuum control valves will be mounted on a manifold on the blender.
4. One (1) Mixer to receive material from the collection chute:
- Either a barrel or center type
- low level switch
- Either gravity dump or vacuum take away outlets
- Stainless steel construction
- Powder chamber with compressed air filter cleaning for powder or dusty materials
- Auger feeders in place of vibratory feeders
- Flow inducers for hard to move materials
- Material sampling/calibration chutes
- Vacuum loader power units to load and unload
- Vacuum Barrel mixers to be mounted above customer process equipment
- Separate Vacuum and weigh hoppers for continuous operation
Model FDP-VII-LWB, Automated Blender Control System. The system is complete with:
- NEMA 12 Enclosures (Low voltage)
- Stain gauge bridge sensors (one per component)
- 24 VDC Power Supplies
- Necessary fuses, blocks, wire way, etc
- Alarm horn
- Alarm light/beacon
- 4” cooling fan and exhaust grill
- TFT Color touch screen display including:
- Custom programming
- Automatic status control
- Multiple recipe configuration
- Weight calibration
- Feeder calibration
- station parameters
- Blender parameters
- Manual control
- Material usage
- Alpha-numeric character entry
- PLC system including:
- Power supply
- Analog input modules
- Analog output modules
- Digital input modules
- Digital output modules
- I/O rack
- Feed rate cards to control vibratory feeders (one per component)
Typical Screens are as follows:
|Gravimetric Status " Control Screen|
|Recipe Entry Screen|
|(Recipes Entered In (%)||(Recipes Entered In (Lbs)|
|Montior Blender / Manual Control Screen|
|(Manual Not Activated)||(Manual Activated)|