Cross-Belt Sampling System
The Hammer Sampler was developed and successfully installed by Siebtechnik in Germany in 1964. Due to ease with which it can be installed or retrofiited to take representative samples from a moving conveyor belt, it has become internationally very popular. The sampler operates to internationally recognized sampling standards.
Multotec Dry Sampling Range
The Multotec dry sampling range of equipment consists of the following:
- Direct drive (or freewheel coupling). Hammer samplers to suit conveyor belts width from 250mm to 2500mm.
- Belt-End and Screen-End cross cut samplers for conveyor, chute or screen discharge applications.
- Rotating Plate Dividers for various material sizes and variable division ratio requirements.
- Turnstile dividers to suit lower material feed rates but with widely adjustable division ratios and multiple samples.
- Electromagnetic Vibratory Feeders o feeder conveyors to suit top size of material and capacity requirements.
- Impact or jaw crushers and hammer mills.
- Stainless steel, 3CR12 or HDPE sampler containers and chute work.
- Feed and/or reject handling system, e.g. bucket elevators; skip hoists, mini conveyors, etc.
- Single and Multi-station hard wired Electrical Control Panels. Mini PLC's with SCADA interfacing capabilities.
- Turnkey sample stations for ROM or product materials in all material industries.
This sampling equipment incorporates all the process and design knowledge gained during Multotec's and Siebtechnik's long involvement within the area of dry sampling.
This sampler is a highly sophisticated piece of equipment that has the following features:
It allows ease of access:
- The sampling swing-arm and cutter can be inspected and accessed via a bolted hatch at the side of the housing.
- The electric drive is self-contained and mounted on the frame.
- The bolt-no rubber scrapper arrangement at back of cutter is all easily replaceable.
It provides efficient and effective sampling:
- The slot width of the cutter is 3 times the normal particle top size of the solids with a minimum of 50mm and a maximum of 750mm.
- The swing-arm cutter cuts the full width of the conveyor belt stream. The rubberscraper and/or nylon brush at the rear wall of the cutter ensure that a complete sample, including fines, is taken. The material is discharge via gravity through the housing discharge chute-work.
- The cutter crosses the material flow just above the surface belt (=5mm) providing an exact cross-section of material. This lower limit positioning of the cutter prevents it from touching the conveyor belt and yet collecting representative samples.
- The volume of the cutter is designed to correspond to the maximum belt loading specified. This ensures that a complete cross-section of material is taken without sample materials pilling up in front of the cutter slot.
- The swing-arm cutter is connected to a gear brake motor, which is activated by a timer. Alternately, a potential free signal from a belt weight meter or another source can be used to energize the motor and initiate sampling.
- Adjustable rubber skirts are located on either side of the of mounting frame and are designed to contains any material turbulence and consequent spillage, which may result during the sampling action. This will work well on 'trained' conveyor belts.
(Click image to enlarge)
The Control Panel
As the control panel- either hard wired or with a mini PLC - controls the operation of the sampler with additional equipment; it is a very important component.
The control panel is IP65 specifications (determined by the client’s requirements). The panel is manufactured from mild steel or as per client requirement, and is painted in control panel orange or can be painted to other stipulated specifications
The panel is fitted with a lockable mains isolator for lockout purposes. This isolator will cut power only from the client’s supply to the rest of the control panel. The control panel houses the motor protection items and operational control items such as overloads, relays, timers, switchgear, etc.
The main components of the housing are:
- The top cover for the sampling swing-arm and cutter.
- The dust cover to minimize pollution and spillage during the sampling action.
- The mounting position for the sensor and proximity switch.
- The sample dishcharge chute work.
Inspection covers are located on the housing for inspection and maintenance of the rubber scraper and / or nylon brush on the back of the cutter. This is done when the cutter is in the ‘parked’ position.
The Mounting Frame
The frame is usually mounted onto the existing conveyor stringers if the unit is relatively small (usually up to 1050) and the conveyor structure is sound. To ensure an accurate fit, the customer is required to complete a sampling questionnaire and idler dimension sheet. Should Multotec consider it necessary we will assign a design draughtsman to measure up on site at extra cost.
The frame is supplied with a number of packing plates of various thicknesses. This is for final adjustment or shimming purposes prior to commissioning. This will ensure that the sampling swing arm passes between 5-10mm from the conveyor surface when sampling.
The Motor and Gearbox
The size of the motor and gearbox is designed to the requirements of each specific application. The motor is of the squirrel cage type. The geared motors are supplied with a built-in, spring applied, electrical release brake on the rear of the motor. The air gap on the brake is factory set. The brake will keep the swing arm in the parked position between 8 o’clock and 11 o’clock. This ensures that the swing arm with cutter is kept out of the stream on the conveyor belt.
During the sampling action, the motor is energized via an OMRON (or other) timer or a belt weightometer signal. The motor is switched off only once the sensor plate has passed the proximity switch.
The Free-Wheel Coupling (typically older models)
The free-wheel coupling is the drive link between the motor and the sampling arm. It operates on a ratchet action. Once the sampling arm passes the 12 o’clock position, the free-wheel coupling allows the sampling arm to accelerate under gravity until it cuts through the material on the conveyor belt.
After the sampling action, the motor is de-energized at approximately the 8 o’clock position. The remaining momentum brings the arm to rest at between 9 o’clock and 11 o’clock depending on the belt loading at the time of sampling.
The non-return/ratchet action of the free wheel coupling then holds the sampling arm in this parked position together with the motor brake until the next sampling pulse is received.
The Sampling Arm
The major components of the sampling swing arm are the following:
The arm extension
The arm is manufactured from mild steel and its length is dependent on the belt width; the trough angle; the number of idlers and their length.
The swing arm cutter
The cutter blades are chamfered on their leading edges to ensure that a clean cut is taken through the material flow. The blades are manufactured from abrasion-resistant (304) stainless steel, VRN steel or other suitable abrasion resistant or non-stick materials. This is determined by the application.
The nylon brush and scraper
The rubber scrapers are mounted on a sliding block at the rear end of the cutter. It is important that they are set at the correct level to ensure that all fines are removed from the belt (on certain applications a nylon brush would be employed as well).
The inductive/proximity sensor and proximity sensor shield
The motor runs from start and is de-energized by the proxy. It is important that the hammer sampler and the conveyor belt are inter-locked to ensure a fail-safe system. The Multotec control panel provides for this safety feature, and this should be taken into account if operated via a central PLC or DSC system.
The inductive sensor or proximity is mounted on a bracket in line with the proximity shield.
The correct position of the swing-arm cutter is dependent of the inductive sensor shield. The shield is either mounted on the swing arm in the case of the overhang unit, or on the shaft in the case of the double bearing unit. The park position of the swing arm cutter depends on the setting of the shields and loading on the belt.
In certain applications Multotec will supply additional equipment such as a metal detector, ‘large’ rock detector, material sensor or weightometer. This is determined by the client’s specific requirements. In addition, Multotec can also supply sample containers and integrated chute work once headroom is known.
In specific cases additional timers will be supplied inside the control panel. This timer can be set by the client to prevent the hammer sampler from taking a cut when a large rock or piece of metal passes under it. This auxiliary equipment can be installed in a ROM application to prevent damage to the sampler and/or conveyor and to prevent belt stoppages. This timer can be adjusted in the same way as the first two, and its operation is identical to these.