How to deal with a slowdown in the laboratory centrifuge’s rotation speed?

　　 Laboratory centrifuge A common problem encountered during use is a slowdown in rotational speed, which can be fatal for some novice users. In many cases, customers don't know how to handle the situation promptly and can only feel helpless and anxious. The extent to which this affects production or work depends on the specific product. As a result, a series of contradictions may arise. By that point, the optimal window for addressing the issue will have already passed. Therefore, our editor would like to advise everyone: If you encounter any problems while using your laboratory centrifuge, be sure to contact the manufacturer immediately. Do not attempt to disassemble it yourself—doing so could lead to even more serious consequences. So, dear new and existing customers, please keep this in mind.
　　Density gradient centrifugation in laboratory centrifuges is further divided into rate-zonal centrifugation and isopycnic zonal centrifugation. In this method, a sample is subjected to centrifugation in a medium with a specific inert density gradient, allowing particles to reach certain positions within the gradient under a given centrifugal force, thereby forming distinct zones of separation. When different centrifugal speeds and durations are employed to sequentially separate particles with varying sedimentation rates, this technique is referred to as differential centrifugation. To perform differential centrifugation, a suspension containing two types of particles is first centrifuged at a moderate speed, causing the larger particles to settle at the bottom. The supernatant is then carefully transferred to another centrifuge tube, after which the centrifugal force is increased and the suspension is centrifuged again for a specified duration, separating the smaller particles. This process is repeated several times until the desired degree of separation is achieved. Differential centrifugation is particularly well-suited for separating particles that differ significantly in size and density.

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　　 In the event that, during a laboratory centrifuge experiment, the motor speed becomes excessively slow and the carbon brushes emit significant sparks, how should this situation be handled? Analysis and Troubleshooting: This fault is caused by dirt or debris between the motor’s carbon brushes and commutator segments, or by a reduction in the spring tension of the carbon brushes, resulting in poor contact between the brushes and the commutator. Solution: Disassemble the machine, unscrew the cover of the brush holder, and remove the carbon brushes along with their springs. First, clean the springs, carbon brushes, and commutator segments thoroughly using anhydrous alcohol to remove any dirt or debris. If there are chipped or damaged areas at the front end of the carbon brushes, use a combination file together with sandpaper to carefully grind these areas into smooth, curved contact surfaces that fit snugly against the round commutator segments. Finally, adjust the spring tension appropriately to increase its elasticity.
　　The laboratory centrifuge’s power indicator light and instruments are functioning normally. Press the start button, and... Laboratory centrifuge Not functioning. Repair and troubleshooting: The control circuit was inspected and no faults were found. After replacing the carbon brushes of the laboratory centrifuge, the machine resumed normal operation. This issue occurs frequently and is typically caused by worn-out carbon brushes. Transformer B burned out, causing the entire machine to fail. Repair and troubleshooting: Transformer B has a primary voltage of 380V and three secondary windings with output voltages of 220V, 150V, and 160V, respectively. The contacts of CJ1 and CJ2 are connected in series across the secondary winding (0–150V) of Transformer B; CJ1 and CJ2 are interlocked contacts. After inspecting the contacts of CJ1 and CJ2, it was found that the contacts of CJ1 had fused together, resulting in damage to CJ1. After replacing CJ1 and Transformer B, the laboratory centrifuge returned to normal operation. Analysis revealed that the fault was caused by an excessively high starting current, which led to the burnout of CJ1. Although the laboratory centrifuge can now run, its maximum speed is limited to only 2,500 rpm, failing to meet operational requirements. Repair and troubleshooting: The adjustable resistor WW for speed regulation was checked and found to be undamaged. The gate trigger voltages Ug of thyristors SCR1 and SCR2 were measured; the Ug voltage of 7V was within the adjustable range and thus considered normal. The forward conduction and reverse blocking characteristics of both SCR1 and SCR2 appeared normal on the surface. However, after replacing SCR2, the rotational speed of the laboratory centrifuge could be adjusted up to 3,200 rpm. Analysis indicated that the cause was a variation in the parameters of SCR2. The laboratory centrifuge operates via one of its rotors driven by a motor; the speed at which the rotor spins directly affects the separation efficiency of the centrifuge. Below, we will explain how to optimize the control system of the laboratory centrifuge to achieve ideal performance.
　　The electric motors typically used in laboratory centrifuges are series-wound motors. These motors consist of two main parts: the stator and the rotor. The stator comprises a centralized, fixed magnetic pole made up of an iron core and magnetic field coils. The rotor consists of an iron core, rotor windings, and a commutator. Laboratory centrifuges harness the powerful centrifugal force generated by the high-speed rotation of the rotor to accelerate the sedimentation rate of particles in a liquid, thereby separating substances within a sample that have different sedimentation coefficients and buoyant densities. When a suspension containing fine particles is left undisturbed, the particles gradually settle downward under the influence of the gravitational field. The heavier the particle, the faster it sinks; conversely, particles with a density lower than that of the liquid will rise to the surface. The rate at which particles move under gravity depends on their size, shape, and density, as well as on the strength of the gravitational field and the viscosity of the liquid. For example, particles roughly the size of red blood cells—diameters on the order of several micrometers—can be observed undergoing sedimentation even under normal gravitational conditions. Finally, when selecting a laboratory centrifuge, we need to determine the appropriate type and specifications based on the processing capacity and the degree of automation required for the operation; this approach makes it easier to achieve the desired results.
　　 Laboratory centrifuge The main issue in day-to-day use is still the one mentioned above, but as long as it’s handled properly, it won’t have any major impact!