This document describes the Weigh Right PMB 1 Net Weigher, an automatic packaging machine designed to fill and dispense dry products into bags, jars, or cartons. The machine utilizes a two-speed belt feed system and an electronic weigh scale for accurate and reliable operation.
Function Description
The core function of the PMB 1 Net Weigher is to automatically weigh and dispense dry products. The process begins with pre-opened perforated bags on a roll being mounted on a spindle at the rear of the machine. The machine's hood opens to expose the bag feeding mechanism, allowing for easy loading of new bag stock. When activated, a powered drive roller pulls the web of bags into position for filling. The operator can adjust the stopping point of the bag opening in the filling and sealing area via a control setting on the machine's control panel. Once initial adjustments are made, the machine consistently feeds each new bag into the same filling position.
Product is fed into a weigh bucket by a two-speed belt feed system, consisting of a bulk (wide) belt and a dribble (narrow) belt. This system operates in a three-stage filling process:
- Cascade Belt: An upper-level vibrator pan that determines the initial amount of product delivered to the bulk and dribble belts.
- Bulk Feed: The bulk belt rapidly fills the weigh bucket. The machine is typically set up to feed 90-95% of the desired weight in this mode.
- Dribble Feed: Once Setpoint 1 (bulk feed cutoff) is met, the bulk belt slows down, and the dribble belt takes over, providing a slower, narrow stream for trickle feeding to achieve the final desired weight. The dribble belt stops when Setpoint 4 (target weight) is reached.
The electronic weigh scale continuously indicates the weight during the filling process via an indicator and digital readout. The operator controls when the machine discharges the product from the Weigh Pan using a dump switch.
Sealing is performed by a steady-heat seal bar mechanism coupled with a pneumatically actuated compressive seal pad. A built-in safety system ensures operator and product protection during the sealing process. Sealing temperature is regulated by a controller with an adjustment knob on the control panel. Each sealed bag is automatically separated from the roll as part of the seal cycle.
Important Technical Specifications
- Power: 120VAC 60Hz 15 AMP grounded service. (Note: The manual also mentions 120/240 VAC 60 cycle single phase for electric supply, suggesting adaptability.)
- Air: 2 CFM @ 80 PSI unlubricated. Requires a good filtration and condensation removal system.
- Environment: Operating temperature range of 50° F (10° C) to 100° F (38° C).
- Scale Accuracy: The system relies on precise control of bulk and dribble feed rates to achieve accurate filling. The bulk feed setting should always be higher than the dribble setting for optimal accuracy.
- Adjustable Flow Controls: All air-operated cylinders have adjustable flow controls, factory-set to smooth out operation. These are located either directly on the air cylinder or on the air valve stack inside the Junction box.
- Timer: A timer in the control panel sequences the air cylinder, allowing adjustment of the bucket open duration.
Usage Features
- Control Panel: Features include:
- Manual Dump: Empties the weigh bucket at the end of production.
- Hopper Vibrator: (If provided) Vibrates product in the supply hopper.
- Master Switch: Turns on feeders, begins machine cycle, and resets alarms.
- Potentiometers: Adjust feed rates of feeders (Incline Belt, Bulk Feed, Dribble Feed) from 0-100.
- Alarm Reset: Resets alarm conditions.
- Alarm Light: Indicates an alarm condition.
- Setpoint Adjustment: The machine uses two setpoints for each scale:
- Setpoint #1: Determines when the bulk feed turns off.
- Setpoint #2: Determines the desired final weight during the dribble cycle. (The manual also mentions Setpoint #2-dr, which is an amount subtracted from Setpoint #2 to determine when bulk feeding stops, and Setpoint #4 as the target weight for dribble belt stop, indicating a potentially more nuanced control system than initially described for Setpoint #2 alone).
- Setpoints are adjusted by trial and error, monitoring the digital readout.
- Emergency Stop: A pull-out switch to power up scales (with master switch "off") and for safety.
- Hopper Flow Gates: Adjustable to control unrestricted product flow.
- Product Level Sensors: Located above the Incline Belt and Bulk Feed Belt, these sensors control the infeed system and must be properly aligned. They have adjustable sensing ranges via potentiometers on the sensors or their power supplies.
- Leveling Screws: Provided for optimal machine leveling.
- Warm-up Period: Scales require a 15-minute warm-up before "zeroing" for production.
- Wash Cycle Pushbutton: Allows belts to run for cleaning when the Master Switch is "off."
Maintenance Features
- Cleaning:
- Use low-pressure water/washdown solution.
- Protect electrical controls and sensors with plastic bags during cleaning.
- Remove plastic bags from photo eyes after washdown.
- Some systems have a "Clean In Place" water spray system for rinsing belts.
- Thoroughly clean under the Bulk/Dribble belt. Tension can be released with red handle levers and tools (6 knobs and 1 quick release pin) for removal.
- The Manual Dump Pushbutton can sweep the Weigh Pan clean when the Master Switch is "Off."
- General Maintenance:
- Unplug the machine before any maintenance.
- Keep the machine as clean as possible.
- Periodically check the Push Plate air cylinder for wear and smooth operation.
- Remove water from the air filter system daily.
- Lubricate the air line with U.S.P. mineral oil.
- Clean scales and belts regularly with care, avoiding excessive pressure (more than 5 lbs.) on the Weigh Pan.
- Motors are maintenance-free.
- Keep the control panel locked and covered with plastic during washdown to protect from dust and moisture.
- Keep the pneumatic lubricator reservoir filled with U.S.P. mineral oil (pressure factory set at ~90 PSI).
- Check all belts for proper tracking and smooth operation.
- Check drive chains for tension (1/4" to 1/2" deflection with minimal pressure).
- Re-tighten all electrical terminals and connections; check for loose nuts and bolts.
Safety Instructions
- NEVER disassemble to clean when the power source is connected.
- NEVER put hands or fingers near weigh buckets, drop spout, or drive shafts when the power source is connected.
- NEVER remove guards while the machine is connected to the power supply.
- NEVER remove hoppers while the machine is connected to the power supply.
- NEVER open the control panel while the power source is connected.
- DO NOT operate without a proper ground.
- DO NOT operate in an explosive atmosphere.
- DO NOT subject the machine to wet or corrosive environments.
- Keep all flammable and caustic substances away from the machine.
- DO NOT connect air or power until the machine has been properly unpacked and inspected.
- NEVER work on or near the machine while the power supply is connected.
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