German Dr. TRETTER bearings Dr. TRETTER models Dr. TRETTER prices

Dr. TRETTER roller bearings with cylindrical rollers, where the rollers are thin and long relative to their diameter. These rollers are called needle rollers. Despite having a small cross-section, the bearings still have high load-carrying capacity. Needle roller bearings are equipped with thin and long rollers (roller diameter D ≤ 5mm, L/D ≥ 2.5, L is the roller length), resulting in a compact radial structure. When the inner diameter size and load capacity are the same as other types of bearings, the outer diameter is the smallest, making them particularly suitable for support structures with limited radial installation space. Depending on the application, bearings without an inner ring or needle roller and cage assemblies can be selected. In this case, the journal surface of the shaft and the housing bore surface directly serve as the inner and outer rolling surfaces of the bearing. To ensure that the load capacity and operating performance are the same as bearings with rings, the hardness, machining precision, and surface quality of the raceway surfaces on the shaft or housing bore should be similar to those of the bearing rings. This type of bearing can only withstand radial loads.

Dr. TRETTER bearing classification

1) Combined type: Combined needle roller bearings are bearing units composed of radial needle roller bearings and thrust bearing components. They feature a compact structure, small volume, and high rotational precision, allowing them to withstand high radial loads while also accepting certain axial loads. The product offers diverse structural forms, wide adaptability, and ease of installation. Combined needle roller bearings are widely used in various mechanical equipment such as machine tools, metallurgical machinery, textile machinery, and printing machinery, enabling highly compact and agile mechanical system designs. [2) Thrust type: Thrust bearings consist of thrust cage assemblies with needle rollers, cylindrical rollers, or balls, along with thrust washers. The needle rollers and cylindrical rollers are retained and guided by the thrust cage. When used with DF thrust bearing washers of different series, many different combinations can be provided for the bearing configuration. The use of high-precision cylindrical rollers (needle rollers) increases the contact length, allowing this bearing to achieve high load capacity and high stiffness in a very small space. Another advantage is that if the surfaces of adjacent parts are suitable as raceways, the washers can be omitted, resulting in a compact design. The cylindrical surfaces of the needle rollers and cylindrical rollers used in DF thrust needle roller bearings and thrust cylindrical roller bearings are profiled surfaces, which can reduce edge stress and improve service life.

Dr. TRETTER bearing installation

Installation of full-complement needle roller bearings is usually carried out using an auxiliary sleeve. At this time, the auxiliary roller or auxiliary sleeve supports the needle rollers to prevent them from falling out. The chamfer of the journal lifts the needle rollers, and as the needle roller bearing moves slowly inward on the journal, the auxiliary roller or auxiliary sleeve gradually withdraws until it reaches the working position. The outer diameter of the auxiliary roller or auxiliary sleeve should be 0.1―0.3mm smaller than the shaft diameter. During installation, first apply grease to the inner surface of the bearing outer ring, place the needle rollers against the inner surface (leaving a gap when inserting the last needle roller), then push the auxiliary roller or auxiliary sleeve, replacing the journal or bearing inner ring, into the outer ring hole. Align its end face with the installation shaft end face or the end face of the bearing inner ring already installed on the shaft, and then apply pressure using a press or hand hammer. Needle roller bearings can also be installed by coating the outer diameter of the auxiliary sleeve with a thin layer of lubricating oil, inserting it into the bearing outer ring to form an annular hole with the bearing outer ring, and then installing the needle rollers in the annular hole. After installing the needle rollers, push out the auxiliary sleeve with the working shaft. For needle roller bearings without an inner or outer ring, during installation, first apply a thin layer of grease to the rolling surface of the shaft or housing bore, and place the needle rollers closely against the grease at the installation site. A gap should be left when placing the last needle roller; the size of the gap on the circumference of the needle roller bearing should be approximately 0.5mm. Do not forcibly squeeze in the last needle roller or install one less needle roller, as forcible insertion will jam the bearing preventing rotation, while installing too few will create excessive gap, causing the needle rollers to twist and break during operation. For needle roller bearings with only a stamped outer ring, since the outer ring wall is very thin, do not install by striking with a hand hammer; instead, use a press for insertion. Striking with a hand hammer causes uneven pressure, which can easily cause local deformation of the needle roller bearing's outer ring.

Dr. TRETTER bearing usage methods

1) Bearing disassembly and assembly: Clean the bearing thoroughly before installation. During installation, use special tools to press the bearing in evenly and straight; do not strike it with a hand hammer, and strictly prohibit striking the bearing directly. If the fit between the bearing ring and the housing bore is loose, repair the housing bore or replace the bearing; do not resort to makeshift measures such as knurling the fitting surface or inserting copper shims. When removing the bearing, use an appropriate puller to extract it; do not strike the bearing with chisels, hand hammers, or other tools. 2) Bearing lubrication: The common lubricants for rolling bearings are lubricating oil and grease. When the circumferential speed of the shaft is less than 4-5m/s, or for automotive components where lubricating oil cannot be used, grease lubrication is adopted. The advantages of grease lubrication include simple sealing structure, minimal loss of grease, low sensitivity to temperature changes, and long service intervals per application. Two points must be noted when using grease: First, select the appropriate grade of grease according to the vehicle manual. For example, sodium-based grease is not suitable for water pump bearings due to its poor water resistance. Second, add an appropriate amount of grease into the bearing; generally, filling 1/2-l/3 of the bearing cavity is advisable. Excessive grease is not only useless but also increases operating resistance, causing heating. Special attention should be paid to wheel hub bearings; "empty-hub lubrication" is recommended, meaning only a moderate layer of grease should be applied to the bearing itself. Otherwise, it will not only cause waste and poor heat dissipation but also lead to grease overflow due to heating, which may affect braking performance. The advantage of oil lubrication is low frictional resistance and effective heat dissipation; it is mainly used for high-speed bearings and those operating in high-temperature environments. Select the grade of lubricating oil according to the vehicle manual and replace it promptly according to the maintenance schedule. After draining the old oil, clean the mechanism before adding new oil. Fill the oil to the specified mark or level with the filler port (depending on the specific structure and requirements of the vehicle); do not overfill.

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