• operational principle

China has currently manufactured the ZGS series self-synchronous probability screening machines. This machine utilizes two vibrating motors rotating in opposite directions; the unbalanced force (inertial force) generated by the eccentric masses at both ends of the motors drives the screening unit to undergo reciprocating vibration in a specified direction. When the two vibrating motors rotate synchronously in opposite directions, the excitation forces produced by their eccentric masses cancel each other out in the direction parallel to the motor axes, while their resultant force in the direction perpendicular to the motor axes combines to form a single resultant force. As a result, the motion trajectory of the screening unit is a straight line. The relative surfaces of the two motor shafts are inclined at an angle in the vertical direction; under the combined action of this excitation force and the gravitational force of the material, the material is thrown upward, jumps, or moves forward in a straight line along the surface, thereby achieving the purpose of screening and grading the material.

Since the vibrating motor is directly fixed to the screen frame without any elastic connection in between, it forms a single-particle forced vibration system; as the screen machine operates outside the resonance range, it remains insensitive to load variations, ensuring smooth operation. The unbalanced forces generated add up or cancel each other out, causing the screen machine to undergo linear reciprocating motion, thereby defining its linear vibration trajectory. When materials are fed into the screen machine through the inlet and fall onto the first layer of the screen surface, large particles—whose size exceeds the aperture spacing of the first layer—are accelerated by the screen surface’s vibration, facilitating their separation; the remaining small-and medium-sized particles are then further separated by the second and third layers according to the same principle. The large particles on the first, second, and third screen layers simultaneously enter the coal crusher inlet for crushing, while the material passing through the third screen layer constitutes the qualified product, which is then directed to the next processing stage.

• design feature

The probability screening system primarily consists of two main components: the vibration damping system and the screening unit.

(1) Shock Absorption System

The ZGS series self-synchronizing probability sieve features a suspended load-reducing system: the sieve body is hoisted onto a support frame using a rope clamp that connects a shock-absorbing spring, a cable helical buckle, and a steel wire rope; the spring serves to dampen vibrations.

(2) Sieving Unit

The screening unit consists of a screening box, a vibrating motor, and a screening surface.

1. The screening box is the primary load-bearing and operating component of the screening machine; it consists of side panels, a top plate, reinforcing ribs, reinforcing beams, and other parts, and is constructed using a welded assembly. To extend the service life of the machine, wear-resistant rubber plates (10–14 mm thick) are embedded into the side panels; the screening box is secured to the coal discharge pipe using nylon canvas and screws.
2. The vibration motors serve as the source of vibration for the screening machine. The two vibration motors must have identical characteristics; they should rotate smoothly and be securely fastened to the motor base on the screening frame.
3. The screening surface is the primary wear-part component of the screening machine; it is typically divided into three layers and uses welded or screw-fastened screen bars fabricated from round steel bars of sizes 520 mm and F30 mm (the use of round steel bars simplifies the bar structure and facilitates maintenance). The machine’s side panels are constructed from high-quality steel plate; these side panels are secured to the crossbeam exciter base using high-strength bolts, resulting in a rational design that ensures robustness and durability.

III. Maintenance and Adjustment

(1) Lifting of the vibration damping system

Install the vibration damping system on the support frame as specified; suspend the screening machine using steel wire ropes and rope clamps; then adjust the adjustment screw to align the machine’s inlet horizontally and ensure that the four vibration damping springs are subjected to uniform force (this can be verified by measuring the compression height of each spring). If the compression heights are identical, the force distribution is uniform. A permissible tolerance may exist in the compression height of the springs on the front and rear vibration dampers; however, the compression heights of the two springs in each set must be adjusted to be identical. When a spring requires replacement due to damage, the entire set of springs must be replaced simultaneously.

(2) Pre-installation Instructions for Sieve Plate Installation

1. During installation, place a 5–6 mm thick rubber pad between each end of the screening surface and the horizontal beam of the screening machine; when tightening the screws, install a spring washer and secure them with double nuts to prevent loosening.
2. The length of the screening surface should be less than the distance between the two crossbeams by 1–2 mm, which facilitates the application of an appropriate preload.
3. When fabricating the screen surface, attention should be paid to its structural design. Any of the following materials may be used for the surface structure: A3 or Grade 20 steel; for welding, use Type 507 or Type 506 welding electrodes; during welding, ensure that the welding positions are correctly identified.
4. When rubber elastic screen bars are used, in addition to tightening the preload nut, adhesive bonding should be applied to the central support beam of the screen bar. After bonding the screen bars, the screen machine should be left idle for one week before use; if the operating temperature is high, it may be left idle for 3–4 days.

(1) Amplitude adjustment requirements and methods

When the machine is running under no-load conditions, set the screen’s vibration amplitude to 4–5 mm; alternatively, adjust the amplitude appropriately based on the coal quality (for example, use a higher amplitude – generally not exceeding 6 mm – when the coal is dense or the processing volume is high; use a lower amplitude when the coal is loose or the processing volume is low). This approach can extend the machine’s service life and reduce noise levels.

The method for adjusting the amplitude involves changing the eccentric coincidence angle between the two motors; however, the coincidence angles of the four sets of eccentric blocks on both motors must be made identical—otherwise, oscillation will occur. Once the eccentric blocks have been properly adjusted, a locking nut should be applied, and after the desired amplitude has been achieved, a locking washer should be installed and secured. The amplitude value can be directly read from the scale markings on the amplitude indicator plate; the number indicated by the horizontal coordinate of the intersection point of the two lines represents the adjusted amplitude value.

The article data is sourced from 360 Wenku.