Excerpted From Taking the Strain

Over the past 20-30 years, the main technological development in brakes for mine hoists has been the replacement of less efficient drum brakes with hydraulic disc brakes.

These offer many advantages and, along with the introduction of AC motors for soft starting/stopping plus advances in control systems, brake components have become smaller (due to reduced stresses) with longer life cycles. As a result, there are significant cost savings associated with brake design, installation and maintenance.

Brake Selection

When selecting brakes for mine hoists, it is important to consider factors such as the depth of the shaft, number of levels, stopping profile, drum design and payload in order to calculate the braking torque required for each application.

Twiflex, which produces braking systems for mine hoists, is part of the Heavy Duty Overrunning Clutch Brake division of Altra Industrial Motion. Steve Powell, product manager for Twiflex, explains: “Our selection is based on providing enough braking torque to deal with the static out-of-balance load, in addition to considering the dynamic stopping duty. Modern control systems offer lower hoisting cycle times and high production levels, all of which affect the brake selection. The limitation for brake manufacturers is the friction material and the brake-pad swept area, which needs to be carefully chosen for the operating cycle.”

The Twiflex VKSD and VMS modular brake ranges are typically used in mine hoisting. These are spring-applied, hydraulic-release fail-safe brakes, which have a ‘parked off’ feature, meaning they can be adjusted to remove all stored energy. With zero spring-load and no hydraulic pressure, Twiflex says that the brakes are 100% safe for pad replacement and maintenance.

The modular design comprises two off-spring modules that are mounted each side of a plate.

Mono-spring or ‘floating’ versions are also available.

For mine hoisting, brakes are typically rated between 62kN and 320kN braking force, at a nominal 0.4 coefficient of friction with a 2mm gap between brake pad face and brake disc.

At this rating the Twiflex modular range is designed for over 2 million braking cycles to meet exacting hoist requirements.

In addition to testing the braking torque at the start of each shift, hoist operators carry out visual checks for oil leaks and condition of the disc surface. To assist with maintenance, Twiflex brakes incorporate a monitoring system to signal brake-pad wear and loss of braking force.

“All Twiflex modular brakes are subject to a cycling test and pressure test before leaving the factory,” explains Powell. “For mine hoists, all critical brake components undergo non-destructive testing.

New Products/Installations

Powell says: “The main limitation for brake manufacturers is the friction material and the brake pad swept area, which needs to be carfeully selected for the operating cycle.” With this in mind, Twiflex is continually investigating new materials to address this problem, and has installed new test equipment at its plant in Bedford, UK.

Twiflex VMS3/SPS hoist brakes have recently been selected for use at a gold mine in northern Canada. The mine is projected to produce 600,000 oz/y of gold over a 15-year lifecycle.

The order was for VMS3/SPS calipers for use on a 6.1m diameter, double-drum, single-clutch mine hoist that has two brake discs; one positioned on the fixed drum and one on the clutched drum. Each brake produces 240kN of braking force with a 2.5mm air gap.

The VMS3/SPS design also integrates small pistons for quicker reaction times, coupled with an improved drainage system and a reduced retraction pressure of 160 bar (depending on rating).

Download the Pdf of this article

Customer Service
+44 (0) 20 8894 1161
www.twiflex.com

Asia Pacific
For a list of our AP sales offices:
altramotion.com/contactus

The newly improved machine design features all stainlees steel construction to ensure compliance with the very high hygiene standards in bakery facilities.

Bauer 1.5 kW aseptic motors were selected to drive the machine’s powerful rotatingbrush bands due to the motor’s reliability and special paint coating that causes water to drip off the surface (“lotus effect“). This yields superior hygiene properties, better than stainless steel, which is hydrophilic. The aseptic coating is acid and alkali resistant to stand up to the harsh cleaning agents utilized in regularly scheduled machine washdowns. The Bauer aseptic paint is FDA and NSF listed.

The Bauer aseptic motors also feature a unique housing design which eliminates the motor cooling ribs and fan areas where dirt and debris gather, are almost impossible to reach, and where washdown solutions cannot drain off. The unit’s smooth surfaces (roughness value R ≤ 0.8 μm), all slope at least 3° to ensure fast and complete cleaning.

Highlights: • Units are ideal for use in food processing, washdown environments • Aseptic paint coating causes water to drip off surfaces (lotus effect) • Paint is acid and alkali resistant • Coating is FDA and NSF listed • Unique motor housing design eliminates cooling ribs and fan areas • Units feature a high degree of standard protection (IP 67); IP 69K is also available • Motors comply with IE3 energy efficiency class

Download the PDF of this article.

Prämab, the engineering firm that was awarded the conveyor systems contract, called their Bauer sales representative, Bernd Petrasch for technical assistance. In the course of several project meetings, Prämab mentioned that the annealing furnace contact was awarded to Mioba, a central German industrial furnace manufacturer.

