Acme Lead Screw Lubricants: A Brief Overview

Acme lead screws are increasingly the preferred solution for linear actuation. Lubrication for acme screws is just as important. Lubricant types fall into two categories: liquid and non-liquid. Liquid lubricants are petroleum-based mineral oils with 90% or higher base oil. Non-liquid lubricants – or, dry lubricants – are used when an oil-based lubricant is ineffective.

Many of our products are designed to be self lubricating with no need for additional lubrication or external grease. These products are designed to require no maintenance. We offer various lubrication options and the best solution will most often depend upon your particular application requirements.

Proper lubrication must be provided to achieve satisfactory service life. Helix lubricant (E-100 spray lube or PAG-1 grease) is recommended for applications using PowerAc™ nuts. Lubrication intervals are determined by the application. It is required that screw assemblies are lubricated often enough to maintain a film of lubricant on the screw.

Lubrication is important for long-term performance and reliability. Helix provides both wet and dry lubricants for our products. For instance, our E-100 spray lubricant or our PAG-1 grease is recommended for applications using precision lead screws without PTFE coating.

There’s also lubricants available for industry-specific needs.Our grease for medical grade applications is PTFE-thickened, high viscosity, and completely fluorinated in order to withstand high temperatures and exposure to harsh chemicals.

The grease available for semiconductor/static dissipative applications is PTFE-thickened and has a heavy viscosity, with a very low vapor pressure. Military and aerospace industries can use our grease that’s also PTFE-thickened, with a medium viscosity and completely fluorinated.

Does Your Lead Screw Need End Machining?

Linear motion applications utilizing a ball screw or an acme screw require high tolerance screw end machining matched with precision bearing mounts. Helix Linear Technologies has designed a family of standard machined ends applicable to a variety of bearing arrangements.

Specifying standard machined ends results in quicker deliveries. The machined ends shown below represent designs that are compatible with common application requirements for either simple or fixed bearing support. Included in the chart are the locknut and lockwasher identication.These standard ends may be machined and ground to finish size.

End machining for lead screws is not required, however, the majority of lead screw applications involve some sort of modification on one or both of the ends.

To obtain optimum performance of your acme screw assembly, it is recommended that the machining be performed at the Helix factory. Screws may be purchased machined to your specifications or to standard end machining designs.

So What Are End Machining Types? 

  • 1K, 2K, 3K, 4K and 5K are designed with a shaft extension and keyway for square keys.
  • 1L, 2L, 3L, 4L and 5L are designed with a shaft extension without a keyway.
  • 1N, 2N, 3N and 4N are designed to be a non-driven support end.
  • Double bearing supports use a Type 3N, 3L and 3K.
  • Single bearing supports use Type 1N.

Where standard ends do not satisfy the application requirements, special ends may be machined to customer specifications. Please submit a print for a prompt and competitive quotation.


Electrical Systems Special Report (2015)

This four-page article touches on the good, the bad, and the ugly of legacy vs modern electrical systems. Included topics are:

  • Electric actuators and valve control
  • Motor technology breakdown
  • Mechanical powertrain options
  • Ideal ball and roller screw applications

What is the best approach for your electrical system?

For more details, check it out here!

Premature Damage to Actuator Bearings?

Are you hearing unusual noises or seeing blackened grease leaking out of your pulley housings resulting in unplanned machine downtime? If you are, you’re not alone. Your actuator may be degrading due to a phenomenon known as electrical discharge (ED).

Premature actuator damage due to ED?Stray electrical voltages are traveling from motor shafts through couplings, pulleys, bearings, and housings in a search for ground. Since ball bearings are rolling contacts with lubricant between surfaces, the voltage arcs the gap and causes material erosion, lubricant failure, heat, and ultimately premature bearing failure.

This damage can reduce the life of bearings that should last 6 to 10 years to as little as 2 to 6 months. Your root cause investigation should focus on the motor grounding system as voltage discharges as low as 3.2 volts will cause current discharges across a ball bearing and raceway lubricant gap.


How it works:

Electrical Discharge Machining, sometimes called “spark machining” is a common manufacturing process where material removal is done by triggering a rapidly recurring current discharge between two electrodes separated by a dielectric liquid and subjected to an electrical voltage. One of the electrodes is the part being machined and the other is the “tool” electrode, typically a wire or carbon shape.

The gap between each electrode is precisely controlled and the dielectric liquid fills this gap. As voltage is applied and increased, the intensity of the electrical field in the gap rises and becomes stronger than the dielectric liquid, allowing current to flow or arc across the gap. As a result, material is removed from each electrode and carried away by the dielectric fluid. Performing this arcing at a high frequency results in an efficient erosion machining process that is very good for hardened materials.

Whereas EDM is a practical manufacturing process, it is not desirable in Motion Control systems and applications.

How do you recognize Electrical Discharge?

Stage One:

At first, the continuous arcing will start pitting the bearing raceways and reduce the ball diameter. Ball retainers will also start eroding and break apart. The heat builds due to arcing and friction causing the grease lubrication to breakdown and become contaminated with metal particulate. Blackened grease may leak out of the bearing and be visible on the pulley housing and pulley shaft.

Stage Two:

As the bearing degrades and becomes unlubricated, heat and friction build causing metal to metal contact noise. If the actuator drive shaft is decoupled from the motor, you may feel a roughness or bumpiness when rotating the drive shaft. The electrical discharge continues and works its way to all the bearings in the actuator as these are the points of arcing.

Stage Three:

As the bearings degrade (balls, retainer cage and polymer seals disappear) and become non-functional the actuator will begin running erratic and make significant noise. In a fully catastrophic case there are no bearings remaining and the pulley is unsupported, the actuator timing will be compromised and other parts of the machine system will be affected.

Here is a Stage 2 ED-damaged drive pulley housing that has been disassembled.

The shaft-side bearing (left) shows no seal, blackened lubricant and damaged ball cage. The pulley housing and bearing (right) show no visible damage but the bearing rotates with a rough feel indicating Stage 1 damage.

Determining if your actuator has been damaged by ED:

  1.  Measure actuator pulley housings and shafts for a voltage using an Oscilloscope or an Electrical Discharge Pen TKED1 made by SKF. Presence of voltage is a good indicator that ED is contributing to the failure.
  2.  Check all drive system ground connections and cables for proper ground bonding and shielding. If inconsistencies are found, correct and recheck for voltages.
  3. Measure temperatures of the motor, adaptor and pulley housings for excess heat generation. Hot spots may indicate failure point.
  4. Replace noisy drive or idler pulley assemblies. Record change dates and monitor the performance over time. It is quite rare for a pulley assembly to fail within 6 months of installation