(Reference Standards: ISO 3117:1977, IS 2291:1990/ DIN 268,271)

The tangential or tangent key arrangement is an uncommon, but nevertheless an interesting mean of securing the hub and the shaft to prevent relative movement between a power transmitting shaft and an attached component. This blog posts provides a brief explanation of this design and its applications.

Key attributes of the design:

• Used for large shafts in heavily loaded applications.
• A tangent key transmits torsion in one direction only, by means of compressive force only. This allows to increase the load transmission capability of the assembly.
• A tangential key consists of two tapered keys mated together.

Shortcomings of the design:

• When a single tangential key assembly is chosen, the torque can be transmitted in one direction only. Therefore, two tangential keys, placed 90° to 180° apart, are required for bi-directional rotation applications.
• Assembly is more complex when compared to standard sunk key designs.

Machining:

• Shaft and hub are typically machined to a transition fit tolerance.
• Typically, the hub or coupling is machined by keyway slotting or wire erosion.
• Tapered keys are machined with 1:100 slope and Ra finish of 32 or better.

Assembly:

• Correct fitting of the keys is critical to the integrity and long-term reliability.
• The keys are typically hand fit by verifying contact with transfer blue.
• After correct fit has been established, both sets of keys are hammered simultaneously, or equally into position.
• The keys are then locked into place with a pin or other method such as set screw or tack weld.

Typical drive applications where it is used:

• Large mixers, steel rolling mills.
• Grinding mill drives, mining hoists.

The Bottom Line

Although not common, the tangential key arrangement remains a viable option for large drive applications involving high torque/torsion loads.

Water can find its way into lube systems in numerous ways. Although immediate failure may not occur, the effects of water contamination will eventually lead to costly damage to equipment. Therefore, it is a condition that should be taken seriously and monitored for regularly, as the oil truly is the life blood of machinery such as grinding mills and crushers.

The main effects of water contamination in oil:

• Rust and corrosion: water combines with acids in oil and corrodes ferrous and non-ferrous metals. Rust particles are abrasive and therefore shorten the life of various mechanical components.
• Water compromises the lubricant film strength, by slowly breaking down the oil and depleting it of its key additives. As a result, metal to metal contact and contact fatigue will eventually occur.

Signs of water contamination in oil:

Some of the common signs of presence of oil in water are:

• Significant condensation on the inside surfaces of access hatches to various reservoirs.
• Visible corrosion on system components.
• Milky appearance of oil.

How to keep the oil dry:

Here are some key preventative measures to keep water out of oil in lubrication systems:

• Prevent or minimize condensation by installing desiccant air breathers on vents and monitor their condition regularly.
• Periodically drain water from low points of lubrication system.
• Do not spray water directly on seals and breathers when washing down equipment. As a rule of thumb, keep water off seals as much as possible.
• Monitor the condition of heat exchangers and the quality of the cooling water, as this is where oil and water are susceptible to mix with each other in case of a failure due to corrosion.
• Use quality seals, inspect them regularly and replace as soon as possible when worn out or damaged.

The Bottom Line

It is of the highest importance that preventative maintenance routines of equipment include check points specific to the detection of water in oil. If neglected, water will slowly lead to costly damage and downtime.

The importance of adequate packaging/crating of critical spare parts

Industry: mining / mineral processing

Application: grinding mills

Sub-assembly: main bearing insert

Minimal packaging requirements seems to have become the norm as suppliers are reducing their costs to remain competitive in today’s market. Unless requested or specified, today’s packaging will typically be designed for a one-time or one-way use and will not take into consideration any site-specific requirements. Risks of injury to personnel and damage to components can increase substantially when this type of packaging is reused over time to store or reship components out for repair

Case Study: Grinding Mill Main Bearing Insert

• A main bearing insert is considered as a critical spare part for a grinding mill, mainly because of the long lead times required to repair or manufacture a replacement. Such bearings are commonly lined with babbitt or bronze, soft alloys which make the part vulnerable to damage if not handled and stored with proper care.

• During a replacement of a main bearing insert for one of our customers, it was observed that the new spare part, weighing around 4000 lbs, had been stored in a poorly built plywood box that was showing evidence of damage and rot. This crating made the spare main bearing vulnerable to damage.

• To address this situation, TÄASK designed and supplied a reusable heavy-duty fabricated steel crate, for shipping and storage of spare main bearings, featuring:

• • • Excellent protection against physical damage and the elements.
    • Secure lifting points, making the crate and bearing easier and safer to handle.
    • Bearing orientation (bore side down) for quick servicing, which eliminates additional manipulations during which the part is exposed to damage.

The Bottom Line

Poorly or marginally designed packaging/crating of high value and/or long lead time critical spare parts is a risky practice. The additional cost of well thought out and rugged packaging/crate is minimal, when considering the risks of downtime and loss of production if a critical spare part is damaged during transportation or handling.