Mioba had already started to plan and design the system using competitive motor drives. Together with Miroslav Slawik (global account manager at Basic Metal), Petrasch designed a new more cost-effective layout using Bauer BG Series gear motors. It turned out that, instead of the 2.2 kW power maintained by the competition, in fact, only 30 watts was necessary, which provided additional cost reductions. Another advantage was the BG Series’ ability to perform in an ambient temperature of 80°C.

In the end, Mioba, who had now become a Bauer customer, decided on the design change utilizing the Bauer gear motors. In October 2012, the furnace was put into operation and runs to the satisfaction of all.

BG Series compact, economical gear motors feature high-tensile cast housings Complies with NA and International standards, including NEMA, IEC, CSA, and CE Torque rating to 18500 Nm Low noise gearing IP65 Enclosure (Standard), IP66 (Optional) Completely enclosed, sealed against dust and moisture Corrosion protection CORO1, CORO2, CORO3 Connection Standard with CAGE CLAMP®

Download a PDF of this article

S.F.E.L. is the manufacturing arm of Sheffield Forgemasters International, a company that specialises in steel production and machining for global supply. Using steel supplied by a sister company it produces some of the world’s largest steel castings (1 to 350 tonnes), steel forged items (up to 280 tonnes) and forged steel bars. Its unique manufacturing facilities include a 10,000 ton press pump which is capable of moving over 6,500 litres of water every minute.

To keep such a large pump flowing a coupling is required to transfer the 6,000HP produced by the motor at speeds of between 70/83 RPM. Pump applications are notorious for high levels of shock loading and vibration, meaning a coupling was required that could deal with these stresses. Grid couplings provide the ideal solution as the metal grid which connects the hubs to the shaft allows for small amounts of movement which smoothes out torque spikes and minimises the negative effects of misalignment.

During a recent site inspection it was decided that the current coupling was approaching the end of its operational life and a replacement would be needed to prevent a breakdown. To avoid a costly and time consuming re-engineering project to the pump, S.F.E.L. needed to source a new coupling that would match the dimensions of the outgoing coupling. Most of the coupling manufacturers that it approached didn’t have the facilities to manufacture a coupling of the required dimensions.
David Bartholomew, Engineering Manager at S.F.E.L., comments: “The outside diameter of the coupling is 1620mm and its width is approximately 650mm. While some manufacturers could meet the load requirements for the project, none could offer a grid coupling which met these dimensions. The original coupling was manufactured by Bibby, now part of Altra, so we asked if its coupling division would be able to help with a replacement. It was able to use the original design to manufacture a bespoke coupling which matched our criteria exactly.”

Bibby was one of the original pioneers of grid coupling technology and has long been known as a leading manufacturer of large, high performance, flexible couplings. Using the design for the pump’s original coupling, which was manufactured in the 1970’s, as a starting point, Altra engineers were able to use the company’s high-tech manufacturing facilities to produce a new grid coupling. The new unit matches the same performance envelope as the original, but employing modern materials and the latest grid profile to provide the flexibility and also the longevity required by the application, all on a very short lead time.

David Proud, Sales Director for Altra Industrial Couplings, adds: “It is extremely rare that a grid coupling is required of this size, and there aren’t many manufactures with the means and experience to complete the project. Fortunately Altra Industrial Couplings has the capabilities to make couplings of almost any size. To make this project even more special Sheffield Forgemasters Engineering Ltd. acted as a supply partner for the couplings hub material. Working with our customer as a manufacturing partner helped us to ensure that this coupling will keep turning for another 40 years.”

Altra Industrial Couplings is the couplings division of Altra Industrial Motion, a leading transmission component specialist. The division represents some of the oldest and best known names in the coupling industry including Bibby, Huco, TB Woods and Ameridrives. It is able to offer coupling solutions for almost any industrial application thanks to each brands’ unique knowledge and expertise in differing fields.

About Altra Industrial Motion Inc.

Altra Industrial Motion, Inc, is a leading multinational designer, producer and marketer of a wide range of mechanical power transmission products. The company brings together strong brands covering over 40 product lines with production facilities in nine countries and sales coverage in over 70 countries. Altra’s leading brands include Warner Electric, Matrix International Wichita Clutch, Stieber Clutch, Twiflex Limited, Bibby Transmissions, Huco Dynatork, TB Wood’s, Formsprag Clutch, Ameridrives Couplings, Industrial Clutch, Boston Gear, Marland Clutch, Nuttall Gear, Inertia Dynamics, Warner Linear and Kilian Manufacturing. Altra Holdings, Inc. (Nasdaq:AIMC), a leading global supplier of clutch brakes, couplings, gearing, belted drives, linear actuators and power transmission components.

Download a PDF of this article