General Choice Criteria
The choice between different types of screws and nuts available is generally carried out in light of the following considerations:
For positioning Screws it is necessary to control the error of the thread pitch. We provide customer Screws with an accuracy class of 50 (50μm/300mm), 100 (100μm/300mm) and Screws with a class of 200 (200μm/300mm) in C45. For standard carriage Lead Screws class 200 ones can be used.
Complete irreversibility occurs with Trapezoidal Screw with helix angle < 2° 30′. In all other cases, torque may be transmitted to the drive gear when the screw is still, subject to a load on the nut (especially under vibration). However, good irreversibility is present up to 5 or 6 degrees.
Choice of the Nut
Materials used for the production of Nuts, (Bronze and Stainless Steel 316), are resistant to standard oxidizing agents, that occur in various applications. If corrosive agents are present please contact our Technical Department directly. In applications where the presence of added lubricant (grease or oil) is not allowed we recommend the use of self lubricating Plastic Nuts.
The use of Plastics is constrained by the actual working conditions.
This is because Plastics sometimes have excellent self- lubrication features, but have at the same time, restrictions on working temperature or moisture absorption problems. They may also have some mechanical properties that may not be suitable for the intended use.
A preliminary study of the application, is therefore recommended. Please contact our Technical Department.
Choice of the screw
For working environments where there are no particular corrosive or oxidizing agents C45 Screws can be used. Where these conditions are not met, we recommend using Stainless Steel screws A4 (316), which are particularly suitable in the following case
- With relative humidity of 70/80% and above
- Immersed in water, even in sea water
- In the presence of particular corrosive agents, such as Chlorides. In case of highly corrosive agents please contact our Technical Department
- Where, due to special construction requirements, components must not oxidise; for example in the food industry, where they are coupled with Nuts HDA
- Where Screws cannot be reached for lubrication; In particular, for lubricating “maintenance-free” fittings that are coupled with Plastic Nuts
- Where working temperature is relatively high, because the Stainless Steels A4 feature a relatively high slag temperature, due to the austentitic structure of the material