SKF in plastics industry: bearings for extruders, injection molding machines and winders

In a plastic extruder, the screw generates a significant axial force when pushing the molten material towards the head. That load must be absorbed by a specific bearing, which in most equipment is an SKF axial spherical roller bearing. This design supports high axial loads and allows some misalignment between the shaft and the housing, which is common due to thermal expansion of the machine. If the axial bearing fails, the screw loses position and the process goes out of control.

SKF axial spherical roller bearings are identified with codes such as 29316, 29248, 29230 E or 29330 E. The engraving on the side face of the ring allows verifying the code and brand, even with the bearing mounted. It is also advisable to note the inner diameter, outer diameter and width measurements, because sometimes the code is worn or covered by grease.

When ordering this bearing, send the complete code and a photo of the machine plate if you have it. At MR we distribute SKF bearings for extruders and we quote you via WhatsApp or email. A common mistake is replacing the axial bearing with a deep groove ball bearing: it does not support the thrust and is destroyed in a short time. Another mistake is not checking the axial clearance after assembly, which generates vibrations and premature wear.

The gearboxes of extruders and injection molding machines work with high radial loads and moderate speeds. There, SKF cylindrical roller bearings are the usual choice because they support high radial load and allow axial displacement of the shaft due to expansion. They are used on the intermediate and output shafts of the gearbox, and also in some winders for supporting the traction rollers.

The codes in this category start with NU, such as NU 221 ECP, NU 224 ECM, NU 320 ECP or NU 326 ECJ. In plastic machinery it is common to find these bearings with sheet metal or solid cages, depending on speed and working temperature.

To quote an SKF cylindrical roller bearing, send the complete code and the dimensions if you know them. A photo of the old bearing, where the engraving is visible, also works. At MR we distribute SKF bearings for gearboxes and we quote them by code or by dimensions. Avoid mounting these bearings with direct blows on the rings: the cage deforms and the bearing fails prematurely.

SKF deep groove ball bearings appear in almost all plastic machines: at the ends of the feed screws, on the shafts of vacuum pumps, on cooling fans and on the idler rollers of winders. They are versatile, support radial and moderate axial loads, and work at high speeds with low friction.

The most common codes in this industry are from the 62 and 63 series, such as 6211, 6310, 6212 or 6311. If the bearing works in an environment with plastic dust or humidity, it is advisable to order it with 2RS seals, which are rubber on both sides and retain the grease. If the shaft temperature is high, it can be ordered with C3 internal clearance, which is greater than normal and prevents seizing due to expansion.

When ordering an SKF deep groove ball bearing, indicate the code and whether it has seals or shields. For example, a 6211 with 2RS seal is different from a 6211 with 2Z shield: the first has a rubber seal and the second a metal shield. At MR we distribute SKF deep groove ball bearings for the plastics industry and we quote you by code or by dimensions. A frequent mistake is replacing a sealed bearing with an open one: the grease becomes contaminated and the service life is shortened.

Lubrication is critical in extruder and injection molding machine bearings. The screw axial bearing is usually lubricated with oil, which also helps to evacuate the heat coming from the heating barrel. The gearbox bearings can be oil or grease lubricated, depending on the design. In winders, deep groove ball bearings are usually greased for life if they have 2RS seals.

The temperature of the barrel area directly affects the axial bearing. If the heat is excessive, the oil degrades and the bearing loses the lubricating film. Therefore, it is advisable to control the housing temperature and use an oil with the appropriate viscosity for the working temperature. In machines that process high-melting plastics, such as polycarbonate or polyamide, heat is a determining factor.

When consulting about a bearing for this industry, mention whether it works with oil or grease and the approximate temperature of the area. At MR we distribute SKF bearings for plastics and we quote you according to your machine code. Do not mix greases with different bases: softening occurs and the grease escapes from the bearing. Also do not over-grease: excess generates heat and leaks.

The first step to order a spare part is to read the code engraved on the bearing ring. In SKF bearings, the code is on the side of a ring, sometimes with small letters. If the bearing is mounted, it may be necessary to remove the cover or the housing to see it. In extruders, the axial bearing is usually behind the gearbox, in its own housing.

In addition to the code, it is advisable to measure the inner diameter, outer diameter and width with a caliper. These data serve to confirm the code or to find an alternative if the engraving is illegible. In cylindrical roller and deep groove ball bearings, the dimensions are standard and can be verified in tables. In axial spherical roller bearings, the width is greater than in a deep groove ball bearing of the same diameter.

If you cannot disassemble the machine, take photos of the bearing from various angles and of the machine plate. At MR we distribute SKF bearings and we help you identify the code with those photos. Also send us the type of machine (extruder, injection molding machine, winder) and the brand if you know it. A common mistake is ordering only by the inner dimension: two bearings with the same inner diameter can have different width or load capacity.

One of the most common mistakes is mounting the axial bearing backwards. In SKF axial spherical roller bearings, the shaft ring and the housing ring are not the same: if they are reversed, the bearing does not seat properly and is damaged. Another mistake is not checking the preload or axial clearance after assembly. In the screw of an extruder, excessive clearance produces knocking and wear of the screw thread.

When ordering the spare part, a frequent mistake is omitting the suffix. For example, NU 221 ECP and an NU 221 without that suffix are not the same bearing. In deep groove ball bearings, a 6310 with 2RS seal is different from a 6310 with 2Z shield: the rubber seal retains grease better in dusty environments, but generates more friction at high speed.

At MR we distribute SKF bearings for the plastics industry and we quote you by the complete code. If you have doubts about the suffix, send us a photo of the old bearing and we will confirm the specification. Do not replace a bearing with C3 clearance with a normal one if the machine works hot: the bearing seizes. And do not use a deep groove ball bearing where an axial spherical roller bearing goes: the screw thrust destroys it.

To quote an SKF bearing for your plastic machine, gather these data: the complete bearing code, the dimensions if you have them, a photo of the old bearing and the machine plate. With that, at MR we quote you the exact spare part. It also helps to know whether the bearing works with oil or grease.

You can write to us via WhatsApp or email with the code, the dimension or a photo of the part. At MR we distribute SKF bearings for extruders, injection molding machines and winders. If your machine has a bearing of another brand, send us the code and we will look for the SKF equivalent.

Do not wait for the bearing to fail completely: a new noise or vibration in the extruder is a sign of wear. Order the spare part in advance and avoid long production stoppages. MR distributes SKF bearings from Buenos Aires, Argentina, and we respond promptly with the quote.